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SERS detection of pesticide residues using transparent adhesive tape and coated silver nanorods Jiaolai Jiang, Sumeng Zou, Lingwei Ma, Shaofei Wang, Junsheng Liao, and Zhengjun Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b18039 • Publication Date (Web): 22 Feb 2018 Downloaded from http://pubs.acs.org on February 23, 2018

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ACS Applied Materials & Interfaces

SERS Detection of Pesticide Residues Using Transparent Adhesive Tape and Coated Silver Nanorods Jiaolai Jianga, Sumeng Zoub, Lingwei Mab, Shaofei Wanga, Junsheng Liaoa*, Zhengjun Zhang b* a

Institute of Materials, China Academy of Engineering Physics, P. O. Box No.9-11,

Huafengxincun, Jiangyou, Sichuan, 621908, P. R. China. b

Key Laboratory of Advanced Materials (MOE), School of Materials Science and

Engineering, Tsinghua University, Beijing, 100084, P.R. China. ABSTRACT: The efficient extraction of analytes from complex and severe environment is significant for promoting the SERS technique to actual applications. In this paper, a proof-of-concept strategy is proposed for rapid detection of pesticide residues by utilizing the flexible, transparent, and adhesive properties of commercial tape and SERS performance of Al2O3 coated silver nanorod (AgNR@Al2O3) arrays. The function of tape is to rapidly transfer the analytes from actual surface to SERS substrate. The novel “Tape wrapped SERS (T-SERS)” approach was constructed by simply “paste, peel off, and paste again” procedure. The easily obtained but clearly distinguished SERS signals allow us to quickly determine the constituents of complex surface, such as tetramethylthiuram disulfide and thiabendazole pesticides from fruits and vegetables, which may be practically applied to food safety, environmental monitoring, and industrial production process controlling. Key words: Al2O3 coated silver nanorods, tape, SERS, pesticide detection, extraction

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Surface-enhanced Raman scattering (SERS) technique, as a surface sensitive analytical tool, has shown enormous application potential in various fields such as catalysis,1-2 environmental monitoring,3-5 food safety,6-7 biotechnology,8-9 and surface science.10-11 SERS offers a huge enhancement (106 ~108) of Raman signal for molecules close (within several nanometer) to plasmonic nanostructures due to the localized surface plasmonic resonance (LSPR) effect.12 Recently, great efforts have been dedicated to fabricate excellent SERS substrates by controlling the shape, size, and compositions of nanostructures with physical and chemical methods.13-16 Besides the substrate, how to effectively and rapidly collect target molecules from real complex surface to SERS substrate is another challenging issue. Conventional SERS substrates based on silicon wafer or glass side are usually rigid and unsuitable directly for practical analysis.17-18 Thus, extra solvent extraction procedure is needed. But the addition of solvents is time-consuming, subversive, and environmentally unfriendly especially for non-aqueous-soluble analytes.19-20 Recently, flexible materials such as cotton, paper,21 and polydimethylsiloxane (PDMS)22-23 have been used as SERS substrate by decorating them with noble metallic nanoparticles. Flexible substrates can be easily swabbed onto curved surfaces, endowing the convenience for SERS detection. Despite the enormous potential of flexible substrates for real sample detection from complex environments, there are still some problems such as low extraction efficiency, inhomogeneous and small-scale surface nanostructures, which may bring about poor reproducibility as well as low sensitivity. Adhesive tape is known in scientific research fields for successfully exfoliating graphene from graphite due to its “sticky” property.24 Widely used in our daily life, adhesive tape has the advantages of cheapness, stickiness, flexibility and transparency.25 Double-sided tape based SERS substrate was reported in the previous literature by Liu et al.26 A very convenient SERS tape was also demonstrated by Chen et al. through dropping gold nanoparticles onto the tape.27 Pesticide residues in fruits can be easily detected by simply “paste and peel off” method. But the uniformity of gold nanoparticles dispersed on tape is difficult to control in this way. Herein, we proposed a tape wrapped SERS (T-SERS) approach by combining the transparency, adhesiveness, and flexibility of tape and the SERS activity of Al2O3 coated silver nanorod (AgNR@Al2O3) arrays. Through a “paste and peel off” procedure, analytes can be easily extracted from complex surfaces such as vegetables


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based on the flexible and sticky feature of adhesive tape. Then the SERS signal was obtained by pasting adhesive tape loaded with analytes onto the AgNR@Al2O3 substrate. The excellent transparency feature of tape reduced the signal intensity by less than 2 times, which almost does not affect the real detection sensitivity by T-SERS strategy. AgNR@Al2O3 substrate possesses highly thermal and long-term stability in air as well as high sensitivity, making T-SERS approach possible for practical sample detection. SERS is a versatile method, and any Raman active analyte may be rapidly detected, exhibiting great potential for practical application in food safety, environmental monitoring, and industrial production process controlling especially in severe condition.

