Sonoelectrochemical synthesis of spike-like gold-silver alloy nanoparticles from bulk substrates and the application on surface-enhanced Raman scattering

The synthesis of non-spherical spike-like gold-silver alloy nanoparticles on platinum substrates was first developed by sonoelectrochemical methods in this study. First, a silver substrate was roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 M HCl. Silver-containing complexes were found in the solution after the ORC treatment. Then a gold substrate was subsequently roughened by the similar ORC treatment in the same silver complexes-containing solution. After this procedure, Au- and Ag-containing complexes were left in the solution. Subsequently, the Au working electrode was immediately replaced by a Pt electrode. A cathodic overpotential was applied under controlled sonication and slight stirring to synthesize Au-Ag alloy nanoparticles on the Pt substrate. Encouragingly, the surface-enhanced Raman scattering (SERS) of Rhodamine 6G on the Au-Ag alloy nanoparticles-deposited Pt substrate exhibits a higher intensity by eight-fold of magnitude and a better resolution, as compared to that obtained on the Au nanoparticles-deposited Pt substrate.     

Differential SERS activity of gold and silver nanostructures enabled by adsorbed poly(vinylpyrrolidone)

We report that poly(vinylpyrrolidone) (PVP), a common stabilizer of colloidal dispersions of noble metal nanostructures, has a dramatic effect on their surface-enhanced Raman scattering (SERS) activity and enables highly selective SERS detection of analytes of various type and charge. Nanostructures studied include PVP-stabilized Au-Ag nanoshells synthesized by galvanic exchange reaction of citrate-reduced Ag nanoparticles (NPs), as well as solid citrate-reduced Ag and Au NPs, both before and after stabilization with PVP. All nanostructures were characterized in terms of their size, surface plasmon resonance wavelength, surface charge, and chemical composition. While the SERS activities of the parent citrate-reduced Ag and Au NPs are similar for rhodamine 6G (R6G) and 1,2-bis(4-pyridyl)ethylene (BPE) at various pH values, PVP-stabilized nanostructures demonstrate large differences in SERS enhancement factors (EFs) between these analytes depending on their chemical nature and protonation state. At pH values higher than BPE's pK(a2) of 5.65, where the analyte is largely unprotonated, the PVP-coated Au-Ag nanoshells showed a high SERS EF of >10(8). In contrast, SERS EFs were 10(3)- to 10(5)-fold lower for the protonated form of BPE at lower pH values, or for the usually highly SERS-active cationic R6G. The differential SERS activity of PVP-stabilized nanostructures is a result of discriminatory binding of analytes within-adsorbed PVP monolayer and a subsequent increase of analyte concentration at the nanostructure surface. Our experimental and theoretical quantum chemical calculations show that BPE binding with PVP-stabilized Au-Ag nanoshells is stronger when the analyte is in its unprotonated form as compared to its cationic, protonated form at a lower pH.     

金银合金纳米粒子表面处理及其表面增强拉曼光谱研究

采用水合肼还原的方法制备了金银比例为1∶1的金银合金纳米粒子, 紫外可见吸收光谱显示合成的溶胶只有一个介于金和银之间的吸收峰, 证明了合金结构的形成. 通过氨基耦联方法将合金纳米粒子组装到硅片表面, 利用氯金酸与合金中银的反应对基底上合金纳米粒子表面进行了改性处理. 以吡啶为探针分子, 研究了表面处理前后基底的SERS效应的差别, 结果表明随着浸泡时间延长, 信号强度先逐渐增强后降低至不变, 这与合金纳米粒子表面结构的变化有关, 氯金酸与表面银的反应经历了两个过程, 即粒子表面形成小的孔洞(去合金过程)和AgCl(s)在粒子表面的沉积, 前者有利于SERS效应的提高, 而后者导致SERS效应快速衰减.     

