IN-SITU ATTENUATED TOTAL REFLECTANCE FT-IR ANALYSIS OF AN ENZYME-MODIFIED MIDINFRARED FIBER SURFACE USING CRYSTALLINE BACTERIAL SURFACE-PROTEINS

This paper presents a new method for chemically modifying the surface of a chalcogenide glass optical fiber under permanent control by in situ IR-ATR spectroscopy. In order to immobilize glucose oxidase on the surface of such an IR-transparent wave guide, crystalline bacterial cell surface layers (S-layers) were used as a carrier, instead of using silanes as an enzyme coupler as frequently described in the literature. S-layer proteins which have the capability for self-assembling on suitable surfaces, were cross-linked and further activated with glutaraldehyde before the immobilization procedure. The reactive enzyme layer coating the core of the fiber serves to catalyze chemical reactions specifically when the fiber is used as chemical sensor. The chalcogenide fiber was coupled to a Fourier transform infrared (FT-IR) spectrometer which yielded spectra at various stages of the chemical processes as well as developments of signal bands as a function of time. The fiber was used as ATR element and could provide evanescent-field IR spectra in the range of 4000-800 cm-1 of the covering surface film thickness estimated at approximately 40 nm. All experimental surface modifications were carried out in situ in a 12-cm-long flow cell into which the fiber was positioned initially.