Synthesis of gold nanoparticles stabilized with poly(N-isopropylacrylamide)-co-poly(4-vinyl pyridine) colloid and their application in responsive catalysis

The copolymer of poly(N-isopropylacrylamide)-co-poly(4-vinylpyridine) was synthesized by free radical copolymerization of 4-vinylpyridine and N-isopropylacrylamide. The copolymer synthesized with the feed monomer ratio of 4-vinylpyridine/N-isopropylacrylamide equal to 1/3 was associated to form thermoresponsive colloid in neutral water at room temperature, the average size and the cloud-point temperature of which were 40 nm and 32 °C, respectively. The thermoresponsive colloid was used as scaffold to load 2-nm Au nanoparticles to form the responsive catalyst of colloid-stabilizing gold nanoparticles. The catalysis in the model reduction of 4-nitrophenol with NaBH₄ suggested that the catalytic reduction could be modulated due to the thermoresponsive phase-transition of the colloid-stabilizing gold nanoparticles. That was, the catalytic reduction firstly accelerated with the increase in temperature below the cloud-point temperature and then decelerated with the increase in temperature above the cloud-point temperature of the thermoresponsive colloid-stabilizing Au nanoparticles.     

Synthesis and properties of isocyanate curable millable polyurethane elastomers based on castor oil as a renewable resource polyol

Millable polyurethane elastomers based on difunctional castor oil and poly(propylene glycol), 2,4-toluene diisocyanate and 1,4-butane diol were prepared and cured using toluene diisocyanate dimer as crosslinking agent. All elastomers were characterized by conventional methods. Physical, thermal and mechanical properties of elastomers were studied. Investigation of these properties showed that the elastomers could be tailor made in order to fulfill industrial needs.     

A label-free electrochemical immunosensor based on gold nanoparticles for detection of paraoxon

An electrochemical immunosensor for the direct determination of paraoxon has been developed based on the biocomposites of gold nanoparticles loaded with paraoxon antibodies. The biocomposites are immobilized on the glassy carbon electrode (GCE) using Nafion membrane. On the immunosensor prepared paraoxon shows well-shaped CV with reduction and oxidation peaks located −0.08 and −0.03 mV versus SCE, respectively. The detection of paraoxon performed at −0.03 mV is beneficial for guaranteeing sufficient selectivity. The amount of the biocomposite consisting gold nanoparticles loaded with antibodies and the volume of Nafion solution used for fabricating the immunosensor have been studied to ensure sensitivity and conductivity of the immunosensor. The immunosensor has been employed for monitoring the concentrations of paraoxon in aqueous samples up to 1920 μg l⁻¹ with a detection limit of 12 μg l⁻¹.     

Simple and sensitive colorimetric detection of cysteine based on ssDNA-stabilized gold nanoparticles

In this paper, we demonstrate a simple and sensitive colorimetric detection of cysteine based on the cysteine-mediated color change of ssDNA-stabilized gold nanoparticles (AuNPs). Cysteine is capable of absorbing onto AuNPs surfaces via the strong interaction between its thiol group and gold. ssDNA molecules which stabilize AuNPs against salt-induced aggregation are removed away by cysteine encapsulation on the AuNPs surfaces, resulting in a characteristic color change of AuNPs from red to blue as soon as salt is added. The ratio of absorptions at 640 to 525 nm (A ₆₄₀/A ₅₂₅) is linear dependent on the cysteine concentration in the range from 0.1 to 5 μM. Furthermore, amino acids other than cysteine cannot mediate the color change under the identical conditions due to the absence of thiol groups, suggesting the selectivity of the proposed method toward cysteine. The employment of complicated protocols and sophisticated processes such as the preparation of modified AuNPs are successfully avoided in design to realize the simple and low-cost cysteine detection; and the high sensitivity and low cost of the method is favorable for practical applications. Figure In the presence of cysteine, cysteine binds to the AuNPs surface via Au-S bond, spontaneously driving ssDNA molecules away from the nanoparticles, which leads to the AuNPs aggregation under the condition of NaCl introduction, and the corresponding color change from red to blue. However, the presence of other amino acids results in no color change due to the absence of thiol groups. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A novel immunoassay based on the dissociation of immunocomplex and fluorescence quenching by gold nanoparticles

