Facile One-Pot Synthesis of Nanodot-Decorated GoldâSilver Alloy

Subscriber access provided by Kaohsiung Medical University

Functional Nanostructured Materials (including low-D carbon)

Facile One-Pot Synthesis of Nanodot Decorated GoldSilver Alloy Nanoboxes for Single-Particle SERS Activity Junrong Li, Guannan Zhang, Jing Wang, Ivan Maksymov, Andrew D. Greentree, Jiming Hu, Ai-Guo Shen, Yuling Wang, and Matt Trau ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b10112 • Publication Date (Web): 31 Aug 2018 Downloaded from http://pubs.acs.org on September 1, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35 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

ACS Applied Materials & Interfaces

Facile One-Pot Synthesis of Nanodot Decorated Gold-Silver Alloy Nanoboxes for Single-Particle SERS Activity Junrong Li,

†

Guannan Zhang,

‡

Jing Wang,

†

Ivan S. Maksymov,

‽

Andrew D. Greentree,

‽

Jiming Hu, ‡ Aiguo Shen,*, ‡ Yuling Wang,*, ¶ and Matt Trau*,†,§ †

Centre for Personalized Nanomedicine, Australian Institute for Bioengineering and

Nanotechnology (AIBN), The University of Queensland, Brisbane, QLD 4072, Australia §

School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD

4072, Australia ‡

Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education),

College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072 ‽

Australian Research Council Centre of Excellence for Nanoscale BioPhotonics, School of

Science, RMIT University, Melbourne, Victoria 3001, Australia ¶

Department of Molecular Sciences, Australian Research Council Centre of Excellence for

Nanoscale BioPhotonics, Faculty of Science and Engineering, Macquarie University, Sydney, NSW, 2109 KEYWORDS: gold-silver alloy nanoboxes, nanodot, one-pot synthesis, aqueous phase synthesis, single-particle, surface-enhanced Raman scattering (SERS)

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 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

Page 2 of 35

ABSTRACT: Surface-enhanced Raman scattering (SERS) is an important, highly sensitive technique for chemical and biological analysis, which is critically dependent upon high performance metallic substrates. Anisotropic gold (Au)-silver (Ag) alloy nanoboxes are attractive SERS substrates due to the greatly enhanced Raman signals from the strong electromagnetic fields on the sharp corners. Yet, the routine approach of Au-Ag alloy nanobox synthesis is still challenging because of the complicated procedures and use of biologically/environmentally unfriendly reagents. To facilitate the usage of Au-Ag alloy nanoboxes for broad SERS applications, we propose a facile green strategy to synthesize Au-Ag alloy nanoboxes with superior single-particle SERS sensitivity. Our novel straightforward strategy involves HAuCl4 and AgNO3 reduction by ascorbic acid, which is achieved in an aqueous one-pot reaction at ambient temperature. Significantly, the surfaces of the prepared AuAg alloy nanoboxes are judiciously designed to introduce nanodots, generating numerous “hot spots” for high Raman signal enhancement as indicated by rigorous numerical simulations. By combining scanning electron microscope (SEM) and Raman mapping images, we demonstrate the application of Au-Ag alloy nanoboxes for single-particle sensing SERS activity. The asprepared Au-Ag alloy nanoboxes are expected to facilitate their further applications in quantitative and ultrasensitive SERS detection.

1. INTRODUCTION Surface-enhanced Raman scattering (SERS) is a highly sensitive fingerprint spectroscopic technique that can reach single molecule detection level.1 The high sensitivity of SERS enables a wide range of applications, such as immunoassay, disease diagnosis, and environmental surveillance.2 For these applications, the properties of SERS substrates are crucial, which


2

Page 3 of 35 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


amplify Raman signals via the excitation of localized surface plasmon resonance (LSPR).3 As such, designing, synthesizing and investigating SERS substrates have aroused great interest to achieve sensitive analysis. Anisotropic nanostructures are of particular importance for the high SERS activity due to the enhanced electromagnetic fields on specific regions (i.e. “hot spots”), like edges and tips.4 Anisotropic Au-Ag alloy nanoboxes generate hot spots on the sharp corners that contribute to strong SERS signals, and the alloy property improves the chemical stability.5-7 The Xia group has pioneered the preparation of Au-Ag alloy nanoboxes utilizing the two-step Ag templateengaged galvanic replacement reaction with chloroauric acid (HAuCl4) solution, which has become a prevalent route to obtain the nanoboxes.8,9 However, this approach suffers from several limitations, such as the requirement of organic solvent, high temperature (140-160 oC) and surfactants, making it relatively inconvenient and biologically/environmentally unfriendly. Furthermore, the nanoboxes synthesized in this galvanic replacement strategy lose Ag atoms significantly as the generation of one Au atom costs three Ag atoms, thereby diminishing SERS activity.5 To enhance SERS activity of the above-mentioned nanoboxes, co-reduction has been employed along with the galvanic replacement reaction to synthesize Ag enriched Au-Ag alloy nanoboxes.5 Nevertheless, development of a facile green strategy to prepare Au-Ag alloy nanoboxes with strong SERS activity is an outstanding goal for this field. Herein we demonstrate a straightforward, benign method to prepare the nanodot decorated AuAg alloy nanoboxes that possess single-particle SERS activity. Our one-pot approach allows the preparation of nanoboxes by HAuCl4 and silver nitrate (AgNO3) reduction using ascorbic acid (AA), which is conducted in an aqueous phase under ambient temperature without any surfactant. AA sustains the Ag enriched structure via reducing the lost Ag+ into Ag as well as


3


Page 4 of 35

adjusts the surface structures of the nanoboxes (smooth surfaces and surfaces with nanodots) with different concentrations. By adjusting the AgNO3 concentration, we can control the dominant products to be nanoboxes rather than spherical nanoparticles (NPs). Importantly, the nanodot decorated nanoboxes have a great potential to facilitate ultrasensitive and reliable SERS detection due to the single-particle SERS activity. 2. EXPERIMENTAL SECTION 2.1. Chemicals and Reagents. Hydrogen tetrachloroaurate trihydrate (HAuCl4·3H2O), AgNO3, and 4-mercaptobenzoic acid (MBA) were bought from Sigma Aldrich. AA and sodium citrate were obtained from MP Biomedicals, Inc.. The above purchased analytical reagents were used as received without any treatments. Ultrapure water (resistivity ˃ 18.2 MΩ·cm) was utilized in the whole NP preparation experiments. 2.2. Synthesis of the Au-Ag Alloy Nanoboxes. To prepare the nanodot decorated Au-Ag alloy nanoboxes, 45 µL of 1% (wt %) HAuCl4 stock solution was injected into 10 mL of ultrapure water, followed by stirring at 850 rpm for 1 min. Then, 170 µL of AgNO3 (6 mM) was introduced forming a milky white turbidity solution. One minute later, 500 µL of AA (0.1 M) was introduced into the solution. The appearance of visible blue color after about 6 sec indicated the generation of the products, and the magnetic stirring was stopped after 1 min. The Au-Ag alloy nanoboxes with relatively smooth surfaces were prepared in a similar way by adjusting the volume of AA into 30 µL. 1 mL of the as-prepared products were purified using centrifugation (200 g, 20 min) and resuspended into 500 µL of H2O before characterizations. To demonstrate the rapid synthesis of nanoboxes, 0.3 µL of the products were directly taken from the reaction


