Shuhao Wang

Determination of 17β-oestradiol by fluorescence immunoassay with streptavidin-conjugated quantum dots as label

A sensitive and selective method for the determination of 17beta-oestradiol by fluorescence immunoassay (FIA) was established on the basis of quantum dots (QDs) as label. The complex of biotin-labelled anti-rabbit IgG and strepavidin conjugated by quantum dots (QD-SA) was regarded as a probe in this system and the strepavidin-biotin system as signal amplification system. After optimising the conditions of the immunoreaction, such as the concentration of the reagent and the pH of the buffer solution, the linear range and the limit of detection of 17beta-oestradiol were 0.01-10,000ngml(-1) and 0.00542ngml(-1), respectively. This method was applied to determine oestradiol in water samples, with the percent recoveries in the range of 86-113%.

Aptamer-based fluorescent detection of ochratoxin A by quenching of gold nanoparticles

A simple, rapid, low cost and highly sensitive method for the detection of ochratoxin A (OTA) was developed based on the principle that dispersed AuNPs show a better fluorescence quenching effect than aggregated AuNPs. In the absence of OTA, the aptamer is adsorbed onto the surface of AuNPs, which helps to enhance the stability of AuNPs against salt-induced aggregation, and also enhances the fluorescence quenching of the fluorescein-labeled aptamer. With the addition of OTA, the conformation of the aptamer changed, which induced aggregation of AuNPs in the presence of high-salt conditions. The fluorescence intensity was clearly recovered. The assay showed a linear response toward OTA concentration in the range of 25 nM to 300 nM with a correlation coefficient of 0.9957. The limit of detection for OTA was experimentally determined to be 22.7 nM. This method has the advantages of simple operation, low-cost and high sensitivity compared to conventional methods and can be applied to the detection of real samples.

A time-resolved fluorescence immunoassay for the ultrasensitive determination of diethylstilbestrol based on the double-codified gold nanoparticles.

An ultrasensitive and selective method is presented for the determination of diethylstilbestrol (DES) using time-resolved fluorescence immunoassay (TRFIA) based on double-codified gold nanoparticles (DC-AuNPs). In this system, the DC-AuNPs, that are gold nanoparticles (AuNPs) modified with anti-DES antibody and SH-dsDNA-biotin, was regarded as signal amplifier. A competitive immunoreaction was performed on polystyrene microtitration plates, where the DES compete with the immobilized DES-ovalbumin on polystyrene microtitration plates to bind to anti-DES antibodies on DC-AuNPs, and the europium(III)-labeled streptavidin was added to link to the SH-dsDNA-biotin as a tracer. Fluorescence signal was amplified via the AuNPs and the biotin-streptavidin double amplification systems. Under the optimized condition, DES can be quantified by TRFIA. The linear range and the limit of detection of DES were 1.0×10(-6)-10ngmL(-1) and 0.4fgmL(-1), respectively. This method was applied to determine DES in beef sample, with the recoveries ranging from 88% to 105%.

Sensitive fluorescent detection of fibrin based on the inner filter effect of gold nanoparticles

A simple, rapid and sensitive fluorescent assay for determination of fibrin has been developed based on the inner filter effect (IFE) of gold nanoparticles (AuNPs). When fibrinogen (Fib), as the precursor of fibrin, was added into the AuNPs solution, the fluorescence of fluorescein was very weak due to the intensive absorption of AuNPs. In the presence of thrombin, Fib was transformed to fibrin which interacted with AuNPs, thereby inducing the aggregation of AuNPs, which induced the recovery of fluorescence. As a result, the present IFE-based approach can detect fibrin ranging from 0.125–2.5 nM with a correlation of 0.9926. The limit of detection for fibrin was experimentally determined to be 40 pM, based on a signal-to-noise ratio (S/N) of 3. Notably, the present IFE-based approach had advantages of being simple, time-saving, and economical compared with conventional fluorescent assays. The method is successfully applied to the quantification of fibrin in human plasma samples.

