Colorimetric and fluorometric dual-mode determination of hypochlorite based on redox-mediated quenching

Abstract

We have successfully created a dual-modal probe, labeled as of iron(II)–ortho-phenanthroline/N, S@g-CDs, which combines both fluorometric and colorimetric techniques for the accurate and sensitive detection of hypochlorite (ClO⁻). The mechanism behind this probe involves the fluorescence quenching interaction between nitrogen and sulfur co-doped green emissive carbon dots (N, S@g-CDs) and the iron(II)–ortho-phenanthroline chelate, utilizing both the inner filter effect and redox processes. As the concentration of ClO⁻ increases, the iron(II) undergo oxidation to iron(III) as follows: Fe(II) + 2HClO = Fe(III) + Cl₂O + H₂O, leading to the restoration of N, S@g-CDs fluorescence. Simultaneously, the color of the system transitions gradually from red to colorless, enabling colorimetric measurements. In the fluorometric method with an excitation wavelength of 370 nm, the ClO⁻ concentration exhibits a wide linear correlation with fluorescence intensity ranging from 0.07 to 220 μM. The detection limit achieved in this method is 0.02 μM (S/N = 3). In contrast, the colorimetric method exhibits a linear range of 1.12 to 200 μM, with a detection limit of 0.335 μM (S/N = 3). The proposed selective absorbance for this method is 510 nm. The probe has been effectively utilized for the detection of ClO⁻ in various samples, including water and milk samples. This successful application showcases its potential for determining ClO⁻ in complex matrices, highlighting its broad range of practical uses.