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。     

Thermal,morphological, and mechanical properties of ethyl vanillin immobilized in polyvinyl alcohol by electrospinning process

In this study, polyvinyl alcohol (PVA) nanofibers with ethyl vanillin as an active compound were prepared using electrospinning technique. The final products of electrospinning process were in the form of nanofibers films. PVA/ethyl vanillin nanofibers, having fibers diameters in the range 100–1700 nm, were successfully electrospun from ethanol/water mixture of PVA and ethyl vanillin. The effects of immobilization process on ethyl vanillin thermal properties were investigated by differential scanning calorimetry (DSC). The results of DSC showed significant influence of immobilization process on thermal properties of ethyl vanillin. It was noticed that melting point of immobilized ethyl vanillin was lower (~55 °C) compared to free flavor (~77 °C). Our results showed that films based on PVA/ethyl vanillin nanofibers are mechanically stable.     

Preparation of biocompatible system based on electrospun CMC/PVA nanofibers as controlled release carrier of diclofenac sodium

Nanofibers of naturally modified polymer such as carboxymethyl cellulose (CMC) blended with poly(vinyl alcohol) (PVA) at different ratios was obtained by electrospinning technique. The blended solutions of CMC and PVA loaded with and without diclofenac sodium (DS) were electrospun using environmentally benign electrospinning technique in the absence of organic solvents. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) were used to investigate the surface morphology functional groups, as well as the thermal stability of DS loaded CMC/PVA nanofibers mat. The mechanical properties of the as prepared electrospun nanofibers was also evaluated. The entrapment efficiency and the in vitro release of DS loaded CMC/PVA nanofibers were characterized using UV-Vis spectroscopy. The obtained results displayed that the blended nanofibers have shown a smooth morphology, no beads formation when the concentration of CMC was equal or below 5% and beads formation above 5%. FTIR data demonstrated that there were good interactions between CMC and PVA possibly via the formation of hydrogen bonds. The electrospun blended CMC/PVA nanofibers exhibit good mechanical properties. From the in vitro release data, it was found that with the presence of CMC, the release of DS from the nanofibers mats became sustained controlled. Due to the biocompatibility and low cost of the two blended polymers (CMC and PVA), the blended nanofibers system can be considered as one of the promising materials for the preparation of excellent drug carrier.     

Synthesis, characterization and SERS activity of Au-Ag nanorods

The formation mechanism and morphology of Au-Ag bimetallic colloidal nanoparticles depend on the composition. Ag coated Au colloidal nanoparticles have been prepared by deposition of Ag through chemical reduction on performed Au colloid. The composition of the Au(100-x)-Ag(x) particles was varied from x=0 to 50. The obtained colloids were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The Au(80)-Ag(20) colloid consists of alloy nanorods with dimension of 25nmx100nm. The activity of these nanorods in surface enhanced Raman spectroscopy (SERS) was checked by using sodium salicylate as an adsorbate probe. Intense SERS bands are observed indicating its usefulness as a SERS substrate in near infrared (NIR) laser excitation.     

Synthesis of block copolymer-stabilized Au-Ag alloy nanoparticles and fabrication of poly(methyl methacrylate)/Au-Ag nanocomposite film

[Poly(2-(N,N-dimethylamino)ethyl methacrylate)]-b-poly(methyl methacrylate)-b-[poly(2-(N,N-dimethylamino)ethyl methacrylate)] (M(n)=45,000; 20K-5K-20K; PDI = 1.2) block copolymer surfactant stabilized amphiphilic gold-silver alloy nanoparticles (Au-Ag(PDMA-b-PMMA-b-PDMA)) has been synthesized in both water and in organic medium. The block copolymer stabilized pre-made alloy nanoparticles were successfully dispersed in hydrophobic poly(methyl methacrylate) homopolymer matrix (PMMA) of molecular weight 30,000. The successful synthesis of alloy nanoparticles was accessed by Transmission Electron Microscope (TEM), Energy Dispersed X-ray (EDX), and UV-visible spectrophotometric analysis. The surface functionality of the nanoparticles was confirmed by quantitative determining the grafting density of polymer chain around the nanoparticle surface using combination of thermo gravimetric (TGA) and TEM analysis. The hydrodynamic diameter of the alloy particles including the polymer chains was obtained from dynamic light scattering measurement (DLS). The mechanism of synthesis of high concentration of Au-Ag alloy particles from HAuCl(4) and AgNO(3) (in presence of Cl(-) from reduction of gold salt) metal particles precursors and the successful preparation of poly(methyl methacrylate)/gold-silver nanocomposite films have been discussed.     

