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Review

Recent Developments in Rhodamine-Based Chemosensors: A Review of the Years 2018–2022

by
Yujiao Wang
,
Xiaojun Wang
,
Wenyu Ma
,
Runhua Lu
,
Wenfeng Zhou
and
Haixiang Gao
*
College of Science, China Agricultural University, Mingyuanxilu No.2, Haidian District, Beijing 100193, China
*
Author to whom correspondence should be addressed.
Chemosensors 2022, 10(10), 399; https://doi.org/10.3390/chemosensors10100399
Submission received: 30 August 2022 / Revised: 23 September 2022 / Accepted: 26 September 2022 / Published: 3 October 2022
(This article belongs to the Special Issue Chemosensors for Ion Detection)
Browse Figures
Versions Notes

Abstract

:
Chemosensors based on traditional fluorescent dyes have always contributed to the development of chemical sensor areas. In this review, the rhodamine-based chemosensors’ improvements and applications from 2018 to 2022 are discussed, mainly focusing on cations (metal ions and H+), anions (CN−, F−, etc.), and small bio-functional molecules’ (thiols, amino acids, etc.) detection. Specifically, this review highlights the detection target, detection limit, detection solution system, detection mechanism, and performance of the rhodamine-based sensors. Although these rhodamine-based sensors are well developed, their repeatability and sensitivity still need significant improvement. This review is expected to bring new clues and bright ideas to researchers for further advances in rhodamine-based chemosensors in the future.
Keywords:
chemosensor; rhodamine

1. Introduction

Chemosensors, since their first exploitation in 1864, have since then been playing a vital role in analytical chemistry due to their high sensitivity, time efficiency, simple operation, and less complicated instruments [1,2,3,4,5]. These sensors have been useful in identifying targets such as cations (H+ and metal ions), anions (CN−, F−, etc.), and biomolecules (NADH, ATP, etc.) [6,7,8]. The detection of those targets is of great significance for monitoring food safety and human health. According to the Chinese standard, the threshold limit values in drinking water of Hg2+, Pb2+, As3+, CN−, F− are 0.001, 0.01, 0.01, 1.5, 0.01 mg/L (5.0 × 10−9, 4.8 × 10−8, 4.8 × 10−7, 7.9 × 10−5, 3.8 × 10−7 M), respectively [9]. Traditional organic dyes contain a fluorescent core skeleton with a large conjugate system and auxochrome group altering wavelengths and enhancing fluorescence (such as amino, amide, etc.). In addition, many kinds of fluorescent materials have been developed, such as gold nanoparticles [10], quantum dots [11], metal-organic frameworks [12] covalent organic frameworks [13], and so on, as the development in fluorescent detection technology continues [14]. Although these emerging materials are widely used as fluorescent probes, cheap and easily synthetic organic dyes, such as rhodamine and its derivatives, are not replaced because of their great characteristics of convenience for structural modification, excellent molecular stability, and gratifying environmental compatibility [6].
Rhodamine, a group of xanthene-derivative dyes (Figure 1A) [15], was first prepared in 1905 by Noelting and Dziewonsky [16] and used for analytical research purposes (colorimetric detection of zinc, silver, etc.) from the middle of the 20th century [17]. Since Czarnik et al. [18] and Tae et al. [19], who pioneered works on rhodamine B and rhodamine 6G derivatives, respectively, as the fluorescent chemosensors for metal ions (Cu2+ and Hg2+), a lot of sophisticated researches on rhodamine have been published, among which rhodamine B-based and rhodamine 6G-based chemosensors were those most often referred. As displayed in Figure 1B, the unique and convenient close-open ring structure of rhodamine derivatives before and after the addition target would induce color and fluorescent changes, helping greatly to detect target analyte. The coordination between the sensor and target ion induces spirolactam ring opening and pronounces the colorimetric and/or fluorescent responses, which are usually non-fluorescent and colorless before the coordination (Figure 1B). Additionally, the rhodamine derivatives’ properties of fine biocompatibility and near-infrared fluorescence make them an excellent choice for bio-sensor construction.
Many reviews on chemosensors research have been reported in the last two decades. Chen et al. described and discussed mercury-ion sensors from 2008 to 2015 [20]. Kaur et al. comprehensively summarized the developments of colorimetric sensors for metal ions from 2011–2016 [1]. Roy, P. discussed recently reported sensors for aluminum detection [21]. These reviews mainly focused on chemosensor targets. Chen et al. described the progress of benzazole-based fluorescent probes, reported in 2017–2019, combining the design strategy, synthetic route, sensing mechanism, and applications [6]. Jain, N. and Kaur, N. published a review on chemosensors based on 1,8-naphthalimide reported during 2017–2021 [22]. Zhu, H., et al. reviewed the advances of 4-hydroxy-1,8-naphthalimide-based chemosensors in the past decade [23]. These reviews elaborated on the chromophores of chemosensors.
However, as a classic chromophore for chemosensor construction, there are no reviews on the developments of rhodamine-based chemosensors in recent years. The sensing mechanism of rhodamine-based sensors has been proposed to guide the sensor’s design [24]. The most common sensing mechanisms are photoinduced electron transfer (PET) [25,26], intramolecular charge transfer (ICT) [27,28], and fluorescence-resonance energy transfer (FRET) [24,29]. In this review, the endeavors of chemosensors based on rhodamine and its derivative from 2018 to 2022 are summarized and discussed. Generally, the colorless and non-fluorescent rhodamine turns red and shows a strong fluorescence when its closed spiro-ring is opened by metal complexation, analyte binding, or exposure to acidic conditions [17,30]. The rhodamine-based chemosensors are divided into three main categories according to the chemo sensor’s targets: cations (metal ions, H+), anions (CN−, F−, etc.), and small bio-functional molecules (H2O2, ATP, NADH). The concrete progress in this research area is elaborated in following sections. This review could bring new clues or bright ideas for further advances in rhodamine-based chemosensors in the future.

2. Rhodamine-Based Sensors for Metal Ions

Metal ions are partly beneficial to the body up to a certain concentration level. For example, iron (Ⅲ), zinc (Ⅱ), and copper (Ⅱ) play vital roles in neurophysiology and neuropathology [31], however, their alleviated levels are harmful and may cause physiological disorders [32]. Other metals, such as mercury (Ⅱ), lead (Ⅱ), cadmium (Ⅲ), and chromium (Ⅲ) are potentially toxic to both humans and the environment [1,5]. Hence, monitoring the levels of these metal ions in living bodies and the environments (groundwater, industrial sewage, and so on) is quite significant. Table 1 shows the reported fluorescent probes based on rhodamine derivatives, generally designed for divalent (Hg2+, Cu2+, Pb2+, Zn2+, Cd2+, Co2+) and trivalent (Fes3+, Cr3+, Al3+, As3+) metal ions.

