AQUA-FINS: Advanced Quantitative Underwater Analysis by a Flexible Integrated Nitrate Sensor

This work presents a novel, integrated sensor array for real-time monitoring of key water quality parameters in aquaculture: nitrate, pH, and temperature. The array, fabricated on a flexible substrate, comprises potentiometric nitrate and pH sensors, and a resistive temperature sensor. The nitrate sensor, utilizing a polymer nanocomposite and ion-selective membrane, exhibited a near-Nernstian response with high selectivity, a low detection limit of 0.44 mg L⁻¹, and a sensitivity of −50 mV dec⁻¹. The polyaniline-based pH sensor demonstrated a sensitivity of −56.959 mV dec⁻¹ in recirculating aquaculture water samples, along with a high repeatability. The temperature sensor showed a linear response to changes in temperature (R² = 0.921). While testing in recirculating aquaculture tanks with catfish, the nitrate sensor initially showed a root mean square error of 4.779 mg L⁻¹ due to pH fluctuations, but a multiple linear regression model effectively corrected this error, and significantly improved accuracy (with a root mean square error of 3.090 mg L⁻¹). The pH sensor measurements also closely matched commercial meter readings (with root mean square error of 0.072). This integrated sensor array offers a promising solution for real-time, in situ monitoring of critical water quality parameters in aquaculture.