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Article

Surface-Enhanced Raman Spectroscopic Investigation of PAHs at a Fe3O4@GO@Ag@PDA Composite Substrates

by
Junyu Liu
1,2,
Wencan Cui
3,
Shihua Sang
1,*,
Liang Guan
2,*,
Kecheng Gu
2,*,
Yinyin Wang
2 and
Jian Wang
2
1
College of Material and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, China
2
Department of Petroleum, Oil and Lubricants Army Logistics Academy of PLA, Chongqing 401331, China
3
Department of Basic Courses, Army Logistic Academy of PLA, Chongqing 401331, China
*
Authors to whom correspondence should be addressed.
Micromachines 2022, 13(8), 1253; https://doi.org/10.3390/mi13081253
Submission received: 23 June 2022 / Revised: 31 July 2022 / Accepted: 1 August 2022 / Published: 4 August 2022
(This article belongs to the Section D：Materials and Processing)
Browse Figures
Versions Notes

Abstract

:
A method for surface-enhanced Raman spectroscopy (SERS) sensing of polycyclic aromatic hydrocarbons (PAHs) is reported. Fe3O4@PDA@Ag@GO is developed as the SERS substrate prepared by classical electrostatic attraction method based on the enrichment of organic compounds by graphene oxide (GO) and polydopamine (PDA) and the good separation and enrichment function of Fe3O4. The morphology and structure of the SERS substrate were represented by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and the UV–visible absorption spectrum (UV–vis spectra). The effect of different temperatures on SERS during synthesis was investigated, and it was found that the best effect was achieved when the synthesis temperature was 90 °C. The effect of each component of Fe3O4@PDA@Ag@GO nanocomposites on SERS was explored, and it was found that Ag NPs are of great significance to enhance the Raman signal based on the electromagnetic enhancement mechanism; apart from enriching the polycyclic aromatic hydrocarbons (PAHs) through π–π interaction, GO also generates strong chemical enhancement to the Raman signal, and PDA can prevent Ag from shedding and agglomeration. The existence of Fe3O4 is favored for the fast separation of substrate from the solutions, which greatly simplifies the detection procedure and facilitates the cycle use of the substrate. The experimental procedure is simplified, and the substrate is reused easily. Three kinds of PAHs (phenanthrene, pyrene and benzanthene) are employed as probe molecules to verify the performance of the composite SERS substrate. The results show that the limit of detection (LOD) of phenanthrene pyrene and benzanthene detected by Fe3O4@PDA@Ag@GO composite substrate are 10−8 g/L (5.6 × 10−11 mol/L), 10−7 g/L (4.9 × 10−10 mol/L) and 10−7 g/L (4.4 × 10−10 mol/L), respectively, which is much lower than that of ordinary Raman, and it is promising for its application in the enrichment detection of trace PAHs in the environment.

1. Introduction

Polycyclic aromatic hydrocarbons, which are widespread in the environment, are a kind of hydrocarbon containing two or more conjoined aromatic rings [1]. PAHs are mainly produced during the incomplete combustion of organic matter. Their carcinogenic, teratogenic and mutagenic effects are great threats to human health [2,3,4,5]. Nsibande et al. summarized the concentration of polycyclic aromatic hydrocarbons in various waters between 10−6–10−11 mol/L [6].
Therefore, the monitoring of the content and types of PAHs in the environment has attracted extensive attention. The detection methods for PAHs, such as gas chromatography, high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR) [7,8,9,10,11,12,13], etc., are accurate and used widely. Although the detection methods mentioned above have high sensitivity and stability, they usually demand expensive instrument and complex pre-treatment and enrichment processes, which are time-consuming. These shortcomings bring difficulties to the universal application of these methods. Therefore, a rapid and economical method with high-sensitivity and high-selectivity for PAH detection is necessary.
As an analytical technique with high sensitivity and strong feature recognition ability, surface-enhanced Raman spectroscopy (SERS) has been used widely in rapid detection [14,15,16,17,18]. According to the SERS enhancement mechanism, the target molecules must usually adsorb onto the surface of the SERS substrate by physical or chemical means or be in a short effective enhancement range. However, it is difficult to detect SERS substrates by conventional methods [16] because hydrocarbons such as PAHs do not have special functional groups that interact with metal substrates. Especially when the content of SERS is low, the difficulty of detection increases significantly. Therefore, surface functionalization of SERS substrate is necessary. At present, nanomaterials of noble metals (Au and Ag), transition metals and non-metallic graphene are mainly used to prepare substrates [19,20,21,22,23,24,25,26,27,28,29,30,31].
Currently, one of the most used methods mainly focuses on fixing PAH molecules on SERS substrate surfaces by self-assembly layer modification. For example, Harris et al. modified the metal substrate with the substitution of C18, and, with the help of portable Raman spectrometer, SERS detection of polycyclic aromatic hydrocarbon molecules pyrene and phenanthrene was carried out, with detection limits of 10−8 mol/L and 10−7 mol/L, respectively [32]. Jones et al. and Costa et al. assembled a layer of mercaptan molecules on Ag and Au membrane substrates by self-assembly. The minimum concentrations detected by pyrene are 7 × 10−10 mol/L [31,33]. The ability of SERS substrate to capture PAH molecules was improved. Through the improvement of nanoparticles, Jing et al. and Wang et al. prepared Fe3O4@Ag magnetic nanoparticles modified by thiol molecules and “bowl-shaped” Ag substrates modified by thiol, respectively, realizing the highly sensitive detection of PAHs molecules [34,35]. Wang et al. prepared an Ag-nanoparticle–graphene hybrid for the direct detection of PAHs. The synthesis process is relatively simple, and the raw materials are not expensive, while the limit of detection for pyrene, phenanthrene are as low as 0.73 ppb and 0.57 ppb, respectively [36].
Although this method has achieved SERS detection of PAHs, the organic molecules used for modification are usually difficult to synthesize, which limits the application of SERS.
Until now, the combination of Fe3O4, PDA, GO and Ag as a SERS substrate for the detection of PAHs has not been reported. PDA is a substance with rich functional groups, good hydrophilicity and excellent biocompatibility, which can cover many organic and inorganic materials such as magnetic nanomaterial Fe3O4. The existence of Fe3O4 can separate the substrate quickly and simplify the experimental steps. Graphene oxide (GO) is also known as functional graphene which has a two-dimensional spatial structure and is a carbon-based nanomaterial with abundant hydroxyl, epoxy, carboxyl and other oxygen-containing energy groups. It has high specific surface energy, good hydrophilic and mechanical properties and good adsorption of many chemicals. The accumulation and hydrophobic action of π–π between GO and PAHs can be used to enable the PAHs to show a strong enrichment ability. Ag and GO enhances the Raman signal in Fe3O4@PDA@Ag@GO substrate. PDA has good adhesion and reactivity. The composite nanoparticles have good magnetic response, which can quickly separate and enrich the molecules to be measured and shorten the pretreatment time.
In this study, Fe3O4@PDA@Ag@GO composite material was synthesized by assembly method to detect phenanthrene, pyrene and benzoanthracene in aqueous solution. The limit of detection for phenanthrene, pyrene and benzoanthracene are 10−8 g/L (5.6 × 10−11 mol/L), 10−7 g/L (4.9 × 10−10 mol/L) and 10−7 g/L (4.4 × 10−10 mol/L), respectively, which is much lower than that of ordinary Raman (Wang et al. prepared an Ag-nanoparticle/graphene hybrid for the direct detection of PAHs. The limit of detection for phenanthrene is 3.2 nM (~0.57 ppb) [24]). Our team synthesized Fe3O4@PDA@Au@GO substrate for the detection of phenanthrene. The limit of detection (LOD) of phenanthrene is 10−7 g/L. The raw materials for Fe3O4@PDA@Ag@GO substrates are much cheaper than those of Fe3O4@PDA@Au@GO.