This study reports a novel, simple and sensitive immunoassay using fluorescence quenching caused by gold nanoparticles coated with antibody. The method is based on a non-competitive heterogeneous immunoassay of human IgG conducted by the typical procedure of sandwich immunocomplex formation. Goat anti-human IgG was first adsorbed on polystyrene microwells, and human IgG analyte was captured by the primary antibody and then sandwiched by antibody labeled with gold nanoparticles. The sandwich-type immunocomplex was subsequently dissociated by the mixed solution of sodium hydroxide and trisodium citrate, the solution obtained, which contains gold nanoparticles coated with antibody, was used to quench fluorescence. The fluorescence intensity of fluorescein at 517 nm was inversely proportional to the logarithm of the concentration of human IgG in the dynamic range of 10-5000 ng mL⁻¹ with a detection limit of 4.7 ng mL⁻¹. The electrochemical experiments and the UV-vis measurements were applied to demonstrate whether the immunoglod was dissociated completely and whether the gold nanoparticles aggregated after being dissociated, respectively. The proposed system can be extended to detect target molecules such as other kinds of antigen and DNA strands, and has broad potential applications in disease diagnosis.     

Detection of flavonoids and assay for their antioxidant activity based on enlargement of gold nanoparticles

We report our findings that natural flavonoids such as quercetin, daizeol and puerarin can act as reductants for the enlargement of gold nanoparticles (Au-NPs). Consequently, the UV–vis spectra of a solution containing Au-NPs will be gradually changed, and the molecules of the natural herbs can be detected by making use of changes in the UV–visible spectra. Furthermore, we have prepared a self-assembled monolayer modified electrode by modifying cysteamine on a gold substrate electrode, which is further modified by some Au-NP seeds. When the modified electrode is immersed in a solution containing flavonoids and tetrachloroauric acid as a gold source for the growth of the Au-NP seeds, with the increase of the concentration of flavonoids, the Au-NP seeds on the surface of the modified electrode can be enlarged to varying degrees. As a result, the peak currents in the corresponding cyclic voltammograms are inversely decreased, and simultaneously the peak separation is increased. Therefore, an electrochemical method to detect flavonoids is also proposed. Compared with the optical detection method, the electrochemical method has an extraordinarily lower detection limit and a significantly extended detection range. Moreover, the optical and electrochemical experimental results can be also used to assay and compare the relative antioxidant activities of the flavonoids. Figure Enlargement of Au nanoparticles by flavonoids at cysteamine modified electrode     

Visual detection of melamine in milk samples based on label-free and labeled gold nanoparticles

Melamine that can cause serious damage to the organs of animal or human beings was found to bind to polythymine via hydrogen bonding. With this novel discovery, colorimetric detection of melamine based on label-free and labeled gold nanoparticles was developed, respectively. Both of the methods revealed good selectivity for melamine over other components that may exist in milk and good anti-influence ability. The raw milk samples were pretreated according to the National standard method combined with a solid phase extraction monolithic column. The accurate quantification of melamine as low as 41.7 nM and 46.5 nM was obtained, respectively. It also guarantees fast and reliable readout with naked eyes, making visual detection possible. Further comparison between label-free and labeled based methods was discussed in this paper.     

Label-free detection of adenosine based on fluorescence resonance energy transfer between fluorescent silica nanoparticles and unmodified gold nanoparticles

