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23 pages, 7115 KiB

Open AccessArticle

Synthesis and Evaluation of the (S)-BINAM Derivatives as Fluorescent Enantioselective Detectors

by Alexander V. Shaferov, Anna S. Malysheva, Alexei D. Averin, Olga A. Maloshitskaya and Irina P. Beletskaya

Sensors 2020, 20(11), 3234; https://doi.org/10.3390/s20113234 - 06 Jun 2020

Cited by 2 | Viewed by 2435

Abstract

Pd(0)-catalyzed amination was employed for the synthesis of a new family of (S)-1,1′-bianaphthalene-2,2′-diamine derivatives possessing additional chiral and fluorophore substituents. The Compounds thus obtained were tested as potential detectors of seven amino alcohols, and some of them were found to be [...] Read more.

Pd(0)-catalyzed amination was employed for the synthesis of a new family of (S)-1,1′-bianaphthalene-2,2′-diamine derivatives possessing additional chiral and fluorophore substituents. The Compounds thus obtained were tested as potential detectors of seven amino alcohols, and some of them were found to be able to recognize individual enantiomers of certain amino alcohols by specific changes of their emission spectra in the presence of these analytes. A pronounced dependence of the detecting abilities on the nature of the substituents in the (S)-BINAM derivatives was observed. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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27 pages, 12810 KiB

Open AccessArticle

Double Role of Diphenylpyridine Derivatives as Fluorescent Sensors for Monitoring Photopolymerization and the Determination of the Efficiencies of the Generation of Superacids by Cationic Photoinitiators

by Monika Topa, Filip Petko, Mariusz Galek and Joanna Ortyl

Sensors 2020, 20(11), 3043; https://doi.org/10.3390/s20113043 - 27 May 2020

Cited by 17 | Viewed by 3231

Abstract

Novel fluorescent sensors with electron-donating or electron-withdrawing substituents incorporated into a chromophore group based on 2,6-diphenylpyridine were designed and synthesised. The spectroscopic properties of these compounds were studied. Moreover, the positive solvatochromism of 2,6-bis-(4-methylsulphanylphenyl)pyridine (PT-SCH₃) in selected solvents was studied by [...] Read more.

Novel fluorescent sensors with electron-donating or electron-withdrawing substituents incorporated into a chromophore group based on 2,6-diphenylpyridine were designed and synthesised. The spectroscopic properties of these compounds were studied. Moreover, the positive solvatochromism of 2,6-bis-(4-methylsulphanylphenyl)pyridine (PT-SCH₃) in selected solvents was studied by measurement of the absorption and emission spectra and analysed using the Dimroth–Reichardt solvent parameter set. After that, the performance of a series of 2,6-diphenylpyridine derivatives as fluorescent molecular sensors for monitoring free-radical and cationic photopolymerization processes by the Fluorescence Probe Technique (FPT) was studied. As a consequence of this stage of research, the effect of substituents on the sensitivity of the 2,6-diphenylpyridine derivatives as sensors during photopolymerization has been evaluated and discussed. It has been found that compounds containing strong electron-donating substituent (PT-SCH₃) slightly shift their fluorescence spectrum during the free-radical polymerization of monomer, which enables the monitoring of the polymerization progress using the fluorescence intensity ratio measured at two different wavelengths as the progress indicator. The position of the fluorescence spectrum of 2,6-diphenylpyridine derivatives with electron-withdrawing substituents is practically insensitive to changes occurring in their environment. Hence, it is recommended to use these compounds with different indicators of the progress of the photopolymerization process based on normalised intensity of fluorescence (I_max/I₀). Among the compounds studied, 2,6-bis(4-methylsulphanylphenyl)pyridine (PT-SCH₃) turned out to be the best fluorescent sensor for the purpose of monitoring free-radical polymerization by FPT. Consequently, the dual application of the selected 2,6-diphenylpyridine derivatives is proposed: (a) as fluorescent sensors for monitoring the free-radical photopolymerization progress, and (b) as spectroscopic sensors for the determination of efficiencies of the generation of superacids by cationic photoinitiators during the cationic photopolymerization process. Finally, a new method for determining the relative efficiency of the photogeneration of superacids during the photo cleavage of onium salt has been devised and applied for the evaluation of the performance of 2,6-diphenylpyridine derivatives. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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12 pages, 4409 KiB

