A colorimetric sensor array for protein discrimination based on carbon nanodots-induced reversible aggregation of AuNP with GSH as a regulator

Abstract

We have proposed a doubled nanoplasmonic colorimetric sensor array for protein recognition based on car-bon nanodots (CDs)-induced reversible aggregation of gold nanoparticle (AuNP) with GSH as a regulator. It is found that different kinds of CDs can induce the aggregation of AuNP with different degrees and cause different color change. Adding reduced glutathione (GSH) into the CDs/AuNP system can make the AuNP disperse again accompanying with a second color change. Based on this phenomenon, three kinds of CDs originated from different amino acids and citric acid are used to fabricate a colorimetric sensor array with three sensing elements. Upon addition of target proteins into CDs/AuNP conjugates, the competitive protein-AuNP affinity disrupts the SPR absorption peak of CDs/AuNP, generating cross-reactive three-unit colorimetric signal. Subsequently, GSH is introduced into each unit containing protein samples in situ. The SPR absorption peak of AuNP is substantially affected due to the stronger affinity between AuNP and GSH, producing an-other three-unit response signal. With this strategy, each sensing element can give two output signals to each target protein, which doubles the number of unit from three to six without changing the three-cell configuration, resulting in greatly improved discrimination ability of proteins and identification accuracy of unknown samples. Twelve proteins at 50 nM can be well discriminated by this novel colorimetric sensor array. Moreover, our sensing system is very stable in the high concen-tration of salt, make it suitable for the real sample analysis. This method effectively identifies twelve proteins at 200 nM spiked in human urine.