A sensitive and convenient strategy was developed for label-free assay of adenosine. The strategy adapted the fluorescence resonance energy transfer property between Rhodamine B doped fluorescent silica nanoparticles (SiNPs) and gold nanoparticles (AuNPs) to generate signal. The different affinities of AuNPs toward the unfolded and folded aptamers were employed for the signal transfer in the system. In the presence of adenosine, the split aptamer fragments react with adenosine to form a structured complex. The folded aptamer cannot be adsorbed on the surface of AuNPs, which induces the aggregation of AuNPs under high ionic concentration conditions, and the aggregation of AuNPs leads to the decrease of the quenching ability. Therefore, the fluorescence intensity of Rhodamine B doped fluorescent SiNPs increased along with the concentration of adenosine. Because of the highly specific recognition ability of the aptamer toward adenosine and the strong quenching ability of AuNPs, the proposed strategy demonstrated good selectivity and high sensitivity for the detection of adenosine. Under the optimum conditions in the experiments, a linear range from 98 nM to 100 μM was obtained with a detection limit of 45 nM. As this strategy is convenient, practical and sensitive, it will provide a promising potential for label-free aptamer-based protein detection.     

Room temperature synthesis and mechanical properties of two kinds of elastomeric interpenetrating polymer networks based on castor oil

Two kinds of interpenetrating polymer networks (IPNs) composed of two-component polyurethane (PU) and vinyl or methacrylic polymer (PV), namely, (polyether-castor oil)PU/PV IPN(I) and (polybutadiene-castor oil)PU/PV IPN(II), were synthesized at room temperature using benzoyl peroxide and N,N-dimethylaniline as redox initiator and dibutyltin dilaurate as catalyst. The former IPN was prepared by polymerization of castor oil, NCO-terminated polyether and vinyl or methacrylic monomer together and the latter IPN was obtained by polymerization of castor oil, NCO-terminated polybutadiene, NCO-terminated castor oil and vinyl or methacrylic monomer together. Various synthesis conditions affecting mechanical properties of the two kinds of IPNs were studied. Acrylonitrile (AN) is a good monomer for synthesizing IPN(I), but is a poor monomer for preparing IPN(II). At optimum conditions for the synthesis, both the (polyether-castor oil)PU/PAN IPNs and the (polybutadiene-castor oil)PU/polystyrene (PSt) IPNs possess permanent set about 10%, tensile strength over 13 and 11 MPa and ultimate elongation over 240% and 270%, respectively, thus behaving as elastomers. TEM micrograph of a (polybutadiene-castor oil)PU/PSt IPN showed a microphase separation in the IPN.     

Self-repairing and superhydrophobic film of gold nanoparticles and fullerene pyridyl derivative based on the self-assembly approach

In this paper, we report that thin gold films can be prepared on the water/toluene interface by self-assembly of gold nanoparticles (NPs) and fullerene pyridyl derivatives. The assembled films were characterized using UV–vis spectroscopy and transmission electron microscope (TEM). The films show self-repairing and superhydrophobic properties.     

Highly selective and sensitive visualizable detection of Hg2+ based on anti-aggregation of gold nanoparticles

For the widely used gold nanoparticles (AuNPs)-based colorimetric probes, AuNPs generally change from dispersion to aggregation state accompanying with corresponding color turning from red to blue. Although colorimetric probes based on the anti-aggregation of AuNPs show exceptional selectivity and sensitivity, few examples have been reported in literature. A facile but highly sensitive and selective colorimetric probe based on the anti-aggregation of AuNPs transferred from the deactivation of aggregation agent 4,4′-dipyridyl by Hg²⁺ was developed in this work. This reported probe is suitable for real-time detection of Hg²⁺ in water with a detection limit of 3.0 ppb for Hg²⁺, and exhibits a selectivity toward Hg²⁺ by two orders of magnitude over other metal ions. The dynamic range of this probe can be conveniently tuned by adjusting the amount of 4,4′-dipyridyl used.     

Visual detection of arginine based on the unique guanidino group-induced aggregation of gold nanoparticles

A simple, cost-effective and rapid method for visual detection of arginine based on the citrate-capped gold nanoparticles (AuNPs) aggregation has been developed in this paper. Arginine is the only amino acid with guanidino group, and has the highest isoelectric point (pI) at about 10.8. At pH 9.62, negatively charged citrate-capped AuNPs are well dispersed because of strong electrostatic repulsion. However, positively charged arginine (pH < pI) easily induces negatively charged citrate-capped AuNPs aggregation through electrostatic and hydrogen-bonding interactions, resulting in a red to blue color change of the solution. Using a UV–vis spectrophotometer, the method enables the detection of arginine in the range of 0.08–13.2 μM with a detection limit (3σ/slope) of 16 nM. Particularly, as low as 0.4 μM arginine can be easily detected by the naked eye without using any complicated or expensive instruments. Furthermore, this method can provide satisfactory results for the determination of arginine in arginine injection and compound amino acid injection samples.     

