Microalgae-based biosensing technologies for environmental monitoring and emerging food safety applications: Opportunities and challenges.

Microalgae have long been investigated as biological sensing elements, yet their translation into robust, deployable biosensors remains limited by challenges related to cell viability, analyte selectivity, and transducer integration. Their sensing function is based on pollutant-induced alterations in photosynthesis, respiration, enzyme activity, and metabolism, which can be converted into measurable optical or electrochemical signals. Optical sensors typically monitor changes in chlorophyll fluorescence associated with photosystem II inhibition, while electrochemical systems detect variations in oxygen evolution or enzyme activity through amperometric, potentiometric, or conductometric responses. Despite promising sensitivity, practical deployment is hindered by poor operational stability, limited selectivity, and lack of standardized fabrication methodologies. Emerging advances in cell immobilization, microalgae-derived nanomaterials, microfluidic platforms, and biomimetic recognition elements offer opportunities to enhance sensor performance and reproducibility. This review examines whole-cell and photosynthetic-component algal biosensors, highlighting key biological and engineering challenges that must be addressed to enable reliable environmental and food-safety monitoring applications.