Silver nanoparticles embedded temperature-sensitive nanofibrous membrane as a smart free-standing SERS substrate

To develop a smart free-standing surface enhanced Raman scattering(SERS) substrate,silver nanoparticles(AgNPs) embedded temperature-sensitive nanofibrous membrane was fabricated by electrospinning their aqueous solution containing the copolymer poly(N-isopropylacrylamide-co-Nhydroxymethylacrylamide),followed by heat treatment to form crosslinking structure within its constituent nanofibers.To avoid negative effect of the additive like stabilizer and the reactant like reductant on their SERS efficiency,the AgNPs were in-situ synthesized through reducing Ag~+ions dissolved in the polymer solution by ultraviolet irradiation.The prepared hybrid nanofibrous membrane with high stability in aqueous medium can reach its swelling or deswelling equilibrium state within 15 seconds with the medium temperature changing between 25℃and 50℃alternately.When it was used as a free-standing SERS substrate,10~(-12) mol/L of 4-nitrothiophenol in aqueous solution can be detected at room temperature,and elevating detection temperature can further lower its low detection limit.Since its generated SERS signal has desirable reproducibility,it can be used as SERS substrate for quantitative analysis.Moreover,the hybrid membrane as SERS substrate is capable of real-time monitoring the reduction of 4-nitrothiophenol into 4-aminothiophenol catalyzed by its embedded AgNPs,and the detected intermediate indicates that the reaction proceeds via a condensation route.     

三明治结构纳米银/氧化石墨烯基底的制备及SERS性能

采用易操作且低成本的静电自组装方法, 在质子化的玻璃基片上, 通过交替沉积氧化石墨烯(GO) 和带正电荷的银纳米粒子(AgNPs) 获得少数层GO和AgNPs复合薄膜(AgNPs/GO). 采用紫外-可见光吸收光谱、 原子力显微镜和扫描电子显微镜对复合薄膜的生长和表面形貌进行了表征. 结果表明, 通过调控AgNPs 溶胶浓度和自组装循环次数, 可以获得AgNPs/GO/AgNPs 的三明治结构, 并在基底表面形成均匀的AgNPs 聚集体. 表面增强拉曼散射(SERS)研究结果表明, AgNPs/GO-4基底具有最佳的SERS性能, 其对罗丹明6G(R6G) 和结晶紫的平均拉曼增强因子分别为3.4×10⁸和1.3×10⁹, 对R6G的最低检测浓度约为10^-12 mol/L. 多层三明治结构和较小颗粒间距使得AgNPs层之间产生强烈的耦合作用, 并在GO片层间产生大量的“热点”, 显著提高SERS性能, 而少数层GO具有强吸附性, 有利于分子在基底中富集, 从而起到化学增强作用, 提高SERS灵敏度.     

Silver nanoparticle-treated filter paper as a highly sensitive surface-enhanced Raman scattering (SERS) substrate for detection of tyrosine in aqueous solution

Highly sensitive SERS substrates based on deposition of silver nanoparticles on commercially available filter paper were prepared in this work, and used to overcome problems found in analyses of aqueous samples. To prepare silver nanoparticle- (AgNP) doped filter substrates, a silver mirror reaction was used. The procedures for substrate preparation were systematically optimized. Pretreatment of filter paper, reaction time, temperature, and concentration of reagents for silver mirror reactions were studied. The morphologies of the resulting substrates were characterized by field-emission scanning electron microscopy (FE-SEM) and correlated with the SERS signals by probing with p-nitrothiophenol (pNTP). Filter papers with different pretreatments were found to have different sizes and distributions of AgNPs. The best performance was found when filter paper was pre-treated with ammonia solution before growth of AgNPs. Based on the SEM images, the resulting AgNPs had roughly spherical shape with a high degree of uniformity. The silver-coated filter paper substrates provide much higher SERS signals compared to glass substrates and the reproducibility was improved significantly. Based on statistical analyses, the relative standard deviations for substrate-to-substrate and spot-to-spot were both were less than 8% and the enhancement factors for the substrates were, in general, higher than 107. The SERS substrates were used to selectively detect tyrosine in aqueous solution. Results indicate that filter-based SERS substrates are highly suited to detection of tyrosine. Compared to glass-based SERS substrates, 50 times more SERS signal was observed in detection of tyrosine. The linear range can be up to 100 μM with a detection limit of 625 nM (SN(-1)=3).     

