8 research outputs found
Active Control of SPR by Thermoresponsive Hydrogels for Biosensor Applications
The use of thermoresponsive polyÂ(<i>N</i>-isopropylacrylamide)-based
hydrogel (pNIPAAm) for rapid tuning of surface plasmon resonance (SPR)
is reported. This approach is implemented by using an SPR layer architecture
with an embedded indium tin oxide microheater and pNIPAAm film on
its top. It takes advantage of rapid thermally induced swelling and
collapse of pNIPAAm that is accompanied by large refractive index
changes and leads to high thermo-optical coefficient of d<i>n</i>/d<i>T</i> = 2 Ă 10<sup>â2</sup> RIU/K. We
show that this material is excellently suited for efficient control
of refractive index-sensitive SPR and that it can serve simultaneously
as a 3D binding matrix in biosensor applications (if modified with
biomolecular recognition elements for a specific capture of target
analyte). We demonstrate that this approach enables modulating of
the output signal in surface plasmon-enhanced fluorescence spectroscopy
biosensors and holds potential for simple time-multiplexing of sensing
channels for parallelized readout of fluorescence assays
Temperature-Controlled Diffusion in PNIPAM-Modified Silica Inverse Opals
We report a new strategy for the
preparation of well-defined and
mechanically stable porous nanostructures with tunable porosity. Silica
inverse opals, which are known as a model system for a porous periodic
nanostructure, were grafted with brushes of the thermoresponsive polyÂ(<i>N</i>-isopropylacrylamide) grown via atom transfer radical polymerization.
By tuning the temperature, the swelling state of the brush layer is
reversibly altered, and with this we were able to control the overall
porosity of the system and, thus, the mobility of small penetrants.
Fluorescence correlation spectroscopy, a method combining single molecule
sensitivity with small probing volume (<1 ÎŒm<sup>3</sup>),
was used to directly monitor and quantify in situ the changes in the
penetrantsâ mobility
Simultaneous Measurement of Mechanical and Surface Properties in Thermoresponsive, Anchored Hydrogel Films
Hydrogel films have been used extensively in the preparation
of
biosensors and biomedical devices. The characteristics of the aqueous
interface of the polymer layer are significant for the biosensor or
device function; likewise, the changing mechanical properties of thermoresponsive
polymers are an important feature that affects the polymer behavior.
Atomic force microscopy was used here to characterize both the surface
and the mechanical properties of polymeric hydrogel films prepared
from a thermoresponsive terpolymer of <i>N</i>-isopropylacrylamide
and acrylic acid with benzophenonemethacrylate as a photoreactive
cross-linker comonomer. The forceâdistance curves thus obtained
were analyzed to assess both the surface forces and the mechanical
response that were associated with the hydrogel. These properties
were investigated as a function of temperature, in water and in Tris
buffer, for different degrees of polymer cross-linking. For samples
in water, the distance over which the surface forces were effective
was found to remain constant as the temperature was increased from
26 to 42 °C, even though the mechanical response indicated that
the samples had been heated past the lower critical solution temperature,
or LCST. The bulk of the polymer becomes less soluble above the LCST,
although this does not seem to affect the surface properties. This
may be due to the segregation of the acrylic acid-rich polymer segments
near the gel surface, which is in agreement with reports for related
systems
Enhanced Differentiation of Human Preosteoblasts on Electrospun Blend Fiber Mats of Polydioxanone and Anionic Sulfated Polysaccharides
The
viability and differentiation of SaOS-2 preosteoblasts on fiber
mats of blends comprising of the biodegradable polyÂ(ester-ether) polydioxanone
(PDX) and the sulfate-containing anionic polysaccharides kappa-carrageenan
(KCG) and fucoidan (FUC) were investigated for a range of different
blend compositions. The detailed analysis of the blend nanofiber properties
revealed a different degree of miscibility of PDX and the polysaccharide
leading to a different enrichment at the surface of the blend nanofibers,
which were observed to be stable in phosphate buffer solution (PBS)
for up to 5 weeks. The fibrous mats of PDX/FUC led to the highest
