Device for Electrochemical Caffeine Analysis in Fluids (DECAF): A Stir‐Bar‐Embedded Sensor for Real‐Time Caffeine Analysis in Commercial and Homemade Beverages

Caffeine (CAF) is the most widely consumed psychoactive compound worldwide; however, accurate labeling of its concentration in commercial beverages remains unregulated. To address this gap and minimize the risks of unintentional overconsumption, a portable electrochemical sensor-DECAF (Device for Electrochemical Caffeine Analysis in Fluids)-is developed for real-time quantification of caffeine in both commercial and homemade beverages. The sensor incorporates Nafion-modified laser-induced graphene (LIG) electrodes and a phosphate-buffered glass fiber (PBS-GF) layer, facilitating rapid absorption and buffering of liquid samples to ensure stable electrochemical response. Designed in the form of a stir bar, the device operates using square wave voltammetry (SWV) and achieves a detection limit of 0.06 mM, with a linear detection range from 0.5 to 5.0 mM. The system demonstrates high selectivity under varying pH and temperature conditions. DECAF requires only 200 µL of sample and delivers results within 5 min, interfacing wirelessly with a smartphone for real-time data visualization and storage. This compact, low-cost, and user-friendly platform enables on-site caffeine monitoring and holds potential for extension to biofluid analysis and detection of other target analytes, offering a scalable solution for personal health tracking and dietary management.