Amino Acids Functionalized Fluorescent Carbon‐based Nanoparticle for Dual Detection of Co(II) and Cu(II) Based on Synergistic Effect of Surface Groups

Abstract

Using citric acid, urea, phosphoric acid, and amino acids as raw materials, doped carbon‐based nanoparticles (Ami‐CNPs) with approximately 100 nm grain diameter were synthesized via a hydrothermal method. Infrared spectroscopy revealed the presence of ‐NH₂, ‐COOH, and amino acid residues on the particle surface. Under 365 nm excitation, Ami‐CNPs emitted blue fluorescence with persistent stability in acidic, alkaline, and saline environments. Among carbon‐based nanoparticles doped with various amino acids, only the one doped with cysteine (Cys‐CNPs) exhibit unique fluorescence responses to Co²⁺ and Cu²⁺ ions, and behaved excellent linear relationships: the former quenched (LOD = 0.479 µM) while the latter enhanced (LOD = 0.547 µM) fluorescence. Moreover, the quenched fluorescence of Cys‐CNPs by Co²⁺ could be restored by the addition of Cu²⁺, while Co²⁺ had no effect on the fluorescence of Cys‐CNPs coexisting with Cu²⁺. The dual metal sensing properties of Cys‐CNPs were attributed to the synergistic effects of surface functional groups. The surface cysteine residues of the particles specifically bind to Co²⁺ ions, inducing fluorescence quenching via electron transfer to nonfluorescent Cys‐Co complexes, while the ‐NH₂ and ‐COOH groups chelated with Cu²⁺ to induce forming rigid structures among particles, thereby enhancing fluorescence efficiency of Cys‐CNPs.