Surface enhanced Raman scattering (SERS) fabrics for trace analysis

Accepted Manuscript Title: Surface enhanced Raman scattering (SERS) fabrics for trace analysis Author: Jun Liu Ji Zhou Bin Tang Tian Zeng Yaling Li Jingliang Li Yong Ye Xungai Wang PII: DOI: Reference:

S0169-4332(16)31180-1 http://dx.doi.org/doi:10.1016/j.apsusc.2016.05.150 APSUSC 33343

To appear in:

APSUSC

Received date: Revised date: Accepted date:

24-2-2016 26-5-2016 26-5-2016

Please cite this article as: Jun Liu, Ji Zhou, Bin Tang, Tian Zeng, Yaling Li, Jingliang Li, Yong Ye, Xungai Wang, Surface enhanced Raman scattering (SERS) fabrics for trace analysis, Applied Surface Science http://dx.doi.org/10.1016/j.apsusc.2016.05.150 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Surface enhanced Raman scattering (SERS) fabrics for trace analysis Jun Liua,b, Ji Zhoub, Bin Tanga,c,*, Tian Zengb, Yaling Lib, Jingliang Lic, Yong Ye b,*, Xungai Wanga,c a

National Engineering Laboratory for Advanced Yarn and Fabric Formation and

Clean Production, Wuhan Textile University, Wuhan 430073, China. b

Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials &

Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Ministry of Education & College of Chemistry & Chemical Engineering, Hubei University, Wuhan 430062, PR China. c

Institute for Frontier Materials, Deakin University, Geelong, Victoria 3216,

Australia. ∗Corresponding

authors. E-mail addresses: [email protected] (B. Tang);

[email protected] (Y. Ye).

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Graphical Abstract

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Highlights

 Gold nanoparticles are in-situ synthesized on silk fabrics by heating  Flexible silk fabrics with gold nanoparticles are used for surfaceenhanced Raman scattering (SERS)  SERS activities of silk fabrics with different gold contents are investigated

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Abstract Flexible SERS active substrates were prepared by modification of silk fabrics with gold nanoparticles. Gold nanoparticles were in-situ synthesized after heating the silk fabrics immersed in gold ion solution. Localized surface plasmon resonance (LSPR) properties of the treated silk fabrics varied as the concentration of gold ions changed, in relation to the morphologies of gold nanoparticles on silk. In addition, Xray diffraction (XRD) was used to observe the structure of the gold nanoparticle treated silk fabrics. The SERS enhancement effect of the silk fabrics treated with gold nanoparticles was evaluated by collecting Raman signals of different concentrations of p-aminothiophenol (PATP), 4-mercaptopyridine (4-MPy) and crystal violet (CV) solutions. The results demonstrate that the silk fabrics corresponding to 0.3 and 0.4 mM of gold ions possess high SERS activity compared to the other treated fabrics. It is suggested that both the gold content and morphologies of gold nanoparticles dominate the SERS effect of the treated silk fabrics. Keywords: Silk; Gold nanoparticle; SERS; Biomass; Flexible substrate.

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1. Introduction Surface-enhanced Raman scattering (SERS) is one of the most powerful spectroscopic techniques and has been widely used in many areas, such as chemistry, materials science and biosciences [1-4]. SERS provides an ultrasensitive, rapid and non-destructive detection method. Generally, SERS enhancement is observed for analytes adsorbed onto SERS active substrates. Most of the SERS substrates are nanostructured coinage metals such as gold and silver nanoparticles [5, 6]. A highly SERS active substrate is very important to obtain SERS enhancement [7]. Developing effective enhancement substrates has been one of the greatest challenges associated with the SERS technique. Various techniques have been attempted to fabricate SERS substrates with good enhancement factors [8-10]. Diverse active SERS substrates, including porous substrates, metal nanoparticle films, and bimetallic nanostructures, have been produced by sophisticated designs [11-13]. Many of these substrates are expensive and time consuming [14]. Compared to conventional fragile solid SERS substrates such as glass, quartz slides and silicon wafers, flexible SERS substrates are expected to play an important role in next generation sensing devices because of the advantages in application, as well as low cost and good processability. Different types of flexible SERS substrates involving metal nanoparticles have been developed and investigated. Paper-based SERS substrates have attracted great interest of researchers, due to their low cost and environmentally friendly nature [15, 16]. Various papers such as filter papers [17], photocopy papers [18], and cellulose papers [19] have been impregnated with noble metal nanoparticles for SERS applications. Natural rubber latex was successfully used as a matrix to synthesize gold nanoparticles and the gold-nanoparticle-loaded rubber film as a flexible SERS substrate produces outstanding SERS enhancement effect [20]. 5

