Determination of Co²⁺ ions in blood samples: A multi-way sensing based on NH₂-rich carbon quantum dots

Multiple forms of detecting Co²⁺ are reported in this work to quantify these ions in real blood plasma samples. Carbon Quantum Dots (CQDs) were used as a fluorescent nanoprobe. The CQDs were obtained from a bottom-up approach using a hydrothermal method and choline chloride and branched poly(ethyleneimine) as precursor molecules. Several spectroscopic and structural characterizations were performed. The efficient fluorescence quenching of CQDs related to the Co²⁺ ion was used for the detection of the analyte, generating a sensing strategy with a limit of detection (LOD) of 0.98 μmol L⁻¹. Furthermore, the interaction between the Co²⁺ ion with the CQDs resulted in the color change of the solution from colorless to pale yellow. Thus, a colorimetric Co²⁺ sensor was also developed, since there was an absorption band at 315 nm attributed to the formation of the complex CQD + Co²⁺. The colorimetric method showed an excellent sensitivity to Co²⁺, with a LOD of 3.01 μmol L⁻¹. In addition, Principal Component Analysis (PCA) together with Linear Discriminant Analysis (LDA) were used successfully to distinguish different concentrations of Co²⁺ and different interfering ions present in the solution. Finally, a real sample of blood plasma was properly treated and doped with different concentrations of Co²⁺, which was successfully quantified via fluorescent method. Therefore, the CQDs obtained in this work are a powerful and versatile Co²⁺ detection tool.