2.1. Rhodamine-Based Sensors for Hg2+

A rhodamine-fluorene-based dual channel sensor was synthesized for selective detection of Hg2+ via both colorimetry and fluorometry (Table 1, No. 1), and the sensor’s solubility was greatly improved by the alkyl chain in the fluorene moiety, enabling its utility in 100% H2O [33]. The prepared sensor selectively detected Hg2+ in 100% water using a strip with a good response and was then used as a digital printing material.
Hong M., et al. synthesized a spectral sensor through a one-step reaction between rhodamine B and thiobisethylamine, named 2-(2-((2-aminoethyl)thio)ethyl)-3′,6′-bis(diethylamino)spiro [isoindoline-1,9′-xanthen]-3-one (RMTE) (as shown in Table 1, No. 2) [34]. RMTE emitted a new fluorescence peak at 578 nm in the presence of Hg2+ with a remarkable visual change in fluorescence color (Figure 2).
Cicekbilek, F. et al., reported a Hg2+ sensor synthesized a facile Schiff base-type reaction between 9-anthraldehyde and aminated rhodamine [35] and used to detect Hg2+ with observable sensitivity and selectivity via colorimetric and fluorescence methods (Table 1, No. 3). The detection limit of the proposed sensor was 0.87 μM. The sensing mechanism of the as-prepared sensor to Hg2+ was based on a spirolactam ring-opening reaction, verified through UV-Vis, FTIR, and NMR titration analyses.
A promising colorimetric and fluorometric chemosensor named RDV was designed by Patil S. K., et al. for specific detection of Hg2+ (Table 1, No. 4) [36]. The color of the “turn-on” fluorescence sensor changed from colorless to pink before and after the addition of Hg2+ in an aqueous acetonitrile medium (Figure 3). The sensing limit of RDV for Hg2+ was 136 nM, revealing a high sensitivity of the sensor.
Kan, C. et al. constructed a novel reversible fluorescent probe named RBST (Table 1, No. 5), by the reaction of 2-thiopheneacetyl chloride and rhodamine B, [37]. RBST showed a sensitive and selective response to Hg2+ in EtOH/H2O (2,1, v/v) with the detection limit of 0.11 μM (Figure 4). The reversibility of RSBT was attributed to the strong affinity of S2− and Hg2+. Besides, the RSBT was used to detect Hg2+ in real water samples, suggesting its promising practicality.
Dewangan S., et al. synthesized a significant molecule through the functioning of the cymantrenyl hydrazone system by fluorescent tagging of rhodamine (Table 1, No. 6) [38]. The synthesized molecule displayed high selectivity and responsiveness to Hg2+ (Figure 5). The prepared sensor was applied to recognize Hg2+ in bacterial strains and THP-1 cancer cells, indicating its potential in bioimaging applications.
Wang Q., et al. synthesized three rhodamine based probes 1, 2, and 3 (Table 1, No. 7) and applied them for Hg2+ detection in Tris-HCl/C2H5OH (v:v = 3:7, 10 mM, pH = 7.2). All three probes were colorless at first but turned to visible pink after the addition of Hg2+ with the fluorescence increment. The detection limits of probes 1, 2, 3 to Hg2+ were 18 nM, 16 nM, 56 nM, respectively. These probes were successfully applied to both environmental samples and bioimaging applications, as shown in Figure 6.
A ferrocene-based rhodamine-hydrazone molecular probe (Table 1, No. 2) was synthesized using the solid-state synthetic method by Dewangan S., et al. [40]. The probe showed selective recognition of Hg2+. It was therefore applied to intracellular metal detection and bioaccumulation analysis, showing its promising application prospects. The proposed sensing mechanism of the prepared probe to Hg2+ was shown in Figure 7.
Gauthama B. U., et al. designed a rhodamine-based sensor named RhB, with a selective and sensitive response for Hg2+ (Table 1, No. 9) [41]. The UV-Vis and fluorescence spectral profiles changed in the presence of Hg2+ due to the formation of the coordinate bond between RhB and Hg2+ (Figure 8). The detection limit was around 2.57 × 10−6 M and the prepared sensor detected Hg2+ in 100% aqueous solution by the naked eye.
Li, X., et al. synthesized a fluorometric and colorimetric chemosensor, named 1O and studied its responses for Hg2+ (Table 1, No. 10). The results suggested that Hg2+ induced remarkable colorimetric and fluorescent changes, due to the reaction between 1O and Hg2+ (Figure 9). Singh S., et al. described a rhodamine-based fluorescence sensor for Hg2+ detection in water samples (Table 1, No. 11) [43]. The influences of different analytical parameters on the analytical performance of the sensors were discussed. Results showed that replacing the fluorophore of rhodamine B with rhodamine 6G on the prepared sensor improved the limit of detection. In addition, the buffer optimization improved detection limits and selectivity. The prepared sensor was successfully applied for Hg2+ detection in tap and river samples.
Yilmaz, B., et al. [44] reported a novel rhodamine-based sensor, using the calixarene as the skeleton and appended with four rhodamine units at the upper rim (Table 1, No. 12). The prepared sensor showed high selective and sensitive response to Hg2+ with immediately turning on fluorescence output. Through in vitro and bio-imaging studies, the prepared sensor was cell permeable and suitable for real-time imaging of Hg2+ in living cells. Aduroja O., et al. synthesized a rhodamine-based sensor, RD6 (Table 1, No. 13) [45], with excellent selectivity sensitivity to Hg2+ in an aqueous buffer solution by colorimetric and fluorescent methods. The detection limit of RD6 for Hg2+ was 1.2 × 10−8 M. With the CN− assistance, the prepared sensor realized reversibility due to the strong stability of Hg(CN)2 (Figure 10).
Li M., et al. constructed a novel rhodamine-based material, FFC, for the detection and adsorption of Hg2+ (Table 1, No. 14) [46]. The cellulose was chosen as the skeleton and the rhodamine moiety was conjugated with cellulose as the recognition group, enabling excellent optical signals in the presence of Hg2+. After adding Hg2+, the intensity of fluorescence enhancement of FFC showed a 7-fold enhancement by triggering the spirolactam ring-opening reaction. The adsorption process of FFC to Hg2+ was fitted with the Langmuir adsorption model and pseudo-second-order kinetics. The prepared FFC was successfully applied for the detection and adsorption of Hg2+ in tap water. Liang F. et al. introduced an anthocyanin functional group in the rhodamine spiro ring and constructed a sensitive and selective near-infrared (NIR) fluorescent sensor, CCS-Hg for Hg2+ (Table 1, No. 15) [47]. The prepared CCS-Hg was applied to determine Hg2+ distribution in living cells. The sensing mechanism was verified through theoretical calculations (Figure 11).
Zhang Q., et al. designed a rhodamine-based sensor for selective detection of Hg2+ via the FRET mechanism (Table 1, No. 16) [48]. The synthesized material possessed great pseudo-Stokes (174 nm) in the presence of Hg2+ and showed fluorescent and ratiometric response with a fast reaction time (less than 30 s) (Figure 12). The limit of detection for Hg2+ was found to be 0.38 × 10−6 M.

2.2. Rhodamine-Based Sensors for Cu2+

Zhang J., et al. constructed a FRET-based sensor for the detection of Cu2+ (Table 1, No. 17) [24], by conjugating rhodamine with a 2-(1,3,3-trimethylindolin-2-ylidene) acetaldehyde moiety. The designed sensor demonstrated colorimetric and ratiometric responses to Cu2+ with a detection limit of 1.168 × 10−8 M (Figure 13). The prepared sensor was successfully applied to detect Cu2+ by test paper strips and in real water samples.
During grape wine production, copper could disorientate volatile sulfur compounds and cause turbidity formation, thus lowering the wine quality [71]. By decorating rhodamine B with a tetra azamacrocyclic ring, a probe was created to monitor the Cu2+ in wine with a detection limit of 4.38 × 10−8 M (Table 1, No.18) (Figure 14) [49]. The prepared sensor responded to Cu2+ only in acidic conditions (< pH 5.5).
Deepa A., et al. synthesized a fluorescent and colorimetric sensor, named 6GS2, exhibiting a specific response after binding with Cu2+ (Table 1, No.19) [50]. The spirocyclic structure of 6GS2 transformed into a non-cyclic form in the presence of Cu2+ and the fluorescent peak intensity increased in the H2O/DMSO (9/1, v/v) medium. The fluorescence intensity increments of 6GS2 induced by Cu2+ is attributed to the PET mechanism (Figure 15).
Hosseinjani-Pirdehi H., et al., prepared a biocompatible fluorogenic chemosensor named RHA (Table 1, No. 20) [51]. Furan-2,5-dione and rhodamine combined with an iminohydrazine crosslinker were the receptor and fluorophore of RHA, respectively. The RHA served as a pH indicator in acidic media and a sensitive sensor with high selectivity to Cu2+ RHA was used for bio-imaging applications in acidic and neutral pH. A novel sensor, named RhP, was synthesized by integrating the rhodamine phosphonate group (Table 1, No. 21) [52]. RhP demonstrated highly sensitive and selective recognition for Cu2+ and the detection limit of RhP was 15 × 10−6 M. The sensing of Cu2+ by RhP was achieved in less than 15 s (Figure 16).
Wang Y., et al. synthesized a naked-eye and fluorescent chemosensor, by introducing pyrazinyl hydrazine in rhodamine B, for Cu2+ detection (Table 1, No. 22) [53]. The sensor color changed from colorless to amaranth after Cu2+ addition. The proposed response mechanism of the prepared sensor (Figure 17) was extrapolated through the results of mass spectra, fluorescence spectra, and theoretical calculations.
Yang L., et al. reported a novel rhodamine-based sensor, poly-NRG, modified by picolyl groups serving as the recognizing ligand for Cu2+ (Table 1, No. 23) [54]. The prepared poly-NRG was further modified into gel balls for the Cu2+ adsorption which showed a specific reaction in the presence of Cu2+ with obvious color changes and achieved recycling after treatment with EDTA solution (Figure 18). Hu L., et al. reported a NIR fluorescent sensor EtRh-N-NH2 employing rhodamine as a fluorescent core and a hydrazine group as a responsive site for Cu2+ (Table 1, No. 24) [27]. The sensitivity and selectivity of the prepared sensor turned out to be satisfactory with the low detection limit (6 × 10−6 M). The proposed sensing mechanism was shown in Figure 19. Furthermore, EtRh-N-NH2 was used in the bio-imaging of Cu2+ in living cells.

2.3. Rhodamine-Based Sensors for Fe3+

Cheng Z., et al. synthesized a rhodamine-based sensor, named J1, for Fe3+ detection (Table 1, No. 25) [32]. The colorless sensor solution visibly turned pink in the presence of Fe3+, realizing the detection of Fe3+ in an aqueous environment. The prepared sensor was successfully used in the bio-imaging of Fe3+ in living cells, indicating its promising application prospects. Liu Y., et al. synthesized an N, N-dithenoyl-rhodamine-based sensor for fluorescent and colorimetric Fe3+ detection (Table 1, No. 26) [55]. The excellent selectivity of the prepared sensor was attributed to the coordinating functional recognition group of two thiophene carbonyl groups and the detection limit was around 3.76 × 10−9 M (Figure 20). The reported sensor also exhibited satisfactory membrane permeability and was also used for bio-imaging in living cells.
Wang K. P., et al. (Table 1, No. 27) reported a Fe3+-detecting fluorescence sensor, BYY, synthesized by the reaction of 2-thiopheneacetic acid and N-(rhodamine-B)lactam-ethylenediamine [56]. The BYY sensor exhibited high sensitivity toward Fe3+ in EtOH/H2O (2/3, v/v, pH = 7.2) with a fast response rate. Owing to a strong affinity between Na4P2O7 and Fe3+, BYY realized the reversible binding of Fe3+ (Figure 21). BYY was successfully applied for the bio-imaging of Fe3+ in living cells.
Wang, Y., et al. designed a simple rhodamine-based fluorescent and colorimetric sensor, L1, exhibiting a good selectivity and sensitivity to Fe3+ (Table 1., No. 28) [57]. The detection limit of the L1 sensor was 0.29 × 10−6 M. The sensing process, which was shown in Figure 22, was chemically reversible at least three times on the alternate addition of AcO− and Fe3+.
Zhang M., et al. synthesized four rhodamine-based sensors through simple, high yield, and one-step Mannich reactions, and the acquired product M3 (Table 1, No. 29) exhibited a specific and sensitive response to Fe3+ in acetonitrile/Tris-HCl buffer solution (3:7, v/v; pH = 7.4) (Figure 23) [58]. The prepared Fe3+ sensor was successfully applied in bio-imaging by confocal laser scanning microscopy.
A rhodamine salicylaldehyde sensor, named RS, was constructed to modify a fluorescent PU foam named PU-RS, as a sensitive fluorescence sensor for Fe3+ (Table 1, No. 30) [59]. PU-RS showed ring-opened amide form and higher fluorescence intensity, due to the coordination between RS and Fe3+ in pure water (Figure 24). Liu X., et al. synthesized a rhodamine-based sensor (RhBUEA) by functionalizing the polyacrylamide hydrogel through free radical polymerization of RhBUEA and then constructed a fast, visual detection device for Fe3+ (Table 1, No. 31) [60]. The fabricated hydrogel showed good selectivity and sensitivity to Fe3+ in the pH range of 4.95 to 8.02 with a fast response time (less than 20 min). The prepared device was successfully used for Fe3+ detection in real environmental water samples.
A novel rhodamine-based sensor (RhB-EDA) was constructed by functionalizing rhodamine with the Fe3+ recognition group ethylenediamine (EDA) (Table 1, No. 32) [61]. The colorless and non-fluorescent RhB-EDA turned pink and showed high fluorescence in the presence of Fe3+ through the coordination-induced lactam ring opening mechanism (Figure 25).
Zhang J., et al. reported a rhodamine-based sensor named LXY (Table 1, No. 33) for quantitative and qualitative Fe3+ detection in HEPES buffer (10 mM, pH = 7.4)/CH3CN (2:3, v/v) [62]. The detection limit of the LXY sensor for Fe3+ was 3.47 × 10−9 M. The prepared sensor achieved a visual detection of Fe3+ through the color and fluorescence change before and after the addition of Fe3+ (Figure 26) and was successfully used in bio-imaging of Caenorhabditis elegans, adult mice, and plant tissue.
A filter paper grafted with rhodamine B (paper-g-RhBUEA) was reported to detect Fe3+ via fluorescent and colorimetric assay by Liu X., et al. (Table 1, No. 34) [63]. The sensor paper-g-RhBUEA realized the on-site detection of Fe3+ using a self-developed smartphone mini application named “Colorimetric detector”. In addition, the fast visual detecting device paper-g-RhBUEA was successfully applied to the on-site detection of Fe3+ in environmental water samples. Cuc T. T. K., et al. designed and synthesized a multi-stimuli responsive rhodamine-based sensor, pseudo [3] rotaxane NI-DBC/RB-DBA (Table 1, No. 35), for the detection of Fe3+ [29]. The prepared mono-fluorophoric pseudo [3] rotaxane NI-DBC/RB-DBA transformed into bi-fluorophoric pseudo [3] rotaxane NI-DBC/RB-DBA-Fe3+ in the presence of Fe3+ by triggering the FRET process (Figure 27). The sensor exhibited high sensitivity to Fe3+ with a very low detection limit (3.90 × 10−8 M) and was applied to detect Fe3+ in pristine water samples.
Qiu X., et al. reported a water-soluble rhodamine-poly ethylene glycol (DRF-PEG) conjugated sensor as a dual-responsive sensor for Fe3+ detection (Table 1, No. 36) [28]. DRF-PEG was comprised of rhodamine 6G hydrazide and benzaldehyde-functionalized polyethylene glycol and synthesized by Schiff base reaction. The water solubility of this prepared sensor was significantly improved by introducing the PEG segment. The designed sensor was successfully used in ratiometric imaging of Fe3+ in living cells and Fe3+ detection in fetal bovine serum. The possible sensing mechanism of DRT-PEG is shown in Figure 28.

