Graphene quantum dot spray-coated indium tin oxide electrode for Fe3+ detection

Ferric ion (Fe3+) contamination in water sources poses significant risks, making reliable detection technologies essential. In this study, electrochemical sensors were developed by spray-coating Graphene quantum dots (GQDs) on indium tin oxide (ITO) electrodes to enhance Fe3+ detection in aqueous systems. The performance of Assembly GQDs and GQDs on ITO electrodes was compared, and the electrochemical sensing of Fe3+ was investigated. GC-358 exhibited a 3D structure with aggregated particles and high electroconductivity, while CLS-3 showed a broad absorption peak around 300 nm and green photoluminescence at 505 nm due to carboxyl groups. Cyclic voltammetry showed the highest current response for CLS-3 at 4 mg with Nafion, reaching 1.32 × 10-6 A at 0.04 V, due to increased film thickness and Nafion enhancement. In comparison, GC-358 at 4 mg with Nafion exhibited a current of 6.29 × 10⁻⁷ A at 0.58 V, with slower charge transfer rates. Nafion improved electron transfer for both electrodes. GC-358 at 4 mg with Nafion provided the best Fe3+ detection performance, attributed to its stable sp2 hybridization and sheet-like morphology. CLS-3 at 4 mg with Nafion showed similar performance but with faster charge transfer and less efficient electron transfer due to its dot-like morphology. The sensor performance showed that ITO had the highest (Limit of detection) LOD of 1041.08 mg/L and limit of quantification (LOQ) of 3470.27 mg/L, with a low sensitivity of 6.85 × 10-9 AL/mg. GC-358/ITO at 4 mg with Nafion had a lower LOD of 0.53 mg/L, LOQ of 1.77 mg/L, sensitivity of 1.41 × 10-7 AL/mg, and high R2 of 0.9802. CLS-3/ITO at 4 mg with Nafion exhibited even higher sensitivity of 2.45 × 10-7 AL/mg, lower LOD of 1.16 mg/L, and excellent precision with R2 of 0.9905 and relative standard deviation (RSD) of 17.59%.