Conducting Polymers as Antennas for Probing Biophysical Activities

Polypyrrole-supported membrane proteins for bio-inspired ion channels

Biomedical platforms constructed by immobilizing membrane proteins in matrixes made of synthetic organic polymers is a challenge because the structure and function of these proteins are affected by environmental conditions. In this work, an operative composite that regulates the diffusion of alkali ions has been prepared by functionalizing a supporting matrix made of poly(N-methylpyrrole) (PNMPy) with a β-barrel membrane protein (Omp2a) that forms channels and pores. The protein has been unequivocally identified in the composite, and its structure has been shown to remain unaltered. The PNMPy-Omp2a platform fulfills properties typically associated with functional bio-interfaces with biomedical applications (e.g., biocompatibility, biodegrabadility, and hydrophilicity). The functionality of the immobilized protein has been examined by studying the passive ion transport response in the presence of electrolytic solutions with Na(+) and K(+) concentrations close to those found in blood. Although the behavior of PNMPy and PNMPy-Omp2a is very similar for solutions with very low concentration, the resistance of the latter decreases drastically when the concentration of ions increases to ∼100 mM. This reduction reflects an enhanced ion exchange between the biocomposite and the electrolytic medium, which is not observed in PNMPy, evidencing that PNMPy-Omp2a is particularly well suited to prepare bioinspired channels and smart biosensors.

Kinetic study of the formation of polypyrrole nanoparticles in water-soluble polymer/metal cation systems: a light-scattering analysis

A facile way to synthesize nanometer-sized polymer (polypyrrole, PPy) particles is explored on the basis of the formation of complexes between water-soluble polymers and metal cations in aqueous solution. The metal cation is used as an oxidizing agent to initiate the chemical oxidation polymerization of the corresponding monomer, and the water-soluble polymer effectively provides a steric stability for the growth of polymer nanoparticles during the polymerization process. Light-scattering analyses are performed to give insight into the behavior of the complexes in aqueous solution. In addition, major physical parameters affecting the formation of polymer nanoparticles are investigated, including hydrodynamic radius, radius of gyration, shape factor, and viscosity. By judicious control of these parameters, PPy nanoparticles with narrow size distribution can be readily fabricated in large quantities. It is also possible to control the diameter of the nanoparticles by changing critical synthetic variables. Importantly, PPy nanoparticles of approximately 20-60 nm in diameter can be prepared without using any surfactants or specific templates; this novel strategy offers great possibility for mass production of polymer nanoparticles.

Monitoring intermediate states of bacteriorhodopsin monolayers using near-field optical microscopy

We demonstrate single-molecule-level features using near-field optical microscopy on bacteriorhodopsin (bR), a membrane protein that functions as a light-driven proton pump. The photophysical properties of bR are utilized in this imaging technique, using a combination of photoexcitation sources, to accurately identify the active regions and quantify the optical parameters. The studies of bR monolayers are carried out on inert quartz substrates as well as active conducting polymer (polyaniline) substrates. The substrate also plays an important role in the photocycle quantum efficiencies. We speculate on mechanisms governing the higher near-field absorption strength of bR molecules.