2.4. Rhodamine-Based Sensors for Other Metal Ions

A novel rhodamine-based sensor, RBTPA was proposed for the detection of Pb2+ by Chen H., et al. (Table 1, No. 37) [25]. This prepared sensor displayed a specific response for Pb2+ driven by the PET process and the proposed sensing mechanism is shown in Figure 29. Furthermore, RBPTA was successfully applied to detect Pd2+ in actual water samples and living cells. By test paper, RBPTA realizes the on-site and real-time quantitation of Pd2+.
Luo M., et al. synthesized a rhodamine-based sensor (R1) by appending indole to rhodamine B (Table 1, No. 38) [26]. The prepared sensor showed a fluorescent and colorimetric response in the addition of Pb2+. The detection limit of R1 for Pb2+ was 0.17 × 10−9 M which was suitable for the intra-cellular imaging of Pb2+. Xie X. et al. synthesized a rhodamine 6G hydrazide complex, (R6GH), synthesized for fluorescent and visual detection of Pb2+ (Table 1, No. 39) [64] which turned out to be an “off-on” output platform (Figure 30). A paper-based array was also developed by immobilizing R6GH on ordinary filter paper.
Karmegam M. V., et al. synthesized a phenothiazine–rhodamine (PTRH) sensor for Zn2+ sensing in solution and living cells (Table 1, No. 40) [65]. Several factors contributed to the FRET-ON mechanism for Zn2+ detection including the spectral overlap of the donor emission band, the phenothiazine groups in PTRH, and the absorption band, the ring-opened of the rhodamine fluorophore group. The possible binding model of PTRH with Zn2+ was shown in Figure 31 and the limit of detection of the proposed sensor was 2.89 × 10−8 M.
Zhang X., et al. designed and synthesized both rhodamine-B and rhodamine-based sensors, RBS and R6S (Table 1, No. 41), for Zn2+ detection [66] and both sensors showed good selectivity to Zn2+. The pink sensor solution changed to colorless after Zn2+ addition with “turn-on” fluorescence enhancement. RBS and R6S were all successfully applied for Zn2+ quantification inside mitochondria via fluorescence imaging. Paul S., et al. reported an electronically enriched rhodamine-based sensor, PBCMERI-23, via spirolactam ring opening by As3+ (Table 1, No. 42) [67]. The colorless and non-fluorescent PBCMERI-23 turned pink and showed bright yellow fluorescence after the addition of As3+ (Figure 32). PBCMERI-23 also exhibited nice cell permeability and was successfully applied to As3+ bio-imaging in living cells.
Kan C., et al. reported a supramolecular fluorescent sensor (RBGP) for Al3+ detection (Table 1, No. 43) [68]. The prepared sensor showed a fast and stable response to Al3+. Additionally, the response of RBGP was reversed by the addition of F− (Figure 33). The prepared sensor was used in Al3+ bio-imaging in living cells, plant cells, and animal bodies.
RB-CR (Table 1, No. 44), conjugation between rhodamine B and phenylthiourea, was reported by Jiang T. et al. [69]. Spirolactam ring of RB-CR would open when triggered by Cr3+ (Figure 34). The UV-Vis absorption and fluorescence signal of RB-CR displayed pronounced enhancement.
A rhodamine-based sensor (Rh-Hyd) was reported by Rathinam B., et al. (Table 1, No. 45) [70]. The carbonyl and terminal amino groups of Rh-Hyd showed high affinity to Sn2+. The presence of Sn2+ induced spirolactam ring-opening reaction of Rh-Hyd and then changed the color and fluorescence of the prepared sensor. The proposed sensing mechanism of Rh-Hyd to Sn2+ was shown in Figure 35.

3. Rhodamine-Based Sensors for H+

It is significant to investigate dynamic pH in living cells since pH is an indicator of the body’s health and also plays a critical role in cellular processes, such as cell adhesion, cell growth, and ion transport [72,73,74]. The design inspiration for the H+ sensor, named Lyso-NIR-pH, was drawn from the certain correlation between heat stroke and lysosome acidity (Table 2, No. 1) [75]. Thus, the probe structured with an openable deoxylactam served as a response group to pH and the morpholine moiety acted as a recognizing unit for lysosome (Figure 36). This sensor acquired photo-bleaching and auto-fluorescence in vivo, revealed by previous similar sensors as a result of the fluorophore, Si-rhodamine with excellent photostable and NIR fluorescence.
Sensor No. 2 (Table 2) was developed for pH changes in lysosomes during induced abnormal cells, thus promoting cellular signaling responses [76]. This pH sensor exhibited excellent selectivity, sensitivity, and water solubility with a pKa value of 4.10. Remarkably, it was reused for five cycles, demonstrating strong and reproducible performances. pH probes with pKa around six were appropriate for monitoring intracellular pH changes and studying cell processes [77].
The NIR fluorescence sensor of pH, based on hydroxymethyl germanium-rhodamine, showed an optimal pKa for the successful visualization of tumors in a mouse model. The proposed sensor was ranked at the top list among similar probes (Table 2, No.3) [78]. In comparison, the three pH-triggered NIR fluorescent probes (Table 2, No.4) with different pKa values (4.4 for Probe No. 4.1, 4.6 for Probe No. 4.2, and 4.8 for Probe No. 4.3) were synthesized with rhodamine dyes and tetraphenylethene used as FRET or through-bond energy transfer (TBET) donors [79]. The ratiometric sensors caused the aggregation-quenching effect, inducing 98.9% energy transfer from TPE to rhodamine and consequently showing excellent photostability and good selectivity for pH.
Yan Y., et al. reported a BODIPY-rhodamine-based sensor, BDP-RhB to measure the variation in pH of lysosomes in macrophages during inflammation (Table 2, No. 5) [80]. Based on FRET, BDP-RhB responded to the pH range of 8.0 to 4.0 (Figure 37). Importantly, the prepared sensor exhibited good lysosome targeting ability and demonstrated a decrease in pH value during inflammation in macrophages.
Table
Table 2. Rhodamine-based sensors for H+.
Table 2. Rhodamine-based sensors for H+.
No.Molecular StructureTargetSensing MechanismSensor
Type		Sensitive pH RangepKaSolution SystemsApplicationRef.
1Chemosensors 10 00399 i046H+/Fluorescent sensor/4.63
/Living cells[75]
2Chemosensors 10 00399 i047H+/Fluorescent sensorpH = 4.0–7.04.10/Living cells[76]
3Chemosensors 10 00399 i048H+/Fluorescent sensor/6.24NaPi bufferLiving cells[78]
4Chemosensors 10 00399 i049H+TBET and
FRET		Fluorescent sensorpH = 3.0–7.44.4 (1)
4.6 (2)
4.8 (3)		/Living cells[79]
5Chemosensors 10 00399 i050H+FRETRatiometric sensorpH = 4.0–8.07.1/Living cells[80]
6Chemosensors 10 00399 i051H+FRETFluorescent and
colorimetric sensor		//DMF/H2O (v/v, 1:4) (pH = 7.2)Living cells[81]
7Chemosensors 10 00399 i052H+PETFluorescent and
colorimetric sensor		pH = 1.0–7.52.59THF/H2O (v/v, 1: 1)/[82]
A novel aggregation-induced emission target molecule was proposed by Liu Z., et al. (Table 2, No. 6) [81], acquired from rhodamine 6G hydrazine and tetrastyrene carbaldehyde through a high boiling solvent (DMF/H2O) volatilization method. The change in pH induced spiro ring opening structure and the color change (colorless to pink) of the prepared sensor (Figure 38).
Srivastava P., et al. reported a novel pH-responsive fluorescent sensor that consisted of three units (two phenanthrene and one rhodamine B), linked by click chemistry and possessed dual excitation and three color-emitting characteristics (Table 2, No. 7) [82]. Two phenanthrene units in the prepared structure provided more choices for signal response due to the abundant optical-spectral characteristics (Figure 39). The prepared sensor (pKa = 2.59 ± 0.04) showed a specific response in the pH range of 1.0 to 7.5 in THF-water mixtures in Britton-Robinson (B-R) buffer.

