Protein adsorption on thermo-responsive surfaces

1 Analysis and evaluation of protein adsorption on PNIPAAm-modified surfaces 

Switchable and Responsive Surfaces and Materials for Biomedical Applications 

Compared with the qualitative methods discussed above, surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) are two instrumentation methods for quantitative evaluation of protein adsorption that are highly sensitive and examine adsorption kinetics. For example, the adsorption of two proteins (hbrino-gen and lysozyme) with different charges and sizes on a PNIPAAm hhn was compared using SPR, and the results indicated that the effect of temperature on adsorption (amount and kinetics) is different (Teare et al., 2005). In another report, QCM was employed to analyze the kinetics of bovine serum albumin (BSA) adsorption on P(NlPAAm-co-di(ethylene glycol) divinyl ether) cross-linked hhns at different temperatures (Alf, Hatton, Gleason, 2011). Above the LCST, a simple monolayer of BSA was adsorbed on the surface, whereas below the LCST, there are two processes involved initial protein adsorption onto the surface followed by protein diffusion into the swollen hydrogel matrix. 

From another point of view, atomic force microscopy is focused on the intermolec-ular interactions between proteins (coated on the atomic force microscopy probe) and PNIPAAm surfaces at different temperatures. Using this method, Cho et al. reported several studies on intermolecular force between BSA and PNIPAAm surfaces (Cho, Kim, Cho, 2004 Cho, Kim, Cho, 2005 Cho, Kim, Cho, 2008). They observed a temperature-dependent adhesion force (defined as the maximum attractive force during retraction of the surface from the tip), which is negligible at lower temperatures and suddenly increases to a maximum value as the temperature increases above a transition temperature (27-29 °C). The lower transition temperature compared with the LCST of PNIPAAm in water (32 °C) may be due to the addition of salts becanse the experiments were conducted in a phosphate bnffer solution. The change in adhesion force is consistent with the affinity between soluble proteins and a PNIPAAm surface, which, at room temperature, is approximately an order of magnitude lower than at 37 °C (Cheng et al., 2006). 

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