One-step signal amplified lateral flow strip biosensor for ultrasensitive and on-site detection of bisphenol A (BPA) in aqueous samples.

A one-step signal amplified lateral flow strip (LFS) biosensor has been developed for ultrasensitive and on-site visual detection of bisphenol A (BPA). This signal amplified LFS was based on the dual labeling using different-sized gold nanoparticles (Duo-LFS). This Duo-LFS could achieve BPA detection with 0.5 ng/mL as the visual sensitivity by naked eye observation and with 0.076 ng/mL as the limit of detection (LOD) for semi-quantitative detection by software analysis, which is at least 10-fold improvement of the sensitivity of traditional LFS based methods. This one-step signal amplified lateral flow strip biosensor and related signal enhancement method could be adopted as a potential generous technique for all LFS-based detection methods.

Ultrasensitive one-step rapid visual detection of bisphenol A in water samples by label-free aptasensor.

A simple, one-step, rapid method to detect bisphenol A (BPA) using a label-free aptasensor is presented. A high selective anti-BPA aptamer was added to gold nanoparticles (GNPs) to prepare the label-free aptasensor for BPA, which maintains good tolerance of GNPs under aqueous conditions with high salt concentrations. With the presence of BPA in the aptasensor system, the GNPs would aggregate by competitive binding of BPA and aptamer. Detection results can be visualized by the aggregation-induced color change of GNPs without the use of any instrumentation. The limit of visual detection (LOD) was found to be 0.1ng/mL by naked-eye observation, which was competitive to some current rapid BPA detection methods, even some instrumental based methods. Besides the obvious advantages, including reduced detection time and operation procedures, the results of this method meet the various detection requirements for BPA and are comparable to the traditional ELISA and instrument-based methods. The proposed one-step, label-free method was successfully used to determine BPA in actual water samples.

Ultrasensitive one-step rapid detection of ochratoxin A by the folding-based electrochemical aptasensor.

A one-step electrochemical aptasensor using the thiol- and methylene blue- (MB-) dual-labeled aptamer modified gold electrode for determination of ochratoxin A (OTA) was presented in this research. The aptamer against OTA was covalently immobilized on the surface of the electrode by the self-assembly effect and used as recognition probes for OTA detection by the binding induced folding of the aptamer. Under the optimal conditions, the developed electrochemical aptasensor demonstrated a wide linear range from 0.1 pg mL(-1) to 1000 pg mL(-1) with the limit of detection (LOD) of 0.095 pg mL(-1), which was an extraordinary sensitivity compared with other common methods for OTA detection. Moreover, as a practical application, this proposed electrochemical aptasensor was used to monitor the OTA level in red wine samples without any special pretreatment and with satisfactory results obtained. Study results showed that this electrochemical aptasensor could be a potential useful platform for on-site OTA measurement in real complex samples.

Crown ether assembly of gold nanoparticles: melamine sensor.

Melamine toxicity causing the renal failure and death of animals and humans has recently attracted worldwide attention. Developing an easy, fast, and sensitive method for the routine melamine detection is of great importance. Herein, we report the colorimetric sensing of melamine, based on the 18-crown-6 ether functionalized gold nanoparticles (GNPs) through the formation of cavity complexes with amines. Based on high extinction coefficients and spectral sensitivity of the surface plasmon resonance band of the GNPs, the rapid and sensitive melamine detection was achieved both visually and spectroscopically. Under the optimal conditions, melamine could be selectively detected in a concentration range from 10 to 500 ppb with a limit of detection as 6 ppb (3σ), which is much lower than the strictest melamine safety requirement of 1 ppm. To demonstrate the selectivity and practicality of the method, melamine detection was realized in the real complex samples (dairy) with excellent analyte concentration recovery, indicating its applicability for real-time monitoring of toxins in common products. Crown ether assembly of GNP also opens a new route for the formation of three-dimensional pseudorotaxane-like assemblies of nanoparticles that can be applicable to a variety of amine-bearing ligands.

Fabricated aptamer-based electrochemical "signal-off" sensor of ochratoxin A.

An ultrasensitive and rapid electrochemical platform for the specific detection of ochratoxin A (OTA) was developed. In this method, three single-stranded DNA molecules, including the aptamer, were immobilized on the surface of an electrode. Binding of the OTA target analyte to the aptamer changed the redox current of methylene blue (MB), which was used as the electrochemical probe, in a manner that was dependent on OTA concentration. With signal enhancement from gold nanoparticle-functionalized DNA, the sensitivity of this method for OTA was as low as 30 pg/mL, and the effective sensing range was from 0.1 to 20 ng/mL. To investigate the sensing process, the conformational switch of the aptamer was studied by circular dichroism (CD), which confirmed the recognition of the aptamer by the target OTA. Given its sensitivity and rapid detection, we believe this approach has the potential to be a main technology for the detection of toxins in the field of food safety, and in other areas.