Recently, SERS substrates based on fibrous materials were developed [7, 21-23]. Ballerini et al. employed cotton thread assembled with gold nanoparticles as an efficient SERS active substrate for probing p-aminothiophenol (PATP). Amplification of SERS signals for a range of analytes was achieved by controlling the aggregation state of the gold nanoparticles on thread using a cationic polymer [23]. The threads with gold nanoparticles can be used to form fabric, which can potentially be used for detection of biological hazards or chemical warfare reagents. Gong et al. assembled silver nanoparticles onto cotton swabs and in-situ grew silver on the treated cotton swabs. The cotton swabs modified with silver nanoparticles enhanced the Raman signals of a primary explosive marker 2,4-dinitrotoluene (2,4-DNT) [22]. Due to their large specific surface, flexibility, softness, lightness and permeability, textile materials are suitable for the design of chemosensors or biosensors that can be constantly worn without affecting an individual's daily routine [24]. Fabric-based SERS substrates with flexibility and laundry ability can be integrated into wearable sensors to design smart clothes for monitoring chemical information. Robinson et al. modified metal-coated zari fabric with silver nanoparticles and then used the treated fabric as a SERS substrate for analytical applications [7]. However, it remains a challenge to develop simple and convenient methods to realize the fabrication of SERS active fabric substrates using common textile fabrics purchased such as silk. Silk as a protein fiber is widely used in the textile industry due to its inherently elegant sheen, excellent flexibility, environmental friendliness and good comfort. Gold and silver nanoparticles have been used to modify silk fibers/fabrics to endow silk with different functions including bright colors, antibacterial and UV protection in our previous research work [25, 26]. The localized surface plasmon resonance (LSPR) properties of noble metal nanoparticles on the surface of fibers leads to

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fascinating colors on the treated silk and may give rise to enhanced electromagnetic field for amplification of optical signals. SERS enhancement is expected from the noble metal nanoparticles that are assembled or synthesized on silk fibers/fabrics. Herein, a soft and flexible SERS substrate was fabricated based on silk fabric using a simple method in which gold nanoparticles were in-situ synthesized on silk fabrics by heating. Colored silk fabrics were obtained under different concentrations of precursor of gold nanoparticles (HAuCl4). The optical features of silk fabrics treated with gold nanoparticles were observed. The structures and surface properties of the treated silk fabrics were characterized and analyzed. Furthermore, the SERS activity for different silk fabrics with gold nanoparticles was investigated by observing the Raman signals corresponding to different concentrations of probe molecules. 2. Experimental section 2.1. Materials Tetrachloroauric(III)

acid

(HAuCl4·3H2O,

>99%),

PATP

(97%),

4-

mercaptopyridine (4-MPy, 95%), crystal violet (CV, ≥90.0%) were purchased from Sigma-Aldrich. All chemicals were of an analytical grade and used as received. Crepe satin silk fabrics, with a weight of 123.4 g/m2 and a density of 51 threads/cm in the warp direction and 41 threads/cm in the weft direction, were purchased from a local retailer. 2.2. Characterization The UV-vis diffuse reflection absorption spectra of samples were recorded by a Varian Cary 5000 UV-VIS-NIR spectrophotometer with a diffuse reflectance accessory (DRA-2500). Scanning electron microscopy (SEM) measurements were

