Stimuli-responsive hydrogel-silver nanoparticles composite for development of localized surface plasmon resonance-based optical biosensor

In this paper, the development of a localized surface plasmon resonance (LSPR)-based optical enzyme biosensor using stimuli-responsive hydrogel-silver nanoparticles composite is described. This optical enzyme biosensor was constructed by immobilizing glucose oxidase (GOx) into the stimuli-responsive hydrogel. When a sample solution such as glucose was applied to the surface of this optical enzyme biosensor, the interparticle distances of the silver nanoparticles present in the stimuli-responsive hydrogel were increased, and thus the absorbance strength of the LSPR was decreased. Furthermore, hydrogen peroxide, which was produced by the enzymatic reaction, induced the degradation of highly clustered silver nanoparticles by the decomposition of hydrogen peroxide. Hence, a drastic LSPR absorbance change, which depends on the glucose concentrations, could be observed. On the basis of the abovementioned mechanism, the characterization of the LSPR-based optical enzyme biosensor was carried out. It was found that the LSPR-based optical enzyme biosensor could be used to specifically determine glucose concentrations. Furthermore, the detection limit of this biosensor was 10 pM. Therefore, this LSPR-based optical enzyme biosensor has the potential to be applied in cost-effective, highly simplified, and highly sensitive test kits for medical applications.     

Biogenic synthesis of gold and silver nanoparticles used in environmental applications: A review

Due to their physical, chemical, optical, and mechanical properties, metallic nanoparticles (MNPs) are increasingly being used, with an emphasis on silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs). In recent years, green synthesis has gained prominence for exploring the use of naturally available biological sources for the obtention of metallic nanoparticles. Among these, algae and plants stand out due to the presence of polysaccharides, proteins, polyphenols, and vitamins (among others) in their composition, which can act in the reduction and stabilisation of MNPs, and these biogenic materials have been characterised mainly by spectrometric and microscopic techniques. In addition, due to the numerous advantages of nanoparticles (NPs) synthetize from biogenic source, such as their simplicity and cost benefits, they have been used in the development of sensors applied in the determination of contaminants present in environmental samples and in the catalytic reduction of organic and inorganic contaminants. Therefore, this review describes the synthesis, mechanisms, characterization, and environmental analytical applications of NPs obtained by biogenic synthesis as well as the perspectives and challenges of these NPs.     

表面等离激元金属纳米粒子的多元化结构及应用

目前, 单一的金属纳米粒子结构已经难以满足多学科交叉发展的需求. 因此, 将多种金属纳米粒子(如不同尺寸、 形状、 组分等)集成在同一基底表面, 能够充分发挥不同金属纳米粒子的性质和优势, 极具研究价值和应用价值. 本文介绍了多元化表面等离激元纳米粒子结构的构筑方法, 以及其在信息编码、 光电器件、 能源催化等领域的应用. 最后, 提出了当前在多元化结构制备中存在的挑战, 并展望了利用多元化结构实现性能提升的前景.     

Highly sensitive colorimetric detection of NH3 based on Au@Ag@AgCl core-shell nanoparticles

As an important component of the atmosphere, ammonia (NH₃) plays a very important role in maintaining the balance of environment. However, it is also one of the most toxic gases that can cause damage to the human respiratory system and mucous membranes even at low concentrations. As such, development of highly sensitive and selective NH₃ sensors is of high significance for environmental monitoring and health maintenance. Herein, we have synthesized Au@Ag@AgCl core-shell nanoparticles (NPs) by oxidative etching and precipitating Au@Ag core-shell NPs using FeCl₃ and further used them as optical probes for the colorimetric detection of NH₃. The sensing mechanism is based on the fact that the etching of NH₃ on AgCl and Ag shell leads to the variations of ingredients and core-to-shell ratio of the Au@Ag@AgCl NPs, thereby inducing noticeable spectral and color changes. By replacing the outmost layer of Ag with AgCl, not only is the stability of the sensor against oxygen significantly enhanced, but also is the sensitivity of the method improved. The method exhibits good linear relationship for the detection of NH₃ from 0 to 5000 μmol/L with the limit of detection of 6.4 μmol/L. This method was successfully applied to the detection of simulated air polluted by NH₃, indicating its practical applicability for environmental monitoring. This method shows great potential for on-site NH₃ detection particularly in remote area, where a simple, fast, low-cost, and easy-to-handle method is highly desirable.     

