Gold nanoparticles in nanomedicine: Preparations, imaging, diagnostics, therapies and toxicity
This critical review provides an overall survey of the basic concepts and up-to-date literature results concerning the very promising use of gold nanoparticles (AuNPs) for medicinal applications. It includes AuNP synthesis, assembly and conjugation with biological and biocompatible ligands, plasmon-based labeling and imaging, optical and electrochemical sensing, diagnostics, therapy (drug vectorization and DNA/gene delivery) for various diseases, in particular cancer (also Alzheimer, HIV, hepatitis, tuberculosis, arthritis, diabetes) and the essential in vitro and in vivo toxicity. It will interest the medicine, chemistry, spectroscopy, biochemistry, biophysics and nanoscience communities (211 references).
This article was published as part of the
2009 Themed issue dedicated to
Professor Jean-Pierre Sauvage
Guest editor Professor Philip Gale
Please take a look at the issue 6 table of contents to access
the other reviews.
Gold nanoparticles in nanomedicine: preparations, imaging, diagnostics,
therapies and toxicityw
Elodie Boisselier and Didier Astruc*
Received 12th January 2009
First published as an Advance Article on the web 21st April 2009
This critical review provides an overall survey of the basic concepts and up-to-date literature
results concerning the very promising use of gold nanoparticles (AuNPs) for medicinal
applications. It includes AuNP synthesis, assembly and conjugation with biological and
biocompatible ligands, plasmon-based labeling and imaging, optical and electrochemical sensing,
diagnostics, therapy (drug vectorization and DNA/gene delivery) for various diseases, in
particular cancer (also Alzheimer, HIV, hepatitis, tuberculosis, arthritis, diabetes) and the
essential in vitro and in vivo toxicity. It will interest the medicine, chemistry, spectroscopy,
biochemistry, biophysics and nanoscience communities (211 references).
Medicinal problems are a quest of all civilizations. Since
nanoscience is one of the major areas of present scientiﬁc
progress, it should shortly result in essential advancement for
the beneﬁt of human health. The biomedical applications of
metal nanoparticles started in the 1970s with the use of
nanobioconjugates after the discovery of immunogold labeling
by Faulk and Taylor.
Traditional imaging techniques remain
crucial in diagnostic, and AuNPs proves to be superior to
classic chemicals. Subsequently, nanostructures have been
introduced in a broad range of biological applications.
Supramolecular chemistry principles have also catalyzed
major advances in this area including both imaging and
sensors using biological host–guest recognition of
Presently, research is now also emphasizing
along with physical methods such as
electron microscopy and spectroscopy.
bringing a key contribution, a crucial property being the
plasmon absorption and scattering of AuNPs. It is involved
particularly in both the photodiagnostics and photothermal
therapy of cancers and other main diseases.
The goal of drug
vectorization, promised to a bright future, is to diminish or
suppress side eﬀects due to toxicity, improve therapeutic
eﬃciency and biodistribution, and overcome the problems of
solubility, stability and pharmacokinetics of drugs.
In this critical review, we will concentrate our attention on
AuNPs, also including non-spherical AuNPs, in biochemistry
and nanomedicine with emphasis on the above areas. This
broad ﬁeld presently involves a considerably increasing
number of publications, thus we will focus on major ideas
and most recent studies.
2. Gold nanoparticles (AuNPs) and
Gold was discovered in Bulgaria ﬁve thousand years ago, and
the ancient colloidal gold must have ﬁrst appeared in antiquity
in China and Egypt for therapeutic and decorative purposes.
A famous example is the Lycurgus cup, from the 4th century,
visible at the British Museum in London. Gold colloids have
Institut des Sciences Mole
culaires, UMR CNRS No. 5255,
Bordeaux I, 33405, Talence Cedex, France.
w Dedicated to our distinguished colleague Dr Jean-Pierre Sauvage at
the occasion of his 65th birthday.
Elodie Boisselier obtained
her bachelor of science degree
in biochemistry from the
Bordeaux II. She
is presently studying for a
PhD under the guidance of
Professor Didier Astruc at
Bordeaux I in
the area of Au nanoparticles.
Her interests are in the syn-
thesis and biomedical applica-
tions of Au nanoparticles.
Didier Astruc is Professor of
Chemistry at the Universite
Bordeaux I and Member of
the Institut Universitaire de
France. He did his PhD in
Rennes with R. Dabard and
his postdoctoral work at
MIT with R. R. Schrock. His
present interests are in
dendrimers and nanoparticles
and their applications in
catalysis, molecular materials
science, and nanomedicine.
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The Royal Society of Chemistry 2009 Chem. Soc. Rev., 2009, 38, 1759–1782 | 1759
CRITICAL REVIEW www.rsc.org/csr | Chemical Societ y Reviews
been recommended for curing various diseases over the
centuries and till recently, although the mechanisms of action
are still poorly understood. In 1857, Faraday reported the ﬁrst
scientiﬁc article on AuNPs, attributing the red color to the
colloidal nature of AuNPs,
and in 1908 Mie rationalized
their visible absorption using Maxwell’s electromagnetic
AuNPs are available in the range from 1 to more
than 120 nm, and their plasmon band visible absorption can
be observed above 3 nm (vide infra). They disclose consider-
able applications in optics, catalysis, materials science and
nanotechnology also including biology and nanomedicine.
There are a large number of ways to synthesize AuNPs most
of the time starting from commercial HAu
reduction of Au
in water was introduced by
Turkevitch et al. in 1951,
a method that is still used
nowadays to subsequently replace the citrate ligand of these
AuNPs by appropriate ligands of biological interest.
modiﬁcations of the Turkevitch method have allowed better
size distribution and size control within the 9–120 nm range.
Although AuNPs can be stabilized by a large variety of
stabilizers (ligands, surfactants, polymers, dendrimers, bio-
the most robust AuNPs were disclosed by
Giersig and Mulvaney to be stabilized by thiolates using the
strong Au–S bond between the soft acid Au and the soft
Along this line, by far the most popular
synthetic method using such sulfur coordination for AuNP
stabilization is the Shiﬀrin–Brust biphasic synthesis using
, a thiol, tetraoctylammonium bromide and NaBH
in water–toluene yielding thiolate-AuNPs.
thiolates can also be introduced using this method or upon
subsequent bimolecular substitution of a thiolate ligand by
such a functional thiol:
AuNP + mR
SH - (RS)
AuNP + mRSH
Oligonucleotides, peptides and PEGs are easily attached to
AuNPs in this way. Since the solubility of these AuNPs is
controlled by the solubilizing properties of the terminal group
of the thiolate ligands, AuNPs can be transferred from
an aqueous phase to an organic phase or vice versa by
appropriate ligand exchange. Water-soluble AuNPs typically
contain terminal carboxylate groups at their periphery.
The carboxy group is used to attach the amino groups of bio-
molecules using 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide-
HCl abbreviated EDC (bioconjugate chemistry).
Another useful protocol consists in using the famous
‘‘click’’ reaction linking a terminal alkyne and an azide.
