Highly selective colorimetric and electrochemical sensing of iron (III) using Nile red functionalized graphene film

We report a highly selective method for identification and detection of iron (III) (ferric iron, Fe³⁺) using Nile red (NR) as a complexing agent. Fe³⁺ preferentially binds with NR in dimethylformamide (DMF)/water (1:1) solution over other cations such as Fe²⁺, Cu²⁺, Pb²⁺, Hg²⁺, Mn²⁺, Ni²⁺, Zn²⁺, Co²⁺ and Cd²⁺ at room temperature. In the presence of Fe³⁺, the color of NR solution changes from purple to dark brown, which is detectable with bare eyes. Using UV-vis spectroscopy, we could measure the amount of Fe³⁺ in the sample solution by monitoring changes in absorption from 540 to 580nm; the linear range and the limit of detection are 30-1000µM and 24.9µM, respectively. Taking advantage of the NR selectivity, we treated partially oxidized graphene sheets (po-Gr) with NR to obtain po-Gr-NR dispersion by ultrasonication. The NR-treated po-Gr flakes (po-Gr-NR) were characterized by UV-vis, FT-IR, and Raman spectroscopies and FE-SEM, which indicated attachment of NR on po-Gr sheets. The po-Gr-NR hybrid film deposited glassy carbon electrode (po-Gr-NR/GCE) served as the Fe³⁺ sensor. Differential pulse voltammetry was used to investigate the detection of Fe³⁺ in 0.05M HCl+0.05M KCl solution. The linear range and the limit of detection of Fe³⁺ were from 37.5nM to 21.53µM and 18.7nM, respectively. Furthermore, this sensor was successfully used to measure Fe³⁺ content in red wine samples.