Shape dependent protein induced
stabilization of gold nanoparticles: from protein corona perspective
Anastasiia Tukova, Yihan NieϮ, Mohammad Tavakkoli
YarakiϮ, Ngoc Thanh Tran, Jiaqiu Wang, Alison Rodger,
Yuantong Gu, Yuling Wang*
Anastasiia Tukova
School of Natural Sciences, Faculty of Science and Engineering,
Macquarie University, Sydney, NSW 2109, Australia
Yihan Nie
School of Mechanical, Medical and Process Engineering, Queensland
University of Technology (QUT), Brisbane, QLD 4001, Australia
Dr. Mohammad Tavakkoli Yaraki
School of Natural Sciences, Faculty of Science and Engineering,
Macquarie University, Sydney, NSW 2109, Australia
Ngoc Thanh Tran
School of Natural Sciences, Faculty of Science and Engineering,
Macquarie University, Sydney, NSW 2109, Australia
Dr. Jiaqiu Wang
School of Mechanical, Medical and Process Engineering, Queensland
University of Technology (QUT), Brisbane, QLD 4001, Australia
Centre for Biomedical Technologies, Queensland University of Technology
(QUT), Brisbane, QLD 4001, Australia
Prof. Alison Rodger
School of Natural Sciences, Faculty of Science and Engineering,
Macquarie University, Sydney, NSW 2109, Australia
Prof. Yuantong Gu
School of Mechanical, Medical and Process Engineering, Queensland
University of Technology (QUT), Brisbane, QLD 4001, Australia
Centre for Materials Science, Queensland University of Technology (QUT),
Brisbane, Queensland 4001, Australia
Prof. Yuling Wang
School of Natural Sciences, Faculty of Science and Engineering,
Macquarie University, Sydney, NSW 2109, Australia
E-mail:
yuling.wang@mq.edu.au
* Corresponding author
Ϯ These authors made equal contributions
Keywords: anisotropic gold nanoparticles, protein corona, stability,
SERS, molecular dynamics simulation
Gold nanoparticles (GNPs) are promising materials for many
bioapplications. However, upon contacting with biological media, GNPs
undergo changes. The interaction with proteins results in the so-called
protein corona (PC) around GNPs, leading to the new bioidentity and
optical properties. Understanding the mechanisms of PC formation and its
functions can help us to utilise its benefits and avoid its drawbacks.
To date, most of the previous works aimed to understand the mechanisms
governing PC formation and focused on the spherical nanoparticles
although non-spherical nanoparticles are designed for a wide range of
applications in biosensing. In this work, we investigated the
differences in PC formation on spherical and anisotropic GNPs (nanostars
in particular) from the joint experimental (extinction spectroscopy,
zeta potential and surface enhanced Raman scattering [SERS]) and
computational methods (the finite element method and molecular dynamics
[MD] simulations). We discovered that protein does not fully cover
the surface of anisotropic nanoparticles, leaving SERS hot-spots at the
tips and high curvature edges ”available” for analyte binding (no SERS
signal after pre-incubation with protein) while providing
protein-induced stabilization (indicated by extinction spectroscopy) of
the GNPs by providing a protein layer around the particle’s core. The
findings are confirmed from our MD simulations, the adsorption energy
significantly decreases with the increased radius of curvature, so that
tips (adsorption energy: 2762.334 kJ/mol) would be the least
preferential binding site compared to core (adsorption energy: 11819.263
kJ/mol). These observations will help the development of new
nanostructures with improved sensing and targeting ability.
Introduction
Gold nanoparticle (GNPs) possesses unique optoelectronic properties,
which originate from their localized surface plasmon resonance
(LSPR).[1–3] LSPR is a collective oscillation of
conduction electrons caused by interaction with an electromagnetic wave
(light) of specific (resonant) wavelength.[3,4]The optoelectronic properties of GNPs can be fine-tuned through
colloidal chemistry, via engineering nanostructures’ size and
shape.[5,6] For instance, anisotropic
nanoparticles such as gold nanostars and nanorods have strong extinction
coefficient in the near-infrared region where light shows deeper tissue
penetration whereas spherical GNPs have distinct bright colour, that is
due to light extinction in the visible region and sensitivity to change
of their size.[7,8] As such, GNPs have the
potential for extensive medical applications in diagnosis and treatment.
