RESUMEN
Ion-selective field effect transistor (ISFET) is a robust platform to develop biosensors. A variety of methods are used including covalent attachment or polymer entrapment, to associate enzymes or antibodies to the gate surface of a FET. We have employed a novel method of retaining the enzyme molecules at the gate surface by immobilizing the enzyme on magnetic nickelferrite nanoparticles and applying a permanent magnet below the gate of the FET. We were able to estimate the triglyceride concentrations in the range of 0.1-1.5% by immobilizing a thermostable lipase on nanoparticles. Tributyrin, trioctanoate and triolein have given similar results. The reaction volume could be scaled down to 0.2ml without a loss in slope or sensitivity. Ionic strength (>150mM NaCl) has a strong influence on the sensitivity of the measurement. The advantages of this configuration of enzyme biosensor are reduction of mass transfer problems, increasing the amount of enzyme at the gate surface besides providing an opportunity to use a single FET device for multiple analyte detection.