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In the process of preparing a solid surface-enhanced Raman scattering (SERS) substrate, there is a need to devise a simple and efficient method that will ensure an even distribution of nanoparticles (NPs) on the surface of the solid substrate. In this study, silver NP (Ag NP) colloids, with different particle sizes, were prepared by adjusting the pH value, and anodized aluminium oxide (AAO) was used as a template to assemble Ag NPs into AAO holes using interface self-assembly technology. Due to the limiting effect of the AAO template, the distribution of Ag NPs on the substrate was uniform. With 4-mercaptobenzoic acid (4-MBA) as a probe, the sensitivity of this SERS substrate was evaluated, with an analysis enhancement factor (AEF) of up to 1.17 × 106. In addition, the signal repeatability of this SERS substrate was excellent, with a relative standard deviation (RSD) of 6.45%, and the SERS signal was basically consistent within a period of 30 days. Furthermore, the SERS identification of levofloxacin in milk was demonstrated, with a minimum detection limit of 1.88 × 10−6 M. Additionally, within the concentration range of 1 × 10−6 to 2 × 10−5 M, the levofloxacin concentration had a linear relationship with its SERS intensity, with a linear correlation coefficient as high as 0.986. The recovery rate was estimated to be between 97.61% and 107.58%, indicating the reliability of this SERS method. This simple and rapid approach is expected to be applied for the on-site measurement of antibiotics in food.

A portable and highly reproducible lab-on-capillary surface-enhanced Raman scattering (SERS) platform was developed using a specially designed homemade device for rapid on-site SERS measurement. In particular, this platform was composed of a capillary with a tiny orifice, which allows an effective and lossless sample extraction, resulting in high SERS performance. The capillary-based plasmonic substrate was prepared by compactly assembling Au@Ag core-shell nanorods (NRs) embedded with the 4-mercaptobenzoic acid (4-MBA) molecule as an internal standard onto the inner wall of a capillary tube. The fabrication process is facile and convenient with no requirement for complicated procedures. The exclusively prepared nanoparticles were able to significantly improve the signal consistency and overcome the limitations of reliable quantitative SERS analysis compared with conventional methods. Importantly, it was found that this capillary-based substrate with higher sensitivity was essentially attributed to more valid nanoparticles in the effective laser excitation region derived from the unique structure of the capillary. Furthermore, the applicability of the Au@4-MBA@Ag nanorod-decorated capillary for the quantitative identification of fungicides (malachite green and crystal violet) on the shell was demonstrated. As a result, this proposed lab-on-capillary sensor holds promising practical potential for rapid on-site analysis, especially for various contaminants on an uneven surface.

This paper described how a high-yield, monodisperse Au nanobipyramids (Au NBs) sol was prepared by a seed-mediated method, and gold nanoparticles were assembled on the surface of a silicon wafer by self-assembly technology to obtain a solid SERS substrate. Scanning electron microscopy (SEM) showed that the average length of Au NBs was 34.31 nm, and the analysis enhancement factor (AEF) was approximately 7.3 × 105 with rhodamine 6G (R6G) used as a probe. SERS detection of chlortetracycline hydrochloride (CCH) in milk was performed utilizing the prepared Au NBs substrate, and the limit of detection was 0.01 mg/mL. In the range of 0.01 - 1 mg/mL, the mass concentration of CCH and the SERS signal intensity satisfied the linear relationship y = 258.467x + 150.501; the value of the correlation coefficient was 0.9785. In addition, the recovery of spiked samples fluctuated between 96.80 to 111.38%. These results proved that the method is simple and fast, and it is promising to be applied to the field detection of antibiotics in milk.

