Cysteine‐Mediated N, S‐Graphene Quantum Dots Adorned UiO‐MOFs Nanocomposite: A Fast and Ultrasensitive Fluorescence Sensor for Para‐Amino Hippuric Acid

Estimating para-aminohippuric acid (PAH) as a potential bioindicator for diagnosing renal diseases is gaining prominence. Hence, this study aims to develop a novel nanoprobe using cysteine-mediated N, S-graphene quantum dots (N, S-GQDs) embedded in UiO metal-organic frameworks (N, S-GQDs@UiO-MOFs) for PAH monitoring. Simultaneous green synthesis and doping of GQDs were initially done using Alstonia scholaris leaves and L-cysteine via the one-pot hydrothermal method to enhance their selectivity and optical properties. Fluorescent UiO-MOFs were then synthesized by 2-aminoterephthalic acid (2-ATA) and zirconium tetrachloride (ZrCl₄) providing a large surface area suitable for decorating N, S-GQDs. Adding copper ions (Cu II) results in FL quenching (turn-off) to the probe solution. In contrast, PAH addition led to FL recovery (turn-on), attributed to interaction with the amino functionality of PAH and the formation of a Cu (II)-PAH complex. The developed sensor exhibited a broad dynamic range (3 -17 ng mL^-1), an impressive detection limit (LOD: 662 pg mL^-1), and a quantification limit (LOQ: 2 ng mL^-1). Validation in artificial urine confirmed the sensor's specificity and suitability for real-time PAH analysis, demonstrating good stability, repeatability, and selectivity. The integrated N, S-GQDs@UiO-MOFs nanoprobe shows promise as a preferred method for PAH detection in clinical samples.