Abstract:
Significant development has been witnessed in electrode surface nanostructuring to improve sensitivity and selectivity in electroanalysis. This work aimed at nanostructuring glassy carbon electrode surface with nanohole using electrochemically nucleated gold nanoparticles as a template. The surface modification procedure developed helps to minimize oxidation potential of caffeine and also to increases mass transport of caffeine to electrode surface thereby increasing sensitivity and selectivity of the modified electrode for determination of caffeine. Randomly nanostructured surface have been fabricated based on sequential electrochemical deposition of gold nanoparticles from H2SO4 solution containing KAuCl 4 on glassy carbon electrode. To increase the number density of the nucleated nanoparticles at glassy carbon electrode, three rounds of deposition-passivation cycles has been done using chronoamperometry. The growth of nucleated nanoparticles in sequential deposition process was prevented using self assembled monolayer of 2-marcapitoethnol capping agent. Following the nucleation steps, p-nitroaniline film was grafted from its diazonium salt. The nanohole structured surface was fabricated after stripping of the nucleated gold nanoparticles. Nanohole modified electrode showed high electrochemical sensitivity towards oxidation of caffeine due to remarkably increased anodic peak current and decreased over potential of caffeine oxidation. The effect of different experimental parameters was investigated on the peak height of caffeine. The method enables determination of caffeine in the range from 1.0×10 −7 to 1.0×10 −3 mol L −1 , with limit of detection (LOD = 3δ/slope) of 7.28 × 10 –8 mol L -1 . The effect of theophylline and theobromine on the determination of caffeine was studied and found to be minimal. Besides, the sensor displayed good stability and reproducibility. The proposed method showed high sensitivity, selectivity and stability in determination of caffeine in coffee
