绿色银纳米粒子的共振散射光谱研究

以柠檬酸钠作光还原剂,采用紫外光-可见光二步光化学法制备了绿色银纳米离子,在399.4nm和691.5nm处有二个紫外-可见吸收峰;在340nm,470nm和520nm处有三个共振散射峰,从超分子和纳米粒子这一整体出发,探讨了共振散射光谱产生的原因及银超分子光反应机理。     

Dissolution-accompanied aggregation kinetics of silver nanoparticles

Bare silver nanoparticles with diameters of 82 ± 1.3 nm were synthesized by the reduction of the Ag(NH(3))(2)(+) complex with D-maltose, and their morphology, crystalline structure, UV-vis spectrum, and electrophoretic mobilities were determined. Dynamic light scattering was employed to assess early stage aggregation kinetics by measuring the change in the average hydrodynamic diameter of the nanoparticles with time over a range of electrolyte types (NaCl, NaNO(3), and CaCl(2)) and concentrations. From this the critical coagulation concentration values were identified as 30, 40, and 2 mM for NaNO(3), NaCl, and CaCl(2), respectively. Although the silver nanoparticles were observed to dissolve in all three electrolyte solutions, the aggregation results were still consistent with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dissolution of the silver nanoparticles, which were coated with a layer of Ag(2)O, was highly dependent on the electrolyte type and concentration. In systems with Cl(-) a secondary precipitate, likely AgCl, also formed and produced a coating layer that incorporated the silver nanoparticles. Aggregation of the silver nanoparticles was also examined in the presence of Nordic aquatic fulvic acid and was little changed compared to that evaluated under identical fulvic acid-free conditions. These results provide a fundamental basis for further studies evaluating the environmental fate of silver nanoparticles in natural aquatic systems.     

Fabrication of flower-like silver nanoparticles for surface-enhanced Raman scattering

The flower-like silver nanoparticles have been synthesized by reducing silver nitrate (AgNO₃) with ascorbic acid (AA) as the reductant and polyvinyl pyrrolidone (PVP) as the capping agent under vigorous stirring. Such flower-like nanoparticles are aggregates of small nanoplates and nanorods. They were tested as substrates for the surface-enhanced Raman scattering (SERS), showing high sensitivity for detecting Rhodamine 6G (R6G) at a concentration as low as 10^-7 mol/L. It has been found that replacing mechanical stirring with ultrasound sonication would drastically change the particle morphology, from flower-like nanoparticles to well-dispersed smaller nanoparticles. Furthermore, when trace amounts of NaCl were added into the reagents, well-dispersed Ag nanoparticles formed even in vigorous stirring. These phenomena can be explained with the diffusion and reactant supply during nucleation and growth of Ag nanoparticles.     

Determination of critical micelle concentration by hyper-rayleigh scattering

The critical micelle concentration (CMC) of several surfactants that contain an NLO chromophore, either at the hydrocarbon tail, or at the hydrophilic headgroup, or even as a counterion, was determined by hyper-Rayleigh scattering (HRS). In all cases, the HRS signal exhibited a similar variation with surfactant concentration, wherein the CMC is inferred from a rather unprecedented drop in the signal intensity. This drop is attributed to the formation of small pre-micellar aggregates, whose concentrations become negligible above CMC. In addition, a probe molecule, which upon protonation yielded a species with significantly enhanced HRS intensity, was developed and its utility for the determination of the CMC of simple fatty acids was demonstrated.     

Surface-enhanced Raman scattering of 4-aminobenzenethiol on silver nanoparticles substrate

Active surface-enhanced Raman scattering (SERS) silver nanoparticles substrate was prepared by multiple depositions of Ag nanoparticles on glass slides. The substrate is based on five depositions of Ag nanoparticles on 3-aminopropyl-trimetoxisilane (APTMS) modified glass slides, using APTMS sol–gel as linker molecules between silver layers. The SERS performance of the substrate was investigated using 4-aminobenzenethiol (4-ABT) as Raman probe molecule. The spectral analyses reveal a 4-ABT Raman signal enhancement of band intensities, which allow the detection of this compound in different solutions. The average SERS intensity decreases significantly in 4-ABT diluted solutions (from 10⁻⁴ to 10⁻⁶ mol L⁻¹), but the compound may still be detected with high signal/noise ratio. The obtained results demonstrate that the Ag nanoparticles sensor has a great potential as SERS substrate.     