Metal oxide nanoparticles: synthesis, characterization and application

The synthesis of metal oxide nanoparticles is described in terms of precursor formation, nucleation, growth, and aging processes. The main parameters governing these processes are the solution properties, including the solvent viscosity, dielectric constant and the presence of adsorbing anions, the solubility of the metal oxide, and the metal oxide surface energy.     

Colloidal AgCl induced-growth of thorny gold nanoparticles and their SERS activity

In this paper, we exploited a unique procedure for obtaining thorny gold nanoparticles (Au NPs) with controllable length of thorns without using seeds and surfactants. The obtained Au NPs exhibited shape-determined surface-enhanced Raman spectroscopy activity toward rhodamine 6G.     

Tuning the size,concaveness, and aspect ratio of concave cubic gold nanoparticles produced with high reproducibility

Reproducible fabrication of concave cubic gold nanoparticles with precise control over size, concaveness, and aspect ratio is important because the nanoscale structural characteristics can influence their plasmonic and catalytic properties. However, this is particularly challenging because the number of synthetic parameters involved in the fabrication strategy adds complexity to the reaction mechanism. Here, we introduce a simplified seed-mediated method and uncover the unknown conceptual insights on how the different halides and their concentration influence the surface structure and stability of underpotential silver monolayer deposited on the high energy facets of nanoparticles. The results reveal that adding Br^? and I^? ions to growth solution offers a predominant way to control the reaction kinetics and engineering nanoparticles with a predefined size, morphology, concaveness, aspect ratio, and plasmonic properties. Using spectroscopy and microscopy techniques, we shed new light on the reaction kinetics of concave cubic gold nanoparticles using the combined influence of silver underpotential deposition and halides. The strategy developed here can be expanded to fabricate gold nanoparticles of complex geometries. The results from our electromagnetic calculations suggest that the self-assembled superstructure of concave cubic gold nanoparticles can be more appealing for developing an ultra-sensitive sensing platform than to self-assembled superstructures of truncated cubic gold nanoparticles.     

Ganoderma applanatum-mediated green synthesis of silver nanoparticles: Structural characterization,and in vitro and in vivo biomedical and agrochemical properties

This study presents the use of basidiomycete extracts as an effective platform for “green synthesis” of silver nanoparticles (AgNPs). Out of seven basidiomycete species, Ganoderma applanatum displayed the highest antimicrobial properties against the tested pathogens. Thus, G. applanatum methanol crude extract was fractionated using column chromatography, and the obtained fractions were subjected to an antimicrobial assay followed by phytochemical analyses using high-performance liquid chromatography to select the best fraction for synthesis of AgNPs. Fraction 3 displayed potent antimicrobial activities as evidenced by its high phenolic content, and thus was used for AgNP biosynthesis. The G. applanatum fraction 3-synthesized AgNPs were then characterized using various microscopy, spectroscopy and X-ray diffraction techniques. The characteristic features of the synthesized AgNPs indicated the spherical shape of AgNPs with an average size of 20–25 nm. The synthesized AgNPs exhibit high antioxidant capacity, in vitro antibacterial activity against Staphylococcus aureus and Escherichia coli, and in vivo antifungal properties against Botrytis cinerea and Colletotrichum gloeosporioides in tomato and strawberry leaflet assays, respectively. Our results demonstrated that G. applanatum can be efficiently used in synthesis of AgNPs with potent antimicrobial properties, which can be used for both clinical and agrochemical purposes.     

