Evaluation of Chlorella vulgaris as sensitive, cost-effective, and environmentally sustainable biosensor tools for heavy metal monitoring in aquatic ecosystems

This study evaluates the effectiveness of single-cell microalgae as sensitive, cost-effective, and environmentally sustainable biosensors for detecting heavy metal contamination in aquatic ecosystems. A preliminary investigation compared the sensitivity of Nostoc commune and Chlorella vulgaris to chromium (Cr), cadmium (Cd), and mercury (Hg). C. vulgaris exhibited greater sensitivity, with Kautsky fluorescence increases of 67.82% (Cr VI, 200 µmol), 67.1% (Cd II, 100 µmol), and 35.27% (Hg, 1 µmol), whereas N. commune showed 124.70% (Cr VI, 200 µmol), 118.04% (Cd II, 200 µmol), and 61.96% (Hg, 1 µmol). Given its higher sensitivity, C. vulgaris was selected for biosensor development. The biosensor was optimized for pH (5–9), metal concentrations (Cr⁶⁺ and Cd²⁺ at 1–100 µmol, Hg²⁺ at 1–20 µmol), and algal density, while also evaluating immobilization effects on storage stability and sensitivity. Results showed a time-dependent increase in fluorescence with rising metal concentrations, demonstrating the biosensor’s efficacy in detecting heavy metals. The calculated LC₅₀ values were 67.32 µmol (Cd²⁺), 79.2 µmol (Cr⁶⁺), and 7.2 µmol (Hg²⁺), indicating the highest sensitivity to mercury. Immobilization enhanced biosensor stability, but sensitivity declined over extended storage, particularly at higher metal concentrations. Naked eye assessments confirmed superior sensitivity to mercury, reinforcing C. vulgaris as a promising biosensor for trace metal detection.