EXPERIMENTAL SECTION Chemicals and materials. 4-Mercaptopyridine (C5H5NS, ≥ 96%; 4-Mpy), 1,4-benzenedithiol (C6H6S2, ≥98%; 1,4-BDT), rhodamine 6G (C28H31ClN2O3, R6G, 95%), and 4-mercaptobenzoic acid (C7 H6O2S, ≥98%; 4-MBA) were purchased from J&K Scientific Ltd, Beijing. Tetramethylthiuram disulfide (C6H12N2S4; TMTD) was bought from Adamas. TMTD was dissolved in ethanol to make a 0.5 mM stock solution, and then diluted to the final concentration before use. Thiabendazole (C10H7N3S; TBZ) was purchased from AccuStandard. Ethanol (C2H6O) was obtained from Beijing Chemical Glass Station Co. Ltd. Adhesive tapes, apples, pears, cucumbers, and spinaches were purchased from the local supermarket. All reagents were used without further purification. Milli-Q-grade water (resistivity >18.0 MΩ cm) was used for the experiments. AgNR@Al2O3 SERS substrate fabrication. Oblique angle deposition (OAD) method was utilized to fabricate AgNR arrays through electron-beam system (GLAD,Thermionics) reported by Ma et al.28 The monocrystalline silicon wafer was used as the substrate material and was first washed with acetone, ethanol and ultrapure water before deposition to remove organic impurities. The vacuum level of the depositing chamber was maintained on the order of 10-5 Pa. The incident angle between the vapor flux and Si surface was set at ~86°. The deposition rate was controlled at 0.75 nm/s. The deposition process was terminated when the thickness reached ~1000 nm read by quartz crystal microbalance. AgNR@Al2O3 SERS substrate was fabricated by wrapping the Al2O3 layer on AgNR arrays with an atomic



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layer deposition method (ALD, MNT-100, Wuxi MNT Micro and Nanotech Co.). The trimethylaluminum (150 ℃) precursor and water (150 ℃) were alternatively pumped into the reaction chamber with high pure N2 (99.999%) as the carrier to form Al2O3 layer. The process included the following 4 steps: (1) trimethylauminum pumping, 20 ms; (2) N2 purging, 10 s; (3) water vapor pumping, 10 ms; and (4) N2 purging, 20 s. After 1 ALD cycle, the thickness of Al2O3 layer is ~0.9 nm. The AgNR@Al2O3 substrate was placed in the air for further use. Tape wrapped SERS (T-SERS) substrate was obtained by pasting and pressing the tape on AgNR@Al2O3 with a certain force. Characterizations. TEM observation was obtained by transmission electron microscope (HRTEM, JEOL-2011) with an operating voltage of 200 KV. SEM image was obtained by filed-emission scanning electron microscope (SEM, ZEISS, MERLIN

Compact).

UV-vis

absorption

spectroscopy

was

collected

with

angle-resolved micro spectrometer (Idea Optics Co., ARM62). The Raman measurements were conducted with an optical fiber micro-Raman spectrometer (i-Raman Plus, B&W TEK Inc.). A laser with the wavelength of 785 nm was used as the excitation source. The beam spot can be focused to ~80 µm in diameter. The excitation power of laser was set to be 75 mW, and the spectrum collection time was 10 s.

RESULTS AND DISCUSSION The proof-of-concept design of T-SERS approach. The proposed T-SERS approach for rapidly sample analysis by “paste, peel off, and paste again” procedure was illustrated in Scheme 1. Adhesive tape is very commonly used in our daily life, such as removing wrong words from paper, encapsulating boxes, and fastening some daily goods. Adhesive tape is cheap, and has excellent sticky feature, thus it was used as the solid phase extractant in our experiments for collecting analytes from real surfaces, without the assistance of organic solution. Through simply “paste and peel off” process, adhesive tape is easily loaded with target analytes. Then we covered the tape on the SERS substrate surface, and pressed the tape with a certain pressure for 4 s to make analytes tightly close to the “hot spot” zone of SERS substrate.