2. Experimental

2.1. Materials and Apparatus

Materials and apparatus used in the experiment are shown in the following Table 1 and Table 2:

2.2. Material Synthesis

2.2.1. Synthesis of Fe3O4 Nanoparticles

A total of 0.9 g of FeCl3·6H2O was dissolved in 28 mL of ethylene glycol (EG) by 15 min ultrasonic vibration to make FeCl3·6H2O completely dissolve. Then, 2.4 g of anhydrous sodium acetate and 0.2 g of polyethylene glycol (PEG) were added to the FeCl3 solution and stirred for 30 min. Ultrasound was performed for 15 min after stirring PEG for 30 min, for PEG was difficult to dissolve. Finally, the mixed solution was transferred to a 50 mL high-pressure reactor and continuously heated to 200 °C in an electric blast-drying oven for 8 h. Then, the blast-drying oven was turned off and the solution was cooled at room temperature naturally. The Fe3O4 solution was poured into a beaker to separate the Fe3O4 nanoparticles by a magnet and the supernatant was removed. Then, Fe3O4 nanoparticles were washed with ultrapure water and anhydrous ethanol, alternately, 3 times, and were dried at 60 °C for 6 h in an electric blast-drying oven [1,18,19].

2.2.2. Synthesis of Fe3O4@PDA

First, 2 mg dopamine was added to 6 mL Tris-HCl buffer solution (pH = 8.4) and ultrasound to obtain a uniform PDA@Tris-HCl dispersion. Next, 40 mg Fe3O4 nanoparticles were added to the solution under constant ultrasound until they were completely dissolved in the PDA/Tris-HCl solution, and, then, after magnetic stirring for 3 h, Fe3O4@PDA products were separated from the solution by an external magnetic field. Lastly, the as-obtained products were washed with ultrapure water three times and dried at 50 °C for 12 h to yield Fe3O4@PDA [20].

2.2.3. Synthesis of Fe3O4@PDA@Ag

First, 10 mg Fe3O4@PDA was added to 20 mL ultrapure water to obtain a uniform dispersion under ultrasound. Next, 100 mL 0.001 mol/L AgNO3 solution was poured gently into the solution mentioned above with constant stirring and heating [19]. When the solution temperature reached 90 °C, 0.0258 g sodium citrate solution was added, and the reaction took 1.5 h. Fe3O4@PDA@Ag products were separated from the solution by an external magnetic field. Eventually, the as-obtained products were washed with ultrapure water 3 times and dried at 50 °C for 12 h to yield Fe3O4@PDA@Ag [16].

2.2.4. Synthesis of Fe3O4@PDA@Ag@GO

First, 10 mg of Fe3O4@PDA@Ag was dissolved in water, 0.5 mL 0.5 mol/L of GO dispersion was added, and ultrapure water was added to make the volume of solution 12 mL with magnetic stirring for 3 h. Next, the as-obtained products were washed with ultrapure water 3 times [20], and Fe3O4@PDA@Ag@GO products were separated from the solution by an external magnetic field. At last, ultrapure water was added to make the volume of solution 10 mL [16].

3. Results and Discussion

3.1. Characterization

3.1.1. UV-Visible Characterization

The UV-vis spectra in Figure 1 illustrate the maximum absorption of Ag NPs synthesized by various reaction temperatures, which are located at the range of 300~700 nm to study the effect of reaction temperature on the preparation of silver sol. The reaction temperatures were 70 °C, 80 °C, 90 °C and 100 °C, respectively.
The prepared AgNO3 solution (0.001 mol/L, 100 mL) were added to four beakers, respectively, and 0.0258 g sodium citrate were added to each of the four beakers and were heated, respectively, to 70 °C, 80 °C, 90 °C and 100 °C for 1.5 h.
It was observed that the color of the solution heated to 70 °C was lighter than others, and precipitation occurred in the solution that was heated to 100 °C. It is shown in Figure 1 that the strongest absorption peaks of the four beakers of silver sol were located between 400~500 nm, and the strongest absorption peak for each of the silver sol was located at 425 nm when the solution was heated to 70 °C, 80 °C and 90 °C. When the silver sol was heated to 70 °C, the concentration was low for the reaction was incomplete. When the temperature was as high as 100 °C, the strongest absorption peak moved to right and the concentration was also low for the aggregate sank to the bottom. The preparation of Ag NPs followed the procedure reported in the literature [37,38]. Therefore, the most suitable heating temperature for synthesizing Fe3O4@PDA@Ag is 90 °C.

