Multifunctional sensing of cobalt ions and methylcobalamin using doped Carbon Quantum Dots

In this work, a new fluorescent probe highly sensitive to Cobalt ions and Methylcobalamin (MC) was developed. For this purpose, sulfur- and nitrogen-doped carbon quantum dots (CQDs) with a Quantum Yield (QY) of 8 % were employed in a novel platform capable of discriminating different analytes in solution and detecting MC and Co²⁺ at concentrations as low as 1.36 ppm and 50.6 ppm, respectively. The MC, the active form of vitamin B12, is essential for DNA synthesis and neurological health. Its deficiency can lead to neuropathies and severe neurological disorders. It contains cobalt in its structure, a trace element recognized as vital for maintaining nervous system functions and erythropoiesis. Consequently, cobalt is also utilized by athletes to enhance performance during anaerobic exercise. The precise quantification of cobalt concentrations in the human body is crucial for the diagnosis of various pathologies and for the optimization of therapeutic interventions. The N,S-CDs were synthesized through a bottom-up approach, utilizing a hydrothermal method with citric acid, mercaptosuccinic acid (MSA), and ethylenediamine as precursor molecules. The efficient quenching of N,S-CDs fluorescence by Co²⁺ and MC was employed for the detection of these analytes, achieving a limit of detection (LOD) of 50.6 ppm for Co²⁺ and 1.36 ppm for MC, with recovery assays of 100.71 % and 99.33 % for Co²⁺ and MC, respectively. Furthermore, Co²⁺ and MC ions were identified in real water samples, in the presence of various interfering ions present in the solution, from Linear Discriminant Analysis (LDA), with 100 % of accuracy.