Luminescent Polyelectrolytes for use in Biosensors

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Luminescent polyelectrolytes exhibit enhanced fluorescence quenching ("superquenching") with very large Stern-Volmer quenching constants. The superquenching arises from a combination of two effects. First, it has been demonstrated that a single acceptor (functioning as an acceptor for photoinduced electron transfer) can quench the fluorescence emission from an entire macromolecule in aqueous solution. Second, in aqueous solution, such luminescent polyelectrolytes are charged. As a result, the positively charged acceptor and the anionic polymer form a weakly bound complex thereby enabling static superquenching. The superquenching of the photoluminescence (PL) can be used for sensing biomolecules with specificity and with high sensitivity. Thus, determining and controlling the magnitude of the Coulomb binding energy of the polymer/quencher complex is of particular importance to the use of luminescent polyelectrolytes in biosensor applications. If the binding between the ligand tethered to the quencher and the analyte is smaller than that between the quencher and the polymer, the quencher/ligand cannot be effectively pulled away from the luminescent polymer. In addition, the photoluminescence (PL) quantum efficiency is sensitive to the conformation of the polymer in solution. It is known that polyelectrolytes can form stable complexes with oppositely charged amphiphilc molecules (surfactants). Experiments have shown that addition of sufactant to solutions containing luminescent polyelectrolytes significantly increases the PL efficiency. Thus, studies of the chain conformation of luminescent polyelectrolytes is of clear scientific relevance and importance.%%% This project is directed toward determining the chain conformation of luminescent polyelectrolytes and the magnitude of the Coulomb binding energy of the polymer: quencher complexes. The luminescent polyelectrolytes to be studied include water soluble PPV derivatives and novel poly-lysine polymers (polypeptide chains with cyanine dyes in J-aggregate configuration attached as side-chains). A series of quenchers with different charges have been developed and are available for these studies. Quenching of PL will be studied by changing the ion concentration in buffered aqueous solutions, by changing the concentration of acceptors, and by varying the temperature. The chain conformation of the luminescent polyelectrolytes will be determined (with and without quencher, surfactant etc), as a function of the Debye screening length (ion concentration) and as a function of molecular weight using light scattering and neutron scattering.