4

Page 5 of 35 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


system onto a silica wafer at different time points (30 s, 1 min, 3 min and 10 min), and fast dried on a 100 oC hot plate for SEM characterization. 2.3. Synthesis of 60 nm AuNPs and AgNPs. 60 nm AuNPs were prepared following a previously reported strategy.10 AgNPs were synthesized using the Lee-Meisel method.11 2.4. Raman Measurements. SERS enhancement measurements were conducted in a cuvette with the sample volume of 60 µL in H2O solution. The SERS spectra were acquired with a 785 nm wavelength laser source for 1 s of illumination, 5 times and each spectrum represented the average spectrum from 3 replicates. 2.5. Characterization. A DCS disc centrifuge 24000UHR (CPS Instruments Inc.) loaded with 14.4 mL of sucrose gradient fluid (8-24% sucrose in H2O) was utilized to conduct the particle size distribution (PSD) measurements. A JEOL-7100 FE-SEM microscope at 20 kV voltage was used to obtain the scanning electron microscope (SEM) images. A Hitachi HT7700 microscope under the voltage of 120 kV was utilized to obtain the transmission electron microscope (TEM) images. A JEOL-2100 microscope with the accelerating voltage of 200 kV was employed to perform high-resolution (HR) TEM, energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED), and nanobeam diffraction (NBD) analysis. A UV-2450 UV-vis spectrophotometer (Shimadzu) was utilized to record the extinction spectrum of the nanoboxes. X-ray photoelectron spectroscopy (XPS) was performed on a Kratos Axis Ultra photoelectron spectrometer using mono Al Kα (1486.6eV) X-ray radiation source. Casa XPS data processing software was adopted to fit all the XPS spectra. X-ray diffraction (XRD) patterns were obtained from a Bruker D8 Advance MKII XRD diffractometer using Cu Kα radiation (λ=1.5418 Å). An IM-52 portable Raman microscope (Snowy Range Instruments) with 785 nm laser excitation (73


5


Page 6 of 35

mW) was employed to acquire the Raman signals from bulk solutions. The NP concentration was determined by Malvern NanoSight NS300. Single nanobox SERS mapping was recorded from a WITec alpha 300 R microspectrometer with 632.8 nm He-Ne laser as excitation source using a 100× objective with 0.1 s integration time and an EMCCD. The first-order photo peak of silica at 520 nm was utilized to calibrate the system. 2.6. Simulation. The optical properties of the nanodot decorated nanobox were simulated using CST Microwave Studio 2016. First, the optical |E|4-field spectrum was calculated using the timedomain solver, which uses a rectangular mesh to discretise the structure of the nanobox. To properly discretise the fine elements of the nanobox, such as the corners and the surface roughness, the mesh had a variable step size and in our case the smallest mesh elements were 0.1 nm. Here, an advantage of the time-domain solver is the ability to calculate the spectrum in a wide range of optical frequencies in a single simulation run by choosing a narrow time-domainpulse as the incident signal. Detectors were placed in the middle of the nanobox as well as near its corners, i.e. in the areas where the highest localisation of the optical field is expected, and the detected signals were Fourier-transformed to obtain the spectrum in the frequency domain. The incident light was a plane wave polarised along the x-coordinate axis. The dielectric constant of silver was used from reference.[27] We used Perfectly Matched Layers as the boundary conditions truncating all edges of the computational domain. To calculate the corresponding spatial |E|4-field profile, the frequency-domain solver that calculates the field distribution using a triangular mesh was used. A triangular mesh allows for a better discretisation of small features of the nanobox and nanodots and it uses an iterative process that ensures high accuracy of the resulting field profile. The polarisation of the incident


6

Page 7 of 35 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


light, boundary conditions, dielectric permittivity of materials and other relevant parameters were consistent with the time-domain simulations. 3. RESULTS AND DISCUSSION 3.1. Synthesis and characterization of the nanodot decorated Au-Ag alloy nanoboxes. The synthesis of Au-Ag alloy nanoboxes was conducted by the reduction of HAuCl4 and AgNO3 with AA in an aqueous phase at room temperature. As shown in the SEM images (Figure 1), the nanoboxes were completely formed within 30 s (Figure 1A) and stayed the same afterwards (Figure 1B, C, D). Such a fast reduction rate can be attributed to the relatively strong reduction activity of AA, which is similar to the rapid preparation of Au/Ag nanostars in 20s using AA reduction.12 Thus, our fast workflow for nanobox synthesis exhibits an obvious advantage over the traditional approach that requires at least 2.5 hr.13


7


Page 8 of 35

Figure 1. Rapid synthesis of the nanodot decroated Au-Ag alloy nanoboxes. SEM images of the nanoboxes took at (A) 30 s; (B) 1 min; (C) 3 min; (D) 10 min. The as-prepared nanoboxes had an average edge length of 120 nm and many small NPs (termed as “nanodots”) on the surfaces. The morphology of the products became nanoboxes at 30 s and remained the same at 10 min, demonstrating the rapidness of this reaction. The elemental distribution of the as-prepared nanoboxes was investigated with EDS. As shown in the EDS line scan (inset in Figure 2A), an apparent signal increase for both Au and Ag can be observed on the walls compared to the inner parts, which indicates the nanobox has the hollow


8

Page 9 of 35 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


structure. Figure 2B, C and D show the uniformly distributed Au (M) and Ag (Lα) signals, demonstrating the alloy rather than core-shell structure of the nanobox. The formed alloy nanoboxes are good alternatives to monometallic NPs due to the improved stability6 and SERS activity.5 EDS also demonstrates the nanobox retains most of Ag amounts, because the molar ratio of Ag/Au (0.94) determined from the EDS mapping spectrum closes to the AgNO3/HAuCl4 molar ratio (0.90) (Figure S1). Thus, the obtained Ag enriched nanoboxes are expected to improve SERS activity due to the high amount of Ag component in the nanostructures.5 The structural information of the nanoboxes was explored by HR-TEM and electron diffraction (ED). Figure 2A shows the HR-TEM image, where the two lattice fringes with the d-spacing of 0.236 nm and 0.204 nm correspond to the (111) and (200) planar distances of Au-Ag alloy nanostructures, respectively.14 Several diffraction rings in the SAED pattern of the single nanobox (Figure F) can be assigned to (111), (200), (220), and (311) plane of Au-Ag alloy NPs and indicates the polycrystalline nature of the nanobox.15 In contrast to the SAED mode for the whole nanobox, NBD pattern taken from the blue circle in Figure 2A shows some separated diffraction spots (Figure 2G) that can be attributed to the Au-Ag alloy (111) and (200) facets. Therefore, unlike the single crystalline nanoboxes prepared in the Xia’s group, our Au-Ag alloy nanoboxes have polycrystalline structure.8 The optical property of the nanoboxes was investigated with extinction spectroscopy. The recorded extinction spectrum of the Au-Ag alloy nanoboxes exhibits a distinctive surface plasma resonance (SPR) peak at around 673 nm (Figure 2H), which red shifts remarkably in relative to the SPR of solid spherical AuNPs and AgNPs owing to the anisotropic hollow alloy structure. The red-shifted SPR allows the nanoboxes to be used with NIR laser excitation, thereby facilitating in vivo SERS analysis.


