Periodic Porous Alloyed Au-Ag Nanosphere Arrays and Their Highly

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Periodic Porous Alloyed Au-Ag Nanosphere Arrays and Their Highly Sensitive SERS Performance with Good Reproducibility and High Density of Hotspots Tao Zhang, Yiqiang Sun, Lifeng Hang, Huilin Li, Guangqiang Liu, Xiaomin Zhang, Xianjun Lyu, Weiping Cai, and Yue Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17461 • Publication Date (Web): 26 Feb 2018 Downloaded from http://pubs.acs.org on February 26, 2018

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ACS Applied Materials & Interfaces

Periodic Porous Alloyed Au-Ag Nanosphere Arrays and Their Highly Sensitive SERS Performance with Good Reproducibility and High Density of Hotspots Tao Zhang,ab Yiqiang Sun,ab Lifeng Hang,a Huilin Li,ab Guangqiang Liu,a Xiaomin Zhang,c Xianjun Lyu,d Weiping Cai,a and Yue Li*a a Key Lab of Materials Physics, Anhui Key Lab of Nanomaterials and Nanotechnology, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, 230031, P. R. China b University of Science and Technology of China, Hefei, 230026, P. R. China c College of Materials and Mineral Resources, Xi’an University of Architecture and Technology, Xi’ an, 710055, P.R. China d College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao, 266590, P.R. China KEYWORDS: porous, Au-Ag alloy, array, SERS, reproducibility ABSTRACT: Periodic porous alloyed Au-Ag nanosphere (NS) arrays with different periodic lengths and tunable composition ratios were prepared on Si substrates on a large scale (~ cm2) using stepwise metal deposition-annealing and subsequent chemical corrosion from a monolayer of colloidal polystyrene (PS) microspheres as the initial template. The porous alloyed Au-Ag

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NSs possessed a high porosity and bicontinuous morphology composed of hierarchically interconnected ligaments, which were obtained from an optimized dealloying process in nitric acid. Interestingly, when the dealloying time was prolonged, the average size of the porous alloyed NSs slightly decreased, and the width of the ligaments gradually increased. The periodic length of the array could be facilely changed by controlling the initial particle size of the PS template. Moreover, the porous alloyed Au-Ag NS arrays were explored as a platform for the surface-enhanced Raman scattering (SERS) detection of 4-aminothiophenol (4-ATP) and exhibited excellent reproducibility and high sensitivity due to the periodic structure of the arrays and the abundance of inherent “hotspots”. After optimization experiments, a low concentration of 10-10 M 4-ATP could be detected on these porous Au-Ag NS array substrates. Such highly reproducible SERS activity is meaningful for improving the practical application of portable Raman detection equipment. 1. INTRODUCTION Plasmonic noble metal nanoparticles (NPs) have received considerable attention because of their intense size- and shape-dependent localized surface plasmon resonance (LSPR) properties.13

These intriguing properties offer the promise of enabling important applications in many fields,

including surface-enhanced Raman scattering (SERS), biomedicine, and catalysis.4-12 Among these properties, SERS, a highly effective strategy, can detect target molecules at very low concentrations. Thus, many plasmonic noble metal NPs with “hotspots,” including Au nanostars, porous Au NPs, Au nanorods, Ag nanoflowers, Ag nanoplates, and Au@Ag nanorods, have been successfully synthesized to construct SERS-active substrates.13-23 Moreover, recent studies have proven that Au nanosponges with tuned structures have excellent optical properties and enhanced electronic fields.24, 25 Additionally, the combination of Au and Ag can tune the LSPR properties,


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which might improve their SERS or catalytic performance.26-30 The large surface-to-volume ratio and high density of interior “hotspots” generated by the nanopores of porous Au-Ag NPs may further enhance their SERS sensitivity and activity in catalytic reactions.31-34 Therefore, various methods, including dealloying, galvanic replacement, and dual-templating, have been performed to fabricate porous Au-Ag nanomaterials,35-39 such as porous films, nanosponges, ribbons, disks, membranes, and nanowires.40-43 For instance, monodisperse porous Au-Ag nanospheres (NSs) or porous alloyed Au-Ag nanocubes (NCs), which possess a high density of “hotspots,” were successfully synthesized by a dealloying process.31,44 Through the cyclic electroless deposition method, mesoscopically bicontinuous Ag-Au hybrid nanosponges were prepared for application in SERS detection32. These novel nanostructures show excellent SERS activities, but the reproducibility of their SERS performances on a large scale is still difficult to realize, which has substantially limited their further practical applications. In this research, we report an effective and reproducible method for preparing highly ordered porous alloyed Au-Ag NS arrays with a high density of accessible SERS “hotspots” and good SERS reproducibility. First, Au NS arrays with hexagonal non-close-packed (hncp) arrangements were synthesized by using a monolayer of colloidal polystyrene (PS) NSs as an initial template through an Au deposition-annealing process.45 Second, solid alloyed Au-Ag NS arrays were fabricated on silicon (Si) substrates by a subsequent Ag deposition-annealing process. After chemical etching of these arrays with nitric acid (HNO3), porous alloyed Au-Ag NS arrays with an hncp arrangement were finally synthesized via etching the Ag from the solid alloyed Au-Ag NSs. By changing the periodicity of the monolayer template, the periodic length of the porous alloyed Au-Ag NS array could be easily tailored. Moreover, the pore size and composition of the porous alloyed Au-Ag NSs could be tuned by changing the dealloying time.


