A Nafion-Modified Laser-Induced Graphene Sensor for Spontaneous Monitoring of Caffeine and Vanillin

<b>Introduction: </b>Coffee is a globally consumed beverage, widely known for its main active ingredient, caffeine. Although a daily caffeine limit of 400 mg is considered safe, exceeding this limit can lead to adverse effects such as depression, anxiety, irritability, and other health issues. Another frequently used compound in the food and beverage industry is vanillin, which provides a characteristic sweet and creamy aroma. Like caffeine, excessive consumption of vanillin can also lead to adverse effects like headaches and gastrointestinal disturbances. Despite the widespread consumption of caffeine and vanillin, accurately determining their content in different foods and beverages is challenging. This complicates the monitoring of daily intake, making it difficult to manage potential health risks effectively. Laser-Induced Graphene (LIG) is a specialized form of 3D porous carbon nanomaterial with unique properties. It is created through a process called direct laser writing, which is performed on certain polymer materials in ambient conditions. The technique is both simple and quick, making LIG an attractive material for a variety of applications. Due to its excellent physical and chemical attributes, including a large surface area and superior electrochemical performance, LIG has become particularly valuable in the development of medical sensing devices.<br/><b>Methods: </b>We fabricated Laser-Induced Graphene (LIG) with 30 W 9.3 μm CO₂ laser engraver (VLS 2.30, Universal Laser System), and used it as working electrode by applying a Nafion monolayer to its surface. The electrode was then dried at room temperature for 30 minutes. A LIG reference electrode was prepared using screen printing to cover silver ink on LIG, leaving the counter electrode blank. The sensor's performance was tested using varying concentrations of caffeine and vanillin in PBS (pH=7.26). Testing methodologies included cycle voltammetry and square wave voltammetry with an electrochemical working station (CHI760E, CH Instruments, Inc.).<br/><b>Results: </b>To facilitate the monitoring of daily caffeine and vanillin intake, we have utilized Nafion-modified LIG sensor to develop an electrochemical point-of-care sensor. Based on the extensive surface area and superior electrochemical performance of LIG and the protective Nafion layer that imparts high stability for long-term storage and multi reproducibility, this novel sensor can detect caffeine, that shows a peak around 1.4 V, and vanillin which has a peak around 0.6 V, both within a linear range of 10 µM to 200 µM.<br/><b>Conclusions: </b>The developed Nafion-modified LIG sensor offers a promising approach for effectively monitoring caffeine and vanillin consumption. This technological advance aids in better dietary management, thereby contributing to overall health.<br/><b>Acknowledgment:</b> Haozheng Ma would like to acknowledge the Viterbi Graduate School Fellowship.