γ-Aminobutyric acid-modified graphene oxide as a highly selective and low-toxic fluorescent nanoprobe for relay recognition of copper(II) and cysteine

A sensitive and selective graphene oxide (GO)-based fluorescent nanoprobe has been developed for the relay recognition of Cu²⁺ and cysteine (Cys) by covalently grafting γ-aminobutyric acid (GABA) onto GO. The fluorescence of the probe (with excitation/emission maxima at 360/445 nm) is selectively quenched by Cu²⁺ via static fluorescence quenching. Fluorescence drops linearly as the concentration of Cu²⁺ is increased from 50 nM to 1.0 µM, and the detection limit for Cu²⁺ is calculated as 15 nM. By virtue of the strong interaction between Cys and Cu²⁺, the GO-GABA/Cu²⁺ complex can further sensitively recognize Cys in a "switch-on" mode. The linear range for Cys detection is from 50 nM to 1.0 µM, and the detection limit is 38 nM. The probe has low cytotoxicity, and it works well inside living cells, which is verified by the successful application in imaging of LLC-PK1 cells.

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