An immunoassay using an electro-microchip, nanogold probe and silver enhancement

• Published in: Microfluidics and nanofluidics 2009, Vol.6 (1), p.93-98
• Main Authors: Su, Kuei-Ling, Huang, Hao-Hsuan, Chang, Tsung Chain, Lin, Hong-Ping, Lin, Yu-Cheng, Chen, Wei-Ting
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Biological and medical sciences; Biomedical Engineering and Bioengineering; Electrodes; Engineering; Engineering Fluid Dynamics; Fundamental and applied biological sciences. Psychology; Fundamental immunology; Immunoassay; Impedance; Molecular immunology; Nanotechnology and Microengineering; Research Paper; Silver; Studies; Techniques
• ISSN: 1613-4982; 1613-4990
• DOI: 10.1007/s10404-008-0299-z

This paper presents a novel immunoassay using an electro-microchip to detect the immuno-reaction signal, gold nanoparticles (ANPs) as a label of antigen or antibody and as a catalyst for silver precipitation, and the silver enhancement reaction to magnify the detection signal. This study is based on the direct immunoassay (two-layer format) and the sandwich immunoassay (three-layer format). The ANPs are introduced to the electro-microchip by the specific binding of the antibodies–ANPs conjugates and then coupled with silver enhancement to produce black spots of silver metal. The silver precipitation constructs a “bridge” between two electrodes of the electro-microchip allowing the electrons to pass, and the variation of the impedance can be easily measured with a commercial LCR meter. Different gap sizes (20, 50, 100, and 200 μm) of the electrodes of electro-microchips were designed for the sensitivity study. The experimental data show that a chip with a 200 μm gap has the highest sensitivity. There is a significant difference in impedance between the experiment and the negative control after 10 min reaction time. The proposed method requires less time and fewer steps than the conventional enzyme-linked immunosorbent assay. In addition, it shows a high detection sensitivity [10 μg/mL of 1st antibody (IgG) immobilized on slides and 10 ng/mL of antigen (protein A)], and there is a clear distinction between the signal intensity and the logarithm of the sample concentration. This new immunoassay has potential applications in proteomics research and clinical diagnosis.