From colors to currents: a hybrid electrochemical and colorimetric sensor for real-time detection of emerging pollutants and pH monitoring†

The development of new tools for detecting and monitoring emerging pollutants is highly desired in the environmental field. Here, we report a hybrid multiplexed sensor for colorimetric detection of nitrite (NO₂⁻) and pH, along with simultaneous electrochemical detection of methylparaben (MP) and bisphenol A (BPA) in tap, lake and natural water. Through a portable potentiostat and a smartphone, our device provides relevant environmental parameters within two minutes. The colorimetric sensors were fabricated through spot tests, detecting NO₂⁻ at a concentration ranging from 1 to 200 μmol L⁻¹, with a limit of detection (LOD) of 3.0 μmol L⁻¹. The electrochemical sensors for MP and BPA were fabricated using the laser-scribed graphene (LSG) technique on a polyamide (PI) substrate. We achieved LODs of 0.22 μmol L⁻¹ (MP) and 0.057 μmol L⁻¹ (BPA), ranging from 1 to 100 μmol L⁻¹ for both, and reproducibility with relative standard deviations (RSDs) of 2.5% (MP) and 4.8% (BPA). As a proof-of-concept, our device was tested using real samples of lake, tap and natural water, achieving recoveries from 93% to 120%, demonstrating its suitability for in-field applications for environmental analyses.