银/金纳米线阵列表面增强拉曼基底的制备及对孔雀石绿的高灵敏度检测

利用种子介导的软模板生长方法制备了金纳米线(Au NWs)阵列, 通过调节生长温度控制Au NWs阵列的形貌, 最后在经硼氢化钠(NaBH₄)清洗过的Au NWs阵列上化学沉积银纳米颗粒(Ag NPs), 制得银/金纳米线(Ag/Au NWs)阵列作为表面增强拉曼散射(SERS)基底. 选用罗丹明6G(R6G)作为拉曼探针分子测定了Ag/Au NWs阵列的SERS性能. 结果表明, Ag/Au NWs阵列作为SERS基底具有高灵敏度、 优异的信号均匀性和良好的稳定性. 使用Ag/Au NWs阵列对孔雀石绿(MG)检测的检出限可低至1×10^-8 mol/L, 线性范围为 1×10^-8~1×10^-4 mol/L. NaBH₄可以在不影响SERS性能的情况下去除Ag/Au NWs阵列上吸附的分子, 使得 SERS基底可以重复使用. 使用Ag/Au NWs阵列对湖水中的MG进行检测, 得到了可靠的回收率, 证明Ag/Au NWs 阵列在检测环境水体中的孔雀石绿上具有应用潜力.     

室温电子还原制备金纳米颗粒与琼脂糖复合膜的表征与应用

利用室温电子还原技术合成了一种金纳米颗粒与琼脂糖复合膜。合成过程采用氩气辉光放电为廉价电子源,方便快捷,绿色环保。通过紫外-可见(UV-Vis)分光光度计、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)仪、光电子能谱(XPS)等表征,发现可以通过改变氯金酸浓度调控复合膜中金纳米颗粒的分布,加入聚乙烯吡咯烷酮(PVP)可有效控制金纳米颗粒的形貌。由于复合膜具有金纳米颗粒密集排布的结构,可作为表面增强拉曼散射(SERS)活性基底。实验表明,以对氨基苯硫酚为探针,该复合膜作为SERS基底,SERS平均增强因子超过了106,检测限达到了10-12mol?L-1。除此之外,作为SERS基底,复合膜具有良好的均一性和稳定性。     

Free-standing nanogold membranes as scaffolds for enzyme immobilization

We demonstrate herein the formation of a free-standing gold nanoparticle membrane and its use in the immobilization of the enzyme, pepsin. The nanogold membrane is synthesized by the spontaneous reduction of aqueous chloroaurate ions at the liquid-liquid interface by the bifunctional molecule bis(2-(4-aminophenoxy)ethyl) ether (DAEE) taken in chloroform. This process results in the formation of a robust, malleable free-standing nanogold membrane consisting of gold nanoparticles embedded in a polymeric background. Recognizing that gold nanoparticles are excellent candidates for immobilization of enzymes, we have immobilized pepsin on the nanogold membrane, leading to a new class of biocatalyst. A highlight of the new pepsin-nanogold biocatalyst is the ease with which separation from the reaction medium may be achieved. The catalytic activity of pepsin in the bioconjugate was comparable to that of the free enzyme in solution. The pepsin-nanogold membrane bioconjugate material exhibited excellent biocatalytic activity over 10 successive reuse cycles as well as enhanced pH, temperature, and temporal stability.     

纳米颗粒银层的电沉积机理及SERS效应

研究了大面积均匀平整的纳米颗粒银层电沉积的机理, 优化了制备工艺, 探索了其在表面增强拉曼光谱检测中的应用. 结果表明, 该纳米颗粒银层的电沉积随着电极电势的负移, 逐步由连续成核转向瞬时成核机理, 在电流密度为1.0 A/dm², 阴阳极面积比为1∶10, 以及20~30 ℃条件下, 银层具有更强的表面增强效应. XRD测试表明, (111)晶面为银电沉积层的择优取向面; 扫描电子显微镜表征表明, 银的颗粒尺度为6~11 nm. 该电沉积层作为表面增强拉曼光谱的活性基底, 具有灵敏度高及检测限低的特点, 对罗丹明6G 分子的检测限低至1.0×10^-12 mol/L, 同时在大范围内的拉曼增强效果均匀, 展现了良好的应用前景.     

