3 research outputs found
Surface PEGylation of Silver Nanoparticles: Kinetics of Simultaneous Surface Dissolution and Molecular Desorption
A quantitative study of the stability
of silver nanoparticles (AgNPs)
conjugated with thiolated polyethylene glycol (SH-PEG) was conducted
using gas-phase ion-mobility and mass analyses. The extents of aggregation
and surface dissolution of AgNPs, as well as the amount of SH-PEG
adsorption and desorption, were able to be characterized simultaneously
for the kinetic study. The results show that the SH-PEG with a molecular
mass of 6 kg/mol (SH-PEG6K) was able to adsorb to the surface of AgNP
to form PEG6K-HS-AgNP conjugates, with the maximum surface adsorbate
density of ∼0.10 nm<sup>–2</sup>. The equilibrium binding
constant for SH-PEG6K on AgNPs was calculated as ∼(4.4 ±
0.9) × 10<sup>5</sup> L/mol, suggesting a strong affinity due
to thiol bonding to the AgNP surface. The formation of SH-PEG6K corona
prevented PEG6K-HS-AgNP conjugates from aggregation under the acidic
environment (pH 1.5), but dissolution of core AgNPs occurred following
a first-order reaction. The rate constant of Ag dissolution from PEG6K-HS-AgNP
was independent of the starting surface packing density of SH-PEG6K
on AgNP (σ<sub>0</sub>), indicating that the interactions of
H<sup>+</sup> with core AgNP were not interfered by the presence of
SH-PEG6K corona. The surface packing density of SH-PEG6K decreased
simultaneously following a first-order reaction, and the desorption
rate constant of SH-PEG6K from the conjugates was proportional to
σ<sub>0</sub>. Our work presents the first quantitative study
to illustrate the complex mechanism that involves simultaneous aggregation
and dissolution of core AgNPs in combination with adsorption and desorption
of SH-PEG. This work also provides a prototype method of coupled experimental
scheme to quantify the change of particle mass versus the corresponding
surface density of functional molecular species on nanoparticles
Quantifying Nanosheet Graphene Oxide Using Electrospray-Differential Mobility Analysis
We
report a high-resolution, traceable method to quantify number
concentrations and dimensional properties of nanosheet graphene oxide
(N-GO) colloids using electrospray-differential mobility analysis
(ES-DMA). Transmission electron microscopy (TEM) was employed orthogonally
to provide complementary data and imagery of N-GOs. Results show that
the equivalent mobility sizes, size distributions, and number concentrations
of N-GOs were able to be successfully measured by ES-DMA. Colloidal
stability and filtration efficiency of N-GOs were shown to be effectively
characterized based on the change of size distributions and number
concentrations. Through the use of an analytical model, the DMA data
were able to be converted into lateral size distributions, showing
the average lateral size of N-GOs was ∼32 nm with an estimated
thickness ∼0.8 nm. This prototype study demonstrates the proof
of concept of using ES-DMA to quantitatively characterize N-GOs and
provides traceability for applications involving the formulation of
N-GOs
Protein–Silver Nanoparticle Interactions to Colloidal Stability in Acidic Environments
We report a kinetic study of Ag nanoparticles
(AgNPs) under acidic
environments (i.e., pH 2.3 to pH ≈7) and systematically investigate
the impact of protein interactions [i.e., bovine serum albumin (BSA)
as representative] to the colloidal stability of AgNPs. Electrospray-differential
mobility analysis (ES-DMA) was used to characterize the particle size
distributions and the number concentrations of AgNPs. Transmission
electron microscopy was employed orthogonally to provide visualization
of AgNPs. For unconjugated AgNPs, the extent of aggregation, or the
average particle size, was shown to be increased significantly with
an increase of acidity, where a partial coalescence was found between
the primary particles of unconjugated AgNP clusters. Aggregation rate
constant, <i>k</i><sub>D</sub>, was also shown to be proportional
to acidity, following a correlation of logÂ(<i>k</i><sub>D</sub>) = −1.627Â(pH)–9.3715. Using ES-DMA, we observe
BSA had a strong binding affinity (equilibrium binding constant, ≈
1.1 × 10<sup>6</sup> L/mol) to the surface of AgNPs, with an
estimated maximum molecular surface density of ≈0.012 nm<sup>–2</sup>. BSA-functionalized AgNPs exhibited highly-improved
colloidal stability compared to the unconjugated AgNPs under acidic
environments, where both the acid-induced interfacial dissolution
and the particle aggregation became negligible. Results confirm a
complex mechanism of colloidal stability of AgNPs: the aggregation
process was shown to be dominant, and the formation of BSA corona
on AgNPs suppressed both particle aggregation and interfacial dissolution
of AgNP samples under acidic environments