Development of Sustainable Nitrogen-Doped Carbon Quantum Dot Nanoprobe Using Red Onion for Ultrasensitive Estimation of Fluoride Ion in Human Saliva

A quick, eco-friendly, and economical approach for the synthesis of self-nitrogen doped carbon quantum dots (N-CQDs) utilizing onion extract was created in the current study. This method used a microwave to heat an onion for 4 min, providing a sustainable source of carbon and nitrogen. The provided N-CQDs exhibited great stability and a fluorescence quantum yield of 12.1% at λex/λem of 340/430 nm, respectively. The produced N-CQDs served as a successful nanoprobe for fluoride measurement, within a concentration range of 20-300 ng/mL with a detection limit of 4.557 ng/mL. In the presence of several potentially conflicting medications, the N-CQDs showed remarkable fluoride selectivity. For the assessment of water's fluoride content, a mean percentage recovery of 100.955 ± 0.416 was obtained. The N-CQDs were employed to measure fluoride in human saliva within the 50-1000 ng/mL concentration range, with a limit of detection of 15.693 ng/mL. Making use of AGREE and complexGABI and complexMoGABI approach, the suggested probe's greenness was assessed. Its good greenness was ascribed to the use of a low-cost plant, low-energy consumption through microwave-assisted synthesis, and avoiding dangerous chemicals and organic solvents. The blueness of the developed approach was assessed using the Blue Applicability Grade Index (BAGI).