Open AccessCommunication

Exploring the Effects of Various Polymeric Backbones on the Performance of a Hydroxyaromatic 1,2,3-Triazole Anion Sensor

by Aikohi Ugboya, Khristal Monroe, Unodinma Ofulue, Kayley Yates, Debanjana Ghosh, Shainaz M. Landge, Rafael Lopes Quirino and Karelle S. Aiken

Sensors 2020, 20(10), 2973; https://doi.org/10.3390/s20102973 - 24 May 2020

Cited by 4 | Viewed by 3451

Abstract

Polymeric chemosensors are vital sensing tools because of higher sensitivity compared to their monomeric counterparts and tunable mechanical properties. This study focuses on the incorporation of a hydroxyaromatic 1,2,3-triazole sensor, 2-(4-phenyl 1H-1,2,3-triazol-1-yl)phenol (PTP), [...] Read more.

Polymeric chemosensors are vital sensing tools because of higher sensitivity compared to their monomeric counterparts and tunable mechanical properties. This study focuses on the incorporation of a hydroxyaromatic 1,2,3-triazole sensor, 2-(4-phenyl 1H-1,2,3-triazol-1-yl)phenol (PTP), into polymers. By itself, the triazole has a selective, fluorometric response to the fluoride, acetate, and dihydrogen phosphate anions, and is most responsive to fluoride. Current investigations probe the suitability of various polymeric backbones for the retention and enhancement of the triazole’s sensing capabilities. Backbones derived from acrylic acid, methyl methacrylate, divinylbenzene, and styrene were explored. UV-illumination, Nuclear Magnetic Resonance (NMR) titration, and ultraviolet-visible (UV-Vis) absorption and fluorescence spectroscopy studies are used to investigate the performance of newly synthesized polymers and the derivatives of PTP that serve as the polymers’ precursors. Among the polymers investigated, copolymers with styrene proved best; these systems retained the sensing capabilities and were amenable to tuning for sensitivity. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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17 pages, 2170 KiB

Open AccessArticle

Use of Spectroscopic Techniques for a Rapid and Non-Destructive Monitoring of Thermal Treatments and Storage Time of Sous-Vide Cooked Cod Fillets

by Abdo Hassoun, Janna Cropotova, Turid Rustad, Karsten Heia, Stein-Kato Lindberg and Heidi Nilsen

Sensors 2020, 20(8), 2410; https://doi.org/10.3390/s20082410 - 23 Apr 2020

Cited by 13 | Viewed by 3975

Abstract

In this work, the potential of spectroscopic techniques was studied to investigate heat-induced changes occurring during the application of thermal treatments on cod (Gadus morhua L.) fillets. Vacuum-packed samples were thermally treated in a water bath at 50, 60, 70 and 80 [...] Read more.

In this work, the potential of spectroscopic techniques was studied to investigate heat-induced changes occurring during the application of thermal treatments on cod (Gadus morhua L.) fillets. Vacuum-packed samples were thermally treated in a water bath at 50, 60, 70 and 80 °C for 5 and 10 min, and further stored for one, four, and eight days at 4 ± 1 °C before analysis. Several traditional (including cooking loss, drip loss, texture, protein solubility, protein oxidation, and color) and spectroscopic (fluorescence and diffuse reflectance hyperspectral imaging) measurements were conducted on the same samples. The results showed a decrease in fluorescence intensity with increasing cooking temperature and storage time, while the impact of cooking time was only noticeable at low temperatures. Diffuse reflectance data exhibited a decrease in absorbance, possibly as a result of protein denaturation and increased scattering at higher cooking temperatures. Both fluorescence and diffuse reflectance data were highly correlated with color parameters, whereas moderate correlations were observed with most other traditional parameters. Support vector machine models performed better than partial least square ones for both classification of cod samples cooked at different temperatures and in prediction of the cooking temperature. The best classification result was obtained on fluorescence data, achieving an accuracy of 92.5%, while the prediction models resulted in a root mean square error of prediction of cooking temperature lower than 5 °C. Overall, the classification and prediction models showed good results, indicating that spectroscopic techniques, especially fluorescence hyperspectral imaging, have a high potential for monitoring thermal treatments in cod fillets. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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14 pages, 2723 KiB

Open AccessArticle

Fluorescence-Sensor Mapping for the in Vineyard Non-Destructive Assessment of Crimson Seedless Table Grape Quality

by Lorenza Tuccio, Lucia Cavigli, Francesca Rossi, Olga Dichala, Fotis Katsogiannos, Ilias Kalfas and Giovanni Agati

Sensors 2020, 20(4), 983; https://doi.org/10.3390/s20040983 - 12 Feb 2020

Cited by 6 | Viewed by 2796

Abstract

Non-destructive tools for the in situ evaluation of vine fruit quality and vineyard management can improve the market value of table grape. We proposed a new approach based on a portable fluorescence sensor to map the ripening level of Crimson Seedless table grape [...] Read more.

