Surface-enhanced Raman scattering substrate of silver nanoparticles depositing on AAO template fabricated by magnetron sputtering

In this report, we describe a fabrication process of low-cost and highly sensitive SERS substrates by using a simple anodizing setup and a low-energy magnetron sputtering method. The structure of the SERS substrates consists of silver nanoparticles deposited on a layer of anodic aluminum oxide (AAO) template. The fabricated SERS substrates are investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM), and a confocal Raman spectroscope. We have verified from the surface morphology that the fabricated SERS substrates consist of high-density round-shape silver nanoparticles where their size distribution ranges from 10 to 30 nm on the top and the bottom of nanopores. The surface-enhanced Raman scattering activities of these nanostructures are demonstrated using methylene blue (MB) as probing molecules. The detection limit of 10⁻⁸ M can be achieved from this SERS substrate.     

纳米颗粒自组装SERS基底的发展及应用进展

表面增强拉曼散射(SERS)技术作为一种分析手段,因其高灵敏度、高选择性、及对样品的非破坏性等,在生物医药、环境检测、分析化学及食品安全等领域获得了广泛应用。金属纳米颗粒阵列因具有较强的局部表面等离子共振效应,能构造出高性能的SERS基底。自组装技术作为可制备出高度有序、可重复性高且结构可控的纳米阵列的方法,迄今仍是SERS基底构造研究领域中的热点。简单介绍了自组装技术的方法及其在SERS基底制备中的发展及应用,并对其未来发展趋势做出展望。     

Surface-enhanced Raman scattering (SERS) characterization of trace organoarsenic antimicrobials using silver/polydimethylsiloxane nanocomposites

Organoarsenic drugs such as roxarsone and 4-arsanilic acid are poultry feed additives widely used in US broilers to prevent coccidosis and to enhance growth and pigmentation. Despite their veterinary benefits there has been growing concern about their use because over 90% of these drugs are released intact into litter, which is often sold as a fertilizing supplement. The biochemical degradation of these antimicrobials in the litter matrix can release significant amounts of soluble As(III) and As(V) to the environment, representing a potential environmental risk. Silver/polydimethylsiloxane (Ag/PDMS) nanocomposites are a class of surfaceenhanced Raman scattering (SERS) substrates that have proven effective for the sensitive, reproducible, and field-adaptable detection of aromatic acids in water. The work presented herein uses for the first time Ag/PDMS nanocomposites as substrates for the detection and characterization of trace amounts of roxarsone, 4-arsanilic acid, and acetarsone in water. The results gathered in this study show that organoarsenic species are distributed into the PDMS surface where the arsonic acid binds onto the embedded silver nanoparticles, enhancing its characteristic 792 cm(-1) stretching band. The chemisorption of the drugs to the metal facilitates its detection and characterization in the parts per million to parts per billion range. An extensive analysis of the distinct spectroscopic features of each drug is presented with emphasis on the interactions of the arsonic acid, amino, and nitro groups with the metal surface. The benefits of SERS based methods for the study of arsenic drugs are also discussed.     

碳载Au/TiO2光催化材料的制备与拉曼增强特性

采用强度高和柔软性好的碳纤维、碳纳米管、氧化石墨烯为载体,负载Au纳米粒子掺杂的TiO2,获得碳载Au/TiO2高效光催化剂.通过X射线衍射、扫描电镜、拉曼等表征手段,考察了所得碳载Au/TiO2的结构、形貌与性能.所得碳载Au/TiO2在汞灯照射下可有效地降解亚甲基蓝染料分子.其中Au粒子有效抑制了TiO2表面光生电子-空穴的复合,增强了光生载流子的分离效率,提高了TiO2的光催化性能;碳载体提高了Au/TiO2催化剂活性组分的分散度,促进了亚甲基蓝分子的吸附,对Au/TiO2的光催化活性具有良好的协同效应.拉曼实验表明,Au/TiO2/CF、Au/TiO2/GO也是一种优秀的表面增强拉曼散射检测基底.同时,Au/TiO2/CF、Au/TiO2/GO可在汞灯照射下“清洗”掉表面吸附的上组表面增强拉曼散射实验中的检测分子,实现基底的循环利用.     

