A developed competitive immunoassay based on impedance measurements for methamphetamine detection

In this study, an electro-microchip was successfully used to detect the impedance signals of various methamphetamine (MET) concentrations based on the developed competitive immunoassay method. MET is a commonly used drug often abused by drug addicts and can cause irregular behavior; therefore, MET concentration detection is important for quantitative analysis. In this study, gold nanoparticles (AuNPs) were introduced into an electro-microchip through the specific binding of antibodies, thus constructing a bridge between two electrodes and allowing electrons to move between them. The decreasing impedance value can be easily measured with a commercial LCR meter. According to the collected measurements, a significant difference was observed in impedance signals after 13 min when MET concentrations were reduced. Additionally, a clear, distinguished impedance (a steep slope for both impedance and MET concentration) in the frequency effect (100 Hz-1 MHz) was observed at 100 Hz. When the concentration of the anti-MET antibody- colloidal gold conjugates was diluted 1009, the detectable limit for MET concentration was 1 ng/mL with 0.5 lg/mL of BSA-MET conjugate. Therefore, the developed electro-microchip is advantageous because it is effective with small sample volumes (30 lL), is a form of rapid quantitative measurement, and works with smaller detectable concentrations than other existing commercial detection prducts which have the best limit of detection of 100 ng/mL.