Small-sized silver nanoparticles for studies of biological effects

The influence of the hydration extent, AOT and silver ion concentration on average particle size and size distribution in micellar solution of silver nanoparticles obtained by biochemical synthesis was investigated. Formation and stability of nanoparticles were controlled by measurements of optical absorption spectra. Particle sizes were determined by transmission electron microscopy. Combinations of varied parameters have been found, making it possible to prepare three micellar solutions of spherical silver nanoparticles with a different average size in the range 4.6–10.5 nm and narrow size distribution (the standard deviation does not exceed 2.5 nm). For the water dispersions prepared from such solutions by the specially developed procedure, possible applications for studies of size effects in the biological action of nanoparticles are also discussed.     

Study of amphiphilic polyester micelles by hyper-rayleigh scattering: invertibility and phase transfer

For the first time, hyper-Rayleigh scattering (HRS) of invertible polymeric micellar structures has been measured. HRS measurements on amphiphilic invertible polyesters with alternating hydrophilic and hydrophobic fragments were carried out in solvents of differing polarity. The observed strong variation of the HRS signals is attributed to the switching behavior of the polyester micelles in the different solvents. The hyperpolarizabilities and the size of the micelles increased with decreasing polarity of the solvent. Observing the dynamics of the solubilization of an insoluble dye (malachite green) by the invertible polyester in toluene confirmed the possibility to reveal conformational changes in polyester macromolecules by HRS. In contrast to UV measurements which showed a continuous increase in absorbance and indicated overall solubilization of the dye, the HRS signals decreased after approaching a maximum value. The decrease of the HRS signals is attributed to the change of dye molecules' orientation within the micelles due to the change of polymeric conformation in toluene. The results have shown that HRS is sensitive to reorientation and ordering of the macromolecules and might become a powerful tool for studying polymer micellar structures as well as phase transfer processes at the nanoscale.     

Surface-enhanced Raman scattering measurements on silver nanoparticles covered with differently formed platinum films

Gold and silver electromagnetic nanoresonators covered by a thin layer of platinum are often used to study adsorption of various molecules on “model platinum surfaces” with surface-enhanced Raman scattering (SERS) spectroscopy. In this contribution spectra of pyridine adsorbed on films formed from core–shell Ag@Pt and Ag@Ag–Pt nanoparticles and pure Pt or Ag nanoparticles were measured using a confocal Raman microscope. The SERS spectra of pyridine adsorbed on alloy Ag@Ag–Pt nanoparticles could not be obtained as a linear combination of spectra measured on pure Ag and Pt surfaces. In other words, for silver electromagnetic nanoresonators covered by platinum there is no simple correlation between the “quality” of the deposited Pt layer and the relative intensity of SERS bands characteristic for adsorbate interacting with silver. The SERS spectra accumulated from various places of a film formed from Ag@Pt or Ag@Ag–Pt nanoclusters may differ significantly. Using Ag@Pt nanoparticles with practically negligible amount of Ag on the surface (as per the stripping measurement), it is possible to record SERS spectrum in which the contribution characteristic for pyridine adsorbed on the Ag surface is well visible. It means that, even for macroscopic samples of core–shell Ag–Pt nanoparticles, averaging of many spectra measured at various locations of the sample should be carried out to characterize reliably their properties.     

Surface-enhanced Raman scattering sensor for theophylline determination by molecular imprinting on silver nanoparticles

A surface-enhanced Raman scattering (SERS)-based sensor for the determination of theophylline (THO) has been developed by imprinting the target molecules on the surface of silver nanoparticles. The desired recognition sites are generated after template removal and homogeneous distribution on the silver nanoparticles that have been incorporated within polymer matrix by the in situ reduction of theophylline-silver complexes, providing molecular recognition ability and SERS active surfaces. The theophylline molecules, complementary to the shape, size, and functionality of the recognition cavities, can selectively bind to the recognition sites at the surface of silver nanoparticles driven by the formation of hydrogen bonding and surface coordination. It has been demonstrated that the SERS signals of the theophylline molecules captured on the surface of the silver nanoparticles have a good reproducibility and a dose-response relationship to the target analytes, showing the potential for reliable identification and quantification of the bioactive compound. The molecular imprinting-based SERS sensor, like antibodies or enzymes, also possesses the ability to distinguish theophylline from the closely related structure caffeine due to the variations of molecular size and shape as well as the different affinity to silver ions.     

Homogeneous immunoassay based on aggregation of antibody-functionalized gold nanoparticles coupled with light scattering detection

A universal platform of homogeneous noncompetitive immunoassay, using human immunoglobulin (IgG) as a model analyte, has been developed. The assay is based on aggregation of antibody-functionalized gold nanoparticles directed by the immunoreaction coupled with light scattering detection with a common spectrofluorimeter. In phosphate buffer (pH 7.0) solution, the light scattering intensity of the gold nanoparticles functionalized with goat-anti-human IgG can be greatly enhanced by addition of the human IgG. Based on this phenomenon, a wide dynamic range of 0.05-10 microg ml(-1) for determination of human IgG can be obtained, and the detection limit can reach 10 ng ml(-1). The proposed immunoassay can be accomplished in a homogeneous solution with one-step operation within 10 min and has been successfully applied to the determination of human IgG in serum samples, in which the results are well consistent with those of the enzyme-linked immunosorbent assay (ELISA), indicating its high selectivity and practicality. Therefore, the gold nanoparticle-based light scattering method can be used as a model to establish the general methods for protein assay in the fields of molecular biology and clinical diagnostics.     