3.1.2. TEM Image of Fe3O4@PDA@Ag@GO

The size, morphology and surface composition of Fe3O4@PDA@Ag@GO were characterized by TEM (FEI Talos F200×, FEI Company, Hillsborough, OR, USA) [16].
As is shown in Figure 2 and Figure 3, most nanoparticles are spherical, with magnifications of 1 μm, 500 nm, 200 nm and 100 nm, respectively. AgNPs are evenly distributed on the GO surface without large aggregate generation, which indicates that Ag NPs can be adsorbed effectively on the GO surface and GO plays a good role in dispersing Ag NPs.
When zoomed to 100 nm, as is shown in the following pictures, Fe3O4 is clustered in the innermost layer. The interlayer between globular Fe3O4 and Ag nanoparticles is PDA, the black dots are Ag nanoparticles and the outermost layer is GO.
The peaks of Ag, Fe, C and O can be obtained by EDS analysis of Fe3O4@PDA@Ag@GO nanocomposite in (6) in the Figure 3, which proves that there are Ag, Fe, C and O in the substrate and Fe3O4@PDA@Ag@GO was successfully synthesized [21].

3.1.3. XRD Characterization

The crystal phase was characterized by D8-Advance X-ray diffraction (XRD, Bruker, Germany, Copper Kα radiation). The range of the scanning angle was (5~85)° and the scanning rate was 8°/min [20].
Figure 4 shows the XRD patterns of Fe3O4@PDA@Ag@GO. The corresponding peaks of Fe3O4 crystal occurred at 30°, 35°, 43°, 57° and 62°. The peaks corresponding to silver crystals were at 38°, 44°, 64° and 77°, which were consistent with the peaks in the literature. According to the XRD analysis above, there were Fe3O4 nanoparticles and Ag nanoparticles in SERS substrate [22].

3.2. Detection of PAHs with SERS Substrate

3.2.1. Sample Preparation

First, 0.1 g of PAHs were added to a moderate amount of alcohol under ultrasound for 30 min and then magnetically stirred for 2 h. Next, the as-prepared solution was poured into a 100 mL volumetric bottle with constant volume to prepare a PAHs methanol solution with a concentration of 1 g/L. Finally, PAHs solutions of different concentrations were prepared by diluting 1 g/L of PAH methanol solution with methanol and ultrapure water [16].

3.2.2. Method for Detection

Raman spectroscopy was performed on a Metage Opal 2800 Raman spectrometer with an excitation wavelength of 785 nm. First, the portable spectrometer was turned on and preheated for 30 min in order to check whether the instrument and laser work properly. Next, the PAHs solution and the prepared Fe3O4@PDA@Ag@GO substrate were added to a brown sample bottle in proportion. The integral time was set for 15~30 s, and the laser intensity was set at 90. Then, the average value of each sample was shown after the value of the sample was recorded 4 times. Finally, the Raman spectrum was obtained when the background was subtracted, and the dark current was deducted.

3.2.3. The Detection of Phenanthrene

Figure 5 illustrates the influences of the synthesis of Fe3O4@PDA@Ag@GO material on the Raman enhancement of PAHs solution. Phenanthrene solid, 10−2 g/L phenanthrene solution, the mixture of 10−2 g/L phenanthrene solution and SERS substrate and Fe3O4@PDA@Ag@GO solution were detected. The detection results are displayed in Figure 5.
PAHs can be differentiated based upon their characteristic SERS peaks [39]. The 10−2 g/L phenanthrene solution ((4) in the Figure 5) has a characteristic peak with a low intensity, while the characteristic peak of Fe3O4@PDA@Ag@GO substrate ((3) in the Figure 5) is negligible. When 10−2 g/L phenanthrene solution is mixed with Fe3O4@PDA@Ag@GO substrate, an obvious Raman characteristic peak ((2) in the Figure 5) appears, which is located at 402.7 cm−1, 1017.12 cm−1, 1238.64 cm−1, 1405.63 cm−1 and 1614.98 cm−1 that corresponds to the peak of phenethene solid ((1) in the Figure 5). The results show that Fe3O4@PDA@Ag@GO substrate enhances the adsorption capacity of 10−2 g/L phenanthrene standard solution, and the Raman effect on the surface phenanthrene is obviously enhanced.
  • Effects of each component in Fe3O4@PDA@Ag@GO on SERS detection performance
It is illustrated by (3) in the Figure 6 and (4) in the Figure 6 that the characteristic peak is negligible. Fe3O4 and Fe3O4@PDA do not enhance the SERS activity of the phenanthrene solution of 10−2 g/L. This may result from the fact that PDA covered Fe3O4, thus the SERS activity of Fe3O4 not being shown. It is illustrated by (1) in the Figure 6 and (2) in the Figure 6 that Fe3O4@PDA@Ag@GO has a stronger Raman signal than Fe3O4@PDA@Ag. Fe3O4@PDA@Ag@GO substrate has a combined enhancement of the electromagnetic enhancement of Ag and the chemical enhancement of GO. The adsorption capacity of the phenanthrene standard solution of 10−2 g/L is increased and the sensitivity is improved.
2.
The influence of the mixing ratio of SERS substrate and phenanthrene solution on SERS detection performance
In the experiment, the ratio of the mixture of the substrate and the solution also affected the value of Raman spectral peak. The volume ratio of the substrate and the solution was studied to find the optimal ratio. The mixed solutions of the different volume ratio of 2:1, 1:1, 1:2 and 1:4 were used to study the influence of the volume ratio of the mixture of SERS substrate with phenanthrene solution on SERS detection performance.
As shown in Figure 7, Raman spectral peaks of the mixed solution of the substrate and the phenanthrene solution change with their different volume ratios. Raman characteristic peaks are located at 590.7 cm−1,1037.3 cm−1, 1238.6 cm−1,1530.5 cm−1 and 1614.9 cm−1.The Raman displacement of the Raman spectral peak of the solution has shifted, possibly due to fluorescence interference. The peak heights of the spectrum from 1 to 4 are 2570.4, 3157.2, 4293.7 and 2904.6, respectively. Therefore, the volume ratio corresponding to spectrum 3 is chosen for the optimal ratio to be ready for the next step of the experiment.
Raman spectral intensity is the strongest when the volume ratio of substrate to standard solution is 1:2. The intensity of Raman spectrum peak reduces as the amount of substrate decreases. The number of molecules in hot spots on SERS substrate increases with the increase in the amount of the substrate. Therefore, the Raman intensity is intensified significantly. However, when the concentration of the substrate increases to a certain value and the enriched phenanthrene solution reaches the limit, the substrate interferes with the Raman signal, thus decreasing the spectral intensity.
3.
Fe3O4@PDA@Ag@GO detection limit for phenanthrene
In order to explore the influence of the synthesis of Fe3O4@PDA@Ag@GO material on the Raman enhancement of phenanthrene solution and to detect the detection limit of phenanthrene, the phenanthrene solution at different concentrations from 10−5 g/L to 10−8 g/L is mixed with the substrate of Fe3O4@PDA@Ag@GO and the Raman spectra is captured as shown in Figure 8.
As shown in Figure 8, the intensity of characteristic peak of the mixture of the phenanthrene solution (10−5~10−8 g/L) and the substrate decreases as the concentration of the solution is decreased. When the concentration of the phenanthrene solution reaches 10−8 g/L, a slight characteristic peak can still be seen, thus demonstrating that the detection limit of Fe3O4@PDA@Ag@GO for phenanthrene solution can reach 10−8 g/L.
In order to study the linear relationship between the intensities of characteristic peaks and the logarithm of phenanthrene concentration, two characteristic peaks of phenanthrene, 411 cm−1 and 590 cm−1, were analyzed which was shown in Figure 9.
The SERS peak intensities versus the logarithm of phenanthrene concentration had a good linear relationship from 10−8 to 10−5 g/L (Figure 9). The calibration equation can be described as (the characteristic absorption peaks located at 411 cm−1) y1 = 9415.1089x + 456.1223. The linear regression equation (the characteristic absorption peaks located at 590 cm−1) is y2 =11,736.837x + 1092.2970. The error bars indicate that the standard is derived from a total of 10 measurements. The present results reveal the potential for this method to be a rapid analysis and detection of phenanthrene at low concentrations.

