A novel BOD biosensor based on entrapped activated sludge in a porous chitosan-albumin cryogel incorporated with graphene and methylene blue

A novel BOD biosensor was fabricated based on activated sludge (AS) entrapped in a chitosan-bovine serum albumin (Chi-BSA) cryogel. Methylene blue (MB) was used as the mediator and electron transfer was enhanced using graphene. The responses of glucose glutamic acid (GGA) solutions were amperometrically measured with an applied potential of −0.20 V versus Ag/AgCl in a flow injection system. Under the optimum conditions, the graphene/MB/Chi-BSA-AS cryogel demonstrated a high operational stability of up to 140 analyses (RSD = 2.9%), a good storage stability (65 days) and a wide linear range, from 1.0-100 mg O2 L−1. At a flow rate of 400 μL min−1 the detection limit (LOD) was 1.0 mg O2 L−1 with a 9 min analysis time. A lower LOD (0.10 mg O2 L−1) could be measured at a lower flow rate of 100 μL min−1 and wastewater with a low BOD value could be measured. In comparison with the standard BOD5 method, the BOD concentrations in the waste water samples measured by this method were in good agreement (P > 0.05). These results demonstrated the potential of this graphene/MB/Chi-BSA-AS cryogel BOD biosensor. The use of this cryogel platform as a microbe immobilization support for other biosensor developments is promising.