Screen-Printed Electrode-Based\nSensing of l‑Ascorbic Acid Using Metal–Organic\nFramework Supported\nCarbon–Palladium-Doped MXene Quantum Dots in Human Serum and\nArtificial Sweat

Carbon-doped MXene quantum dots (MNQDs) were synthesized\nthrough\na hydrothermal reaction involving citric acid and ethylene diamine\nin the presence of MXene. Palladium nanoparticles were subsequently\nincorporated into the MNQDs and integrated into an iron-based metal–organic\nframework, forming MIL-PdMNQDs. The successful synthesis of MIL-PdMNQDs\nwas confirmed by PXRD, SEM, TEM, XPS, and FTIR analyses. Modified\nglassy carbon and screen-printed electrodes with MIL-PdMNQDs were\nused to measure l-ascorbic acid concentrations in a phosphate\nbuffer solution, ranging from 10 to 100 nM. Cyclic voltammetry (CV)\nand differential pulse voltammetry (DPV) revealed a linear anodic\npeak current between 52.05 and 82.44 μA, with a linear regression\n(R<sup>2</sup>) value of 0.9885. In human serum diluted with PBS (5\nmL of serum in 95 mL of PBS), the MIL-PdMNQDs-SPE<sub>1</sub> detected\nascorbic acid concentrations from 10 to 50 μM, illustrating\na DPV redox peak current between 124.39 and 152.54 μA, with\nan R<sup>2</sup> of 0.9901. Additionally, in artificial sweat, the\nDPV sensor detected ascorbic acid concentrations ranging from 100\nto 1000 μM, with current readings between 11.132 and 64.83 μA\nand an R<sup>2</sup> value of 0.9903, demonstrating its selective\nsensing capability. The limit of detection (LOD) for ascorbic acid\nin PBS using MIL-PdMNQDs-GCE was determined to be 4.705 nM. The MIL-PdMNQDs-GCE\nand SPE sensors exhibited high stability and exceptional selectivity\nfor ascorbic acid detection.