3.2.4. Limit of Detection for Pyrene

In order to explore the influence of the synthesis of Fe3O4@PDA@Ag@GO material on the Raman enhancement of pyrene standard solution and to detect the detection limit of pyrene, the pyrene solution at different concentrations from 10−5 g/L to 10−8 g/L is mixed with the substrate of Fe3O4@PDA@Ag@GO and the Raman spectra is captured as shown in Figure 10.
As shown in Figure 10, the intensity of the characteristic peak of the mixture blending the pyrene standard solution (10−5~10−8 g/L) with the substrate decreases with the decrease of the concentration of the solution. When the concentration of the pyrene standard solution reaches 10−7 g/L, the spectral signal is apparent, and the characteristic peak is clearly visible. However, when the concentration reaches 10−8 g/L, the spectral signal disappears and almost becomes a straight line. Therefore, the detection limit of Fe3O4@PDA@Ag@GO for pyrene solution is 10−7 g/L.
In order to study the linear relationship between the intensities of characteristic peaks and the logarithm of pyrene concentration, two characteristic peaks of pyrene, 590 cm−1 and 1016 cm−1, were analyzed which was shown in Figure 11.
The SERS peak intensities versus the logarithm of pyrene concentration had a good linear relationship from 10−8 g/L to 10−5 g/L (Figure 12). The calibration equation can be described as (the characteristic absorption peaks located at 590 cm−1) y1 = 14,572.1942x + 119,844.7988. The linear regression equation (the characteristic absorption peak is located at 1016 cm−1) is y2 = 4596.3096x + 40,710.068. The error bars indicate that the standard is derived from a total of 10 measurements. The present results reveal the potential of this method to do rapid analysis and detection of pyrene at low concentrations.

3.2.5. Detection Limit of Benzanthracene

In order to explore the influence of the synthesis of Fe3O4@PDA@Ag@GO material on the Raman enhancement of benzanthracene solution and to detect the detection limit of benzanthracene, the benzanthracene solution at different concentrations from 10−5 g/L to 10−8 g/L is mixed with the substrate of Fe3O4@PDA@Ag@GO and the Raman spectra is captured as shown in Figure 12.
As shown in Figure 12, the intensity of the characteristic peak of the mixture blending the benzanthracene solution (10−5~10−8 g/L) with the substrate decreases with the decrease of the concentration of the solution. When the concentration of the benzanthracene solution reaches 10−7 g/L, the spectral signal almost disappears, but a weak characteristic peak can still be seen. However, when the concentration reaches 10−8 g/L, the spectral signal disappears and almost becomes a straight line. Therefore, the detection limit of Fe3O4@PDA@Ag@GO for benzanthracene solution is 10−7 g/L.
In order to study the linear relationship between the intensities of characteristic peaks and the logarithm of benzanthracene concentration, two characteristic peaks of benzanthracene located at 356 cm−1 and 1033 cm−1 were analyzed as shown in Figure 13.
The linear relationships between the SERS intensity and the logarithm of benzanthracene concentrations (from 10−8 g/L to 10−5 g/L) are detected in Figure 13. The intensity of the characteristic peak decreases with the decrease of concentration. The fitting linear relationship in line a (the characteristic absorption peaks located at 1033 cm−1) of Figure 13 is y2 = 7481.609x + 60,184.8115 while that in line b (the characteristic absorption peaks located at 356 cm−1) of Figure 13 is y1 = 8614.7051x + 69,751.2923. The x is the logarithm of solution concentration and the y is the relative intensity.