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These porous alloyed Au-Ag NS arrays exhibited outstanding SERS activities, which could be attributed to their large amounts of SERS “hotspots”. The enhancement factor (EF) of the porous alloyed Au-Ag NS array prepared with a chemical dealloying time of 60 min in the detection of 4-minothiophenol (4-ATP) was estimated to be 2.25 × 108. Additionally, a concentration of 10-10 M 4-ATP could be detected on these porous Au-Ag NS array substrates. The observation of a highly uniform Raman intensity on a large scale (100 µm × 100 µm) proved that the obtained SERS performance was highly reproducible. Such SERS-active substrates with good reliability and reproducibility can contribute to the development of practical applications of Raman detection equipment in the detection of certain molecules. EXPERIMENTAL SECTION 2.1. Materials. Monodisperse PS microspheres (diameter: 350, 500, or 750 nm) in aqueous suspensions (2.5 wt%) were purchased from Alfa Aesar. The noble metal targets (Au and Ag, ≥99.9%), single crystalline Si wafers and glass slides were obtained from ZhongNuo Advanced Material (Beijing) Technology Corporation. Ethanol (≥99.7%), acetone (≥99.5%), hydrogen peroxide (35%), ammonium hydroxide (25-28%), concentrated sulfuric acid, and concentrated HNO3 (65-68%) were obtained from Sinopharm Chemical Reagent Corporation. 4-ATP (97%) was purchased from Sigma-Aldrich. Deionized (DI) water was prepared with a Milli-Q water purification system. All chemicals were of analytical grade and used without any purification. 2.2 Preparation of periodic solid alloyed Au-Ag NS arrays. In a representative synthetic method of the periodic solid alloyed Au-Ag NS arrays, a large-area (~ cm2) monolayer of PS microspheres was first constructed on a clean Si substrate via an air/water interfacial selfassembly process.46-49 Then, the PS monolayer on the Si wafer was coated with a layer of Au at a certain thickness using sputtering deposition. An Au NS array was then formed by annealing the


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Au-coated PS monolayer at 1000 °C for 2 h in air. An Ag film was then deposited on the asprepared periodic Au NS array, and the resulting material was annealed at 600 °C under a 10% H2/N2 flow for 2 h to effectively alloy the Ag and Au. The solid alloyed Au-Ag NS array was finally obtained after cooling to room temperature. This process is described in Scheme 1a-e in detail. To obtain periodic solid alloyed Au-Ag NS arrays with different periodic lengths, the diameter of the PS microspheres in the colloidal monolayer and the thicknesses of the Au and Ag films in the preparation process were effectively adjusted. 2.3 Synthesis of periodic porous alloyed Au-Ag NS arrays. The solid alloyed Au-Ag NS arrays were put into 5 M HNO3 to initiate the percolation dealloying process. After dealloying for 30-90 min at room temperature, the dealloyed Au-Ag NS arrays were transferred to DI water to remove the residual HNO3 and Ag ions. Large-scale porous alloyed Au-Ag NS arrays were finally prepared by the abovementioned method. The synthetic process is illustrated in Scheme 1e-f. Periodic porous alloyed Au-Ag NS arrays with various periodic lengths were prepared by using PS microspheres with different diameters. Additionally, the size of the pores, the width of the Au-Ag ligaments, and the elemental composition of Au and Ag could be facilely adjusted by controlling the dealloying time. 2.4 Investigation of the SERS performance. Solutions of 4-ATP with different concentrations (10-6 M, 10-7 M, 10-8 M, 10-9 M, and 10-10 M) were prepared in ethanol. For 4-ATP absorption, the various SERS substrates, including Au NS arrays, solid alloyed Au-Ag NS arrays, and porous alloyed Au-Ag NS arrays on Si wafers, were dipped in the solutions of 4-ATP for 30 min. For SERS EF analysis, a thin, uniform layer of 4-ATP was formed on a 0.5 cm × 0.5 cm Si wafer by dropping 5 µL of the 4-ATP ethanol solution with a concentration of 10-2 M onto the surface. Then, 5 µL of the 10-6 M 4-ATP ethanol solution was dropped onto an equally sized porous


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alloyed Au-Ag NS array, and the ethanol was evaporated. Specifically, we used an excitation laser (wavelength: 785 nm) to collect the SERS data. The integration time was adjusted to 15 s, and the power of the excitation laser was 1 mW. A Raman map of 4-ATP on the porous alloyed Au-Ag NS arrays (dealloying time: 60 min) was obtained with a step size of 5 µm (integral time: 1 s; laser power: 1 mW). 2.5 Instruments. The products were characterized by field emission scanning electron microscopy (FESEM, Sirion 200), transmission electron microscopy (TEM, JEOL, JEM-1400), high-resolution TEM (HRTEM, FEI, Tecnai G2 F20), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDS) and EDS elemental mapping. The products for TEM characterization were obtained by scraping the NSs off of the Si wafer with a scalpel and transferring them onto a commercial copper grid. A sputtering device (Quorum, k550x) was used to deposit a metal film. The investigation of the SERS performance was conducted using a Renishaw inVia Reflex spectrometer. The probe can be regarded a cylinder with a diameter of approximately 1 µm and a detection depth of approximately 20 µm.


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Scheme 1. Diagram depicting the synthesis of porous alloyed Au-Ag NS array. (a) Monolayer of colloidal PS crystals self-assembled on a Si wafer in an hcp arrangement. (b) Deposited thin film of Au on the monolayer of colloidal PS crystals. (c) Au NS array in an hncp arrangement obtained after annealing at 1000 °C for 2 h. (d) Deposited thin film of Ag on the Au NS array. (e) Solid alloyed Au-Ag NS array fabricated via thermal annealing of the substrate in (d) at 600 °C for 2 h. (f) Porous alloyed Au-Ag NS arrays constructed by the dealloying process. 2. RESULTS AND DISCUSSION FESEM analysis revealed that the as-synthesized periodic porous NS array (periodic length: 350 nm) dealloyed for 60 min had an hncp arrangement on a large scale (Figure 1a and 1b). The inset of Figure 1a shows a digital photograph of the as-obtained periodic porous NS array on a large area (2 cm × 2 cm) and the specular color that originated from its well-arranged periodic nanostructures. The average size of these NSs was 204±8 nm (Figure S1a). Interconnected nanopores existed in each NS, and the pore size was 7±3 nm (Figure S1b). TEM images further confirmed that the obtained NSs were porous, as clearly shown in Figure 1c and 1d. Interestingly, a single porous Au-Ag NS was observed to be highly crystalline, as illustrated by HRTEM analysis (Figure 1e). The corresponding fast Fourier transform (FFT) pattern further confirmed


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that this porous Au-Ag NS had good crystallinity (Figure 1f). EDS elemental mapping analysis (Figure 1g-1i) performed by HAADF-STEM demonstrated that Au (green) and Ag (red) were homogeneously distributed in this as-prepared porous NS, verifying that the NS consisted of an Au-Ag alloy with Au as the major component. Based on the above results, Au-enriched periodic porous alloyed Au-Ag NS arrays were successfully prepared.