Non-destructive tools for the in situ evaluation of vine fruit quality and vineyard management can improve the market value of table grape. We proposed a new approach based on a portable fluorescence sensor to map the ripening level of Crimson Seedless table grape in five different plots in the East, Central-North and South of the Macedonia Region of Greece. The sensor provided indices of ripening and color such as SFR_R and ANTH_RG correlated to the chlorophyll and anthocyanin berry contents, respectively. The mean ANTH_RG index was significantly different among all the plots examined due to the occurrence of different environmental conditions and/or asynchronous ripening processes. The indices presented moderate, poor in some cases, spatial variability, probably due to a significant vine-to-vine, intra-vine and intra-bunch variability. The cluster analysis was applied to the plot with the most evident spatial structure (at Kilkis). Krigged maps of the SFR_R, ANTH_RG and yield were classified by k-means clustering in two-zones that differed significantly in their mean values. ANTH_RG and SFR_R were inversely correlated over 64% of the plot. SFR_R appeared to be a potential useful proxy of yield since it was directly correlated to yield over 66% of the plot. The grape color (ANTH_RG) was slightly higher over the low-yield zones with respect to the high-yield zones. Our study showed that the combination of anthocyanins and chlorophyll indices detected in the field on Crimson Seedless table grape by a portable fluorescence sensor can help in defining the best harvest time and the best areas for harvesting. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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9 pages, 1495 KiB

Open AccessArticle

Fluorescence Sensing of Caffeine in Tea Beverages with 3,5-diaminobenzoic Acid

by Chenxu Du, Chaoqun Ma, Jiao Gu, Lei Li and Guoqing Chen

Sensors 2020, 20(3), 819; https://doi.org/10.3390/s20030819 - 03 Feb 2020

Cited by 14 | Viewed by 4692

Abstract

A rapid, selective and sensitive method for the detection of caffeine in tea infusion and tea beverages are proposed by using 3,5-diaminobenzoic acid as a fluorescent probe. The 3,5-diaminobenzoic acid emits strong fluorescence around 410 nm under the excitation of light at 280 [...] Read more.

A rapid, selective and sensitive method for the detection of caffeine in tea infusion and tea beverages are proposed by using 3,5-diaminobenzoic acid as a fluorescent probe. The 3,5-diaminobenzoic acid emits strong fluorescence around 410 nm under the excitation of light at 280 nm. Both the molecular electrostatic potential analysis and fluorescent lifetime measurement proved that the existence of caffeine can quench the fluorescence of 3,5-diaminobenzoic acid. Under the optimal experimental parameters, the 3,5-diaminobenzoic acid was used as a fluorescent probe to detect the caffeine aqueous solution. There exists a good linear relationship between the fluorescence quenching of the fluorescent probe and the concentration of caffeine in the range of 0.1–100 μM, with recovery within 96.0 to 106.2%, while the limit of detection of caffeine is 0.03 μM. This method shows a high selectivity for caffeine. The caffeine content in different tea infusions and tea beverages has been determined and compared with the results from HPLC measurement. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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13 pages, 2187 KiB

Open AccessArticle

Reversible Oxygen Sensing Based on Multi-Emission Fluorescence Quenching

by Efe Armagan, Shankar Thiyagarajan, Kongchang Wei, Akin Gursoy, Giuseppino Fortunato, Esther Amstad, René Michel Rossi and Claudio Toncelli

Sensors 2020, 20(2), 477; https://doi.org/10.3390/s20020477 - 15 Jan 2020

Cited by 10 | Viewed by 4129

Abstract

Oxygen is ubiquitous in nature and it plays a key role in several biological processes, such as cellular respiration and food deterioration, to name a few. Currently, reversible and non-destructive oxygen sensing is usually performed with sensors produced by photosensitization of phosphorescent organometallic [...] Read more.