4. Rhodamine-Based Sensors for Anions and Others

Many small molecule indicators for cells or body state, such as H2S, NO, and NADH, are playing a critical role in physiological and pathological processes including neuromodulation [83,84], apoptosis [85,86], and inflammation regulation [87,88,89]. There rhodamine derivatives sensors are also used for these indicator molecules, extending the application to biological systems.
Sensor No.1 [90] and No.2 (Table 3) [91] were used to detect NO over a wide pH range (4.0–12.0), designed with a characteristic cell membrane permeability for visualizing in vivo NO. Moreover, NO sensors are characterized by a high reaction rate due to their high chemical activity in short existence [90]. A selective and sensitive cationic fluorescent probe, named ROPD (Table 3, No. 1), was prepared by Wang Q., et al. [90] by grafting a NO-trapper o-phenylenediamine on a rhodamine fluorophore at the C-3 position through the Schiff base reaction. The presence of NO would block the PET of ROPD and induce fluorescence change (Figure 40). Sensor No. 2 (Table 3) was constructed from Rhodamine-B-en and 2-(pyridin-2-ylmethoxy) benzaldehyde by Alam R., et al. [91]. The presence of NO improved the formation of nitroso-hydroxylamine via the spirolactam ring opening mechanism (Figure 41). Resultantly, an obvious intensity enhancement in absorption and emission peaks was observed.
Rhodamine-based sensors designed for the detection of 4-dihydronicotinamide adenine dinucleotide (NADH), H2O2 (a kind of reactive oxygen species), and adenosine triphosphate (ATP) have gained significant attention in the bioimaging area. Sensor No.3 (Table 3) was synthesized via a redox-responsive 3-aminoquinoline appended rhodamine by Podder A., et al. This sensor was a sort of reaction type fluorescent sensor and showed a remarkably increasing fluorescent intensity in the presence of NADH [92]. Apart from the common detection function, the sensor (MQR) figured out the connection between NADH levels and metabolic abnormalities of high clinical significance (Figure 42).
Gu T., et al. reported another reaction type sensor, named RhB-NIR (Table 3, No.4), to detect the H2O2 in living cells [93]. This sensor was triggered by a classical Baeyer-Villiger reaction. Specifically, H2O2 attacked the carbonyl carbon of the amide bond in the sensor structure, causing the rearrangements of α-ketoamide groups (Figure 43). The formed intermediates were successively hydrolyzed, decarboxylated, and released into the fluorophore.
Sensor No.5 (Table 3) was also a kind of reaction-type sensor used for ATP detection [94] and Sensor No. 6 (Table 3) discriminated the ATP as hydrogen bonds formed between diethylenetriamine moiety of the sensor and phosphate groups of the target [95]. Three rhodamine derivatives (probes 1, 2, 3) were constructed by Liu Y. et al. (Table 3, No. 5) [94] and probe 2 demonstrated a specific target at mitochondrial and the real-time detection of ATP in living cells. Tikum A. F., et al. synthesized a NIR-fluorescent sensor (Table 3, No. 6), revealing a turn-on fluorescent response by changing the solution color (from colorless to purple) through the interaction with ATP (Figure 44) [95].
Apart from ATP, the rhodamine-based acid phosphatase (ACP)-detection sensor was reported based on the IFE between oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB), and rhodamine B [96]. Specifically, the fluorescence of rhodamine B was quenched by oxTMB, owing to spectral overlap between the emission of rhodamine B and the absorption of oxTMB. oxTMB was reduced by ascorbic acid, generated from ACP-inducing hydrolysis of 2-phospho-L-ascorbic acid trisodium salt. Thus, the internal filtering effect between rhodamine B and oxTMB was inhibited, realizing the determination of ACP.
Sensor Nos. 8–12 (Table 3) [97,98,99,100,101] were applied for anion detections. Among these, sensor No.8 (Table 3) was a Si-rhodamine-based sensor (SiNH) that showed a nanoscale response after capturing amphiphilic copolymers named mPEG-DSPE [97]. The amphiphilic mPEG-DSPE improved the water solubility of the prepared sensor which was applied to real-time analysis of endogenous ONOO− in living cells (Figure 45).
Sensors for SH− and ClO− are useful in the environment and biosafety. SH− is a highly toxic material and harmful to the environment, humans, and animals [102,103], and ClO− is a toxic disinfection by-product of hypochlorite salts [104], often used as a disinfectant in swimming pools and other water environments [105]. SH− sensor (Table 3 No. 9) [98] and ClO− sensors (Table 3 No. 10–11) [99,100] were applied to detect environment water samples and living cells, and both were convenient for monitoring human and animal health. Wu J., et al. chose the DNBS group as a cleavable quencher of rhodamine-based fluorescence since thiophenols removed the group and recovered the rhodamine fluorescence [98]. The sensing mechanism was attributed to the nucleophilic substitution reaction of thiophenols (Figure 46) and confirmed by HPLC.
Wang Z., et al. reported the rhodamine-based fluorescent sensor, named 6G-ClO (Table 3, No. 10), developed from 2-formyl rhodamine and used for ClO− detection in water and HUVEC cells [99]. Apart from the application in ClO−-detection in water and living cells, a test strip was prepared with 6G-ClO and successfully used for semi-quantitative detection of the same molecule (Figure 47).
Zhang D., et al. reported a ClO− sensor (SRh) (Table 3, No. 11) synthesized by the conjugation of dual-binding benzene and rhodamine B [100]. SRh showed an “off-on” response to ClO−, visible to the naked eye (Figure 48). The detection limit was calculated to be 2.43 × 10−9 M. Wang K., et al. synthesized a turn-on NIR fluorescent sensor with rhodamine derivatives for SO32− detection (Table 3, No. 12) [101]. The addition of SO23− attacked the 4-position carbonyl group in levulinic acid and induced the ester bond cleavage, resulting in the formation of the fluorophore. The ICT process was then restored, and the sensor showed the corresponding NIR fluorescence (Figure 49).

