3 research outputs found
Natural Organic Matter Concentration Impacts the Interaction of Functionalized Diamond Nanoparticles with Model and Actual Bacterial Membranes
Changes to nanoparticle surface charge,
colloidal stability, and
hydrodynamic properties induced by interaction with natural organic
matter (NOM) warrant consideration in assessing the potential for
these materials to adversely impact organisms in the environment.
Here, we show that acquisition of a coating, or “corona”,
of NOM alters the hydrodynamic and electrokinetic properties of diamond
nanoparticles (DNPs) functionalized with the polycation poly(allylamine
HCl) in a manner that depends on the NOM-to-DNP concentration ratio.
The NOM-induced changes to DNP properties alter subsequent interactions
with model biological membranes and the Gram-negative bacterium <i>Shewanella oneidensis</i> MR-1. Suwannee River NOM induces changes
to DNP hydrodynamic diameter and apparent ζ-potential in a concentration-dependent
manner. At low NOM-to-DNP ratios, DNPs aggregate to a limited extent
but retain a positive ζ-potential apparently due to nonuniform
adsorption of NOM molecules leading to attractive electrostatic interactions
between oppositely charged regions on adjacent DNP surfaces. Diamond
nanoparticles at low NOM-to-DNP ratios attach to model membranes to
a larger extent than in the absence of NOM (including those incorporating
lipopolysaccharide, a major bacterial outer membrane component) and
induce a comparable degree of membrane damage and toxicity to <i>S. oneidensis</i>. At higher NOM-to-DNP ratios, DNP charge is
reversed, and DNP aggregates remain stable in suspension. This charge
reversal eliminates DNP attachment to model membranes containing the
highest LPS contents studied due to electrostatic repulsion and abolishes
membrane damage to <i>S. oneidensis</i>. Our results demonstrate
that the effects of NOM coronas on nanoparticle properties and interactions
with biological surfaces can depend on the relative amounts of NOM
and nanoparticles
Growth-Based Bacterial Viability Assay for Interference-Free and High-Throughput Toxicity Screening of Nanomaterials
Current high-throughput
approaches evaluating toxicity of chemical
agents toward bacteria typically rely on optical assays, such as luminescence
and absorbance, to probe the viability of the bacteria. However, when
applied to toxicity induced by nanomaterials, scattering and absorbance
from the nanomaterials act as interferences that complicate quantitative
analysis. Herein, we describe a bacterial viability assay that is
free of optical interference from nanomaterials and can be performed
in a high-throughput format on 96-well plates. In this assay, bacteria
were exposed to various materials and then diluted by a large factor
into fresh growth medium. The large dilution ensured minimal optical
interference from the nanomaterial when reading optical density, and
the residue left from the exposure mixture after dilution was confirmed
not to impact the bacterial growth profile. The fractions of viable
cells after exposure were allowed to grow in fresh medium to generate
measurable growth curves. Bacterial viability was then quantitatively
correlated to the delay of bacterial growth compared to a reference
regarded as 100% viable cells; data analysis was inspired by that
in quantitative polymerase chain reactions, where the delay in the
amplification curve is correlated to the starting amount of the template
nucleic acid. Fast and robust data analysis was achieved by developing
computer algorithms carried out using R. This method was tested on
four bacterial strains, including both Gram-negative and Gram-positive
bacteria, showing great potential for application to all culturable
bacterial strains. With the increasing diversity of engineered nanomaterials
being considered for large-scale use, this high-throughput screening
method will facilitate rapid screening of nanomaterial toxicity and
thus inform the risk assessment of nanoparticles in a timely fashion
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