The excellent eﬃciency of this method has recently been
A way to form AuNPs made of a precise
number of metal atoms consists in using dendrimers
containing a pre-organized number of internal ligands, which
leads to dendrimer-encapsulated AuNPs (Fig. 1).
robust AuNPs, stable in the pH 1–14 range and under NaCl
concentrations up to 5 M, were synthesized using PEG
sorbitan fatty acid esters functionalized with lipoic acid. These
scaﬀolds show both strong coordination through the chelating
thiols and van der Waals interactions.
Very interestingly, not only spherical AuNPs are
synthesized, but also the shapes of the nanoparticles can be
varied using appropriate techniques. In particular, Au nano-
rods (AuNRs) with controlled aspect ratio (i.e. the ratio of the
length along the long axis to the short axis) in the range of
2–6 have been synthesized using the micelle-templated seed
and feed technique developed by the groups of Murphy
(Fig. 2) and El Sayed,
and the Halas’ group has developed
the synthesis of Au nanoshells (AuNSs) composed of a silica
core (100–200 nm in diameter) surrounded by a thin Au layer
Citrate-capped AuNPs and AuNSs as well as
cetyl trimethylammonium bromide (CTAB)-capped AuNRs
are not stable in the presence of a buﬀer solution, because salt
ions have an aggregating eﬀect, but these AuNPs are readily
stabilized by thiol-functionalized PEG ligands.
group has successfully engineered the surface chemistry of
AuNRs. Thus, long AuNRs were obtained (500 nm long,
20 nm wide). The cationic surfactant used in the synthesis
remains on the sides of the AuNR in the form of a bilayer
resulting in a cationic charge to the AuNR, leaving the AuNR
ends available for subsequent reaction. Bifunctional thiols
such as biotin-disulﬁde can be bound to the Au(111) crystal
face on the AuNR ends, whereas the CTAB bilayer is
maintained on the AuNR sides. Addition of streptavidin
further leads to end-to-end linkage of the AuNRs. Similarly,
Fig. 1 (a) AuNPs stabilized by several G
dendrimers; (b) G
-dendrimer-encapsulated AuNPs. Reprinted with permission of the Royal Society of
Chemistry (ref. 24, Astruc’s group).
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The Royal Society of Chemistry 2009
mercaptopropionic acid preferentially binds the AuNR ends
leading to end-to-end bonded AuNRs linked by hydrogen
bonds. Upon using Ag(
Guyot-Sionnest also grew AuNRs,
I) selectively slows down the growth of these
AuNRs at faces that are less energetically favorable with
‘‘under-potential’’ Ag(0) deposition.
In summary, the aﬃnity of the surface of AuNPs having
various sizes and shapes for thiols, disulﬁdes, dithio-
carbamates and amines allows facile bioconjugation with a
variety of biomolecules. In particular, AuNPs conjugation
with thiolated PEG masks them from the intravascular
immune system and multifunctionalization for drug delivery
Since surfactants including CTAB have been
found to be cytotoxic, other types of stabilization have been
searched. For instance non-toxic liquid crystals have been used
especially if the NaBH
reduction that leaves boride contami-
nation can be avoided. Thus, liquid-chlorin photosensitizers
based on purpurin-18 from green algae Spirulina maxima
and choline hydroxide were recently used to synthesize AuNPs
in the absence of surfactant and other reducing agent.
3. The surface plasmon resonance (SPR) of
According to the Mie theory,
an electromagnetic frequency
induces a resonant coherent oscillation of the free electrons,
called the surface plasmon resonance (SPR), at the surface of a
spherical NP if it is much smaller than the light wavelength.
This absorption lies in the visible region for Au, Ag and Cu.
For metal nanoparticles, the localized surface plasmon
resonance results in an enhanced electromagnetic ﬁeld at the
metal nanoparticle surface. The plasmon resonance of
is observed down to 3 nm diameter, below which
the AuNP can no longer be considered as a piece of metal with
a conduction band but becomes a molecule depicted by
molecular orbitals (then the term cluster should be used rather
than nanoparticle). As a result, an enhanced electromagnetic
ﬁeld appears at the AuNP surface above this size allowing
surface-enhanced optical properties revealed using spectro-
scopic techniques. Thus, the extinction coeﬃcients of the
SPR bands are extremely high, up to 10
is several orders of magnitude larger than those or all the
organic dyes. AuNPs give rise to both absorption and
scattering whose proportions depend on the AuNP size.
AuNPs with a diameter smaller than 20 nm essentially show
absorption, but size increase to 80 nm also increases the ratio
of scattering to absorption. A high scattering cross section
is indeed required for biological imaging based on light
For spherical AuNPs of 5 nm diameter, the surface plasmon
band is located at 520 nm in ethanol, but it is very sensitive to
the composition, size, shape, inter-particle distance and
environment (dielectric properties) of the AuNPs. It is the
high sensitivity to these factors that makes the basis of their
use for biological labeling, detection, diagnostic and sensing.
For instance, 5-nm AuNPs are orange-red, but they turn
blue-purple upon aggregation (network formation) to larger
AuNPs. Likewise, a change of refractive index of the solvent
shifts the plasmon band. From the Mie theory, it follows that
the frequency of the plasmon band varies from spherical to
non-spherical nanoparticles of various shapes (rods, prisms,
triangles, tetrapods, dogbones, cubes, shells). For instance,
with AuNRs, two plasmon bands are observed, one corres-
ponding to oscillations along the length of the AuNR
(longitudinal plasmon band) and the other along the width
of the AuNR (transverse plasmon band). The positions of
these two bands vary with the AuNR aspect ratio. Thus
AuNRs exhibit plasmon bands with maxima around 500 and
Fig. 2 The optical properties of gold and silver nanoparticles change drastically with nanoparticle shape. The photograph shows aqueous
solutions of 4 nm gold nanospheres (vial 0) and progressively higher aspect ratio gold nanorods (1–5). The optical spectra and transmission
electron micrographs for the particles in vials 1–5 are also shown. Scale bars in micrographs are all 100 nm. Reprinted with permission of the Royal
Society of Chemistry (ref. 26, Murphy’s group).
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1600 nm. Since the ratio inﬂuences the position of the plasmon
band absorption, the syntheses of AuNRs can be adjusted
with suitable ratio so that they correspond to commercial
lasers (e.g. 360 nm, 785 nm and 1064 nm). Moreover, the shift
of the plasmon band to the near-IR region for AuNRs allows
obtaining a penetration into living tissues that is much deeper
than that of visible light and exciting less background
ﬂuorescence. In addition the multi-component plasmon
absorption provides richer information than the single visible
band of spherical AuNPs. Similarly, the plasmon band of
AuNSs is shifted to the near-IR region and can be tuned by
adjusting the ratio of the thickness of the AuNS to the
diameter of the silica pore. The Halas group has shown that
the smaller this ratio, the more redshifted is the plasmon
absorption of the AuNS.
4. Labeling and imaging
4.1 General: the techniques
Beside the most routine technique, transmission electron
microscopy (TEM) that uses the high atomic weight of Au,
several imaging techniques involve the surface plasmon band.
