2 research outputs found
Resonantly Enhanced Nonlinear Optical Probes of Oxidized Multiwalled Carbon Nanotubes at Supported Lipid Bilayers
With
production of carbon nanotubes surpassing billions of tons
per annum, concern about their potential interactions with biological
systems is growing. Herein, we utilize second harmonic generation
spectroscopy, sum frequency generation spectroscopy, and quartz crystal
microbalance with dissipation monitoring to probe the interactions
between oxidized multiwalled carbon nanotubes (O-MWCNTs) and supported
lipid bilayers composed of phospholipids with phosphatidylcholine
head groups as the dominant component. We quantify O-MWCNT attachment
to supported lipid bilayers under biogeochemically relevant conditions
and discern that the interactions occur without disrupting the structural
integrity of the lipid bilayers for the systems probed. The extent
of O-MWCNT sorption was far below a monolayer even at 100 mM NaCl
and was independent of the chemical composition of the supported lipid
bilayer
Direct Probes of 4 nm Diameter Gold Nanoparticles Interacting with Supported Lipid Bilayers
This work presents molecular-level
investigations of how well-characterized
silica-supported phospholipid bilayers formed from either pure DOPC
or a 9:1 mixture of DOPC:DOTAP interact with positively and negatively
charged 4 nm gold metal nanoparticles at pH 7.4 and NaCl concentrations
ranging from 0.001 to 0.1 M. Second harmonic generation (SHG) charge
screening measurements indicate the supported bilayers carry a negative
interfacial potential. Resonantly enhanced SHG measurements probing
electronic transitions within the gold core of the nanoparticles show
the particles interact irreversibly with the supported bilayers at
a range of concentrations. At 0.1 M NaCl, surface coverages for the
particles functionalized with the negatively charged ligand mercaptopropionic
acid (MPA) or wrapped in the cationic polyelectrolyte polyÂ(allylamine)
hydrochloride (PAH) are estimated from a joint analysis of QCM-D,
XPS, AFM, and ToF-SIMS to be roughly 1 × 10<sup>7</sup> and 1
× 10<sup>11</sup> particles cm<sup>–2</sup>, respectively.
Results from complementary SHG charge screening experiments point
to the possibility that the surface coverage of the MPA-coated particles
is more limited by interparticle Coulomb repulsion due to the charges
within their hydrodynamic volumes than with the PAH-wrapped particles.
Yet, SHG adsorption isotherms indicate that the interaction strength
per particle is independent of ionic strength and particle coating,
highlighting the importance of multivalent interactions. <sup>1</sup>H NMR spectra of the lipids within vesicles suspended in solution
show little change upon interaction with either particle type but
indicate loosening of the gold-bound PAH polymer wrapping upon attachment
to the vesicles. The thermodynamic, spectroscopic, and electrostatic
data presented here may serve to benchmark experimental and computational
studies of nanoparticle attachment processes at the nano–bio
interface