Colorimetric sensor array with unmodified noble metal nanoparticles for naked-eye detection of proteins and bacteria

Herein we report a novel strategy for the detection and identification of proteins using unmodified noble metal nanoparticles. Five gold nanoparticles (AuNPs) and two silver nanoparticles (AgNPs) with different sizes were utilized as sensing elements to create a colorimetric sensor array. In the presence of proteins, the UV-vis absorbance of the noble metal nanoparticles changed due to the interactions between the protein and nanoparticles, producing distinct absorbance response patterns which can be visually detected by the naked eye. The color pattern of the array is a unique "fingerprints" for each protein sample, which can be differentiated by linear discriminant analysis (LDA). Ten different proteins at concentrations of 0.5, 5 and 50 mu M have be successfully discriminated. Moreover, the array was also able to discriminate different bacteria at a concentration of 0.05 OD in 200 mu L, as well as cancer cells at the level of 5000 cells in 200 mu L. This work demonstrates that an unmodified noble metal nanoparticle-based protein detection array has potential for applications in medical diagnostics.