4. Conclusions

Fe3O4@PDA@Ag@GO substrate with high SERS activity was prepared and its morphology and structure were characterized in the experiment. By investigating the effects of different heating temperatures on the preparation of silver sol, it is discovered that the concentration of AgNPs is the highest when heated to 90 °C and the SERS signal intensity of surface polycyclic aromatic hydrocarbons (PAHs) is the highest. The study on the influence of different components of composite substrate on SERS also observes that Ag and GO enhanced the Raman signal in the Fe3O4@PDA@Ag@GO substrate [16]; the detection limit of phenanthrene is 10−8 g/L, that of pyrene 10−7 g/L and that of benzoanthracene 10−7 g/L, when Fe3O4@PDA@Ag@GO is used as SERS substrate. The composite nanoparticles have good magnetic response, can separate quickly and enrich the molecules to be measured and shorten the pretreatment time [16]. Therefore, Fe3O4@PDA@Ag@GO can be used as SERS substrate for the enrichment and detection of trace PAHs in the environment [23].

Author Contributions

The first author J.L. conceptualized the experiments and wrote the manuscript, and submitted it for publication.; J.W. performed experiments, data curation, and the design methodology.; Y.W. performed analysis and participated in technical discussion.; L.G. and K.G. performed visualization and supervision.; W.C. performed review and editing.; S.S. performed principal investigator (PI) of the research and organized the data, All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Science and technology research project of Chongqing Education Commission in China (No. KJQN202012907), Natural Science Foundation of Chongqing in China (No. cstc2020jcyj-msxmX0274).