Plant-assisted synthesis of gold nanoparticles for photocatalytic,anticancer, and antioxidant applications

The current study is the first to disclose a quick, cost-effective, and environmentally safe phytofabrication of gold nanoparticles (AuNPs) that remained stable for three months utilizing the aqueous extract of T. capensis leaves to uphold the principles of green chemistry such as less hazardous chemical syntheses, safer solvents and auxiliaries, design for energy efficiency, and use of renewable feedstocks. Several approaches were used to describe T. capensis-AuNPs, with the findings revealing the successful phytoformation of crystalline AuNPs with a dark brown color, spherical nanoparticles with a size range of 10–35 nm, a surface plasmon peak at 515 nm, and a surface charge of ? 24.5 mV. T. capensis-AuNPs showed 72% photodegradation efficacy against malachite green. The MTT experiment revealed that T. capensis-AuNPs and T. capensis extract had excellent potency in preventing the development and proliferation of human breast cancer cells (MCF7 cell line), with IC50 values of 9.6 g/mL and 23.3 g/mL, respectively. Both T. capensis-AuNPs and T. capensis extract had significant antioxidant efficacies, with DPPH scavenging percentages of 70.73% for T. capensis-AuNPs and 85.62% for T. capensis extract. Consequently, these findings suggest a new and sustainable route for the green synthesis of AuNPs using the aqueous extract of T. capensis.     

Colloidal micelles of block copolymers as nanoreactors,templates for gold nanoparticles,and vehicles for biomedical applications

Target drug delivery methodology is becoming increasingly important to overcome the shortcomings of conventional drug delivery absorption method. It improves the action time with uniform distribution and poses minimum side effects, but is usually difficult to design to achieve the desire results. Economically favorable, environment friendly, multifunctional, and easy to design, hybrid nanomaterials have demonstrated their enormous potential as target drug delivery vehicles. A combination of both micelles and nanoparticles makes them fine target delivery vehicles in a variety of biological applications where precision is primarily required to achieve the desired results as in the case of cytotoxicity of cancer cells, chemotherapy, and computed tomography guided radiation therapy.     

Detection of antinuclear antibodies by a colloidal gold modified optical fiber: comparison with ELISA

A fiberoptic evanescent-wave sensor has been developed for the measurement of antinuclear antibodies in sera from patients and healthy individuals. The sensor was constructed on the basis of modification of the unclad portion of an optical fiber with self-assembled gold colloids, where the colloidal gold surface was further functionalized with extractable nuclear antigens. Results show that detection of antinuclear antibodies by this sensor agrees quantitatively with the clinically accepted enzyme-linked immunosorbent assay (ELISA) method. This sensing platform has the following advantages: label-free and real-time detection capability, simple to construct and use, highly sensitive, and does not require a secondary antibody. The sensitivity of this platform is at least an order of magnitude higher than that of the ELISA method and thus may lead to a new direction in recognition of immune response. Biomolecular binding of antinuclear antibodies (ANA) with extractable nuclear antigens (ENA)-functionalized gold nanoparticles results in a change of surface plasmon absorption. When light propagates in an optical fiber by multiple total internal reflection, such a change in signal can be significantly enhanced.     

A novel one step synthesis of silver nanoparticles using room temperature ionic liquid and their biocidal activity

This article reports the synthesis of silver Nan particles (SNPs) using 1-(dodecyl) 2 amino-pyridinium bromide ionic liquid. This is a new one phase method for the synthesis of uniform monodispersed crystalline silver nanoparticles in a water-ionic liquid system. In this work, the functionalized room temperature IL acts as stabilizing agent and solvent. Hydrazine hydrate acts as reducing agent. To the best of our knowledge, there is no report of the synthesis of metal nanoparticles using this ionic liquid. The synthesis of silver nanoparticles is very primarily studied by UV-Visible spectroscopic analysis. The TEM and particle size distribution was used to study morphology and size of the particles. The charge on synthesized SNPs was determined by Zeta potential. The silver nanoparticles have been known to have inhibitory and bactericidal effect. The investigation of antibacterial activities of ionic liquid stabilized silver nanoparticles was performed by measurement of the minimum inhibitory concentration.     

