Sensitive and Selective Detection of Vitamin C in Complex Real-Sample Matrices (Blood and Fruits) using a Coomassie Brilliant Blue-Modified Electrode

Vitamin C (ascorbic acid, AA) is a vital biochemical ubiquitous in foods, fruits, vegetables, pharmaceuticals, and clinical systems. Beyond diseases associated with vitamin C deficiency, it has been linked to several clinical disorders, including diabetes, anemia, osteoporosis, and heart disease. As a result, the development of simple, sensitive, and selective analytical methods for AA detection in real samples remains a significant research priority. In this study, we introduce a novel Coomassie Brilliant Blue (CBB) dye-functionalized multiwalled carbon nanotube (MWCNT) chemically modified electrode, denoted as MWCNT@CBB, as an efficient molecular electrocatalyst for real-time AA detection. The fabricated GCE/MWCNT@CBB electrode exhibits a distinct redox peak signal at E° = 92.5 mV vs Ag/AgCl, with a surface excess value (Γ_CBB) of 11.3 × 10⁻⁹ mol cm⁻². Physicochemical characterization using scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy revealed that CBB is immobilized on MWCNT via robust π–π interactions between the aromatic π-electrons of CBB and the sp² carbon of the graphitic sites on MWCNT. The electroanalytical applications of the sensor electrode were investigated using cyclic voltammetry, amperometric i-t, and batch injection analysis (BIA), yielding an ultra-low detection limit of 33.5 nM (BIA method). To demonstrate practical utility, the electrode was applied to the sensitive detection of ascorbic acid concentrations in fruit and healthy blood serum samples using the standard addition approach. This resulted in straightforward AA detection with recovery values close to 100%, highlighting the potential of the developed electrode for real-world applications in analytical chemistry.