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Wang, X.; Hao, W.; Zhang, H.; Pan, Y.; Kang, Y.; Zhang, X.; Zou, M.; Tong, P.; Du, Y. Analysis of polycyclic aromatic hydrocarbons in water with gold nanoparticles decorated hydrophobic porous polymer as surface-enhanced Raman spectroscopy substrate. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2015, 139, 214–221. [Google Scholar] [CrossRef] [PubMed]
  2. Chen, H.; Xia, D.; Yuan, Y. Surface Enhanced Raman Spectroscopic Investigation of PAHs at a PDMS-Au Composite Substrate PDMS-Au. Chem. Res. 2017, 38, 376–382. [Google Scholar]
  3. Wang, M.; Zhang, S.; Wang, C. Assessment of gaseous phase PAHs emitted from marine diesel engine using vortex-assisted dispersive liquid-liquid microextraction followed by GC/MS. In First International Conference on Information Sciences, Machinery, Materials and Energy; Atlantis Press: Amsterdam, The Netherlands, 2015; pp. 1841–1846. [Google Scholar] [CrossRef] [Green Version]
  4. Rota, M.; Bosetti, C.; Boccia, S.; Boffetta, P.; la Vecchia, C. Occupational expo-cancers:an updated systematic review and a me-ta-analysis to 2014. Arch. Toxicol. 2014, 88, 1479–1490. [Google Scholar] [CrossRef] [PubMed]
  5. White, A.J.; Bradshaw, P.T.; Herring, A.H.; Teitelbaum, S.L.; Beyea, J.; Stellman, S.D.; Steck, S.E.; Mordukhovich, I.; Eng, S.M.; Engel, L.S.; et al. Exposure to multiple sources of polycyclic aromatic hydrocarbons and breast cancer incidence. Environ. Int. 2016, 89–90, 185–192. [Google Scholar] [CrossRef] [Green Version]
  6. Nsibande, S.A.; Montaseri, H.; Forbes, P.B.C. Advances in the application of nanomaterial-based sensors for detection of polycyclic aromatic hydrocarbons in aquatic systems. Trends Anal. Chem. 2019, 115, 52–69. [Google Scholar] [CrossRef]
  7. Marzooghi, S.; di Toro, D.M. A critical review of polycyclic aromatic hydrocarbon phototoxicity models. Environ. Toxicol. Chem. 2017, 36, 1138–1148. [Google Scholar] [CrossRef] [Green Version]
  8. Ni, Y.; Wang, P.; Song, H.; Lin, X.; Kokot, S. Electrochemical detection of benzo(a)pyrene and related DNA damage using DNA/hemin/nafion-graphene biosensor. Anal. Chim. Acta 2014, 821, 34–40. [Google Scholar] [CrossRef]
  9. De Paepe, E.; Wauters, J.; Van Der Borght, M.; Claes, J.; Huysman, S.; Croubels, S.; Vanhaecke, L. Ultra-high-performance liquid chromatography coupled to quadrupole orbitrap high-resolution mass spectrometry for multi-residue screening of pesticides, (veterinary) drugs and mycotoxins in edible insects. Food Chem. 2019, 293, 187–196. [Google Scholar] [CrossRef]
  10. Martakidis, K.; Gavril, D. New inverse gas chromatographic methodology for studying mass transfer caused by the evapo-ration of volatile liquids. Instrum. Sci. Tchnol. 2019, 47, 389–409. [Google Scholar] [CrossRef]
  11. Rama, M.J.R.; Ruiz-Medina, A.; Díaz, A.M. A Simple and Straightforward Procedure for Monitoring Phenol Compounds in Waters by Using UV Solid Phase Transduction Integrated in a Continuous Flow System. Mikrochim. Acta 2003, 141, 143–148. [Google Scholar] [CrossRef]
  12. Matthew, B.; Paolo, B.; Mariangela, C. Analysis of poly-cyclic aromatic hydrocarbons (PAHs) in airborne particles by direct sample introduction thermal desorption GC / MS. Atmos. Environ. 2008, 42, 6144–6151. [Google Scholar]
  13. Chen, Y.; Liu, H.; Tian, Y.; Du, Y.; Ma, Y.; Zeng, S.; Gu, C.; Jiang, T.; Zhou, J. In situ recyclable surface-enhanced Ramanscat-tering-based detection of multicomponent pesticide residues on fruits and vegetables by the flower-like MoS2@Ag hybrid substrate ACS. Appl. Mater. Inter. 2020, 12, 14386–14399. [Google Scholar] [CrossRef]
  14. Du, Y.; Liu, H.; Chen, Y.; Tian, Y.; Zhang, X.; Gu, C.; Jiang, T.; Zhou, J. Recyclable label-free SERS-based immunoassay of PSA in human serum mediated by enhanced photocatalysis arising from Ag nanoparticles and external magnetic field. Appl. Surf. Sci. 2020, 528, 146953. [Google Scholar] [CrossRef]
  15. Kalachyova, Y.; Mares, D.; Jerabek, V.; Elashnikov, R.; Švorčík, V.; Lyutakov, O. Longtime stability of silver-based SERS substrate in the environment and (bio)environment with variable temperature and humidity. Sens. Actuators A Phys. 2018, 285, 566–572. [Google Scholar] [CrossRef]
  16. Botta, R.; Eiamchai, P.; Horprathum, M.; Limwichean, S.; Chananonnawathorn, C.; Patthanasettakul, V.; Maezono, R.; Jomphoak, A.; Nuntawong, N. 3D structured laser engraves decorated with gold nanoparticle SERS chips for paraquat herbicide detection in environments. Sens. Actuators B Chem. 2019, 304, 127327. [Google Scholar] [CrossRef]
  17. Zhou, Y.; Liang, P.; Zhang, D.; Tang, L.; Dong, Q.; Jin, S.; Ni, D.; Yu, Z.; Ye, J. A facile seed growth method to prepare stable Ag@ZrO2 core-shell SERS substrate with high stability in extreme environments. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2020, 228, 117676. [Google Scholar] [CrossRef]
  18. Liu, J.; Liu, Y.; Cao, Y.; Sang, S.; Guan, L.; Wang, Y.; Wang, J. Preparation of FeO@PDA@Au@GO Composite as SERS Substrate and Its Application in the Enrichment and Detection for Phenanthrene. Micromachines 2022, 1, 128. [Google Scholar] [CrossRef]
  19. Liu, K.; Bai, Y.; Zhang, L.; Yang, Z.; Fan, Q.; Zheng, H.; Yin, Y.; Gao, C. Porous Au–Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis. Nano Lett. 2016, 16, 3675–3681. [Google Scholar] [CrossRef]
  20. Yi, Z.; Niu, G.; Luo, J.; Kang, X.; Yao, W.; Zhang, W.; Yi, Y.; Yi, Y.; Ye, X.; Duan, T.; et al. Ordered array of Ag semishells on different diameter monolayer polystyrene colloidal crystals: An ultrasensitive and reproducible SERS substrate. Sci. Rep. 2016, 6, 32314. [Google Scholar] [CrossRef] [Green Version]
  21. Zhu, T.; Sun, Y.; Lu, W.; Wang, G.; Zhang, X.; Chen, S.; Zhang, C.; Li, Z.; Man, B.; Yang, C. Theoretical and experimental investiga-tion of the flexible Ag nano-tree@Cu mesh SERS substrate. J. Alloys Compd. 2022, 908, 164622. [Google Scholar] [CrossRef]
  22. Trang, T.N.Q.; Vinh, L.Q.; Doanh, T.T.; Thu, V.T.H. Structure-adjustable colloidal silver nanoparticles on polymers grafted cellulose paper-based highly sensitive and selective SERS sensing platform with analyte enrichment function. J. Alloys Compd. 2021, 867, 159158. [Google Scholar] [CrossRef]
