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.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Materials Chemistry