Chemical sensor thin film-based Carbon Quantum Dots (CQDs) for the detection of heavy metal count in various water matrices

Rising pollution of heavy metals is one of the greatest concerns, especially in water resources globally and has led to significant adverse effects to human health. To uplift the status of human health, detection of heavy metals is of key importance. This study establishes the ability of carbon quantum dot (CQD)-based thin films for the detection of total heavy metal counts based on a fluorescence-based mechanism in various water resources using a fiber optic spectrometer (FOS) device. CQDs and CQD thin films were characterized using various techniques, such as X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and confocal laser scanning microscopy (CLSM), and the sensing capability was evaluated for the detection of heavy metals using an optical fiber system. The analytical parameters of the CQD-based thin film were compared with the estimation carried out using a micro plasma-atomic emission spectroscopy (MP-AES) method. The sensing performances of CQD thin films indicate that they are able to detect five heavy metals individually (lead, nickel, manganese, cobalt and chromium) in combination with a response time of 1 minute. The CQD thin films were able to detect heavy metals with a detection limit of 0.006-0.019 ppm for the analyzed heavy metals with a linear range of estimation analyzed as 0-100 μM. The accuracy of the estimation of all five heavy metals when spiked in various real water samples lies in the range of 100-103%. The result of the study clearly indicates that CQD thin films associated with a fiber optic device have the potential to play a role in point-of-care devices for total heavy metal count detection in complex matrices of water.