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Biomedical subjects

L A Lyon

Publications and source records attributed to L A Lyon.

5 recordsLinked to original sources
PubMed2001

Temperature-jump investigations of the kinetics of hydrogel nanoparticle volume phase transitions.

The dynamics of the deswelling and swelling processes in thermoresponsive poly-N-isopropylacrylamide (pNIPAm) hydrogel nanoparticles have been studied by using time-resolved transmittance measurements, in combination with a nanosecond laser-induced temperature-jump (T-jump) technique. A decrease in the solution transmittance associated with deswelling of the particles has been observed as the solution temperature traverses the volume phase transition temperature of the particles. Upon inducing the T-jump, the deswelling transition only occurs in a small percentage (<10%) of the particle volume, which was found to be a thin periphery layer of the particles. The particle deswelling occurs on the microsecond time scale, and as shown previously, the collapse time can be tuned via adding small amounts of hydrophobic component to the particle shell. In contrast, the reswelling of the particles was thermodynamically controlled by bath equilibration, and only small differences in particle reswelling kinetics were found due to sluggish heat dissipation (millisecond time scale) from the sample cell.

Acrylic Resins↗
PubMed2001

Interfacial nonradiative energy transfer in responsive core-shell hydrogel nanoparticles.

Fluorescently labeled core-shell latex particles composed mainly of the thermoresponsive polymer poly-N-isopropylacrylamide (p-NIPAm) have been synthesized such that an energy transfer donor (phenanthrene) and an energy transfer acceptor (anthracene) are covalently localized in the core and shell, respectively. When the thermally induced particle deswelling is interrogated by photon correlation spectroscopy (PCS), a continuous (non-first order) phase transition is observed. Conversely, when the nonradiative energy transfer (NRET) efficiency is used to probe the collapse of these same particles, the phase transition event is observed to occur over a much smaller temperature range and approaches first-order (discontinuous) behavior. Furthermore, core-shell particles with differing shell thicknesses display identical phase transition temperatures when PCS is used to monitor the transition, while NRET measurements show a clear increase in collapse temperature as the shell thickness is increased. These apparently contradictory results are discussed in terms of a radial phase coexistence that exists in the microgel particles, which arises from a similarly radial inhomogeneity in the cross-linker concentration. The prospects for the NRET technique as a molecular-scale probe of nanostructured microgels are also discussed.

Biocompatible Materials↗
PubMed2001

Tunable swelling kinetics in core--shell hydrogel nanoparticles.

Thermoresponsive, core--shell poly-N-isopropylacrylamide (p-NIPAm) nanoparticles (microgels) have been synthesized by seed and feed precipitation polymerization, and the influence of chemical differentiation between the core and shell polymers on the phase transition kinetics and thermodynamics has been examined. The results suggest that the core--shell architecture is a powerful one for the design of colloidal "smart gels" with tunable properties. To examine these materials, differential scanning calorimetry (DSC), (1)H NMR, and temperature-programmed photon correlation spectroscopy (TP-PCS) have been employed. These measurements show that the addition of small concentrations of a hydrophobic monomer (butyl methacrylate, BMA) into the particle shell produces large decreases in the rate of thermo-induced particle collapse. Conversely, these low levels of hydrophobic modification do not perturb the thermodynamics of the particle phase transition. When these results are examined in light of previous studies of macroscopic hydrogels, they suggest that the formation of a thin, stable skin layer at the particle exterior during the early stages of particle collapse is the rate limiting factor in particle deswelling. Finally, the hydrophobicity (BMA content) of the shell determines the magnitude of the hydrogel collapse rate, while the thickness of the BMA containing region does not impact the observed kinetics. Together, these results suggest that control over the kinetics of microgel deswelling events can be accomplished simply by modification of the particle periphery, and therefore do not require homogeneous modification of the entire polymer structure.

Journal Article↗
PubMed1998

Colloidal Au-enhanced surface plasmon resonance immunosensing.

Surface plasmon resonance (SPR) biosensing using colloidal Au enhancement is reported. Immobilization of approximately 11-nm-diameter colloidal Au to an evaporated Au film results in a large shift in plasmon angle, a broadened plasmon resonance, and an increase in minimum reflectance. The incorporation of colloidal Au into SPR biosensing results in increased SPR sensitivity to protein-protein interactions when a Au film-immobilized antibody and an antigen-colloidal Au conjugate comprise the binding pair. A highly specific particle-enhanced analogue of a sandwich immunoassay is also demonstrated by complexing the Au particle to a secondary antibody. A tremendous signal amplification is observed, as addition of the antibody-Au colloid conjugate results in a 25-fold larger signal than that due to addition of a free antibody solution that is 6 orders of magnitude more concentrated. Picomolar detection of human immunoglobulin G has been realized using particle enhancement, with the theoretical limits for the technique being much lower. Finally, a quasi-linear relationship between particle coverage and plasmon angle shift is presented, thereby providing for a direct correlation between plasmon shift and solution antigen concentration. Together, these results represent significant advances in the generality and sensitivity of SPR as it is applied to biosensing.

Colloids↗