Gold Nanorod-Coated Capillaries for the SERS-Based Detection of

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Gold Nanorod-Coated Capillaries for the SERS-Based Detection of Thiram Yan Yu, Pan Zeng, Cheng Yang, Junyi Gong, Rongqing Liang, Qiongrong Ou, and Shuyu Zhang ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b02075 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 9, 2019

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ACS Applied Nano Materials

Gold Nanorod-Coated Capillaries for the SERSBased Detection of Thiram Yan Yu †,§, Pan Zeng †,§, Cheng Yang †, Junyi Gong †, Rongqing Liang †,‡, Qiongrong Ou *,†,‡, Shuyu Zhang *,†,‡ † Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433, People’s Republic of China ‡ Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Shanghai 200433, People’s Republic of China KEYWORDS surface enhanced Raman scattering; capillary tube; gold nanorod; tunable plasmon resonance; stability; thiram detection

ABSTRACT Surface enhanced Raman scattering (SERS)-based capillary system is a promising route towards fast, real-time and in-situ detection using a facile sampling process. Here, we demonstrate for the first time resonance-tunable SERS-active capillaries with high sensitivity, reproducibility and stability. The strong signal consistency independent of measurement spots or storage time supports the long-term storage and signal tracking of analytes in practical use. The capillaries were successfully applied to the in-situ detection of pesticide residues, and the sampling process provides operation conveniency compared to conventional methods. These results indicate

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that our SERS-active capillaries have great potentials in fast in-situ detection for many practical applications.

INTRODUCTION SERS has become one of the most promising sensing techniques in chemical analysis due to its noninvasive sensing, high sensitivity, fast response and fingerprint-type identification of target molecules since its discovery in 1970s.1,2 SERS effect can be generated simply from Au or Ag nanostructures by utilizing their electromagnetic resonance properties, therefore SERS substrates are mainly prepared by fabricating nanostructures (such as nanodomes,3,4 nanourchins,5 nanosnowmen,6 metal-coated nanopillars,7 nanorod bundles,8 silver dendrites9 and gold nanostars10 etc.) on planar substrates (such as silicon wafers and glass sheets) utilizing top-down lithography and bottom-up self-assembly processes.10,11 However, the application of planar substrates to fast, real-time SERS detection is subject to limitations on the density of SERS-active sites within the detection volume and the time-consuming sampling process.12 Contrast to planar SERS substrates, SERS-active capillaries offer a variety of unique properties and advantages. The capillaries are capable of conveniently sampling and analyzing the analytes in liquids in real time using capillary forces and generating more SERS-active sites by providing a large surface area in a focus volume. The evenly distributed analytes in liquids produce measurements with better repeatability and reliability.13 The SERS-active capillaries not only provide fast, real-time detection for liquid samples such as water, blood and urine, but also offer a solution to the challenge of on-site analyte extraction on irregular surfaces. Moreover, SERS-


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active capillaries are compatible with other liquid-based detection techniques such as chromatographic systems14,15 and microfluidic platforms.15,16 To date, SERS-active capillaries were fabricated by forming a gold or silver layer on the inner walls via (i) interface-based assembly which organizes nanoparticles using interfacial-ordering effect;17,18 (ii) in-situ reduction or deposition of metal nanoparticles using laser-induced microwave synthesis13, photochemical synthesis19 and liquid phase deposition20; and (iii) chemical functionalization which directly functionalizes metal nanoparticles onto the capillary tubes using linker groups.21 Among these methods, chemical functionalization has been widely adopted due to its simplicity and cost-effectiveness.14-16, 21,22 For practical applications, the capillaries not only need to be provided with a high level of sensitivity, but also possess the features of signal reproducibility, long-term stability, plasmon resonance tunability, fast and low cost in-situ detection. However, the reported SERS-active capillaries so far have not demonstrated the tunability of surface plasmon band,15,21 which limits their application to the fields such as biomedical sensing and treatment. Moreover, the stability of SERS-active capillaries for practical use and their application to in-situ detection was seldom explored.14,15,21 Here, aiming to fabricate resonance-tunable SERS-active capillaries for practical applications, we have functionalized uniformly distributed gold nanorods (AuNRs) onto the inner walls of capillaries, which is a simple and effective method and has not yet been demonstrated. By changing the aspect ratio and the particle density of AuNRs, the resonance tunability across the visible and near-infrared (NIR) region with optimized Raman hot spots and signals has been experimentally verified and our plasmonic capillaries have shown better SERS performance compared to gold nanosphere (AuNS)-coated capillaries. More importantly, we systematically investigated the signal reproducibility and long-term stability of the SERS-active capillaries, which were seldom


