DETERMINATION OF IMMUNOGLOBULIN-M CONCENTRATION BY PIEZOELECTRIC CRYSTAL IMMUNOBIOSENSOR COATED WITH PROTAMINE

In the present study, the specific binding between protamine and immun oglobulin M (IgM) has been exploited to construct a piezoelectric crys tal based immunobiosensor for the determination of concentration of Ig M. The system consisted of highly stable IC based oscillator, 8-digit frequency counter and modified piezoelectric crystal device. The cryst al surface was physically modified and chemically treated (refluxed) w ith strong acid to produce stable hydroxylic groups of silicon oxide. The modified surface reacted strongly with coupling reagents for bindi ng of protein molecules. The protamine was immobilized by using either gamma-aminopropyltriethoxy silane (gamma-APTES) or 2.2.2-trifluoroeth anesulfonyl chloride (tresyl chloride). Scanning electron microscope i mages of piezo crystal revealed that tresyl activated surface presente d more surface area for binding than gamma-APTES modified surface and showed better sensitivity. This immobilization technique also improved the reproducibility and long term stability of the detection system. Using the system described, the IgM concentration up to the level of 1 0 ng/ml could be detected without interference of IgG.