An efficient and facile strategy for producing core-shell Au@Ag nanorods (NRs) with controllable width and length as excellent surface enhanced Raman scattering (SERS) substrate was proposed. Au nanodipyramids (NDPs) of three various widths were prepared by overgrowth along the radial orientation, and together with Au NDPs as seed, silver was deposited in the axial orientation to successfully obtain core-shell Au@Ag NRs with diverse length (73 nm–157 nm) and width (25 nm–43 nm). The morphology, optical properties and SERS performance of the as-synthesized Au@Ag NRs were investigated systematically. The broadly tunable UV-Vis absorption range for Au@Ag NRs as far as the near-infrared (NR) region was able to be obtained. Furthermore, the SERS property of Au@Ag NRs two-dimensional monolayer was explored by using crystal violet (CV) as Raman probe. The optimal SERS enhancement effect with enhancement factor (EF) as high as 6.13✕105 could be achieved for Au@Ag NRs with wider width and longer length, which was confirmed by the simulation results of electromagnetic (EM) field distribution by FDTD method. Our novel approach provides some facinating insights into adjusting the width of Au@Ag NRs, which also significantly influences the SERS behaviors of the Au@Ag NRs. It allows to fabricating SERS substrate with superior SERS performance compared to previously reported Au@Ag NRs only with tunable length via direct overgrowth. Besides, this as-compounded Au@Ag NRs are expected to have promising application and significant value in other fields.

In this work, self-assembly monolayers of faceted gold nanocrystals were employed as surface-enhanced Raman scattering (SERS) substrates for the examination of facet-dependent SERS performance. In ...

Surface-enhanced Raman spectroscopy (SERS) has gradually proved to be a powerful tool with wide applications in various fields. Here, a simple and rapid SERS method was developed for the determination of ketamine in urine based on silver aggregates as a SERS substrate. Ketamine in urine were demonstrated by the SERS technique with silver sol aggregated by a 0.5 M NaBr solution. The limit of detection for ketamine in urine could be obtained as low as 7.5 ppm, and a linear relationship for ketamine in urine between the Raman intensity and the concentrations was achieved in the range from 7.5 to 150 ppm (R2 = 0.977). Additionally, the recovery of this method ranged from 95.7 to 104.9%, which laid a favorable foundation for the rapid and reliable quantitative detection of ketamine in urine. Therefore, this SERS approach with high sensitivity and simplicity has a great prospect for the real-world application of ketamine in urine.

In this work, a dual-functional SERS platform was developed via a paper-based SERS substrate with the aid of hydrophobic polydimethylsiloxane (PDMS) for effective and reliable measurements of thiram on fruit surfaces and in juice. Specifically, the paper-based SERS substrate was fabricated by coating with a core-shell Au@Ag nanorod monolayer, and the SERS performance was optimized compared with multilayer adsorption. Moreover, a versatile SERS platform was constructed by simply pasting the paper-based substrate in reverse onto PDMS using polymethyl methacrylate (PMMA) tape. On the one hand, this detection platform was able to realize sample enrichment due to the excellent hydrophobicity of PDMS, thereby increasing the sensitivity of measurements, and its function was successfully displayed through the identification of thiram in orange juice. On the other hand, PDMS could also play a supporting role and the paper-based substrate reversely stuck on PDMS was able to extract samples on the side without nanoparticles, which greatly avoids damage to nanoparticles on the substrate. Therefore, the accuracy of analysis was significantly improved and the inspection of thiram on the surface of an orange was demonstrated based on this function. As a result, this proposed SERS platform provides a new strategy for preparing multifunctional SERS sensors for the on-site monitoring of chemical contaminants in the food-safety field.

Pesticide residues have been the focus of widespread attention in the field of food safety. Here, we describe a new portable polydimethylsiloxane (PDMS) flexible surface-enhanced Raman spectroscopy (SERS) substrate decorated with silver-coated gold nanocubes (Au@Ag NCs) to rapidly measure pesticide residues on the surface of agricultural products. The finite difference time domain (FDTD) method and density functional theory (DFT) were used to optimize the preparation of the substrates, and the attribution of the imazalil (IMZ) characteristic peaks is discussed in detail. The relationship between the concentration obtained by in situ SERS detection and the maximum residue limits (MRLs) of pesticides was established accurately by three mass measurements. The minimum pesticide concentration on the surface could reach 2 mg L−1, which corresponds to an apple's MRL of just 0.073 mg kg−1. The feasibility of this method was further verified by the detection of phosmet pesticide residues. The results demonstrated that the method has great potential for detection of low-concentration pesticides.