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performed with a Supra 55 VP field emission SEM. X-ray diffraction (XRD) patterns were collected using a Bruker D8 Advance X-ray diffractometer with Cu Kα radiation. 2.3. Fabrication of SERS fabric Gold nanoparticles were in-situ synthesized on silk fabrics for SERS detection of trace analytes. The gold-nanoparticle-treated silk fabrics were prepared according to the modified method in our previous report [26]. 6 pieces of pristine silk fabrics (0.2 g each) were immersed in different concentrations of HAuCl4 aqueous solutions (0.1 ~ 0.6 mM, 50 mL), respectively. The HAuCl4 solutions with silk were shaken for 30 min at room temperature before heating. Subsequently, the solutions were heated at 85 oC for 60 min in a shaking water bath. The color of silk in the solutions became red or brown. The silk fabrics were rinsed with running deionized water and dried at room temperature. The fabric samples corresponding to 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mM of HAuCl4 solutions were designated as SF-01, SF-02, SF-03, SF-04, SF-05 and SF-06. 2.4. SERS measurement of PATP, 4-MPy and CV based on SERS fabrics The as-prepared silk fabrics with gold nanoparticles were immersed into 20 mL of ethanol solution of PATP at different concentrations (10-9 M ~ 10-3 M) for 12 h. After that, the silk fabrics were taken out from solution and rinsed with ethanol to remove the non-specifically bound PATP. Finally, SERS fabrics with PATP were obtained after drying under ambient condition. SERS analysis was performed on a Renishaw inVia Raman microscope system (Renishaw plc, Wotton-under-Edge, UK). A 50×/N.A. 0.75 objective and a 785-nm near-IR diode laser excitation source (500 mW, 0.5%) were used in all measurements. The spectra within a Raman shift window between 600 and 1800 cm-1 were recorded using a mounted CCD camera with integration time of 10 s by single scan. SERS spectra corresponding to different

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concentrations of 4-MPy (10-9 M ~ 10-5 M) ethanol solutions and CV (10-9 M ~ 10-6 M) aqueous solutions were obtained according to the same procedure as PATP. 3. Results and Discussion Fig. 1 displays a photograph of silk fabrics after the in-situ synthesis of gold nanoparticles. The treated silk fabrics exhibit light red, red and brownish red. The silk fabrics treated with low concentration of HAuCl4 (SF-01) were light red. The color of treated silk fabrics darkened with an increase in the concentration of HAuCl4. The colors of treated silk fabrics imply that the gold nanoparticles were synthesized in-situ on silk fabrics. The LSPR properties of gold nanoparticles on silk lead to the bright colors of treated fabrics. In order to investigate the optical property of the treated silk fabrics, the UV-vis reflectance absorption spectra of the treated fabrics corresponding to different concentrations of HAuCl4 were measured. A reflectance absorption band can be seen in the range of 520 ~ 550 nm in each curve, which indicates gold nanoparticles were in-situ synthesized on the silk fabrics. The absorption bands corresponding to SF-01, SF-02, SF-03, SF-04, SF-05 and SF-06 are located at 535, 533, 541, 534, 526 and 530 nm, respectively (Fig. 2), which are attributed to the LSPR of gold nanoparticles on the silk fabrics [27]. The LSPR properties of gold nanoparticles are related to the size and shape of nanoparticles. To investigate the surface morphologies of the silk fibers treated with gold nanoparticles, SEM characterization was performed. Numerous nanoparticles can be seen on the surface of silk fibers (Fig. 3). Spherical particles dominated the nanoparticles on the surface of SF-01 corresponding to 0.1 mM of HAuCl4 (Fig. 3a). Compared with those on the other treated silk fabrics (Fig. 3b-f), the gold nanoparticles on SF-01 were smaller, which may result in the low intensity of LSPR band in the UV-vis reflectance absorption spectrum (Fig. 2). The in-situ synthesized gold nanoparticles increased in 9

