A digital quantification method for the detection of biomarkers on a microfluidic array chip

In this study, a digital quantification method is proposed for the detection of biomarkers. The proposed method is applied to detect alpha-fetoprotein (AFP), which is a biomarker of hepatocellular carcinoma. This digital quantification method is implemented with modified magnetic microparticles (MMPs) and a microfluidic array chip. The MMPs are modified with 186 +/- 6 beta-galactosidases (beta-gal) and 117 +/- 8 anti-human AFP antibodies (capture Ab) with a high capture efficiency and catalytic ability. The microfluidic array chip is modified with an AFP monoclonal antibody (coating Ab). The AFP captured by the modified MMPs is distributed in microwells, obeying the Poisson distribution. The modified MMPs that captured the AFP are captured by a coating Ab and anchored in the microwells, while the modified MMPs that did not capture the AFP are removed by a washing process. Therefore, the AFP can be detected by this digital quantification method with high sensitivity, selectivity and anti-interference ability. There is a linear relationship between -ln (1 - proportion of positive microwell (PPM)) and the AFP concentrations from 1 to 100 fg/mL, and the lowest AFP concentration that can be quantified is 1 fg/mL. This digital quantification method can also be used for real serum sample analysis, which holds great potential for the early diagnosis of cancer and therapeutic management.