Interaction of Proteins with a Planar Poly(acrylic acid) Brush: Analysis by Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D)

Jacek Walkowiak,Michael Gradzielski,Stefan Zauscher,Matthias Ballauff

doi:10.3390/polym13010122

Abstract

We describe the preparation of a poly(acrylic acid) (PAA) brush, polymerized by atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) and subsequent acid hydrolysis, on the flat gold surfaces of quartz-crystal microbalance (QCM) crystals. The PAA brushes were characterized by Fourier transform infrared (FT-IR) spectroscopy, ellipsometry and water contact angle analysis. The interaction of the PAA brushes with human serum albumin (HSA) was studied for a range of ionic strengths and pH conditions by quartz-crystal microbalance with dissipation monitoring (QCM-D). The quantitative analysis showed a strong adsorption of protein molecules onto the PAA brush. By increasing the ionic strength, we were able to release a fraction of the initially bound HSA molecules. This finding highlights the importance of counterions in the polyelectrolyte-mediated protein adsorption/desorption. A comparison with recent calorimetric studies related to the binding of HSA to polyelectrolytes allowed us to fully analyze the QCM data based on the results of the thermodynamic analysis of the binding process.

Highlights

Polymer brushes consist of polymer chains densely grafted by one end to an interface [1]
We recently showed that proteins can adsorb onto like-charged spherical polyelectrolyte brushes (SPBs) [21,29,30]
We have successfully demonstrated the activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) polymerization of poly(acrylic acid) (PAA) brushes grafted from a planar gold surface of quartz-crystal microbalance (QCM) crystals

Summary

Introduction

Polymer brushes consist of polymer chains densely grafted by one end to an interface [1]. In many cases polymer brushes are studied to control the protein adsorption onto surfaces [8,9]. This becomes more complex when the brush is composed of charged polymer chains, i.e., polyelectrolytes [4,10,11,12,13,14]. Surfaces modified with polyelectrolyte brushes have been frequently investigated as they are related to “smart” or stimuli responsive surface coatings [15]. It is known that proteins adsorbed and immobilized onto polyelectrolyte brushes can retain their conformation [17] as well as their (enzymatic) activity [18,19]

Methods

Results

Conclusion