Silver Phosphate Nanoparticle-Based Electrochemical Sensing of Epinephrine Using a Paper-Based Analytical Device

Epinephrine is an essential catecholamine neurotransmitter and hormone, and its accurate detection is critical not only for clinical diagnostics but also for pharmaceutical monitoring, where precise quantification is necessary for assessing therapeutic efficacy, optimizing drug dosage, and managing patient treatment outcomes. In this study, hexamine-stabilized silver phosphate nanoparticles were synthesized via a complexation-mediated route and utilized as the active catalyst for epinephrine sensing. Spectroscopic and microscopic analyses confirmed the successful formation of crystalline silver phosphate particles, exhibiting a well-defined nanoscale size distribution. The catalyst was integrated into a paper-based electrochemical device and showed the sensitivity and limit of detection values of 8.89 μA·μM^–1·cm^–2and 0.27 μM, respectively, evaluated using a portable smartphone-based potentiostat. An extended-gate field-effect transistor platform using nanocomposite-modified ITO electrodes also showed a current sensitivity of 1.24 μA·μM^–1·cm^–2and a detection limit of 0.56 μM, with stable and reproducible responses. The practical applicability of the EGFET-based sensor was evaluated using a commercially available epinephrine solution, which demonstrated reliable detection performance and confirmed both the accuracy and real-life utility of the sensor.