Adsorption of pNIPAM Layers on Hydrophobic Gold Surfaces, Measured in Situ by QCM and SPR

Abstract

In situ surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) measurements have been employed to measure the adsorption kinetics and absolute adsorbed amount of the poly(N-isopropyl acrylamide) (pNIPAM) from bulk aqueous solution onto a hydrophobized gold substrate. The adsorption was carried out at 31 °C, which is just below the lower critical solution temperature of pNIPAM in water. We find that the shift in the coupling angle of the surface plasmon (proportional to the "optical thickness") and the shift in the resonance frequency of the quartz crystal (proportional to the "acoustic thickness") increase in parallel for most of the adsorption. Also, the change of dissipation is proportional to the change in frequency. These observations suggest that the buildup of the polymer layer proceeds via growth in thickness rather than by densification of a layer with constant thickness. We interpret this finding in the sense that the dense high-temperature phase wets the hydrophobic gold surface. The wetting layer has a fixed density and grows in thickness. In addition, the QCM has been used to study the temperatureinduced conformational change for pNIPAM around the critical temperature. It was found that the technique was able to monitor additional adsorption that occurs when crossing the critical point, which was due to bulk phase separation. Desorption was also noted when crossing the critical point from the opposite direction, and for the given system the process was entirely reversible.

Copper‐Assisted Weak Polyelectrolyte Multilayer Formation on Microspheres and Subsequent Film Crosslinking

“…It is noted that in the QCM measurements, the total oscillating mass is detected, and therefore any water hydrodynamically coupled to the films will contribute to the observed frequency change. [26] This effect has previously been reported for polyelectrolyte multilayer films. [27,28] PAA/PAH layers were then deposited onto PS spheres with a diameter of 496 nm.…”

Interactions between inorganic nanoparticles and cellulose nanofibrils

“…3) suggests that the layer is viscous and contains much water. However, it is misleading to only consider the quantity of the frequency and dissipation change, and therefore, QCM-D response is often presented as a ratio of dissipation and frequency change (Df-ratio) enabling examination of the intrinsic layer properties (Plunkett et al 2003;Du and Johannsmann 2004). Dissipation as a function of frequency can indicate variation in the adsorption kinetics and layer viscosity (Höök et al 1998b) as well as conformational changes in the layer (Saarinen et al 2008).…”

A survey of the 2001 to 2005 quartz crystal microbalance biosensor literature: applications of acoustic physics to the analysis of biomolecular interactions

“…There are a large number of published papers describing the interaction of proteins and peptides with polymeric and planar thin films (Briseno et al, 2001;Yamashita et al, 2001;Fant et al, 2002;Hibbert et al, 2002;Linder et al, 2002;Park et al, 2002;Takada et al, 2002;Andersson et al, 2002a;Forzani et al, 2003;Hamada et al, 2003;Plunkett et al, 2003;Haynie et al, 2004;Heuberger et al, 2004;Lin et al, 2004;Lojou and Bianco, 2004;Notley et al, 2004;Welle, 2004;Evans-Nguyen and Schoenfisch, 2005). There are a further 55 papers in our database that, whilst involving the interaction of polymer films with protein, have been excluded from this review as they were thought to be of minimal relevance to the readership of this journal.…”