OPTICAL-FIBER SENSOR FOR BIOLOGICAL OXYGEN-DEMAND

We describe the first fiber-optic microbial sensor for determination o f biochemical oxygen demand (BOD). The sensing membrane at the tip of the fiber consists of layers of (a) an oxygen-sensitive fluorescent ma terial, (b) Trichosporon cutaneum immobilized in poly(vinyl alcohol), and (c) a substrate-permeable polycarbonate membrane to retain the yea st cells. The layers are placed, in this order, on an optically transp arent gas-impermeable polyester support. ris(4,7-diphenyl-1,10-phenant hroline)ruthenium(II) perchlorate is used as the oxygen indicator. Typ ical response times are 5-10 min, and the dynamic range is from 0 to 1 10 mg/L BOD when a glucose/glutamate BOD standard is used. The fluores cent signal is affected by various parameters, including the thickness of the layers, the cell density of the yeast, and the rate at which t he substrate is passed through the flow-through cell. BOD values estim ated 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 meth od which requires 5 days), (b) the fact that optical oxygen sensors do not consume oxygen, (c) the possibility of performing in situ monitor ing using fiber optics, and (d) the option of designing inexpensive di sposable sensor cells.