Detection of Enzyme Activity through Catalytic Signal Amplification with Functionalized Gold Nanoparticles

A new chemical methodology to detect enzyme activity at nanomolar concentrations is described. The sensing mechanism relies on the use of a catalytic Au MPC, which highly efficiently cleaves HPNPP causing the release of p-nitrophenolate, a yellow reporter molecule. Catalysis is completely inhibited in the presence of low micromolar concentrations of biologically important oligoanions, such as ATP, ADP or an Asp-tripeptide, which bind with high affinities to the Au MPC surface. The change in free energy of binding, ΔG, increases in a perfect linear manner as a function of the number of charges present in the analyte. The enzymatic hydrolysis of an Asp-tripeptide turns on the catalytic production of p-nitrophenolate by the catalytic Au MPC, since the products of hydrolysis have a lower affinity for the Au MPC surface. The cascade of the two catalytic processes causes a strong signal amplification allowing the detection of nanomolar enzyme concentrations.