The detection of heavy metal contamination is critical for environmental and food safety, given the toxicity of metals like cadmium (Cd²⁺), lead (Pb²⁺), and copper (Cu²⁺). Optical biosensors have emerged as a powerful solution due to their sensitivity, rapid response time, and adaptability for in situ monitoring. Recent advances have integrated novel materials, whole-cell approaches, and functional nanomaterials to enhance optical transduction mechanisms. For example, Durrieu et al. developed an optical algal biosensor utilizing Chlorella vulgaris cells with alkaline phosphatase as the biological recognition element, demonstrating strong inhibition of enzyme activity in the presence of cadmium and lead ions, measurable through fluorescence detection​ [1]. Similarly, Tsai et al. designed a sol–gel-based urease biosensor for detecting Cu²⁺ and Cd²⁺, utilizing FITC-dextran as a pH-sensitive fluorescent probe immobilized within a sol–gel matrix, achieving detection limits as low as 10 µM​ [2].

The incorporation of synthetic biology in whole-cell biosensors has also been shown to improved optical signal generation. For instance, Singh and Kumar reviewed genetically engineered whole-cell biosensors with optical readouts, highlighting the use of bacterial transcriptional regulators such as ArsR and MerR families for arsenic (As³⁺) and mercury (Hg²⁺) detection [3]. Further advancements have utilized quantum dots and gold nanoparticles for signal amplification in fluorescence- and surface plasmon resonance (SPR)-based sensors. These nanomaterials enhance sensitivity by lowering detection limits into the nanomolar range. This review highlights the most recent innovations in optical biosensing for heavy metals, focusing on enzyme inhibition-based methods, whole-cell biosensors, and nanomaterial-enhanced platforms. Optical biosensors represent a promising and sustainable approach to address heavy metal contamination in environmental and food systems.