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explored before. We further demonstrated that these capillaries are suitable for long-term analyte storage and signal tracking, since they can be easily sealed after sampling and achieve an air-free condition to preserve the samples. In addition, we demonstrated the in-situ detection using these capillaries for the first time and these capillaries exhibited outstanding SERS performance and operation conveniency compared to conventional planar substrates. These capillaries provide a promising route to the fast in-situ detection for a wide variety of practical applications. RESULTS AND DISCUSSION Figure 1 shows the schematic diagram of the fabrication process of SERS-active glass capillaries. (3-Aminopropyl)triethoxysilane (APTES) was first used to functionalize the inner wall of a bare glass capillary with amino groups. By placing the APTES-treated capillary into the concentrated AuNR solution, AuNRs were aspirated into the capillary and anchored to the inner wall. After being rinsed by water and subsequently dried by heat, the capillary presented an even color of reddish brown, indicating an effective and uniform coating of AuNRs. In order to achieve resonance tunability, we synthesized AuNRs with different sizes. The AuNRs with a width of around 60 nm and an aspect ratio of 1.8 (denoted as AR-1.8) were synthesized to resonate with the incident laser wavelength of 633 nm for Raman measurements, while those with an aspect ratio into 3.2 and a width of around 35 nm (denoted as AR-3.2) were synthesized for the resonance wavelength of 785 nm. The synthesized AuNRs show high uniformity and their TEM images and absorption spectra were presented in Figure S1. We first investigated how the particle density of AuNRs distributed on the inner wall of a capillary affects the enhancement of SERS signals using AuNRs with an aspect ratio of 1.8. The concentrated AuNR solution with a concentration of 1 nM, 5 nM and 7.5 nM were used for coating


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and the corresponding AuNR distributions on the inner wall characterized by SEM are shown in Figure 2a - 2c. The particle density increased as the concentration of the AuNR solution increased. A particle density of 31 ± 2.4 particles/μm2, 55 ± 3.1 particles/μm2 and 84 ± 21.4 particles/μm2 was achieved using the concentrated AuNR solution of 1 nM, 5 nM and 7.5 nM, respectively. A monolayer of AuNRs was formed without any aggregates when the concentration was 1 nM or 5 nM, while the AuNRs started to aggregate as the concentration reached 7.5 nM. A 10-6 M rhodamine 6G (R6G) solution filled the open capillaries as analyte for SERS measurement under the excitation wavelength of 633 nm. Figure 2d - 2f show the R6G Raman signals as a function of the AuNR density. The glass capillaries having a particle density of 55 ± 3.1 particles/μm2 show maximum Raman signal enhancement. The decreased number of Raman hot spots in those with lower particle density compromises the signal enhancement, and the aggregates formed in those with higher particle density also have negative contributions to signal enhancement by preventing the effective adsorption of analyte molecules onto hot spots. Therefore, AuNR-coated capillaries with a particle density of 55 ± 3.1 particles/μm2 were used for further investigation of SERS performance and application. The same phenomenon was also observed when AuNRs with an aspect ratio of 3.2 were excited by a 785 nm laser. The corresponding SEM images and Raman signals are shown in Figure S2. To prove the resonance tunability, we measured the Raman spectra of optimized plasmonic capillaries coated by AR-1.8 and AR-3.2 with the same test conditions under different excitation wavelengths. Due to the plasmonic resonance with the excitation wavelength, AR-1.8 and AR-3.2 shows maximum signal intensity under the excitation of 633 nm (Figure S3a) and 785 nm (Figure S3d), respectively. By tuning the resonance wavelength from visible to NIR, these plasmonic capillaries extend their application fields into biomedical sensing and treatment, since the NIR


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window in biological tissue enables deep penetration of light without significant absorption due to the low endogenous absorption coefficient of soft tissues.23,24 The Raman performance of AuNR-coated capillaries was also compared with that of gold nanosphere (AuNS)-coated ones. The synthesized citrate-stabilized AuNSs with a diameter of 50 nm (Figure S1c) have a surface plasmon band located at 544 nm (Figure S1f). AuNS-coated capillaries were fabricated through the same process as AuNR-coated capillaries and the SEM image of the inner wall is shown in Figure S4. Excited by a 633 nm laser, the Raman intensity was estimated to be more than 100,000 counts for 10-6 M R6G solution in capillaries coated by AR-1.8 (Figure S3a) and less than 2,000 counts for 10-4 M R6G solution in AuNS-coated ones (Figure S3e). While excited by a 785 nm laser, the Raman intensity was estimated to be more than 20,000 counts for 10-6 M R6G solution in coated by AR-1.8 (Figure S3d) and around 1,000 counts for 10-4 M R6G solution in AuNS-coated ones (Figure S3f). The superiority of the AuNR-coated capillaries over AuNS-coated ones in SERS performance is attributed to the resonance tunability. To further unveil the SERS performance of AuNR-coated capillaries, we investigated the limit of detection, the enhancement factor (EF), the reproducibility of Raman signals and the stability of the plasmonic capillaries using R6G as the probe molecule. AuNR-coated capillary (AR-1.8) was used for analysis and the excitation wavelength was 633 nm. The limit of detection was found to be 10-8 M. As shown in Figure S5, when the molecule concentration reaches 10−8 M, all of the Raman bands can still be clearly identified and matches well with characteristic peaks of R6G Raman spectrum. This limit of detection does not necessarily represent the full potential of our capillaries, since the absolute SERS signal is subject to the instrument conditions such as the sensitivity of detector.25,26 In addition to the limit of detection, the EF value was estimated by comparing the peak at 1363 cm-1 measured from a 10−6 M R6G solution in a AuNR-coated


