Atomically-tailored graphene oxide displaying enhanced fluorescence for the improved optical sensing of MMP-2

Abstract

Modulation of the optical properties of two-dimensional nanomaterials is a crucial step to improve their sensing performance for the optical detection of target molecules of interest. Here, we report a mild, simple and effective approach for heteroatoms-doping of graphene oxide (GO) without size alteration, resulting in enhanced fluorescence properties. Sulfur and nitrogen atoms were chemically doped onto the basal plane of GO (NSGO) via a sonic wave-assisted reaction with cysteine as an S and N dopant under acidic conditions at room temperature. As-prepared NSGO retained the same lateral size as pristine GO, but possessed a large proportion of thiopyran sulfur and pyrrolic nitrogen. In addition, NSGO exhibited highly enhanced fluorescence with strong resistance to the pH and polarity of solution. Mechanistic investigation suggested that S-doping was essential for the improved fluorescence properties of NSGO. Finally, to investigate the effect of heteroatoms-doping on sensing performance, fluorescent NSGO was employed as a fluorescent biosensor for the detection of matrix metalloproteinases 2 (MMP-2) via a peptide-induced assembly and self-quenching principle. As compared to pristine GO, NSGO assemblies exhibited more significant fluorescence quenching, but upon addition of MMP-2, the NSGO assemblies were disassembled, leading to the higher restoration of the quenched fluorescence, eventually resulting in the more sensitive detection of MMP-2.