Photochemical decoration of silver nanoparticles on magnetic microspheres as substrates for the detection of adenine by surface-enhanced Raman scattering

In this work, silver nanoparticles (AgNPs) decorated magnetic microspheres (MMs) are prepared as surface-enhanced Raman scattering (SERS) substrate for the analysis of adenine in aqueous solutions. To prepare these substrates, magnetic particles were first synthesized by coprecipitation of Fe(II) and Fe(III) with ammonium hydroxide. A thin layer of cross-linked polymer was formed on these magnetic particles by polymerization through suspension of magnetic particles into a solution of divinyl benzene/methyl methacrylate. The resulted polymer protected magnetic particles are round in shape with a size of 80 μm in diameter. To form AgNPs on these MMs, photochemical reduction method was employed and the factors in photochemical reduction method were studied and optimized for the preparation of highly sensitive and stable AgNPs on MMs substrates (abbreviated as AgMMs substrates). By dispersing the AgMMs in aqueous samples, cylindrical magnet was used to attract the AgMMs for SERS detections. The observed enhancement factor of AgMMs reached 7 orders in magnitude for detection of adenine with a detection limit approaching to few hundreds of nanomolar.     

纳米氧化锰负载钛基电催化膜制备及其苯甲醇催化氧化性能

利用乳液法制备出MnO_x纳米颗粒,将其负载于微孔管式钛膜制得MnO_x负载钛基电催化膜(MnO_x/Ti).运用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、循环伏安法(CV)和计时电流法(CA)等表征方法系统考察了不同焙烧温度下MnO_x晶型结构、MnO_x/Ti催化膜电化学性能以及催化氧化苯甲醇的变化规律.结果表明:随着焙烧温度的升高, MnO_x的晶型由初始的Birnessite-MnO₂逐渐转变为K_0.27MnO₂,再由Mn3O4最终转变为α-MnO₂.所得MnO_x/Ti膜中, α-MnO₂晶粒尺寸小于30 nm,结晶度较高,颗粒分布均匀.同时,由于其含有不饱和配位的锰原子和氧空位以及与基体Ti之间存在键合作用,表现出优异的电化学性能和催化性能.以450 ℃焙烧所得的α-MnO₂/Ti为阳极构建电催化膜反应器催化氧化苯甲醇.在反应温度为25 ℃, 50mmol·L^-1苯甲醇水溶液,电流密度为2 mA·cm^-2,停留时间为15 min的条件下,膜反应器苯甲醇转化率达64%,苯甲醛选择性为79%.     

General method for ultrathin free-standing films of nanofibrous composite materials

A simple and general method for the preparation of ultrathin, large-area, free-standing films of nanofibrous composite materials was developed. First, positively charged cadmium hydroxide nanostrands of 1.9 nm in diameter and micrometers in length were prepared by mixing dilute aqueous solutions of cadmium chloride and aminoethanol. Negatively charged dye molecules, proteins, nanoparticles, and water-soluble fullerene or carbon nanotubes were mixed with the nanostrands to give a well-dispersed solution of the corresponding nanofibrous composites. After filtration of the dispersions with a polycarbonate membrane filter, uniform films with a thickness of a few tens to hundreds of nanometers and a diameter of a few centimeters were obtained. The films were readily peeled off from the membrane filter by immersion in ethanol. The resultant free-standing films could be further transferred to other substrates, such as quartz plate, gold electrode, and porous alumina membrane, and were characterized by scanning and transmission electron microscopies. We provide herein various nanofibrous free-standing films with optical, biological, metallic, and magnetic properties.     