size when the initial concentration of HAuCl4 increased from 0.1 mM to 0.2 mM (Fig. 3b). A few anisotropic gold nanoparticles were observed on fiber surface of SF-02. Moreover, most of the anisotropic nanoparticles were triangular nanoplates and truncated nanoprisms that can be found in the SEM images of SF-02, SF-03 and SF04 (Fig. 3b-d). However, many large polygonal nanoparticles appeared when the concentration of HAuCl4 increased to 0.5 and 0.6 mM (Fig. 3e and f). The production of these large polygonal gold nanoparticles brings about the broadening and decreasing of LSPR band of SF-05 and SF-06 (Fig. 2). The detailed data on the morphologies of silver nanoparticles on different fabrics is shown in Table 1. Fig. 4 shows the XRD patterns of silk fabrics before and after treatment with gold nanoparticles. Pristine silk fabric shows a strong diffraction peak (2θ = 20.7°), a weak diffraction peak (2θ = 24.5°) and two shoulder diffraction peaks (2θ = 28.8° and 40.0°). These XRD diffraction peaks are assigned to the β-sheet structure of native silk [28, 29], indicating a high crystallinity of pristine silk fabric. Compared with the XRD pattern of pristine silk fabric, five new XRD peaks appeared in the XRD pattern of treated silk fabric with 2θ = 38.4°, 44.6°, 64.8°, 77.8° and 81.9° (Fig. 4b), which are ascribed to (111), (200), (220), (311) and (222) planes of a face centered cubic (fcc) lattice of gold (JCPDS, File No. 4-0784) [30]. These results also indicate that the gold nanoparticles were synthesized on silk fabrics. Moreover, the characteristic XRD peaks of silk did not change visibly after in-situ synthesis of gold nanoparticles, demonstrating that crystal structures of silk remained unchanged. The interaction between gold nanoparticles and silk was investigated by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies in the previous studies [26, 31, 32]. The gold nanoparticles were found to have no observable influences on the structures of silk. Although it is not believed that the gold nanoparticles are 10

covalently attached to the silk fibers, the combination between gold nanoparticles and silk is strong [26], which makes for the practical applications of the treated fabrics. Noble metal nanostructured materials such as gold and silver nanoparticles have been widely used for active substrates to enhance Raman signal of analytes. In this study, gold nanoparticles were in-situ synthesized on silk fabrics that are notably different from the general supports for metal nanoparticles in the fabrication of SERS substrates. The silk fabrics with as-synthesized gold nanoparticle were expected to enhance the Raman signals of molecules adsorbed on fabrics. The SERS spectra of the silk with gold nanoparticles were measured (Fig. 5). The SERS signal of silk (SF01 and SF-02) was weak when the gold content of silk fabrics was low, which may be due to limited number and small size of gold nanoparticles. Compared with SF-01 and SF-02, the silk with higher gold contents (SF-03, SF-04, SF-05 and SF-06) exhibited stronger Raman signals (Fig. 5). The SERS intensity of silk increased as the initial concentration of HAuCl4 increased. SERS enhancement from gold nanoparticles on silk fabrics may be used for ultrasensitive identification of components in archaeological and historical textiles as well as forensic analysis [32-35]. Model target analytes including PATP, 4-MPy and CV were chosen to investigate the SERS activity of gold-nanoparticle-treated silk fabrics. Fig. 6 shows the SERS spectra of PATP of different concentrations from different SERS fabrics. The characteristic SERS peaks were observed around 1004, 1080, 1140, 1170, 1390, 1435, 1485 and 1580 cm-1 [36, 37]. The peak at ~1080 cm-1 is attributed to C-C and C-S stretching modes. Two weak peaks at ~ 1140 and 1170 cm-1 result from the bending of C-H modes. The peak at ~ 1580 cm-1 is due to the C-C stretching mode of PATP. Two weak peaks around 1170 and 1140 cm-1 could be assigned to C-H bending. The peaks around 1390, 1435 and 1485 cm-1 originate from a combination of C-C stretching and