Oxygen is ubiquitous in nature and it plays a key role in several biological processes, such as cellular respiration and food deterioration, to name a few. Currently, reversible and non-destructive oxygen sensing is usually performed with sensors produced by photosensitization of phosphorescent organometallic complexes. In contrast, we propose a novel route of optical oxygen sensing by fluorescence-based quenching of oxygen. We hereby developed for the first time a set of multi-emissive purely organic emitters. These were produced through a one-pot hydrothermal synthesis using p-phenylenediamine (PPD) and urea as starting materials. The origin of the multi-emission has been ascribed to the diversity of chemical structures produced as a result of oxidative oligomerization of PPD. A Bandrowski’s base (BB, i.e., trimer of PPD) is reported as the main component at reaction times higher than 8 h. This indication was confirmed by electrospray-ionization quadrupole time-of-flight (ESI-QTOF) and liquid chromatography-mass spectrometry (LC-MS) analysis. Once the emitters are embedded within a high molecular weight poly (vinyl alcohol) matrix, the intensities of all three emission centers exhibit a non-linear quenching provoked by oxygen within the range of 0–8 kPa. The detection limit of the emission centers are 0.89 kPa, 0.67 kPa and 0.75 kPa, respectively. This oxygen-dependent change in fluorescence emission is reversible (up to three tested 0–21% O₂ cycles) and reproducible with negligible cross-interference to humidity. The cost-effectiveness, metal-free formulation, cross-referencing between each single emission center and the relevant oxygen range are all appealing features, making these sensors promising for the detection of oxygen, e.g., in food packaged products. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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19 pages, 4732 KiB

Open AccessArticle

Developing a Silk Fibroin Composite Film to Scavenge and Probe H₂O₂ Associated with UV-Excitable Blue Fluorescence

by Tze-Wen Chung, Chun-Yi Chang, Chun-Ning Chang, Chiu-Hsun Liao, Yun-Jen Jan, Li-Ting Chen and Weng-Pin Chen

Sensors 2020, 20(2), 366; https://doi.org/10.3390/s20020366 - 08 Jan 2020

Cited by 1 | Viewed by 2722

Abstract

A silk fibroin composite film that can simultaneously scavenge and probe H₂O₂ in situ was developed for possibly examining local concentrations of H₂O₂ for biomedical applications. A multi-functional composite film (GDES) that consists of graphene oxide (G), [...] Read more.

A silk fibroin composite film that can simultaneously scavenge and probe H₂O₂ in situ was developed for possibly examining local concentrations of H₂O₂ for biomedical applications. A multi-functional composite film (GDES) that consists of graphene oxide (G), a photothermally responsive element that was blended with polydopamine (PDA, D)/horseradish peroxidase (HRP, E) (or DE complex), and then GDE microaggregates were coated with silk fibroin (SF, S), a tyrosine-containing protein. At 37 °C, the H₂O₂-scavenging ability of a GDES film in solution at approximately 7.5 × 10⁻³ μmol H₂O₂/mg film was the highest compared with those of S and GS films. The intensities of UV-excitable blue fluorescence of a GDES film linearly increased with increasing H₂O₂ concentrations from 4.0 μM to 80 μM at 37 °C. Interestingly, after a GDES film scavenged H₂O₂, the UV-excitable blue fluorescent film could be qualitatively monitored by eye, making the film an eye-probe H₂O₂ sensor. A GDES film enabled to heat H₂O₂-containing samples to 37 °C or higher by the absorption of near-IR irradiation at 808 nm. The good biocompatibility of a GDES film was examined according to the requirements of ISO-10993-5. Accordingly, a GDES film was developed herein to scavenge and eye-probe H₂O₂ in situ and so it has potential for biomedical applications. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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9 pages, 2165 KiB

Open AccessArticle

Robust Classification of Tea Based on Multi-Channel LED-Induced Fluorescence and a Convolutional Neural Network

by Hongze Lin, Zejian Li, Huajin Lu, Shujuan Sun, Fengnong Chen, Kaihua Wei and Dazhou Ming

Sensors 2019, 19(21), 4687; https://doi.org/10.3390/s19214687 - 28 Oct 2019

Cited by 18 | Viewed by 3148

Abstract

A multi-channel light emitting diode (LED)-induced fluorescence system combined with a convolutional neural network (CNN) analytical method was proposed to classify the varieties of tea leaves. The fluorescence system was developed employing seven LEDs with spectra ranging from ultra-violet (UV) to blue as [...] Read more.