Ag纳米粒子在TiO2四棱柱阵列上的可控生长及其SERS效应

采用水热法在导电玻璃FTO导电面上沉积TiO₂四棱柱阵列; 并以其为基体, 分别采用聚乙烯基吡咯 烷酮(PVP)还原Tollens试剂以及柠檬酸三钠(TSC)还原硝酸银溶液, 将Ag纳米粒子(AgNPs)沉积在TiO₂四棱柱阵列上形成TiO₂@AgNPs-PVP和TiO₂@AgNPs-TSC微纳结构作为表面增强拉曼散射(SERS)基底. 实验结果表明, Ag纳米粒子在TiO₂四棱柱阵列上的尺寸和分布可通过改变Tollens试剂的浓度和TSC还原硝酸银溶液的反应时间来调控, 进而优化基底的SERS灵敏度. TiO₂@AgNPs-PVP微纳结构对罗丹明6G(R6G)的检出限为10^-12 mol/L, 对低活性小分子三聚氰胺的检出限为0.01 mg/mL; TiO₂@AgNPs-TSC微纳结构对R6G的检出限为10^-10 mol/L, 对三聚氰胺的检出限为0.01 mg/mL. TiO₂@AgNPs-PVP和TiO₂@AgNPs-TSC微纳结构基底的SERS活性、 循环可回收性与还原剂种类紧密相关: 包覆在Ag纳米粒子上的PVP可以作为隔离层避免Ag纳米粒子直接接触, 防止电磁场耦合作用减弱, 增强基底的SERS活性; 同时, PVP是一种水性聚合物, 有较强的亲水性, 作为循环可回收SERS基底使用时, 吸附小分子物质清洗难度较大.     

One-pot synthesis of silver colloid with body-heat for surface-enhanced Raman spectroscopy detections

In this study, a convenient method of preparing the substrate is proposed with one-pot synthesis of silver colloid under body heat, and the SERS detection uses the fresh substrate to avoid the drawback of substrates' short life of use. The synthesis of silver colloid is carried out in a 10 mL vial by using ascorbic acid as a reductant and trisodium citrate as a stabilizer. The vial is grasped with the palm of the experimenter for several minutes without shaking. The proposed method is simple, rapid, green energy and cost-effective. By adjusting the concentration of trisodium citrate, not only the particle size can be controlled from about 110 nm to 50 nm but also the homogeneity of nanoparticles can be improved. As a SERS substrate, the silver colloid has high batch reproducibility and showed good SERS activity. The relative standard deviation between different manufacturers is 5.51% when the substrate of silver colloid is used for the detection of rhodamine 6 G. Using the substrate, the lowest detection concentrations of rhodamine 6 G, crystal violet, enrofloxacin, melamine and leucomalachite green are 1.0×10~(-8), 6.1×10~(-8),1.4 × 10~(-6), 7.1 ×10~(-5) and 5.1 ×10~(-8) mol/L, respectively. Results demonstrate that the developed method has the advantage of convenience and high efficiency in the field preparation of reliable SERS substrate.     

银纳米枝的合成及表面增强拉曼效应

利用硝酸银与铜之间发生置换反应原理, 在铜箔上得到了有序的银纳米枝结构, 用十二烷基磺酸钠(SDS)为表面活性剂, 通过调控前驱体硝酸银的浓度, 可在铜箔上得到不同密度的银纳米枝. 表面拉曼增强实验结果表明, 当分别以对巯基苯胺(4-ATP)、腺嘌呤和罗丹明G6为探针分子时, 有序的银纳米枝结构比无序的银纳米粒子具有更好的拉曼增强活性; 且随银纳米枝密度的增加, 表面拉曼增强活性有所提高. 该有序的银纳米枝结构是较好的表面增强拉曼(SERS)活性基底, 在有机分子和生物分子的SERS检测方面将具有一定的应用前景.     

Preparation and characterization by surface-enhanced infrared absorption spectroscopy of silver nanoparticles formed on germanium substrates by electroless displacement

