Visual detection of collective highly toxic metals in water by a handheld whole-cell biosensing detector: From circuit to field.

Whole-cell biosensors can detect toxic aquatic heavy metals without requiring expensive instruments and trained operators, making them promising for on-site detection. However, most remain confined to laboratory research, with few developed into integrated devices, and face challenges in simultaneously quantifying two highly toxic heavy metals, cadmium and mercury. To address this, we developed a portable platform for the simultaneous detection of them in contaminated water. We first engineered Vibrio natriegens into a whole-cell fluorescent biosensor. Paired with this biosensor, we built a palm-sized, battery-operated fluorescent reader featuring temperature-controlled incubation. This reader converts visual signals directly into numerical readings without computer processing. The biosensor can tolerate total metal concentrations up to 5 mg L-1 and collectively quantify Cd2+ and Hg2+ as low as 10-100 μg L-1 in real river water samples. At ∼$401.5 per device and ∼$0.33 per test, it is more cost-effective than commercial field detection devices or commercial kits.