In this investigation, surface-enhanced Raman spectroscopy (SERS) technology was performed to detect bucinnazine hydrochloride (BH) injection in water and urine. The theoretical Raman spectrum of BH with characteristic peaks was calculated and identified by density functional theory (DFT). Employing an improved silver sol as a SERS active substrate, the SERS spectra of a BH solution with different concentrations were acquired with a 0.5 mol/L KI solution as an aggregation agent. It was determined that the limit of detection (LOD) was low, to 0.01 μg/mL. A good linear relationship of BH between the Raman intensity and the concentrations was obtained in water at a concentration range from 0.5 to 6 μg/mL (R2 = 0.9914), which laid a favorable foundation for quantitative analysis. In addition, the recovery rate of spiked samples from 95.13 to 120.54% were calculated. Finally, the detection of BH injection in artificial urine was completed and the detection limit could reach 0.5 μg/mL, which met the requirements of a rapid on-site detection of drugs in urine. As a result, it indicates that the inspection of BH by the SERS method is with simplicity and high sensitivity, having a great potential for real-time detection.

Because of their perfect geometrical symmetry, spherical metal nanoparticles have attracted much attention for various applications, including fundamental studies and construction of plasmonic devices. In this work, monodisperse silver nanospheres (Ag NSs) in aqueous solution were directly prepared by a continuous process of seed-mediated growth followed by oxidative etching. Silver nanocubes (Ag NCs) were synthesized by a seed-mediated growth method and subsequently were transformed to Ag NSs by simple injection of Cu2+ to the freshly prepared Ag NCs solution. Not requiring any centrifugation steps at both growth and etching stages makes this procedure convenient and efficient. The etching process and morphology evolution of silver nanostructure were monitored by UV–vis spectromater, SEM, and XRD. Monodisperse Ag NSs with broadly tunable diameters (from 37 to 68 nm) have been successfully prepared. The optical property of Ag NSs has been studied and the experimental results show fairly good consistency w...

Large-scale ordered two-dimensional (2D) superlattices at oil/water interface were fabricated using single-crystal Au nanospheres (NSs) with different diameters as building blocks. A “drain-to-deposit” strategy was used to successfully transfer the ordered superlattices onto silicon wafer. Due to the ultra-smooth and highly spherical morphology of the monodisperse Au NSs, the UV-Vis extinction spectra of individual Au nanosphere (NS) obtained from theoretical calculations by finite-difference time-domain (FDTD) method could match well with the experimental test results. Moreover, the extinction spectra of the 2D superlattice based on the different diameters of Au NSs were also measured and calculated. Additionally, with R6G as probe molecules, the surface-enhanced Raman spectroscopy (SERS) performances of the prepared superlattices were evaluated. Through investigating the electromagnetic (EM) field distribution simulation results of 2D superlattices of Au NSs with different diameters, the two results reveal rather consistently. The large-scale 2D plasmonic superlattices possess precise and tunable localized surface plasmon resonance (LSPR) property, which enables them to have great application prospect in solar cells, SERS detection, and other fields.

