Hydrothermal synthesis of N,S-doped carbon quantum dots as a dual mode sensor for azo dye tartrazine and fluorescent ink applications

Abstract

In this paper, blue-emitting N,S-doped carbon quantum dots (N,S-CQDs) were fabricated via a hydrothermal process from a mixture of o-phenylenediamine and methionine. They exhibit photoluminous (PL) emission at 440 nm, with a quantum yield (QY) of 20 %. Various physio-chemical approaches were employed to explore the structural, morphological, optical and electrochemical behaviour of the N,S-CQDs. The functional groups such as carboxyl (–COOH), hydroxyl (–OH), amino (–NH2) and thiol (-SH) on the N,S-CQDs surface allows it to have good QY, and excellent water solubility. The proposed sensor could detect tartrazine (TT), a common synthetic food dye using fluorescence and electrochemical approaches. The fluorescence method achieved a limit of detection (LOD) of 80 nM within the linear range of 0–10 μM. A combination of static quenching process and inner filter effect (IFE) was involved in the sensing mechanism. In electrochemical sensing, the differential pulse voltammetric (DPV) method was successfully applied within the linear range of 5–35 nM and a LOD of 2 nM. Both methods were successfully used to determine tartrazine levels in soft drinks and candies. In addition, the N,S-CQDs based fluorescent ink was developed for writing, drawing and fingerprint imaging applications.