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Giant Vesicles with Anchored Tiny Gold Nanowires: Fabrication and Surface-Enhanced Raman Scattering Yaru Jia, Lei Zhang, Liping Song, Liwei Dai, Xuefei Lu, Youju Huang, Jiawei Zhang, Zhiyong Guo, and Tao Chen Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b03261 • Publication Date (Web): 23 Oct 2017 Downloaded from http://pubs.acs.org on October 26, 2017

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Giant Vesicles with Anchored Tiny Gold Nanowires: Fabrication and Surface-Enhanced Raman Scattering Yaru Jia,a,b† Lei Zhang ,b† Liping Song,b Liwei Dai,b Xuefei Lu,b Youju Huang,∗b Jiawei Zhang,b Zhiyong Guo, *a Tao Chen*b a.

Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, P.R. China

b.

Division of Polymer and Composite Materials, Ningbo Institute of Materials Technology

& Engineering, Chinese Academy of Sciences, Ningbo 315201, P. R. China †These authors contribute equally to this work. ABSTRACT: Sensitivity and reproducibility are two major concerns to improve the performance and extend the range of practical applications of Surface Enhanced Raman Scattering (SERS). Theoretical report reveals that hot spots formed by gold nanoparticles with tip-to-tip configuration would generate the maximum electric field enhancement because of lightning rod effect. In our present study, we constructed a giant vesicle consisting of anchored tiny gold nanowires to provide the high density of sharp tip-to-tip nanogaps for SERS application. The tiny gold nanowires were directly grown and anchored onto the surfaces of polystyrene (PS)

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E-mail: [email protected].

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microspheres by seed-mediated method. Then the removing of PS microspheres by tetrahydrofuran (THF) led to the formation of the gold giant vesicles with hierarchical cage structures, providing the sharp tips and high density of hot spots for improving SERS performance. Compared with non-wires structure (island and inhibited nanoparticle), gold giant vesicles with tiny wires showed higher SERS enhancement factor (9.90×107) and quantitative SERS analysis in the range of 10-4 to 10-7 M. In addition, the large scale gold giant vesicle array on the silica substrate resulted in the high reproducibility of SERS signals with the variation of intensities less than 7.6%. KEYWORDS: Gold giant vesicle, gold nanowire, anisotropic growth, seed-mediated growth, Surface Enhanced Raman Scattering 1. Introduction Since the first discovery in the process of surface roughing treatment to silver electrode by Fleischmann in the 1970s, SERS (Surface Enhanced Raman Scattering)1 has been regarded as a powerful technique for the detection of probe molecule in various fields, such as biological diagnosis,2-3 medicine,4 food safety5 and environmental monitoring etc.6-8 While, there is still a great challenge in improving the SERS performances such as sensitivity and reproducibility to broaden their practical applications. It is believed that there are two major factors contributing to SERS enhancement: chemical9-10 and electromagnetic mechanism (EM).11 The electromagnetic enhancement is considered to be the main factor to influence the SERS performance. According to the EM enhancement theory,11 SERS signal is strongly dependent on the resonance frequency of the noble metal substrate. The field enhancement would achieve the maximal value when the plasmon frequency of nanaoparticles (NPs) is in resonance with the laser radiation. Therefore, it


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is important to design a proper geometry of noble metal particles as ideal SERS substrate. The materials with protuberant or sharped nanostructures such as nanostars,3,12 nanowires,13 nanocubes,14-16 nanobars/nanorice,17 mesocages,18 compass19 and flower-liked20 structure have more surface roughness than gold spheres. The extreme small radii of curvature in this class of NPs result in strong electric field enhancement and subsequently large SERS enhancement factors per surface molecule, which is referred to as a “sharp tip effect”.21-23 Deeper investigation found that not only the sharp tips in single molecule can enhance SERS Intensity, but the “hot spots” created within crevices and gaps between two or more nanoparticles in an aggregated state can also improve even more. That is because LSPR (localized surface plasmon resonance) as a unique optical property of assembled nanostructures, triggers a huge surface-enhanced optical effect and the SERS effect comes from “hot spots” in which LSPR coupling produce a strong electric field. For example, many efforts have been devoted into the synthesis of dimer,24-25 trimer26 or monolaye27-28 to obtain maximum SERS enhancement factor by adjusting gaps between the nanoparticles. Recently, Li and co-workers29 reported a strategy to obtain hot spots with large volume and maximum electric field enhancement, breaking the general limitation that large-volume hot spots usually comes with a weak electric field enhancement. Among the three modes of spiky nanoparticle dimers, tip-to-tip exhibits lager electric field enhancement than the two other modes of tip-to-sphere and sphere-to-sphere, which can be ascribed to the synergistic effect interaction of “interparticle coupling” and “lightning rod effect”. Thus, the materials with abundant sharp tips and dense gaps from tip-to-tip mode can be the ideal substrate for SERS application. In addition to the noble metal structures, well-designed semiconductor is another kind of important material for ideal SERS substrate. It is reported that the optimization of the structure and promotion of the interfacial charge transfer process (ICTP) are the key to