Figure 1. (a) Low- and (d) high-magnification FESEM images of the as-obtained sample after dealloying for 60 min; the inset of (a) shows a digital photograph of the as-prepared sample; the inset of (b) shows one typical unit. (c) Low-magnification TEM image of the Au-Ag NSs. (d) TEM image of a single unit with higher magnification. (e) Local HRTEM image of the area in


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the red frame in (d). (f) Corresponding FFT pattern of the area in (e). (g) HAADF-STEM image of a single unit. (h-i) EDS elemental maps of (e) Au and (f) Ag. The UV−Vis-NIR spectrum of the porous alloyed Au-Ag NS array is displayed in Figure 2. Interestingly, the porous alloyed Au-Ag NS array exhibited three strong peaks that are located at 434, 529 and 772 nm. The first peak (ca. 434 nm), known as the diffraction peak, was derived from the periodic structure of the NS arrays, which can result in the specular color observed in the inset of Figure 1a.50 Such a diffraction peak may be used to develop a dual-channel biosensor based on the effects of the diffraction and LSPR peaks.51 The main absorption band appeared at a wavelength of ∼772 nm. Generally, this band can be ascribed to the dipolar LSPR resonance derived from the porous alloyed Au-Ag NSs. Furthermore, this band shows a significant redshift compared with the corresponding band observed for the solid NSs due to the presence of abundant nanopores.24,52 In addition, the weak LSPR band observed at a wavelength of ∼529 nm can be ascribed to the survival of some solid alloyed Au-Ag NSs in the chemical dealloying process (Figure S2).31 The solid alloyed Au-Ag NSs may possess some regions with high Au/Ag ratios that are less susceptible to dealloying, which is in accordance with the results of reported works.53, 54


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Figure 2. UV-Vis-NIR spectrum of the porous alloyed Au-Ag NS array prepared with a dealloying time of 60 min. One diffraction peak located at 434 nm and two LSPR absorption peaks located at 529 and 772 nm were observed. The periodic porous alloyed Au-Ag NS arrays could be used as SERS-active substrates. To investigate the enhancement of the Raman signal by the SERS-active substrates, we used 4-ATP as a target molecule. During SERS detection, an excitation laser with a wavelength of 785 nm was used, which matched the absorption band of the porous alloyed Au-Ag NS arrays. The black curve in Figure 3a shows the Raman spectrum of 4-ATP with a concentration of 10-6 M on the porous alloyed Au-Ag NS array. The intensity of the Raman signal at 1080 cm-1 was substantially enhanced on this array, measuring ~104 and ~7 times higher than the corresponding signals on the pure Au NS array and the solid alloyed Au-Ag NS array, respectively. This enhancement can be attributed to the effective adsorption of 4-ATP onto the large number of SERS “hotspots” generated by the nanopores with sizes below 10 nm.52, 55 Figure 3b shows the Raman intensity map of 4-ATP at 1080 cm-1 on the porous alloyed Au-Ag NS array shown in Figure 1. The Raman map was obtained on a 100 µm ×100 µm square, and the step length was


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set to 5 µm. The diameter of the laser spot (d) was approximately 1 µm; thus, every spot covered approximately 7 NPs, which sufficiently confirmed the SERS reproducibility of the array. Figure 3c shows that the Raman intensity distribution had a low standard deviation of 7.7% (more than 400 points) on the porous alloyed Au-Ag NS array. The high uniformity of the Raman intensity on a large scale proved that the obtained SERS performance exhibited excellent reliability and reproducibility. Notably, the SERS substrates fabricated by us from a monolayer of colloidal PS crystals as the initial template were easily scalable and reproducible. Figure 3d depicts the intensities of the Raman spectra on the porous alloyed Au-Ag NS array with 4-ATP concentrations from 10-6 M to 10-10 M. A very small quantity of 4-ATP down to approximately 10-10 M could be detected, meaning that the prepared SERS substrate showed excellent sensitivity to the target molecule, even at very low concentrations. The EF of the porous alloyed Au-Ag NS array prepared with a dealloying time of 60 min was calculated using the following reported equation:48 EF = ( I SERS / N ads ) / ( I normal / N normal )

All the SERS performance experiments were conducted under the same conditions. To calculate the EF, the intensities of the SERS and normal Raman peaks at 1080 cm−1 with 4-ATP concentrations of 10−7 and 10−2 M, respectively, were measured, as shown in Figure S3. The EF was estimated to be 4.37 × 107.


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Figure 3. (a) Raman signals of 4-ATP with a concentration of 10-6 M on the porous alloyed AuAg NS array, Au NS array, and solid alloyed Au-Ag NS array. (b) Raman map of 4-ATP on the porous alloyed Au-Ag NS array with a step size of 5 µm (integral time: 1 s; laser power: 1 mW). (c) Raman intensity distribution on the porous alloyed Au-Ag NS array, exhibiting a standard deviation of 7.7%. (d) Raman spectra of 4-ATP concentrations from 10-6 M to 10-10 M on the porous alloyed Au-Ag NS array. The periodic porous alloyed Au-Ag NS arrays were synthesized via a multistep procedure. A monolayer of PS microspheres on Si wafers in a hexagonal close-packed (hcp) arrangement (Figure 4a and S4a) served as the initial template. As indicated in Figure 4b, the monolayer of colloidal PS crystals was coated with a moderately thick Au film by sputtering deposition. The thickness of the Au film was 27 nm (Figure S5a). Au NS array in an hncp arrangement (Figure 4c and S4b) was formed after the prepared Au-coated PS monolayer array was annealed at 1000 °C for 2 h in air. During the thermal treatment, the PS sphere template was removed through