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C-H bending [36, 38]. Recently, it was suggested that p,p’-dimercaptoazobenzene (DMAB) is formed from PATP via N–N coupling induced by LSPR excitation [39, 40]. The peaks at ~ 1140, 1390 and 1435 cm-1 were assigned to the C–N and N=N stretching vibration of DMAB [39, 41]. The peaks at ~1080 and ~ 1580 cm-1 were selected for analysis of SERS activity of silk fabrics treated with gold nanoparticles. The SERS intensity of PATP from SF-01 was low though the Raman peaks were observed clearly in the spectra (Fig. 6a). The quality of SERS spectra improved visibly when the initial concentration of HAuCl4 increased to 0.2 mM from 0.1 mM (Fig. 6b). Fig. 7 depicts the plot of the intensities of SERS signals around 1080 cm-1 and 1580 cm-1 from different SERS fabrics as a function of the concentrations of PATP. The Raman peak around 1080 cm-1 was visible on SF-01, but the intensity of this SERS peak was low. As can be seen, the intensity around 1080 cm -1 corresponding to SF-03, SF-04, SF-05 and SF-06 was much higher than that corresponding to SF-01 and SF-02. Similarly, regarding the peak at ~ 1580 cm-1, the SERS fabrics with high gold content exhibit much higher intensity, compared with SF-01 and SF-02. However, the sensitivity of SERS fabrics was not increased as the initial concentration of HAuCl4 increased. The strongest SERS signal of PATP was obtained on the silk fabrics corresponding to 0.3 mM and 0.4 mM of HAuCl4 (SF-03 and SF-04). In addition to the gold content, the morphologies of gold nanoparticles on silk fabrics may affect the SERS activity of SERS fabrics. The intensity of SERS peaks decreased with a decrease in concentration of PATP (Fig. 7). Whereas, the characteristic peaks of PATP were still observable on SERS fabrics even when its concentration was decreased to 10-9 M (Fig. 8), which indicates the silk fabrics with gold nanoparticles have strong SERS effects.

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Moreover, 4-MPy was employed as another probe molecule to investigate the SERS effect of the treated silk fabrics. Fig. 9a-e displays the SERS spectra of 4-MPy at different concentrations (10-9 ~ 10-5 M), obtained on different SERS fabrics (SF-02 ~ SF-06). The Raman peaks located at ~ 1003, 1060, 1095, 1200, 1575, and 1609 cm-1 are present in the SERS spectra of 4-MPy. The peak at ~ 1003 is assigned to the ring breathing mode [42]. The two peaks at ~ 1575 and 1609 cm-1 are due to the pyridine ring C=C stretching modes [43]. The peaks at ~ 1200 and ~ 1095 cm-1 are from CH/NH deformation modes and the trigonal ring breathing vibration with C=S, respectively [42, 44]. The peak at ~ 1003 cm-1 was selected to assess the SERS activity of the treated silk fabrics. Fig. 9f shows the plot of peak intensity at ~ 1003 cm-1 as a function of the concentrations of 4-MPy corresponding to different SERS fabrics. SF-02 exhibited low SERS intensity, which may be due to the low density of gold nanoparticles on the fiber surface, consistent with that of PATP. The optimal SERS spectra of 4-MPy were obtained on SF-03 and SF-04, the same as the case of PATP. Nevertheless, SERS enhancement effect of SF-06 was not striking, which may be attributed to the large size of gold nanoparticles on the surface of silk fabrics (Table 1). SF-03 and SF-04 manifested high SERS activity, which were prepared in 0.3 and 0.4 mM of HAuCl4 solution respectively. Characteristic Raman peaks of 4MPy were observed clearly on the SERS fabrics even though the concentration of probe molecules was decreased to 10-9 M, further verifying that the silk fabrics treated with gold nanoparticles possess high SERS activity. Additionally, CV molecules as the analytes were utilized to further evaluate the sensitivity of SERS fabrics (SF-03) in the present study. Fig. 10 displays the SERS spectra of CV with concentrations of 10-9 M to 10-6 M. The characteristic Raman peaks of CV (i.e. 915, 1174, 1583 and 1617 cm-1) are present in the SERS spectrum of CV with 10-6 M [45]. These

