Troy S. Bergstedt

Building highly sensitive dye assemblies for biosensing from molecular building blocks

Fluorescence superquenching is investigated for polyelectrolytes consisting of cyanine dye pendant polylysines ranging in number of polymer repeat units (NPRU) from 1 to 900, both in solution and after adsorption onto silica nanoparticles. As NPRU increases, the absorption and fluorescence evolve from monomer spectra to red-shifted features indicative of molecular J aggregates. In solution, the superquenching sensitivity toward an anionic electron acceptor increases by more than a millionfold over the NPRU range from 1 to 900. The dramatic increase is attributed to enhanced equilibrium constants for binding the quenchers, and the amplified quenching of a delocalized exciton of ≈100 polymer repeat units. The self-assembly of monomer onto silica and clay nanoparticles leads to formation of J aggregates, and surface-activated superquenching enhanced 10,000× over the monomer in solution, indicating the formation of “self-assembled polymers” on the nanoparticle surface. Utilization of these self-assembled polymers as high-sensitivity biosensors is demonstrated.

Amplified fluorescence quenching and biosensor application of a poly (para-phenylene) cationic polyelectrolyte

The quenching behavior of a water-soluble cationic poly (para-phenylene) bearing quaternized ammonium side groups (P-NEt3+) was studied. P-NEt3+ is efficiently quenched by sodium anthraquinone-2,6-disulfonate (AQS) and sodium 1,4,5,8-naphthalenediimide-N,N’-bis (methylsulfonate) (NDS) in aqueous solution via a photo-induced electron-transfer mechanism. Absorption spectra of the NDS/P-NEt3+ ion-pair complex indicated formation of a stable charge-transfer complex in the ground state. A large spectral shift and band broadening occurred during AQS/P-NEt3+ complex formation, which is believed to arise due to P-NEt3+ conformational changes induced by hydrophobic interactions. Finally, a protein sensor that relies on the quenching behavior of P-NEt3+ was designed based on the quencher-tether-ligand (QTL) approach. AQS tethered to biotin (AQS-E-Biotin) was used along with P-NEt3+ to sense avidin.

Photolithographically defined electropolymerized films. Fabrication of an electrochemically switchable diffraction grating comprised of poly-(bpy)2Ru(vpy)22+

A combination of photolithography and electropolymerization is utilized to fabricate spatially patterned films of poly-(bpy)2Ru(vpy)22+; the method has been applied to fabricate poly-(bpy)2Ru(vpy)22+ based diffraction gratings.