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Scheme 1. Schematic illustration of the T-SERS approach proposed for detection of analytes extracted from fruit surface. Adhesive tape wrapped on SERS substrate may weaken the intensity of both incident laser and Raman scattering signal because of the absorption and reflection effects. To investigate the effect of tape on the SERS signal, we compared the intensity change of 4-Mpy on AgNR@Al2O3 before and after wrapped with adhesive tape. 4-Mpy was chosen as the target molecule. AgNR@Al2O3 substrates were immersed in the 4-Mpy ethanol solution (10-6 M) for 20 min. Then they were washed with ethanol for 3 times and dried under nitrogen atmosphere for SERS analysis. The tape was wrapped on the AgNR@Al2O3 surface with a certain pressure for further T-SERS measurement. Four strong bands of 4-Mpy at 1011, 1062, 1096, 1579 cm-1 were observed, which are assigned to the ring stretching vibration, in-plane bending of C-H, C-S vibration, and ring deformation with C=C antisymmetric stretch, respectively (Figure 1A).29-30 The intensities of 4-Mpy at 1096 cm-1 were calculated based on the peak area through measuring 10 points randomly and averaging them. The intensity of 4-Mpy was reduced by 1.61 times (calculated by the ratio of ISERS/IT-SERS) after wrapped with tape (T-SERS), which usually has little effect on the performance of SERS substrate, indicating a good transparent ability of tape. The same results were obtained by detecting other molecules such as 1,4-BDT and 4-MBA (see Figure S1 and Figure S2). The absorbance of tape less than 0.05 near 785 nm also demonstrates the excellent transparency (see Figure S3).



In order to investigate the feasibility of the proposed T-SERS approach to detect analytes from real surface, the 4-Mpy from glass side was collected by the tape and detected by T-SERS. 3 µL of 4-Mpy solution was dropped on the glass side, and dried in air. The transparent adhesive tape was utilized to gather 4-Mpy by “paste and peel off” procedure, and then pasted tightly onto SERS substrate for T-SERS analysis. The clear T-SERS signal of 4-Mpy was obtained (Figure 1B), which demonstrated the feasibility of proposed strategy for sample detection from real surfaces.

Figure 1. (A) Comparison of SERS signals of (a) Blank AgNR@Al2O3 substrate, (b) Blank tape wrapped AgNR@Al2O3, (c) 10-6 M of 4-Mpy on AgNR@Al2O3, (d) 10-6 M of 4-Mpy on AgNR@Al2O3, then wrapped with tape. (B) The feasibility of T-SERS strategy for detection of 4-Mpy (1 mM) on glass surface (Black line: 4-Mpy on tape for Raman; red line: 4-Mpy for T-SERS. Symbol “*” represents the peaks of tape, the dotted lines represent the peaks of 4-Mpy). The choice and characterization of SERS substrate material. In the proposed T-SERS approach, SERS substrate materials can be arbitrarily selected, but the sensitivity and reproducibility of T-SERS mainly depend on the SERS substrate part. The performance of substrates is determined by material, size, shape of the nanostructures and the excitation wavelength. Silver and gold are mostly used for SERS substrates in all metallic plasmonic nanomaterials due to their superior localized surface plasmon properties. Here we use slant AgNR@Al2O3 arrays as the SERS substrate for T-SERS measurement. There are three reasons: (1) silver is superior than gold of the same structure in enhancement despite better chemical stability of gold; (2) anisotropic shape of nanorods can match well with long wavelength laser because of the longitudinal plasmon resonance compared with spherical nanostructure;31 (3) Al2O3 layer can effectively protect silver from being


