A CONCANAVALIN A-COATED PIEZOELECTRIC CRYSTAL BIOSENSOR

The lectin concanavalin A (Con A) has been immobilized on the surface of AT-cut quartz crystals to produce piezoelectric sensors for sugars in solution. Immobilization has been achieved by treating the crystals with 3-aminopropyltriethoxysilane followed by terephthaldicarboxaldehyde to which the lectin is then bound. The change in resonance frequency of the coated crystal, when immersed in glucose solutions of millimolar concentrations, confirms the efficacy of Con A as a detector of glucose having a sensitivity of approximately 100 Hz/millimole at concentration below 2 millimole. By analysing the viscoelastic response of the system to shear waves, we demonstrate that the measured changes in resonance frequency cannot be interpreted in the conventional way as simple changes in mass of the active layers. Instead, it is probable that they arise because reaction with the analyte alters the conformation of the sensing Con A layer and so changes the viscoelastic response of the system to the transmission of shear waves. The ability to detect changes in the viscoelastic response of a molecular layer produced by a reaction offers a means of examining liquid-phase reactions at the monolayer level, and has significant implications for the design of sensing systems based on coated quartz.