The effect of glutaraldehyde cross-linking layer on QCM based alpha-fetoprotein biosensor

To identify the extreme low concentration of alpha-fetoprotein (AFP) antigen in human serum for early detection of hepatocellular carcinoma (HCC), this paper aims to develop a high-sensitivity and low-cost AFP biosensor using quartz crystal microbalance (QCM) and cystamine self-assembly monolayer (SAM) technologies. QCM-based biosensors usually require smaller sampling, lower testing cost and fewer responding time than the conventional analysis system. The QCM-based AFP biosensor coated with a 20 mM cystamine SAM and a 1.0 mg/mL AFP antibody layer shows a high mass-sensitivity (0.35 Hz mL mg^-1) and sensing linearity (98.6%). However, its mass-sensitivity will be reduced to 0.092 Hz mL mg^-1 as the concentration of AFP antibody is decreased to 0.1 mg/mL. In this study, a 1.25 % glutaraldehyde cross-linking layer was added between the cystamine SAM and the AFP antibody to improve the mass-sensitivity (0.128 Hz mL mg^-1) as the AFP antibody concentration is low (0.1 mg/mL). The surface topographies of cystamine and glutaraldehyde will be analyzed by an atomic force microscope (AFM) system to investigate the effects of the glutaraldehyde layer on the QCM based AFP biosensor.