4 research outputs found
Nanoparticle–Protein Interactions: A Thermodynamic and Kinetic Study of the Adsorption of Bovine Serum Albumin to Gold Nanoparticle Surfaces
Investigating the adsorption process
of proteins on nanoparticle
surfaces is essential to understand how to control the biological
interactions of functionalized nanoparticles. In this work, a library
of spherical and rod-shaped gold nanoparticles (GNPs) was used to
evaluate the process of protein adsorption to their surfaces. The
binding of a model protein (bovine serum albumin, BSA) to GNPs as
a function of particle shape, size, and surface charge was investigated.
Two independent comparative analytical methods were used to evaluate
the adsorption process: steady-state fluorescence quenching titration
and affinity capillary electrophoresis (ACE). Although under favorable
electrostatic conditions kinetic analysis showed a faster adsorption
of BSA to the surface of cationic GNPs, equilibrium binding constant
determinations indicated that BSA has a comparable binding affinity
to all of the GNPs tested, regardless of surface charge. BSA was even
found to adsorb strongly to GNPs with a pegylated/neutral surface.
However, these fluorescence titrations suffer from significant interference
from the strong light absorption of the GNPs. The BSA–GNP equilibrium
binding constants, as determined by the ACE method, were 10<sup>5</sup> times lower than values determined using spectroscopic titrations.
While both analytical methods could be suitable to determine the binding
constants for protein adsorption to NP surfaces, both methods have
limitations that complicate the determination of protein–GNP
binding constants. The optical properties of GNPs interfere with <i>K</i><sub>a</sub> determinations by static fluorescence quenching
analysis. ACE, in contrast, suffers from material compatibility issues,
as positively charged GNPs adhere to the walls of the capillary during
analysis. Researchers seeking to determine equilibrium binding constants
for protein–GNP interactions should therefore utilize as many
orthogonal techniques as possible to study a protein–GNP system
Colloidal Stability of Citrate and Mercaptoacetic Acid Capped Gold Nanoparticles upon Lyophilization: Effect of Capping Ligand Attachment and Type of Cryoprotectants
For
various applications of gold nanotechnology, long-term nanoparticle
stability in solution is a major challenge. Lyophilization (freeze–drying)
is a widely used process to convert labile protein and various colloidal
systems into powder for improved long-term stability. However, the
lyophilization process itself may induce various stresses resulting
in nanoparticle aggregation. Despite a plethora of studies evaluating
lyophilization of proteins, liposomes, and polymeric nanoparticles,
little is known about the stability of gold nanoparticles (GNPs) upon
lyophilization. Herein, the effects of lyophilization and freeze–thaw
cycles on the stability of two types of GNPs: Citrate-capped GNPs
(stabilized via weakly physisorbed citrate ions, Cit-GNPs) and mercaptoacetic
acid-capped GNPs (stabilized via strongly chemisorbed mercaptoacetic
acid, MAA-GNPs) are investigated. Both types of GNPs have similar
core size and effective surface charge as evident from transmission
electron microscopy and zeta potential measurements, respectively.
Plasmon absorption of GNPs and its dependence on nanoparticle aggregation
was employed to follow stability of GNPs in combination with dynamic
light scattering analysis. Plasmon peak broadening index (PPBI) is
proposed herein for the first time to quantify GNPs aggregation using
nonlinear Gaussian fitting of GNPs UV–vis spectra. Our results
indicate that Cit-GNPs aggregate irreversibly upon freeze–thaw
cycles and lyophilization. In contrast, MAA-GNPs exhibits remarkable
stability under the same conditions. Cit-GNPs exhibit no significant
aggregation in the presence of cryoprotectants (molecules that are
typically used to protect labile ingredients during lyophilization)
upon freeze–thaw cycles and lyophilization. The effectiveness
of the cyroprotectants evaluated was on the order of trehalose or
sucrose > sorbitol > mannitol. The ability of cryoprotectants
to prevent
GNPs aggregation was dependent on their chemical structure and their
ability to interact with the GNPs as assessed with zeta potential
analysis
Colloidal Stability of Citrate and Mercaptoacetic Acid Capped Gold Nanoparticles upon Lyophilization: Effect of Capping Ligand Attachment and Type of Cryoprotectants
For
various applications of gold nanotechnology, long-term nanoparticle
stability in solution is a major challenge. Lyophilization (freeze–drying)
is a widely used process to convert labile protein and various colloidal
systems into powder for improved long-term stability. However, the
lyophilization process itself may induce various stresses resulting
in nanoparticle aggregation. Despite a plethora of studies evaluating
lyophilization of proteins, liposomes, and polymeric nanoparticles,
little is known about the stability of gold nanoparticles (GNPs) upon
lyophilization. Herein, the effects of lyophilization and freeze–thaw
cycles on the stability of two types of GNPs: Citrate-capped GNPs
(stabilized via weakly physisorbed citrate ions, Cit-GNPs) and mercaptoacetic
acid-capped GNPs (stabilized via strongly chemisorbed mercaptoacetic
acid, MAA-GNPs) are investigated. Both types of GNPs have similar
core size and effective surface charge as evident from transmission
electron microscopy and zeta potential measurements, respectively.
Plasmon absorption of GNPs and its dependence on nanoparticle aggregation
was employed to follow stability of GNPs in combination with dynamic
light scattering analysis. Plasmon peak broadening index (PPBI) is
proposed herein for the first time to quantify GNPs aggregation using
nonlinear Gaussian fitting of GNPs UV–vis spectra. Our results
indicate that Cit-GNPs aggregate irreversibly upon freeze–thaw
cycles and lyophilization. In contrast, MAA-GNPs exhibits remarkable
stability under the same conditions. Cit-GNPs exhibit no significant
aggregation in the presence of cryoprotectants (molecules that are
typically used to protect labile ingredients during lyophilization)
upon freeze–thaw cycles and lyophilization. The effectiveness
of the cyroprotectants evaluated was on the order of trehalose or
sucrose > sorbitol > mannitol. The ability of cryoprotectants
to prevent
GNPs aggregation was dependent on their chemical structure and their
ability to interact with the GNPs as assessed with zeta potential
analysis
Selected Standard Protocols for the Synthesis, Phase Transfer, and Characterization of Inorganic Colloidal Nanoparticles
Synthesis,
characterization, and applications of colloidal nanoparticles
have been a prominent topic of current research interests within the
last two decades. Available reports in the literature that describe
the synthesis of colloidal nanoparticles are abundant with various
degrees of reproducibility and simplicity. Moreover, different methods
for the characterization of colloidal nanoparticle’s basic
properties are employed, resulting in conflicting results in many
cases. Herein, we describe “in detail” selected standard
protocols for the synthesis, purification, and characterization of
various types of colloidal inorganic nanoparticles including gold
nanoparticles, silver nanoparticles, iron oxide nanoparticles, and
quantum dots. This report consists of five main parts: The first and
the second parts are dedicated to describing the synthesis of various
types of hydrophobic and hydrophilic nanoparticles in organic solvents
and in aqueous solutions, respectively. The third part describes surface
modification of nanoparticles with a focus on ligand exchange reactions,
to allow phase transfer of nanoparticles from aqueous to organic solvents
and vice versa. The fourth and the fifth parts describe various general
purification and characterization techniques used to purify and characterize
nanoparticles, respectively. Collectively, this contribution does
not aim to cover all available protocols in the literature to prepare
inorganic nanoparticles but rather provides detailed synthetic procedures
for important inorganic nanocrystals with a full description of their
purification and characterization process