IR-biosensor: flat silver halide fiber for bio-medical sensing?

Cylindrical optical fibers, made of various materials, have been used for decades for chemical and biological sensing. Optical fibers transparent in the mid-infrared (IR) enable absorption measurements in remote locations. New techniques will enable the use of IR fibers for measurements in ATR-mode. If the fiber is in contact with a sample that has characteristic absorption lines, the total transmission of the fiber and sample of these lines will decrease. In this way the absorption of a sample can be determined using a non-destructive method. This work proves that flattened silver halide fibers could be useful as sensing elements in analytical systems. First measurements using flattened IR-fibers have been carried out on biological targets. The experimental set-up used was made up of an FTIR-spectrometer, fiber optic cables and an external detector. A segment of 1.9 cm at the center of the fiber was flattened to approximately 100–150 μm. Transmission spectra of flattened fibers have been compared to those of the cylindrical fibers. IR-spectra were recorded for biochemical compounds such as glucose, bovine serum albumin (BSA), gelatin and bio-fluids, and native tissue was compared to coagulated tissue. Spectral differences were obtained indicating a possible use for the study of thermal damage in tissues.