Photoacoustic immunoassay using temperature responsive polymer as carrier and its application

A novel ultrasensitive immunoassay method that uses poly ( N-isopropylacrylamide) as carrier and laser-induced photoacoustic quantitation is proposed. Ultratrace determination by laser spectroscopy in immunoassay has often plagued by nonspecific binding to the solid phase. This obstruction can be suppressed by introducing temperature responsive polymer, poly(N-isopropylacrylamide). A monoclonal antibody which has been conjugated to the polymer reacts with antigen and enzyme-labelled antibody below the critical solution temperature of the polymer. The polymer/immune complex sandwich can precipitate from the solution above the critical temperature. In this system, it is possible to minimize the opportunities for nonspecific binding and enhance reaction rate. Furthermore, when we use TMB as the substate of horseradish peroxidase and SDS and Na2SO3 as stop reagents, the color is stable for. long time and can. match the absorption wavelength of He-Ne laser. The method was employed to detect HBsAg in serum. A significant difference from the background was obtained for 3.5 �� 10-11 g/mL. This value was almost one order of magnitude better than results obtained by ELISA.