Large AuNPs (420 nm) can be imaged using an optical
microscope in phase contrast or diﬀerential interference
contrast mode. Detection with an optical microscope only
involves scattered light in dark-ﬁeld microcopy. Small AuNPs
only absorb light, provoking heating of the environment that
can be detected by photothermal imaging that record local
variations of the refractive index by DIC microscopy or by
photoacoustic imaging using heat-induced liquid expansion.
Other techniques are (i) ﬂuorescence microcopy that allows
detection at the single particle level, as the above plasmon-
based techniques, (ii) photothermal coherence tomography
(OCT) that is an optical analogue to ultrasound with relatively
good penetration depth (1–2 mm) and resolution (1–10 mm),
(iii) multiphoton SPR microscopy (when illuminated by laser
light in resonance with their plasmon frequency, these AuNPs
generate an enhanced multiphoton signal measured in a laser
(iv) X-ray scattering, involving better
contrast AuNP agents than organic molecules with high
signal-to-noise ratio with X-ray computer tomograpy, and
(v) gamma radiation using neutron activation.
The traditional application called immunostaining involves
antibody-conjugated AuNPs that bind antigens of ﬁxed,
permeabilized cells thereby providing visualization by contrast
using TEM. On the other hand, diluted AuNPs labeled with
antibodies can label the outer cell surface without ﬁxation and
permeabilization, so that the inter-particle distance is larger
than the optical resolution limit, which leads to single-particle
imaging of cell movement. Receptor molecules that are
bound to the membrane are observed in this way by time-
resolved imaging within the cell membrane using the above
Magnetic Resonance Imaging (MRI) can
be enhanced with or without gadolinium, and the main
techniques are now discussed below.
In summary, facile bioconjugation and the variety of
traditional and modern techniques including in particular
the spectroscopic ones related to the plasmon resonance make
AuNPs a remarkable up-to-date tool as imaging label and
contrast agent (Fig. 3).
4.2 Enhancement of magnetic resonance imaging
The development of new contrast agents based on AuNPs for
MRI is progressing fast. In addition to Gd chelates, several
novel and highly eﬃcient contrast agents were recently
reported. The sensitivity of magnetic resonance imaging
(MRI) can indeed be improved by using AuNPs as templating
carriers of gadolinium chelates that are currently used for
clinical diagnosis. Thus, the 2-nm-sized AuNPs carry about
150 ligands and exhibit a high relaxativity (r = 586 nM
as compared to 3 nM
for the AuNP-free Gd chelate,
which renders them very attractive as contrast agents for MRI
The strong magnetism of magnetic NPs enhances MRI
signals, and this property has recently been used. Iron oxide
) embedded in AuNP shells appears to be useful for this
purpose, because the iron oxide provides magnetism, whereas
the Au shell allows to use the optical properties of AuNPs.
In another study, Co@Pt-AuNPs with enhanced magnetism
Fig. 3 NIR transmission images of mice prior to PPTT treatments.
Inset shows intensity line-scans of NIR extinction at tumor sites for
control (’), intravenous (m), and direct (K) administration of
pegylated gold nanorods. Control mice were interstitially injected with
15 mL 10 mM PBS alone, while directly administered mice received
interstitial injections of 15 mL pegylated gold nanorods (OD
40, 2 min accumulation), and intravenously administered mice
received 100 mL pegylated gold nanorod (OD
= 120, 24 h
accumulation) injections. Reprinted with permission of Elsevier
(ref. 37, El Sayed’s group).
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The Royal Society of Chemistry 2009
and high stability were used. Binding to this AuNP surface is
ensured using lipoic acid connected to neutravidin that shows
strong interaction with biotin. These Co@Pt-AuNPs serve as
MRI agents to monitor the structural evolution of Aß
protoﬁbrils, responsible for Alzheimer disease, in the early
reversible stages. Magnetic NP-assisted MRI detection could
also potentially be applied as sensitive probes of other
proteins self-assemblies including prions, a-synuclein and
4.3 Surface-enhanced Raman scattering (SERS)
Molecules located on the AuNP surface are submitted to the
large ﬁeld caused by the plasmon resonance of the AuNP up to
a distance of approximately 10 nm at most from the AuNP
surface. Among the diﬀerent spectroscopic techniques that
characterize the electromagnetic ﬁeld resulting from the
plasmon resonance of AuNPs (surface-enhanced ﬂuorescence,
surface-enhanced Rayleigh scattering, surface-enhanced
absorption and surface-enhanced Raman scattering, SERS),
SERS is most attractive, because of the huge enhancement of
the SERS signal, by a factor of ca. 10
, which improves
the detection limit from ensembles of molecules to the
single-molecule level. The Raman eﬀect in molecules that are
not located at a metal nanoparticle surface is normally weak,
because visible light that is not absorbed by this molecule
is only weakly inelastically scattered oﬀ the molecular
vibrations. The selection rule for Raman spectroscopy is the
polarizibility change along the vibration, which usually
provides only a weak Raman-active signal at usual concentra-
tion levels. Considerable enhancement occurs at the AuNP
surface, however, because the intensity of the Raman signals
depends on the fourth power of the local electric ﬁeld that is
very high at the AuNP surface due to the plasmon resonance.
This enhancement also originates, in addition, from electronic
coupling between adsorbed molecules and the AuNP surface
resulting from charge transfer between the AuNP metal
surface and adsorbed molecules. Since the selective enhance-
ment of SERS is correlated with polarization-dependant
resonance bands, ampliﬁed electromagnetic ﬁelds at AuNP
junctions contribute to SERS. Thus, in addition to the
elastically scattered visible light by the AuNPs themselves that
can be imaged using a dark-ﬁeld optical microscope, the
AuNP surface provoke an inelastic SERS eﬀect due to
adsorbed molecules providing a Raman spectrum that leads
to the identiﬁcation of these molecules.
The two main
strategies for SERS detection are (i) direct identiﬁcation of
Raman-active AuNP-adsorbed molecules and (ii) indirect
detection of molecules incorporated into a biolabel. Inter-
ference from competing adsorbates can sometimes inhibit the
Fig. 4 Schematic illustration of the DTDTPA shell grafted onto gold nanoparticles (Au@DTDTPA). Reprinted with permission of Wiley
InterScience (ref. 35, Roux’s group).
Fig. 5 This series of images show how multiplexed assays are carried
out with a suspension array. (A) The suspension array, composed of
encoded microspheres conjugated to capture antibodies, is mixed with
a sample containing diﬀerent cytokines. (B) The cytokines are sand-
wiched between the capture antibodies and the corresponding
biotinylated detector antibodies. (C) Bound detector antibodies are
labeled with ﬂuorescent reporter molecules. (D) A stream of individual
microspheres ﬂows through the sensing points of a cytometer. (E–G)
Images of a single encoded microsphere with bound reporter molecules
as it ﬂows past (E) a green laser that excites the reporters and (G) a red
laser that excites the code. (Courtesy of Luminex Corp.) Reprinted
with permission of Wiley InterScience (ref. 44, Wilson’s group).
