α-fetoprotein analysis in human serum through quartz crystal microbalance

Abstract

The quartz crystal microbalance (QCM) has been used as the transducer to analyze microelement in term of its physical properties. It has been used for human’s microelement assay or immunoassay in liquid phase. This experiment mainly focuses on measuring human serum in gas phase to avoid the problems of variation in viscosity and the need of a lot amount of sample. According to the Sauerbrey equation, the mass change is proportional to the square of basic oscillation frequency that is 10 MHz in this experiment. The QCM electrode provides a gold-plated surface with modify 11-mercaptoundecanoic acid (11-MUA), one of self-assembled monolayer (SAM) compounds. X-ray photoelectron Spectroscopy (XPS) is utilized to characterize 11-MUA onto gold coated QCM surface. XPS spectrums demonstrate 11-MUA existence through peaks shift of C1s and O1s binding energy. Iodine 125 labeled anti-α-fetoprotein (anti-AFP) was immobilized onto the 11-MUA modified chips through reacting -COOH of 11-MUA with 1-ethyl-3-dimethylamino-propyl carbodimide (EDC) and N-hydrocysuccinimide sodium (NHS). The frequency and count rate was measured and compared after AFP immobilization process. The detection limit of QCM biosensor in AFP standard curve detection can reach to 15 ng/mL. Comparing with radioimmunoassay in clinical human serum samples, QCM biosensor method showed a good correlation.