9


Page 10 of 35

Figure 2. The compositional, structural and optical characterizations of Au-Ag alloy nanoboxes. (A) TEM image of a single nanobox and EDS line profile of the nanobox; (B) EDS mapping of Au; the signal from Au (M) is shown in red; (C) EDS mapping of Ag; the signal from Ag (Lα) is shown in green; (D) Mixed EDS mapping of Au and Ag; the uniformly distributed red and green color suggests the Au-Ag alloy property of nanoboxes; (E) HR-TEM image of the nanobox from the red circle in figure (A); (F) SAED image of the nanobox in figure (A); the diffraction rings demonstrate the polycrystalline structure of the nanoboxes; (G) NBD image of the nanobox from the blue circle in figure (A); (H) Extinction spectrum of the nanoboxes. The surface elemental composition and chemical state of the nanoboxes was further characterized by XPS. Figure 3A shows a survey scan pattern of the nanoboxes, where Ag 3d, Au 4f, O 1s, C 1s and Cl 2p can be observed. Figure 3B, C, and D show the high-resolution scan for the Au 4f, Ag 3d and Cl 2p, respectively. Compared with the pure Ag 3d5/2 peak at 368.48 eV,16 the peak in the nanoboxes shifts towards 368.02 eV (∆ = 0.46 eV). The Au 4f7/2 peak in the nanoboxes shifts towards 83.95 eV in comparison with the pure Au peak at 83.70 eV (∆ = 0.25


10

Page 11 of 35 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


eV).17 Such shifts are presumably caused by the charge transfer between Au and Ag in the alloy nanostructures.16, 18 Considering no higher than 0.7 eV shift is observed in the Au and Ag XPS spectra, the nanoboxes are believed to be consist of metallic Au and Ag.19-21 Relatively weak Cl 2p1/2 and Cl 2p3/2 peaks can be observed by doubling the acquisition time, which is most likely due to the adsorption of Cl- onto the surfaces as the easy formation of Cl adlayer on the top of Ag.22-23 The semi-quantitative atomic ratio analysis suggests a relatively high amounts of Ag on the nanobox surfaces (Au: Ag: Cl=6.2: 8.4: 1). This Ag enriched surface structure is beneficial for SERS activity considering the generally high Raman enhancement capability of Ag. Furthermore, the relatively low concentration of halides (about 6.4% Cl-) on the surfaces is expected to sustain the good stability of the nanoboxes under oxidative environments and thus can extend their utility as SERS substrates in high oxidizing conditions.24-25


11


Page 12 of 35

Figure 3. XPS analysis of the surface composition and chemical state of the nanodot-decorated Au-Ag alloy nanoboxes. (A) Survey scan; (B) Au 4f region high resolution scan; (C) Ag 3d region high resolution scan; (D) Cl 2p region high resolution scan. The XPS spectra for Au 4f and Ag 3d in the nanoboxes matched monometallic Au and Ag. The crystal structure and grain sizes of the nanoboxes were explored by XRD. As shown in Figure S2, the nanodot decorated nanoboxes have five diffraction peaks at 38.21o, 44.37o, 64.72o, 77.57o, and 81.67o, which is in line with the reported (111), (200), (220), (311), and (222) reflections, respectively.26 This pattern matches well with the fcc phase of Au-Ag alloy (ICDD File Card No. 04-002-1174). Based on the full width at half-maximum (FWHM) of the diffraction peak at 38.21o, the crystalline size is determined to be 8.26 nm in Scherrer equation.


12

Page 13 of 35 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


None of the diffraction peaks can be indexed to AgCl (ICDD File Card No. 00-001-1013), which further indicates the absence of AgCl in the nanoboxes and thus the SERS enhancement property of the nanoboxes will not be influenced. 3.2. Influence of synthetic Conditions. To fully understand the role played by each reagent or reaction condition, we investigated the influence of AgNO3, AA, concentrations of HAuCl4 and AgNO3 and temperature on the preparation of the nanoboxes. AgNO3 has been widely used to improve the yield or promote the growth of anisotropic NPs, including Au nanorods, nanobipyramids, and platinum polyhedra.27-28 To explore the function of AgNO3 in the current synthesis system, the AgNO3 concentration was adjusted from 0.022 mM to 0.132 mM under the given HAuCl4 concentration (0.11 mM). It was found that the nanoboxes began to appear at 0.022 mM of AgNO3, but the dominant products were small quasi-spherical NPs as indicated in SEM image (Figure 4A). When the concentration of AgNO3 was increased to 0.044 mM, the yield of the nanoboxes improved, but the smaller NPs still dominated (Figure 4B). With the increase of the AgNO3 concentration to 0.099 mM, almost all the NPs turned into nanoboxes (Figure 4C). However, upon a further increase of the AgNO3 concentration to 0.132 mM, the nanoboxes became bigger (~ 200 nm) and the amounts of smaller NPs increased again (Figure 4D). To further validate the SEM results, the products were measured by differential centrifugal sedimentation (DCS), which separates particles in a density gradient solution based on particle mass and yields a high-resolution and accurate PSD graph. PSD graphs (Figure 4E-H) show three separate peaks that relate to the small quasi-spherical NPs and the nanoboxes in SEM images. The relative weight intensities of peaks corresponding to the nanoboxes (~ 93 nm) kept


13


Page 14 of 35

increasing until the concentration of AgNO3 reached 0.099 mM, while this trend began to reverse at the AgNO3 concentration of 0.132 mM. Thus, DCS characterization was consistent with SEM results, and both of them illustrated a gradually growing size of the nanoboxes with the increasing of AgNO3 concentrations. It is noteworthy that DCS shows an underestimated size (~93 nm) of the nanoboxes than that obtained by SEM (~120 nm) due to the following two reasons: (1) an oversimplified assumption was used in which the density of the nanoboxes is that of Au (19.3 g/cm3); (2) DCS underestimates particle size for non-spherical objects according to the

technical

support

documents

of

CPS

Instruments

InC.