In this paper, the feasibility of applying electroless displacement to prepare silver nanoparticles (AgNPs) on the surface of germanium (Ge) substrate is demonstrated, and the performances of surfaces prepared in this manner for surface-enhanced infrared absorption (SEIRA) spectroscopy are reported. The process used to produce suitable AgNPs for SEIRA by electroless deposition is simple and effective, requiring only pretreatment of the germanium surface with hot air, immersion of the substrate in a dilute solution of silver nitrate, and washing of the resulting plate. To quantify the behavior of AgNPs on a Ge substrate and to optimize the conditions for the preparation of AgNPs on Ge substrates, a monolayer of p-nitrothiophenol (PNTP) was bonded to the surface of the AgNPs by immersion of the plate in a dilute solution of PNTP and measurement of the transmission spectrum. The factors that influenced the formation of AgNPs, and hence the SEIRA signals, included the concentration of AgNO₃, the reaction time and the temperature. Results indicated that stronger absorption bands in the SEIRA spectrum of a monolayer of PNTP were obtained if the reaction rate for the displacement of silver ions by Ge was slow. This condition was achieved by keeping the concentration of AgNO₃ and the reaction temperature low. Under the optimal conditions found in this work, an enhancement factor of approximately 100 was achieved for commonly used probe molecules in SEIRA measurements.     

The adsorption of methamphetamine on Ag nanoparticles dispersed in agarose gel – Detection of methamphetamine in fingerprints by SERS

Surface-enhanced Raman scattering (SERS) has been used to investigate the adsorption of methamphetamine hydrochloride (MA) on AgNPs surfaces characterized by the dispersion of AgNPs on agarose gel (AgNPs/Agar). The AgNPs/Agar was characterized by transmission electron microscopy (TEM) as being formed by AgNPs with a mean diameter of 13.5 nm. The AgNPs/Agar films presented a surface plasmon resonance absorption band centered at 421 nm. SERS spectra, excited at 632.8 nm, of MA adsorbed onto AgNPs/Agar films were recorded for MA concentrations down to 1.0 × 10⁻⁵ mol L^-1. The results have also shown that MA adsorbs on the Ag surface forming ionic pairs with adsorbed chloride following a Frumkin adsorption isotherm with a ΔG_ads of −24 kJ mol^-1 and a g parameter characteristic of attractive lateral interaction. The AgNPs/Agar SERS substrate was further evaluated for MA detection on latent fingerprints (LFP). The AgNPs/Agar films prove to be a suitable substrate for recording fingerprints contaminated with MA making possible the detection of ca. 190 μg of MA, before and after LFP development. The SERS signal of MA adsorbed onto AgNPs/Agar films remained stable for at least 180 days.     

Immobilization of silver nanoparticles into POEGMA polymer brushes as SERS‐active substrates

Surface‐enhanced Raman scattering (SERS) has attracted a great deal of interest during the past four decades and emerged as an ultrasensitive optical technique for chemical and biomedical analysis. It is widely accepted that the facile fabrication of SERS substrates with high activity and good reproducibility is of crucial importance for their applications. Herein, we report on a fast and robust method for the synthesis and immobilization of silver nanoparticles (AgNPs) into poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes under mild conditions without using any reducing agents. POEGMA brushes of different chain lengths were synthesized directly on silicon wafers by surface‐initiated atom transfer radical polymerization with various reaction time. X‐ray photoelectron spectroscopy and field emission scanning electron microscope measurements indicated that the AgNPs were firmly and homogeneously embedded into POEGMA brushes. The resulting POEGMA–AgNP hybrid films were employed as SERS substrates for the detection of 4‐aminothiophenol, giving rise to an enhancement factor of up to 1.9 × 10⁶. The influence of the POEGMA's chain length on SERS performance was also investigated. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of highly ordered AgNPs-coated silica photonic crystal beads for sensitive and reproducible 3D SERS substrates

3 D highly ordered silver nanoparticles(AgNPs) coated silica photonic crystal beads(Ag/SPCBs) were prepared and exploited as a novel surface enhanced Raman scattering(SERS) substrate.The monodisperse and size-controlled SPCBs were prepared via self-assembly of silica nanoparticles process using a simple microfluidic device.Then the Ag/SPCBs were easily obtained by in situ growth of AgNPs onto the NH₂-modified SPCBs.Field emitting scanning electron microscopy(SEM) and energy dispersive X-ray spectrometry(EDX) were used to characterize the Ag/SPCBs.The effect of silica nanoparticle size and AgNO₃ concentration on the SERS performance of the resultant Ag/SPCBs substrate were discussed in detail.The results indicate that the Ag/SPCBs have highest SERS signals when silica nanoparticle size is250 nm and AgNO₃ concentration is 0.8 mg/mL.Using malachite green(MG) as model analyte,the Ag/SPCBs substrate displayed a high sensitivity and a wide linear range for MG.The well-designed Ag/SPCBs show high uniformity and excellent reproducibility,and can be used as an effective SERS substrate for sensitive assay application.     