Surface enhanced Raman spectroscopy (SERS) has emerged as a powerful spectroscopic tool, which offers information about the vibrational modes of molecules. However, performing quantitative analysis using SERS still faces great challenges. Here, we report a facile and reliable strategy for quantitative SERS determination using Au@Ag core–shell nanocubes (NCs) embedded with an internal standard (4-methylthiobenzoic acid) as the SERS substrate. To optimize the SERS property, Au@Ag NCs with finely tuned edge lengths in the range of 46 nm to 82 nm were synthesized. Au@Ag NCs with four different edge lengths were assembled into monolayer films using an interfacial self-assembly technique and transferred onto a silicon wafer. Their SERS performance was investigated using crystal violet (CV) as a target molecule and the corresponding electromagnetic (EM) near-field distribution was calculated using the FDTD method. The results clearly indicate that Au@Ag NCs with an edge length of 56 nm possess the highest Raman enhancement. Furthermore, we employed the Au@Ag NCs with an edge length of 56 nm, embedded with 4-methylthiobenzoic acid (4-MBA) as an internal reference, for quantitative SERS determination. Successful quantitative SERS measurements were demonstrated for CV in water and aspartame (APM) in drinks as analytes. The use of an internal standard and a monolayer film as a SERS substrate in solid form reduced the variability of the SERS signal and improved the reproducibility of the SERS response. To sum up, our approach is versatile and effective, and has the potential for the on-site quantitative detection of a wide variety of analytes.

In this study, surface-enhanced Raman spectroscopy (SERS) technology was used to rapidly detect illegally added sildenafil drugs. A detailed attribution analysis by density functional theory (DFT) was used to guide specific experiments. The Raman signals were obtained from a silver colloid (Ag col) substrate, and they increased in the presence of the mineral salt, potassium iodide (KI). These methods detected sildenafil in aqueous solutions as low as 1 µg/mL with high signal uniformity (RSD=3.77%). Prior to this study, traditional Raman techniques detected substances in solid samples only. Here, Raman technology detected low contents of sildenaful drugs in liquid nutraceuticals. Therefore, SERS technology has great potential for on-site and real-time detection of illegal drugs in water and in liquid nutraceuticals.

Diazepam injection was detected based on a droplet surface enhanced Raman spectroscopy (SERS) platform, which overcomes the disadvantages of the poor uniformity and time-consuming sample treatment process of the conventional "drop and dry" detection strategy. The Raman peak positions of diazepam injection were determined and identified, they are mainly located in the 689, 1002, 1170 and 1598 cm-1, etc. Different concentrations of diazepam injection were detected. It was found that the intensity of 1002 cm-1 increases linearly with concentration in the range from 0.05 to 10 μg/mL and the linear correlation coefficient is 0.988. The limit of detection can reach 0.05 μg/mL. The SERS method is easy, fast and efficient. The results are accurate and reliable. It has favorable application potential in the detection of diazepam injection.

Estazolam (EST) is a common sedative-hypnotic drug with a risk of abuse. Therefore, rapid on-site detection of EST is necessary to control the abuse of EST. In this paper, a fast, simple, and sensitive method is demonstrated for the detection of EST in both water and beverages, using surface-enhanced Raman spectroscopy (SERS) techniques. Au@Ag core-shell nanoparticles (NPs) assembled on the filter paper as a SERS substrate exhibit good applicability and practicality. At the same time, density functional theory (DFT) is used to assign the vibration mode of the EST molecules, which can be used as a guide for subsequent experiments. The lowest detectable concentration of EST in aqueous solution can be as low as 5 mg/L, and signal uniformity is excellent (RSD687 = 5.56%, RSD1000 = 4.35%). In addition, EST components artificially added to orange juice and pomegranate juice can be effectively detected by simple pretreatment with a minimum detection concentration as low as 10 mg/L. Therefore, this study found that the use of Au@Ag core-shell nanoparticles paper-based SERS substrate provides a quick and easy method for the detection of illegally added drugs in beverages.