One-step Synthesis of Shape-controllable Gold Nanoparticles and Their Application in Surface-enhanced Raman Scattering

Gold nanoparticles（NPs） of various shapes were synthesized by a one-step method at ambient temperature in the presence of NaCI.2-mercaptosuccinic acid（MSA） was used as both reducing agent and stabilizing agent.The shapes of gold NPs were controllable by simply tuning S/Au ratio（S is from MSA molecule,and S/Au ratio is controlled by tuning the volume of added MSA solution）,and triangle,polygonal and spherical nanoparticles were obtained.This result suggested a new way to consider the effects of MSA on the growth of nanoparticles,which showed that MSA is a strong capping agent and facilitates more uniform growth of nanoparticles in every dimension.And other important factors on nanoparticles growth including NaCI and temperature were discussed.Furthermore,a typical probe molecule,4-aminothiophenol（4-ATP） was used to test the surface-enhanced Raman scattering（SERS） activity of these gold NPs and the results indicated good Raman activity on these substrates.And the enhancement factor（EF） at 1078 cm^-1（a₁） was estimated to be as large as 6.3×10⁴ and 5.5×10⁴ for triangular plates and truncated particles,respectively.     

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS): a review of applications

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) can provide positive identification of an analyte or an analyte mixture with high sensitivity and selectivity. Better understanding of the theory and advances in the understanding of the practice have led to the development of practical applications in which the unique advantages of SERS/SERRS have been used to provide effective solutions to difficult analytical problems. This review presents a basic theory and illustrates the way in which SERS/SERRS has been developed for practical use.     

Interactive effect of agitation rate and oxidative etching on growth mechanisms of silver nanowires during polyol process

In this work, the interaction between agitation rate and oxidative etching on the growth mechanisms of silver nanowires during polyol process, the most conventional applied method for metallic nanoparticles synthesis, is evaluated. It was found that the main reason for the formation of multidiameter nanowires (MDNWs) is the local accumulation of silver ions in the system, i.e. even at a low concentration of silver ions (94 mM) under the mild agitation conditions, MDNWs were producible. Moreover, it was inferred that the more stress (stemming from the high agitation) applied on the initially formed decahedron Ag particles affects the ‘re-entrant grooves opening’ process which results in the formation and growth of irregular nanostructures. A polynomial equation for tuning aspect ratio of silver nanowires using different concentration of CuCl₂ solution was also proposed. Finally, based on the obtained experimental data together with the thermodynamic considerations, a growth mechanism was proposed which can promisingly be employed for describing the one-dimensional growth of silver nanowires in both surfactant-modified and surfactant-free procedures.     

Femtosecond laser irradiation induced heterojunctions between carbon nanofibers and silver nanowires for a flexible strain sensor

We report the direct joining of carbon nanofibers(CNFs)to silver nanowire(Ag NWs)by controlled irradiation with femtosecond(fs)laser pulses.Two separate types of nano-junction dependent on joint geometry,laser fluence and irradiation time are identified in irradiated mixtures.In one type of junction,the tip of an Ag NW is melted and flows to form a bond with an adjacent CNF.The second type of junction occurs without significant heating of the Ag NW and involves the softening and flow of carbon in the CNF in response to the transfer of plasmonic energy from the Ag NW into the CNF.Bonding in a T-type joint configuration can be of either kind depending on the relative orientation of the incident optical field and the long axis of the Ag NW.FDTD simulations were used to explore this effect for different joint geometries and laser polarization.The electrical properties of a heterojunction involving a single Ag NW-CNF structure have been measured,and it is found that the junction resistance can be reduced by six orders of magnitude after laser joining.Finally,we have investigated the properties of a strain sensor based on an Ag NW-CNF hybrid nanowire network and find that this device can exhibit high sensitivity.This sensitivity occurs as nano-junctions induced by fs laser irradiation greatly reduces the initial resistance.This laser-based technique for direct nanojoining of CNF and Ag NWs may enable the design of robust nanowire structures for application in a variety of new devices.     

