Characterization of surface modification on self-assembled monolayer-based piezoelectric crystal immunosensor for the quantification of serum α-fetoprotein.

Self-assembled monolayers (SAMs) on coinage metallic material can provide versatile modeling systems for studies of interfacial electron transfer, biological interactions, molecular recognition and other interfacial phenomena. Recently, a bio-sensing system has been produced by analysis of the attachment of antibody using alkanethiols, to form SAMs on the face of Au-quartz crystal microbalance (QCM) surfaces. In this study, the attachment of anti-α-fetoprotein monoclonal antibody to a SAMs surface of 11-mercaptoundecanoic acid was achieved using water-soluble N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide as coupling agents. Surface analyses were utilized by X-ray photoelectron spectroscopy and atomic force microscopy. The quantization of immobilized antibody was characterized by the frequency shift of QCM and the radioactivity change of ¹²⁵I labeled antibody. The limit of detection and linear range of the calibration curve of the QCM method were 15 ng/ml and 15-850 ng/ml. The correlation coefficients of α-fetoprotein concentration between QCM and radioimmunoassay were 0.9903 and 0.9750 for the standards and serum samples, respectively. This report illustrates an investigation of SAMs for the preparation of covalently immobilized antibody biosensors.