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detection of molecules in complex solutions. The plasmon
band can also be tuned from the visible region for spherical
AuNPs to the NIR by changing the size (redshift with larger
size), shape (AuNRs and AuNSs), aggregation (inter-AuNP
distance lower than AuNP size) and medium (increase of the
refractive index). A number of studies have optimized the
SERS of small AuNP-adsorbed molecules with non-spherical
AuNPs, and on the biological side El-Sayed et al. have recently
shown that oral cancer cells can align AuNRs that have
been conjugated with anti-epidermal growth factor receptor
antibodies on the cell surface, leading to a SERS ﬁngerprint
speciﬁc of the cancer cells.
The Halas group has discrimi-
nated between acidic cancer cells and healthy cells by
monitoring changes in the Raman spectrum induced by pH
changes over a suitable range with carboxy groups of a
mercaptobenzoic acid layer on AuNSs that were active in
the NIR region where blood and tissues are less absorbing.
The Wilson group has recently reported the use of this
SERS method as signatures in multiplexed detection, based on
the fact that each spectrum is unique and composed of
multiple bands that are much narrower than those of
ﬂuorescent dyes or quantum dots (Fig. 5).
reviewed this ﬁeld,
and a number of companies have
marketed Raman detectors, such as Oxonica (Oxford, UK),
with biotags that detect up to three respiratory viruses in the
same sample (Fig. 6).
A few SERS applications of AuNPs follow. Mammalian
cells surfaces were imaged using SERS with nitrile-
functionalized AuNPs. SERS hot sites correlate well
with small aggregated AuNPs oriented preferentially in the
direction of incident laser polarization.
probing and imaging of pH in live cells was demonstrated by
SERS using 4-mercaptobenzoic acid-AuNP aggregates
AuNPs conjugated with heterofunctional PEG
ligands allowed facile conjugation of ScFv antibody as a
targeting ligand for SERS detection of small tumors
) at a penetration of 1–2 cm.
SERS imaging has
been used for the targeting and highly sensitive imaging of
speciﬁc cancer markers in live cells using core-shell Au-AgNPs
conjugated with monoclonal antibodies (live HEK293 cells
expressing PLCg1) (Fig. 8).
4.4 Optical biosensors
Parak indicated that, whereas labeling and imaging above use
AuNPs in a passive way, sensing involves an active role of the
The AuNP-distance dependence of the analyte
detection (antigens, nucleic acids, aptamers, enzymatic
reactions) using the plasmon resonance as well as size and
refractive-index dependence have recently been compre-
hensively reviewed by Wilson.
Thus, only some representative
and new examples of plasmon-related sensors are illustrated
below. The dramatic inﬂuence of the inter-AuNP distance on
the plasmon resonance, when this distance is reduced to less
than the AuNP diameter, is indeed the crucial factor in the
sensor applications of AuNPs. Thus, linking AuNPs with a
biological analyte results in color change that makes the basis
of sensing, a principle pioneered by Leuvering,
sensitivity is now improved using hyper-Raleigh scattering
(HRS), a diﬀerential light-scattering spectroscopy (DLSS).
Fig. 6 Architectures used in SERS experiments. (A) 2D substrate with adenine on the surface. (B) Bare particle. (C) Antibody-targeted particle.
(D) Reporter labeled particle. (E) Targeted and labeled particle. (F) Targeted particle with encapsulated Raman label. A Represents the substrate
approach, B and C are examples of the inserted particle approach while D, E, and F can all be thought of as SERS nanotags/Raman spectra of six
diﬀerent Nanoplex biotags. From top to bottom, the label molecules used were 4-[4-hydroxyphenylazo]pyridine, 4,4
dipyridyl, bis(4-pyridyl)ethylene, bis(4-pyridyl)acetylene, 4,4
-dipyridyl. Reprinted with permission of Wiley InterScience (ref. 46, Freeman’s
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Mirkin and co-workers were the ﬁrst to report colorimetric
sensing of nucleic acids. Double-stranded DNA indeed link
AuNPs with an inter-AuNP distance of only 0.34 nm causing a
temperature-reversible red-to-purple color change. Each
AuNP bears several oligonucleotides resulting in the
formation of a network (aggregation) leading to the color
change of the AuNPs to blue-violet, because of the reduced
Removing aliquots for spotting onto a
C18 reverse-phase thin-layer chromatography plate as the
temperature is increased results in a visual record of the color
change that is known as the ‘‘Northwestern spot test’’, the most
well-known example of AuNP-based sensor. The addition of
complementary target oligonucleotide strand by hybridization
can be colorimetrically detected also leading to speciﬁc
melting-temperature test for mismatched DNA.
even single DNA sequence mismatch results in a diﬀerent
disaggregation (melting) temperature provoking a color
Studies of AuNP-DNA interactions have subsequently been
pursued by several groups,
and quantitative detection of
DNA sequences at very low concentration including detection
of genetic mutations is now achievable using such a
The Mirkin group has recently extended this
method from speciﬁc detection of DNA sequences to a
real-time screening assay for endonuclease activity.
The Franco group has developed a non-cross-linking
hybridization method also based on color changes, in which
AuNP aggregation is induced by an increasing salt
concentration. This method was used to detect eukaryotic
gene expression (RNA) without need for retro-transcription
Fig. 7 Probing and imaging pH values in individual live cells using a SERS nanosensor. (a) Photomicrograph of an NIH/3T3 cell after 4.5 h
incubation with the pMBA gold nanosensor. Numerous gold nanoparticles have accumulated in the cell, enabling pH probing in diﬀerent
endosomes over the entire cell based on the SERS signature of pMBA. Lysosomal accumulations can be observed as black spots at the resolution
of the light microscope. (b) pH map of the cell displayed as false color plot of the ratios of the SERS lines at 1423 and 1076 cm
. The values given
in the color scale bar determine the upper end value of each respective color. Scattering signals below a deﬁned signal threshold (i.e., where no
SERS signals exist) appear in dark blue. (c) Typical SERS spectra collected in the endosomal compartments with diﬀerent pH. The spectra were
collected in 1 s each using 830 nm cw excitation (3 mW). Reprinted with permission of the American Chemical Society (ref. 48, Kneipp’s group).
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The Royal Society of Chemistry 2009 Chem. Soc. Rev., 2009, 38, 1759–1782 | 1765
or PCR ampliﬁcation. It was possible to detect mRNA from
0.3 mg of unampliﬁed total RNA.
The detection of proteins
and antibodies (anti-protein A, biotin and streptavidin and
lectin) as well as molecules (adenosine, glucose) and metal ions
(Pb, Hg, Cd, Li) has also been achieved using AuNPs in this
way (Fig. 9).
Although spherical AuNPs work well, non-spherical ones
have also been used, the advantage being that the plasmon
frequency can be ﬁnely adjusted with AuNRs and AuNSs. For
instance, the Halas group has synthesized AuNSs with a
96-nm diameter and a 22-nm shell thickness to carry out
distance-dependent immunoassays in dilute serum,
the Murphy group has used biotin-avidin as a model system
for optical detection of aggregated AuNRs (i.e. biotinylated
AuNR aggregation upon addition of the protein streptavidin).
