2 research outputs found
Probing the Orientation of βâLactoglobulin on Gold Surfaces Modified by Alkyl Thiol Self-Assembled Monolayers
The adsorption of a globular protein
on chemically well controlled
surfaces was investigated in order to correlate its orientation to
the surface properties. To this end, three different alkyl thiols,
differing by their end group (âCOOH, âCH<sub>3</sub>, and âNH<sub>2</sub>), were used to build up self-assembled
monolayers (SAMs) on gold substrates. β-Lactoglobulin (βLG)
was then adsorbed on these SAMs by immersion in a phosphate buffer
solution. The surface modification with alkyl thiols and the subsequent
adsorption of proteins were characterized <i>ex situ</i> by polarization modulated infrared reflectionâabsorption
spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS).
The adsorption behavior of proteins was also monitored <i>in
situ</i> using quartz crystal microbalance with dissipation measurements
(QCM-D). Direct evidence regarding the protein orientation in the
adsorbed state was obtained by means of time-of-flight secondary ion
mass spectrometry (ToF-SIMS). Principal component analysis (PCA),
performed on the ToF-SIMS results, enables to separate the samples
and shows that the proteins display different distributions of amino
acids at the surface depending on the conditioning thiol layer. Our
results revealed that the adsorption mode of the protein is influenced
by the thiol end groups, and specific orientations of the protein
on the surface are proposed for the different substrates
Design of Mixed PEO/PAA Brushes with Switchable Properties Toward Protein Adsorption
Adsorption of proteins at interfaces is an ubiquitous
phenomenon
of prime importance. Layers of polyÂ(ethylene oxide) (PEO) are widely
used to repel proteins. Conversely, proteins were shown to adsorb
deeply into brushes of polyÂ(acrylic acid) (PAA), and their subsequent
partial release could be triggered by a change of pH and/or ionic
strength (I). Mixed brushes of these polymers are thus promising candidates
to tune protein adsorption onto new smart surfaces. In this work,
the synthesis of such mixed brushes was performed based on a âgrafting
toâ approach, the two polymers being either grafted sequentially
or simultaneously. Detailed characterization of the obtained brushes
using static water contact angle measurements, X-ray photoelectron
spectroscopy, electrochemical impedance spectroscopy, and polarizationâmodulation
reflectionâabsorption infrared spectroscopy is presented. While
sequential grafting of the two polymers for different reactions times
did not give rise to a broad range of composition of mixed brushes,
simultaneous grafting of the polymers from solutions with different
compositions allows for the synthesis of a range of mixed brushes
(mass fraction of PEO in the mixed brushes from 0.35 to 0.65). A key
example is then chosen to illustrate the switchable behavior of a
selected mixed PEO/PAA brush toward albumin adsorption. The adsorption
behavior was monitored with a quartz crystal microbalance. The mixed
brush could adsorb high amounts of albumin, but 86% of the adsorbed
protein could then be desorbed upon pH and I change. The obtained
properties are thus a combination of the ones of PEO and PAA, and
a highly switchable behavior is observed toward protein adsorption