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characteristic peaks of CV can be identified clearly even though the concentration of CV decreased to 10-9 M (Fig. 10), indicating the high sensitivity of SERS fabrics. These results demonstrate that silk fabrics treated with gold nanoparticles can be used as SERS substrate for trace analysis. In the previous study [26], the silk fabrics with in-situ synthesized gold nanoparticles were demonstrated to have good colorfastness to washing. It is inferred that the silk fabrics with gold nanoparticles could keep the strong SERS activity after laundering. 4. Conclusion The present study describes a rapid and convenient approach to prepare SERS active substrate based on silk fabrics. Gold nanoparticles were in-situ synthesized on silk fabrics in the presence of HAuCl4 at different concentrations (0.1 ~ 0.6 mM). The localized surface plasmon resonance (LSPR) properties of the treated silk fabrics varied as the HAuCl4 concentrations changed, relevant to the morphologies of gold nanoparticles on fiber surface. XRD further demonstrated the production of gold nanoparticles on the silk fabrics. Significantly, the obtained SERS fabrics possess strong SERS activity. The gold nanoparticle treated silk fabrics enhanced obviously the Raman signals of analytes (PATP, 4-MPy and CV) at the excitation of 785-nm laser. The treated silk fabrics corresponding to 0.3 and 0.4 mM of HAuCl4 (SF-03 and SF-04) exhibited more significant SERS enhancement effects both PATP and 4-MPy, compared with the other treated silk fabrics. The SERS activity is related to not only the gold content of fabrics, but also the morphologies of gold nanoparticles on fabrics. This research would facilitate the development of sensing fabrics with functional components.

Acknowledge 14

This research was supported by the National Natural Science Foundation of China (No. 51403162, 51273153, 21003034), the MoE Innovation Team Project in Biological Fibers Advanced Textile Processing and Clean Production (No. IRT13086), “Future Star” project of Wuhan Textile University (No. 143054) and the Educational Commission of Hubei Province of China (No. T201101).

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[42] L. Zhang, Y. Bai, Z. Shang, Y. Zhang, Y. Mo, Experimental and theoretical studies of Raman spectroscopy on 4-mercaptopyridine aqueous solution and 4mercaptopyridine/Ag complex system, J. Raman Spectrosc. 38 (2007) 1106-1111. [43] H. Hu, W. Song, W. Ruan, Y. Wang, X. Wang, W. Xu, B. Zhao, Y. Ozaki, Fabrication of one-dimensional ZnO/4-MPy/Ag assemblies and their spectroscopic studies, J. Colloid Interface Sci. 344 (2010) 251-255. [44] Z. Gan, A. Zhao, M. Zhang, D. Wang, W. Tao, H. Guo, D. Li, M. Li, Q. Gao, A facile strategy for obtaining fresh Ag as SERS active substrates, J. Colloid Interface Sci. 366 (2012) 23-27. [45] K. Zhang, T. Zeng, X. Tan, W. Wu, Y. Tang, H. Zhang, A facile surfaceenhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates, Appl. Surf. Sci. 347 (2015) 569-573.

20

Fig. Captions Fig. 1. Photograph of the silk fabrics treated with in-situ synthesized gold nanoparticles. Fig. 2. UV-vis reflectance absorption spectra of the silk fabrics treated with gold nanoparticles. Fig. 3. SEM images of the silk fabrics treated with gold nanoparticles: (A) SF-01, (B) SF-02, (C) SF-03, (D) SF-04, (E) SF-05 and (F) SF-06. Fig. 4. XRD patterns of (A) the pristine silk fabric and (B) the treated silk fabric (SF03). Fig. 5. SERS spectra of the silk fabrics with gold nanoparticles. Fig. 6. SERS spectra of different concentrations of PATP on gold nanoparticle treated silk fabrics: (A) SF-01, (B) SF-02, (C) SF-03, (D) SF-04, (E) SF-05 and (F) SF-06. Fig. 7. Plot of the intensities of SERS signals around (A) 1080 cm-1 and (B) 1580 cm-1 as a function of the concentrations of PATP. Each point in the plot represents the average value of ten random measurements on silk fabrics. Fig. 8. SERS spectra of 10-9 M PATP on the silk fabrics treated with gold nanoparticles: (a) SF-03, (b) SF-04, (c) SF-05 and (D) SF-06. Fig. 9. SERS spectra of different concentrations of 4-MPy on the gold nanoparticle treated silk fabrics: (A) SF-02, (B) SF-03, (C) SF-04, (D) SF-05 and (E) SF-06. (F) Plot of the intensities of SERS signals around 1003 cm-1 as a function of the concentrations of 4-MPy. Each point in the plot represents the average value of ten random measurements on silk fabrics.

