An “on–off–on” fluorescent nanoprobe for recognition of Cu2+ and GSH based on nitrogen co-doped carbon quantum dots, and its logic gate operation

Abstract

Novel nitrogen co-doped carbon dots (NCDs) were synthesized as a fluorescent “on–off–on” switch for the highly sensitive and selective sensing of Cu²⁺ and glutathione (GSH) by a straightforward pyrolysis route. The as-prepared NCDs exhibited not only high optical stability but also superior biocompatibility and biolabeling potentials. The “on–off” process was realized by the introduction of Cu²⁺ on luminescent NCDs, which formed an NCDs–Cu²⁺ complex and quenched the fluorescence of NCDs efficiently. “Off–on” was also recovered upon addition of GSH owing to the competitive binding of GSH and Cu²⁺ leading Cu²⁺ to escape from the surface of the NCDs. The probe demonstrated high sensitivity and selectivity toward Cu²⁺ and GSH over other analytes, with a low detection limit of 3.62 × 10⁻⁴ μM and 6.32 × 10⁻⁴ μM, respectively. Concurrently, an “AND” logic gate was constructed based on the as-fabricated NCDs. Thanks to the highly intense emission of NCDs, the gradual quenching and restoration of their fluorescence with the addition of Cu²⁺ and further GSH could also be observed with the naked eye. More importantly, the probe was also extended to cellular imaging. The probe demonstrates high selectivity, repeatability, and stability, which offers a promising platform for environmental and biological sensing applications.