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oxidation despite the decrease of sensitivity,28 because the stability of substrate is an important aspect for actual application. Figure 2A shows the representative SEM and HRTEM images of fabricated AgNR@Al2O3 by OAD and ALD techniques on Si (001) surface. Adjacent AgNR@Al2O3 are well separated to form nanorod arrays structure. Al2O3 film is covered tightly to AgNR with a thickness of about 0.9 nm, which is accessible for both maintaining good sensitivity and air stability.28 We selected 4-Mpy as a model probe to evaluate the performance of the AgNR@Al2O3 wrapped by adhesive tape (T-SERS substrate). AgNR@Al2O3 substrates were immersed in 4-Mpy with different concentrations for 20 min. Before Raman measurement, tape was wrapped on the AgNR@Al2O3 substrates. 10-8 M can be detected by this method (Figure 2B), indicating the good sensitivity of AgNR@Al2O3. To examine the reproducibility of T-SERS substrate, we collected the T-SERS spectra of 4-Mpy from 15 random-selected places (Figure 2C). The relative standard deviation (RSD) at 1096 cm-1 (Figure 2D) is 3.61%, indicating an excellent reproducibility and uniformity of the substrate, which is consistent with SEM result (Figure 2A). Furthermore, the large laser light spot size (~80 µm) used in the experiments also contributes to the good reproducibility due to the statistical effect. These results indicate that AgNR@Al2O3 wrapped with adhesive tape substrate is a good choice by T-SERS approach for real sample analysis.



Figure 2. (A) SEM and TEM (the insert) images of AgNR@Al2O3. (B) T-SERS spectra of 4-Mpy of different concentrations on AgNR@Al2O3 and then wrapped with tape. (C) T-SERS spectra of 4-Mpy (10-6 M) on AgNR@Al2O3 and then wrapped with tape, acquired from 15 random sites. (D) The corresponding bar chart for the peak intensity at 1096 cm−1 from 15 random sites of (C). The extraction efficiency of tape for analytes. SERS owns the advantage of high sensitivity, short spectrum collecting time, fingerprint characteristic spectrum, and no complex pretreatment process of samples, endowing it a very promising candidate for fast detection of targets from real environment.32-33 However, the rapid and efficient extraction of analytes from complex surfaces may be the main restriction in the practical analysis process. The traditional extraction methods, such as solvent-assisted extraction, microextraction, and membrane extraction technique, are usually time-consuming, expensive, complicated, and environmentally unfriendly.34-35 In our present study, we proposed a novel proof-of-concept T-SERS approach, where rapid and universal SERS detection becomes possible with transparent and adhesive tape as the collector. To investigate the extraction efficiency of tape, Contrast T-SERS spectra of target molecule were collected by dropping 3 µL of 10-5 M R6G aqueous solution onto the tape and Si (extracted by tape through “paste and peel off” process),


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respectively (Figure 3A). The extraction efficiency of tape is defined by the concentration ratio of R6G from extracted tape and Si. The concentration of R6G from extracted tape can be approximately evaluated by T-SERS measurement. Therefore, a linear calibration curve (R2=0.983) between the average T-SERS intensity of R6G at 1509 cm-1 measured from 10 random-selected places and its concentration ranging from 10-5 to 10-6 M was obtained (Figure 3B) by dropping R6G of different concentration on tape (see Figure S4). The concentration of R6G from extracted tape was calculated approximately to 9.16 1.76 μM through the above calibration equation (Figure 3B, the blue dot). The errors of R6G were larger than that of the above 4-Mpy measured through immersing method (Figure 2C and 2D), which may originate from the non-uniformity of R6G dispersed on tape or Si and the pasting way of tape onto SERS substrate. Thus, the extraction efficiency was evaluated to be 91.6% with an uncertainty of 17.6%, exhibiting excellent collection capacity of transparent adhesive tape. The result indicates that commercial adhesive tape can be used as the effective extractant for rapid targets pick-up from complex surfaces.

Figure 3. (A) Comparison of T-SERS signals: (a) blank T-SERS, (b) R6G (10-5 M) dropped on the tape, (c) R6G (10-5 M) dropped on the Si, and then extracted by tape. (B) The calibration plot of the T-SERS intensity at 1509 cm-1 of R6G dropped on the tape with its concentration (the Y values of the blue dot is the average intensity of (c) in (A), and the X value is its concentration calculated by the calibration curve). The application of T-SERS for pesticides detection from fruits and vegetables surfaces. Pesticides are widely used in agricultural production. Residual pesticides, which pose a great threat to human health, have been the worldwide food safety concerns.36-37 Tetramethylthiuram (TMTD ) is one of the most commonly used pesticides as a protective fungicide in agriculture to prevent fungal diseases in crops,



