Search

Here, a fully integrated multicolor immunosensor was developed for sensitive and reliable semiquantitative analysis of HIV-1 p24, which integrates the multistep reactions of horseradish peroxidase (HRP)-linked immunoassay and gold nanorod (AuNR)-based multicolor assay into a single microfluidic chip. The HRP-linked immunoassay functions by moving magnetic beads bound to a capture antibody through different aqueous phases containing immunoassay reagents. HRP-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) is used to mediate AuNRs etching for producing various color changes. Multiple etching processes can be activated by simple mixing of the reagents from the reagent storage reservoir. The fully integrated strategy with sample-in answer-out capability is initiated by simple chip manipulation and finally concluded by converting recognition of antigen-antibody into a vivid color variation for direct visualization and semiquantitative analysis. By bare eye observation, our integrated multicolor immunosensor allows sensitive and reliable semiquantitative analysis of HIV-1 p24 within 1 h. The microfluidic chip device demonstrated here simplifies the operation significantly and thus allows broader application of a multicolor immunosensor for point of care (POC) testing in low-resource settings.

Herein, we report for the first time a colorful chromogenic substrate, which displays vivid color responses in the presence of different concentration of analytes. Our investigation reveals that the selective shortening of gold nanorods (AuNRs) could generate a series of distinct colors that covers nearly the whole visible range from 400 to 760 nm. These vivid colors can be easily distinguished by the naked eye; as a result, the accuracy of visual inspection could be greatly improved. Next, we demonstrate the utility of AuNRs as multicolor chromogenic substrate to develop a number of colorimetric immunoassay methods, e.g., multicolor enzyme-linked immunosorbent assay (ELISA), multicolor competitive ELISA, and multicolor magnetic immunoassay (MIA). These methods allow us to visually quantify the concentration of a broad range of target molecules with the naked eye, and the obtained results are highly consistent with those state-of-the-art techniques that are tested by the sophisticated apparatus. These multicolor portable and cost-effective immunoassay approaches could be potentially useful for a number of applications, for example, in-home personal healthcare, on-site environmental monitoring, and food inspection in the field.

The electronic balance, one of the most common pieces of equipment in the laboratory, is normally used to directly measure the weight of a target with high accuracy. However, little attention has been paid to the extension of its applications. In this study, an electronic balance was used as a readout to develop a novel aptasensor for protein quantification for the first time. Thrombin was selected as a model target, and its two aptamers recognizing different sites of the protein were used (one aptamer was immobilized on the surface of magnetic microparticles and the other aptamer was functionalized with platinum nanoparticles). The two aptamers were specifically bound with the thrombin to form a sandwich structure; thus, the platinum nanoparticles were linked to the magnetic microparticles, and they were separated by a magnet easily. The captured platinum nanoparticles effectively catalyzed the decomposition of H2O2, generating a large volume of O2 to discharge a certain amount of water in a drainage dev...

On the basis of the different diffusivity and existence of electrostatic repulsion between long and short DNA on the negatively changed indium tin oxide (ITO) microelectrode, a simple but sensitive immobilization free solution-phase electrochemical method for DNA methylation detection and inhibitor screening has been developed. Electroactive substance (methylene blue) tagged at the penultimate base T close to the 3'-terminal first, in the absence of DNA methylation, methylene blue-labeled electroactive fragments cannot be generated by Dpn I and results in a weak electrochemical response being detected on the ITO electrode. On the contrary, a remarkable electrochemical response can be achieved by the cleavage in the presence of DNA methylation since methylene blue-labeled electroactive fragments can be generated and aggregate on the ITO electrode. The proposed system does not need complex operation procedures such as bisulfite treatment, PCR amplification, and electrode immobilization. Six ITO microelectrodes had been assembled on the same microchip, which can achieve the parallel detection of the same sample and improve the experimental efficiency of drug screening. The system was used to conveniently and specifically monitor the change of the DNA methylation level with high sensitivity and selectivity. The proposed system has the potential application to screen the drugs as inhibitors on the activity of methyltransferase in the clinic.