Earth-abundant Fe1−xS@S-doped graphene oxide nano–micro composites as high-performance cathode catalysts for green solar energy utilization: fast interfacial electron exchange

In the process of conversion of solar energy into electricity and fuel, efficient electrocatalysts are indispensable. Rieske iron–sulfur protein and FeS catalysts play an important role in natural photosynthesis (NPS), and in artificial photoelectrochemical cells, respectively. Nano–micro composite catalysts (NMCCs) possess not only high catalytic activity but also fast electron transport. Herein, we prepared a nano–micro composite (NMC) of Fe1−xS nanoparticles decorated on sulfur-doped graphene oxide (S-GO) sheets (namely, Fe1−xS@S-GO–NMC) to be used as a cathode in dye-sensitized solar cells (DSCs). The GO effectively inhibit the aggregation of Fe1−xS nanoparticles. Notably, DSCs based on an Fe1−xS@S-GO–NMC cathode achieved a high solar-to-electrical conversion efficiency up to 7.23%. The conversion efficiency is, to our knowledge, one of the highest efficiencies for DSCs based on an FeS or FeS2 cathode. Although the Fe1−xS@S-GO–NMC exhibited a low thermodynamic possibility for redox reactions, it showed a higher kinetic rate than that of Pt for the charge transfer between the reaction medium and the cathode. This indicates that a fast electron exchange process occurs at the interface between the reaction and the cathode. The value of the time constant (τ) corresponding to the charge exchange resistance based on Fe1−xS@S-GO–NMC (0.0215 ms) was smaller than that obtained with Pt (0.261 ms). Therefore, we ascribed the superior performance of the photoelectrochemical device based on Fe1−xS@S-GO–NMC to its good electrocatalytic performance. The results are of great interest for fundamental research and for practical applications of FeS and FeS2 and their composites in the solar splitting of water, artificial photoelectrochemical cells, and electrocatalysts.

A competitive fluorescence quenching-based immunoassay for bisphenol A employing functionalized silica nanoparticles and nanogold

We have developed a fast and sensitive immunoassay for the determination of bisphenol A (BPA), using the fluorescence quenching effect between gold nanoparticles and fluorescein isothiocyanate (FITC). Herein, carboxyl-modified single-strand DNA (COOH-ssDNAs) and anti-BPA antibodies were simultaneously conjugated with silica nanoparticles, and FITC-labeled single-strand DNA (FITC-ssDNA, the complement of COOH-ssDNA) was hybridized with COOH-ssDNA to form a signal platform, and the BPA coated antigen-functionalized nanogold was regarded as an acceptor. In the presence of BPA, a competitive immunoreaction takes place between BPA and BPA coated antigen-functionalized nanogold for the binding sites of the anti-BPA antibodies on the signal platform. Due to the fact that the photoluminescence of FITC was strongly quenched by the AuNPs, the fluorescence emission was decreased significantly. Under optimized conditions, the fluorescence intensity had a linear signal response range with a BPA concentration from 2.0 × 10−3 ng mL−1 to 1.0 ng mL−1 with a low limit of detection of 1.44 × 10−3 ng mL−1. Furthermore, this new signal platform was successfully applied to detect real samples for low levels of BPA.

A sensitive sandwich structure time-resolved fluorescence method for thrombin detection

We designed a sensitive and specific time-resolved fluorescence assay for detection of human thrombin. This design was based on the amplification of nanoparticles and the specificity of aptamers. The DC@AuNPs were prepared by the conjugation of AuNPs to BSA–Eu3+–DTPA and SH-Apt29. In the presence of thrombin, the formation of a quadruplex–thrombin complex could lead to the formation of a MNPs@Apt15–thrombin–DC@AuNP sandwich structure. In the presence of enhancement solution, Eu3+ interacted with the enhancement solution to produce strong fluorescence. Under the optimized conditions, the linear range of the method was from 1 pM to 100 pM of thrombin, and the limit of detection was 0.78 pM. Furthermore, the method could specifically recognize thrombin in the presence of other analogous proteins. The method is successfully used to determine thrombin in human plasma. This method has the advantages of high sensitivity and selectivity. It showed great potential for medical diagnosis.

A simple and sensitive fluorescence method for detection of telomerase activity using fusion protein bouquets

Telomerase is considered as a widely accepted cancer biomarker for early cancer diagnostics. Herein, we develop a simple, ultrahigh sensitivity method for detection of telomerase activity, which relied on that RecA-GFP fusion proteins wrapped around telomeric DNA to form fluorescence bouquets. RecA-GFP fusion protein was synthesized through fusion protein technology. In the presence of telomerase, telomerase elongation products are wrapped around by RecA-GFP fusion protein to form big fluorescent bouquets, which resulted in strong fluorescence. This method has the linear range from 50 to 1000 HeLa cells and the detection limit is 8 HeLa cells, based on a signal-to-noise ratio (S/N) of 3. Compared with conventional methods, this method has the advantages of low toxicity, outstanding sensitivity, and excellent selectivity. Hence, it provides a promising approach for the detection of telomerase activity and diagnosis of cancer.