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decomposition. Meanwhile, due to the minimization of the surface free energy, the Au film on the PS sphere completely melted and formed a NS in situ, which produced a periodic Au NS array on the Si substrate. The Au NSs were uniform and had an average size of 140 nm. A moderately thick Ag film was then deposited on the periodic hncp Au NS array, as shown in Figure 4d. The thickness of the Ag film was 70 nm (Figure S5b). The Ag film coated both the Au NSs and any exposed Si substrate and made the surface of the obtained array slightly rough. Furthermore, the particle size increased with the deposition of the Ag film. The Ag-coated Au NS array was further annealed, and the Au NSs and Ag coating formed alloyed Au-Ag spheres. Meanwhile, the Ag film on the exposed substrate migrated to the large Au NSs or alloyed Au-Ag NSs according to the Ostwald ripening mechanism. Therefore, a solid alloyed Au-Ag NS array was obtained on the Si wafer in situ (Figure 4e), and the average size of the solid alloyed Au-Ag NSs was 240 nm. The newly formed alloyed Au-Ag NS array maintained the hncp arrangement. This alloyed Au-Ag NS array was dealloyed by exposure to HNO3, which partially dissolved the Ag species from the alloyed Au-Ag NSs. An Au-rich periodic porous alloyed Au-Ag NS array was thus formed, as indicated in Figure 4f.


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Figure 4. FESEM images of (a) the monolayer of colloidal PS crystals with a periodic length of 350 nm, (b) the monolayer of colloidal PS crystals with a 27-nm-thick Au coating, (c) the periodic Au NS array obtained by annealing the sample in (b), (d) the periodic Au NS array after the deposition of a 70-nm-thick Ag film, (e) the solid alloyed Au-Ag NS array obtained after annealing the sample in (d), and (f) the porous alloyed Au-Ag NS array obtained after dealloying. The influence of the dealloying time on the formation of the porous alloyed Au-Ag NS array was also investigated. Chemical dealloying is a kinetically controlled process, which makes tuning the structure of the porous alloyed Au-Ag NS array possible. In this work, the dealloying process was performed by a chemical etchant, HNO3, and the porosity and composition of the porous alloyed Au-Ag NSs could be facilely controlled by adjusting the dealloying time. Although Ag leached from the Au-Ag alloyed NSs in a continuous process, the partially dealloyed NSs could be effectively quenched by separating the particles from the HNO3 solution and immediately immersing them in water. Figure 5 displays typical FESEM and TEM images of the as-prepared porous alloyed Au-Ag NSs (and magnified TEM image of one NS) obtained from dealloying times of 30, 60, and 90 min, which confirmed the formation of a periodic hncp arrangement and a high porosity for all the samples. The average size of the porous alloyed AuAg NSs gradually decreased from 236±9 nm to 204±8 and 192±10 nm as the reaction time increased (Figure 6a, Figures S1a and S6). The average ligament width of the porous alloyed AuAg NSs correspondingly increased from 7 ± 4 nm to 12 ± 3 and 16 ± 2 nm (Figure S7). Meanwhile, the average pore size increased from 4±2 to 7±3 and 11±2 nm, as displayed in Figure 6b and Figure S8. EDS elemental mapping indicated that the obtained NSs were also alloyed structures (Figure S9). Moreover, EDS measurements were conducted to explore the elemental compositions of Au and Ag. The results showed that the percentage of Au rose from


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65.1% to 90.8% and 95.8% as the dealloying time increased, while the amount of Ag decreased from 34.9% to 9.2% and 4.2% (Figure 6c and S10). On account of the sensitivity of LSPR to the structure of the NPs, including the nanopores and the ligaments, the LSPR peak of the porous alloyed Au-Ag NS array varied with the dealloying time. As illustrated in Figure 6d, the main LSPR peak shifted from 718 to 772 and 845 nm with the increase in the dealloying time from 30 to 60 and 90 min, respectively. However, the diffraction peak remained nearly unchanged since the periodic structure of the NS array was maintained during the dealloying process. The easy tunability of the LSPR properties of the porous alloyed Au-Ag NS arrays makes it possible to achieve optimal activity in many plasmonic applications. Additionally, the SERS activities of the porous alloyed Au-Ag NS arrays obtained from different dealloying durations were also systematically investigated (Figure 7). The Raman intensity maps of 4-ATP at 1080 cm-1 on the porous alloyed Au-Ag NS arrays showed a stronger intensity for a dealloying time of 60 min than for times of 30 and 90 min. In addition to the formation of active SERS “hotspots” and the effective adsorption of 4-ATP onto the porous alloyed Au-Ag NSs,28,

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note that the SERS

performance was examined under irradiation a 785 nm laser, which was a nearly resonant condition for the porous alloyed Au-Ag NSs prepared with a dealloying time of 60 min.


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Figure 5. FESEM and TEM images of the porous alloyed Au-Ag NSs and a single NS obtained with dealloying times of (a-c) 30, (d-f) 60, and (g-i) 90 min. The average size of the initial Au NSs was 140 nm; a 70-nm-thick Ag film was then coated on the Au NS arrays, which was followed by thermal treatment at 600 °C for 2 h.


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Figure 6. Histograms of the average particle size (a), average width of the Au-Ag ligaments and average size of the nanopores (b) as a function of the dealloying time. (c) Elemental compositions of Au and Ag in the porous alloyed Au-Ag NSs prepared with different dealloying times, as measured by EDS. (d) Corresponding UV-Vis-NIR spectra of the porous alloyed AuAg NS arrays.

Figure 7. Raman scattering spectra of 4-ATP (10-6 M) on the porous alloyed Au-Ag NS arrays obtained after dealloying for 30 (black curve), 60 (red curve), and 90 min (green curve).


