10 research outputs found
Nuclear magnetic resonance studies of complex materials systems: from amplification to anisotropy
This dissertation explores complex materials systems, with a special focus on developing nuclear resonance spectroscopy (NMR) techniques to decipher chemical environments at the molecular level. Chapter 1 describes the design and synthesis of a two-state materials system based on an autocatalytic, positive feedback loop that amplifies a rare input into a massive output. Chapters 2 - 4 probe nanoparticle systems with shape or functional anisotropy. Chapter 2 details new approaches to add functionality to shape-anisotropic particles. Chapter 3 establishes NMR spectroscopy as a powerful tool for interpreting the ligand shell morphology, spatial arrangement, dynamics, and distinct chemical environments that are trademarks of shape- and functionally-anisotropic particles. Chapter 4 exploits the heterogeneous reactivity of shape-anisotropic particles to fabricate sophisticated, supramolecular building blocks that can form dynamic assemblies controlled by their association constants. Chapter 5 builds on the robust NMR techniques in the preceding chapters to analyze complex nano-bio interactions that are otherwise difficult to probe
Biological Responses to Engineered Nanomaterials: Needs for the Next Decade
[Image: see text] The interaction of nanomaterials with biomolecules, cells, and organisms is an enormously vital area of current research, with applications in nanoenabled diagnostics, imaging agents, therapeutics, and contaminant removal technologies. Yet the potential for adverse biological and environmental impacts of nanomaterial exposure is considerable and needs to be addressed to ensure sustainable development of nanomaterials. In this Outlook four research needs for the next decade are outlined: (i) measurement of the chemical nature of nanomaterials in dynamic, complex aqueous environments; (ii) real-time measurements of nanomaterial–biological interactions with chemical specificity; (iii) delineation of molecular modes of action for nanomaterial effects on living systems as functions of nanomaterial properties; and (iv) an integrated systems approach that includes computation and simulation across orders of magnitude in time and space
Quantification of Free Polyelectrolytes Present in Colloidal Suspension, Revealing a Source of Toxic Responses for Polyelectrolyte-Wrapped Gold Nanoparticles
Polyelectrolyte
(PE) wrapping of colloidal nanoparticles (NPs)
is a standard method to control NP surface chemistry and charge. Because
excess polyelectrolytes are usually employed in the surface modification
process, it is critical to evaluate different purification strategies
to obtain a clean final product and thus avoid ambiguities in the
source of effects on biological systems. In this work, 4 nm diameter
gold nanoparticles (AuNPs) were wrapped with 15 kDa polyÂ(allylamine
hydrochloride) (PAH), and three purification strategies were applied:
(a) diafiltration or either (b) one round or (c) two rounds of centrifugation.
The bacterial toxicity of each of these three PAH-AuNP samples was
evaluated for the bacterium <i>Shewanella oneidensis</i> MR-1 and is quantitatively correlated with the amount of unbound
PAH molecules in the AuNP suspensions, as judged by X-ray photoelectron
spectroscopy, nuclear magnetic resonance experiments and quantification
using fluorescent assay. Dialysis experiments show that, for a 15
kDa polyelectrolyte, a 50 kDa dialysis membrane is not sufficient
to remove all PAH polymers. Together, these data showcase the importance
of choosing a proper postsynthesis purification method for polyelectrolyte-wrapped
NPs and reveal that apparent toxicity results may be due to unintended
free wrapping agents such as polyelectrolytes
On Electronic and Charge Interference in Second Harmonic Generation Responses from Gold Metal Nanoparticles at Supported Lipid Bilayers
Second
harmonic generation (SHG) is useful for studying the properties
of interfaces, including the surfaces of nanoparticles and the interaction
of nanoparticles with biologically relevant surfaces. Gold nanoparticles
at the biological membrane represent a particularly interesting system
to be probed by SHG spectroscopy given the rich electronic structure
of gold nanoparticles and the charged nature of the nano-bio interface.
Here we describe the interplay between the resonant and nonresonant
components of the second harmonic response as 4 and 14 nm spherical
gold nanoparticles (AuNPs) wrapped in the cationic polyelectrolyte
polyÂ(allylamine hydrochloride) (PAH) adsorb to negatively charged
supported lipid bilayers. In contrast to the SHG response of 4 nm
PAH-AuNPs, that we have shown previously to be dominated by resonance
enhancement, the SHG response from the adsorption of the 14 nm PAH-AuNPs,
with similar hydrodynamic diameters, to a 9:1 DOPC:DOTAP bilayer is
dominated by the nonresonant, interfacial, potential-dependent component
of the signal. We hypothesize that the difference in the SHG response
is attributable to the differences in the number of PAH molecules
associated with the particles and, therefore, differences in the number
of positively charged ammonium groups associated with the 4 vs the
14 nm particles. For 14 nm PAH-AuNPs with larger hydrodynamic diameters,
we determined two regimes in the adsorption behavior, one where the
resonance enhancement from the gold core of the nanoparticle dominates
the signal and a second where the nonresonant, interfacial, potential-dependent
term dominates the signal. The results presented in this study provide
insight into the interplay between resonant and nonresonant components
of the second harmonic signal from the adsorption of charged AuNPs
and are valuable for future studies with other functionalized particles
and lipid systems by SHG
Lipid Corona Formation from Nanoparticle Interactions with Bilayers and Membrane-Specific Biological Outcomes
While mixing nanoparticles with certain
biological molecules can result in coronas that afford some control over how engineered
nanomaterials interact with living systems, corona formation mechanisms remain
enigmatic. Here, we report spontaneous lipid
corona formation, i.e. without active mixing, upon attachment to stationary lipid
bilayer model membranes and bacterial cell envelopes, and present ribosome-specific
outcomes for multi-cellular organisms. Experiments show that polycation-wrapped
particles disrupt the tails of zwitterionic lipids, increase bilayer fluidity, and
leave the membrane with reduced ζ-potentials. Computer simulations show contact
ion pairing between the lipid headgroups and the polycations’ ammonium groups leads
to the formation of stable, albeit fragmented, lipid bilayer coronas, while microscopy
shows fragmented bilayers around nanoparticles after interacting with Shewanella oneidensis. Our mechanistic insight
can be used to improve control over nano-bio interactions and to help understand
why some nanomaterial/ligand combinations are detrimental to organisms, like Daphnia magna, while others are not. </a
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 Ă— 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
Lipid Corona Formation from Nanoparticle Interactions with Bilayers and Membrane-Specific Biological Outcomes
<a></a><a>While mixing nanoparticles with certain
biological molecules can result in coronas that afford some control over how engineered
nanomaterials interact with living systems, corona formation mechanisms remain
enigmatic. Here, we report spontaneous lipid
corona formation, i.e. without active mixing, upon attachment to stationary lipid
bilayer model membranes and bacterial cell envelopes, and present ribosome-specific
outcomes for multi-cellular organisms. Experiments show that polycation-wrapped
particles disrupt the tails of zwitterionic lipids, increase bilayer fluidity, and
leave the membrane with reduced ζ-potentials. Computer simulations show contact
ion pairing between the lipid headgroups and the polycations’ ammonium groups leads
to the formation of stable, albeit fragmented, lipid bilayer coronas, while microscopy
shows fragmented bilayers around nanoparticles after interacting with <i>Shewanella oneidensis</i>. Our mechanistic insight
can be used to improve control over nano-bio interactions and to help understand
why some nanomaterial/ligand combinations are detrimental to organisms, like <i>Daphnia magna</i>, while others are not. </a