Type I collagen-mediated synthesis of noble metallic nanoparticles networks and the applications in Surface-Enhanced Raman Scattering and electrochemistry

In this paper, we demonstrated an effective enviromentally friendly synthesis route to prepare noble metallic (Au, Ag, Pt and Pd) nanoparticles (NPs) networks mediated by type I collagen in the absence of any seeds or surfactants. In the reactions, type I collagen served as stabilizing agent and assembly template for the synthesized metallic NPs. The hydrophobic interaction between collagen and mica interface as well as the hydrogen bonds between inter- and intra-collagen molecules play important roles in the formation of collagen-metallic NPs networks. The noble metallic NPs networks have many advantages in the applications of Surface-Enhanced Raman Scattering (SERS) and electrochemistry detection. Typically, the as-prepared Ag NPs networks reveal great Raman enhancement activity for 4-ATP, and can even be used to detect low concentration of DNA base, adenine, without any label step. Furthermore, the cyclic voltammograms showed Pt NPs networks have good electrocatalytic ability for the reduction of O₂.     

Bioinspired synthesis of multifunctional silver nanoparticles for enhanced antimicrobial and catalytic applications with tailored SPR properties

In the developing nanotechnology world, numerous attempts have been made to prepare the nobel metallic nanoparticles (NPs), which can improve their applicability in diverse fields. In the present work, the biosynthesis of silver (Ag) NPs has been successfully achieved through the medicinal plant extract (PE) of G. resinifera and effectively used for the catalytic and antibacterial applications. The size dependant tuneable surface plasmon resonance (SPR) properties attained through altering precursor concentrations. The X-ray and selected area diffraction pattern for Ag NPs revealed the high crystalline nature of pure Ag NPs with dominant (111) phase. The high-resolution TEM images show the non-spherical shape of NPs shifting from spherical, hexagonal to triangular, with wide particle size distribution ranging from 13 to 44 nm. Accordingly, the dual-band SPR spectrum is situated in the UV–Vis spectra validating the non-spherical shape of Ag NPs. The functional group present on the Ag NPs surface was analysed by FT-IR confirms the capping and reducing ability of methanolic PE G. resinifera. Further, the mechanism of antimicrobial activity studied using electron microscope showed the morphological changes with destructed cell walls of E. coli NCIM 2931 and S. aureus NCIM 5021 cells, when they treated with Ag NPs. The Ag NPs were more effective against S. aureus and E. coli with MIC 128 μg/ml as compared to P. aeruginosa NCIM 5029 with MIC 256 μg/ml. Apart from this, the reduction of toxic organic pollutant 4-NP to 4-AP within 20 min reveals the excellent catalytic activity of Ag NPs with rate constant k = 15.69 s^?1.     

Measurement of antibody binding to protein immobilized on gold nanoparticles by localized surface plasmon spectroscopy

Antibody binding to bovine serum albumin (BSA) and human serum albumin (HSA) immobilized onto gold nanoparticles was studied by means of localized surface plasmon resonance (LSPR) spectroscopy. Amine-modified glass was prepared by self-assembly of amine-terminated silane on substrate, and gold (Au) nanoparticles were deposited on the amine-modified glass substrate. Au nanoparticles deposited on the glass surface were functionalized by BSA and HSA. BSA immobilization was confirmed by LSPR spectroscopy in conjunction with surface-enhanced Raman scattering spectroscopy. Then, LSPR response attributable to the binding of anti-BSA and anti-HSA to BSA- and HSA-functionalized Au nanoparticles, respectively, was examined. Anti-HSA at levels larger than ∼10 nM could be detected by HSA-immobilized chips with LSPR optical response, which was saturated at concentrations greater than ∼650 nM of anti-HSA. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorized users.     

Production and structural characterization of crystalline silver nanoparticles from Bacillus cereus isolate

To date, biosynthesis of metal nanoparticles has been intensively studied using bacteria and fungi. We have isolated and identified metal resistant bacterial strains from electroplating industries, they produce silver nanoparticles. The reduction reaction of aqueous silver nitrate with bacterial biomass was carried out for 120 h. Bacteria produced metallic nanoparticles showed a strong absorbance at surface plasmon resonance wavelength around 420 nm. The size and morphology of these nanoparticles were typically imaged using high resolution transmission electron microscopy, the particles size ranges between 4 and 5 nm and are spherical in shape. The crystal structure of the particles was characterized by X-ray diffraction pattern. The full width half maxima from X-ray diffraction measurements indicated that the particles exhibited face-centered cubic phase.     

