Voltage-Tunable Volume Transitions in Nanoscale Films of Poly(hydroxyethyl methacrylate) Surfaces Grafted onto Gold

Abstract

Surface grafting of a polymerizable monomer onto Au was used to produce nanometer-scale planar hydrogel films with controllable volume. A self-assembled monolayer of 11-mercaptoundecanoic acid on a planar Au surface was activated through water-soluble carbodiimide and N-hyroxysuccinimide followed by reaction with 2-aminomethacrylate to produce a methacrylate-terminated surface layer, which readily polymerized under UV radiation in the presence of hydroxyethyl methacrylate monomer, ethylene glycol dimethacrylate cross-linker, and a photoinitiator. The reaction steps were characterized by external reflection mode Fourier transform IR spectroscopy. Under controlled UV exposure, thin (3 nm < d < 10 nm) hydrogel films were obtained from 1:1 ethanol/H(2)O. Surface plasmon resonance measurements were used to characterize both the synthesis of the hydrogel and the potential-induced volume changes. The nanometer-scale hydrogels thus produced undergo reproducible changes in thickness, when a potential is applied across the film. Thickness changes increasing with applied potential were obtained for both voltages in the range |V(appl)| </= 600 mV. In NaCl, electrolyte films swell with application of negative potentials and shrink with positive potentials, due to the imbibing or extrusion of hydrated Na(+) ions, respectively. Thickness changes as large as 50% can be achieved. An increase in the cross-linker content results in thicker films, but at the cost of dramatically restricted swelling. Response times are generally faster for smaller applied potentials, as expected if the volume change results from mass transport of electrolyte.

Stimuli-Responsive Polymer Brushes for Flow Control through Nanopores

“…Similarly, polymers that respond to electric fields [20,21] offer an additional triggering mechanism. In general, three distinct approaches have been used to functionalize membranes with smart polymers.…”

Spatiotemporally Controlled Formation of Two‐Component Counterpropagating Lateral Graft Density Gradients of Mixed Polymer Brushes on Planar Au Surfaces

“…PHEMA is an important polymer that has been used in drug delivery and tissue-engineering applications, and has been shown to exhibit voltage-induced free volume transitions. [43] The present work is focused on PNIPAAm-PHEMA polymer-brush systems because of their potential applications, especially temperature-voltage-induced shape changes. However, the polymer-brush gradient-formation strategy reported here is quite general, because any material amenable to ATRP growth on Au can be manipulated, and it is not limited by the physical size of the substrate, down to the micrometer scale.…”

Optical Biosensing of Bacteria and Bacterial Communities

“…As predicted by Mie theory, the spectral position of the surface plasmon resonance can be tuned by changing the material and thickness of the metallic thin film as well as the refractive index of its local environment. In the context of SPR, the local environment can be understood as the volume over which the plasmon field decays in the dielectric medium [106]. An especially useful variant of SPR, localized surface plasmon resonance (LSPR) spectroscopy, utilizes surface confined plasmons from nanoparticles.…”