21

Fig. 10. SERS spectra of different concentrations of CV on the gold nanoparticle treated silk fabrics (SF-03). Table 1. Detailed data of the silver nanoparticles on different fabrics.

22

SF-01

SF-02

SF-03

SF-04

SF-05

SF-06

Fig. 1. Photograph of the silk fabrics treated with in-situ synthesized gold nanoparticles.

23

1.0

SF-01 SF-02 SF-03 SF-04 SF-05 SF-06

Intensity (a.u.)

0.8

0.6

0.4

0.2 300

400

500

600

700

800

Wavelength (nm)

Fig. 2. UV-vis reflectance absorption spectra of the silk fabrics treated with gold nanoparticles.

24

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 3. SEM images of the silk fabrics treated with gold nanoparticles: (A) SF-01, (B) SF-02, (C) SF-03, (D) SF-04, (E) SF-05 and (F) SF-06.

25

10

20

30

40

50

60

2 (degree)

70

80

10

20

30

40

50

60

(311) (222)

(220)

(200)

(111)

Intensity (a.u.)

(b)

Intensity (a.u.)

(a)

70

80

2 (degree)

Fig. 4. XRD patterns of (A) the pristine silk fabric and (B) the treated silk fabric (SF03).

26

SF-01 SF-02 SF-03 SF-04 SF-05 SF-06

Intensity (a.u.)

5000

600

800

1000

1200

1400

1600

1800

-1

Raman Shift (cm )

Fig. 5. SERS spectra of the silk fabrics with gold nanoparticles.

27

600

800

1000

1200

1400

1600

1800

600

800

-1

Raman Shift (cm

800

1000

1200

1400

Raman Shift (cm )

Intensity (a.u.)

Intensity (a.u.)

-1

1200

1400

1600

1800

600

800

1600

1800 600

10000

800

1000

1200

1400 -1

Raman Shift (cm )

1000

1200

1400

1600

1800

1600

1800

Raman Shift (cm-1)

10-3 M 10-4 M 10-5 M 10-6 M 10-7 M

(e)

10 M -4 10 M -5 10 M -6 10 M -7 10 M

10000

1000

Raman Shift (cm-1)

-3

(d)

600

)

10000

Intensity (a.u.)

10000

-3

10 M -4 10 M -5 10 M -6 10 M -7 10 M

(c)

1600

-3

10 M -4 10 M -5 10 M -6 10 M -7 10 M

(f) Intensity (a.u.)

Intenstiy (a.u.)

100

10-3 M 10-4 M 10-5 M 10-6 M 10-7 M

(b) Intensity (a.u.)

10-3 M 10-4 M 10-5 M 10-6 M 10-7 M

(a)

1800

600

10000

800

1000

1200

1400 -1

Raman Shift (cm )

Fig. 6. SERS spectra of different concentrations of PATP on gold nanoparticle treated silk fabrics: (A) SF-01, (B) SF-02, (C) SF-03, (D) SF-04, (E) SF-05 and (F) SF-06.

28

6x10

4

5x10

4

4x10

4

3x10

4

2x10

4

1x10

4

(a)

SF-01 SF-02 SF-03 SF-04 SF-05 SF-06

0 10

-7

10

-6

10

-5

10

-4

Concentration of PATP (M)

10

-3

Intenstiy around 1580 cm-1 (a.u.)

