Fiberoptic Evanescent Wave Spectroscopy (FEWS) for blood diagnosis: The use of polymer coated AgClBr fibers and neural network analysis

Infrared spectral analysis of human blood serum was carried out using FTIR - FEWS (Fourier Transform Infrared Fiberoptic Evanescent Wave Spectroscopy). The fiberoptic sensor elements were short (10.5 cm) lengths of unclad AgClBr fibers of diameter 0.9 mm. In order to protect the fibers from interaction with the blood serum we developed a dip coating technique, which made it possible to control the coating thickness. Three polymer materials were tested: polysulfone, polystyrene and room temperature vulcanized silicone elastomer. It was found that layers of thickness 2-3 μm provide chemical protection, while making it possible to carry out FEWS measurements. The measured spectra were analyzed by neural network analysis, to predict the concentrations of urea, uric acid, cholesterol, total protein and cretonne. The predicted concentrations were compared with the results obtained using standard chemical analysis of the blood (SMAC) and good correlation was observed, with errors of only few percent.