In recent years, paper-based Surface-enhanced Raman spectroscopy (SERS) substrates have received extensive attention in the field of rapid analysis. However, obtaining quantitative SERS results is still challenging because of the inferior uniformity originating from the irregular morphology of the filter paper. In this work, a novel paper-fluidic SERS sensor was developed and its in-depth applications in the real-word quantitative analysis of contaminants in complex matrices were demonstrated. In particular, the Au@Ag core-shell nanospheres were labeled with an internal standard molecule to successfully normalize the fluctuation of the SERS signal caused by the microstructure of the filter paper, which could significantly improve the detection accuracy and accomplish the SERS quantitative analysis. In addition, a facile and robust strategy for the fabrication of a paper-based SERS sensor, which uses a dropper and mask to transfer the nanoparticle monolayers, was developed. This convenient and flexible approach effectively achieved a precise patterned assembly of nanoparticles on the filter paper. Furthermore, the paper-fluidic SERS sensor was fabricated by cutting and packaging for two detection modes, i.e., lateral-flow and vertical-flow, which generates the functionalization of the paper-based SERS substrate. Both detection modes integrated sample pretreatment and sample enrichment with SERS detection were applied to accurately detect the pesticide thiram in a complex sample of orange juice with pulp. In summary, this paper-fluidic SERS sensor with a simple preparation process and integrated functions is an ideal candidate for real sample analysis without pretreatment.

Recently, the phenomenon of fentanyls overdose leading to death is emerging in an endless stream. There is an urgent requirement to quickly identify fentanyl content in body fluids for medical and judicial purposes. With this in mind, we present a paper-based SERS substrate decorated with uniform gold nanospheres treated by chloride ion for the detection of fentanyl citrate in urine and serum. In particular, the paper-based SERS sensor was prepared by liquid/liquid self-assembly technique and chloride ion was introduced to clean and modify the substrate surface, which improved the sensitivity of the solid substrate with an enhancement factor (EF) as high as 1.64 × 105. Moreover, the uniformity of each paper-based substrate and the repeatability on different batches of substrate were excellent, and there was no obvious change in the intensity response of Raman spectra within a month. As a result, the quantitative analysis of fentanyl citrate in artificial urine and rat serum were performed based on the modified paper-based substrate with the limit of detection as low as 0.59 μg/mL and 2.78 μg/mL, respectively. Both the concentrations of the two biological samples with the Raman signal intensity were linearly plotted and the recovery of the spiked samples with different concentrations was collected to verify the accuracy of the quantitative curves. All the results suggest that this work makes SERS method available for the rapid identification and quantitative analysis of illicit drug in the real biological samples.

Quantitative analysis is an important aspect of surface-enhanced Raman spectroscopy (SERS). However, due to changes in the enhancing performance of SERS substrates, it is difficult to obtain reliable analysis results. In this work, a reliable quantitative method is introduced to overcome this problem by an external standard method. To achieve the external standard method, a self-assembled film of activated carbon nanoparticles is first prepared at the air/liquid (KCl aqueous solution) interface. Next, the activated carbon film transferred onto the surface of a Teflon slice (extraction film) is dipped into a high concentration of analyte to achieve reliable saturated adsorption, and the extraction film under saturated adsorption is called the reference (external standard). The uniformity is very good in one extraction film and thus the extraction film is cut into halves (used to prepare the determinand and reference) to eliminate deviation of different batches. The saturated adsorption time of the extraction film is different for different concentrations of analyte and the concentration can be therefore quantified by saturated adsorption time. Because the enhancing performance of the SERS substrate is almost unchanged in a short time and all of the SERS measurements are conducted at a similar measurement condition (saturated adsorption), the SERS intensity of the determinand and reference is almost the same under saturated adsorption. The SERS intensity of the determinand normalized by the reference is therefore very stable and uniform (approximately equal to “1” under saturated adsorption). The preparation conditions of the determinand and the reference are the same except for the concentration of the analyte, thus the interference can be eliminated by an external standard method. Any perturbations caused by the performance change of colloid substrates can be therefore effectively overcome. Moreover, the saturated adsorption time of the extraction film for different concentrations of analyte has a large time margin. This method is very simple and the cost is very low. Based on this method, a concept of time-discretized quantitative SERS (TDQ-SERS) is introduced. Thus, a reliable, simple, and economic quantitative SERS technique can be achieved.

