Synthesis of glutamine-based green emitting carbon quantum dots as a fluorescent nanoprobe for the determination of iron (Fe³⁺) in Solanum tuberrosum (potato)

Herein, we reported the use of N-doped green-emitting carbon quantum dots (N-CQDs) as a fluorescent probe for determining of Fe³⁺ ions in Solanum tuberosum for the first time. The N-CQDs were synthesised through an efficient, one-step, and safe hydrothermal technique using citric acid as the carbon source and glutamine as a novel nitrogen source. The temporal evolution of the optical properties was investigated by varying the synthetic conditions with respect to temperature (160 °C, 180 °C, 200 °C, 220 °C and 240 °C) and citric acid: glutamine precursor ratio (1:1, 1:1.5, l.2,1:3 and 1:4). The N-CQDs was characterised using Fourier-Transform Infra-red Spectroscopy (FTIR) High-resolution transmission electron microscope (HRTEM), ultraviolet–visible spectroscopy (UV–vis) and X-Ray diffraction analysis (XRD) while its stability was evaluated in different media; NaCl, Roswell Park Memorial Institute (RPMI) and Phosphate Buffered Saline (PBS), and at different pHs. The N-CQDs displayed green (525 nm) emission and were spherical with an average particle diameter of 3.41 ± 0.76 nm. The FTIR indicated carboxylic, amino, and hydroxyl functional groups. The as-synthesised N-CQDs were stable in NaCl (up to 1 M), RPMI, and PBS without any significant change in its fluorescent intensity. The pH evaluation showed pHs 6 and 7 as the optimum pHs, while the fluorometric analysis showed selectivity towards Fe ³⁺ in the presence and absence of interfering ions. The detection limit of 1.05 μM was calculated, and the photoluminescence mechanism revealed static quenching. The as-synthesised N-CQDs was used as a fluorescent nanoprobe to determine the amount of Fe³⁺ in Solanum tuberosum (Potatoes) tubers. The result showed a high level of accuracy (92.13–96.20%) when compared with an established standard analytical procedure with excellent recoveries of 99.23–103.9%. We believe the as-synthesised N-CQDs can be utilised as a reliable and fast fluorescence nanoprobe for the determining of Fe³⁺ ions.