Creating “Smart” Surfaces Using Stimuli Responsive Polymers

Surfaces modified with stimuli‐responsive polymers (SRPs) dynamically alter their physico‐chemical properties in response to changes in their environmental conditions. The triggered control of interfacial properties provided by immobilized SRPs at the solid–water interface has application in the design of biomaterials, regenerable biosensors, and microfluidic bioanalytical devices. In this article, we briefly summarize recent research in this area, followed by two recent examples of research from our laboratory on stimuli‐responsive surfaces. First, we present a new assay to quantify the phase transition behavior of SRPs at the solid–water interface. This assay, which is based on the distance‐dependent colorimetric properties of gold nanoparticles, provides a technically simple and convenient method to determine the effect of different variables on the lower critical solution temperature (LCST) behavior of SRPs at the solid–water interface. Second, we show that stimuli‐responsive surfaces can be created by the immobilization of an elastin‐like polypeptide (ELP), a thermally responsive biopolymer, on a glass surface. We exploit the phase transition of the ELP at a surface to reversibly address an ELP fusion protein to a surface. This method, which we term thermodynamically reversible addressing of proteins (TRAP), enables the reversible, spatio‐temporal modulation of protein binding at the solid‐liquid interface, and will enable the realization of new bioanalytical applications.     

Evolution of Superconducting and Normal-State Properties in C60 “Polymer” Doped with K

Abstract:

Bulk superconductivity was observed in a new iodine-treated aggregated form of solid C₆₀, believed to be a “polymer”, by doping with alkali metal. Evolution of superconducting (T_c = 17.2 K) and normal-state properties, has been studied as a function of doping with K. The normal-state dc susceptibility exhibited a complex behavior with the increasing K uptake, evolving from an enhanced paramagnetism at low doping level, to a weakly temperature-dependent diamagnetism at the optimum doping level for superconductivity, and ending with a strong temperature-independent diamagnetism in over-doped samples. The measured superconductivity parameters, such as T_c, London penetration depth and the Ginzburg-Landau coherence length, are compared with those of the monomer K₃C₆₀. and the main factors determining the differences between the two systems are discussed.