MXene-polydopamine-cyanobacteria photobioelectrochemical biosensor for atrazine detection in environmental waters

A cyanobacteria-based photobioelectrochemical biosensor was developed for the first time using Synechococcus elongatus whole cells immobilized on a Ti₃C₂Tₓ MXene electrode modified with an electropolymerized polydopamine (PDA) layer. This surface created a biotic-abiotic interface that facilitated light-driven electron transfer for the sensitive screening of photosystem II (PSII)-inhibiting herbicides in environmental waters, using atrazine (ATZ) as a model analyte. The biosensor was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The detection strategy relies on the inhibition of PSII photosynthetic activity, which produces a concentration-dependent decrease in photocurrent. Under optimized conditions, the biosensor achieved a limit of detection (LOD) of 1.92 nM (0.414 ppb), a linear range of 5-200 nM, and a sensitivity of 177.71 nA decade⁻¹ cm⁻². Interference studies demonstrated class selectivity toward PSII-inhibiting herbicides (e.g., DCMU, simazine, desethylatrazine), with negligible response (< 10%) from non-PSII pesticides and common inorganic ions. Regarding operational stability, the device retained > 95% for 1 day and approximately 93% at day 2. However, a 61% signal loss was observed by day 5 (stored at 4 °C), highlighting an operational limitation inherent to whole-cell biological systems. The biosensor was successfully applied to determine ATZ in groundwater, river water, and seawater, delivering accurate recoveries (99.75-103.9%) and offering a green alternative for on-site environmental monitoring.