Conjugated polyelectrolytes for protein assays and for the manipulation of the catalytic activity of enzymes

A new method has been developed to discriminate between proteins with different isoelectric points by using fluorescent conjugated polyelectrolytes. Charged water-soluble polyfluorenes that contain 2,1,3-benzothiadiazole (BT) units demonstrate intramolecular energy transfer from the fluorene units to the BT sites when oppositely charged proteins are added to the mixture. This results in a shift in emission color from blue to green and a change in the emission intensity of conjugated polyelectrolytes, which makes it possible to assay proteins. The formation of conjugated polyelectrolyte/enzyme complexes by electrostatic interactions can be utilized to manipulate the activity of enzymes by means of local alteration of enzyme charge density. The oppositely charged substrate binds to conjugated polyelectrolyte and reduces the distance between the enzyme and the substrate, leading to an increase in the cleavage reaction rate. The new method has three important features: 1) it offers a convenient "mix-and-detect" continuous approach for protein assays and rapid detection of enzyme activity; 2) the use of water-soluble conjugated polyelectrolytes imparts the sensor with a high sensitivity; 3) this method does not require fluorescent labels on the targets, which should significantly reduce the cost.