5. Rhodamine-Based Sensors for Multi-Targets

Sensors No. 1, 2, and 3 (Table 4) were developed for the detection of both Hg2+ and Cu2+. Chang L. L., et al. reported a Hg2+ and Cu2+-responsive sensor, RhBH-HB-Ac, based on a completely different sensing mechanism in the absence and presence of UV irradiation (Table 4, No. 1) [106]. Without UV irradiation, this probe selectively recognized Hg2+ through colorimetric and fluorescent responses. Under UV irradiation, Cu2+ induced a significant color change in the sensor (Figure 50).
Wang K., et al. designed a novel bifunctional rhodamine-based sensor, comprising hydrazide and formylformic acid (Table 4, No. 2) [107]. The prepared sensor was used for differential detection of Cu2+ and Hg2+ by different sensing assays in CH3CN-HEPES buffer solution (20 mM, pH 7.4) (1:9, v/v). A colorimetric change in the presence of Cu2+ was observed along with the fluorescent enhancement due to the coordination-induced spirolatam-ring opening process (Figure 51).
RHB (Table 4, No. 3) was a reusable spherical solid supported sensor prepared by a simple two-step route. (1) synthesis of aldehyde functional spherical crosslinked poly(vinylbenzaldehyde-co-divinylbenzene) microbeads (PVBA-DVB) via precipitation polymerization and (2) attaching the rhodamine hydrazide to aldehyde groups via imine linkages [108]. The prepared RHB sensor displayed selective turn-on fluorescence and colorimetric response to Cu2+ and Hg2+ (Figure 52).
Sensor No. 4, 5, and 6 (Table 4) were developed for the co-detection of Al3+ and Hg2+. Among these, sensor No. 4 was a chromenone-based rhodamine, synthesized by Mondal S., et al. [109], and was used for fluorometric and colorimetric recognition of Al3+ and Hg2+ in CH3CN:H2O (3:1, v/v, 10 mM HEPES buffer, pH = 6.85). In addition, the recognition of Al3+ and Hg2+ was discriminated by adding the tetrabutylammonium iodide salts. In the presence of I−, the color change was completely discharged, induced by Hg2+, and color was retained by Al3+ (Figure 53). Sensor TR (Table 4, No.5), was a rhodamine-based sensor appended with triphenylamine and developed for Al3+ and Hg2+ detection with different sensing mechanisms (Figure 54) [110]. Furthermore, TR-coated test papers were successively prepared for the rapid detection of Al3+ and Hg2+.
Hazra A., et al. synthesized a rhodamine-based sensor, named RBO (Table 4, No. 6) through the reaction of N-(rhodamine-6G)lactam-ethylenediamine and 2,1,3-benzoxadiazole-4-carbaldehyde [111] and used for selective detection of Al3+ and Hg2+ in 10 mM HEPES buffer in water: ethanol (1:9, pH = 7.4) (Figure 55). Furthermore, the induced response by Al3+ and Hg2+ was recovered with the assistance of fluoride or sulfide ions, thus opening a path for the construction of logic gates.
Chan W. C., et al. reported a novel rhodamine-based sensor, R34 (Table 4, No. 7), synthesized by the reaction of rhodamine B hydrazide and 3,4- dihydroxybenzaldehyde [112]. R34 exhibited a sensitive and selective response to Al3+ and Cu2+ and displayed significant color change from colorless to pink and colorless to orange for Al3+ and Cu2+, respectively (Figure 56). The prepared sensor was successfully used in actual water samples and living cells bio-imaging.
Zhang Z., et al. reported a rhodamine-based sensor with solvent-dependent binding properties for differential detection of Cr3+ and Cu2+ (Table 4, No. 8) [113]. The sensor depicted a turn-on fluorescence response with high selectivity and sensitivity to Cr3+ and Cu2+ in acetonitrile and ethanol solution, respectively (Figure 57). In acetonitrile medium, the acquired sensor showed different colorimetric, providing easy and differential analysis of Cr3+ and Cu2+ through naked eyes.
A sensor, with a dual function of distinguishing Al3+ and CN−, named sensor No.9 in Table 4 [114], showed strong fluorescence and pink color for Al3+, specifically recognizing CN− with a detection limit of 0.815 × 10−8 M accompanied by reduced fluorescence intensity. The possible binding mechanism of the prepared sensor with Al3+ and CN− is shown in Figure 58.
A rhodamine-based sensor, MF-N3 (Table 4, No. 10), was reported by Zhu L., et al. to selectively accumulate in lysosomes and show turn-on fluorescence for both H2S and H+ [115]. Owing to ingenious molecular design, MF-N3 exhibited strong fluorescence with H2S only in acid conditions, since endogenous H2S is mainly produced in cells with pH in the acidic range. This sensor containing the spirolactam group was modified with 4-azidobenzyl carbamate that reacted with H2S and then transformed to amine, enabling strong fluorescence (Figure 59).
Five rhodamine-based sensors (Table 4, No. 11–15) were designed with distinctive characters for the detection of trivalent metal ions, such as Fe3+, Cr3+, and Al3+. Among these, sensor No.11 (RDP), reported by Kilic H. and Bozkurt E., possessed the best selectivity and the lowest detection limit (2.50 × 10−9 M, 3.16 × 10−9 M, and 1.17 × 10−9 M for Fe3+, Cr3+ and Al3+, respectively). The interaction ratio between the prepared RDP and target ions was 1:2. Similarly, sensor No. 12 (Table 4) was a rhodamine 6G-benzylamine, synthesized by Das D., et al. [117]. The prepared sensor exhibited crystal structure due to only hydrocarbon skeletons in the extended part. In the presence of Fe3+, Cr3+, and Al3+, the sensor showed large enhancements in fluorescence intensity, thus, realizing bio-imaging in living cells.
Sensor No. 13 (Table 4), named RFMS, was constructed by rhodamine 6G functionalized mesoporous silica and served to recognize the target ions and remove them from the matrix [118]. The prepared RFMS had no absorption band in the visible region and possessed low fluorescence at 550 nm. In the presence of Fe3+, Cr3+, and Al3+, RFMS exhibited an absorption band at around 528 nm and the intensity was also enhanced (Figure 60). The opening of the spirolactam ring, induced by the interactions with Fe3+, Cr3+, and Al3+, resulted in a visible color change of RFMS solution from colorless to pink. The removal efficiency of RFMS for Fe3+, Cr3+, and Al3+ was up to 90%.
Roy A., et al. reported a rhodamine-based chemosensor, HL-CHO (Table 4, No. 14) for Fe3+, Cr3+, and Al3+ ions [119]. The fluorescence intensity of HL-CHO in HEPES buffer in methanol: water (9: 1, v/v) (pH 7.4) at 550 nm increased by 800, 588, and 1466 for Fe3+, Cr3+, and Al3+, respectively (Figure 61). Sensor No. 15 (Table 4), TAT-ROD was reported by Sadak A. E. and Karakuş E., showing high sensitivity and selectivity to Fe3+, Cr3+, and Al3+ via TBET pathway. The TAT-ROD enabled Fe3+, Cr3+, and Al3+ recovery in the presence of ethylenediaminetetraacetic acid (EDTA), as shown in Figure 62. Banerjee M., et al. reported a multi-signaling rhodamine-based sensor for rapid recognition of Zn2+, Cd2+, and Hg2+ (Table 4, No. 16) [121]. The prepared sensor displayed a specific response to Zn2+, Cd2+, and Hg2+ via PET-CHEF-FRET processes and was applied to detect Zn2+, Cd2+, and Hg2+ in sea fish and water samples.
Wang Y., et al. designed a rhodamine hydrazone (Table 4, No. 17), displaying exceptional selectivity to Cu2+, Co2+, and Al3+ (Figure 63) [122]. The prepared sensor exhibited fluorescence enhancement in methanol solution when Co2+ was added to the solution and showed a specific response to Al3+ in nearly pure water media. For Cu2+, the acquired sensor demonstrated a color change response in methanol or water solutions.
Pungut N. A. S., et al. reported a colorimetric sensor (RBOV) that displayed a sensitive and selective response to Cu2+, Ni2+, and Co2+ in an aqueous medium (Table 4, No. 18) [123]. The detection limits for three metal ions were 4.0 × 10−8 M, 3.2 × 10−7 M, and 4.8 × 10−7 M, respectively. The sensing mechanism of RBOV for Cu2+, Ni2+, and Co2+ was analyzed, demonstrating a 1:1 stoichiometry of sensor-metal complex for all target ions. Hazra A. and Roy P. synthesized a new rhodamine-based sensor (Table 4, No. 19) for the colorimetric and fluorescence detection of group 13 cations (Al3+, Ga3+, In3+, and Tl3+) in 10 mM HEPES buffer (pH = 7.4) in water/ethanol (1:9, v/v) [124]. The prepared sensor demonstrated fluorescence enhancement and color change because of spirocyclic ring opening induced by the target ions (Figure 64).
Podshibyakin V. A., et al. reported a solvent-dependent multifunctional rhodamine-based sensor for visible selective detection of Al3+, Cu2+, Hg2+, S2− and CN− (Table 4, No. 20) [125]. This prepared sensor showed selectivity to Al3+ in ethanol. The complexes of the sensor and Cu2+ and Hg2+ were used to detect S2− and CN−, respectively (Figure 65).

6. Conclusions and Perspective

Rhodamine and its derivatives possess excellent optical properties: good photo-irradiation stability, high fluorescence quantum yield, and so on. Chemosensors based on rhodamine and its derivatives have attracted extensive attention in areas of chemistry material, biology, medical, and health care. These sensors play an important role as simple, fast, economic, and efficient tools for monitoring environmental quality, health, and mechanism of physiological activity disorder. The unique and convenient close-open ring structure of rhodamine derivatives before and after the addition target induce color and fluorescent changes, showing great benefit for obviously detecting target analyte. Moreover, the fine biocompatibility and near-infrared fluorescence of rhodamine derivatives make them an excellent choice for bio-sensor construction. This review has summarized the development and achievements of rhodamine-based sensors in the past four years and found that there are still spaces for improvements in sensor design and synthesis. The review is intended to bring new clues or bright ideas for further advances in rhodamine-based chemosensors.
The Schiff base reaction is the most common synthesis mechanism when designing rhodamine-based sensors. Other reactions, such as the Mannich reaction, and the Baeyer-Villiger reaction, could be considered in the future. As for the sensing mechanism, coordination between the sensor and target ions is the most common and the coordination atoms are mainly N, O, and S. Other sensing mechanisms, such as reaction-type sensing, especially reversible reaction-type sensing mechanisms, are also attractive choices.
For sensitivity and selectivity, the coordination groups containing electron-rich structures such as carbon-oxygen double bonds. Carbon-nitrogen double bonds are the primary choice when designing the sensors. Apart for sensitivity and selectivity, water solubility is the most significant property of rhodamine-based sensors, concerning the applications in environmental samples. Besides, cell membrane-permeability, cytotoxicity, and organelle localization are all necessary factors that should be taken into consideration in biological applications. In addition, probes based on fluorophore with NIR fluorescence are better due to their anti-interference capability.
As for the rhodamine-based sensor for multi-targets, there are a few strategies for selective recognition; for example, the “multi recognition group” strategy, and the “solvent-dependent sensing” strategy. The former is more reported whereas the latter is superior in sensing performance due to the advantage of interference elimination. Thus, the rhodamine-based sensors for multi-targets via the “solvent-dependent sensing” strategy need to be further developed.

