Mat Stick–Derived CQD/Fe³⁺ Sensor for Ascorbic Acid Detection and Fluorescent Ink Applications

Abstract

Ascorbic acid (AA) (C6H8O6), also known as vitamin C, is a water-soluble vitamin consisting of a skeleton of six-carbon lactone derived from fruits and vegetables. Detection of ascorbic acid in cells is crucial for evaluating antioxidant status, maintaining redox balance, supporting enzymatic functions, and monitoring cellular health under physiological and pathological conditions. The present study highlights the development of luminescent carbon quantum dots (CQDs) using a locally available mat stick plant, and the resulting CQDs are characterised using FTIR, UV, SEM, TEM, EDAX, and XPS studies. The quenching of the luminescent property of CQDs is observed in the presence of Fe (III) ions with a quenching constant value of 5.80 × 105 M-1, and this quenching is subsequently inhibited by the addition of AA, resulting in a recovery of fluorescence. The fluorescence intensity of the CQDs/Fe(III) sensor shows a linear relationship with ascorbic acid concentration over the range of 0–100 µM, with a limit of detection (LOD) of 4.68 µM. This sensing system offers ultrafast detection with a micromolar detection limit, outperforming many existing assays. Notably, it demonstrates good selectivity for AA detection in the presence of various biomolecules. As a practical application, the CQDs/Fe complex can detect ascorbic acid in different fruit samples and human plasma samples. Besides, CQDs can be effectively used as fluorescence ink. The system's applicability is successfully validated in real sample assays, yielding satisfactory results. This CQDs-based sensing system holds promise for efficient AA detection in various applications.