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vegetables, and fruits.38 In order to exhibit the application possibility for pesticide residues detection from real fruit surfaces, TMTD spread on apple surface was detected by the proposed T-SERS strategy through “paste, peel off, and paste again” procedure. Apple peels were washed with ultrapure water carefully before use, and then cut into 0.5×0.5 cm2. 3 µL of as-prepared TMTD solution was spread on the peels and dried naturally in air. Transparent tape was pasted to the peel and pressed with a certain pressure for 4 s, and peeled off slowly and carefully. Then the tape was pasted and pressed again onto the AgNR@Al2O3 SERS substrate for T-SERS measurements. TMTD was dropped directly onto AgNR@Al2O3 for SERS measurement. Figure 4A shows the Raman spectra of solid TMTD (line a), SERS (line b) and T-SERS (line c) of 0.5 mM TMTD, respectively. The SERS and T-SERS of TMTD are greatly different from normal Raman spectrum of solid powder, suggesting that the S-S bond of TMTD undergoes a breakdown to form two dimethylthiocarbamate fragments under the effect of laser irradiation and the possible charge transfer of silver.39 Three main Raman bands of TMTD at 564, 1383, 1513 cm-1 can be clearly identified, which are attributed to S-S stretch, C-N stretch, C-N stretch or CH3 deformation vibration, respectively. The lowest concentration visually detectable for TMTD from apple peels was 10 µM (Figure 4B). The limit of detection (LOD) of TMTD converted to mass-to-area ratio was 28.8 ng/cm2 (~0.1 µg/g, the calculation details see the “concentration conversion” part of supporting information), lower than the maximum allowed residue

levels

in

apple

(5

µg/g,

GB2763-2016,

http://www.eshian.com/sat/pesticidenew/list/4), which indicates that the sensitivity of the proposed strategy is enough for actual application. The LOD of the proposed T-SERS method for TMTD is comparable to those SERS methods based on silver or printed gold on paper,40-41 but a little higher than others based on complex nanostructures reported previously,20, 42 which may be caused by the relative large distance between TMTD loaded on the tape and SERS “hot spots”. But our method owns the advantages of simplicity, rapidness, and convenience, which are significant for practical analysis. In addition, the sensitivity can be further improved if needed, such as by heating the T-SERS substrate to shorten the distance between targets and hot spot (see Figure S5), dropping silver nanoparticles colloid onto the tape, or fabricating SERS substrate with higher performance.


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The Raman spectra of TMTD from different fruit and vegetable peels such as apples, pears, cucumbers, and spinaches, were also collected by T-SERS approach (Figure 4C). Despite the high background interference resulted from the adsorbed tissues, the Raman bands of TMTD is clear and can be easily identified, demonstrating that the proposed T-SERS strategy can be utilized for qualitative detection of pesticide residues on various surfaces. To demonstrate the universality of the proposed strategy, another pesticide thiabendazole (TBZ) was detected under the same condition. TBZ is a postharvest pesticide commonly used to prevent agricultural products from rotting caused by fungi.43 Compared with the SERS result of TBZ (Figure 4D, plot b), the Raman bands of TBZ collected from apple peel surface by T-SERS can be identified at 784, 1010, 1280, 1578 cm-1 (Figure 4D, plot c), exhibiting the feasibility for multiple pesticides detection.44-45 Thus, with the flexible, transparent, and adhesive commercial tape as the effective extractant, the proposed T-SERS strategy has the huge potential for rapid qualitative detection of analytes from complex surfaces.

Figure 4. (A) Raman spectra of TMTD: (a) normal Raman band of solid powder, (b) SERS of TMTD (0.5 mM) and (c) T-SERS of TMTD extracted from apple peel (the dotted lines represent the character bands of TMTD). (B) T-SERS of TMTD with different concentrations extracted from apple peel. (C) T-SERS of TMTD (100 µM)



extracted from different surfaces: (a) apple, (b) pear, (c) cucumber, and (d) spinach. (D) (a) Normal Raman spectrum of TBZ powder, (b) SERS of TBZ, and (c) T-SERS of TBZ (0.2 mM) extracted from apple peel.