Author Contributions

Writing–Review and Editing, Investigation, Y.W.; Investigation, X.W.; Investigation, W.M.; Supervision, R.L. and W.Z.; Funding Acquisition, Validation, H.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Chemical structures of rhodamine B and rhodamine 6G (A) and the general sensing principles of rhodamine-based sensors (B).
Figure 1. Chemical structures of rhodamine B and rhodamine 6G (A) and the general sensing principles of rhodamine-based sensors (B).
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Figure 2. The proposed sensing mechanism of RMTE (Table 1, No. 2) for Hg2+ [34].
Figure 2. The proposed sensing mechanism of RMTE (Table 1, No. 2) for Hg2+ [34].
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Figure 3. The possible mechanism of RDV (Table 1, No. 4) to Hg2+ [36].
Figure 3. The possible mechanism of RDV (Table 1, No. 4) to Hg2+ [36].
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Figure 4. The proposed sensing mechanism of RBST (Table 1, No. 5) to Hg2+ [37].
Figure 4. The proposed sensing mechanism of RBST (Table 1, No. 5) to Hg2+ [37].
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Figure 5. The possible sensing mechanism of the prepared sensor (Table 1, No. 6) to Hg2+ [38].
Figure 5. The possible sensing mechanism of the prepared sensor (Table 1, No. 6) to Hg2+ [38].
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Figure 6. The possible mechanism of Probe 2 (Table 1, No. 7) to Hg2+ [39].
Figure 6. The possible mechanism of Probe 2 (Table 1, No. 7) to Hg2+ [39].
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Figure 7. The proposed sensing mechanism of the prepared probe (Table 1, No. 8) to Hg2+ [40].
Figure 7. The proposed sensing mechanism of the prepared probe (Table 1, No. 8) to Hg2+ [40].
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Figure 8. The possible sensing mechanism of RhB (Table 1, No. 9) to Hg2+ [41].
Figure 8. The possible sensing mechanism of RhB (Table 1, No. 9) to Hg2+ [41].
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Figure 9. The proposed reaction mechanism between 1O (Table 1, No. 10) and Hg2+ [42].
Figure 9. The proposed reaction mechanism between 1O (Table 1, No. 10) and Hg2+ [42].
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Figure 10. The proposed sensing mechanism of RD6 (Table 1, No.13) to Hg2+ [45].
Figure 10. The proposed sensing mechanism of RD6 (Table 1, No.13) to Hg2+ [45].
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Figure 11. The proposed sensing mechanism of CCS-Hg (Table 1, No. 15) [47].
Figure 11. The proposed sensing mechanism of CCS-Hg (Table 1, No. 15) [47].
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Figure 12. The proposed sensing mechanism of the prepared sensor (Table 1, No. 16) for Hg2+ [48].
Figure 12. The proposed sensing mechanism of the prepared sensor (Table 1, No. 16) for Hg2+ [48].
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Figure 13. The proposed sensing mechanism of the prepared sensor (Table 1, No. 17) [24].
Figure 13. The proposed sensing mechanism of the prepared sensor (Table 1, No. 17) [24].
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Figure 14. The proposed reaction mechanism of the prepared sensor (Table 1, No.18) [49].
Figure 14. The proposed reaction mechanism of the prepared sensor (Table 1, No.18) [49].
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Figure 15. The proposed mechanism of 6GS2 (Table 1, No. 19) for sensing Cu2+ [50].
Figure 15. The proposed mechanism of 6GS2 (Table 1, No. 19) for sensing Cu2+ [50].
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Figure 16. The proposed detecting mechanism of RhP (Table 1, No. 21) [52].
Figure 16. The proposed detecting mechanism of RhP (Table 1, No. 21) [52].
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Figure 17. The proposed response mechanism of the prepared sensor (Table 1, No. 22) for Cu2+ [53].
Figure 17. The proposed response mechanism of the prepared sensor (Table 1, No. 22) for Cu2+ [53].
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Figure 18. The proposed sensing process of NRG (Table 1, No. 23) [54].
Figure 18. The proposed sensing process of NRG (Table 1, No. 23) [54].
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Chemosensors 10 00399 g019 550
Figure 19. The proposed sensing mechanism of EtRh-N-NH2 (Table 1, No. 24) [27].
Figure 19. The proposed sensing mechanism of EtRh-N-NH2 (Table 1, No. 24) [27].
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Chemosensors 10 00399 g020 550
Figure 20. The proposed sensing mechanism of the prepared sensor (Table 1, No. 26) to Fe3+ [55].
Figure 20. The proposed sensing mechanism of the prepared sensor (Table 1, No. 26) to Fe3+ [55].
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Chemosensors 10 00399 g021 550
Figure 21. The proposed sensing mechanism of BYY (Table 1, No. 27) for Fe3+ [56].
Figure 21. The proposed sensing mechanism of BYY (Table 1, No. 27) for Fe3+ [56].
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Chemosensors 10 00399 g022 550
Figure 22. The proposed sensing mechanism of the prepared sensor L1 (Table 1, No. 28) to Fe3+ [57].
Figure 22. The proposed sensing mechanism of the prepared sensor L1 (Table 1, No. 28) to Fe3+ [57].
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Chemosensors 10 00399 g023 550
Figure 23. The proposed sensing mechanism of M3 (Table 1, No. 29) to Fe3+ [58].
Figure 23. The proposed sensing mechanism of M3 (Table 1, No. 29) to Fe3+ [58].
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Chemosensors 10 00399 g024 550
Figure 24. The proposed binding mechanism of RS (Table 1, No. 30) to Fe3+ [59].
Figure 24. The proposed binding mechanism of RS (Table 1, No. 30) to Fe3+ [59].
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Chemosensors 10 00399 g025 550
Figure 25. The proposed sensing mechanism of RhB-EDA (Table 1, No. 32) for Fe3+ [61].
Figure 25. The proposed sensing mechanism of RhB-EDA (Table 1, No. 32) for Fe3+ [61].
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Chemosensors 10 00399 g026 550
Figure 26. The proposed sensing mechanism of LXY (Table 1, No. 33) to Fe3+ [62].
Figure 26. The proposed sensing mechanism of LXY (Table 1, No. 33) to Fe3+ [62].
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Figure 27. The possible coordination mechanism of pseudo [3]rotaxane NI-DBC/RB-DBA (Table 1, No. 35) with Fe3+ [29].
Figure 27. The possible coordination mechanism of pseudo [3]rotaxane NI-DBC/RB-DBA (Table 1, No. 35) with Fe3+ [29].
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Chemosensors 10 00399 g028 550
Figure 28. The proposed coordination mechanism of DRF-PEG (Table 1, No. 35) towards Fe3+ [28].
Figure 28. The proposed coordination mechanism of DRF-PEG (Table 1, No. 35) towards Fe3+ [28].
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Chemosensors 10 00399 g029 550
Figure 29. The proposed sensing mechanism of RBTPA (Table 1, No. 37) to Pb2+ [25].
Figure 29. The proposed sensing mechanism of RBTPA (Table 1, No. 37) to Pb2+ [25].
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Chemosensors 10 00399 g030 550
Figure 30. The possible sensing mechanism of R6GH (Table 1, No. 39) to Pb2+ [64].
Figure 30. The possible sensing mechanism of R6GH (Table 1, No. 39) to Pb2+ [64].
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Chemosensors 10 00399 g031 550
Figure 31. The proposed binding mode of PTRH (Table 1, No. 40) with Zn2+ [65].
Figure 31. The proposed binding mode of PTRH (Table 1, No. 40) with Zn2+ [65].
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Chemosensors 10 00399 g032 550
Figure 32. The proposed sensing mechanism of PBCMERI-23 (Table 1, No. 42) to As3+ [67].
Figure 32. The proposed sensing mechanism of PBCMERI-23 (Table 1, No. 42) to As3+ [67].
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Figure 33. The proposed sensing mechanism of RBGP (Table 1, No. 43) to As3+ [68].
Figure 33. The proposed sensing mechanism of RBGP (Table 1, No. 43) to As3+ [68].
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Figure 34. The possible binding mechanism of RB-CR (Table 1, No. 44) to Cr3+ [69].
Figure 34. The possible binding mechanism of RB-CR (Table 1, No. 44) to Cr3+ [69].
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Chemosensors 10 00399 g035 550
Figure 35. The possible sensing mechanism of Rh-Hyd (Table 1, No. 45) to Sn2+ [70].
Figure 35. The possible sensing mechanism of Rh-Hyd (Table 1, No. 45) to Sn2+ [70].
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Figure 36. The response mechanism of Lyso-NIR-pH (Table 2, No. 1) to pH in lysosome [75].
Figure 36. The response mechanism of Lyso-NIR-pH (Table 2, No. 1) to pH in lysosome [75].
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Figure 37. The response mechanism of BDP-RhB (Table 2, No. 5) to pH [80].
Figure 37. The response mechanism of BDP-RhB (Table 2, No. 5) to pH [80].
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Figure 38. The concluded sensing mechanism of this prepared sensor (Table 2, No. 6) for pH [81].