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capillary and that from a 2 mM R6G solution in a bare capillary. The EF value was calculated to be 6.09 × 106 and the details of calculation are provided in the Supporting Information. The EF value is comparable to many of the reported high-quality capillary-based SERS substrates,14, 20 indicating that our AuNR-coated capillary is an effective and sensitive tool for SERS detection. Uncontrollable irreproducibility in the SERS signal limits the practical applications of SERS substrates.27,28 To evaluate the reproducibility of our AuNR-coated capillaries, fifteen SERS signals of 1.0 ×10−6 M R6G from randomly selected spots on a capillary are showed in Figure 3a. The variation in intensity of the Raman bands at 613 and 1363 cm−1 is shown in Figure 3b. The relative standard deviations (RSDs) of the Raman band at 613 and 1363 cm−1 is 15.6% and 14.9%, respectively. The good reproducibility is mainly attributed to the uniform AuNR coverage on the inner walls of capillaries, which effectively reduces the difference in signal intensity at different laser spots. The temporal stability of these AuNR-coated capillaries was also investigated. The AuNRcoated capillaries were stored over different periods of time (from 1 week to 10 weeks). The corresponding SERS spectra of 1.0 × 10−5 M R6G solution using these capillaries were recorded and the results are shown in Figure 4a. Compared with fresh capillaries, the capillaries stored for weeks do not suffer any notable decrease in SERS signals and the signal fluctuation is kept within a reasonable range. One of the merits of these capillaries is that they can be easily sealed after sampling and achieve an air-free condition to preserve the samples, so we measured the signal intensity of a sealed capillary filled with 1.0 × 10−5 M R6G solution as a function of time for which the R6G solution had been stored in the capillary (Figure 4b). The results show strong signal consistency, which is


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attributed to the stable chemical property of AuNRs that were anchored firmly on the inner wall of capillary by electrostatic force. Therefore, these AuNR-coated capillaries not only support longterm storage in practical use, but also benefit long-term tracking of SERS signals. These merits as well as the reliable SERS signals achieved by good reproducibility can meet the requirements for practical SERS detection. In order to confirm their practical use, these SERS-active capillaries (AR-1.8) were applied to thiram detection under the excitation wavelength of 633 nm. Thiram, a dithiocarbamate (DTC) pesticide, is widely used during the growth of fruits and vegetables to control fungal diseases and prevent their deterioration during storage and transport.29 However, its extensive use poses a risk to human beings and the repeated exposure or ingestion of its residues may cause diseases such as lethargy, loss of muscle tone, and even severe fetal malformations.30,31 Typically, large-scale analytical instruments such as high-performance liquid chromatography (HPLC) or HPLC−mass spectrometry (HPLC−MS) are employed for the detection of DTC pesticides,32,33 which are timeconsuming and require an extensive manual handing of toxic fungicide samples and a large amount of organic solvents.30,34 Our SERS-active capillaries can be applied as a promising alternative for rapid and sensitive detection of pesticides. Figure 5a shows the SERS spectra of thiram at different concentrations. They are dominated by the CH3 stretching mode at 1503cm−1, CN stretching mode at 1380 cm−1, CN stretching mode and CH3 rocking mode at 1144 cm−1, CS stretching mode and CH3NC deformation mode at 440cm-1, and SS stretching mode at 560 cm−1.30, 35 The characteristic peaks are still well recognizable at the concentration of 1×10−7 M (0.024 ppm), which is lower than the maximal residue limit of 7 ppm in fruits as specified by the U.S. Environmental Protection Agency (EPA).36 Although the limitof-detection (LOD) value achieved by capillaries is still higher than the reported value of 0.3 μg/L


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(1.2×10-9 M) analyzed by GC-MS,37 this work does not aim to replace GC-MS, but to provide an alternative method with distinctive features GC-MS does not have. The dependence of the peak intensity at 1380 cm-1 on the negative logarithm of thiram concentration is shown in Figure 5b. A good linear response in the range from 10−4 M to 10−7 M with a coefficient of determination (R2) of 0.9777 was observed, indicating the applicability of the technique in quantitative analysis. Since the SERS-active capillaries are capable of conducting on-site sampling on irregular surfaces, we chose a thiram-adsorbed apple peel as the testing subject for non-destructive identification and in-situ detection. A AuNR-coated glass sheet was used as the reference, which was fabricated by the same procedure with the same concentrated AuNR solutions. As shown in Figure 6a, the thiram solution was sprayed onto the peel of a clean apple and the pesticide molecules adsorbed onto the surface after the solution was dried in air. Subsequently, 10 μL ethanol was dropped onto the apple peel. For the first approach, a AuNR-coated glass sheet was used to extract the pesticide molecules by touching the apple peel with AuNR coating (inset of Figure 6b). However, according to Figure 6b, no characteristic thiram peaks were detected when the thiram concentration on the apple peel was 2.4 μg/cm2. For the second approach, the SERS-active capillary touched the apple peel to extract the ethanol and the filled capillary was then ready for Raman test (Figure 6a). The whole sampling process only takes a few seconds. Due to the feature of noninvasive on-site sampling on irregular surfaces, the sampling process of our plasmonic capillaries is not influenced by the testing samples. The thiram detection on other samples follows the same procedure as we presented on apple peels. Typical SERS spectrum for real apple without the addition of thiram through this sampling process is presented in Figure S7, showing only Raman peaks of ethonal (884 cm-1, 1453 cm-1) with no characteristic peaks of thiram. The detection results of extracted thiram are shown in Figure 6c