CONCLUSIONS We have demonstrated the T-SERS approach with flexible, transparent and adhesive tape as an effective collector and AgNR@Al2O3 as the sensitive and uniform SERS substrate for rapid detection of analytes from actual environment. The commercial tape exhibits excellent transparency and extraction capacity. The tape extracted method shows the merits of simplicity, fastness, low cost, and innocuity. As a practical application, we undertook the qualitative detection of tetramethylthiuram disulfide and thiabendazole pesticide residues from apples, pears, cucumbers, and spinaches. The proposed T-SERS strategy is a universal and convenient approach, and can be used to detect various analytes from complex or specific surfaces, such as the body, or solvent-sensitive surface. It is expected that the proposed T-SERS approach will bring SERS technology closer to practical analysis.

ASSOCIATED CONTENT Supporting information The supporting information is available free of charge on the ACS Publications website at DOI: Including: the SERS and T-SERS of 1,4-BDT and 4-MBA, the absorption spectrum of transparent adhesive tape, the T-SERS of R6G dropped on the tape with different concentration, the T-SERS of 4-Mpy with a heat treatment process, the calculation of concentration conversion from mole-to-ratio to mass per gram. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]. *E-mail: [email protected]. ORCID Jiaolai Jiang: 0000-0002-1878-5817 Junsheng Liao: 0000-0002-0643-7292 Notes


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The authors declare no competing financial interest. ACKNOWLEDGMENTS We thank the Basic Science Center Project of NSFC (No. 51788104), China Academy of Engineering Physics for the sponsored research (TCSQ2016203), Radiochemical Discipline 909 Funds by China Academy of Engineering Physics (No. XK909-2), and the Natural Science Foundation of China (No. 21501157, No. 51531006 and No. 51572148), the key project of the Ministry of Science and Technology of China (grant No. 2016YFE0104000). REFERENCES 1.

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Figure 1. (A) Comparison of SERS signals of (a) Blank AgNR@Al2O3 substrate, (b) Blank tape wrapped AgNR@Al2O3, (c) 10-6 M of 4-Mpy on AgNR@Al2O3, (d) 10-6 M of 4-Mpy on AgNR@Al2O3, then wrapped with tape. (B) The feasibility of T-SERS strategy for detection of 4-Mpy (1 mM) on glass surface (Black line: 4Mpy on tape for Raman; red line: 4-Mpy for T-SERS. Symbol “*” represents the peaks of tape, the dotted lines represent the peaks of 4-Mpy).

338x190mm (300 x 300 DPI)


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Figure 2. (A) SEM and TEM (the insert) images of AgNR@Al2O3. (B) T-SERS spectrums of 4-Mpy of different concentrations on AgNR@Al2O3 and then wrapped with tape. (C) T-SERS spectrums of 4-Mpy (10-6 M) on AgNR@Al2O3 and then wrapped with tape, acquired from 15 random sites. (D) The corresponding bar chart for the peak intensity at 1096 cm−1 from 15 random sites of (C).

254x190mm (300 x 300 DPI)



Figure 3. (A) Comparison of T-SERS signals: (a) blank T-SERS, (b) R6G (10-5 M) dropped on the tape, (c) R6G (10-5 M) dropped on the glass side, and then extracted by tape. (B) The calibration plot of the T-SERS intensity at 1509 cm-1 of R6G dropped on the tape with its concentration (the Y values of the green dot is the intensity of (c) in (A), and the X value is its concentration calculated by the calibration curve). 338x190mm (300 x 300 DPI)


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Figure 4. (A) Raman spectrums of TMTD: (a) normal Raman band of solid powder, (b) SERS of TMTD (0.5 mM) and (c) T-SERS of TMTD extracted from apple peel (the dotted lines represent the character bands of TMTD). (B) T-SERS of TMTD with different concentrations extracted from apple peel. (C) T-SERS of TMTD (100 µM) extracted from different surfaces: (a) apple, (b) pear, (c) cucumber, and (d) spinage. (D) (a) Normal Raman spectrum of TBZ powder, (b) SERS of TBZ, and (c) T-SERS of TBZ (0.2 mM) extracted from apple peel. 254x190mm (300 x 300 DPI)



Scheme 1. Schematic illustration of the T-SERS approach proposed for detection of analytes extracted from fruit surface. 595x446mm (72 x 72 DPI)


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