An integrated carbon dots-based sensing platform via alkali-assisted hydrothermal reaction for pH/Fe(II) detection and a sensing array for sulfur species

Abstract

In this study, the nitrogen-doped carbon dots (NCDs) were synthesized from phenolphthalein and m-phenylenediamine via a NaOH-mediated hydrothermal reaction. The blue-emitting NCDs functioned as dual-mode pH sensors, exhibiting a quenching effect in acidic solutions (pH=2–7) and colorimetric changes in alkaline environments (pH=8–12). Notably, the sensor exhibited stable performance up to five consecutive test cycles. The reliability of the method was verified through the pH analysis of commercial beverages. The highly stable NCDs exhibited a selective fluorescence quenching to Hg²⁺ through electron transfer and redox reactions, enabling the successful construction of an on-off-on sensor array (NCDs@Hg) for the selective analysis of sulfite, sulfide, and thiosulfate with high selectivity. The three sulfur compounds were successfully differentiated and analyzed via principal component analysis (principal component 1 with a variance of 95%). Notably, EDTA-modified NCDs exhibited enhanced selectivity towards Fe²⁺ through static quenching, enabling its detection over the concentration range of 2.25–45.00 μM, with a detection limit of 0.169 μM. The applicability of the sensor was validated in real samples, demonstrating satisfactory recovery rates. These findings demonstrate that NCDs are promising nanomaterials for multi-target detection through tunable sensing parameters, thereby enabling diverse practical applications.