An optical biochemical oxygen demand biosensor chip for environmental monitoring

An optical biochemical oxygen demand (BOD) biosensor chip has been developed by embedding a biofilm onto an oxygen sensing film (OSF) shielded with polyethylene–polypropylene (PE–PP) film for effect free detection of organic pollution in environmental samples. The biofilm was prepared by immobilizing baker's yeasts (Saccharomyces cerevisiae) with polyvinyl alcohol–styrylpyridinium (PVA–SbQ) matrix and the OSF film was developed by coating the oxygen sensing ruthenium complex (dichloro tris (1,10-phenanthroline)–ruthenium(II)) dye solution (solubilized in nafion fluoropolymer matrix) onto a SO₃ glass slide. Silicone rubber (SR) sheet was used to control the biofilm thickness and make the sample injection cavity. Fluorescence intensity (FI) of the biosensor was recorded by an inverted microscope which varies with the concentration of dissolved oxygen (DO) in samples. The biosensor responses were drawn as the changing of FI due to microbial respiration with BOD standard solutions, glucose–glutamic acid soluton (GGA). A good linear relationship was observed between the maximum responses, I_{t = 3}/I₀ (I_{t = 3} = intensity at 3 min time and I₀ = intensity at 0 min time) and GGA concentrations (1 to 20 mg/L, R² = 0.99, n = 3) either in phosphate buffer solution (PBS) or in environmental samples such as river water (RW). The effects of environmental samples upon the sensor performance were completely eliminated due to shielding with only oxygen permeable PE–PP film onto the OSF. In addition, the suitable biofilm type, effects of heavy metals ions as well as preservation and stability of the biosensor also have been investigated. Finally, the newly proposed approach offers a promising and prospective tool for frequent monitoring of organic pollution in environmental samples.