Lab-on-nanoparticle as a multidimensional device for colorimetric discrimination of proteins

We report on a method for sensitive detection and discrimination of multiple proteins. The peroxidase-like activity of gold nanoparticles (AuNPs) is employed to catalyze the oxidation of 3′,3′,5′,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Depending on the protein, this produces colorations with different absorbance. The catalytic activity of the reaction system is affected because different proteins are absorbed onto the surface of the AuNPs. The absorbance values at 370, 450, and 650 nm are different in the presence of different proteins. The array can discriminate 8 proteins at 50 nM concentration levels with 100% accuracy. It also can discriminate proteins being present in different concentrations and mixtures with different molar ratios of proteins. Human urine spikes with 8 proteins (Concanavalin A), Cytochrome C, Horseradish peroxidase, Human serum albumin, Myoglobin, Pepsin, Trypsin, Papain) can be differentiated by applying hierarchical cluster analysis. The system also can discriminate proteins at different concentrations and the mixtures with different molar ratios in bovine serum. This indicates that the array has a great potential in terms of analyzing biological fluids.