Circular Sensing of Nitrate Levels in Water With Flexible Screen-Printed Sensors on Biodegradable Cellulose Substrate

Inorganic nitrate (NO 3 − ) is ubiquitous in the environment and has become a center of attention in industrial and agricultural sectors, but it is regarded as a major contaminant in water and soil. In this letter, we present a flexible, cost-effective amperometric sensor that is screen-printed on a biodegradable cellulose substrate. The sensor's working electrode was functionalized with Cu nanoclusters, followed by the application of a solid-state ion-selective membrane (ISM), enabling continuous monitoring of nitrate levels in the water. The optimized electrodeposition of Cu nanoclusters served as a metal catalyst to reduce nitrate ions, whereas the optimized ISM cocktail selectively detected nitrate ions. The sensor showed a wide linear detection range from 1 (16 μ M) to 100 ppm (1.6 mM) with a high sensitivity of 684 nA/ppm. Selectivity tests conducted with common interfering substances (Na + , Cl − , SO 4 − , HCO 3 − , and NO 2 − ) showed minimal impact on nitrate sensing. The sensors also showed reproducible and stable responses up to the first 3 days. The mechanical durability of the sensor was also assessed using a customizable bending setup. In addition, Fourier transform infrared spectroscopy (FTIR) results demonstrated the gradual degradation of the cellulose substrate into the soil, highlighting the attainment of sustainable and circular sensing capabilities.