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which includes all the feature information of thiram with a detectable concentration down to 24 ng/cm2. This value is not only much lower than the maximum permitted residue of thiram on apples (∼2 μg/cm2) but also comparable to many currently reported flexible SERS substrates.38,39 The detection performance of recent SERS methods for thiram residues is compared in Table S1. Considering the outstanding SERS performance and operation conveniency, our SERS-active capillaries hold great potentials in in-situ detection of pesticide molecules. It is worth noting that the selectivity of our AuNR-coated capillaries is limited. Molecules which can bind strongly to gold (such as the formation of Au-S bond) will be detected more easily. To address the challenge of selectivity, one solution is to modify AuNRs by molecular imprinted polymers (MIP) using thiram as the template in order to combine the high sensitivity of SERS with the high selectivity of MIP. CONCLUSIONS In conclusion, we fabricated resonance-tunable SERS-active capillaries by coating AuNRs with pre-designed aspect ratios onto the inner walls of capillaries using electrostatic force. The number of Raman hot spots can be controlled by the concentration of AuNR solution to achieve an optimized Raman enhancement. Using R6G as the probe molecule, these capillaries show an EF of 6.09 × 106 and a limit of detection of 10-8 M. The good reproducibility of Raman signals benefits from uniform coverage of AuNRs and the strong signal consistency over time is attributed to the firm bonding between the chemically stable AuNRs and the inner walls of capillaries. These properties can facilitate the long-term storage and signal tracking in practical use. The capillaries were then applied to thiram detection and they were capable of analyzing the residues below the EPA-specified detection limit. The in-situ thiram detection on the surface of an apple was


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successfully demonstrated with a facile sampling process using one of these SERS-active capillaries. We believe these capillaries have great potentials in environmental analysis and can be readily extended to a variety of detection fields in real life such as medical examination and security. EXPERIMENTAL SECTION Chemicals and materials. All chemicals were purchased from commercial suppliers and used without further purification. Cetyltrimethyl ammonium bromide (CTAB > 98.0%), sodium oleate (NaOL, > 97.0%), and ascorbic acid (AA, BioUltra, ≥ 99.5%) were purchased from SigmaAldrich. Gold chloride trihydrate (HAuCl4•3H2O, ≥ 99.9%), sodium borohydride (NaBH4, 98%), silver nitrate (AgNO3, AR, 99.8%), hydrochloric acid (HCl, 37 wt. % in water), Polyvinylpyrrolidone (PVP, K13-18) and APTES (98%) were purchased from Aladdin. Preparation of AuNRs. The AuNRs were prepared via a modified seed-mediated method.40 Briefly, the seed solution were prepared by adding fresh NaBH4 (0.01 M, 0.6 mL) into the mixed solution of HAuCl4 (0.5 mM, 5 mL) and CTAB (0.2 M, 5 mL) under vigorous stirring for 2 minutes. To prepare the growth solution, HAuCl4 (1 mM, 250 mL) and AgNO3 (4 mM) were added into the CTAB and NaOL (1.234 g) solution of 250 mL under gentle stirring. HCl (12 M) and ascorbic acid (64 mM, 1.25 mL) were added into the solution when the color of the solution changed from dark orange to colorless after 90 minutes of stirring. The AuNR solution was then obtained by rapidly injecting the seed solution into the growth solution under gentle stirring for 30 seconds and leaving the mixture undisturbed overnight. The AuNR solution used for SERS characterization and thiram detection with LSPR at 650 nm was synthesized using 7 g CTAB, 1.8mL HCl, 12 mL AgNO3 and 0.8 mL seed solution, while that with LSPR located at 785 nm was


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synthesized by the same method using 9 g CTAB, 1.5 mL HCl, 24 mL AgNO3 and 0.2 mL seed solution. The obtained AuNR solution was centrifuged at 8800 rpm for 8 minutes to remove excess CTAB before being transferred into 20 mg/mL PVP solution in ethanol for negative charge modification. After being stirred for 5 h, the obtained PVP-capped AuNR solution was centrifuged again at 8800 rpm for 8 minutes and redispersed in ethanol for further use. Preparation of gold AuNSs. The AuNSs were synthesized through a seed growth method with a slight modification.41 Initially, sodium citrate solution (1.5 mL, 34 mM) was rapidly injected into a boiling HAuCl4 solution (50 mL, 0.25 mM) under stirring and the mixture was kept boiling for 15 minutes to obtain the seed solution. 20 mL reaction mixture was then extracted after it was cooled down to 80 ℃. Deionized water (17 mL), HAuCl4 solution (0.2 mL, 0.25 mM) and sodium citrate solution (2.8 mL, 34 mM) were added subsequently into the extracted solution, and the obtained solution was then used as seed. This iterative process was repeated for four times to yield citrate-stabilized AuNSs with a diameter around 50 nm. Preparation of SERS-active glass capillaries. Capillaries (inside diameter: 0.3 mm, length: 100 mm) were first washed with hot piranha solution (H2SO4: H2O2 in a 7:3 ratio by volume), followed by rinsing with water and drying in air. The cleaned glass capillaries were immersed in an APTES/ethanol (1/50 v/v) solution for 12 hours to functionalize the inner walls with amino groups. After being rinsed with ethanol for three times and dried in air at 80 ℃ for 10 minutes, the positively charged glass capillaries were obtained. The PVP-capped AuNR solution or sodium citrate stabilized-AuNS solution was centrifuged at 8800 rpm for 8 minutes to obtain the concentrates. The AuNRs or AuNSs were then aspirated into the capillaries by capillary force for 30 minutes for effective coating. After being rinsed by water and dried at 80 ℃, the plasmonic capillaries were obtained. In order to set up a contrast experiment for on-site application, the glass


