Protein quantitation by complexation of fluorescent tetraphenylthiophene cation to anion-terminated poly(N-isopropylacrylamide): Aggregation-enhanced emission and electrostatic interaction

A fluorescent biological sensor utilizing aggregation-enhanced emission (AEE) property was developed in our laboratory. First, the AEE-active fluorescent tetraphenylthiophene (TP) unit was synthetically connected to poly(N-isopropylacrylamide) by covalent and ionic bonds, resulting in the respective c- and i-TP-PNIPAM for the detection and quantification of the bovine serum albumin (BSA) model protein. When bind to BSA, the ionic i-TP-PNIPAM shows much better fluorescence (FL) sensitivity compared to c-PNIPAM. The fluorescence (FL) intensity of i-TP-PNIAPM displays a good linear dependence on concentration of BSA (0–1 mg/mL), indicating quantitative fluorimetric protein detection can be achieved. Further addition of anionic surfactant of sodium dodecylsulfate (SDS) considerably raised the FL intensity of the complex solution. All the FL response was discussed in term of conformational freedom of the TP unit under different environmental constraints.