Biotransformation-electrochemistry coupling for multiplexed on-site detection of hydrophobic polycyclic aromatic...

Rapid on-site detection of polycyclic aromatic compounds (PACs), such as biphenyl and carbazole, remains challenging because of their poor aqueous solubility, weak electroactivity, and matrix interference. Here, we developed a biotransformation-enabled electrochemical decoding strategy that couples a biphenyl 2,3-dioxygenase (BphA)-expressing whole-cell module with a miniaturized reduced graphene oxide/colloidal gold (rGO/CG)-modified screen-printed electrode for biphenyl and carbazole quantification. BphA from Pseudomonas putida B6-2 was heterologously expressed in Escherichia coli to convert parent PACs into water-compatible, redox-active hydroxylated/dihydrodiol-bearing metabolites, while the geometry-optimized premixed rGO/CG interface enhanced faradaic responses and reduced charge-transfer resistance, yielding a peak current density of 169.53 μA cm^-2. Molecular docking of BphA oxygenase α-subunit and electrochemically derived apparent kinetics indicated favorable binding of both substrates and an apparent preference for biphenyl (apparent K_m 4.87 mg L^-1; apparent V_max 8.13 U mg^-1 DCW) over carbazole (apparent K_m 6.64 mg L^-1; apparent V_max 6.29 U mg^-1 DCW), consistent with stronger biphenyl responses. The assay achieved detection limits of 0.021 mg L^-1 for biphenyl and 0.037 mg L^-1 for carbazole, enabled simultaneous quantification in mixtures (R² ≥ 0.995), and showed good reproducibility (deviation ≤3.81%). Results for lake water and petroleum wastewater agreed well with high-performance liquid chromatography (R² up to 0.996), demonstrating the potential of this platform for point-of-need monitoring of complex aromatic pollutants in environmental samples.