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sheets gone through the same procedure of washing with hot piranha solution, functioning with amino groups and coating with AuNR solution with the same concentration used for capillary coating. Numerical calculation. Rigorous calculation based on finite element method was carried out using COMSOL. The AuNRs and AuNSs were located at the center of the physical domain, which was enclosed by a perfect match layer. The distance between nanoparticles was set to 2 nm, and the incident electric field was polarized in-plane with a wavelength of 633 nm and 785 nm. Morphology characterization and absorption measurement. Transmission electron microscopy (TEM) images were acquired on a JEM-1400 microscope operating at 120kV. Optical spectra were recorded using a Cary 5000 UV/Vis/NIR spectrophotometer. Scanning electron microscopy (SEM) imaging was performed with a field emission SEM (Sigma VP, Carl Zeiss AG, Jena, Germany) at 3 kV utilizing the in-lens detector at a working distance of approximately 3 mm. To investigate the morphology of the nanoparticle coatings on the inner walls of capillaries, the samples were cut to expose the inner surfaces and then affixed to a conductive carbon tab with adhesive for SEM measurements. Raman measurements for R6G and thiram. Raman measurements were conducted by using a Renishaw inVia Raman microscope system equipped with He-Ne laser with excitation wavelength at 633 nm and 785 nm. For capillaries coated by AuNRs with the aspect ratio of 1.8, a 633 nm excitation wavelength with a laser power of 0.17 mW and 0.85 mW was used for R6G and thiram measurements, respectively. And for capillaries coated by AuNRs with the aspect ratio of 3.2, a 785 nm excitation wavelength with a laser power of 15 mW was used for R6G measurement. The laser spot was focused through a 50× objective (Leica, numerical aperture: 0.5) onto the inner wall


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of a capillary which was filled with solution of target analytes. All the spectra were obtained with an acquisition time of 10 seconds unless otherwise stated. The baselines of Raman spectra were subtracted in all cases for corrections. Calculation of EF. The EF was estimated by using the following equation:

EF =

ISERS Nnormal Inormal NSERS

Equation 1

where ISERS and Inormal refers to Raman intensities of R6G molecules in the SERS-active capillary and the bare one, respectively. NSERS and Nnormal is the number of molecules contributing to ISERS and Inormal, respectively. Since the decrease of inner diameter of capillary due to the coating of gold nanoparticles is negligible, the probing volume remains constant for NSERS and Nnormal, therefore the equation for EF calculation can be modified as:21

EF =

ISERS Cnormal Inormal CSERS

Equation 2

where CSERS and Cnormal is the concentration of analyte solution contributing to ISERS and Inormal, respectively. SERS detection for pesticide residues on the apple peel. To demonstrate the in-situ detection of thiram on the fruit peel using our SERS-active capillary, the thiram solution was sprayed onto the apple peel which has been washed with water and ethanol thoroughly beforehand. After the sprayed thiram solution was dried in air, the SERS-active capillary was used for on-site sampling by dropping 10 μL ethanol onto the apple peel and subsequently for Raman detection with the same parameters mentioned above. In order to meet the practical standards, the concentration of


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thiram was presented in the unit of ng/cm2, which was determined by measuring the coverage area of the sprayed thiram solution and calculating the volume of thiram solution per unit area (around 100 μL/cm2).

ASSOCIATED CONTENT Supporting Information. Details on the characterization of synthesized AuNRs and AuNSs, the SERS performance affected by AuNR distributions excited at 785 nm, the performance comparison of AuNR-(AR-1.8, AR-3.2) and AuNS-coated capillaries, the limit of detection, the calculation of enhancement factor, and the detection performance of recent SERS methods for thiram residues, etc. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (Q. O.) *E-mail: [email protected] (S. Z.) ORCID Shuyu Zhang: 0000-0002-5036-0480 Author Contributions § Y.

Y. and P. Z. contributed equally to this work.

Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT The authors would like to acknowledge the financial support of the National Natural Science Foundation of China (61705042, 51677031) and Shanghai Sailing Program (16YF1400700).