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improving the sensitivity of semiconductor-based SERS. Cong and co-workers30 have employed vacancy into the tungsten oxide materials, which is 100–10,000 times higher than the previously reported values from other semiconductor SERS-active substrates. Wang31 et al further developed a novel semiconductor of amorphous ZnO nanocages owning remarkable SERS activity with EF up to 6.62×105. For ideal SERS substrate, reproducibility and reliability are also required except for the high sensitivity especially in the practical applications. Usually, it is very difficult to fabricate the macroscopically uniform SERS substrates with the high density of hot spots, which leads to a low reproducibility of SERS signals. The key to solve this problem is to prepare large-scale uniform SERS substrates, ensuring the approximate signals at random sites. Preliminary attempt has been reported to fabricate the noble metal nanoparticles arrays with nanogaps between neighbored particles using lithography technique.32-34 The patterning technique surely improved the repeatability, but it also resulted in a high cost and low output restricting its practical applications. Recently, Jiang et al35 reported a large-area two dimensional (2D) gold nanoparticle monolayers with high density of uniform sub-1-nm gaps to improve the reproducibility of SERS signals. Fang and co-workers36 have also prepared large-area 2D silver nanoparticles layer using mesoporous silicon as template to obtain highly ordered structure with uniform nanogaps of less than 3 nm between nanoparticles. Our recent work5 has achieved a novel flexible and adhesive SERS active tape with highly reproducible SERS signals by decorating the commercial tape with gold nanoparticles for the rapid and sensitive pesticide detection in fruits and vegetables. Therefore, considering both sensitivity and reproducibility for an ideal SERS substrate, it is highly important to fabricate the spiky or sharp-tip noble metal NPs based macroscopically uniform SERS substrate.


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Herein, we reported a simple and robust strategy to fabricate giant vesicles consisting of anchored tiny gold nanowires on the surface by controlling the anisotropic growth of nanowires from polystyrene (PS) microsphere surface-bound seeds and successional remove of PS template. The obtained gold giant vesicles can not only provide the inner hollow structure for easily and efficiently capturing SERS probe molecules, but also offer the high density of sharp tips and tipto-tip nanogaps for significantly improve SERS sensitivity. Compared with non-wires structure (island and inhibited nanoparticle on the surface), giant vesicles with tiny wires showed higher SERS EF (9.90×107) and quantitative SERS analysis in the range of 10-4 to 10-7 M. In addition, by using the conventional drop-dry method, a large area array of PS-Au seeds was achieved and then a uniform large-scale film with closely packed Au giant vesicles can be formed, resulting in the high reproducibility of SERS signals with the variation of intensities less than 7.6%. 2. Experimental Section Materials: Poly (N-vinylpyrrolidone) (Mw 550,000), 3-aminopropyltriethoxysilane (APTES), sodium citrate tribasic dihydrate (99.0%), L-ascorbic acid (L-AA) and 4-Mercaptobenzoic acid (MBA, 90%,) were provided by Sigma Aldrich. 2,2-azobisisobutyronitrile (AIBN) was purchased from Aladdin company in Shanghai, China. Chloroauric acid (HAuCl4·4H2O, 99.9%) was obtained from the Alfa Aesar. Styrene was distillated to refine under reduced pressure and AIBN was recrystallized three times in methanol before using (analytical grade). Other chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd in Shanghai, China and used as received. Milli-Q-grade water (18.2 MΩ·cm) was used for all experiments. Instrument: The morphologies in the experiment were characterized by scanning electron microscopy (SEM), which was conducted on the JEOL S4800 electron microscope. The structures of gold seeds were observed by transmission electron microscopy (TEM), which was


