Thermoresponsive polymer-stabilized gold nanoparticles for protein detection

Abstract

Gold nanoparticles stabilized by thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM-AuNPs), were prepared by surface grafting of thiol-terminated PNIPAM (having two targeted molecular weight 6 and 8 kDa) onto citrate-stabilized AuNPs. The color change of the PNIPAM-AuNPs solution from red to blue-purple without precipitation when the solution was heated to 40 ºC, above the lower critical solution temperature (LCST) of PNIPAM indicated the thermoresponsive property of the synthesized AuNPs. In this work, PNIPAM-AuNPs were used to detect proteins by chemical nose approach based on fluorescence quenching of fluorophore by AuNPs. In the detection, upon an addition of protein analyte, quenched fluorophore absorbed on the AuNPs surface can be attracted by protein and released from the AuNPs surface resulting in the recovery of fluorescence signal of the fluorophore. An array-based sensing platform for detection of six proteins can be developed from the PNIPAM-AuNPs having different molecular weight and conformation in combination with a G0 dendritic phenylene-ethynylene fluorophore having positively charged N(CH3)3+ groups. From Linear Discriminant Analysis (LDA), it was found that 100% accuracy of protein classification can be achived by using only two types of PNIPAM-AuNPs.