REFERENCES (1) Fleischmann, M.; Hendra, P. J.; Mcquillan, A. J. Raman-Spectra of Pyridine Adsorbed at a Silver Electrode. Chem. Phys. Lett. 1974, 26, 163-166. (2) Mcquillan, A. J.; Hendra, P. J.; Fleischmann, M. Raman Spectroscopic Investigation of Silver Electrodes. J. Electroanal. Chem. Interfacial Electrochem. 1975, 65, 933-944. (3) Choi, C. J.; Xu, Z. D.; Wu, H. Y.; Liu, G. L.; Cunningham, B. T. Surface-Enhanced Raman Nanodomes. Nanotechnology 2010, 21, 415301. (4) Kahraman, M.; Ozbay, A.; Yuksel, H.; Solmaz, R.; Demir, B.; Caglayan, H. Tunable Plasmonic Silver Nanodomes for Surface-Enhanced Raman Scattering. Plasmonics 2018, 13, 785795. (5) Liu, Z.; Yang, Z.; Peng, B.; Cao, C.; Zhang, C.; You, H.; Xiong, Q.; Li, Z.; Fang, J. Highly Sensitive, Uniform, and Reproducible Surface-Enhanced Raman Spectroscopy from Hollow AuAg Alloy Nanourchins. Adv. Mater. 2014, 26, 2431-9. (6) Lee, J. H.; You, M. H.; Kim, G. H.; Nam, J. M. Plasmonic Nanosnowmen with a Conductive Junction as Highly Tunable Nanoantenna Structures and Sensitive, Quantitative and Multiplexable Surface-Enhanced Raman Scattering Probes. Nano Lett. 2014, 14, 6217-6225.


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(7) Kang, G.; Matikainen, A.; Stenberg, P.; Färm, E.; Li, P.; Ritala, M.; Vahimaa, P.; Honkanen, S.; Tan, X. High Aspect-Ratio Iridium-Coated Nanopillars for Highly Reproducible SurfaceEnhanced Raman Scattering (SERS). ACS Appl. Mater. Interfaces 2015, 7, 11452-11459. (8) Zhu, C.; Meng, G.; Zheng, P.; Huang, Q.; Li, Z.; Hu, X.; Wang, X.; Huang, Z.; Li, F.; Wu, N. A Hierarchically Ordered Array of Silver-Nanorod Bundles for Surface-Enhanced Raman Scattering Detection of Phenolic Pollutants. Adv. Mater. 2016, 28, 4871-4876. (9) Gu, H.-X.; Xue, L.; Zhang, Y.-F.; Li, D.-W.; Long, Y.-T. Facile Fabrication of a Silver Dendrite-Integrated Chip for Surface-Enhanced Raman Scattering. ACS Appl. Mater. Interfaces 2015, 7, 2931-2936. (10) Su, Q. Q.; Ma, X. Y.; Dong, J.; Jiang, C. Y.; Qian, W. P. A Reproducible SERS Substrate Based on Electrostatically Assisted APTES-Functionalized Surface-Assembly of Gold Nanostars. ACS Appl. Mater. Interfaces 2011, 3, 1873-1879. (11) Shiohara, A.; Wang, Y.; Liz-Marzán, L. M. Recent Approaches Toward Creation of Hot Spots for SERS Detection. J. Photochem. Photobiol. C 2014, 21, 2-25. (12) Guo, Y. B.; Oo, M. K. K.; Reddy, K.; Fan, X. D. Ultrasensitive Optofluidic SurfaceEnhanced Raman Scattering Detection with Flow-Through Multihole Capillaries. ACS Nano 2012, 6, 381-388. (13) Yüksel, S.; Schwenke, A. M.; Soliveri, G.; Ardizzone, S.; Weber, K.; Cialla-May, D.; Hoeppener, S.; Schubert, U. S.; Popp, J. Trace Detection of Tetrahydrocannabinol (THC) with a SERS-Based Capillary Platform Prepared by the In Situ Microwave Synthesis of AgNPs. Anal. Chim. Acta 2016, 939, 93-100.


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Page 18 of 29

(14) Wang, W.; Xu, M.; Guo, Q.; Yuan, Y.; Gu, R.; Yao, J. Rapid Separation and On-line Detection by Coupling High Performance Liquid Chromatography with Surface-Enhanced Raman Spectroscopy. RSC Adv. 2015, 5, 47640-47646. (15) Lee, S. J.; Moskovits, M. Visualizing Chromatographic Separation of Metal Ions on a Surface-Enhanced Raman Active Medium. Nano Lett. 2011, 11, 145-150. (16) Chen, F.-Y.; Chang, W.-C.; Jian, R.-S.; Lu, C.-J. Novel Gas Chromatographic Detector Utilizing the Localized Surface Plasmon Resonance of a Gold Nanoparticle Monolayer inside a Glass Capillary. Anal. Chem. 2014, 86, 5257-5264. (17) Lee, J. W.; Kim, K.; Shin, K. S. A Novel Fabrication of Au-Coated Glass Capillaries for Chemical Analysis by Surface-Enhanced Raman Scattering. Vib. Spectrosc. 2010, 53, 121-125. (18) Lee, J. W.; Lee, H. B.; Kim, K.; Shin, K. S. Novel Fabrication of Silver-Coated Glass Capillaries for Ready SERS-Based Detection of Dissolved Chemical Species. Anal. Bioanal. Chem. 2010, 397, 557-562. (19) Herman, K.; Szabo, L.; Leopold, L. F.; Chis, V.; Leopold, N. In Situ Laser-Induced Photochemical Silver Substrate Synthesis and Sequential SERS Detection in a Flow Cell. Anal. Bioanal. Chem. 2011, 400, 815-20. (20) Park, H. K.; Lee, H. B.; Kim, K. A Facile Deposition of Silver onto the Inner Surface of a Glass Capillary Tube for Micro-Surface-Enhanced Raman Scattering Measurements. Appl. Spectrosc. 2007, 61, 19-24.


