Dual-response whole-cell microalgae biosensor based on ALP-associated electrochemical sensing of heavy metal cations in freshwater

The increasing contamination of freshwater with heavy metal cations has accelerated the development of eco-friendly microalgae-based biosensors due to their high sensitivity and sustainability. However, most existing systems rely solely on inhibitory (turn-off) responses, limiting their analytical capabilities. In this study, a chronoamperometric biosensor was developed using living Scenedesmus sp. MN738556 immobilized on a glassy carbon electrode within a bovine serum albumin-glutaraldehyde matrix. The biosensor demonstrated distinct ALP-associated electrochemical responses for different heavy metal cations. An ultralow detection limit of 0.1 μg/L was achieved for Cd²⁺ through enzyme inhibition (turn-off). In contrast, Zn²⁺ and Ni²⁺ exhibited concentration-dependent biphasic responses, including enzyme activation (turn-on) below critical concentrations (5 mg/L for Zn²⁺ and 300 μg/L for Ni²⁺) and inhibition at higher levels. The biosensor also showed good selectivity in binary mixtures with minimal interference below threshold concentrations. This biphasic response system supports a promising strategy for cation-dependent modulation of electrochemical biosensing of heavy metal cations in freshwater environments.