Combination of AFM and Electrochemical QCM-D for Probing Zwitterionic Polymer Brushes in Water: Visualization of Ionic Strength and Surface Potential Effects
Journal
Langmuir
Journal Volume
37
Journal Issue
42
Pages
12476-12486
Date Issued
2021
Author(s)
Abstract
The surface modification of soft zwitterionic polymer brushes with antifouling properties represents a facile approach to enhancing the performance of bioelectronics. Ionic strength and applied potentials play a crucial role in controlling polymer brushes' conformation and hydration states. In this study, we quantitatively investigated and compared poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(sulfobetaine methacrylate) (PSBMA) brushes at different salt concentrations and applied surface potentials. Initiator-containing poly(3,4-ethylenedioxythiophene) films (poly(EDOT-Br)) were prepared by electropolymerization. After the conducting polymer was deposited, polymer brushes grew from the electrode surface through surface-initiated atom-transfer radical polymerization (SI-ATRP). Polymer brushes were carefully characterized for their surface morphologies using an atomic force microscope (AFM). The force volume method measured using AFM enabled the analysis of the Young's modulus of the two polymer brushes. Hydration states and protein binding behaviors of polymer brushes were examined using quartz crystal microbalance with dissipation (QCM-D). We further integrated a potentiostat with the QCM-D to conduct an electrochemical QCM-D study. The energy dissipation and frequency changes corresponded to the ion adsorption on the film surface under different ionic strengths. The results of both hydration states and nonspecific protein binding behavior indicate that PMPC brushes have greater ionic strength independency, implying the conformation of the unchanged PMPC brushes. Moreover, we illustrated how the surface potential influences nonspecific and specific binding behavior on PMPC brushes on PEDOT films compared with electrified poly(EDOT-PC) electrodes. We concluded that PMPC brushes exhibit unique behaviors that are barely affected by ion concentration, and that the brushes' modification results in less influence by surface potential due to the finite Debye length influencing the electrode surface to outer environment in an NaCl aqueous solution. ? 2021 American Chemical Society.
Subjects
Atom transfer radical polymerization
Binding energy
Biochemistry
Conducting polymers
Dendrimers
Elastic moduli
Electrodes
Electrolytes
Energy dissipation
Hydration
Polypyrroles
Proteins
Quartz crystal microbalances
Sodium chloride
Sodium sulfate
Surface potential
Voltage regulators
2-methacryloyloxyethyl phosphorylcholine
Atomic force
Binding behaviour
Electrochemical quartz crystal microbalance
Electrode surfaces
Hydration state
Polymer brushes
Protein-binding
Quartz crystal microbalance with dissipation
Zwitterionic polymers
Ionic strength
polymer
water
adsorption
osmolarity
quartz crystal microbalance
surface property
Adsorption
Osmolar Concentration
Polymers
Quartz Crystal Microbalance Techniques
Surface Properties
Water
Type
journal article