(http://www.cpsinstruments.eu/pdf/Introduction%20Differential%20Sedimentation.pdf). Nevertheless, DCS is still an effective method for the evaluation of nanobox yield. Taken together, the AgNO3 concentration significantly affected the yields of the nanoboxes with the highest yield achieved at 0.99 mM.

Figure 4. The influence of AgNO3 concentration on the yield of the nanoboxes. (A-D) SEM images; (E-H) Corresponding PSD graphs determined by DCS under the same HAuCl4


14

Page 15 of 35 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


concentration (0.11 mM) with the concentration of AgNO3=0.022, 0.044, 0.099 and 0.132 mM, respectively. The yield of the nanoboxes kept increasing with the concentration of AgNO3 adjusted from 0.022 to 0.099 mM but decreased at AgNO3 concentration of 0.132 mM. The nanoboxes gradually increased the sizes with the increase of AgNO3 concentration. The amounts of reducing agent can affect the nucleation rate and nucleation concentration, and thus the sizes of the final products according to the nucleation-growth mechanism.29 The nanoboxes were thus synthesized with 1.5 and 23 times stoichiometric quantity of AA required for the reduction of HAuCl4 and AgNO3 to study the size variation. Unexpectedly, both types of nanoboxes showed similar sizes, probably because of the same amounts of nuclei generated by the mid-strong reducing agent AA.30 However, the morphology of the nanoboxes were significantly different under these two conditions. At 1.5 times stoichiometric quantity of AA, the nanoboxes possessed relatively smooth surfaces (Figure 5A, C). Furthermore, under this circumstance, the nanoboxes had a smaller size (~ 80 nm) by introducing AgNO 3 and AA simultaneously.31 Nevertheless, 23 times stoichiometric quantity of AA made the nanoboxes exhibit many nanodots with the sizes around 7-10 nm on the surfaces (Figure 5B, D), which was possibly derived from the reduction of residual Au or Ag precursor ions. Thus, the amount of AA affects the morphology of nanoboxes but not their sizes.


15


Page 16 of 35

Figure 5. The influence of AA amounts on the morphology of the nanoboxes. (A, C) SEM and TEM

images

of

the

nanoboxes

synthesized

with

the

molar

ratio

of

AA/(1.5HAuCl4+2AgNO3)=1.5; (B, D) SEM and TEM images of the nanoboxes prepared with the molar ratio of AA/(1.5HAuCl4+2AgNO3)=23. The SEM and TEM images indicated low concentration of AA generated relatively smooth nanoboxes while high concentration of AA facilitated the formation of nanodots on the nanobox surfaces.


16

Page 17 of 35 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


Low precursor concentration is a generally required condition to synthesize anisotropic NPs.32 As such, we investigated this effect by systematically adjusting the concentration of AgNO3 and HAuCl4 at the constant AgNO3/HAuCl4 molar ratio of 0.9. Compared to the nanoboxes synthesized at 0.11 mM HAuCl4 (Figure 1), many tetrahedral NPs started to blend in the products (Figure S3A) after lowered the HAuCl4 concentration to 0.075 mM, presumably due to the incomplete etching of twinned seeds.33 With the HAuCl4 concentration increased to 0.15 mM, around 60 % of nanoboxes were broken and the products became smaller in size. A further increase of HAuCl4 concentration can reduce the amounts of broken nanoboxes but at the expense of increasing multi-branched NPs (Figure S3C, D). The reasons for the morphological changes of nanoboxes caused by concentration are still under investigation. Therefore, the suitable HAuCl4 concentration for preparing nanoboxes was 0.11 mM. Temperature controls the reaction kinetics and thereby the final shape of the products.34 Thus, we changed the reaction temperature from 0 oC to 50 oC to study their relationship with the morphology of nanoboxes. Figure S4A shows the products became concave nanoboxes at 0 oC. When the reaction was performed at 15 oC, the prepared NPs (Figure S4B) were very similar to the nanoboxes obtained at 25 oC (Figure 1). However, with the increasing of temperature to 35 o

C and 50 oC, some irregular shaped NPs appeared in the products, such as nanorods and

nanotetrahedra (Figure S4C and D). Decreasing temperature favours more thermodynamically stable products, while raising temperature creates a preference for the growth of kinetically more favourable particle morphologies owing to the increased reduction rate. Therefore, the suitable temperature for the nanobox synthesis (15 oC to 25 oC) is more attractive compared with the high temperature (140-160 oC) required in the traditional method.


17


Page 18 of 35

3.3. Mechanism for the formation of the Au-Ag alloy nanoboxes. We propose a potential five-step formation mechanism for the nanoboxes (scheme 1) based on the above-mentioned systematic characterizations. In the first step, AgCl is generated due to the combination of Cl and Ag+. Under our experimental conditions, the calculated solubility product for cө(Ag+)×cө(Cl-) is 1.17×10-8, assuming one quarter of Cl- in HAuCl4 can be released. The relatively higher solubility product than the AgCl solubility product constant ksp at 25 oC (1.56×10-10)13 facilitates the formation of AgCl. The theoretical calculation is supported by the experimental phenomenon that an obviously milky white color appeared after adding AgNO3. The milky white product was highly sensitive to electron beam under SEM and TEM (Figure S5A, B), a characteristic commonly observed for AgCl.35 The XRD pattern (Figure S5C) of the milky white product further confirms the existence of AgCl as the peaks can be indexed to AgCl crystals (ICDD File Card No. 04-002-1174). In the second step, Au seeds are formed by the reduction of AuClxy- with AA. AuClxy- instead of AgCl is preferentially reduced by AA due to a higher standard reduction potential of AuClxy-/Au than AgCl/Ag.36 Then, the reaction proceeds to the third step, where the formed Au seeds can act as both nuclei and catalysts (the mediator of electron transfer) to catalyze the reduction of AgCl into Ag. The transformation from AgCl to Ag is believed to be complete considering the lack of AgCl peaks in the XRD pattern of the nanoboxes. Concurrently, Cl- derived from AuClxy- and AgCl can selectively bind to the (100) crystal facets of Ag.35 The capping effect of Cl- finally promotes the formation of cubic templates and agrees well with halides selectively stabilizing (100) facets of Au@Ag NPs.22 In the fourth step, a galvanic replacement reaction takes place between Ag in the cubic templates and AuClxy- driven by their large reduction potential differences. Ag layers are constantly


18

Page 19 of 35 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


oxidized into Ag+ while AuClxy- are reduced into Au, which is similar to Xia et.al’s work.13, 37-38 Meanwhile, the galvanic replacement reaction is accompanied by AA reduction to reduce the released Ag+ into Ag atoms and co-deposit with Au atoms. The final products inherit the underlying cubic shape of the templates and constitute Au-Ag alloy nanostructures. In the fifth step, the nanodots can be formed on the surfaces of the nanoboxes with an excess amount of AA. The co-reduction of residual AuClxy- and Ag+ instead of galvanic replacement reaction is believed to be responsible for the formation of the nanodots because of the relatively smooth nanoboxes obtained under the low concentrations of AA (Figure 5A, C).

