We have developed an enzyme−nanoparticle sensor array where the sensitivity is amplified through enzymatic catalysis. In this approach cationic gold nanoparticles are electrostatically bound to an enzyme (β-galactosidase, β-Gal), inhibiting enzyme activity. Analyte proteins release the β-Gal, restoring activity and providing an amplified readout of the binding event. Using this strategy we have been able to identify proteins in buffer at a concentration of 1 nM, substantially lower than current strategies for array-based protein sensing. Moreover, we have obtained identical sensitivity in studies where the proteins are spiked into the complex protein matrix provided by desalted human urine (1.5 μM total protein; spiked protein concentrations were 0.067% of the overall protein concentration), demonstrating the potential of the method for diagnostic applications.