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conducted on the JEOL JEM2010 electron microscope. Ultraviolet−visible (UV−vis) absorption spectra were recorded by Shimadzu UV-2450 spectrophotometer in transmission mode. Raman spectra were recorded by Renishaw inVia Reflex Confocal micro Raman spectrometer from Renishaw. Preparation of spherical Au seeds: The gold seeds were prepared according to the Frens method. Briefly, 100 mL of 2.5×10–4 M HAuCl4 solution was heated to 120°C in an oil bath under vigorous stirring for 30 min. Subsequently, 1% sodium citrate solution was added into the above solution with continuous boiling. After 20 min, the color of the boiled solution changed to ruby red, indicating the formation of Au NPs in the solution. Synthesis of gold coated PS microspheres: PS microspheres were prepared by means of dispersion polymerization.37-38 In brief, 6.5g of styrene monomer and 0.65 g of stabilizer PVP were added into 20 mL of ethanol containing 0.065 g of AIBN. The mixture was stirred at 70 °C for 10 h. After the reaction finished, the resultant mixture were centrifugated at 5000 rpm and washed with ethanol before drying at 30℃ under vacuum. The prepared 20 mg of purified PS microspheres were dispersed in 20 mL of ethanol. Subsequently, 0.4 mL of APTES solution (5×10-2 M) dispersed in anhydrous ethanol was added into above solution and stirred for 2 h at room temperature. Then the APTES-functionalized PS microspheres were washed respectively with ethanol and water for three times by repeated centrifugation and finally re-dispersed in 20 mL of water. The NH2-PS microsphere dispersion (1 mg/mL) was stored for at least 20 h before using. By simply mixing amino-decorated PS microspheres and sufficient citrate-stabilized gold spheres at room temperature for 1h, the Au seeds coated PS microspheres were obtained because of the electrostatic force between amino and carboxyl. At last, the compound was centrifuged, washed with water to remove excess Au seeds and then redissolved in 1 mL of water.


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Growth of gold nanowires on the PS: Gold nanowires were grown from the PS substrate coated with gold seeds by seed-mediated growth method. The specific steps were as follows: 10 µL of seed-adsorbed microspheres were dropped onto the silicon wafer (0.5 × 0.5 cm2) and then the wafer was immersed in a reaction solution containing MBA at a pre-set concentration, HAuCl4 (1.7 mM) and L-ascorbic acid (4.1 mM) for 1 h. It was then rinsed to remove the spare MBA with a mixture of ethanol/water and dried in air. Preparation and characterization of SERS samples: In order to test the property of active SERS substrate, R6G39 was used as the Raman probe molecules. Briefly, some amount of R6G solution was dipped onto the silicon wafer, after drying at room temperature, it was washed with absolute ethanol and deionized water for several times to remove the free R6G molecules. The density of the analyte crystal R6G was calculated as 1.28 g cm-3. Raman spectra were collected on a Renishaw in Via Reflex Confocal micro Raman spectrometer from Renishaw using a HeNe laser source (633 nm). Exposure time was 1 s, exposure time was 1 s and laser power was 0.15 mW through 50× aperture (NA = 0.75) for all spectra. The laser spot diameter W0 is calculated with the formula of 1.22λ/NA (λ=633 nm, NA=0.75), the area value of each site is 1.05 µm2. In experimental process, we chosen 10 random sites from near the top of the Au vesicles to keep the laser spot almost all on the vesicles. Enhancement Factor (EF) = (ISERS/IBULK) ×(NBULK/NSERS), where ISERS and NSERS are the intensity of the ratio of sample/MBA and number of the adsorbed molecules for SERS, respectively. IBULK and NBULK are the intensity of the ratio of band/MBA and number of molecules for free R6G scattering on the silicon wafer. 3. Results and Discussion