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The thickness of the deposited Ag film could also influence the formation of the periodic porous alloyed Au-Ag NS arrays. The Au NS array (average size: 140 nm) was coated with an Ag film of varying thicknesses (42, 56, and 70 nm) and annealed to produce solid alloyed Au-Ag NS arrays with average particle sizes of 180, 200, and 240 nm, respectively (Figure S11a-c). However, when the thickness of the Ag film was increased to 84 nm, the solid alloyed Au-Ag NPs had random shapes and a disordered arrangement (Figure S11d). When a 42-nm-thick Ag layer was deposited, the resultant periodic porous alloyed Au-Ag NSs (150 nm) had concave surfaces, as shown in Figure 8a. In fact, the chemical dealloying process of the Au-Ag alloyed NPs can be interpreted in the context of the parting limit and critical potential for subsequent percolation dealloying.52 The formation of concave surfaces can be attributed to the lower Ag content, which was under the parting limit for dealloying. The use of a 56- or 70-nm-thick Ag film increased the average particle size of the porous alloyed Au-Ag NSs to 108 or 204 nm, respectively, and was accompanied by the formation of more micropores in each NS, as shown in Figure 8b and 8c. When the thickness of the Ag coating was increasing to 84 nm, the periodic structure of the porous NS array disappeared completely, as shown in Figure 8d. This change occurred because the initial Au NS array was not in a perfect hncp arrangement. A few of the more closely spaced Ag-coated Au NSs melted and formed a random morphology when dealloying occurred, resulting in disordered porous alloyed Au-Ag NPs. Thus, the thickness of the Ag film plays an essential role in the fabrication of periodic porous alloyed Au-Ag NS arrays.


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Figure 8. FESEM images of the samples synthesized through sputtering Ag layers with thicknesses of (a) 42, (b) 56, (c) 70, and (d) 84 nm on the ordered Au NS arrays and subsequent thermal treatment at 600 °C for 2 h and dealloying for 60 min. The periodic length of the porous alloyed Au-Ag NS arrays could be adjusted by using monolayers of colloidal PS crystals with different diameters as the original template and by changing the thicknesses of the Au and Ag layers. First, Au NS arrays with periodic lengths of 350, 500, and 750 nm were prepared from Au films with thicknesses of 27, 21, and 16 nm, respectively (Figure 9a-9c). The average sizes of the Au NSs with periodicities of 350, 500, and 750 nm were 140, 150, and 180 nm, respectively. Then, by regulating the sputtering time of Ag, the thickness of the Ag film on the Au NS array was changed from 70 to 50 and 40 nm to match the samples with longer periodic lengths. For example, when the periodic length of the Au NS array was 350 nm, the thickness of the Ag was adjusted to 70 nm. However, for periodic lengths of 500 and 750 nm, 50- and 40-nm-thick Ag layers, respectively, were sputtered. Through thermal treatment of the Ag-coated Au NS arrays with periodic lengths of 350, 500, and 750 nm


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at 600 °C for 2 h, solid alloyed Au-Ag NS arrays with average sizes of 240, 250, and 500 nm, respectively, were fabricated successfully, as illustrated in Figure 9d-9f. This relationship occurred because as the periodic length of the Au NS array increased, the quantity of Au NSs in the same area of the Si wafer gradually decreased. To maintain the initial periodic length, the thickness of the Ag film was reduced accordingly. Ultimately, high-quality porous alloyed AuAg NS arrays with different periodic lengths were fabricated after immersing the as-prepared solid alloyed Au-Ag NS arrays in 5 M HNO3 for 60 min, as illustrated in Figure 9g-9i. Lowmagnification FESEM images of the porous alloyed Au-Ag NS arrays are displayed in Figure S12 and reveal that porous alloyed Au-Ag NS arrays with periodic lengths can be fabricated on a large scale. In addition to binary porous Au-Ag NS arrays, the strategy reported here could be extended to other binary or ternary porous alloyed NSs arrays, such as the porous alloyed Au-Cu and Au-Ag-Cu NS arrays shown in Figures S13 and S14. In addition, the SERS performance of the porous alloyed Au-Ag NS arrays with periodic lengths of 350, 500, and 750 nm was further investigated with 10-6 M 4-ATP, as depicted in Figure 10. Analysis of their performances showed that the Raman intensity gradually decreased as the periodic length increased. This decrease is mainly because the larger periodic length caused fewer porous alloyed Au-Ag NSs to be covered by the laser beam, leading to a low Raman intensity.


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Figure 9. FESEM images of Au NS arrays with different periodic lengths: (a) 350, (b) 500 and (c) 750 nm. (d), (e) and (f) show the corresponding solid alloyed Au-Ag NS arrays. (g), (h) and (i) show the corresponding porous alloyed Au-Ag NS arrays obtained from the arrays in (d), (e) and (f), respectively.

Figure 10. Raman spectra of 10-6 M 4-ATP on the porous alloyed Au-Ag NS arrays with various periodic lengths (350, 500, and 750 nm).


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4 Conclusions In conclusion, an effective and reproducible synthetic route was developed to prepare highly ordered, large-scale porous alloyed Au-Ag NS arrays with different periodic lengths by exploiting a monolayer of colloidal PS crystals as a template. Due to the high density of accessible SERS “hotspots” and the periodic structure of the porous alloyed Au-Ag NS array, this array showed excellent SERS sensitivity and reproducibility in the detection of 4-ATP. The size of the nanopores, width of the ligaments, elemental composition and periodic length of the porous alloyed Au-Ag NS arrays could be easily tailored by changing the diameter of the PS microspheres, thickness of the Au and Ag films, and dealloying time, which tuned the LSPR properties of the arrays. Moreover, this method can be used to fabricate other binary or ternary porous alloyed NP arrays with different elements. The presented strategy will be highly useful for the further development of various applications, including SERS-based analysis, dualchannel biosensors, energy storage, and catalysis. ASSOCIATED CONTENT Supporting Information. Additional TEM, HAADF-STEM, FESEM, EDS mapping data, SERS result are included in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.