Other 3-D assemblies of AuNRs and AuN wires using DNA
Transducers have been set up to detect
streptavidin concentration through the speciﬁc recognition
with biotin-conjugated AuNPs. Polyelectrolyte functionaliza-
tion provides a simple way to conjugate AuNPs with charged
molecules such as biotin.
Chilkoti et al. have tracked
scattering changes at 780 nm from a single AuNR to sense
streptavidin in nanomolar concentration, using a dark-ﬁeld
microscope (Fig. 10 and 11).
Willner and co-workers reported the ﬁrst example of AuNP
combination with thiolated aptamers (i.e. DNA-, RNA- or
peptide-based sequences) thereby showing how thrombin
could be detected upon aptamer-conjugated-AuNP linking.
PEG-15-nm-AuNPs covalently bound to F19 monoclonal
antibodies via terminal PEG carboxylate group were used to
label stroma tumor in resected pancreatic adenocarcinoma,
and the tissues were imaged by darkﬁeld microscopy at
Wilson has summarized the methods of detection
that involve separation steps including microsphere assays and
Detection methods based on separation,
must be used to improve sensitivity when naked eye detection
is insuﬃcient. Deposition of Ag onto the AuNPs upon Ag(I)
reduction, called Ag enhancement was pioneered by Mirkin’s
It allows imaging with unaided eye as the spot size
after enhancement reaches 200 nm (a technique improved
upon replacing Ag by Au).
Unampliﬁed DNA and RNA
target sequences can be detected in the presence of genomic
DNA in this way, and CCD cameras and CD players have
been used for recording such biosensing events.
Fig. 8 Fluorescence and SERS images of normal HEK293 cells and PLCc¸ 1-expressing HEK293 cells. (a) QD-labeled ﬂuorescence images of
normal cells: (left) brightﬁeld image, (right) ﬂuorescence image. (b) SERS images of single normal cell: (left) brightﬁeld image, (right) Raman
mapping image of single normal cell based on the 1650 cm
R6G peak. The cell area was scanned with an interval of 1 mm. Intensities are scaled to
the highest value in each area. (c) Overlay image of brightﬁeld and Raman mapping for single normal cell. Colorful spots indicate the laser spots
across the middle of the cell along the y axis. (d) QD-labeled ﬂuorescence images of cancer cells: (left) brightﬁeld image, (right) ﬂuorescence image.
(e) SERS images of single cancer cell: (left) brightﬁeld image, (right) Raman mapping image of single cancer cell based on the 1650 cm
The cell area was scanned with an interval of 1 mm. Intensities are scaled to the highest value in each area. (f) Overlay image of brightﬁeld and
Raman mapping for single cancer cell. Colorful spots indicate the laser spots across the middle of the cell along the y axis. Reprinted with
permission of the American Chemical Society (ref. 50, Choo’s group).
Fig. 9 Chemical structure of the modiﬁed 1,10-phenanthroline ligand
that binds to gold nanoparticles through the thiols, and to lithium ion
through the chelating phenanthroline nitrogens. Two ligands are
required to bind to one lithium ion in a tetrahedral fashion. Reprinted
with permission of the Royal Society of Chemistry (ref. 26, Murphy’s
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AuNP supports are 0.5-m-polystyrene microspheres, but
assays also use planar supports (glass, nitrocellulose, nylon
and thin ﬁlms
). Magnetic microspheres that facilitate
separation of bound AuNPs have also been reported.
separation methods involve lateral ﬂow devices for immuno-
assays, nucleic acid ﬂow devices, ﬂow-through devices, blots
and arrays, silver-enhanced arrays, ‘‘biobarcode’’ (marker)
assays, electrical detection, SERS and ﬁngerprint detection.
Fluorescence of AuNPs includes ﬂuorescence spectrometry,
ﬂuorescence correlation spectroscopy (FCS) and ﬂuorescence
microscopy. Especially, the ﬂuorescence of AuNPs possesses
the excellent behavior of antiphotobleaching under strong
light illumination. Despite low quantum yields, AuNPs exhibit
strong native ﬂuorescence under relatively high excitation
power. The ﬂuorescence of AuNPs could be characterized by
ﬂuorescence imaging and FCS at the single-particle level.
A new ﬂuorescence method for cell imaging involves, after
cells stained with AuNPs are illuminated with strong light, the
ﬂuorescence of AuNPs on cell membrane or inside cells that
can be collected for cell imaging.
Fluorescence Resonance Energy Transfer (FRET) is a
spectroscopic technique whereby the excitation energy of the
donor is transferred to the acceptor via an induced-dipole,
Fig. 10 (a) TEM of gold nanorods used for biodetection experiments and (b) dark-ﬁeld micrograph of gold nanorods immobilized on a glass
substrate. (c) Scattering spectra of a single gold nanorod on a glass substrate (red) and the extinction spectrum of an ensemble of gold nanorods
suspended in water (blue). Scale bar is 100 nm in (a) and 5 mm in (b). Reprinted with permission of the American Chemical Society
(ref. 70, Chilkoti’s group).
Fig. 11 (a and b) Scattering spectra of a single gold nanorod after
sequential incubation in EG3SH/MHA (blue), biotin (red), and 10 nM
streptavidin (black). (c and d) Scattering spectra of a single gold
nanorod in EG3SH/MHA (blue), biotin (red), and 100 nM strepta-
vidin presaturated with free biotin (black). Reprinted with permission
of the American Chemical Society (ref. 70, Chilkoti’s group).
Fig. 12 Fluorophore displacement protein sensor array. (a) Dis-
placement of quenched ﬂuorescent polymer (dark green strips, ﬂuores-
cence oﬀ; light green strips, ﬂuorescence on) by protein analyte
(in blue) with concomitant restoration of ﬂuorescence. The particle
monolayers feature a hydrophobic core for stability, an oligo(ethylene
glycol) layer for biocompatibility, and surface charged residues for
interaction with proteins. (b) Fluorescence pattern generation through
diﬀerential release of ﬂuorescent polymers from gold nanoparticles.
The wells on the microplate contain diﬀerent nanoparticle-polymer
conjugates, and the addition of protein analytes produces a ﬁngerprint
for a given protein. Reprinted with permission of the Nature
Publishing Group (ref. 80, Rotello’s group).
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induced dipole interaction. The eﬃciency of energy transfer E
is given by 1/1[1 + (R/R
] where R is the distance between
the donor and the acceptor and R
is the distance at which
50% of the energy is transferred; thus small distance changes
result in sizeable change in E. With AuNPs, at small distance
(o1 nm), radiative rate enhancement is observed; at 2–3 nm,
energy transfer dominates, and at large distances (450 nm),
ﬂuorescence oscillations take precedence. AuNP-based FRET
monitors DNA hybridization and DNA cleavage by nucleo-
bases. For instance, after hybridization, by varying the DNA
length, the separation distance between AuNP and Cy3 dye
was systematically varied between 3 and 100 nm, and 50%
quenching eﬃciency was observed even at 25 nm separation.