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Unlike the common approach for the fabrication of plasmonic vesicles by assembling from amphiphilic gold nanoparticles,40 in our present work, the giant gold vesicles were constructed via combined “anisotropic growth” and “sacrificing template” strategies, shown in scheme 1. There are mainly three steps in the whole process for the preparation of giant gold vesicles. Uniform-sized PS microspheres, served as templates, were firstly synthesized by dispersion polymerization. Then the surfaces were functionalized for the subsequent interaction with small sized gold nanoparticles for anisotropic growth of Au wires (Fig S1).41 The PS surface-bound gold nanoparticles were used for the selective deposition of gold atoms at the interface between gold seeds and PS surfaces for final growth of gold wires by precisely controlling the concentration of ligand MBA molecules. The curving surface of PS microspheres can guarantee the crossing packing of nanowires when the gold wires were long enough. After removing the PS template, the hollow vesicles were built due to the dense packing gold nanowires on the PS surfaces. The obtained gold vesicles provide abundant sharp tips and dense gaps from tip-to-tip mode for amplifying SERS signals. For construction of giant vesicles coated with gold wires rather than other shaped gold particles, ligand molecule, 4-Mercaptobenzoic acid (MBA) plays a crucial role in tuning the selective deposition of gold atoms onto the gold seeds. Usually, gold atoms deposited continuously on the surface of gold seeds in the conventional isotropic growing mode. While in the present system, the instant binding of MBA inhibits the growth at the perimeter of this active site and promotes alternatively the asymmetric growth, pushing the nanocrystals upward into nanowires. As shown in Fig 1A, PS microspheres were prepared by dispersed polymerization with the uniform size 2.1±0.3 µm (Fig S2A). Then the surfaces of PS spheres were modified with amino groups using 3-aminopropyltriethoxysilane (APTES) facilitating the adsorption of gold


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seeds to form PS-Au composite (Fig 1B). After anistropic growth, the PS surface was packed with a dense layer of random AuNWs (gold nanowires) overlapping with each other (Fig 1C). It is clear to see that the length and width of wires were 1.0±0.3 µm (Fig S2B) and 16.7±2.3 nm (Fig S2C/1F), respectively. The process was simple and reproducible despite the complex hierarchical structure. It was worth noting that most of AuNWs can support itself as a cavity on account of the close packing after dissolving the PS with THF as shown in Fig 1D. Fortunately, the inset image of Fig 1D and Fig 1E show the broken morphology of the inside of AuNWs vesicle, indicating the hollow structure.

Scheme 1. Schematic illustration of synthesis of three different Au structures by substrate anchored seed-mediated growth (nanowires/island/inhibited AuNPs) and SERS application of Au vesicles.


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Fig 1. SEM images of (A) PS, (B)PS-Au composites, and the inset of High resolution SEM images of (B), (C) AuNWs growing on the surface of PS, and the inset of High resolution SEM images of (C), (D) remove of the template PS and the inset of broken AuNWs vesicle, (E) TEM of AuNWs vesicles, (F) high magnification TEM of AuNWs vesicles. To optimize the gold structure packing on the surface of PS template, we systematically investigate the concentration of binding ligand MBA. Since the exposed surfaces of Au seeds were occupied by adsorbed MBA when it was added to a proper degree, Au atoms which were reduced by the L-AA can only be deposited at the Au-PS interface during the growth of Au wires; so the application of MBA can easily regulate the morphology of formed Au nanostructure. Briefly, when the concentration of MBA was at a relative low level of around 50 µM, we attained bulk gold or known as island structure (Fig 2A). It is mainly resulted from the less dense coverage of MBA on the PS surface to induce the isotropic growth. That is to say, there will be an increasing preference for lateral over vertical growth. As the MBA concentration was increased to 150 µM, a mass of Au nanowires packed randomly on the surface of PS


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substrate (Fig 2C). Different from the vertically-aligned Au nanowire bundles13 and forest of gold nanowires,42 the gold wires cannot arrange perpendicular to the diameter of PS spheres. The reason is probably that larger curvature prevents the formation of Au nanowires array standing up-right on the PS surface compared to the horizontal silicon wafer. By further increasing the concentration up to 500 µM even 1000 µM, the morphology of Au nanowires nearly disappeared. At such high concentration, MBA packed strongly and the growth of the Au seeds was inhibited (Fig 2 E/F). So only by controlling the MBA at a suitable concentration, can it lead to achieving nanowires vesicles. It is clearly considered that these vesicles consisting of sharp tips and abundant nanogaps among stacked nanowires, form many “hot spots” areas around the surface. The unique feature would lead to the efficient SERS enhancement. In addition, a high density of Au seeds adsorbing on the PS surface is rather important for the fabrication of such vesicle super-structures. Except for sufficient adding of Au solution, we also controlled the volume ratio of Au / PS solution at 1/3, 1/2 and 1/1 in a certain amount of total volume. As Fig S3 shows, compared with the one used before, another three less packing density of Au seeds on PS spheres were synthesized. Using the three different Au-PS mentioned above, we tried to systematically study the influence of Au seeds density packing on the PS surface. When the density of Au seeds was rather low, gold nanowires are difficult to come no matter how we adjust the MBA ligand concentration. SEM images in Fig S4A-E shows there were only nanoparticles of different size on the surface; As the Au seeds density increased, it shows that similar results (Fig S4F-J) come out as the lower packing; when controlling the volume ratio of Au seeds and PS spheres at a high level, but still lower than the one used before, relative lower MBA concentration will induce the come out of sparse gold nanowires on the PS spheres (Fig S4K), which is much less than the


