IMMUNOASSAYS BASED ON SURFACE-ENHANCED INFRARED-ABSORPTION SPECTROSCOPY

A new type of biosensor for pathogens has been developed. The sensor p roduces spectral fingerprints of biological systems by using surface-e nhanced infrared absorption (SEIRA) spectroscopy. Antibodies were immo bilized onto a 10-nm-thick film of gold which had been previously depo sited on a Si wafer. SEIRA spectra of the antibodies measured in the e xternal reflection mode exhibited two new bands at 1085 and 990 cm(-1) . These new bands were observed with p-polarized radiation but were ab sent with s-polarized radiation. The spectrum of water on the surface of the sensor was observed under both directions of polarization. The sensor was first tested with a model system consisting of glucose oxid ase (GOX) and the antibodies for glucose oxidase (anti-GOX). In additi on to the bands due to the anti-GOX at 1085 and 990 cm(-1), new bands were observed at 1397, 1275, and 930 cm(-1) when the GOX antigens were present. The same type of sensor was prepared for Salmonella (SAL) by immobilizing antibodies for Salmonella (anti-SAL) on a gold-surfaced Si wafer. The SEIRA spectra for anti-SAL antibodies were very similar to those for anti-GOX, with bands at 1085 and 990 cm(-1); however, a s harp new band was observed at 1045 cm(-1) after the sensor was exposed to the SAL antigens. In addition to specific new bands due to antigen s, both GOX and SAL sensors exhibited changes in the regions of water absorptions at similar to 3500 and 850 cm(-1) when the antigens were p resent.