Fluorescent dyes and quantum dots are quenched by close
proximity of AuNPs, even at distances larger than 2 nm.
Quenching eﬀects have even been shown to operate over much
larger distances than the Fo
rster resonance quenching transfer
distance between dyes.
Therefore, increase of ﬂuorescence is
observed upon hybridization to a complementary nucleic acid
sequence, because the ﬂuorescent dye or quantum dot and the
quencher are forced apart. In this way, large molecules such as
proteins can be sensed, and Rotello et al. have applied this
principle using a ﬂuorescent polymer to decode the response
produced by nanomolar concentrations of proteins in
unknown samples based on selective AuNP-protein
aﬃnities (Fig. 12).
For instance, 20-nm AuNPs stabilized
by Cy5.5-Gly-Po-Leu-Gly-Val-Arg-Gly-Cys-(amide) showing
selectivity for a matrix metalloprotease served as ﬂuorescent
imaging probe for in vivo drug screening and protease activity
4.6 Electrochemical biosensors
AuNPs are useful in electrochemical bioassays, in particular
to connect enzymes to electrode surfaces, mediate electro-
chemical reactions as redox catalysts and amplify recognition
signals for biological processes.
Their ﬁrst use as labels for
immunosensors was reported by the group of Degrand and
which was followed by hundred of electrochemical
bioassay articles including excellent reviews.
Fig. 13 (A) NIRF tomographic images of normal and subcutaneous-SCC7-tumor-bearing mice after injection of the AuNP probe with and
without inhibitor (blue: low intensity, red: high intensity). (B) NIRF images of excised AuNP-probe-treated SCC7 tumors with and without MMP-
2 inhibitor. (C) Immunohistology results for SCC7 tumors with MMP-2. H&E = Hematoxylin/eosin stain; lower row: NIRF microscopy of SCC7
tumors containing AuNP probes without and with inhibitor. (D) 2D slices of the image from (A) reconstructed in the z direction (blue: low
concentration, red: high concentration). (E) Quantitative image analysis performed by counting the total number of photons in the tumors as a
function of time. Reprinted with permission of Wiley InterScience (ref. 81, Ahn’s group).
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main research areas are AuNP nanoelectrodes for bioassays
and AuNPs as biomolecular tracers, and in both of them
applications are found in enzymatic biosensing, genosensing
As a representative example, AuNPs are used as wires
connecting electrode surfaces to the redox center of enzymes.
Fixation of the AuNPs onto the electrode surface provides a
microenvironment comparable to that of redox proteins and
more protein freedom for orientation. In this way, the
insulation by the protein shell is reduced, and electron transfer
can occur through the conducting tunnels of the AuNPs
Thus, AuNPs attached to enzymes such as,
typically, glucose oxidase (GO), serve as nanoelectrodes so
that the turnover rate of electrons transferred via AuNPs to
the electrode surface reaches about 5000 which is seven times
higher than the turnover rate of electrons from the active site
of GO to O
As an amperometric and potentiometric
immunosensor example, multilayer ﬁlms of negatively charged
AuNPs/positively charged tris(2,2
assembled on a Pt electrode surface covered with a layer of
plasma-polymerized Naﬁon ﬁlm for hepatitis B surface
For genosensor applications (DNA electrochemical
sensing), AuNPs modiﬁed with thiol-functionalized oligo-
nucleotides were submitted to hybridization of the target
DNA sequence. This type of assay relies on the release of
AuNPs by oxidative metal dissolution and indirect determina-
tion of the HBr solubilized Au(
III) ions by anodic stripping
Subsequently, methods based on the direct
electrochemical detection of the AuNP tag were developed in
order to avoid the high toxicity of the HBr/Br
A signal ampliﬁcation strategy consists in attaching ferrocenyl-
hexanethiol or electrogenerated chemiluminescence (ECL)
indicator to the AuNP label. AuNP-streptavidin conjugate
to which 6-ferrocenylhexanethiol was bound were attached
onto a biotinylated DNA detection probe of a sandwich
DNA complex. A detection limit of 5 10
target DNA was reached.
The use of AuNPs for
‘‘ﬁngerprint’’ detection involves immersion of a substrate in
AuNPs at low pH provoking electrostatic binding to the print
that is enhanced by catalytic deposition of Ag or better, Au.
AuNPs bearing alkylthiolate ligands terminated with redox
proved to be useful for the redox recognition,
sensing and titration of ATP
method based on the shift of redox potential of the redox
system attached to the ATP recognition site (ferrocenylsilyl or
AuNP-centered dendrimers are most
useful for this type of sensing, because the positive dendritic
eﬀect (increase of potential shift as the dendrimer generation
increases) facilitates sensing.
Large dendritic AuNPs adsorb
so strongly on Pt electrodes for sensing using the AuNP-
dendrimer-modiﬁed electrode that the modiﬁed electrodes
are robust enough to be washed for further re-use.
5. Clinical diagnostics
AuNPs have been used as radioactive labels in vivo since the
1950s, and immuno-AuNPs conjugated to antibodies have
been used since the 1980s for biological staining in electron
microscopy. They present several advantages in biodiagnostic
over quantum dots and organic dyes: (i) much reduced or no
toxicity (vide infra), (ii) much better contrast agents for
imaging (compare with organic dyes that suﬀer from rapid
photobleaching), (iii) surface-enhanced and distance- and
refractive index-dependent spectroscopic properties. In their
excellent micro-review article, Baptista et al. distinguish three
approaches for biodiagnostics based on AuNPs: (i) inter-
AuNP distance dependent colorimetric sensing for speciﬁc
DNA hybridization for the detection of speciﬁc nucleic
acid sequences in biological samples (the most developed
approach), (ii) surface-functionalized AuNPs providing highly
selective nanoprobes, and (iii) electrochemical-based methods
for signal enhancement.
The bases of these methods are
detailed in the preceding sections. Here, we are essentially
emphasizing clinical diagnosis applications.
Fig. 14 (a) Schematic representation of the preparation of an immunosensing layer. (b) Schematic view of electrochemical detection of mouse IgG
or prostate speciﬁc antigen. Reprinted with permission of the American Chemical Society (ref. 85, Wang’s group).
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Among the clinical diagnosis methods involving AuNPs
immunoassays, promising applications are found in signal
enhancement of the standard enzyme-linked immunosorbent
assays (ELISAs) such as immunochromatographic test strips
where both the primary and secondary antibodies are
conjugated with the AuNPs.
The detection of the chorionic
gonadotropin hormone reaches 1 pg mL
using this set-up.
Other sensors are based on AuNP-functionalized ﬁber-optic
or AuNP-functionalized Cy5-antibody as
the ﬂuorescence probe which could replace the standard
ELISA assay, because they do not require a secondary
antibody and oﬀer increased sensitivity.
Chemiluminescent analysis of antibodies, such as anti-IgG
to determine IgG content in human plasma, is optimized with
irregular-shaped AuNPs that are more active than spherical
Hirsch et al. have reported a rapid whole-blood
immunoassay using AuNSs capable of detecting sub-
nanogram-per-mililiter quantities of various analytes upon
aggregation of antibody-AuNS conjugates including
successful detection of immunoglobulins in saline serum and
whole blood. The simplicity of this assay also makes it
superior to conventional ELISAs, because it requires less
technical proﬁciency than ELISAs.