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high packing density in the condition of high seed density. Undoubtedly, the abundant Au solution is necessary for the structure in SERS application.

Fig 2. SEM images of Au nanostructures by using substrate anchored seed mediated growth at different concentrations of MBA ((A) 50 µM, (B) 100 µM, (C) 150 µM, (D) 200 µM, (E) 500µM, (F) 1000µM). The inset images are magnification SEM of corresponding to A-F. The SERS activity of the Au vesicles assembled substrate was studied and R6G dye was selected as the SERS probe molecule. According to the electromagnetic theory, when the frequency of incident light is synchronized with the electron on nanoparticles surface, the field enhancement can come to the greatest. For maximal SERS amplification, the excitation wavelength is usually chosen to match the position of the surface plasmon resonance band for the structure we achieved.43 That is to say, SERS intensity is strongly dependent on the wavelength of laser. To achieve the highest enhancement, an appropriate exciting light wavelength was determined to match three different kinds of substrates nanowires, island and inhibited NPs substrate in Figure 3C, respectively, using three different wavelengths of 532 nm, 633 nm and 785 nm. As shown in Fig S6, when the exciting light was set at 633 nm, the Raman Intensity was higher than the two other wavelengths of 532 nm and 785 nm at the same condition,


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which is closed to the maximum UV absorption peak of about 650 nm (Fig S5). That is to say the enhancement of emission light is similar to that of incident light, and the electromagnetic enhancement factor scales about as the fourth power of the local electric field magnitude (|E|4 / |E0|4).1,44 (Ten µL of 100 µM R6G solution was added onto the SERS substrate and then it was washed with water for several times before obtaining the signals using a 633nm HeNe laser source with 1 accumulation, 1s exposure time and 0.15mW laser power. Fig 3A shows the Raman patterns of R6G deposited onto Au structures. From the spectra, we can see that SERS Raman Intensities from the AuNWs sample (Fig 3A/C-a) shows the greatest enhancement compared to the two other structures of Au island (Fig 3A/C-b), inhibited nanoparticles (Fig 3A/C-c) and control sample (Fig 3A-d). In the histogram of Fig 3B, the different enhancement on R6G between the three kinds of Au structures (Fig 3C) can be clearly present. Several distinctive Raman signals at 612 cm-1, 774 cm-1, 1181 cm-1, 1310 cm-1, 1361 cm-1, 1509 cm-1, 1572 cm-1 and 1650 cm-1 are found in the Raman spectra. They are corresponding to the C-C-C in-plane bending, C-H out-of-plane bending, C-H in-plane bending, C-O-C stretching and C-C stretching modes for aromatic rings exhibited peaks.45-47 And the residual MBA was also found in the Raman spectrum of as-prepared Au vesicle/Au island/inhibited AuNPs at 1090 cm-1 and 1590 cm-1 (Fig S7). To further evaluate the SERS property, the enhancement factor (EF) was calculated according to previous work48 using 4-MBA as an internal standard. The averaged EF was calculated by comparing R6G signals from bare silicon. Averaged EFs of approximately 9.90×107 was obtained for the AuNWs samples, 3.25×106 for the Au island and 1.53×104 for the inhibited Au nanoparticles, respectively. This can be ascribed into the nanowire vesicles as the “tip-to-tip” structure because of the sharp tips from the nanowire and abundant gaps from the assembly. The sequence in SERS intensity is in accordance with the result that among the “tip-


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to-tip”, “tip-to-sphere” and “sphere-to-sphere” modes, the “tip-to-tip” mode shows the largest electric field enhancement. Undoubtedly, the AuNWs assembly can provide large-volume hot spots among the net structure because of sharp tips to fabricate the tip-to-tip structure and abundant gaps, thus enhancing the electromagnetic intensity. By comparison, the designed structure can be enhanced by two orders of magnitude than the previous reports.

