Novel Rhizophus oryzae esterase-immobilized chitosan/carbon nanomaterials as sensing support for enzyme inhibition-based biosensor in the detection of organophosphorus pesticide residues on crops

The use of mobile biosensor would allow for cost-effective and rapid on-site detection of organophosphorus (OP) pesticide. Immobilizing enzyme on electrode would improve the sensitivity of biosensor due to the nature of its specific active site-binding. OP inhibition on esterase enzyme is used as the sensing mechanism of the biosensor. In this study, microbial esterase from Rhizopus oryzae (RoE) was immobilized into modified screen-printed carbon electrode (SPCE) for the fabrication of novel RoE/chitosan/nanomaterial-COOH/SPCE biosensor for the detection of methyl parathion, an OP pesticide. The first phase of this study aims to analyze biochemical characteristics of 1-naphthyl acetate (1-NA) hydrolysis by RoE and enzymatic inhibition of RoE by OP pesticide. RoE kinetic showed the best fit with Langmuir model with the highest linear regression (R² = 0.996). The inhibition of RoE by OP was shown to be linearly proportional to the enzyme activity (R² = 0.827). The second phase of this study aims to analyze electrochemical performance of RoE-immobilized biosensor. Various carbon-based sensing support nanomaterials (graphene nanoplatelets (GNP), graphite and multi-walled carbon nanotube (MWCNT)) was functionalised by carboxyl (-COOH) group and screened, where all nanomaterials showed effective sensitivity towards detecting 0.01 ng/L methyl parathion pesticide. GNP-based biosensor exhibited the highest degree of inhibition (9.94 %) and better reproducibility after the first cycle. RoE/chitosan/GNP-COOH/SPCE biosensor is promising to be developed as cost-effective and highly sensitive biosensor for OP pesticide detection.