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.