Preparation of silver nanoparticles by photo-reduction for surface-enhanced Raman scattering

A substrate for surface-enhanced Raman scattering (SERS) has been developed. Based on the surface-catalyzed reduction of Ag⁺ by citrate on the silver nanoparticles surface under light irradiation, small silver seeds on a quartz slide can be enlarged. The optical properties and characteristics of the silver films have been investigated by ultraviolet-visible spectroscopy, scan electron microscope and atomic force microscopy (AFM). The results indicate that the particle size and shape are different at different reduction time. At the first 3 h, some triangular and hexagonal nanoparticles formed; with the reduction proceeding, the shape of the silver particles became irregular and the size became larger. The silver films obtained are very suitable as SERS active substrate. The relationship between SERS intensity and the reduction time has been investigated for 1,4-bis[2-(4-pyridyl)ethenyl]-benzene molecule adsorbed on the silver film. The SERS intensity reached a maximum at 8 h reduction. The AFM measurements indicate that roughness features with an average size of 100 nm are present on the surface, which yielded the strongest SERS signal. Pyridine was used as a probe molecule to investigate the enhancement factor (EF) of the silver films. According to the formalism of Tian and co-workers, the EF of the silver films is estimated to be 3.4 × 10⁵. The silver film that can remain active for more than 50 days would seem to be suitable for various analytical applications.     

Dynamic rastering surface-enhanced Raman scattering (SERS) measurements on silver nanorod substrates

Surface-enhanced Raman spectra of a thiol-modified biotin derivative on oblique-angle-deposited silver nanorod (AgNR) array substrates were measured using both static and rotating rastering methods. We find that the rotating rastering method has a strong tendency to decrease the point-to-point relative standard deviation (RSD) compared to static measurements as well as decrease the effects of cumulative excitation exposure. The AgNR substrates treated with the modified biotin typically demonstrate intra-substrate RSDs of <10%, with an average RSD of ～3% when the rastering radius r=1 mm. The quantitative studies on the relationship between rastering radius, sampling area, and rastering frequency show that only the rastering radius appears to have significant effect on the measured RSD. Our results demonstrate that under the proper measurement and sample preparation conditions, the Ag nanorod substrates are very uniform.     

十八胺作为还原剂和包裹剂制备具有SERS活性的金纳米线

采用化学还原方法,在有机相中利用十八胺作为还原剂和包裹剂,在油酸的辅助下,合成了具有一维结构的金纳米线,并将制得的金纳米线用作基底,在其表面获得了罗丹明B分子的SERS光谱,实验结果表明,金纳米线具有良好的SERS活性,有望应用于高灵敏度光学检测。     

Surface-enhanced raman scattering (SERS) detection of low concentrations of tryptophan amino acid in silver colloid

The surface-enhanced Raman scattering (SERS) spectrum of L-tryptophan has been studied in the concentration range 1.4 × 10(-8) to 5 × 10(-4) M. A borohydride-reduced silver colloid was employed as the nanoparticle enhancing agent and different electrolytes have been tested for activation of the colloid. The optimum conditions have been determined for achieving high sensitivity of detection. The experimental procedure developed, which includes the use of a composite electrolyte (a mixture of NaHCO(3) and NaCl) for colloid activation, results in very high enhancement of the Raman signal (up to 10(8)). This gives the possibility of studying SERS spectra of L-tryptophan at concentrations as low as 10(-8) M, which is several orders of magnitude lower than previously reported in the literature. The observed SERS spectra were very reproducible and were detectable 2 minutes after mixing, reaching maximum strength approximately 15 minutes after mixing. The spectral characteristics were stable over the entire period of observation. We have found that SERS spectra of tryptophan in silver colloid differ in several features at low (below ～10(-5) M) and at high (above ～10(-4) M) concentrations. The most important difference is the absence of the peak near 1000 cm(-1) at low concentrations, which is usually assigned to the indole ring breathing mode. The observed spectra allow us to suggest that at low concentrations Trp molecules bind to the surface through the indole ring, which remains flat on the surface. This is in contrast to the previously reported observation of SERS spectra from Trp performed at concentration levels above 10(-5) M.     