Analysis and applications of nanoparticles in the separation sciences: A case of gold nanoparticles

Nanometer-sized gold particles—gold nanoparticles (Au NPs)—are attracting a great deal of attention for their use in various technologies, including catalysis, optical and electronic devices, and separation science. In the emerging field of nanomaterials, the design, synthesis, and characterization of nanostructures are critical features because the manipulation of these structures has a direct effect on their resulting macroscopic properties. Nanostructures fabricated in layers on surfaces—for example, through self-assembly processes—have several potential applications in separation science. This review provides an introduction to the characterizations of Au NPs using size exclusion chromatography, high performance liquid chromatography (HPLC), and electrophoresis, and their self-assembly onto solid supports for analyses based on HPLC, gas chromatography, and capillary electrophoresis. In addition, sample concentration strategies involving the use of self-assembly approaches for surface modification of Au NPs are also discussed.     

The effect of drug position on the properties of paclitaxel-conjugated gold nanoparticles for liver tumor treatment

Structure-efficacy effect of small molecular drug attracts wide attentions,but it has always been ignored in nanomedicine research.To reveal the efficacy modulation of nanomedicine,we developed a new type of paclitaxel(PTX)-conjugated gold nanoparticles(PTX-co njugated GNPs) to investigate the influence of drug position in controlling their in vitro properties and in vivo performance.Two therapeutic ligands(TA-PEG-NH-N=PTX and TA-PTX=N-NH-PEG) were synthesized to conjugate PTX on the surface of GNPs at different positions,locating on the surface of gold conjugate and inserting between GNPs and polyethylene glycol(PEG,molecular weight 1000 Da),respectively.It was found that PEG-PTX@GNPs with PTX located between GNP and PEG exhibited higher aqueous solubility,biocompatibility,and stability.In addition,an acid sensitive hydrazone bond has been inserted between PTX and PEG in both ligands for drug release of PTX and PTX-PEG segment,respectively,at the tumor site.Further release of PTX from PTX-PEG segment is based on the esterase hydrolysis of an ester bond between PTX and PEG.This two-step drug release mechanism offers PEG-PTX@GNPs effective and sustained release behavior for desirable anticancer activity,enhanced therapeutic efficacy,and lower systematic toxicity in Hepsbearing animal models.     

Electrochemical biosensors for detection of point mutation based on surface ligation reaction and oligonucleotides modified gold nanoparticles

An electrochemical method for point mutation detection based on surface ligation reaction and oligonucleotides (ODNs) modified gold nanoparticles (AuNPs) was demonstrated. Point mutation identification was achieved using Escherichia coli DNA ligase. This system for point mutation detection relied on a sandwich assay comprising capture ODN immobilized on Au electrodes, target ODN and ligation ODN. Because of the sequence-specific surface reactions of E. coli DNA ligase, the ligation ODN covalently linked to the capture ODN only in the presence of a perfectly complementary target ODN. The presence of ligation products on Au electrode was detected using chronocoulometry through hybridization with reporter ODN modified AuNPs. The use of AuNPs improved the sensitivity of chronocoulometry in this approach, a detection limit of 0.9 pM complementary ODN was obtained. For single base mismatched ODN (smODN), a negligible signal was observed. Even if the concentration ratio of complementary ODN to smODN was decreased to 1:1000, a detectable signal was observed. This work may provide a specific, sensitive and cost-efficient approach for point mutant detection.     