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Page 19 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(21) Shanthil, M.; Fathima, H.; George Thomas, K. Cost-Effective Plasmonic Platforms: Glass Capillaries Decorated with Ag@SiO2 Nanoparticles on Inner Walls as SERS Substrates. ACS Appl. Mater. Interfaces 2017, 9, 19470-19477. (22) Wang, W.; Guo, Q.; Xu, M.; Yuan, Y.; Gu, R.; Yao, J. On-line Surface Enhanced Raman Spectroscopic Detection in a Recyclable Au@SiO2 Modified Glass Capillary. J. Raman Spectrosc. 2014, 45, 736-744. (23) Turcheniuk, K.; Dumych, T.; Bilyy, R.; Turcheniuk, V.; Bouckaert, J.; Vovk, V.; Chopyak, V.; Zaitsev, V.; Mariot, P.; Prevarskaya, N.; Boukherroub, R.; Szunerits, S. Plasmonic Photothermal Cancer Therapy with Gold Nanorods/Reduced Graphene Oxide Core/Shell Nanocomposites. RSC Adv. 2016, 6, 1600-1610. (24)Tian, L.; Tadepalli, S.; Fei, M.; Morrissey, J. J.; Kharasch, E. D.; Singamaneni, S. OffResonant Gold Superstructures as Ultrabright Minimally Invasive Surface-Enhanced Raman Scattering (SERS) Probes. Chem. Mater. 2015, 27, 5678-5684. (25) Chen, H. Y.; Lin, M. H.; Wang, C. Y.; Chang, Y. M.; Gwo, S. Large-Scale Hot Spot Engineering for Quantitative SERS at the Single-Molecule Scale. J. Am. Chem. Soc. 2015, 137, 13698-13705. (26) Zong, C.; Xu, M.; Xu, L. J.; Wei, T.; Ma, X.; Zheng, X. S.; Hu, R.; Ren, B. SurfaceEnhanced Raman Spectroscopy for Bioanalysis: Reliability and Challenges. Chem. Rev. 2018, 118, 4946-4980.


19


Page 20 of 29

(27) Kim, M.; Ko, S. M.; Kim, J. M.; Son, J.; Lee, C.; Rhim, W. K.; Nam, J. M. Dealloyed IntraNanogap Particles with Highly Robust, Quantifiable Surface-Enhanced Raman Scattering Signals for Biosensing and Bioimaging Applications. ACS Cent. Sci. 2018, 4, 277-287. (28) Kim, W.; Lee, S. H.; Kim, S. H.; Lee, J.-C.; Moon, S. W.; Yu, J. S.; Choi, S. Highly Reproducible Au-Decorated ZnO Nanorod Array on a Graphite Sensor for Classification of Human Aqueous Humors. ACS Appl. Mater. Interfaces 2017, 9, 5891-5899. (29) Zhang, C.-H.; Zhu, J.; Li, J.-J.; Zhao, J.-W. Small and Sharp Triangular Silver Nanoplates Synthesized Utilizing Tiny Triangular Nuclei and Their Excellent SERS Activity for Selective Detection of Thiram Residue in Soil. ACS Appl. Mater. Interfaces 2017, 9, 17387-17398. (30) Zhu, C.; Wang, X.; Shi, X.; Yang, F.; Meng, G.; Xiong, Q.; Ke, Y.; Wang, H.; Lu, Y.; Wu, N. Detection of Dithiocarbamate Pesticides with a Spongelike Surface-Enhanced Raman Scattering Substrate Made of Reduced Graphene Oxide-Wrapped Silver Nanocubes. ACS Appl. Mater. Interfaces 2017, 9, 39618-39625. (31) Zhu, J.; Chen, Q.; Kutsanedzie, F. Y. H.; Yang, M.; Ouyang, Q.; Jiang, H. Highly Sensitive and Label-Free Determination of Thiram Residue Using Surface-Enhanced Raman Spectroscopy (SERS) Coupled with Paper-Based Microfluidics. Anal. Methods 2017, 9, 6186-6193. (32) Filipe, O. M. S.; Santos, S. A. O.; Domingues, M. R. M.; Vidal, M. M.; Silvestre, A. J. D.; Santos, E. B. H. Effect of Copper Ions on the Degradation of Thiram in Aqueous Solution: Identification of Degradation Products by HPLC-MS/MS. J. Hazard. Mater. 2014, 279, 125-132.