Silver nanoclusters films for single molecule detection using Surface Enhanced Raman Scattering (SERS)

A highly efficient Surface Enhanced Raman Scattering (SERS) substrate was prepared using a nanocluster deposition system that enabled detection of Crystal Violet molecules down to a single molecule level. The large SERS signal enhancement can be attributed to the presence of nano gaps on the surface of the nanoclusters which create abundant hot spots for electric field enhancement. Observed variations in the Raman peaks at very low molar concentrations in the range 4 × 10⁻¹⁴–3.2 × 10⁻¹⁸ M suggest that the spectra are due to a single molecule. Possible mechanisms for ultrahigh SERS sensitivity of the substrates are discussed. These substrates take the detection limit of CV down by two orders of magnitude as compared to those reported in literature.     

交流电沉积制备SnO2纳米线及其电沉积条件研究

采用阳极氧化的方法制备了孔径为30～50nm多孔阳极氧化铝(AAO)模板,用交流(AC)电沉积法在氧化铝模板孔洞内沉积金属锡,然后在空气中750℃加热含锡的模板10h,热氧化制备了直径在30～50nm SnO2纳米线．用扫描电子显微镜,透射电子显微镜,X射线衍射仪对所制备的SnO2纳米线进行了表征,表明所制备的纳米线为多晶结构．并通过改变交流电沉积过程中的电压,频率和热氧化时间来考察不同沉积条件对沉积结果的影响,发现采用交流沉积制备金属纳米线的过程中,频率和电压是影响沉积结果的关键因素．     

Synthesis and characterization of silver molybdate nanowires, nanorods and multipods

Silver molybdate nanowires, nanorods and multipods like structures have been prepared by an organic free hydrothermal process using ammonium molybdate and silver nitrate solutions. The powder X-ray diffraction (PXRD) patterns reveal that the silver molybdate belongs to anorthic structure. The thickness, 200–500 nm, for silver molybdate nanorods/wires and 2–5 μm for microrods are identified from SEM images. UV-visible spectrum of silver molybdate nanorods/nanowires shows maximum absorbance at 408 nm. Photo-luminescence (PL) spectrum exhibits UV emission at 335 nm, violet emission at 408 nm and a weak green emission at 540 nm. The influence of hydrothermal synthesis conditions on silver molybdate nanowires, nanorods and multipods compositions were established.     

A facile synthesis of silver nanoparticle with SERS and antimicrobial activity using Bacillus subtilis exopolysaccharides

In this study, we report a facile synthesis of silver nanoparticle having SERS and antimicrobial activity using bacterial exopolysaccharide (EPS). Bacillus subtilis (MTCC 2422) was grown in nutrient broth and the extracellular EPS secreted by the organism was extracted and purified. The purified EPS was used for the synthesis of silver nanoparticles. The kinetics of silver nanoparticle synthesis was deduced by varying the exposure time and the concentration of EPS. The rate constant (k) for the synthesis of silver nanoparticle was calculated from the slope of ln(A^∞ ? A^t) versus time plot. The k value was found to be 3.49 × 10^?3, 5.81 × 10^?3 and 5.03 × 10^?3 per min for particle synthesis using 2, 5 and 10 mg/mL EPS, respectively. The nanoparticles synthesised had an average particle size of 5.18 ± 1.49 nm, 1.96 ± 0.77 nm and 2.08 ± 0.88 nm for 2, 5 and 10 mg/mL EPS, respectively. The synthesised particles were characterised using UV-Vis absorbance spectroscopy, high-resolution transmission electron microscopy (HRTEM) attached to EDS (energy dispersive spectroscopy), Fourier transform infrared spectroscopy (FTIR), surface enhanced Raman spectroscopy (SERS) and zeta potential analyser. To our knowledge, this is the first study to report SERS activity of microbial Bacillus subtilis EPS-based synthesis of silver nanoparticle. HRTEM images showed silver nanoparticle entrapped in polysaccharide nanocages. Silver nanoparticle showed higher adherence towards the bacterial surface, with good bactericidal activity against Pseudomonas aeroginosa and Staphylococcus aureus.