Scheme 1. A potential five-step formation mechanism for the nanoboxes. The two black arrows on the top of the diagram illustrate the synthetic procedures of the nanoboxes, and the five reddotted arrows indicate the possible reactions that may involve in the synthesis process. Step 1: the formation of AgCl; Step 2: the generation of Au seeds; Step 3: the formation of Au@Ag


19


Page 20 of 35

nanocube template; Step 4: the formation of Au-Ag alloy nanobox with relatively smooth surfaces; Step 5: the formation of nanodots decorated Au-Ag alloy nanobox. We assume the slow release of Cl- by HAuCl4 helps maintain the final morphology of the nanoboxes. To prove this hypothesis, a control experiment was carried out by replacing HAuCl 4 into HCl and NaCl to mimic the role of Cl- in HAuCl4. As shown in Figure S6A, AgCl is obtained after mixing HCl, NaCl and AgNO3 as is the situation in HAuCl4. Nevertheless, in this case, the dominant products after AA reduction were spherical AgNPs instead of cubic NPs (Figure S6B). The formation of spherical NPs can be explained by the unreserved release of Clfrom HCl and NaCl, which exceeded the selectively deposition condition and thus caused the equal binding of all NP facets.39 HAuCl4, however, can release Cl- progressively according to the previous reports.29,

40

This property is advantageous to produce the nanoboxes. Specifically,

HAuCl4 can release part of Cl- to combine with Ag+ forming AgCl first. Then, following the generation of Au seeds, some Cl- can be released as a consequence. These Cl- participates in the capping of (100) planes of AgNPs and greatly facilitates the formation of cubic NPs. Finally, the remaining Cl- in HAuCl4 are relinquished after the galvanic replacement reaction. 3.4. SERS activity of the Au-Ag alloy nanoboxes. In comparison with spherical NPs, nanoboxes possess high curvature features, which can generate strong electromagnetic fields serving as hot spots for high SERS enhancement.27 To prove the high SERS activity of the nanoboxes, they were compared with the 60-80 nm AuNPs that are believed to produce the strongest SERS signals in spherical AuNPs3 and AgNPs. These NPs with the same concentration (2.8 × 109 particles/mL) determined by NanoSight were functionalized with MBA as Raman reporters to enable the direct comparison of SERS signal enhancement. As shown in Figure S7A, the nanodot decorated nanoboxes shows about 10 times and 3.2 times stronger signals than that


20

Page 21 of 35 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


of AuNPs and AgNPs, respectively. This result agrees well with the reports in the literature7, 41 that Au-Ag alloy NPs have a stronger SERS activity than those NPs made of pure Au and Ag. Additionally, we compared the SERS enhancement capability of the nanodot decorated nanoboxes with the relatively smooth nanoboxes and the unoptimized products obtained in Figure 4A, B, and D (Figure S7B), where the nanodot decorated nanoboxes showed the strongest SERS activity. There are two potential reasons responsible for the higher SERS activity of the nanodot decorated nanoboxes than the relatively smooth nanoboxes: (1) the abundant hot spots generated by the nanodots on the surfaces; (2) the more Raman reporters adsorbed on the surfaces of the nanodot decorated nanoboxes due to the increased surface area. As expected, the unoptimized products generated lower SERS signals owing to the low yields of the nanoboxes. Taken together, the nanodot decorated nanoboxes can provide stronger SERS signals and are better substrates than the traditional AuNPs and AgNPs. SERS enhancement factor (EF) was introduced to evaluate the Raman enhancement activity of the nanodot decorated nanoboxes based on the following formula: EF = (ISERS/NSERS)/(IRS/NRS) (1) where ISERS and IRS are the Raman intensities for SERS and Raman measurements, respectively; NSERS and NRS are the adsorbed number of Raman reporters on the substrates for SERS measurements and the number of Raman reporters for Raman measurements, respectively. Based on the Raman spectra in Figure S8, the calculated EF was about 1 × 106 (more details in SI), which is higher than silver@carbon nanoparticles,42 silver-graphene hybrid nanoparticles43 and comparable to the reported nanoboxes.7


21


Page 22 of 35

We further studied the reproducibility and stability of the nanodot decorated nanoboxes as SERS substrates. The consistent SERS spectra of MBA enhanced by five batches of the nanoboxes (Figure S9A) illustrated the reproducible results. Meanwhile, no obvious shift in Raman peaks or significant changes in Raman intensities occurred in the different time points (day 1, day 3, day 5, and day7) (Figure S9B), which demonstrated the good spectral stability of the nanoboxes acting as SERS substrates. 3.5. Theoretical modelling and single-particle SERS activity of the Au-Ag alloy nanoboxes. To validate the SERS enhancement produced by the nanoboxes, we theoretically investigated the distribution of optical fields in the near-field zone of the nanoboxes by using CST Microwave Studio 2016 commercial software. CST Microwave Studio solves Maxwell’s equations in either the time or frequency domain and allows modelling the optical properties of metal nanostructures by using a built-in database of complex refractive indices and Drude dispersion models. We conducted simulations on a model nanobox with 120 nm outer edge length and 15 nm wall thickness. The composition of the nanobox was assumed as pure Ag, because the exact dielectric permittivity values for the real constituent material of the nanoboxes were not available and the nanoboxes had a higher Ag amounts with the Ag/Au molar ratio of 0.94. In the spectral range of interest, a Drude model of the dielectric function of Ag44 serves as a good approximation suitable for a qualitative analysis. To simulate the impact of the nanodots on the plasmonic properties, 7 nm Ag spheres were periodically distributed on all edges of the nanobox. Although the real nanodot distribution can be different, this approximation is warranted as we aim to investigate the physics of the impact of nanodots rather than to reproduce a quantitative effect originating from them. We also note that modelling of the exact nanodot distribution


