Development and application of a miniaturised quartz crystal microbalance (QCM) as immunosensor for bone morphogenetic protein-2

Abstract

We report on the application of a novel miniaturised quartz crystal microbalance (QCM) as biochemical sensor in liquids. Resonators with a frequency of 20 MHz were fabricated by micromechanical engineering of quartz substrates and used as transducers for the label-free analysis of the affinity reaction between a ligand and its receptor. Recombinant human bone morphogenetic protein-2 (rhBMP-2) produced in high-cell-density cultures was chosen as ligand, and binding to the specific extracellular binding domain of the human bone morphogenetic protein (BMP) receptor type IA (BMPR-IA) and also to a specific monoclonal anti-human BMP-2 antibody was investigated. The extracellular binding domain of the receptor was available as fusion protein with the Fc portion of IgG (BMPR-IA-Fc). The shift of the resonant frequency caused by mass accumulation and/or change in the surface conditions was detected. For the detection of rhBMP-2 monoclonal anti-human BMP-2 antibodies or the BMPR-IA binding domain (BMPR-IA-Fc) were immobilised on the sensor surface via binding to protein A. Immobilisation of protein A was optimised and controlled via binding of anti-protein A antibodies. The lower detection limit for rhBMP-2 was 0.5 μg/mL (20 nM) using the specific antibody and 2 μg/mL using the receptor domain.