Au-Ag合金纳米粒子制备及其表面增强拉曼光谱研究

首先采用柠檬酸钠法制得Au-Ag合金纳米种子, 然后采用盐酸羟胺生长法得到不同组成的Au-Ag合金纳米粒子. 在其UV-Vis光谱中只观察到一个位于单金属银和金之间的等离子体共振峰, 表明Au-Ag合金纳米粒子已经形成. TEM结果表明, 合金纳米粒子的粒径约为60 nm, 且颜色均一, 没有明显的核壳结构. 用苯硫酚(TP)作为探针分子研究了合金纳米粒子的表面增强拉曼光谱(SERS). 结果表明, SERS强度与合金纳米粒子的组成和尺寸有关. 当纳米粒子粒径一定时, 除Au25Ag75外, 随着金的增加SERS强度增强. Au25Ag75的粒径比Ag小, 导致SERS强度比Ag低. Au50Ag50和Au75Ag25加入TP分子后, 其聚集方式与Au相似, 等离子体共振峰逐渐靠近1064 nm, 金含量较高时, TP的SERS归于聚集体的等离子体共振增强的贡献.     

Electrospinning preparation and mechanical properties of PVA/HNTs composite nanofibers

In this paper, the PVA/HNTs composite nanofibers with well‐enhanced mechanical properties were successfully prepared by electrospinning technique. The structure and properties of the composite nanofibers were characterized by TEM, XRD, FT‐IR, and DSC. The results indicated that the highly oriented and dispersed HNTs wrapped in polymer matrix were achieved by inducing function during electrospinning processing. The mechanical properties of the PVA/HNTs composite nanofibers depended on HNTs content were investigated, which showed 72.4% increase in tensile strength at optimal filling content. Copyright © 2016 John Wiley & Sons, Ltd.     

In situ encapsulation of laccase in nanofibers by electrospinning for development of enzyme biosensors for chlorophenol monitoring

A biosensor based on Trametes versicolor laccase (Lac) was developed for the determination of phenolic compounds. The biosensor was prepared by in situ electrospinning of a mixture of polyvinyl alcohol (PVA), Lac, PEO-PPO-PEO (F108) and gold nanoparticles (Au NPs), where F108 was used as an enzyme stabilizing additive and Au NPs was used to enhance the conductivity of the biosensor. Laser confocal scanning microscopy and electrochemical impedance spectroscopy proved that the enzyme was successfully encapsulated into the electrospun nanofibers. Under the optimal conditions, the lowest detection limit was found to be 0.04 μM (S/N = 3) for 2,4-DCP and the highest detection limit was found to be 12.10 μM for 4-CP. The sensitivity of the biosensor obtained in the linear range for chlorophenols followed the sequence 2,4-dichlorophenol (2,4-DCP) > 2,4,6-trichlorophenol (2,4,6-TCP) > 4-chlorophenol (4-CP). The sensing performance for chlorophenols was attributed to the suitable electrochemical interface of PVA/F108/Au NPs/Lac, resulting from biocompatibility, a high surface area-to-volume ratio (10.42 m(2) g(-1)) and superior mechanical properties of the electrospun nanofibers. The biosensor exhibited good repeatabilities of 7.6%, 2.8% and 9.0% (R.S.D.) and reproducibilities of 14.9%, 10.4% and 13.7% (R.S.D.) for 4-CP, 2,4-DCP and 2,4,6-TCP, respectively. Lac retained 65.8% of its initial activity after a 30-day storage period.     