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AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (Yue Li); Author Contributions All the authors have made contributions to the manuscript and given their approval of the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The authors acknowledge financial support from the National Key Research and Development Program of China (Grant No. 2017YFA0207101), the Natural Science Foundation of China (Grant Nos. 51771188, 51571189), the Cross-disciplinary Collaborative Teams Program in CAS, and the CAS/SAFEA International Partnership Program for Creative Research Teams. REFERENCES (1)

Mayer, K. M.; Hafner, J. H. Localized Surface Plasmon Resonance Sensors. Chem. Rev.,

2011, 111, 3828-3857. (2)

Bardhan, R.; Grady, N .K.; Cole, J. R.; Joshi, A.; Halas, N. J. Fluorescence Enhancement

by Au Nanostructures: Nanoshells and Nanorods. ACS Nano, 2009, 3, 744 -752. (3)

Nan, F.; Xie, F. M.; Liang,S.; Ma, L.; Yang, D. J.; Liu, X. L.; Wang, J. H.; Cheng, Z. Q.;

Yu, X. F.; Zhou, L.; Wang, Q. Q.; Zeng, J. Growth of Metal–semiconductor Core–multishell


23


Page 24 of 32

Nanorods with Optimized Field Confinement and Nonlinear Enhancement. Nanoscale, 2016, 8, 11969-11975. (4)

Schlücker, S. Surface-Enhanced Raman Spectroscopy: Concepts and Chemical

Applications. Angew. Chem., Int. Ed., 2014, 53, 4756-4795. (5)

Mulvihill, M. J.; Ling, X. Y.; Henzie, J.; Yang, P. D. Anisotropic Etching of Silver

Nanoparticles for Plasmonic Structures Capable of Single-particle SERS. J. Am. Chem. Soc., 2009, 132, 268-274. (6)

Wang, C. Q.; Zhang, Z. R.; Yang, G.; Chen, Q.; Yin, Y. D.; Jin, M. S. Creation of

Controllable High-Density Defects in Silver Nanowires for Enhanced Catalytic Property. Nano Lett., 2016, 16, 5669-5674. (7)

Zheng, T. T.; Li, G. G.; Zhou, F.; Wu, R.; Zhu, J. J.; Wang, H. Gold-Nanosponge-Based

Multistimuli-Responsive Drug Vehicles for Targeted Chemo-Photothermal Therapy. Adv. Mater., 2016, 28, 8218-8226. (8)

Tsao, Y. C.; Rej, S.; Chiu, C. Y.; Huang, M. H.; Aqueous Phase Synthesis of Au–Ag

Core–shell Nanocrystals with Tunable Shapes and Their Optical and Catalytic Properties. J. Am. Chem. Soc., 2013, 136, 396-404. (9)

Wang, G. Q.; Tao, S. Y.; Liu, Y. D.; Guo, L.; Qin, G. H.; Ijiro, K.; Maeda, M.; Yin, Y. D.

High-yield Halide-free Synthesis of Biocompatible Au Nanoplates. Chem. Commun., 2016, 52, 398-401. (10)

Liu, H. P.; Liu, T. Z.; Zhang, L.; Han, L.; Gao, C. B.; Yin, Y. D. Etching-Free Epitaxial

Growth of Gold on Silver Nanostructures for High Chemical Stability and Plasmonic Activity. Adv. Funct. Mater., 2015, 25, 5435-5443.


24

Page 25 of 32 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


(11)

Vu, H.; Siebels, J.; Sonnenberg, D.; Mendach, S.; Kipp, T. Tunable Plasmonic

Nanoantennas in Rolled-up Microtubes Coupled to Integrated Quantum Wells. ACS Photonics, 2017, 4, 2659-2663. (12)

Hao, Q.; Huang, Hao.; Fan, X. C.; Y, Y.; Wang, J. W.; Li, W.; Qiu, T.; Ma, L. B.; Chu, P.

K.; Schmidt, O. G. Controlled Patterning of Plasmonic Dimers by Using an Ultrathin Nanoporous Alumina Membrane as a Shadow Mask. ACS Appl. Mater. Interfaces, 2017, 9, 36199-36205. (13)

Niu, W. X.; Chua, Y. A. A.; Zhang, W. Q.; Huang, H. J.; Lu, X. M. Highly Symmetric

Gold Nanostars: Crystallographic Control and Surface-enhanced Raman Scattering Property. J. Am. Chem. Soc., 2015, 137, 10460-10463. (14)

Zhang, Q. F.; Large, N.; Nordlander, P.; Wang, H. Porous Au Nanoparticles with

Tunable Plasmon Resonances and Intense Field Enhancements for Single-particle SERS. J. Phys. Chem. Lett., 2014, 5, 370-374. (15)

Peng, B.; Li, G. Y.; Li, D. H.; Dodson, S.; Zhang, Q.; Zhang, J.; Lee, Y. H.; Demir, H. V.;

Ling, X. Y.; Xiong, Q. H. Vertically Aligned Gold Nanorod Monolayer on Arbitrary Substrates: Self-assembly and Femtomolar Detection of Food Contaminants. ACS Nano, 2013, 7, 5993-6000. (16)

Jena, B. K.; Mishra, B. K.; Bohidar, S. Synthesis of Branched Ag Nanoflowers Based on

a Bioinspired Technique: Their Surface Enhanced Raman Scattering and Antibacterial Activity. J. Phys. Chem. B, 2009, 113, 14753-14758. (17)

Freeman, R. G.; Grabar, K. C.; Allison, K. J.; Bright, R. M. Self-assembled Metal Colloid

Monolayers: an Approach to SERS Substrates. Science, 1995, 267, 1629-1632.


25


(18)

Page 26 of 32

Cho, W. J.; Kim, Y.; Kim, J. K. Ultrahigh-density Array of Silver Nanoclusters for SERS

Substrate with High Sensitivity and Excellent Reproducibility. ACS Nano, 2011, 6, 249-255. (19)

Cha, S. K.; Mun, J. H.; Chang, T.; Kim, S. Y.; Kim, J. Y.; Jin, H. M.; Lee, J. Y.; Shin, J.;

Kim, K. H.; Kim, S. O. Au–Ag Core–shell Nanoparticle Array by Block Copolymer Lithography for Synergistic Broadband Plasmonic Properties. ACS Nano, 2015, 9, 5536-5543. (20)

Tognalli, N. G.; Cortés, E.; Hernández-Nieves, A. D.; Carro, P.; Usaj, G.; Balseiro, C. A.;

Vela, M. E.; Salvarezza, R. C.; Fainstein, A. From Single to Multiple Ag-Layer Modification of Au Nanocavity Substrates: A Tunable Probe of the Chemical Surface-Enhanced Raman Scattering Mechanism. ACS Nano, 2011, 5, 5433-5443. (21)

Wu, L.; Xiao, X. Y.; Chen, K.; Yin, W. M.; Li, Q.; Wang, P.; Lu, Z. C.; Ma, J.; Han, H.

