Keywords: 
• surface water /
• biochemical oxygen demand /
• fluorescence quenching /
• limnetic microorganisms

Abstract: The fluorescence probe and limnetic microorganisms (such as Candida tropicalis，Escherichia coli，Bacillus subtilis and mixedmicroorganisms)were immobilized on the glass slides by using the organic-modified sol-gel to make the optical BOD sensing films. The prepared optical BOD sensing films were then coupled with the fiber optical chemical sensors to develop the optical BOD microbial sensors. We then conducted experiments on the corresponding fluorescence property, the effect of heavy metal, the stability and the operational life span of different sensors. The sensor with the best capability was screened out based on the experimental results. Then the optical BOD microbial sensors were used in the determination of BOD of the surface water, and results were compared with the conventional BOD5 method. The experimental results showed that, the best BOD microbial sensor was the one with mixed microorganisms of Escherichia coli and Bacillus subtilis. The linearity coefficient was 0.9871. The corresponding fluorescence intensity ranged from 0～120 mg/L and the respond time was less than 60 s.The optical BOD microbial sensors could be continuously employed for 30 days and were especially applicable for the on-line BOD determination. Moreover it showed excellent linearity coefficient with BOD5 in the determination of BOD of the surface water.