In order to improve the stability and reusability of protein A-coated piezoelectric biochips in a continuous repetitive flow injection assay of human immunoglobulin G (IgG), a new simple fabrication method was developed. The gold electrode surface of piezoelectric crystals was first fabricated with a self-assembled layer of hydrazide-terminated long-chain alkanethiols (15-mercpatopentadecan-1-hydrazide, 15-MH) and subsequently covalently modified with a double-sided linker of periodate-oxidized dextran, followed by protein A immobilization. The success of the surface fabrication was verified by Electron Spectroscopy for Chemical Analysis and other analyses. The AFM morphology image of the crystal surface was clearly changed and the contact angle was significantly decreased by the hydrocoating. The prepared protein A biochips exhibited remarkable specificity and fairly good stability after 41 repetitive assays in continuous flow injection assay of human IgG The biochips remained active after 30 days of dry storage at room temperature, after 14 days in buffered solution at 4degreesC, and after 2 days of continuous operation with short-termed storage inside the flow detector cell. The optimal flow rate of the detection system was found to be 225 mul/min. In addition, the study of the binding kinetics of the prepared protein A biochips with human IgG revealed a -DeltaF(max) value, the saturation frequency shift, of 297 +/- 11 Hz and a K-a value, the intrinsic adsorption constant, of 58 +/- 19 muM(-1).