A compact optical system for multi-determination of biochemical oxygen demand using disposable strips

Abstract

A compact optical device and disposable strips for the simultaneous determination of the biochemical oxygen demand (BOD) of multiple samples have been developed. The compact optical device was constructed using three pairs of light emitting diodes (LEDs) and silicon photodiodes (Si-PDs), and the disposable strips were fabricated using inexpensive, transparent polycarbonate plates. Pseudomonas fluorescens bacteria were immobilizedin a layer at the bottom of each reaction cell on the sensor strip using a photocrosslinkable resin (ENT-2000). Using the redox electron acceptor 2,6-dichlorophenolindophenol sodium salt as the chromophore, a linear relationship was observed between the response of the Si-PDs and the BOD value of Organization of Economic Cooperation synthetic wastewater. Real samples from a wastewater treatment plant and a kitchen in our factory were examined, and good correlations were observed between the BOD values derived using this system and those determined by the conventional BOD₅ method. In addition, in spite of the sensor response decreasing to approximately half its initial value after 2 weeks, the correlation coefficients (r²) of calibration curves remained above 0.9 upon storage of the strips in 0.1 M NaCl solution at 4°C for up to 6 weeks. In conclusion, this system is transportable and compact as well as being simple to operate and suitable for rapid, on-site measurements. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 222–227, 2001