The use of AuNPs is very promising in the ﬁeld of immuno-
sensors based on metal-enhanced ﬂuorescence.
examples of the use of electrochemical approaches based on
the derivatization of electrodes with AuNPs, let us mention
the label-free detection of the carcinoembryonic antigen
A sensitivity-enhanced immunosensor based on
the SPR was developed for the detection of by AuNR-
The pathogen Escherichia coli O157:H7
was rapidly detected on a piezoelectric oligonucleotide-
Below, we summarize AuNP
diagnostic for main diseases.
Cancer diagnosis/detection based on the imaging of micro-
anatomical features of diseased tissues uses OCT and RCM
methods (vide supra). Cancer biomarkers and optical contrast
agents provide excellent signal sources from cancer tissues.
The intense scattering of large AuNPs makes them promising
probes for cancer detection based on imaging. Immunotargeting
of antibody-AuNPs label cancer cells by conjugating them
with antigens overexpressed in cancer cells. For instance,
cervical epithelial cancer cells (SiHa cells) that overexpress
the transmembrane glycoprotein, epithelial growth factor
receptor (EGFR), were imaged by immunotargeted AuNPs.
AuNP scattering was strong enough to allow the use of even a
red laser pointer, a resource-poor setting, instead of a scanning
laser to image the cancer cells.
Besides antibodies and some viruses, some biomolecules
such as in particular folate are avidly taken up by cancer cells,
which allows their selective targeting (Fig. 15).
et al. demonstrated the use of dark-ﬁeld microscopy, an
extremely simple and inexpensive technique, for the successful
selective detection of cancerous cells. Thus, 35-nm AuNPs
conjugated with anti-EGFR antibodies immunotargeted to
two malignant epithelial cell lines were selected for optimal
intense surface plasmon scattering using a white-light source
from a conventional microscope resulting in a colored AuNP
image with dark background.
Extension to other optical
imaging techniques such as photo-acoustic tomography,
multiphoton plasmon resonance microscopy, optical
coherence microscopy and third-harmonic microscopy for
cancer imaging is promising.
The nanoprobe method has been used by the Franco group
to detect single nucleotide polymorphisms (SNPs) and muta-
tions due to diseases such as cancer.
Recently, a colori-
metric assay was reported for the direct detection of cancer
cells by using aptamer-conjugated AuNPs. It was shown that
the AuNP-aptamers could be assembled on a cell membrane
surface for spectral changes, providing a direct visualization of
cancer cells. The assay was also demonstrated on two diﬀerent
cell types that had cell-SELEX aptamers selected for them,
indicating possible extension for any cell type. This could
include colorimetric assays for various cancers or other
diseases. The cell-SELEX aptamers have been generated for
leukemia and lymphoma, lung cancer and liver cancer,
suggesting that the assays could work out for the detection
of these diseases.
Purine-9-b-D-ribofuranoside were found
to substantially enhance the anti-proliferative eﬀect against
K-562 leukemia cells, due to enhanced intracellular transport
followed by the subsequent release in lysosomes (Fig. 16).
AuNPs covalently conjugated with PEG and monoclonal
antibody Herceptin, that enables recognition of breast cancer
cells expressing speciﬁc tumor associated antigens, were shown
to be stable and active in vitro in the presence of blood and
in vivo in nude mice model for breast cancer.
Many articles deal with both diagnostic and therapy,
especially those dealing with the SPB-based photothermal
eﬀects, thus the reader is also referred to the other sections
of this review concerning cancer.
Fig. 15 Conceptual diagram of folate receptor-mediated binding,
internalization, endosomal acidiﬁcation, intracellular traﬃcking, and
endosomal escape of F-PEG1500-T:AuNP by folate receptor-positive
cells. Reprinted with permission of the American Chemical Society
(ref. 116, Andres’s group).
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Pioneering work toward an assay of Alzheimer diseases using
AuNPs has been ﬁrstly reported by Van Duyne’s group where
a nanoscale optical biosensor based on LSPR spectroscopy
has been described to monitor the interaction between the
antigen, amyloid derived diﬀusible ligands (ADDLs), and
speciﬁc anti-ADDL antibodies.
The Mirkin traditional
method consisting in AuNP-nanoprobe cross-linking known
for protein detection in attomolar sensitivity was successfully
used for measuring the concentration of amyloid-b-derived
diﬀusible ligands, a potential Alzheimer disease marker
present at extremely low concentration (o1 pmol L
the cerebrospinal ﬂuid of aﬀected individuals.
Multivalent AuNPs were found to inhibit HIV fusion.
Therefore, 2-nm AuNP-mercaptobenzoic acid were conju-
gated to SDC-1721, a derivative of TAK-779, a known
CCR5 antagonist that serves as the main entry co-receptor
for most commonly transmitted strained of HIV-1. In this
way, TAK-779 inhibited HIV-1 replication with an IC
10 nM (Fig. 17).
A highly sensitive screening assay based
on electrochemical impedance spectroscopy (EIS) has been
developed for the detection of HIV-1 protease using a
thiol-terminated ferrocenyl-pepstatin conjugate was therefore
attached to a single-wall carbon nanotube-AuNP modiﬁed
5.5 Hepatitis B
Successfully prepared AuNPs-Hepatitis B virus (HBV) DNA
gene probes could be used to detect HBV DNA directly. The
detection-visualized ﬂuorescence-based method is highly
sensitive, simple, low cost and could potentially apply to
multi-gene detection chips.
A successful application of the AuNP-nanoprobe colorimetric
method to clinical diagnosis reported by Baptista et al. was the
sensitive detection in clinical samples of Mycobacterium
tuberculosis, the human tuberculosis etiologic agent.
A speciﬁc oligonucleotide [5
] derived from the M. tuberculosis RNA polymerase
b-sub-unit gene sequence, suitable for mycobacteria identiﬁca-
tion, was used. At high NaCl concentration, nanoprobe
aggregation in the absence of a complementary DNA sequence
turns the solution purple. In the event of speciﬁc probe
hybridization to a complementary sequence (i.e. DNA from
M. tuberculosis), no nanoprobe aggregation occurs, and the
solution remains red.
Diabetes was characterized as a multifactorial disease using
the AuNP-nanoprobe method mentioned above and involving
the capture of the analyte with a magnetic particle featuring
recognition elements followed by binding of a AuNP with a
second recognition agent and marker DNA strands for cancer
6.1 Photothermal cancer therapy
Conventional treatments of most cancers are surgical removal
that is limited to large, accessible tumors, chemotherapy that
suﬀers from dramatic side eﬀects, and radiotherapy that is also
invasive to healthy tissues along the radiation path. On the
other hand, laser hyperthermia (photothermal therapy) that
uses optical heating for tumor ablation is a mild solution that
Fig. 16 Gold nanoparticles stabilized with 6-mercaptopurine-9-ß-D-
ribofuranoside. (A) Chemical formula of 6-MPR. (B) Schematic of
6-MPR stabilization of AuNPs. Simple geometrical calculations based
on the available surface atoms and/or geometry of the (6-MPR)
moiety indicates that there might be 100–350 molecules of 6-MPR
on the surfaces of the AuNPs. Reprinted with permission of the
American Chemical Society (ref. 122, Kotov’s group).