Figure 38. The concluded sensing mechanism of this prepared sensor (Table 2, No. 6) for pH [81].
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Figure 39. The possible sensing mechanism of the prepared sensor (Table 2, No. 7) for pH [82].
Figure 39. The possible sensing mechanism of the prepared sensor (Table 2, No. 7) for pH [82].
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Chemosensors 10 00399 g040 550
Figure 40. The proposed sensing mechanism of ROPD (Table 3, No. 1) for NO [90].
Figure 40. The proposed sensing mechanism of ROPD (Table 3, No. 1) for NO [90].
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Figure 41. The proposed reaction mechanisms of the prepared sensor (Table 3, No. 2) with NO [91].
Figure 41. The proposed reaction mechanisms of the prepared sensor (Table 3, No. 2) with NO [91].
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Figure 42. The possible sensing mechanism of MQR (Table 3, No. 3) for NADH [92].
Figure 42. The possible sensing mechanism of MQR (Table 3, No. 3) for NADH [92].
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Chemosensors 10 00399 g043 550
Figure 43. The proposed sensing mechanism of RhB-NIR (Table 3, No. 4) for H2O2 [93].
Figure 43. The proposed sensing mechanism of RhB-NIR (Table 3, No. 4) for H2O2 [93].
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Figure 44. The proposed sensing mechanism of the prepared sensor (Table 3, No. 6) for ATP [95].
Figure 44. The proposed sensing mechanism of the prepared sensor (Table 3, No. 6) for ATP [95].
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Figure 45. The proposed sensing mechanism of SiNH (Table 3, No. 8) [97].
Figure 45. The proposed sensing mechanism of SiNH (Table 3, No. 8) [97].
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Figure 46. The proposed sensing mechanism of the prepared sensor (Table 3, No. 9) for PhSH [98].
Figure 46. The proposed sensing mechanism of the prepared sensor (Table 3, No. 9) for PhSH [98].
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Figure 47. The proposed mechanism of 6G-ClO (Table 3, No. 10) with ClO− [99].
Figure 47. The proposed mechanism of 6G-ClO (Table 3, No. 10) with ClO− [99].
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Figure 48. The proposed sensing mechanism of SRh (Table 3, No. 11) with ClO− [100].
Figure 48. The proposed sensing mechanism of SRh (Table 3, No. 11) with ClO− [100].
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Figure 49. The possible reaction mechanism of the prepared sensor (Table 3, No. 12) for SO32− [101].
Figure 49. The possible reaction mechanism of the prepared sensor (Table 3, No. 12) for SO32− [101].
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Chemosensors 10 00399 g050 550
Figure 50. The sensing mechanism of RhBH-HB-Ac (Table 4, No. 1) [106].
Figure 50. The sensing mechanism of RhBH-HB-Ac (Table 4, No. 1) [106].
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Figure 51. Proposed binding modes of the prepared sensor (Table 4, No. 2) with Cu2+ and Hg2+ [107].
Figure 51. Proposed binding modes of the prepared sensor (Table 4, No. 2) with Cu2+ and Hg2+ [107].
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Figure 52. The proposed sensing mechanism of RHB (Table 4, No. 3) to Cu2+ and Hg2+ [108].
Figure 52. The proposed sensing mechanism of RHB (Table 4, No. 3) to Cu2+ and Hg2+ [108].
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Figure 53. The sensing mechanism of the prepared sensor (Table 4, No. 4) for Al3+ and Hg2+ [109].
Figure 53. The sensing mechanism of the prepared sensor (Table 4, No. 4) for Al3+ and Hg2+ [109].
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Figure 54. Proposed sensing mechanism of TR (Table 4, No. 5) for Al3+ and Hg2+ [110].
Figure 54. Proposed sensing mechanism of TR (Table 4, No. 5) for Al3+ and Hg2+ [110].
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Figure 55. The possible sensing mechanism of RBO (Table 4, No. 6) for Al3+ and Hg2+ [111].
Figure 55. The possible sensing mechanism of RBO (Table 4, No. 6) for Al3+ and Hg2+ [111].
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Figure 56. The proposed mechanism for interaction between R34 (Table 4, No. 7) and Al3+/Cu2+ [112].
Figure 56. The proposed mechanism for interaction between R34 (Table 4, No. 7) and Al3+/Cu2+ [112].
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Figure 57. The sensing mechanism of this prepared sensor (Table 4, No. 8) for Cr3+ and Cu2+ [113].
Figure 57. The sensing mechanism of this prepared sensor (Table 4, No. 8) for Cr3+ and Cu2+ [113].
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Figure 58. The possible binding mechanism of the prepared sensor (Table 4, No. 9) for Al3+ and CN− [114].
Figure 58. The possible binding mechanism of the prepared sensor (Table 4, No. 9) for Al3+ and CN− [114].
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Figure 59. The sensing mechanism of MF-N3 (Table 4, No. 10) for dual-response to H2S and protons [115].
Figure 59. The sensing mechanism of MF-N3 (Table 4, No. 10) for dual-response to H2S and protons [115].
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Figure 60. The possible sensing mechanism of RFMS (Table 4, No. 13) to Fe3+, Cr3+ and Al3+ [118].
Figure 60. The possible sensing mechanism of RFMS (Table 4, No. 13) to Fe3+, Cr3+ and Al3+ [118].
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Figure 61. The proposed sensing mechanism of HL-CHO to Fe3+, Cr3+ and Al3+ [119].
Figure 61. The proposed sensing mechanism of HL-CHO to Fe3+, Cr3+ and Al3+ [119].
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Figure 62. The proposed binding mechanism of TAT-ROD (Table 4, No. 15) to Fe3+, Cr3+ and Al3+ [120].
Figure 62. The proposed binding mechanism of TAT-ROD (Table 4, No. 15) to Fe3+, Cr3+ and Al3+ [120].
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Figure 63. The proposed reaction mechanism of the prepared sensor (Table 4, No.17) with Cu2+, Co2+, and Al3+ [122].
Figure 63. The proposed reaction mechanism of the prepared sensor (Table 4, No.17) with Cu2+, Co2+, and Al3+ [122].
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Figure 64. The possible sensing mechanism of the prepared sensor (Table 4, No.19) to Al3+, Ga3+, In3+ and Tl3+ [124].
Figure 64. The possible sensing mechanism of the prepared sensor (Table 4, No.19) to Al3+, Ga3+, In3+ and Tl3+ [124].
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Figure 65. The proposed mechanism of coordination between the prepared sensor (Table 4, No. 20) and the target ions [125].
Figure 65. The proposed mechanism of coordination between the prepared sensor (Table 4, No. 20) and the target ions [125].
Chemosensors 10 00399 g065
Table
Table 1. Rhodamine-based sensors for metal ions.
Table 1. Rhodamine-based sensors for metal ions.
No.Molecular StructureTargetSensing MechanismSensor TypeDetection Limit(M)Bonding Ratio *Solution SystemsApplicationRef.
1Chemosensors 10 00399 i001Hg2+/Colorimetric and fluorescent probe7.48 × 10−91:2100% H2OTest strip[33]
2Chemosensors 10 00399 i002Hg2+/Colorimetric sensor/1:1CH3CN/H2O
(1/99, v/v)
HEPES buffer
(pH = 7.05)		Actual water samples, living cells[34]
3Chemosensors 10 00399 i003Hg2+/Fluorescent and
colorimetric sensor		8.73 × 10−7/DMFLiving cells[35]
4Chemosensors 10 00399 i004Hg2+/Fluorescent and
colorimetric sensor		1.36 × 10−71:1CH3CN/H2O (3/7, v/v)Actual water samples and test paper[36]
5Chemosensors 10 00399 i005Hg2+/Fluorescent and
colorimetric sensor		0.11 × 10−91:1EtOH/H2O (2/1, v/v)Actual water samples, MCF-7 cells, zebrafish and soybean rhizome tissues[37]
6Chemosensors 10 00399 i006Hg2+/Fluorescent sensor/1:1/Living cells[38]
7Chemosensors 10 00399 i007Hg2+/Fluorescent and
colorimetric sensor		1.8 × 10−8
1.6 × 10−8
5.6 × 10−8		1:1Tris-HCl/
C2H5OH
(3/7, v/v,
pH = 7.2)		Living cells[39]
8Chemosensors 10 00399 i008Hg2+ Fluorescent sensor/1:1C2H5OH/
PBS buffer
(2/8, v/v,
pH = 7.4)		Living cells[40]
9Chemosensors 10 00399 i009Hg2+/Fluoric-metric sensor2.57 × 10−61:1EtOH/HEPES buffer
(1:1, v/v)		Test paler and living cells[41]
10Chemosensors 10 00399 i010Hg2+FRETFluorescent and
colorimetric sensor		2.46 × 10−71:1/Water sample[42]
11Chemosensors 10 00399 i011Hg2+/Fluorescent sensor0.27 μg/L1:1/Water sample[43]
12Chemosensors 10 00399 i012Hg2+/Fluorescent and
colorimetric sensor		3.4 × 10−91:1HEPES/DMF (1/1, v/v)Living cells[44]
13Chemosensors 10 00399 i013Hg2+/Fluorescent and
colorimetric sensor		1.2 × 10−81:1CH3CN/H2O (9:1v/v)Test strip[45]
14Chemosensors 10 00399 i014Hg2+/Fluorescent and
colorimetric sensor		9.18 × 10−71:1/Tap water,
colorimetric card		[46]
15Chemosensors 10 00399 i015Hg2+/Fluorescent
sensor		/2:1H2O/EtOH (3/2, v/v,
pH = 7.3);		Living cells[47]
16Chemosensors 10 00399 i016Hg2+FRETColorimetric and ratiometric fluorescent sensor0.81 × 10−61:1CH3CN/H2O
(1/1, v/v)		Living cells[48]
17Chemosensors 10 00399 i017Cu2+FRETColorimetric and ratiometric probe1.168 × 10−81:1CH3CN/HEPES buffer
(4/1, v/v)
(pH = 7.3)		Actual water samples[24]
18Chemosensors 10 00399 i018Cu2+/Fluorescent sensor4.38 × 10−81:1H2OWhite wine samples[49]
19Chemosensors 10 00399 i019Cu2+PETFluorescent and