Functionalized gold nanoparticles as nanosensor for sensitive and selective detection of silver ions and silver nanoparticles by surface-enhanced Raman scattering

We have developed a surface-enhanced Raman scattering (SERS) nanosensor firstly for Ag ions and Ag nanoparticles detection based on 2-mercaptoisonicotinic acid (2MNA)-functionalized Au nanoparticles. Ag(+) can coordinate with 2MNA resutling in a variation of its SERS spectrum, which is used as a criterion to determine Ag(+) in a solution. This sensor exhibits a detection limit no more than 25 nM and has a high selectivity against other metal ions. More importantly, it can be directly applied in real sample detection.     

Self-assembled dynamics of silver nanoparticles and self-assembled dynamics of 1,4-benzenedithiol adsorbed on silver nanoparticles: Surface-enhanced Raman scattering study

Self-assembled dynamics of silver nanoparticles and self-assembled dynamics of 1,4-benzenedithiol (1,4-BDT) adsorbed on silver nanoparticles were investigated experimentally with surface-enhanced Raman scattering (SERS) and theoretically with density functional theory (DFT) and finite difference time domain (FDTD) method. The absorption spectroscopy of 1,4-BDT in silver sol at different time intervals was measured, which give the indirect evidence of self-assembled dynamics of silver nanoparticles and self-assembled dynamics of 1,4-benzenedithiol (1,4-BDT) adsorbed on silver nanoparticles. To obtain the direct evidence of self-assembled dynamics of silver nanoparticles and self-assembled dynamics of 1,4-benzenedithiol (1,4-BDT) adsorbed on silver nanoparticles, the SERS of 1,4-BDT were measured experimentally and investigated theoretically. The appearances of S–S stretching band (revealing the formation of multilayers of 1,4-BDT), and strongly enhanced S–C stretching, C–C ring stretching vibrational modes clearly show self-assembled dynamics of 1,4-BDT.     

Modeling molecular effects on plasmon transport: silver nanoparticles with tartrazine

Modulation of plasmon transport between silver nanoparticles by a yellow fluorophore, tartrazine, is studied theoretically. The system is studied by combining a finite-difference time-domain Maxwell treatment of the electric field and the plasmons with a time-dependent parameterized method number 3 simulation of the tartrazine, resulting in an effective Maxwell∕Schro?dinger (i.e., classical∕quantum) method. The modeled system has three linearly arranged small silver nanoparticles with a radius of 2 nm and a center-to-center separation of 4 nm; the molecule is centered between the second and third nanoparticles. We initiate an x-polarized current on the first nanoparticle and monitor the transmission through the system. The molecule rotates much of the x-polarized current into the y-direction and greatly reduces the overall transmission of x-polarized current.     

Immunoassay using surface-enhanced Raman scattering based on aggregation of reporter-labeled immunogold nanoparticles

A one-step homogenous sensitive immunoassay using surface-enhanced Raman scattering (SERS) has been developed. This strategy is based on the aggregation of Raman reporter-labeled immunogold nanoparticles induced by the immunoreaction with corresponding antigens. The aggregation of gold nanoparticles results in a SERS signal increase of the Raman reporter. Therefore, human IgG could be directly determined by measuring the Raman signal of the reporter. The process of aggregation was investigated by transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. The effects of the temperature, time, and size of gold nanoparticles on the sensitivity of the assay were examined. Using human IgG as a model protein, a wide linear dynamic range (0.1-15 microg mL(-1)) was reached with low detection limit (0.1 microg mL(-1)) under optimized assay conditions. The successful test suggests that the application of the proposed method holds promising potential for simple, fast detection of proteins in the fields of molecular biology and clinical diagnostics.     