Fig 3. (A) SERS spectra a-c of R6G obtained from Au nanostructures ((C) SEM images of a−c) respectively, d obtained from bare silicon coating R6G; (B) histogram of different Au nanostructures. The scale bars is 100 nm in the SEM. The spectra were obtained with λex= 633 nm excitation. Except for the sensitivity, the reproducibility of SERS measurement is also important for the practical application of SERS active Au assembled structures. In order to demonstrate the SERS reproducibility performance, AuNWs was chosen for detecting different concentration of R6G (Fig 4A). The SERS peak at 1509 cm-1 was used as a quantitative evaluation of SERS sensitivity with a limitation of 10 nM, and the linear detection range of R6G was from 10-4 to 10-7 (Fig 4C) which is hardly can be achieved. In addition, we also test the uniformity of SERS from the


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Raman band at 1509 cm-1 by selecting 10 random sites, and showed the data in the histogram (Fig 4D). The results indicate that the variation of SERS intensity is less than 7.6%, which is lower than those in previous work.49-50 Finally, the hollow structure achieving through eliminating the PS sphere can restain electromagnetic to a small interspace, which will largely enhance the Raman intensity (Fig S8). Because SERS enhancement not only depends on the structure of Au nanoparticles such as sharp tips, but also on the density of “hot spots” between adjacent Au nanostructure, the high density of “hot spots” arising from adjacent Au wires packed randomly plays an significant role in SERS signal enhancement. Additionally, the AuNWs interlacing to mixture fabric can easily capture SERS molecules compared to the bare silicon at the same area of laser spot, which would highly improve the amount of SERS molecules in the same test condition, and then improve SERS enhancement.

Fig 4. (A) SERS spectra of R6G with different concentrations on AuNWs, the concentration of R6G in a-g were 1 nM, 10 nM, 100 nM, 1 µM, 10 µM, and 100 µM, 1 mM respectively. The spectra were obtained with λex= 633 nm excitation. (B) The IR6G/IMBA ratio of peak intensity from 1509 cm-1 (R6G) and 1090 cm-1 (4-MBA) were defined as IR6G and IMBA, and the curve was established by plotting the IR6G/IMBA ratio against the logarithm of R6G concentration. (C) The calibration plot related to the logarithm of R6G from 10−7 to 10−4 M. (D) The corresponding bar chart for the peak intensity at 1509 cm−1 from 10 random sites on Au nanowire SERS.


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4. Conclusions In summary, we have demonstrated a simple strategy to construct Au vesicles with the surface coated with high density of tiny Au wires by combining “anisotropic growth” and “sacrificing template” strategies. The morphology and assembled array of Au vesicle can significantly amplify SERS signals mainly because of the sharp tips and abundant tip-tip gaps. The tiny Au wires packed Au vesicle with the inner hollow structure can also enrich more probe molecules compared with other plasmonic structures, resulting in the lower detection limit and a good linear relationship of probe molecules. The high sensitivity, wide quantitative detection range, and good reproducibility make Au vesicles with surfaces coated tiny Au wires promising in practical SERS applications and other fields such as flexible electronic devices, 51 solar cells52 and photothermal therapy 53 in medicine. Acknowledgments We gratefully acknowledge the Natural Science Foundation of China (Grant Nos. 51473179, 21404110, 41576098, 81773483), Excellent Youth Foundation of Zhejiang Province of China (Grant No. LR14B040001), Science and Technology Department of Zhejiang Province of China (2016C33176), Ningbo Science and Technology Bureau (Grant Nos. 2014B82010, 2015A610036, and 2015C110031), Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2016268 and 2017337), and the Bureau of Frontier Science and Education of Chinese Academy of Sciences (QYZDB-SSW-SLH036). Supporting Information Available: TEM images of Au seeds, SERS spectra of R6G (100 µM) obtained from different laser wavelengths and SERS spectra of R6G (100 µM) obtained from Au


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Giant Vesicles with Anchored Tiny Gold Nanowires ... - ACS Publications

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