colorimetric sensor		7.4 × 10−81:1H2O/DMSO
(9/1, v/v)		Test paper[50]
20Chemosensors 10 00399 i020Cu2+/Fluorescent and
colorimetric sensor		0.69 × 10−81:2Acetone/H2O
(1/2, v/v)		Living cells[51]
21Chemosensors 10 00399 i021Cu2+/Fluorescent and
colorimetric sensor		/1:1HEPES
/CH3CN
(4/1, v/v)
(pH = 7.0)		Living cells[52]
22Chemosensors 10 00399 i022Cu2+/Fluorescent and
colorimetric sensor		8.99 × 10−81:2CH3CN/H2O
(1/2, v/v)
(pH = 7.2, 50 mM tris–HCl)		HepG2 living cells[53]
23Chemosensors 10 00399 i023Cu2+/Fluorescent and
colorimetric sensor		3.4 × 10−81:2CH3OH/H2O (4:1, v/v)Gel balls[54]
24Chemosensors 10 00399 i024Cu2+ICTFluorescent sensor6 × 10−62:1PBS/EtOH
(1/1, v/v)		/[27]
25Chemosensors 10 00399 i025Fe3+/Colorimetric sensor2.54 × 10−81:1EtOH/H2O
(5/5, v/v)
Tris–HCl
(pH = 7.4)		Living cells[32]
26Chemosensors 10 00399 i026Fe3+/Fluorescent and
colorimetric sensor		3.76 × 10−91:1MeCN/H2O
(1/1, v/v)
(pH = 7.2)		Living cells[55]
27Chemosensors 10 00399 i027Fe3+/Fluorescent and
colorimetric sensor		2.7 × 10−72:1EtOH/H2O (2/3, v/v)
(pH = 7.2)		Living cells[56]
28Chemosensors 10 00399 i028Fe3+/Fluorescent and
colorimetric sensor		7.4 × 10−62:1CH3CN/
Tris–HCl
buffer
(9/1, v/v;
pH = 7.00)		Actual water samples[57]
29Chemosensors 10 00399 i029Fe3+/Fluorescent
sensor		5.2 × 10−61:1Acetonitrile/
Tris-HCl buffer
(3/7, v/v;
pH = 7.4)		Living cells[58]
30Chemosensors 10 00399 i030Fe3+/Fluorescent
sensor		1.64 × 10−61:1Pure waterWater[59]
31Chemosensors 10 00399 i031Fe3+/Colorimetric sensor0.88 × 10−7/PolyacrylamideWater[60]
32Chemosensors 10 00399 i032Fe3+/Fluorescent and
colorimetric sensor		/1:1//[61]
33Chemosensors 10 00399 i033Fe3+/Fluorescent
sensor		3.47 × 10−9/HEPES/
CH3CN
(2:3, v/v)
(10 mM,
pH = 7.4)		Caenorhabditis elegans, adult mice, plant tissue[62]
34Chemosensors 10 00399 i034Fe3+/Fluorescent and
colorimetric sensor		0.19 × 10−9/Rhodamine-grafted paperEnvironmental water[63]
35Chemosensors 10 00399 i035Fe3+FRETFluorescent
sensor		3.90 × 10−8/Dioxane/H2O
(4:6, v/v)		Paper test strips,
water samples		[29]
36Chemosensors 10 00399 i036Fe3+ICTFluorescent and
colorimetric sensor		3.16 × 10−61:2H2O
(pH = 6.5)		Living cells,
fetal bovine serum samples		[28]
37Chemosensors 10 00399 i037Pb2+PETColorimetric sensor4.2 × 10−91:1EtOH/H2O (3/2, v/v)
HEPES Buffer
(pH = 7.4)		Living cells,
test paper		[25]
38Chemosensors 10 00399 i038Pb2+PETFluorescent and
colorimetric sensor		0.17 × 10−91:1CH3OH/PBS buffer
(1/1, v/v)
pH = 7.40)		Living cells[26]
39Chemosensors 10 00399 i039Pb2+/Fluorescent and
colorimetric sensor		2.5 × 10−61:1/Tap water, soil, fish, shrimp[64]
40Chemosensors 10 00399 i040Zn2+FRETFluorescent
sensor		2.89 × 10−81:1H2O
/Acetonitrile
(8/2, v/v)		Living cells[65]
41Chemosensors 10 00399 i041Zn2+ICTFluorescent
sensor		1.8–1.9 × 10−9/50 mM,
HEPES buffer, pH = 7.54		Living cells,
mitochondria		[66]
42Chemosensors 10 00399 i042As3+/Fluorescent and
colorimetric sensor		0.164 μg/L/Acetonitrile/
HEPES buffer
(4/1, v/v,
pH = 7.4)		Living cells[67]
43Chemosensors 10 00399 i043Al3+/Fluorescent
sensor		0.146 × 10−61:1/Living cells, plant cells and living bodies[68]
44Chemosensors 10 00399 i044Cr3+/Fluorescent
sensor		/1:1/Living cells[69]
45Chemosensors 10 00399 i045Sn2+ICTFluorescent and
colorimetric sensor		1.62 × 10−71:1EtOH/H2O (8/2, v/v)Living cells[70]
*: The bonding ratio is between probe and target.
Table
Table 3. Rhodamine-based sensors for anions and others.
Table 3. Rhodamine-based sensors for anions and others.
No.Molecular StructureTargetProbe TypeSensing MechanismSensor TypeSolution SystemsApplicationRef.
1Chemosensors 10 00399 i053NOTurn-onPET blockedFluorescent probePBS buffers
(pH = 7.4)		Living cells[90]
2Chemosensors 10 00399 i054NOTurn-on/Fluorescent probeHEPES buffers
(pH = 7.4)		Living cells and zebrafish[91]
3Chemosensors 10 00399 i055NADHTurn-on/Fluorescent probePBS buffers
(pH = 7.4)		Living cells[92]
4Chemosensors 10 00399 i056H2O2Turn-onPET blockedFluorescent sensorPBS with 0.1% DMSO
(pH = 7.4,)		Living cells[93]
5Chemosensors 10 00399 i057ATPTurn-on/Fluorescent and
colorimetric sensor		PBS solution
(containing 40% DMSO)		Living cells[94]
6Chemosensors 10 00399 i058ATPTurn-on/Fluorescent and
colorimetric sensor		EtOH/
PBS buffer
(1/99, v/v;
pH = 7.4)		Living lysosomes[95]
7Chemosensors 10 00399 i059ACPTurn-onIFEFluorescent and
colorimetric sensor		/Human serum[96]
8Chemosensors 10 00399 i060Peroxynitrite (ONOO−)Turn-onPET blockedFluorescent probeH2O/CH3CN (7:3, v/v)
HEPES buffers
(pH = 7.4)		Living cells[97]
9Chemosensors 10 00399 i061Thiophenols
(-SH)		Turn-onPET blockedFluorescent probeDMSO/HEPES solution
(1:1, v/v)
(pH = 7.4)		Water and
living cells		[98]
10Chemosensors 10 00399 i062ClO−Turn-on/Fluorescent and
colorimetric sensor		C2H5OH/H2O
(1:1, v/v)		Living lysosomes and real water samples[99]
11Chemosensors 10 00399 i063ClO−Turn-on/Fluorescent and
colorimetric sensor		CH3CH2OH-Tris (7/3, v/v,
pH = 7.4)		Living cells[100]
12Chemosensors 10 00399 i064SO32−Turn-onICTFluorescent probePBS buffer
(10 mM, pH 7.4, 1% DMSO)		Living cells and zebrafish[101]
Table
Table 4. Rhodamine-based sensors for multi-targets.
Table 4. Rhodamine-based sensors for multi-targets.
No.Molecular StructureTargetSensing MechanismSensor TypeLODSolution SystemsApplicationRef.
1Chemosensors 10 00399 i065Hg2+
Cu2+		/Colorimetric and fluorescent probe7.1 × 10−8
1.5 × 10−7		IPA/H2O
(8/1, v/v)
(Iso-Propyl Alcohol)		/[106]
2Chemosensors 10 00399 i066Cu2+
Hg2+		/Fluorescent and
colorimetric sensor		/CH3CN/
HEPES buffer
(1/9, v/v;
pH = 7.4) 		/[107]
3Chemosensors 10 00399 i067Cu2+
Hg2+		/Fluorescent and
colorimetric sensor		5.06 × 10−7
3.90 × 10−7		CH3CN/H2O
(8/2, v/v)
(pH = 7.2)		/[108]
4Chemosensors 10 00399 i068Hg2+
Al3+		FRETFluorescent and
colorimetric sensor		1.26 × 10−7
1.9 × 10−7		MeCN/H2O
(3/1, v/v)
HEPES buffer
(pH = 6.85)		/[109]
5Chemosensors 10 00399 i069Hg2+
Al3+		FRET
PET		Fluorescent probe0.48 × 10−6
7.18 × 10−8		MeCN/H2O (9/1, v/v)Test paper[110]
6Chemosensors 10 00399 i070Hg2+
Al3+		/Fluorescent
sensor		1.60 × 10−5
6.54 × 10−6		H2O/EtOH
(1:9, v/v)
(pH = 7.4)		River water,
paper test		[111]
7Chemosensors 10 00399 i071Cu2+
Al3+		/Fluorescent and
colorimetric sensor		9.90 × 10−9
5.63 × 10−9		MeCN/H2O
(6:4, v/v)		Living cells,
natural mineral water,
tap water		[112]
8Chemosensors 10 00399 i072Cr3+
Cu2+		/Colorimetric sensor4.7 × 10−8
7.6 × 10−8		CH3CN solution
Ethanol solution		/[113]
9Chemosensors 10 00399 i073Al3+
CN−		PET blockedFluorescent and
colorimetric sensor		1.68 × 10−9
0.82 × 10−9		HEPES buffer
(pH = 7.04)		Living cells[114]
10Chemosensors 10 00399 i074H+
H2S		ICT (Intramolecular charge transfer)Fluorescent probe /Living cells[115]
11Chemosensors 10 00399 i075Cr3+
Al3+
Fe3+		/Fluorescent and
colorimetric sensor		3.16 × 10−9
1.17 × 10−9
2.50 × 10−9		H2O/EtOH
(1/1, v/v)		/[116]
12Chemosensors 10 00399 i076Cr3+
Al3+
Fe3+		/Colorimetric sensor2.28 × 10−6
1.28 × 10−6
1.34 × 10−6		H2O/CH3CN (4/1, v/v,
pH = 7.2)		Living cells[117]
13Chemosensors 10 00399 i077Cr3+
Al3+
Fe3+		/Fluorescent and
colorimetric sensor		9.18 × 10−9
5.40 × 10−9
7.23 × 10−7		H2O/EtOH
(14/1, v/v)		/[118]
14Chemosensors 10 00399 i078Cr3+
Al3+
Fe3+		/Fluorescent and
colorimetric sensor		1.58 × 10−8
6.97 × 10−9
1.4 × 10−8		CH3OH/H2O
(9/1, v/v)
HEPES buffer
(pH = 7.4)		Living cells[119]
15Chemosensors 10 00399 i079Cr3+
Al3+
Fe3+		TBETRatiometric fluorescent and colorimetric sensor1.70 × 10−4
2.3 × 10−5
2.5 × 10−5		MeOHTest strips[120]
16Chemosensors 10 00399 i080Zn2+
Cd2+
Hg2+		PET-CHEF
PET-CHEF
PET-FRET		Fluorescent and
colorimetric sensor		1.2 × 10−9
9.6 × 10−9
1.5 × 10−10		MeOH/H2O, (4/1, v/v)
HEPES buffer
(pH = 7.4)		Sea fish and water samples[121]
17Chemosensors 10 00399 i081Cu2+
Co2+
Al3+		/Fluorescent
sensor		8.68 × 10−8
/
1.06 × 10−9		CH3OH
CH3OH/H2O
H2O		Living cells[122]
18Chemosensors 10 00399 i082Cu2+
Ni2+
Co2+		/Colorimetric sensor4.0 × 10−8
3.2 × 10−7
4.8 × 10−7		DMSO/TN
(2:1, v/v)
(pH = 7.5)		Test strips[123]
19Chemosensors 10 00399 i083Al3+
Ga3+
In3+
Tl3+		/Fluorescent and
colorimetric sensor		2.66 × 10−8
1.04 × 10−7
8.19 × 10−8
3.10 × 10−8		10 mM HEPES buffer (pH = 7.4) in water/ethanol (1:9, v/v) River water[124]
20Chemosensors 10 00399 i084Al3+
Cu2+
Hg2+
S2−
CN−		ICTFluorescent and
colorimetric sensor		2.1 × 10−7
3.2 × 10−7
4.0 × 10−7
/
/		CH3CN
(5.0 × 10−5 mol/L)		Logic gate[125]
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MDPI and ACS Style

Wang, Y.; Wang, X.; Ma, W.; Lu, R.; Zhou, W.; Gao, H. Recent Developments in Rhodamine-Based Chemosensors: A Review of the Years 2018–2022. Chemosensors 2022, 10, 399. https://doi.org/10.3390/chemosensors10100399

AMA Style

Wang Y, Wang X, Ma W, Lu R, Zhou W, Gao H. Recent Developments in Rhodamine-Based Chemosensors: A Review of the Years 2018–2022. Chemosensors. 2022; 10(10):399. https://doi.org/10.3390/chemosensors10100399

Chicago/Turabian Style

Wang, Yujiao, Xiaojun Wang, Wenyu Ma, Runhua Lu, Wenfeng Zhou, and Haixiang Gao. 2022. "Recent Developments in Rhodamine-Based Chemosensors: A Review of the Years 2018–2022" Chemosensors 10, no. 10: 399. https://doi.org/10.3390/chemosensors10100399

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