Tyrosinase is an important marker of human diseases such as neurodegeneration associated with Parkinsons disease and melanoma.Sensitive detection of tyrosinase activity in vitro and inside cells is of great significance to medical diagnostics and skin disorders treatment.In this work,QDs functionalized with tyrosine and zwitterionic molecules construct a nanometer scale scaffold to test tyrosinase activity in vitro and inside cells.Tyrosinase oxidizes tyrosine to dopachrome and switches on the electron-transfer access which relates to fluorescence quenching.Enzymatic process curves reveal the enhanced enzymatic activity on conjugated nanoparticle-substrate,which leads to highly sensitive detection of tyrosinase as low as 1 nM.It is also demonstrated that QD-Tyr conjugates can sensitively probe intracellular tyrosinase in melanoma cells,which may promise the potential applications in diseases monitoring and medical diagnostics.