Chemical enhancement in surface-enhanced Raman scattering (SERS) may involve the presence of s charge-transfer (CT) complex either by direct binding (covalent) to the metal or by indirect binding with the assistance of an electrolyte ion. The electrolyte (e.g., NaCl, MgSO4) is very necessary for both direct binding and indirect binding. For the direct binding complex, the electrolyte functions as aggregation agents to create hot spots, while for the indirect binding complex, the electrolyte is used to not only assist the formation of the CT complex but also create hot spots by aggregating nanoparticles. Thus, it is difficult to identify the types of complexes by direct observation. In this article, the types of CT complexes can be distinguished via simply observing the change of saturation point of SERS intensity. The saturation point for indirect binding complex can easily be shifted to higher concentration by simply increasing the concentration of chloride, but the saturation point for the direct bindin...

A high energy 532 nm hundred picoseconds laser based on stimulated Brillouin scattering (SBS) pulse compression and second-harmonic generation (SHG) is demonstrated. The seed is single frequency laser with pulse width 7 ns at 1064 nm delivered from a Cr 4+ :YAG passively Q-switched oscillator with Fabry-Perot etalon (FPE) as a frequency selector. Master oscillator power amplifier (MOPA) and compact single-cell FC–770 pulse compressor are combined to generate high energy output with hundred picosecond pulse width. Without any breakdown of optical devices, single frequency pulses are generated with compressed pulse width less than 450 ps and maximum energy up to 400 mJ. Type-II phase matching nonlinear crystal KDP is adopted for SHG of the fundamental laser. The optical-to-optical frequency conversion efficiency reaches up to 55%. The beam quality factor M 2 is measured to be 2.45 and the output power stability is better than 3.5%.

We propose a simple and rapid surface-enhanced Raman spectroscopy (SERS) method based on the dropping and detection of a sample droplet on a porous alumina ceramic platform (ACP). The SERS versatility of the proposed drop-and-detect method was demonstrated by using well-studied water-soluble melamine and ethanol-soluble 4-mercaptobenzoic acid as Raman probes. Colloidal silver nanoparticles were used as SERS substrates. Because of the fast permeation of the sample droplet by using ACPs, reproducible SERS measurements could be performed within a minute after the dropping of the sample solution. In comparison with its counterpart quartz plate, the cost-effective ACP made the uniformity of the distribution pattern of the dried droplet improved by an order of magnitude. The measurement sensitivity was also greatly improved by using ACPs due to their enrichment functions. The lowest detectable concentrations achieved for melamine and 4-mercaptobenzoic acid were 2.5 µg/l and 2.5 × 10−8 mol/l, respectively. The proposed drop-and-detect method was also demonstrated by quantitative detection of trace level melamine in liquid milk achieving a lowest detectable concentration of 0.1 mg/l, indicating its advantages of simplicity and efficiency for practical SERS applications. Copyright © 2016 John Wiley & Sons, Ltd.

Promethazine and scopolamine are two major components of a drug commonly used as a substitute for heroin addiction but with its own potential for abuse. Here, surface-enhanced Raman spectroscopy experiments were combined with density functional theory computations of the Raman frequencies of promethazine. The enhancement of the SERS substrate was optimized by contrast detection of silver nanoparticles. The optimized substrate was used to detect scopolamine, promethazine and their mixtures. Several mixtures of different concentrations were detected and analyzed. The approach of rapid identification and monitoring of drugs will become an important tool in the detection and control of illicit drug use.