Localized surface plasmon resonance: nanostructures, bioassays and biosensing--a review

Localized surface plasmon resonance (LSPR) is an optical phenomena generated by light when it interacts with conductive nanoparticles (NPs) that are smaller than the incident wavelength. As in surface plasmon resonance, the electric field of incident light can be deposited to collectively excite electrons of a conduction band, with the result being coherent localized plasmon oscillations with a resonant frequency that strongly depends on the composition, size, geometry, dielectric environment and separation distance of NPs. This review serves to describe the physical theory of LSPR formation at the surface of nanostructures, and the potential for this optical technology to serve as a basis for the development bioassays and biosensing of high sensitivity. The benefits and challenges associated with various experimental designs of nanoparticles and detection systems, as well as creative approaches that have been developed to improve sensitivity and limits of detection are highlighted using examples from the literature.     

The preparation and characterization of poly(o-phenylenediamine)/gold nanoparticles interface for immunoassay by surface plasmon resonance and electrochemistry

The poly-o-phenylenediamine (PoPD) nonconducting film and gold nanoparticles (AuNPs) were combined to fabricate AuNPs/PoPD film, which is used as a novel biocompatible interface for the immobilization of antibody and develop a simple and sensitive label-free immunoassay for the detection of the related antigen (human immunoglobulin G (IgG)). Surface plasmon resonance (SPR) and electrochemical methods were used to provide the real-time information about the polymer film growth, assembling of various sizes of gold nanoparticles, anti-human IgG antibody (anti-hIgG) immobilization and the antigen–antibody interaction. The microstructures of the PoPD and AuNPs/PoPD films were characterized by atomic force microscopy (AFM). These results demonstrated that AuNPs were uniformly dispersed on the porous surface of PoPD film, which formed a nano-structure biocompatible AuNPs/PoPD interface. The use of gold nanoparticles and PoPD film could enhance the immunoassay sensitivity and anti-nonspecific property of the resulting immunoassay electrode. Additionally, the reproducibility and preliminary application of anti-hIgG/AuNPs/PoPD/Au electrode for SPR detection of hIgG was also evaluated.     

Synthesis and spectroscopic characterization of gold nanoparticles

Photoluminescent nanoparticles of gold with size 3, 4, 6, and 9nm are prepared by borohydride/citrate reduction in presence of polyethylene glycol (PEG)/tannic acid. The prepared nanomaterials are characterized by UV-vis spectroscopy and dynamic light scattering (DLS) technique. Intense photoluminescence (PL) is observed in nanoparticles prepared by fast reduction with borohydride in presence of PEG. A red shift of PL emission from 408 to 456nm is observed for the change of size from 4 to 6nm. Increase in PL intensity is observed for all the nanoparticles on the addition of KCl. Citrate reduced gold colloid which consists of large particles of size approximately 35nm with anisotropic shapes showing two plasmon peaks is also prepared. The anisotropy is confirmed by TEM measurement. SERS activity of this colloid is tested using glutamic acid as an adsorbate probe. Assignment of the observed bands is given.     

Effect of pH and generation of dendron on single‐step synthesis of gold nanoparticles using PEGylated polyamidoamine dendron in aqueous medium

Three types of PEGylated polyamidoamine (PAMAM) dendrons were synthesized through PEGylation of primary amines at the periphery of second, third, and fourth generation dendrons. Au(III) precursors and the synthesized PEGylated PAMAM dendrons were mixed at various pHs to evaluate the effect of pH on gold nanoparticle (Au NP) synthesis by monitoring the change in surface plasmon resonance. The Au NP synthesis reaction was controlled by pH through the balance between protonated and deprotonated tertiary amines and the reactivity of Au(III) precursors. By using PEGylated PAMAM dendrons with higher generation, the obtained Au NPs had narrow size distribution with small average size because of the limitation of intermolecular space among PEGylated PAMAM dendrons for the growth to Au NP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1391–1398, 2010