A multi-channel light emitting diode (LED)-induced fluorescence system combined with a convolutional neural network (CNN) analytical method was proposed to classify the varieties of tea leaves. The fluorescence system was developed employing seven LEDs with spectra ranging from ultra-violet (UV) to blue as excitation light sources. The LEDs were lit up sequentially to induce a respective fluorescence spectrum, and their ability to excite fluorescence from components in tea leaves were investigated. All the spectral data were merged together to form a two-dimensional matrix and processed by a CNN model, which is famous for its strong ability in pattern recognition. Principal component analysis combined with k-nearest-neighbor classification was also employed as a baseline for comparison. Six grades of green tea, two types of black tea and one kind of white tea were verified. The result proved a significant improvement in accuracy and showed that the proposed system and methodology provides a fast, compact and robust approach for tea classification. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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16 pages, 1810 KiB

Open AccessArticle

Application of a Fluorescent Probe for the Online Measurement of PM-Bound Reactive Oxygen Species in Chamber and Ambient Studies

by Reece Brown, Svetlana Stevanovic, Zachary Brown, Mingfu Cai, Shengzhen Zhou, Wei Song, Xinming Wang, Branka Miljevic, Jun Zhao, Steven Bottle and Zoran Ristovski

Sensors 2019, 19(20), 4564; https://doi.org/10.3390/s19204564 - 21 Oct 2019

Cited by 2 | Viewed by 2732

Abstract

This manuscript details the application of a profluorescent nitroxide (PFN) for the online quantification of radical concentrations on particulate matter (PM) using an improved Particle Into Nitroxide Quencher (PINQ). A miniature flow-through fluorimeter developed specifically for use with the 9,10-bis(phenylethynyl)anthracene-nitroxide (BPEAnit) probe was [...] Read more.

This manuscript details the application of a profluorescent nitroxide (PFN) for the online quantification of radical concentrations on particulate matter (PM) using an improved Particle Into Nitroxide Quencher (PINQ). A miniature flow-through fluorimeter developed specifically for use with the 9,10-bis(phenylethynyl)anthracene-nitroxide (BPEAnit) probe was integrated into the PINQ, along with automated gas phase corrections through periodic high efficiency particle arrestor (HEPA) filtering. The resulting instrument is capable of unattended sampling and was operated with a minimum time resolution of 2.5 min. Details of the fluorimeter design and examples of data processing are provided, and results from a chamber study of side-stream cigarette smoke and ambient monitoring campaign in Guangzhou, China are presented. Primary cigarette smoke was shown to have both short-lived (t_1/2 = 27 min) and long-lived (t_1/2 = indefinite) PM-bound reactive oxygen species (ROS) components which had previously only been observed in secondary organic aerosol (SOA). Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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15 pages, 3032 KiB

Open AccessArticle

CdTe Quantum Dots Modified with Cysteamine: A New Efficient Nanosensor for the Determination of Folic Acid

by Doris E. Ramírez-Herrera, Ana Patricia Reyes-Cruzaley, Giselle Dominguez, Francisco Paraguay-Delgado, Antonio Tirado-Guízar and Georgina Pina-Luis

Sensors 2019, 19(20), 4548; https://doi.org/10.3390/s19204548 - 19 Oct 2019

Cited by 13 | Viewed by 3622

Abstract

In this paper, we report the synthesis, characterization, and application of a new fluorescent nanosensor based on water-soluble CdTe quantum dots (QDs) coated with cysteamine (CA) for the determination of folic acid (FA). CdTe/CA QDs were characterized by high-resolution transmission electron microscopy, the [...] Read more.

In this paper, we report the synthesis, characterization, and application of a new fluorescent nanosensor based on water-soluble CdTe quantum dots (QDs) coated with cysteamine (CA) for the determination of folic acid (FA). CdTe/CA QDs were characterized by high-resolution transmission electron microscopy, the zeta potential, and Fourier-transform infrared (FT-IR), UV-visible, and fluorescence spectroscopy. CdTe QDs coated with mercaptopropionic acid (MPA) and glutathione (GSH) were prepared for comparison purposes. The effect of FA on the photoluminescence intensity of the three thiol-capped QDs at pH 8 was studied. Only CdTe/CA QDs showed a notable fluorescence quenching in the presence of FA. Then, a nanosensor based on the fluorescence quenching of the CdTe QDs at pH 8 was explored. Under optimum conditions, the calibration curve showed a linear fluorescence quenching response in a concentration range of FA from 0.16 to 16.4 μM (R² = 0.9944), with a detection limit of 0.048 μM. A probable mechanism of fluorescence quenching was proposed. The nanosensor showed good selectivity over other possible interferences. This method has been applied for FA quantification in orange beverage samples with excellent results (recoveries from 98.3 to 103.9%). The good selectivity, sensitivity, low cost, and rapidity make CdTe /CA QDs a suitable nanosensor for FA determination. Full article

(This article belongs to the Special Issue Fluorescence-Based Sensors)

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