22

Page 23 of 35 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


taken, for instance, from a SEM image would be challenging, if not impossible, because of significant computational requirements and nanobox to nanobox variability. Figure 6A shows the calculated |E|4-field spectrum and reveals a strong plasmon resonance around ~830 nm. The discrepancy between the plasmon resonance wavelength of the simulated and experimental (~ 673 nm, Figure 2H) may be due to the following factors, each of which is known to result in significant spectral shifts of plasmon resonances. Firstly, in our model, we use the Drude model of Ag to simulate the optical properties of the nanobox. However, the real dielectric function may be different. Secondly, the dimensions of the nanobox used in our model may not exactly coincide with those of the real nanoboxes. Finally, the numerical methods used in the CST Microwave Studio are known to produce artificial shifts in the optical spectra even when a fine meshing is used. Figure 6B shows the corresponding spatial |E|4-field distribution. The optical field intensity near the surfaces of the nanobox paralleling to the y-axis is stronger than the intensity near the remaining surfaces, because the incident light is polarised along the xaxis and therefore the plasmon enhancement is much stronger across this coordinate direction. Simulations with the incident light polarised along the y-axis produce the same picture by rotating 90o. The maximum of the field intensity is observed near the corners of the nanobox and the junctions of the nanodots, which is consistent with the common observations of stronger local optical fields near sharp and narrow metal features, such as sharp corners, tips, gaps, and cracks. 45-46 Although the surface roughness is approximated by small spheres, our modelling serves as a good approximation producing good agreement with the SERS enhancement experiment (Figure S7). We also conducted simulations of a nanobox with perfectly flat surfaces without nanodots and observed peak values of |E|4 of ~600 (data not shown), which is well below the |E|4-values


23


Page 24 of 35

for the nanobox with nanodots. Thus, our simulations confirm the crucial role of the nanodots in enhancing optical fields by generating high density of hot spots on the nanobox surfaces.

Figure 6. Theoretical simulation of the optical field for a single nanobox with nanodots. (A) Average |E|4- field spectrum demonstrating the plasmon resonance enhancement at ~830 nm. This calculated wavelength red shifted compared to the experimental result (~673 nm); (B) |E|4field profile at the plasmon resonance at 830 nm. The color bar in panel (B) is slightly oversaturated for the sake of illustration. This profile demonstrated the greatly enhanced electromagnetic field near the corners of the nanobox and the junctions of the nanodots. The abundant hot spots on the nanobox surfaces illustrated by the simulation inspired us to further explore their single-particle SERS activity. Here, we used non-resonant Raman reporter (MBA) to functionalize the nanoboxes to ensure the enhanced Raman signal is contributed from the electromagnetic field around the nanoboxes. SEM image (Figure 7A) shows three separated individual nanoboxes, and the corresponding Raman mapping image (Figure 7B) indicates a similar pattern with three distinctly bright spots. The Raman spectrum derived from the bright spot (Figure 7C) clearly demonstrates two characteristic peaks (1080 cm-1 and 1585 cm-1) from


24

Page 25 of 35 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


MBA,47 while the black area (Figure 7D) only shows signals from silica wafer (948 cm-1). It is worth noting that the different noise levels in Figure 7C and D could be due to the different Raman scattering on MBA functionalized nanoboxes and silica wafer. The consistent results between Raman mapping and SEM images confirm the single-particle SERS activity of the nanoboxes. On the contrary, the most widely used spherical AuNPs or AgNPs are reported to be non-SERS-active for the single particle.48 Thus, the single-particle active nanoboxes can facilitate highly sensitive and reliable SERS detection.49

Figure 7. Single-particle SERS activity of the nanoboxes. (A) SEM image of the nanoboxes on the silica wafer; (B) SERS mapping of the nanoboxes corresponding to (A); (C) SERS spectrum of MBA from the dashed red circle in figure (B); (D) SERS spectrum from the dashed blue circle in figure (B). 4. CONCLUSIONS


25


Page 26 of 35

In summary, compared with the complex and surfactant involved method for preparing nanoboxes, we have demonstrated a simple, rapid and environmentally friendly strategy to synthesize the nanodot decorated nanoboxes as SERS plasmonic nanostructures. The nanoboxes can be prepared by the reduction of HAuCl4 and AgNO3 with AA in aqueous solutions at room temperature without toxic reagents. The concentration of AgNO3 controls the yield of the nanoboxes. Excess amounts of AA retain Ag contents and contribute to the formation of the nanodots on the surfaces, both of which are beneficial to SERS enhancement. A potential mechanism for the evolution of the nanodot-decorated Au-Ag alloy nanoboxes has been proposed based on the various systematic characterizations, including EDS, HR-TEM, SAED, XPS and XRD. Furthermore, the single-particle SERS activity can be achieved for the nanodot decorated nanoboxes, of which the nanodots play a significant role as indicated by theoretical modelling. We envision the as-prepared nanoboxes can act as highly sensitive SERS substrates for cancer diagnosis and biosensing. ASSOCIATED CONTENT Supporting Information. The Supporting Information is free of charge. EDS spectrum, and XRD pattern of the nanoboxes; SEM images for the influence of HAuCl4 concentration and temperature on the synthesis of the nanoboxes; SEM, TEM images and XRD pattern obtained by mixing HAuCl4 and AgNO3; SEM, TEM images for the products prepared by replacing HAuCl4 with HCl and NaCl; SERS spectra comparison enhanced by different plasmonic nanostructures; EF calculation; and Raman enhancement reproducibility and stability studies of the nanodot-decorated nanoboxes. AUTHOR INFORMATION


26

Page 27 of 35 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


Corresponding Author *Email: [email protected] (A. S.) *Email: [email protected] (Y. W.) *Email: [email protected] (M. T.) Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by Australian Research Council (ARC) Discovery Project (DP160102836), and the National Breast Cancer Foundation of Australia (CG-12-07). We also thank the support of the ARC through its Centre of Excellence for Nanoscale BioPhotonics (CE140100003), Future Fellowship (FT1600357), and LIEF program (LE160100051). We appreciate to receive the technical and scientific guidance from the Australian Microscopy& Microanalysis (CMM) Research Facility in The University of Queensland. Queensland node of the Australian National Fabrication Facility (Q-ANFF) provided the assistance in Raman measurements. The simulation was undertaken on the NCI National Facility in Canberra, supported by the Australian Commonwealth Government. We also thank Dr. Kevin M. Koo for helping us revise the manuscript. Junrong Li and Jing Wang want to thank the support from Australian Government Research Training Program (RTP). REFERENCES (1) Nie, S.; Emory, S. R. Probing Single Molecules and Single Nanoparticles by SurfaceEnhanced Raman Scattering. Science 1997, 275, 1102-1106.


27


Page 28 of 35

(2) Wang, Z.; Zong, S.; Wu, L.; Zhu, D.; Cui, Y. SERS-Activated Platforms for Immunoassay: Probes, Encoding Methods, and Applications. Chem. Rev. 2017, 117, 7910-7963. (3) Wang, Y.; Yan, B.; Chen, L. SERS Tags: Novel Optical Nanoprobes for Bioanalysis. Chem. Rev. 2013, 113, 1391-1428. (4) Reguera, J.; Langer, J.; Jimenez de Aberasturi, D.; Liz-Marzan, L. M. Anisotropic Metal Nanoparticles for Surface Enhanced Raman Scattering. Chem. Soc. Rev. 2017, 46, 3866-3885. (5) Yang, Y.; Zhang, Q.; Fu, Z. W.; Qin, D. Transformation of Ag Nanocubes into Ag-Au Hollow Nanostructures with Enriched Ag Contents to Improve SERS Activity and Chemical Stability. ACS Appl. Mater. Interfaces 2014, 6, 3750-3757. (6) Liu, S.; Chen, G.; Prasad, P. N.; Swihart, M. T. Synthesis of Monodisperse Au, Ag, and Au-Ag Alloy Nanoparticles with Tunable Size and Surface Plasmon Resonance Frequency. Chem. Mater. 2011, 23, 4098-4101.