Y. Ultrasensitive SERS Detection of Bacillus Thuringiensis Special Gene Based on Au@ Ag NRs and Magnetic Bead. Biosens. Bioelectron., 2017, 92, 321-327. (22)

Tang, L. J.; Li, S.; Han, F.; L, L. Q.; Xu, L. G.; Ma, W.; Kuang, H.; Li, A. K.; Wang, L.

B.; Xu, C. L. SERS-active Au@Ag Nanorod Dimers for Ultrasensitive Dopamine Detection. Biosens. Bioelectron., 2015, 71, 7-12. (23)

Ding, H. P.; Xin, G. Q.; Chen, K. C.; Zhang, M.; Liu, Q.; Hao, J.; Liu, H. G. Silver

dendritic nanostructures formed at the solid/liquid interface via electroless deposition. Colloid Surface A, 2010, 353, 166-171. (24)

Vidal, C.; Wang, D.; Schaaf, P.; Hrelescu, C.; Klar, T. A. Optical Plasmons of Individual

Gold Nanosponges. ACS Photonics, 2015, 2, 1436-1442.


26

Page 27 of 32 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


(25)

Hergert, G.; Vogelsang, J.; Schwarz, F.; Wang, D.; Kollmann, H.; Groß, P.; Lienau, C.;

Runge, E.; Schaaf, P. Long-lived Electron Emission Reveals Localized Plasmon Modes in Disordered Nanosponge Antennas. Light: Sci. Appl., 2017, 6, e17075. (26)

Ferrando, R.; Jellinek, J.; Johnston, R. L. Nanoalloys: From Theory to Applications of

Alloy Clusters and Nanoparticles. Chem. Rev., 2008, 108, 845-910. (27)

Yu, H. J.; Yang, S. C.; Ding, B. J.; Yang, H. Synthesis of Colloidal Metal and Metal

Alloy Nanoparticles for Electrochemical Energy Applications. Chem. Soc. Rev., 2013, 42, 28802904. (28)

Wei, X. Y.; Fan, Q. K.; Liu, H. P.; Bai, Y. C.; Zhang, L.; Zheng, H. Q.; Yin, Y. D.; Gao,

C. B. Holey Au–Ag Alloy Nanoplates with Built-in Hotspots for Surface-enhanced Raman Scattering. Nanoscale, 2016, 8, 15689-15695. (29)

Liu, Y. J.; Pedireddy, S.; Lee, Y. H.; Hegde, R. S.; Tjiu, W. W.; Cui, Y.; Ling, X. Y.

Precision Synthesis: Designing Hot Spots over Hot Spots via Selective Gold Deposition on Silver Octahedra Edges. Small, 2014,10, 4940-4950. (30)

Gunawidjaja, R.; Kharlampieva, E.; Choi, I.; Tsukruk, V. V. Bimetallic Nanostructures

as Active Raman Markers: Gold-Nanoparticle Assembly on 1D and 2D Silver Nanostructure Surfaces. Small, 2009, 5, 2460-2466. (31)

Liu, K.; Bai, Y. C.; Zhang, L.; Yang, Z. B.; Fan, Q. K.; Zheng, H. Q.; Yin, Y. D.; Gao, C.

B. Porous Au–Ag Nanospheres with High-density and Highly Accessible Hotspots for SERS Analysis. Nano lett., 2016, 16, 3675-3681.


27


(32)

Page 28 of 32

Yan, Y.; Radu, A. I.; Rao, W. Y.; Wang, H. M.; Chen, G.; Weber, K.; Wang, D.; Cialla-

May, D.; Popp, J.; Schaaf, P., Mesoscopically Bi-continuous Ag–Au Hybrid Nanosponges with Tunable Plasmon Resonances as Bottom-Up Substrates for Surface-Enhanced Raman Spectroscopy. Chem. Mater., 2016, 28, 7673-7682. (33)

Li, G. G.; Lin, Y.; Wang, H. Residual Silver Remarkably Enhances Electrocatalytic

Activity and Durability of Dealloyed Gold Nanosponge Particles. Nano Lett., 2016, 16, 72487253. (34)

Personick, M. L.; Zugic, B.; Biener, M. M.; Biener, J.; Madix, R. J.; Friend, C. M.

Ozone-activated Nanoporous Gold: a Stable and Storable Material for Catalytic Oxidation. ACS Catal., 2015, 5, 4237-4242. (35)

Snyder, J.; McCue, I.; Livi, K.; Erlebacher, J. Structure/Processing/Properties

Relationships in Nanoporous Nanoparticles as Applied to Catalysis of the Cathodic Oxygen Reduction Reaction. J. Am. Chem. Soc., 2012, 134, 8633-8645. (36)

Chauvin, A.; Delacôte, C.; Molina-Luna, L.; Duerrschnabel, M.; Boujtita, M.; Thiry, D.;

Du, K.; Ding, J. J.; Choi, C. H.; Tessier, P. Y.; El Mel, A. A. Planar Arrays of Nanoporous Gold Nanowires: When Electrochemical Dealloying Meets Nanopatterning. ACS Appl. Mater. Interfaces, 2016, 8, 6611-6620. (37)

Mohl, M.; Kumar, A.; Reddy, A. L. M.; Kukovecz, A.; Konya, Z.; Kiricsi, I.; Vajtai, R.;

Ajayan, P. M. Synthesis of Catalytic Porous Metallic Nanorods by Galvanic Exchange Reaction. J. Phys. Chem. C, 2009, 114, 389-393.


28

Page 29 of 32 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


(38)

Sattayasamitsathit, S.; Gu, Y. G.; Kaufmann, K.; Minteer, S.; Polsky, R.; Wang, J.