Derivatized silver nanoparticles as sensor for ultra-trace nitrate determination based on light scattering phenomenon

New silver nanoparticles coated with EDTA (EDTA-AgNPs) have been synthesized by citrate reduction method and characterized by UV-vis spectroscopy, molecular fluorescence and scanning electron microscopy (SEM). The derivatized nanoparticles show fluorescent emission and second order scattering (SOS) signals which in presence of nitrate are both attenuated. The SOS decreasing is greater than its fluorescent quenching; considering this fact, a new ultra sensitive methodology using the derivatized silver nanoparticles as sensor for nitrate determination has been developed. Under optimal established conditions, a linear response has been obtained within the range of 6.4 × 10⁻⁴ to 3.0 μg mL⁻¹ nitrate concentrations, with a detection limit of 1.8 × 10⁻⁴ μg mL⁻¹. This novel technique provides a sensitive and selective methodology for nitrate determination and has been satisfactorily applied to its quantification in parenteral solutions.     

Surface-enhanced Raman scattering of EDOT and PEDOT on silver and gold nanoparticles

Surface-enhanced Raman scattering (SERS) spectra of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and its monomer 3,4-ethylenedioxythiophene (EDOT) on Ag and Au nanoparticles presenting different morphologies and stabilizing agents have been obtained using the excitation radiation at 633 nm. The SERS spectra of the monomer and polymer are strongly dependent both on the metal and capping agent of the substrate. SERS spectra of EDOT on Au nanospheres indicates that adsorption occurs with the thiophene ring perpendicular to the metal surface. In contrast, polymerization takes place on the silver surface of Ag nanospheres. EDOT adsorption on Ag nanoprisms with polyvinylpyrrolidone (PVP) as capping agent occurs similarly to that observed on gold. Surface-enhanced resonance Raman scattering (SERRS) spectra of PEDOT on gold nanostars that present a thick layer of PVP show no chemical interaction of PEDOT with the metal surface; however, when PEDOT is adsorbed on citrate stabilized gold nanospheres, the SERRS spectra suggest that thiophene rings are perpendicular to the surface. Oxidation of PEDOT also is observed on Ag nanospheres. The investigation of the interface between PEDOT and metal surface is crucial for the development in polymer-based optoelectronic devices since this interface plays a crucial role in their stability and performance.     

Detection of ferulic acid based on the plasmon resonance light scattering of silver nanoparticles

In this contribution, a plasmon resonance light scattering (PRLS) detection method of ferulic acid (FA) is proposed based on the formation of silver nanoparticles (NPs). It was found that, FA acted as a reducing agent in alkaline medium and could be oxidized by AgNO₃, resulting in the formation of silver NPs. The formed silver NPs, which were identified by measuring the plasmon resonance absorption spectra, PRLS spectra and transmission electron microscopy (TEM) image, display characteristic plasmon resonance optical absorption and PRLS band in the visible region. It was found that the PRLS intensity, which could be easily measured using a common spectrofluorometer, was in proportion to the concentration of FA over the range from 0.2 to 2.0 μmol l⁻¹ with the corresponding limits of determination (3σ) of 15.2 nmol l⁻¹. With that, ferulate sodium injection samples have been detected with R.S.D. lower than 3.0% and recoveries over the range of 101.2–104.5%. On the other hand, the present reaction maybe provides the basis of an environmentally friendly approach for the synthesization of silver NPs.     

Zinc oxide nanotubes decorated with silver nanoparticles as an ultrasensitive substrate for surface-enhanced Raman scattering

We introduce a novel voltammetric method, so-called sinusoidal envelope voltammetry, for use in electronic tongues. Fourier transformation was used to transform the data of the signal from the time domain to the frequency domain. The four taste substances, acesulfame potassium, monosodium glutamate, potassium chloride and tartaric acid, are shown to exhibit abundant frequency characteristics in the power spectrum of a Fourier transformation. This indicates that the power spectrum from sinusoidal envelope voltammetry can be used as fingerprints of samples for classification. Principal component analysis along with discrimination index and multi-frequency large amplitude pulse voltammetry as a reference technique is used to evaluate the separation ability of sinusoidal envelope voltammetry. The score plots of the method for the four taste substances and for the five brands of Jiafan rice wine show better discrimination ability than multi-frequency large amplitude pulse voltammetry. Sinusoidal envelope voltammetry is considered to be a promising technique for use in voltammetric electronic tongues.

Determination of trace chlorine dioxide based on the plasmon resonance scattering of silver nanoparticles

A plasmon resonance scattering (PRS) method for chlorine dioxide is reported based on the oxidization of silver nanoparticles (NPs) by it, in pH 9.1 ammonia-ammonium nitrate buffer solutions. Silver NPs exhibit strong PRS signals at 470nm, and can be oxidized by ClO(2), which results in PRS quenching at 470nm. It was found that the PRS quenching intensity is proportional to the concentration of chlorine dioxide over the range of 0.0011-0.185microg/mL, with a detection limit (3sigma) of 0.00050microg/mL and the correlation coefficient of 0.9995. The method is simple, rapid and cost effective. It was applied to the determination of chlorine dioxide in drinking water, with satisfactory results.