Enzyme-cascade-amplified colorimetric biosensing platform for sub-nanomolar methylmercury in environmental waters

We developed an enzyme-cascade-amplified whole-cell biosensor for sub-nanomolar methylmercury (MeHg) detection in environmental waters. By integrating a MerB-based organomercurial lyase with a water-soluble indigoidine reporter system in a decoupled genetic circuit, we achieved a limit of detection (LOD) of 0.04 nM and a linear range of 0.02–1.22 nM. Systematic comparison of intracellular versus surface-displayed MerB strategies revealed that intracellular expression (TOP10/pCon-IND-C-B) provided superior sensitivity. The biosensor demonstrated robust performance across tap water, surface water, and seawater matrices (R2 > 0.98) with negligible matrix effects, enabling direct colorimetric quantification of culture supernatants. Notably, metabolic burden from pigment synthesis dominated the dose-response profile rather than MeHg cytotoxicity. This biosensor offers a cost-effective alternative for screening MeHg in environmental water, with detection limits that far exceed WHO drinking water guidelines and a potential for high-throughput environmental monitoring.