Sensitive and selective detection of aspartic acid and glutamic acid based on polythiophene-gold nanoparticles composite

In recent years, gold nanoparticles and water-soluble fluorescent conjugated polymers are promising materials in terms of their potential applications in a variety of fields, ranging from monitoring DNA hybridization to demonstrate the interaction between proteins, or detecting diseased cell, metal ions and small biomolecular. In order to exploit some new properties of the both, many attempts have been devoted to achieve nanoparticle-polymer composite via incorporating metal nanoparticle into polymer or vice versa, however, only few of them are put into practical application. In the present paper, we utilize the “superquenching” property of AuNPs to polythiophene derivatives for detecting aspartic acid (Asp) and glutamic acid (Glu) in pure water, and discuss the factors accounting for fluorescence quenching and recovery via modulating pH. Thus an exceptionally simple, rapid and sensitive method for detecting Asp and Glu is established with a limit of detection (LOD) is 32 nM for Asp and 57 nM for Glu, the linear range of determination for Asp is 7.5 × 10⁻⁸ M to 6 × 10⁻⁶ M and 9.0 × 10⁻⁸ M to 5 × 10⁻⁶ M for Glu. The system is applied to real sample detection and the results are satisfying. Otherwise the composite is very sensitive to pH change of solution, we expect it will be possible to use as pH sensor with wide range in the future.     

Colorimetric detection of urea,urease, and urease inhibitor based on the peroxidase-like activity of gold nanoparticles

Herein, we reported for the first time that gold nanoparticles-catalyzed 3,3′,5,5′-tetramethylbenzidine-H₂O₂ system can serve as an ultrasensitive colorimetric pH indicator. Gold nanoparticles acted as a catalyst and imitated the function of horseradish peroxidase. The absorbance at 450 nm of the yellow-color product in the catalytic reaction exhibited a linear fashion over the pH range of 6.40–6.60. On the basis of this property, we constructed a novel sensing platform for the determination of urea, urease, and urease inhibitor. The limit of detection for urea and urease was 5 μM and 1.8 U/L, respectively. The half-maximal inhibition value IC₅₀ of acetohydroxamic acid was found to be 0.05 mM. Urea in human urine and urease in soil were detected with satisfied results.     

Large-scale self-assembly of hydrophilic gold nanoparticles at oil/water interface and their electro-oxidation for nitric oxide in solution

Mono-/bi-layer Au nanoparticle films with large areas were prepared by the assembly of Au nanoparticles in aqueous colloid at toluene/water interfaces, which can be transferred onto the hydrophilic solid surface and adhere strongly to the substrate without any binding agent. The transferred Au nanoparticle films exhibited satisfactory catalytic performance for electro-oxidizing nitric oxide (NO) in solution, and had a low detection limit (2.7 × 10⁻⁸ mol/L), a rapid response time (less than 0.5 s) and a wide linear range (5.0 × 10⁻⁸–1.0 × 10⁻⁵ mol/L) for the detection of NO in solution. UV–vis spectra, cyclic voltammetry and chronoamperometry were conducted to characterize the prepared Au nanoparticle films.     

Addition of gold nanoparticles to real-time PCR: effect on PCR profile and SYBR Green I fluorescence

Real-time quantitative polymerase chain reaction (qPCR) is the industry standard technique for the quantitative analysis of nucleic acids due to its unmatched sensitivity and specificity. Optimisation and improvements of this fundamental technique over the past decade have largely consisted of attempts to allow faster and more accurate ramping between critical temperatures by improving assay reagents and the thermal geometry of the PCR chamber. Small gold nanoparticles (Au-NPs) have been reported to improve PCR yield under fast cycling conditions. In this study, we investigated the effect of Au-NPs on optimised real-time qPCR assays by amplifying DNA sequences from genetically modified canola in the presence and absence of 0.9 nM Au-NPs of diameter 12 ± 2nm. Contrary to expectations, we found that Au-NPs altered the PCR amplification profile when using a SYBR Green I detection system due to fluorescence quenching; furthermore, high-resolution melt (HRM) analysis demonstrated that Au-NPs destabilised the double-stranded PCR product. The results indicate that effects on the assay detection system must be carefully evaluated before Au-NPs are included in any qPCR assay. Figure Raw amplification profiles in the presence and absence of gold nanoparticles