Nanosensors of Fluorescent Carbon Quantum Dots Derived from Banana Peel: Application in Sr2+ and Co2+ Detection

Abstract

Natural Carbon Quantum Dots (NCQDs) are known to contain photo luminescence property and stand as a promising nanomaterial group. Therefore, we intended to generate an intelligible and effective hydrothermal procedure for performing the green synthesis of this material through the usage of banana peel waste as a feasible and durable natural carbon source. The obtained NCQDs were characterized by the means of UV-visible absorption spectroscopy, spectrofluorometry, Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), zeta potential, Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), and Thermo Gravimetric Analysis (TGA). The lack of utilizing any toxic substances has guaranteed the safety of this procedure in all the biological practices. Therefore, the high crystalline and spherical morphology of synthesized NCQDS with an average roughness of about 5.9 nm were indicated by the results of TEM and XRD. We also observed a high water stability and solubility due to the presence of hydroxyl and carboxyl group and excitation- dependent emission performance with the satisfying quantum yield of 12 %. The zeta potential of prepared NCQDs reached up to -27.4 mV. Furthermore, in order to determine the low toxicity and favorable biocompatibility of this product, we studied the toxic effects of NCQDs on the fibroblast cell line of a normal mouse through the MTT assay. In conformity with the gathered data, these NCQDs contain the potential of being utilized as a nontoxic carrier and a fine alternative for bio-sensor, bio-imaging, and drug delivery applications. The development of these NCQDs was completed with the objective of acting as a highly sensitive fluorescent “on-off-on” switch sensor in the course of the selective and simultaneous sensing of Sr2+ and Co2+. Fluorescence data revealed that the binding constants of Sr2+ and Co2+ to NCQDs were to be 1.39 × 104 M-1 and 1.58 × 104 M-1 respectively. The observations were indicative of a linear relationship among the Sr2+ and Co2+ ions volume and the fluorescence intensity throughout the range of 0 to 0.1 mM.