OPTICAL-FIBER SENSOR FOR BIOLOGICAL OXYGEN-DEMAND

We describe the first fiber-optic microbial sensor for determination of biochemical oxygen demand (BOD). The sensing membrane at the tip of the fiber consists of layers of (a) an oxygen-sensitive fluorescent material, (b) Trichosporon cutaneum immobilized in poly(vinyl alcohol), and (c) a substrate-permeable polycarbonate membrane to retain the yeast cells. The layers are placed, in this order, on an optically transparent gas-impermeable polyester support. Tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate is used as the oxygen indicator. Typical response times are 5-10 min, and the dynamic range is from 0 to 110 mg/L BOD when a glucose/glutamate BOD standard is used. The fluorescent signal is affected by various parameters, including the thickness of the layers, the cell density of the yeast, and the rate at which the substrate is passed through the flow-through cell. BOD values estimated by this new biosensor correlate well with those determined by the conventional BOD5 method. The main advantages of this optical sensor are (a) a more rapid estimation of BOD (in comparison to the BOD5 method which requires 5 days), (b) the fact that optical oxygen sensors do not consume oxygen, (c) the possibility of performing in situ monitoring using fiber optics, and (d) the option of designing inexpensive disposable sensor cells.