(7) Li, J.-M.; Yang, Y.; Qin, D. Hollow Nanocubes Made of Ag-Au Alloys for SERS Detection with Sensitivity of 10-8 M for Melamine. J. Mater. Chem. C 2014, 2, 9934-9940. (8) Sun, Y.; Xia, Y. Shape-Controlled Synthesis of Gold and Silver Nanoparticles. Science 2002, 298, 2176-2179. (9) Ma, Y.; Li, W.; Cho, E. C.; Li, Z.; Yu, T.; Zeng, J.; Xie, Z.; Xia, Y. Au@Ag Core-Shell Nanocubes with Finely Tuned and Well-Controlled Sizes, Shell Thicknesses, and Optical Properties. ACS Nano 2010, 4, 6725-6734. (10) Frens, G. Controlled Nucleation for the Regulation of the Particle Size in Monodisperse Gold Suspensions. Nature 1973, 241, 20-22.


28

Page 29 of 35 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) Lee, P. C.; Meisel, D. Adsorption and Surface-Enhanced Raman of Dyes on Silver and Gold Sols. J. Phys. Chem. 1982, 86, 3391-3395. (12) Cheng, L.-C.; Huang, J.-H.; Chen, H. M.; Lai, T.-C.; Yang, K.-Y.; Liu, R.-S.; Hsiao, M.; Chen, C.-H.; Her, L.-J.; Tsai, D. P. Seedless, Silver-Induced Synthesis of Star-Shaped Gold/Silver Bimetallic Nanoparticles as High Efficiency Photothermal Therapy Reagent. J. Mater. Chem. 2012, 22, 2244-2253. (13) Sun, Y.; Xia, Y. Mechanistic Study on the Replacement Reaction between Silver Nanostructures and Chloroauric Acid in Aqueous Medium. J. Am. Chem. Soc. 2004, 126, 38923901. (14) Jiang, T.; Song, J.; Zhang, W.; Wang, H.; Li, X.; Xia, R.; Zhu, L.; Xu, X. Au-Ag@Au Hollow Nanostructure with Enhanced Chemical Stability and Improved Photothermal Transduction Efficiency for Cancer Treatment. ACS Appl. Mater. Interfaces 2015, 7, 2198521994. (15) Huang, J.; Vongehr, S.; Tang, S.; Lu, H.; Shen, J.; Meng, X. Ag Dendrite-Based Au/Ag Bimetallic Nanostructures with Strongly Enhanced Catalytic Activity. Langmuir 2009, 25, 11890-11896. (16) Chen, L.; Chabu, J. M.; Jin, R.; Xiao, J. Single Gold-Nanoparticles-Decorated Silver/Carbon Nanowires as Substrates for Surface-Enhanced Raman Scattering Detection. RSC Adv. 2013, 3, 26102-26109.


29


Page 30 of 35

(17) Luo, Z.; Yuan, X.; Yu, Y.; Zhang, Q.; Leong, D. T.; Lee, J. Y.; Xie, J. From AggregationInduced Emission of Au(I)-Thiolate Complexes to Ultrabright Au(0)@Au(I)-Thiolate Core-Shell Nanoclusters. J. Am. Chem. Soc. 2012, 134, 16662-16670. (18) Kim, M.-J.; Na, H.-J.; Lee, K. C.; Yoo, E. A.; Lee, M. Preparation and Characterization of Au-Ag and Au-Cu Alloy Nanoparticles in Chloroform. J. Mater. Chem. 2003, 13, 1789-1792. (19) Han, S. W.; Kim, Y.; Kim, K. Dodecanethiol-Derivatized Au/Ag Bimetallic Nanoparticles: TEM, UV/VIS, XPS, and FTIR Analysis. J. Colloid Interface Sci. 1998, 208, 272-278. (20) Zhang, G.; Du, M.; Li, Q.; Li, X.; Huang, J.; Jiang, X.; Sun, D. Green Synthesis of Au-Ag Alloy Nanoparticles Using Cacumen Platycladi Extract. RSC Adv. 2013, 3, 1878-1884. (21) Londono-Calderon, A.; Bahena, D.; Yacaman, M. J. Controlled Synthesis of Au@AgAu Yolk-Shell Cuboctahedra with Well-Defined Facets. Langmuir 2016, 32, 7572-7581. (22) Gómez-Graña, S.; Goris, B.; Altantzis, T.; Fernández-López, C.; Carbó-Argibay, E.; Guerrero-Martínez, A.; Almora-Barrios, N.; López, N.; Pastoriza-Santos, I.; Pérez-Juste, J.; Bals, S.; Van Tendeloo, G.; Liz-Marzán, L. M. Au@Ag Nanoparticles: Halides Stabilize {100} Facets. J. Phys. Chem. Lett. 2013, 4, 2209-2216. (23) Personick, M. L.; Langille, M. R.; Zhang, J.; Mirkin, C. A. Shape Control of Gold Nanoparticles by Silver Underpotential Deposition. Nano Lett. 2011, 11, 3394-3398. (24) Vassalini, I.; Rotunno, E.; Lazzarini, L.; Alessandri, I. “Stainless” Gold Nanorods: Preserving Shape, Optical Properties, and SERS Activity in Oxidative Environment. ACS Appl. Mater. Interfaces 2015, 7, 18794-18802.