  23. Wang, T.; Barveen, N.; Liu, Z.; Chen, C.; Chou, M. Transparent, flexible plasmonic Ag NP/PMMA substrates using chemically patterned ferroelectric crystals for detecting pesticides on curved surfaces. ACS Appl. Mater. Interfaces 2021, 13, 34910–34922. [Google Scholar] [CrossRef]
  24. Kong, L.; Huang, M.; Chen, J.; Lin, M. Fabrication of sensitive silver-decorated cotton swabs for SERS quantitative detection of mixed pesticide residues in bitter gourds. New J. Chem. 2020, 44, 12779–12784. [Google Scholar] [CrossRef]
  25. Guo, X.; Wang, D.; Han, R. Nafion stabilized Ag nanopillar arrays as a flexible SERS substrate for trace chemical detection. Mater. Chem. Phys. 2020, 252, 123291. [Google Scholar] [CrossRef]
  26. Gao, Y.; Hu, Z.; Wu, J.; Ning, Z.; Jian, J.; Zhao, T.; Liang, X.; Yang, X.; Yang, Z. Size-tunable Au@Ag nanoparticles for colorimetric and SERS dual-mode sensing of palmatine in traditional Chinese medicine. Pharm. Biomed. Anal. 2019, 174, 123–133. [Google Scholar] [CrossRef]
  27. Jia, X.; Yu, S.; Cheng, C.; Yang, J.; Li, Y.; Wang, S.; Song, H. Ag nanoparticles modified Fe3O4/reduced graphene oxide and their acetone sensing properties. Mater. Chem. Phys. 2022, 276, 125378. [Google Scholar] [CrossRef]
  28. Luo, M.; Zhang, Y.; Zhao, S. Non-Enzymatic Hydrogen Peroxide Sensor Based on Fe3O4@Polydopamine-Ag Nanocomposite Modified Magnetic Glassy Carbon Electrode. J. Electrochem. Soc. 2021, 168, 067511. [Google Scholar] [CrossRef]
  29. Zhang, Q.; Guo, W.; He, L.; He, L.; Chen, Y.; Shen, X.; Wu, D. A new SERS substrate of self-assembled monolayer film of gold nanoparticles on silicon wafer for the rapid detection of polycyclic aromatic hydrocarbons. Mater. Chem. Phys. 2020, 250, 122994. [Google Scholar] [CrossRef]
  30. Wang, W.; Li, X.; Yan, Y. Preparation of Au/Fe3O4/GO composite as SERS substrate and its application in the enrichment and detection for low-concentration pyrene. Acta Sci. Circumstantiae 2018, 38, 475–483. [Google Scholar]
  31. Jones, C.L.; Bantz, K.C.; Haynes, C.L. Partition layer-modified substrates for reversible surface-enhanced Raman scattering detection of polycyclic aromatic hydrocarbons. Anal. Bioanal. Chem. 2009, 394, 303–311. [Google Scholar] [CrossRef]
  32. Olson, L.G.; Uibel, R.H.; Harris, J.M. C18-Modified Metal-Colloid Substrates for Surface-Enhanced Raman Detection of Trace-Level Polycyclic Aromatic Hydrocarbons in Aqueous Solution. Appl. Spectrosc. 2004, 58, 1394–1400. [Google Scholar] [CrossRef] [PubMed]
  33. Costa, J.C.S.; Sant’Ana, A.C.; Corio, P.; Temperini, M.L.A. Chemical analysis of polycyclic aromatic hydrocarbons by surface-enhanced Raman spectroscopy. Talanta 2006, 70, 1011–1016. [Google Scholar] [CrossRef] [PubMed]
  34. Du, J.; Jing, C. Preparation of Fe3O4@Ag SERS substrate and its application in environmental Cr(VI) analysis. J. Colloid Interface Sci. 2011, 358, 54–61. [Google Scholar] [CrossRef] [PubMed]
  35. Wang, X.; Cheng, H.; Min, Y. Fe3O4@m-ZrO2@Ag ternary magnetic nanocomposites for sensitive SERS sensing and photo-catalytic removal of Cr(VI) and organic dyes. Compos. Part B Eng. 2022, 239, 109959. [Google Scholar] [CrossRef]
  36. Wang, X.; Xu, Q.; Hu, X.; Han, F.; Zhu, C. Silver-nanoparticles/graphene hybrids for effective enrichment and sensitive SERS detection of pol-ycyclic aromatic hydrocarbons. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2020, 228, 117783. [Google Scholar] [CrossRef] [PubMed]
  37. Fan, M.; Brolo, A.G. Silver nanoparticles self assembly as SERS substrates with near single molecule detection lim-it. Phys. Chem. Chem. Phys. 2009, 11, 7381–7389. [Google Scholar] [CrossRef]
  38. Bauer, G.; Hassmann, J.; Walter, H.; Haglmüller, J.; Mayer, C.; Schalkhammer, T. Resonant nanocluster technology—from optical coding and high quality security features to biochips. Nanotechnology 2003, 14, 1289–1311. [Google Scholar] [CrossRef]
  39. Du, J.; Xu, J.; Sun, Z.; Jing, C. Au nanoparticles grafted on Fe3O4 as effective SERS substrates for label-free detection of the 16 EPA priority polycyclic aromatic hydrocarbons. Anal. Chim. Acta 2016, 915, 81–89. [Google Scholar] [CrossRef]
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Figure 1. UV absorption spectra of silver dissolved at different temperatures.
Figure 1. UV absorption spectra of silver dissolved at different temperatures.
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Figure 2. TEM images Fe3O4@PDA@Ag@GO of different magnifications. (1) TEM image zoomed to 1 μm; (2) TEM image zoomed to 500 nm; (3) TEM image zoomed to 200 nm; (4) TEM image zoomed to 100 nm.
Figure 2. TEM images Fe3O4@PDA@Ag@GO of different magnifications. (1) TEM image zoomed to 1 μm; (2) TEM image zoomed to 500 nm; (3) TEM image zoomed to 200 nm; (4) TEM image zoomed to 100 nm.
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Figure 3. TEM mapping and EDS of Fe3O4@PDA@Ag@GO nanocomposites. (1) The elemental mappings of C; (2) the elemental mappings of Ag; (3) the elemental mappings of O; (4) the elemental mappings of Fe; (5) the elemental mappings of N; (6) EDS of Fe3O4@PDA/Ag/GO.
Figure 3. TEM mapping and EDS of Fe3O4@PDA@Ag@GO nanocomposites. (1) The elemental mappings of C; (2) the elemental mappings of Ag; (3) the elemental mappings of O; (4) the elemental mappings of Fe; (5) the elemental mappings of N; (6) EDS of Fe3O4@PDA/Ag/GO.
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Figure 4. XRD of Fe3O4@PDA@Ag@GO.
Figure 4. XRD of Fe3O4@PDA@Ag@GO.
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Figure 5. SERS spectra of phenanthrene (1) phenanthrene solid; (2) the mixture of 10−2 g/L phenanthrene and SERS substrate solution; (3) Fe3O4@PDA@Ag@GO solution; (4) 10−2 g/L phenanthrene solution.
Figure 5. SERS spectra of phenanthrene (1) phenanthrene solid; (2) the mixture of 10−2 g/L phenanthrene and SERS substrate solution; (3) Fe3O4@PDA@Ag@GO solution; (4) 10−2 g/L phenanthrene solution.
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Figure 6. SERS signal of phenanthrene captured on Fe3O4@PDA@Ag@GO, Fe3O4@PDA@Ag, Fe3O4@PDA and Fe3O4, respectively (1) Fe3O4@PDA@Ag@GO substrate; (2) Fe3O4@PDA@Ag substrate; (3) Fe3O4@PDA substrate; (4) Fe3O4 substrate.
Figure 6. SERS signal of phenanthrene captured on Fe3O4@PDA@Ag@GO, Fe3O4@PDA@Ag, Fe3O4@PDA and Fe3O4, respectively (1) Fe3O4@PDA@Ag@GO substrate; (2) Fe3O4@PDA@Ag substrate; (3) Fe3O4@PDA substrate; (4) Fe3O4 substrate.