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

Silver nanoparticles (AgNPs) embedded temperature-sensitive nanofibrous 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.     

Control release of lactate dehydrogenase encapsulated in poly (vinyl alcohol) nanofibers via electrospinning

Sustained release of lactate dehydrogenase (LDH, EC 1.1.1.27) from electrospun poly (vinyl alcohol) (PVA) nanofibers was successfully achieved using the coaxial electrospinning technique. The presence of the encapsulated enzyme in the nanofibers was confirmed by infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) was used to evaluate the morphology and diameter of the nanofibers. The conversion of lactate to pyruvate by LDH coupling with the reduction of the cofactor nicotinamide adenine dinucleotide (NAD⁺) to dihydronicotinamide adenine dinucleotide (NADH) produces an increment in the ultraviolet absorption (UV) at 340 nm. This change in the UV absorbance was used to follow the release kinetic of LDH from the PVA nanofibers and also as a measure to evaluate the residual enzymatic catalytic function. Most of the encapsulated LDH enzyme was released in a sustained manner from the PVA nanofibers within a period of 1 month.     

Transferring CdTe Nanoparticles from Liquid Phase to Polyvinylpyrrolidone Nanofibers by Electrospinning and Detecting Its Photoluminescence Property

The major aim of this work was to synthesize thio-stabilized CdTe nanoparticles(NPs) in an aqueous solution,which was then enwrapped with cetyltrimethylammonium bromide(CTAB),and finally transferred to the polyvinylpyrrolidone(PVP) matrix by electrospinning,The PVP nanofibers containing CdTe NPs were characterized by scanning electron microscopy(SEM) and transmission electron microscopy(TEM),to observe the morphology of the nanofibers and the distribution of CdTe NPs,The selective area electronic diffraction(SAED) pattern verified that CdTe NPs were cubic lattice,The photoluminescence(PL) spectrum indicated that CdTe NPs existed in an optical style in PVP nanofibers,Moreover,X-ray photoelectron spectra(XPS) revealed that thiol-stabilized CdTe NPs were enwrapped by CTAB,and PVP acted as a dispersant in the process of electrospinning.     

Transferring CdTe Nanoparticles from Liquid Phase to Polyvinylpyrrolidone Nanofibers by Electrospinning and Detecting Its Photoluminesccnce Property

The major aim of this work was to synthesize thio-stabilized CdTe nanoparticles（NPs） in an aqueous solution, which was then enwrapped with cetyltrimethylammonium bromide（CTAB）, and finally transferred to the polyvinylpyrrolidone（PVP） matrix by electrospinning. The PVP nanofibers containing CdTe NPs were characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）, to observe the morphology of the nanofibers and the distribution of CdTe NPs. The selective area electronic diffraction（SAED） pattern verified that CdTe NPs were cubic lattice. The photoluminescence（PL） spectrum indicated that CdTe NPs existed in an optical style in PVP nanofibers. Moreover, X-ray photoelectron spectra（XPS） revealed that thiol-stabilized CdTe NPs were enwrapped by CTAB, and PVP acted as a dispersant in the process of electrospinning.     

PVA/DTC纳米纤维的制备及对铅离子的吸附行为

通过高压静电纺丝技术制备了聚乙烯醇/聚乙烯亚胺(PVA/PEI)纳米纤维膜, 对纤维膜进行功能化使其转化为对重金属离子具有高络合能力的聚乙烯醇/二硫代氨基甲酸盐功能化聚乙烯亚胺(PVA/DTC)纳米纤维膜. 研究了PVA/PEI纳米纤维膜的交联和功能化以及PVA/DTC纤维膜对铅离子的吸附行为. 结果表明, 高压静电纺丝法可制备出纤维直径分布均匀、 形貌良好的纳米纤维膜, 且交联、 功能化后仍能保持蓬松纳米纤维状的网状结构. PVA/DTC纳米纤维膜对铅离子吸附速率快, 吸附量容量高, 且具有良好的再生吸附能力, 是一种潜在的重金属离子高效吸附材料.     