osteogenic differentiation with very good cell viability. The electrospun
blend fibers also supported human-induced pluripotent stem (iPS) cells
and iPS cell-derived embryoid bodies with high cell viability, which
underlines the potential of these novel blend fiber systems for optimized
performance in bone tissue engineering applications
Tunable Plasmonic Nanohole Arrays Actuated by a Thermoresponsive Hydrogel Cushion
New
plasmonic structure with actively tunable optical characteristics
based on thermoresponsive hydrogel is reported. It consists of a thin,
template-stripped Au film with arrays of nanoholes that is tethered
to a transparent support by a cross-linked polyÂ(<i>N</i>-isopropylÂacrylamide) (pNIPAAm)-based polymer network. Upon
a contact of the porous Au surface with an aqueous environment, a
rapid flow of water through the pores enables swelling and collapsing
of the underlying pNIPAAm network. The swelling and collapsing could
be triggered by small temperature changes around the lower critical
solution temperature (LCST) of the hydrogel. The process is reversible,
and it is associated with strong refractive index changes of Î<i>n</i> ⌠0.1, which characteristically alters the spectrum
of surface plasmon modes supported by the porous Au film. This approach
can offer new attractive means for optical biosensors with flow-through
architecture and actively tunable plasmonic transmission optical filters
Semifluorinated Alkanes at the AirâWater Interface: Tailoring Structure and Rheology at the Molecular Scale
Semifluorinated alkanes form monolayers
with interesting properties
at the airâwater interface due to their pronounced amphi-solvophobic
nature and the stiffness of the fluorocarbons. In the present work,
using a combination of structural and dynamic probes, we investigated
how small molecular changes can be used to control the properties
of such an interface, in particular its organization, rheology, and
reversibility during compressionâexpansion cycles. Starting
from a reference system perfluorÂ(dodecyl)Âdodecane, we first retained
the linear structure but changed the linkage groups between the alkyl
chains and the fluorocarbons, by introducing either a phenyl group
or two oxygens. Next, the molecular structure was changed from linear
to branched, with four side chains (two fluorocarbons and two hydrocarbons)
connected to extended aromatic cores. Neutron reflectivity at the
airâwater interface and scanning force microscopy on deposited
films show how the changes in the molecular structure affect molecular
arrangement relative to the interface. Rheological and compressionâexpansion
measurements demonstrate the significant consequences of these changes
in molecular structure and interactions on the interfacial properties.
Remarkably, even with these simple molecules, a wide range of surface
rheological behaviors can be engineered, from viscous over viscoelastic
to brittle solids, for very similar values of the surface pressure
Frequency Response of Polymer Films Made from a Precursor Colloidal Monolayer on a Nanomechanical Cantilever
Nanomechanical cantilevers (NMC) were used for the characterization
of the film formation process and the mechanical properties of colloidal
monolayers made from polystyrene (PS). Closely packed hexagonal monolayers
of colloids with diameters ranging from 400 to 800 nm were prepared
at the airâwater interface and then transferred in a controlled
way on the surface of NMC. The film formation process upon annealing
of the monolayer was investigated by measuring the resonance frequency
of the NMC (â12 kHz). Upon heating of non-cross-linked PS colloids,
we could identify two transition temperatures. The first transition
resulted from the merging of polymer colloids into a film. This transition
temperature at 147 ± 3 °C as measured at â12 kHz
remained constant for subsequent heating cycles. We attributed this
transition temperature to the glass transition temperature <i>T</i><sub>g</sub> of PS which was confirmed by dynamic mechanical
thermal analysis (DMTA) and using the time temperature superposition
principle. The second transition temperature (175 ± 3 °C)
was associated with the end of the film formation process and was
measured only for the first heating cycle. Furthermore, the transition
of the colloidal monolayer into a homogeneous film preserved the mass
loading on the NMC which allowed determination of the Youngâs
modulus of PS (â3 GPa) elegantly