A new MoS2 nanosheet-based fluorescent biosensor for protein detection is developed. This method combines the terminal protection of small-molecule-linked DNA (TPSMLD) and exonuclease III (Exo III)-aided DNA recycling amplification to convert protein assay into the highly sensitive detection of DNA. Taking the streptavidin (SA)-biotin system as a model, a detection limit of 0.67 ng mL(-1) SA is obtained with a good selectivity. The study demonstrated here not only offers simple, sensitive and selective detection method for protein assay, but also will expand the application of the emerging 2D nanomaterials into biological assay.