Laser‐Patterned Carbon‐Supported Graphitic Carbon Nitride Quantum Dots for Flexible Nanozyme‐Based Fluoride Sensor

Abstract Graphitic carbon nitride quantum dots (g‐CNQDs)‐based colorimetric sensors are typically solution‐based and hence incompatible with wearable electronics. Today's competitive technology demands safe and reliable, high‐performance sensors suitable for integration with sophisticated electronics—all at a low cost. Herein, a flexible and reusable solid‐state fluoride ion sensor manufactured by combining the intriguing surface properties of laser‐patterned carbon (LP‐C) with the sensitivity of g‐CNQDs is reported. LP‐C is obtained by direct IR‐laser writing onto polyimide films, and g‐CNQDs are synthesized via a solvent‐free and zero‐waste green process. The hybrid of LP‐C and g‐CNQDs (g‐CNQDs/LP‐C), mimics the natural enzyme horseradish peroxidase and oxidizes the chromogenic substrate 3,3’,5,5’‐tetramethylbenzidine in the presence of H₂O₂ in acidic media. The highly selective and user‐friendly nanozyme sensors feature a lower limit of detection of 0.568 ± 0.006 × 10⁻⁶ m (23.8 ± 1.5 µg L⁻¹) with linearity in the range of 0.5 × 10⁻⁶ to 100 × 10⁻⁶ m. A sensing mechanism based on the electronic transitions of g‐CNQDs and LP‐C, the two variants of nitrogen‐containing carbon used in this work, is established. Finally, the device is tested for fluoride ion sensing in natural water samples collected from the Uhl river in Mandi, India.