30

Page 31 of 35 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) Wiley, B.; Herricks, T.; Sun, Y.; Xia, Y. Polyol Synthesis of Silver Nanoparticles: Use of Chloride and Oxygen to Promote the Formation of Single-Crystal, Truncated Cubes and Tetrahedrons. Nano Lett. 2004, 4, 1733-1739. (26) Chew, W. S.; Pedireddy, S.; Lee, Y. H.; Tjiu, W. W.; Liu, Y.; Yang, Z.; Ling, X. Y. Nanoporous Gold Nanoframes with Minimalistic Architectures: Lower Porosity Generates Stronger Surface-Enhanced Raman Scattering Capabilities. Chem. Mater. 2015, 27, 7827-7834. (27) Sau, T. K.; Rogach, A. L.; Doblinger, M.; Feldmann, J. One-Step High-Yield Aqueous Synthesis of Size-Tunable Multispiked Gold Nanoparticles. Small 2011, 7, 2188-2194. (28) Pérez-Juste, J.; Liz-Marzán, L. M.; Carnie, S.; Chan, D. Y. C.; Mulvaney, P. ElectricField-Directed Growth of Gold Nanorods in Aqueous Surfactant Solutions. Adv. Funct. Mater. 2004, 14, 571-579. (29) Ji, X.; Song, X.; Li, J.; Bai, Y.; Yang, W.; Peng, X. Size Control of Gold Nanocrystals in Citrate Reduction: The Third Role of Citrate. J. Am. Chem. Soc. 2007, 129, 13939-13948. (30) Ahmed, W.; Kooij, E. S.; Van Silfhout, A.; Poelsema, B. Controlling the Morphology of Multi-Branched Gold Nanoparticles. Nanotechnology 2010, 21, 125605. (31) Li, J.; Wang, J.; Grewal, Y. S.; Howard, C. B.; Raftery, L. J.; Mahler, S.; Wang, Y.; Trau, M. Multiplexed SERS Detection of Soluble Cancer Protein Biomarkers with Gold–Silver Alloy Nanoboxes and Nanoyeast Single-Chain Variable Fragments. Anal. Chem. 2018, DOI: 10.1021/acs.analchem.8b02216. (32) Xie, J.; Zhang, Q.; Lee, J. Y.; Wang, D. I. The Synthesis of SERS-Active Gold Nanoflower Tags for in vivo Applications. ACS Nano 2008, 2, 2473-2480.


31


Page 32 of 35

(33) Im, S. H.; Lee, Y. T.; Wiley, B.; Xia, Y. Large-Scale Synthesis of Silver Nanocubes: The Role of HCl in Promoting Cube Perfection and Monodispersity. Angew. Chem. Int. Ed. 2005, 117, 2192-2195. (34) Langille, M. R.; Personick, M. L.; Zhang, J.; Mirkin, C. A. Defining Rules for the Shape Evolution of Gold Nanoparticles. J. Am. Chem. Soc. 2012, 134, 14542-14554. (35) Zhou, S.; Li, J.; Gilroy, K. D.; Tao, J.; Zhu, C.; Yang, X.; Sun, X.; Xia, Y. Facile Synthesis of Silver Nanocubes with Sharp Corners and Edges in an Aqueous Solution. ACS Nano 2016, 10, 9861-9870. (36) Joo, J. H.; Kim, B. H.; Lee, J. S. Synthesis of Gold Nanoparticle-Embedded Silver Cubic Mesh Nanostructures Using AgCl Nanocubes for Plasmonic Photocatalysis. Small 2017, 13, 1701751. (37) Ma, Y.; Li, W.; Cho, E. C.; Li, Z.; Yu, T.; Zeng, J.; Xie, Z.; Xia, Y. Au@Ag Core-Shell Nanocubes with Finely Tuned and Well-Controlled Sizes, Shell Thicknesses, and Optical Properties. ACS Nano 2010, 4, 6725-34. (38) Skrabalak, S. E.; Chen, J.; Sun, Y.; Lu, X.; Au, L.; Cobley, C. M.; Xia, Y. Gold Nanocages: Synthesis, Properties, and Applications. Acc. Chem. Res. 2008, 41, 1587-1595. (39) Seo, D.; Park, J. C.; Song, H. Polyhedral Gold Nanocrystals with Oh Symmetry: From Octahedra to Cubes. J. Am. Chem. Soc. 2006, 128, 14863-14870. (40) Balasubramanian, S.; Bezawada, S. R.; Dhamodharan, R. Facile Aqueous Phase Synthesis of (200) Faceted Au-AgCl Cubes Using Bael Gum and Its Activity Toward Oxidation and Detection of o-PDA. ACS Sustain. Chem. Eng. 2016, 4, 2960-2968.


32

Page 33 of 35 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


(41) Fan, M.; Lai, F.-J.; Chou, H.-L.; Lu, W.-T.; Hwang, B.-J.; Brolo, A. G. Surface-Enhanced Raman Scattering (SERS) from Au:Ag Bimetallic Nanoparticles: the Effect of the Molecular Probe. Chem. Sci. 2013, 4, 509-515. (42) Yang, D.; Xia, L.; Zhao, H.; Hu, X.; Liu, Y.; Li, J.; Wan, X. Preparation and Characterization of an Ultrathin Carbon Shell Coating a Silver Core for Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy. Chem. Commun. 2011, 47, 5873-5875. (43) Fan, W.; Lee, Y. H.; Pedireddy, S.; Zhang, Q.; Liu, T.; Ling, X. Y. Graphene Oxide and Shape-Controlled Silver Nanoparticle Hybrids for Ultrasensitive Single-Particle SurfaceEnhanced Raman Scattering (SERS) Sensing. Nanoscale 2014, 6, 4843-4851. (44) Smith, D.; Shiles, E.; Inokuti, M.; Palik, E. Handbook of Optical Constants of Solids. Handbook of Optical Constants of Solids 1985, 1, 369-406. (45) Baginskiy, I.; Lai, T.-C.; Cheng, L.-C.; Chan, Y.-C.; Yang, K.-Y.; Liu, R.-S.; Hsiao, M.; Chen, C.-H.; Hu, S.-F.; Her, L.-J.; Tsai, D. P. Chitosan-Modified Stable Colloidal Gold Nanostars for the Photothermolysis of Cancer Cells. J. Phys. Chem. C 2013, 117, 2396-2410. (46) Zhang, T.; Zhou, F.; Hang, L.; Sun, Y.; Liu, D.; Li, H.; Liu, G.; Lyu, X.; Li, C.; Cai, W.; Li, Y. Controlled Synthesis of Sponge-Like Porous Au-Ag Alloy Nanocubes for SurfaceEnhanced Raman Scattering Properties. J. Mater. Chem. C 2017, 5, 11039-11045. (47) Wang, Y.; Salehi, M.; Schutz, M.; Schlucker, S. Femtogram Detection of Cytokines in a Direct Dot-Blot Assay Using SERS Microspectroscopy and Hydrophilically Stabilized Au-Ag Nanoshells. Chem. Commun. 2014, 50, 2711-2714.


33


Page 34 of 35

(48) Zhang, Y.; Walkenfort, B.; Yoon, J. H.; Schlucker, S.; Xie, W. Gold and Silver Nanoparticle Monomers are Non-SERS-Active: a Negative Experimental Study with SilicaEncapsulated Raman-Reporter-Coated Metal Colloids. Phys. Chem. Chem. Phys. 2015, 17, 21120-21126. (49) Qian, X. M.; Nie, S. M. Single-Molecule and Single-Nanoparticle SERS: from Fundamental Mechanisms to Biomedical Applications. Chem. Soc. Rev. 2008, 37, 912-920.


34

Page 35 of 35 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


TOC 35x15mm (300 x 300 DPI)


Facile One-Pot Synthesis of Nanodot-Decorated GoldâSilver Alloy

Recommend Documents

Facile One-Pot Synthesis of Nanodot-Decorated GoldâSilver Alloy