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Figure 7. SERS spectra of different mixing volume ratios of Fe3O4@PDA@Ag@GO substrate and phenanthrene solution (1) 2:1;(2) 1:1; (3) 1:2; (4) 1:4.
Figure 7. SERS spectra of different mixing volume ratios of Fe3O4@PDA@Ag@GO substrate and phenanthrene solution (1) 2:1;(2) 1:1; (3) 1:2; (4) 1:4.
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Figure 8. The detection limit of phenanthrene captured on Fe3O4@PDA@Ag@GO nanocomposites SERS substrate (1) phenanthrene solid; (2) 10−5 g/L phenanthrene SERS solution; (3) 10−6 g/L phenanthrene SERS solution; (4) 10−7 g/L phenanthrene SERS solution; (5) 10−8 g/L phenanthrene SERS solution.
Figure 8. The detection limit of phenanthrene captured on Fe3O4@PDA@Ag@GO nanocomposites SERS substrate (1) phenanthrene solid; (2) 10−5 g/L phenanthrene SERS solution; (3) 10−6 g/L phenanthrene SERS solution; (4) 10−7 g/L phenanthrene SERS solution; (5) 10−8 g/L phenanthrene SERS solution.
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Figure 9. Linear relationships between the phenanthrene characteristic intensity and the logarithm of phenanthrene concentration. (a) 590 cm−1; (b) 411 cm−1.
Figure 9. Linear relationships between the phenanthrene characteristic intensity and the logarithm of phenanthrene concentration. (a) 590 cm−1; (b) 411 cm−1.
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Figure 10. The detection limit of Pyrene captured on Fe3O4@PDA@Ag@GO nanocomposites SERS substrate (1) Pyrene solid; (2) 10−5 g/L Pyrene SERS solution; (3) 10−6 g/L Pyrene SERS solution; (4) 10−7 g/L Pyrene SERS solution; (5) 10−8 g/L Pyrene SERS solution.
Figure 10. The detection limit of Pyrene captured on Fe3O4@PDA@Ag@GO nanocomposites SERS substrate (1) Pyrene solid; (2) 10−5 g/L Pyrene SERS solution; (3) 10−6 g/L Pyrene SERS solution; (4) 10−7 g/L Pyrene SERS solution; (5) 10−8 g/L Pyrene SERS solution.
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Figure 11. Linear relationships between the pyrene characteristic intensity and the logarithm of pyrene concentration. (a) 1016 cm−1; (b) 590 cm−1.
Figure 11. Linear relationships between the pyrene characteristic intensity and the logarithm of pyrene concentration. (a) 1016 cm−1; (b) 590 cm−1.
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Figure 12. The detection limit of benzanthene captured on Fe3O4@PDA@Ag@GO nanocomposites SERS substrate (1) 10−4 g/L benzanthene standard solution; (2) benzanthene solid; (3) 10−5 g/L benzanthene standard solution; (4) 10−6 g/L benzanthene standard solution; (5) 10−7 g/L benzanthene standard solution; (6) 10−8 g/L benzanthene standard solution.
Figure 12. The detection limit of benzanthene captured on Fe3O4@PDA@Ag@GO nanocomposites SERS substrate (1) 10−4 g/L benzanthene standard solution; (2) benzanthene solid; (3) 10−5 g/L benzanthene standard solution; (4) 10−6 g/L benzanthene standard solution; (5) 10−7 g/L benzanthene standard solution; (6) 10−8 g/L benzanthene standard solution.
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Figure 13. Linear relationships between the benzoanthracene characteristic intensity and the logarithm of benzoanthracene concentration. (a) 1033 cm−1; (b) 356 cm−1.
Figure 13. Linear relationships between the benzoanthracene characteristic intensity and the logarithm of benzoanthracene concentration. (a) 1033 cm−1; (b) 356 cm−1.
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Table
Table 1. Reagents.
Table 1. Reagents.
ReagentGradeManufacturer
Ethylene glycolanalytical purityChengdu Colon Chemicals Co., Ltd. (Chengdu, China)
Methanolanalytical purityChengdu Colon Chemicals Co., Ltd. (Chengdu, China)
Anhydrous ethanolanalytical purityChengdu Colon Chemicals Co., Ltd. (Chengdu, China)
Polyethylene glycolanalytical purityBeijing Chemical Reagent Co., Ltd. (Beijing, China)
Ferric chloride hexahydrateanalytical purityBeijing Chemical Reagent Co., Ltd. (Beijing, China)
Silver nitrateanalytical purityBeijing Chemical Reagent Co., Ltd. (Beijing, China)
Sodium citrateanalytical purityBeijing Chemical Reagent Co., Ltd. (Beijing, China)
Phenanthreneanalytical purityMcLean Biochemical Technology Co., Ltd. (Shanghai, China)
Pyreneanalytical purityMcLean Biochemical Technology Co., Ltd. (Shanghai, China)
Benzanthraceneanalytical purityMcLean Biochemical Technology Co., Ltd. (Shanghai, China)
Graphene oxide dispersion0.5 mg/mLBeijing Chemical Reagent Co., Ltd. (Beijing, China)
Hydrochloric acid-dopamineanalytical purityMcLean Biochemical Technology Co., Ltd. (Shanghai, China)
Anhydrous sodium acetateanalytical purityBeijing Chemical Reagent Co., Ltd. (Beijing, China)
Table
Table 2. Laboratory apparatus.
Table 2. Laboratory apparatus.
Apparatus NamesManufacturersModel Number
Electronic balancesMETTLER TOLEDO, Zurich, Switzerland.XP5003S
Thermostatic magnetic agitatorJintan Fuhua Electric Appliance Co., Ltd.RCT B S25
TG16-WS high speed centrifugeHunan Xiangyi Laboratory Instrument Development Co., Ltd.TG16-WS
SB-5200DT Ultrasonic cleanerNingbo Xinzhi Biotechnology Co., Ltd.SB-5200DT
Metage Opal 2800 spectrometerMetage Co., London, EnglandMetage Opal 2800
50mL Stainless steel reactorChengdu Cologne Chemicals Co., Ltd.PDFE
DZF vacuum ovenBeijing Yongguangming Medical Instrument Co., Ltd.DZF
Electric blower drying boxChongqing Star Test Equipment Co., Ltd.CS101-2EB
SpectrophotometerShanghai Meipuda Instrument Co., Ltd.UV-1600PC
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Liu, J.; Cui, W.; Sang, S.; Guan, L.; Gu, K.; Wang, Y.; Wang, J. Surface-Enhanced Raman Spectroscopic Investigation of PAHs at a Fe3O4@GO@Ag@PDA Composite Substrates. Micromachines 2022, 13, 1253. https://doi.org/10.3390/mi13081253

AMA Style

Liu J, Cui W, Sang S, Guan L, Gu K, Wang Y, Wang J. Surface-Enhanced Raman Spectroscopic Investigation of PAHs at a Fe3O4@GO@Ag@PDA Composite Substrates. Micromachines. 2022; 13(8):1253. https://doi.org/10.3390/mi13081253

Chicago/Turabian Style

Liu, Junyu, Wencan Cui, Shihua Sang, Liang Guan, Kecheng Gu, Yinyin Wang, and Jian Wang. 2022. "Surface-Enhanced Raman Spectroscopic Investigation of PAHs at a Fe3O4@GO@Ag@PDA Composite Substrates" Micromachines 13, no. 8: 1253. https://doi.org/10.3390/mi13081253

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