Carbon Spherical Shells Functionalized with Nitrogen as Sustainable Electrochemical Materials for Rapid Detection of Diclofenac in Saliva, Urine, Water, and Tablets

We introduce a facile strategy to obtain nitrogen-functionalized carbon spherical shells (N-CSSs). These N-CSS were prepared using an eco-friendly hydrothermal synthesis with urea and an aqueous dispersion of carbon spherical shells (CSSs) produced with water and glucose green precursors. The urea/CSS mass ratio was varied to evaluate the effects of the urea amount on N-CSS functionalization and sensitivity. The N-CSS was used as a sustainable electrochemical material for rapid detection of diclofenac in saliva, urine, water, and tablets. The sensitive, selective, and ultralow cost (<US$ 0.068 per unit) sensor for diclofenac was optimal with nitrogen content at 2.6% which also had the largest specific surface area (154.55 m² g^–1) with a sensitivity of 0.12 A M^–1 and limit of detection 0.358 μM (3.58 × 10^–7 M). The disposable sensor detects diclofenac in a linear working range from 0.5 to 5 μM with high reproducibility, selectivity, and stability. Detection of diclofenac was also performed in real samples consisting of saliva, urine, and water and in solutions prepared with commercial tablets with satisfactory recoveries. The environmental impact of N-CSS was evaluated through a life cycle assessment, which indicated that N-CSS is a sustainable choice as an electrochemical sensing material. The high sensitivity, versatility, fast detection, cost-effectiveness, and easy operation of the disposable electrochemical sensor represent significant potentials for on-site, real-time, decentralized analysis, and monitoring of anti-inflammatory contaminants in biological and environmental samples.