4

-1

Intenstiy around 1075 cm (a.u.)

7x10

5x104

(b)

SF-02 SF-03 SF-04 SF-05 SF-06

4x104 3x104 2x104 1x104 0 10-7

10-6

10-5

10-4

10-3

Concentration of PATP (M)

Fig. 7. Plot of the intensities of SERS signals around (A) 1080 cm-1 and (B) 1580 cm-1 as a function of the concentrations of PATP. Each point in the plot represents the average value of ten random measurements on silk fabrics.

29

(b) Intensity (a.u.)

Intensity (a.u.)

(a) 500

600

800

1000

1200

1400

500

600

1600

800

Raman Shift (cm-1)

1200

1400

1600

(d) Intensity (a.u.)

Intensity (a.u.)

(c) 500

600

1000

Raman Shift (cm-1)

800

1000

1200

1400

Raman Shift (cm-1)

1600

500

600

800

1000

1200

1400

1600

Raman Shift (cm-1)

Fig. 8. SERS spectra of 10-9 M PATP on the silk fabrics treated with gold nanoparticles: (a) SF-03, (b) SF-04, (c) SF-05 and (D) SF-06.

30

800

1000

1200

1400

1600

1800

600

800

10-5 M 10-6 M 10-7 M 10-8 M 10-9 M

10000

1200

1400

Raman Shift (cm

1600

600

1800

(e)

800

1000

1200

1400

1600

1800

-1

Raman Shift (cm

)

10-5 M 10-6 M 10-7 M 10-8 M 10-9 M

1000

10-5 M 10-6 M 10-7 M 10-8 M 10-9 M

10000

-1

)

Intenstiy (a.u.)

Intenstiy (a.u.)

(d)

1000

Intenstiy (a.u.)

10000

-1

Raman Shift (cm

(c)

10-5 M 10-6 M 10-7 M 10-8 M 10-9 M

6x104 5x104

Intensity (a.u.)

10000

600

(b)

10-5 M 10-6 M 10-7 M 10-8 M 10-9 M

Intenstiy (a.u.)

Intenstiy (a.u.)

(a)

(f)

)

SF-02 SF-03 SF-04 SF-05 SF-06

4x104 3x104 2x104 1x104 0

600

800

1000

1200

1400

1600

1800

600

800

-1

Raman Shift (cm

)

1000

1200

1400 -1

Raman Shift (cm

)

1600

1800

10-9

10-8

10-7

10-6

10-5

Concentration of 4-MPY (M)

Fig. 9. SERS spectra of different concentrations of 4-MPy on the gold nanoparticle treated silk fabrics: (A) SF-02, (B) SF-03, (C) SF-04, (D) SF-05 and (E) SF-06. (F) Plot of the intensities of SERS signals around 1003 cm-1 as a function of the concentrations of 4-MPy. Each point in the plot represents the average value of ten random measurements on silk fabrics.

31

-6

10 M -7 10 M -8 10 M -9 10 M

Intenstiy (a.u.)

5000

600

800

1000

1200

1400

Raman Shift (cm

-1

1600

1800

)

Fig. 10. SERS spectra of different concentrations of CV on the gold nanoparticle treated silk fabrics (SF-03).

32

Table 1. Detailed data of the silver nanoparticles on different fabrics. Sample ID

Diameter/size of nanospheres/ nanopolyhedra (nm)

Maximum length of nanoplates (nm)

Proportion of nanoplates (%)

SF-01

28.3 ± 8.9

N/A

0

SF-02

56.9 ± 14.6

94.0 ± 21.5

24.8

SF-03

99.8 ± 17.3

197.8 ± 69.7

23.8

SF-04

109.9 ± 21.1

209.4± 60.3

27.7

SF-05

128.6 ± 24.2

206.3 ± 57.7

27.6

SF-06

137.4 ± 35.5

209.7 ± 66.9

28.7

33