Screen-Printed Electrode-Based Sensing of l-Ascorbic Acid Using Metal–Organic Framework Supported Carbon–Palladium-Doped MXene Quantum Dots in Human Serum and Artificial Sweat

Carbon-doped MXene quantum dots (MNQDs) were synthesized through a hydrothermal reaction involving citric acid and ethylene diamine in the presence of MXene. Palladium nanoparticles were subsequently incorporated into the MNQDs and integrated into an iron-based metal–organic framework, forming MIL-PdMNQDs. The successful synthesis of MIL-PdMNQDs was confirmed by PXRD, SEM, TEM, XPS, and FTIR analyses. Modified glassy carbon and screen-printed electrodes with MIL-PdMNQDs were used to measure l-ascorbic acid concentrations in a phosphate buffer solution, ranging from 10 to 100 nM. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) revealed a linear anodic peak current between 52.05 and 82.44 μA, with a linear regression (R2) value of 0.9885. In human serum diluted with PBS (5 mL of serum in 95 mL of PBS), the MIL-PdMNQDs-SPE1 detected ascorbic acid concentrations from 10 to 50 μM, illustrating a DPV redox peak current between 124.39 and 152.54 μA, with an R2 of 0.9901. Additionally, in artificial sweat, the DPV sensor detected ascorbic acid concentrations ranging from 100 to 1000 μM, with current readings between 11.132 and 64.83 μA and an R2 value of 0.9903, demonstrating its selective sensing capability. The limit of detection (LOD) for ascorbic acid in PBS using MIL-PdMNQDs-GCE was determined to be 4.705 nM. The MIL-PdMNQDs-GCE and SPE sensors exhibited high stability and exceptional selectivity for ascorbic acid detection.