Tunable Hierarchical Macro/Mesoporous Gold Microwires Fabricated by Dual-templating and Dealloying Processes. Nanoscale, 2013, 5, 7849-7854. (39)

Li, F.; He, J. B.; Zhou, W. L.; Wiley, J. B. Synthesis of Porous Wires from Directed

Assemblies of Nanospheres. J. Am. Chem. Soc., 2003, 125, 16166-16167. (40)

Zhang, Z. H.; Wang, Y.; Qi, Z.; Zhang, W. H.; Qin, J. Y.; Frenzel, J. Generalized

Fabrication of Nanoporous Metals (Au, Pd, Pt, Ag, and Cu) through Chemical Dealloying. J. Phys. Chem. C, 2009, 113, 12629-12636. (41)

Li, C. L.; Dag, Ö.; Dao, T. D.; Nagao, T.; Sakamoto, Y.; Kimura, T.; Terasaki, O.;

Yamauchi, Y. Electrochemical Synthesis of Mesoporous Gold Films Toward MesospaceStimulated Optical Properties. Nat. Commun., 2015, 6, 6608-6615. (42)

McCurry, D. A.; Bailey, R. C. Nanoporous Gold Membranes as Robust Constructs for

Selectively Tunable Chemical Transport. J. Phys. Chem. C, 2016, 120, 20929-20935. (43)

Qiu, S. Y.; Zhao, F. S.; Zenasni, O.; Li, J. T.; Shih, W. C. Nanoporous Gold Disks

Functionalized with Stabilized G-quadruplex Moieties for Sensing Small Molecules. ACS Appl. Mater. Interfaces, 2016, 8, 29968-29976. (44)

Zhang, T.; Zhou, F.; Hang, L. F.; Sun, Y. Q.; Liu D. L.; Li, H. L.; Liu, G. Q.; Lyu, X. J.;

Li, C. C.; Cai, W. P.; Li, Y. Controlled Synthesis of Sponge-like Porous Au-Ag Alloy Nanocubes for Surface-enhanced Raman Scattering Properties. J. Mater. Chem. C, 2017, 5, 11039-11045.


29


(45)

Page 30 of 32

Sun, Y. Q.; Hang, L. F.; Men, D. D.; Li, H. L.; Liu D. L.; Li, X. Y.; Wen, L. L.; Li, Y.

Periodic Nanostructured Au Arrays on an Si Electrode for High-performance Electrochemical Detection of Hydrogen Peroxide without an Enzyme. J. Mater. Chem. C, 2016, 4, 9864-9871. (46)

Hamon, C.; Novikov, S.; Scarabelli, L.; Basabe-Desmonts, L.; Liz-Marzán, L. M.

Hierarchical Self-assembly of Gold Nanoparticles into Patterned Plasmonic Nanostructures. ACS Nano, 2014, 8, 10694-10703. (47)

Zhang, H. H.; Liu, M.; Zhou, F.; Liu, D. L.; Liu, G. Q.; Duan, G. T.; Cai, W. P.; Li, Y.

Physical

Deposition

Improved

SERS

Stability of

Morphology

Controlled

Periodic

Micro/Nanostructured Arrays Based on Colloidal Templates. Small, 2015, 11, 844-853. (48)

Fu, R. R.; Liu, G. Q.; Jia, C.; Li, X. H.; Tang, X.; Duan, G. T.; Li, Y.; Cai, W. P.

Fabrication of Silver Nanoplate Hierarchical Turreted Ordered Array and its Application in Trace Analyses. Chem. Commun., 2015, 51, 6609-6612. (49)

Sun, Y. Q.; Hang, L. F.; Men, D. D.; Li, H. L.; Liu, D. L.; Li, X. Y.; Wen, L. L.; Li, Y.

Periodic nanostructured Au arrays on an Si electrode for high-performance Electrochemical Detection of Hydrogen Peroxide without an Enzyme. J. Mater. Chem. C, 2016, 4, 9864-9871. (50)

Gu, Z. Z.; Horie, R.; Kubo, S.; Yamada, Y.; Fujishima, A.; Sato, O. Fabrication of a

Metal-coated Three-dimensionally Ordered Macroporous Film and its Application as a Refractive Index Sensor. Angew. Chem., Int. Ed. 2002, 41, 1153-1156. (51)

Hang, L. F.; Zhou, F.; Men, D. D., Li, H. L.; Li, X. Y.; Zhang, H. H.; Liu, G. Q.; Cai, W.

P.; Li, C. C.; Li, Y. Functionalized Periodic Au@ MOFs Nanoparticle Arrays as Biosensors for


30

Page 31 of 32 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


Dual-channel Detection through the Complementary Effect of SPR and Diffraction peaks. Nano Res., 2017, 10, 2257-2270. (52)

Arnob, M. M. P.; Zhao, F.; Li, J.; Shih, W. C. EBL-based Fabrication and Different

Modeling Approaches for Nanoporous Gold Nanodisks. ACS Photonics, 2017, 4, 1870-1878. (53)

Li, X.; Chen, Q.; McCue, I.; Snyder, J.; Crozier, P.; Erlebacher, J.; Sieradzki, K.

Dealloying of Noble-metal Alloy Nanoparticles. Nano Lett., 2014, 14, 2569-2577. (54)

Li, G. G.; Villarreal, E.; Zhang, Q.; Zheng, T.; Zhu, J. J.; Wang, H. Controlled

Dealloying of Alloy Nanoparticles toward Optimization of Electrocatalysis on Spongy Metallic Nanoframes. ACS Appl. Mater. Interfaces, 2016, 8, 23920-23931. (55)

Zhao, F.; Zeng, J.; Arnob, M. M. P.; Sun, P.; Qi, J.; Motwani, P.; Raja, B. Monolithic

NPG Nanoparticles with Large Surface Area, Tunable Plasmonics, and High-density Internal hot-spots. Nanoscale, 2014, 6, 8199-8207.


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Periodic Porous Alloyed Au-Ag Nanosphere Arrays and Their Highly

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