Stimuli-Expressed Protein Qubits for Quantum Quantification of Heavy Metals in Natural Water

Environmental heavy metal pollution poses a severe threat to ecological security and human health, necessitating the development of highly sensitive, specific, and rapid detection technologies. Traditional fluorescent biosensors are often constrained by high background interference and limited sensitivity, while single-target detection systems struggle to meet the demands of complex environmental monitoring. This study constructs a novel magnetically modulated photonic quantum biosensing system based on the CadC-T7 gene circuit, replacing the traditional fluorescent reporter gene EGFP with the magnetically modulated fluorescent protein MagLOV - a quantum biomaterial. To enhance its magnetic modulation performance, the mutant with the highest lock-in amplitude during the directed evolution (R10, MagLOV 2) was selected; Simultaneously, systematic parameter optimization was conducted to determine the optimal magnetic modulation frequency (0.05 Hz), the heavy metal stimulation duration (the 2-hour group exhibited the most significant intra-group variation), and the bacterial concentration at the onset of the heavy metal stimulation (controlled at OD600 = 1 to prevent fluorescence quenching due to culture turbidity). The system demonstrates excellent multi-analyte detection capabilities for lead chloride, lead nitrate, and cadmium chloride across a concentration range of 10-8 to 10-4 M. Compared to conventional steady-state photometric methods based on EGFP and MagLOV 2, the lock-in analysis of MagLOV 2 achieves detection sensitivities enhanced by 1[~]2 orders of magnitude, with detection limits as low as 2.4 nM for cadmium chloride, 4.8 nM for lead nitrate, and 9.9 nM for lead chloride. Langmuir isotherm fitting results demonstrate high quantitative accuracy (R2 > 0.950), with particularly outstanding fitting performance for cadmium chloride (R2 = 0.999) and lead nitrate (R2 = 0.995).