RECENT DEVELOPMENTS IN ELECTROCHEMICAL BIOSENSORS FOR CHLOROPHYLL AND PHOTOSYNTHESIS-RELATED METABOLITE DETECTION

Abstract

Photosynthesis underpins primary productivity, food security and the global carbon and oxygen cycles, and the molecules that drive or report on it chlorophylls, the photosystem II reaction centre, plastoquinone, reactive oxygen species, reduced nicotinamide cofactors, soluble sugars, phytohormones and carotenoids constitute a uniquely informative panel of physiological biomarkers. Conventional analysis of these analytes relies on chromatography, spectrophotometry and fluorometry, which are accurate but laboratory-bound, destructive and ill-suited to continuous or in-field monitoring. Electrochemical biosensors offer a compelling alternative: they are intrinsically sensitive, rapid, low-cost, maintainable and amenable to in vivo and wearable deployment. This review surveys recent progress in electrochemical biosensing of chlorophyll and photosynthesis-related metabolites, organized around the molecular targets of the photosynthetic apparatus. We first outline the fundamentals of electrochemical transduction relevant to these analytes, including voltametric, amperometric and impedimetric methods and the performance metrics that govern analytical quality. We then examine direct voltametric detection of chlorophylls and pigments; whole-cell, thylakoid and photosystem II based bioreceptors that exploit the herbicide-sensitive electron-transport chain; and sensors for the key downstream metabolites hydrogen peroxide, NADH/NADPH, glucose and sucrose, the phytohormones indole-3-acetic acid and salicylic acid, and carotenoids. A dedicated section addresses the nanomaterials and electrode-engineering strategies graphene and laser-induced graphene, carbon nanotubes, MXenes, noble-metal and metal-oxide nanoparticles, metal-organic frameworks and conducting polymers that have driven the most significant gains in sensitivity and stability. Representative analytical figures of merit, recognition elements and detection limits are tabulated. We close by discussing applications in precision agriculture, environmental monitoring and food quality control, and by identifying the principal challenges long-term in vivo stability, selectivity in complex matrices, calibration and standardization, and integration with wireless data platforms that must be resolved for these devices to mature from laboratory demonstrations into deployable tools.