离子色谱-抑制型电导检测法同时测定食品级润滑油中的3种无机阴离子

建立了离子色谱-抑制型电导检测同时测定食品级润滑油中Cl^-、NO₃^-、SO₄^2- 3种代表性无机阴离子的方法。样品经50%(v/v)甲醇水溶液超声提取,离心后所得下层水相用0.22 μm混合纤维过滤膜净化,以15 mmol/L KOH溶液为淋洗液,采用抑制型电导检测器进行检测,外标法定量。在上述条件下,Cl^-、NO₃^-、SO₄^2- 3种无机阴离子在0.10~20.00 mg/L范围内具有良好的线性关系(R²>0.999);检出限(S/N=3)为0.01~0.03 mg/kg;在1.00、5.00、10.00 mg/kg添加水平下,实际样品中3种阴离子的加标回收率为90.0%~103.6%,相对标准偏差为2.8%~5.7%。结果表明,该方法无需燃烧、灰化油相基质等繁琐耗时的前处理过程,可以快速、准确定量测定食品级润滑油中Cl^-、NO₃^-、SO₄^2- 3种无机阴离子的含量,适用于润滑油等油品中痕量无机阴离子的同时分离与测定。     

一种新型比色荧光双通道水相检测氰根离子的化学传感器

合成了一种新型的,能在含水介质中比色荧光双通道单一选择性识别CN^-的传感器分子1-羟基萘甲叉酰肼乙基-3-羟基萘甲叉酰肼甲基苯并咪唑溴鎓盐(J1)。 在J1的DMSO/H₂O (体积比3:2)HEPES 的缓冲体系(pH=7.2)中分别加入F^-、Cl^-、Br^-、I^-、AcO^-、HSO₄^-、ClO₄^-、H₂PO₄^-、SCN^-和CN^-等阴离子后,只有CN^-的加入会使得溶液颜色发生明显的变化,由无色变为深黄色。 相应地在J1的DMSO/H₂O (体积比4:1)HEPES的缓冲体系(pH=7.2)中加入CN^-,溶液发出明亮的黄色荧光。 这一识别过程,不会受到其它阴离子的干扰。 紫外-可见光谱的最低检测限为1.57×10^-7 mol/L,检测线性范围为3.875×10^-4~2.15×10^-2 mol/L。 荧光光谱的最低检测限为4.63×10^-6 mol/L,检测线性范围为0.8×10^-4~1.60×10^-3 mol/L。 此结果表明,J1是一种良好的用于识别 CN^-的化学传感器,在含水介质中对CN^-具有选择性好、灵敏度高以及抗干扰性强的识别性能。 与此同时,基于J1对于CN^-的高选择性识别我们制备了CN^-的检测试纸,该试纸能够方便、快捷、准确地检测水中的CN^-。     

金纳米棒负载的静电纺丝纤维的制备及其表面增强拉曼光谱性能

为简单有效地制备高活性表面增强拉曼光谱(Surface-enhanced Raman Spectroscopy,SERS)基底。本文采用静电纺丝聚乙烯醇(PVA)/聚丙烯酸(PAA)纳米纤维为支撑材料,通过直接浸泡的方法,利用金纳米棒与电纺纤维之间的静电力,使纳米棒在纤维表面自组装,得到了性能优异的SERS基底。通过透射电子显微镜、扫描电子显微镜对金纳米棒以及不同状态下的电纺纤维的形貌进行表征,结果表明,金纳米棒均匀且密集地负载在纤维表面。通过设置不同的浸泡时间确定了金纳米棒组装平衡的时间为12 h,并通过调控纺丝时间和金纳米棒的浓度发现随着纺丝时间和金纳米棒浓度的增加,复合纤维膜SERS增强效果随之提升。该复合纤维膜具有优异的SERS均匀性,并且能够检测到浓度低至10~(-10)mol/L的4-氨基苯硫酚的存在。