In pre-clinical settings, the use of GNPs includes point-of-care
diagnostics[9,10] (lateral flow assays such as
pregnancy tests and rapid COVID-19 tests), in vivo
imaging[11,12] (photoacoustic and computerised
tomography), and therapeutics[13–15](photothermal therapy, radiotherapy, catalytic therapy, and drug
delivery). Although GNPs treatment designs and applications are rapidly
developing with some having reached clinical
trials,[16–18] none has yet been approved for
clinical use primarily because it is hard to predict the changes that
nanoparticles undergo and how they behave in complex biological systems.
Upon exposure to biological media (e.g. plasma or serum), GNPs interact
with large amounts of biomolecules which form layers around the
nanoparticles. The main component of the layer is protein and it is
referred to as the protein corona (PC).[19,20] The
PC characteristically consists of two layers: the “hard corona” – a
layer of tightly bound proteins attached through covalent bonds,
hydrophobic and electrostatic interactions; and the “soft corona” – a
layer of loosely bound proteins outside the “hard corona” that are
attached via weak electrostatic forces. The “soft corona” can easily
be removed and thus exists in a dynamic state of constantly exchanging
proteins, depending on the environment. Contrary to this, the “hard
corona” tends to remain unchanged. Even after several
centrifugation-resuspension cycles, tightly bound proteins remain on the
surface of nanoparticles.[19,20] The PC formation
on GNPs induces high variations in their optical properties, targeting
and sensing abilities, as well as their bio-recognition by cells (caused
by aggregation, morphology changes and surface
fouling).[21,22] Some of the effects of a PC can
also be beneficial to GNPs applications.[23,24]Exposure of naked GNPs to high ionic strength liquids (biological fluids
like blood and urine; buffers, such as phosphate buffered saline
[PBS] or isotonic saline solutions) results in their aggregation due
to the ion-nanoparticle interactions and loss of electrostatic
repulsion.[25,26] PC formation, however, prevents
GNPs aggregation, preserving nanoparticles stability in high ionic
strength liquids thus reducing cytotoxicity, create immunological
stealthiness, increasing blood-circulation time, and preserving optical
properties.[25]
To date, we have not fully explored the mechanisms underlying the
formation of the PC on GNPs, and most of the GNP-protein interaction
studies that have been carried out have been on spherical
particles.[25,27,28] Whilst spherical particles
are often easiest to work with, it has been previously demonstrated that
GNPs with different shapes and surface roughness interact with proteins
differently from spherical nanoparticles.[29,30]For example, in our previous study, we have demonstrated that
ascorbate-capped gold nanostars reduce protein absorption resulting in
enhanced sensing ability in protein-contained
media.[31] Further, non-spherical GNPs have been
developed for a wide range of sensing applications. In order to use them
with biological samples, we need to understand how anisotropic particles
interact with proteins. With the increased demand for new nanostructures
with enhanced optical properties, it is important to account for shape
effects when considering biomedical applications. In this work, we
revisit GNP-protein interaction with different shapes of gold
nanoparticles (spherical, ellipsoidal and star-shaped) and discuss
possible differences in protein-induced stabilization of spherical and
anisotropic nanoparticles. We utilize computational methods including
Finite Element Method (FEM) and molecular dynamics (MD) simulations to
support our experimental observations. Our goal is to understand
GNP-protein interactions and the PC mechanisms of GNPs stabilization
with non-spherical particles to help create nanostructures that optimise
the benefits and mitigate the flaws of PC formation.
2. Results and Discussion
2.1 GNPs synthesis and characterization
For this study, we prepared citrate-capped spherical and elongated gold
nanoparticles of 50 and 70 nm diameter respectively (AuNP50 and AuNP70,Figure 1 A and B ) and ascorbate-capped gold nanostars (AuNS) of
tip to tip diameter about 80 nm (Figure 1 C ). The synthesis
methods are described in the Supporting Information (Table S1) .
AuNP50 and AuNP70 have distinctive LSPR bands at 531 and 551 nm
respectively. AuNS, with sharp tips, have a distinct LSPR peak in the
NIR region at 751 nm and a shoulder in the same wavelength region as the
spherical nanoparticles, which is attributed to the extinction (sum of
all light that is not transmitted through a sample, absorbed and
scattered) mode of the AuNS core (Figure 1 D ). As synthesized
AuNP50, AuNP70 and AuNS were monodispersed due to protective capping
agents (citrate for AuNP and ascorbate for AuNS), that preserve
electrostatic repulsion between the particles (Figure 1 E ).