Optical biosensor chip technology for biochemical oxygen demand monitoring in environmental samples

An optical biosensor chip technology has been studied to perform as an effect free device for rapid biochemical oxygen demand (BOD) monitoring in environmental samples. A biofilm was embedded onto a polyethylene-polypropylene (PE-PP) film shielded oxygen sensing film for developing the biosensor chip. The oxygen sensing film was prepared by coating the ruthenium complex dye solution onto the SO₃^2- group embedded glass slide and the biofilm was prepared by immobilizing baker's yeasts (Saccharomyces cerevisiae) with polyvinyl alcohol-styrylpyridinium (PVA-SbQ) matrix. Sensor sample injection cavity was made by using silicone rubber (SR) sheet upon the embedded biofilm. An inverted microscope was used to measure the biosensor responses as the changing of fluorescence intensity (FI) due to microbial respiration in presence and absence of BOD standard solutions, glucose and glutamic acid solution (GGA) with time profiles. Taking the maximum response at 3 min of the each BOD standard solution, calibration curves were drawn as I_t=3 (intensity at 3 min time) divided by I₀ (intensity at 0 min time) against GGA concentrations. An equal performance was obtained by the biosensor either the GGA in phosphate buffer solution (PBS) or in environmental samples such as river water (RW). A linear relationship was achieved in low GGA concentrations (up to 20 mg/L GGA having BOD 14.6 mg/L, R²=0.99). The PE-PP shielding approach has completely eliminated the effects of heterogeneous components of environmental samples onto the sensor performances.