Quantitative analysis always encounters difficulty in the field of surface-enhanced Raman spectroscopy (SERS) because of the lack of accurate and reliable analytical means. In this work, a new approach was demonstrated for the quantitative SERS measurement by self-assembled superlattice based on ultra-smooth Au nanospheres (NSs) embedded with 4-methylthiobenzoic acid (4-MBA) as the internal reference. Malachite green (MG) in water and chrysoidine in drinks with detection limit of 0.35 µM were successfully and quantitatively measured by employing Au@4-MBA@Au NSs superlattice as solid SERS substrate. Compared with conventional SERS methods, the fitting linearity of the relative SERS intensity vs. analyte concentrations has significantly improved by this new analysis means. As a result, our approach is a reliable analytical strategy to solve quantitative problems in SERS analysis, which can be easily applied for on-site detection and for preliminary monitoring of food samples.

Because of excellent molecular specificity, great success in chemical detection using surface-enhanced Raman scattering (SERS) has been achieved. However, the preparation of a simple and reproducible SERS substrate with good enhancement performance is still a challenge. Here we found that a silver-assisted gold SERS substrate can achieve very excellent reproducibility and high enhancement. Owing to the combined utilization of Au NPs and Ag NPs, the substrate can achieve high enhancement without using extra aggregation agents. Because hot-spots are created only by analyte molecules themselves, the adsorption of analytes on the surface of nanoparticles generating hot-spots is more stable and uniform. For colloids substrate, some problems such as random adsorption, large conglomeration are avoided. Thus the excellent reproducibility can be obtained. Besides, interference between analyte molecule and aggregation agent may occur. Thus, elimination of extra aggregation agents is desirable. The relative standard deviation of

Surface-enhanced Raman spectroscopy (SERS) was used to measure scopolamine hydrobromide. First, the Raman characteristic peaks of scopolamine hydrobromide were assigned, and the characteristic peaks were determined. The optimal aggregation agent was potassium iodide based on a comparative experimental study. Finally, the SERS spectrum of scopolamine hydrobromide was detected in aqueous solution, and the semi-quantitative analysis and the recovery rate were determined via a linear fitting. The detection limit of scopolamine hydrobromide in aqueous solution was 0.5 μg/mL. From 0 - 10 μg/mL, the curve of the intensity of the Raman characteristic peak of scopolamine hydrobromide at 1002 cm-1 is y = 4017.76 + 642.47x. The correlation coefficient was R2 = 0.983, the recovery was 98.5 - 109.7%, and the relative standard deviation (RSD) was about 5.5%. This method is fast, accurate, non-destructive and simple for the detection of scopolamine hydrobromide.

For accurate experimental and theoretical research, the preparation of nanocrystrals with regular morphology is of significant importance. In this work, we investigated a facile and effective route for generating highly spherical Au@Ag nanospheres (NSs) with tuneable size and uniform morphology at room temperature. The aqueous synthesis mainly involved seed-mediated growth method together with oxidation etching employing sodium hypochlorite (NaClO) as etching agent. The termination of the etching reaction with NaClO as etching agent was simply related to the amount of NaClO and had no connection with time. Thus Au@Ag NSs with controllable diameters in range from 24 to 87 nm were prepared only by varying the amount of NaClO added into the solutions of Au@Ag nanocubes. Additionally, combined with interface self-assembly technique, Au@Ag NSs were assembled into densely arranged two-dimensional (2D) monolayer film. Moreover, the SERS performance of these monolayers were evaluated by calculating the analytical enhancement factor using crystal violet as probe molecule. The AEF increased obviously as the diameter of Au@Ag NSs went up, and the maximum AEF could reach to 0.94 × 107 at the laser excitation wavelength of 785 nm. Besides, the electromagnetic field distribution for Au@Ag NSs array were also confirmed by Mie theory and FDTD solutions software and the results revealed the similar trend with the experimental results. In general, this 2D assemblies in term of high quality Au@Ag NSs have broad prospects to act as promising candidates for SERS analytical sensor and other applications.

In this paper, a theoretical model is developed to demonstrate that fluctuations in the Stokes signal and occurrence position contribute to the final compression ratio in stimulated Brillouin scattering (SBS). This theoretical analysis can be applied to the investigation of the temporal characteristics of SBS pulse compression. This model agrees well with the experimental results in a two-stage SBS compressor.