Carbon quantum dot (CQD)-dithizone-based thin-film chemical sensors for the specific detection of lead ions in water resources†

Lead (Pb²⁺) is one of the toxic pollutants that poses hazardous and severe risks to human health and the environment globally. Lead toxicity issues can be addressed primarily by the detection of Pb. Thus, the requirement for accurate sensors for lead detection in environmental samples is tremendously increasing across the globe. Fluorescence-based detection of lead in water samples can serve as a stepping stone towards achieving goals such as point-of-care, portable, and on-site detection. In the present study, a selective fluorometric chemical sensor developed from dithizone and carbon quantum dots (CQDs) embedded in chitosan polymer thin films was evaluated for Pb²⁺ detection in various natural water resources. The fluorescent chemical sensors were characterized using FTIR spectroscopy, XPS, XRD, TEM, CLSM, UV spectroscopy, and fluorescence spectroscopy. Pb²⁺ ions were detected employing a fiber optic spectrophotometer (FOS) paired with a reflectance probe. Two river water samples and household tap water samples were evaluated for the presence of Pb²⁺ ions, and spiking studies were carried out to measure the accuracy of detection. The sensing and analytical results indicated that lead detection with a limit of detection of 18.3 nM was possible in the 0–100 μM range of concentration with a response time of 1 minute. The spiking of Pb²⁺ concentration in the various water resources led to an accurate estimation with a maximum error of 1.4%, indicating an interference-free detection of Pb²⁺. The estimation of Pb²⁺ based on Micro-plasma Atomic Emission Spectroscopy was used as a reference method. The results indicate that the developed fluorescent chemical sensor based on dithizone-CQD-impregnated chitosan thin films coupled with a fiber optic spectrometer device shows tremendous potential for point-of-care and real-time monitoring of Pb²⁺ ions in real water samples.