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(33) Schmidt, B.; Christensen, H. B.; Petersen, A.; Sloth, J. J.; Poulsen, M. E. Method Validation and Analysis of Nine Dithiocarbamates in Fruits and Vegetables by LC-MS/MS. Food Addit. Contam., Part A 2013, 30, 1287-1298. (34) Fateixa, S.; Raposo, M.; Nogueira, H. I. S.; Trindade, T. A General Strategy to Prepare SERS Active Filter Membranes for Extraction and Detection of Pesticides in Water. Talanta 2018, 182, 558-566. (35) Tang, S.; Li, Y.; Huang, H.; Li, P.; Guo, Z.; Luo, Q.; Wang, Z.; Chu, P. K.; Li, J.; Yu, X. F. Efficient Enrichment and Self-Assembly of Hybrid Nanoparticles into Removable and Magnetic SERS Substrates for Sensitive Detection of Environmental Pollutants. ACS Appl. Mater. Interfaces 2017, 9, 7472-7480. (36) EPA (2004) Reregistration Eligibility Decision for Thiram. United States, Environmental Protection Agency. ID: OPP-2004-0183 at: www.epa.gov.edockets. (37) Kawamoto, T.; Yano, M.; Makihata, N. Development of a High-Sensitivity Quantitative Analytical Method for Determining Polycarbamate by Gas Chromatography-Mass Spectrometry Incorporating Temperature-Programmable Inlet On-Column Injection. J. Chromatogr. A 2005, 1074, 155-161. (38) Yang, N.; You, T. T.; Gao, Y. K.; Zhang, C. M.; Yin, P. G. Fabrication of a Flexible Gold Nanorod Polymer Metafilm via a Phase Transfer Method as a SERS Substrate for Detecting Food Contaminants. J. Agric. Food Chem. 2018, 66, 6889-6896. (39) Cui, H.; Li, S.; Deng, S.; Chen, H.; Wang, C. Flexible, Transparent, and Free-Standing Silicon Nanowire SERS Platform for In Situ Food Inspection. ACS Sens. 2017, 2, 386-393.


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(40) Ye, X.; Zheng, C.; Chen, J.; Gao, Y.; Murray, C. B. Using Binary Surfactant Mixtures To Simultaneously Improve the Dimensional Tunability and Monodispersity in the Seeded Growth of Gold Nanorods. Nano Lett. 2013, 13, 765-771. (41) Montes-García, V.; Gómez-González, B.; Martínez-Solís, D.; Taboada, J. M.; JiménezOtero, N.; de Uña-Álvarez, J.; Obelleiro, F.; García-Río, L.; Pérez-Juste, J.; Pastoriza-Santos, I. Pillar[5]arene-Based Supramolecular Plasmonic Thin Films for Label-Free, Quantitative and Multiplex SERS Detection. ACS Appl. Mater. Interfaces 2017, 9, 26372-26382.


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FIGURES

Figure 1. A schematic diagram of the fabrication process of SERS-active glass capillaries and the photograph of a bare capillary and a AuNR-coated capillary.


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Figure 2. SEM images of glass capillaries having a AuNR density of (a) 31 ± 2.4 particles /μm2, (b) 55 ± 3.1 particles /μm2 and (c) 84 ± 21.4 particles /μm2, and (d−f) the corresponding SERS spectra of R6G (10−6 M). The scale bar in each SEM image is 1μm. The excitation wavelength is 633 nm and the laser power is 0.17 mW in these Raman measurements.


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Figure 3. Reproducibility of the SERS signals in the AuNR-coated capillaries. (a) The measured SERS spectra of 1.0 × 10−6 M R6G from 15 random points on a capillary. (b) The variation in SERS intensity of the 613 and 1363cm−1 bands. The excitation wavelength is 633 nm and the laser power is 0.17 mW in these Raman measurements.


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Figure 4. (a) The Raman intensity at 1363 cm−1 of 10-5 M R6G using AuNR-coated capillaries stored over different periods of time, and (b) the intensity of a sealed capillary filled with 10−5 M R6G solution as a function of time for which the R6G solution had been stored in the capillary.


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Figure 5. (a) SERS spectra for different concentrations (1 × 10−4 to 1 × 10−7 M) of thiram and (b) the peak intensity at 1380 cm-1 as a function of thiram concentration. The excitation wavelength is 633 nm and the laser power is 0.85 mW in these Raman measurements.


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Figure 6. (a) A schematic diagram showing the in-situ extraction and detection of pesticide residues on the apple peel using a AuNR-coated capillary (AR-1.8) and a AuNR-coated glass sheet. (b) The SERS spectrum of thiram residues with a concentration of 2.4 μg/cm2 detected by a AuNR-coated glass sheet. (c) The SERS spectra of the thiram residues with a concentration of 2.4 μg/cm2, 240 ng/cm2 and 24 ng/cm2 detected by a AuNR-coated capillary (AR-1.8). The excitation wavelength is 633 nm and the laser power is 0.85 mW in these Raman measurements.


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Gold Nanorod-Coated Capillaries for the SERS-Based Detection of

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