种子生长法制备Au-Ag纳米花

以金纳米花为种子, 抗坏血酸和硝酸银混合物作为生长溶液制备了Au-Ag纳米花. 当Ag/Au的摩尔比从0增加到0.3时, 银可以在Au种子表面沉积, 得到的Au-Ag纳米花光谱在592~518 nm之间连续可调, 同时纳米花的枝长逐渐减小; 而当Ag/Au摩尔比大于0.3时, 还原的银出现自成核现象. 与Au纳米花相比, Au-Ag纳米花体现出了更好的Raman增强活性.     

Preparation and Drug Release of PVA Composite Nanofibers Loaded Chitosan Microsphere

In this paper, we reported the fabrication of poly(vinyl alcohol)-chitosan (PVA-CS) microspheres composite nanofibers by electrospinning technique. The chitosan microspheres were firstly prepared by electrospray with the solution of chitosan and combretastatin A4. The morphology and size distribution of chitosan microspheres were analyzed by scanning electron microscopy. The influencing factors including the concentrations of both PVA and CS microspheres were studied. The physical properties of the composite nanofibers were characterized by X-ray diffraction (XRD). The drug release rate, MTT toxicity test, and cell culture were also investigated in detail. Results indicate that the chitosan microsphere-loaded composite nanofibers can be prepared when the PVA concentration is 120 mg/mL. The continuity of the nanofibers was influenced by the concentration of CS microspheres. The characteristic peaks of CS or PVA were not observed in the diffractograms after the CS and PVA were processed using the high-voltage electrostatic technique. In addition, the drug release rate showed that nanofibers induce an obvious slow-release effect. Composite nanofibers were non-toxic to fibroblasts cells, and the fibroblasts cells could proliferate on the nanofiber mat.     

Raman detection of localized transferrin-coated gold nanoparticles inside a single cell

We investigated the cellular uptake behavior of non-fluorescent metal nanoparticles (NPs) by use of surface-enhanced Raman scattering (SERS) combined with dark-field microscopy (DFM). The uptake of Au NPs inside a single cell could also be identified by DFM first and then confirmed by z-depth-dependent SERS at micrometer resolution. Guided by DFM for the location of Au NPs, an intracellular distribution assay was possible using Raman dyes with unique vibrational marker bands in order to identify the three-dimensional location inside the single cell by obtaining specific spectral features. Au NPs modified by 4-mercaptobenzoic acid (MBA) bearing its –COOH surface functional group were used to conjugate transferrin (Tf) protein using the 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) reaction. The protein conjugation reaction on Au surfaces was examined by means of color change, absorption spectroscopy, and SERS. Our results demonstrate that DFM techniques combined with SERS may have great potential for monitoring biological processes with protein conjugation at the single-cell level.     

Aligned polymer fibers produced via an additive electric field

Electrospinning is known to be a highly versatile method to produce nanofibers, and several techniques have been developed to align nanofibers. In this paper, poly(vinyl alcohol) (PVA), poly(vinylpyrrolidone) (PVP), poly(propylene carbonate) (PC), poly(ethylene oxide) (PEO), PVA/Chitosan and PVA/Fe₃O₄ uniaxially aligned ultrafine fibers were obtained with electrospinning method by adding another electric field in the collection area. Alignment of the nanofibers was characterized by the use of digital cameras and field emission scanning electron microscopy, polarized Fourier transform infrared spectroscopy (FTIR), and wideangle X-ray diffraction (XRD). The mechanism of fiber alignment was investigated as well.