Fig. 17 TAK-779 and SDC-1721. Reprinted with permission of the
American Chemical Society (ref. 127, Feldheim’s group).
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avoids all these drawbacks. Organic photoabsorbers such as
Indocyanine green and inorganic ones such as iron oxide have
been used for photothermal tumor ablation but suﬀer respec-
tively from small cross section requiring high irradiation
energy and the need of iron oxide in high quantities (up to
10% weight) that is more or less toxic. The advantages of
AuNPs are that they have high absorption cross sections
requiring only minimal irradiation energy and are considered
as non-toxic (vide infra). Irradiation of the SPR of AuNPs is
followed by fast conversion of light into heat (about
Relatively small AuNPs (e.g. 10–30 nm) are
delivered more easily to cancer cells using various methods
(physiological transportation, conjugation with antibodies,
etc.) than larger AuNPs.
After delivery, these AuNPs are
self-assembled into larger clusters of closely located AuNPs
directly within cells, resulting in laser-induced bubble forma-
tion that are more eﬀective for cell killing and SPR shift from
the visible region to the 700–1000 nm NIR region.
AuNPs of various shapes absorb light in a broad spectrum
range from near UV to NIR, but the NIR region is especially
crucial in order to penetrate inside living tissues unlike visible
light. The depth of light penetration can reach a few
centimetres in the ‘‘biological window’’ (650–900 nm), a region
ideal for the SPR absorption of AuNSs, AuNRs and Au
nanocages. Thus, localized photothermal destruction of
SK-BR-3 cancer cells was demonstrated by the Halas group
in vitro and in vivo using thiolated-PEG-passivated AuNSs
(passivation avoids aggregation in saline solution) with a
110 nm-diameter core and a 10 nm-thick shell resulting in a
peak absorbance at 820 nm designed to match the emission
wavelength of the diode laser. In vitro, silver staining revealed
that the protein-adsorbent AuNS surface promoted binding to
the AuNS surface. In vivo, the temperature increase upon
AuNS NIR irradiation was of 37.4 6.6 1C at a depth of
2.5 mm beneath the dermal surface on 5 min exposure, which
is well above the temperature at which irreversible tissue
damage occurs (40 1C) with laser dosage 10 to 25 times less
than those used with Indocyanine green dye. Maximal depth of
treatment was 6 mm, but could reach 1 cm or even more in
In order to explain these very positive
therapy results, it appears that thiolated PEG ligands, that
are biocompatible, mask the AuNPs from the immune system
and inhibit aggregation. These PEG ligands also facilitate
accumulation of the AuNSs at the tumor site due to the highly
permeable vascular network in neoplastic tumors, referred to
as the so-called ‘‘enhanced permeability and retention (EPR)
Indeed, PEGs are currently used as carriers of
anticancer drugs, and the eﬃciency of this means must be
related to this EPR eﬀect. In addition, selectively targeting of
AuNPs to biomarkers on cancer cells appears as a very
promising technique of cancer therapy.
AuNSs conjugated with antibodies to HER2, a protein
overexpressed in breast cancer cells, the Halas group
photodamaged breast cancer cells in vitro using NIR laser
The El-Sayed group used immunotargeted 40-nm AuNPs
with two oral squamous cancer cell lines, HOC and HSC, that
overexpress EGFR proteins. For this purpose, they used the
514-nm excitation of a common laser with the spherical
AuNPs whose plasmon band had its maximum at 530 nm.
These cancerous cells underwent photodamage in vitro within
4 min at laser energies of 19- and 25 W cm
Fig. 18 Fluorescence images of a tumor-bearing mouse after being injected with AuNP-Pc4 conjugates in normal saline (0.9% NaCl, pH 7.2),
(a) 1 min, (b) 30 min, and (c) 120 min after intravenous tail injection. Any bright signal is due to Pc4 ﬂuorescence, without which no ﬂuorescence
signals were detected from the mouse. (To reduce autoﬂuorescence, the animal was fed a special diet for more than 2 weeks before the experiment.)
Unprecedented delivery eﬃciency and accumulation rate of the drug in the tumor are monitored via the ﬂuorescence increase in the tumor area
(white circle). For comparison, a mouse that got only a Pc4 formulation without the AuNP vector injected is shown in panel (d). No circulation of
the drug in the body or into the tumor was detectable 2 h after injection without the AuNP as drug vector. Reprinted with permission of the
American Chemical Society (ref. 149, Burda’s group).
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cells. AuNRs with a strong longitudinal absorption in the NIR
region around 800 nm were used to observe malignant HOC
and HSC cells labeled with the AuNR bioconjugate, upon
AuNR red scattering in dark-ﬁeld optical microscopy. The
over expression of EGFR on the cell cytoplasmic membrane
for various tumors was used for the selective delivery of
anti-EGFR biconjugates in high concentrations to cancer cells
Excitation of AuNRs passivated by
phosphatidylcholine using a pulsed Nd-YAG laser provoked
and excitation of AuNRs conjugated to folate
using a CW Ti:saphire laser was used for hyperthermia of KB
Prospects for AuNRs in diagnostic and therapeutic
applications have been reviewed.
AuNSs were also
eﬃciently used in vivo with a subcutaneous prostate cancer
(PC-3 cells) model whereby histological analysis of the
tumor following direct tumor injection of AuNPs revealed
even distribution throughout the tumor.
gated to dextran aﬀorded both photonic-based imaging and
therapy of macrophage cells in vitro, which should prove
useful for diseases such as arthrosclerosis and in-stent
Hollow dendrite-shaped Au
NPs were used as NIR
photothermal absorbers for destroying A549 lung cancer cells
with laser powers required for cell damage signiﬁcantly
reduced relative to those used for AuNRs (Fig. 18).
110-nm AuNSs with 10-nm shell thickness were used for
prostate cancer ablation (PC-3 cells) using a 810-nm NIR
laser with a 200-nm laser ﬁber and an energy setting of
4 W cm
, and resulted in 98% tumor necrosis.
Phototherapies that do not use the AuNP SPB have also
been reported. Photodynamic therapy using a PEG-5-nm-
AuNP-Si-phthalocyanine conjugate generates singlet oxygen,
very eﬃciently inducing apoptosis or necrosis directly in
tumor-bearing mice as shown by ﬂuorescence images. In this
case, a crucial point is that the Au-PEG vector preferentially
accumulates in tumor sites through the leaky tumor vascula-
ture (‘‘enhanced permeability and retention’’, EPR eﬀect).
6.2 Radiofrequency therapy
Radiofrequency (RF) current, with a frequency between
10 kHz and 900 MHz has been applied for medical purposes
for nearly a century with limited use due to thermal injury, but
has been proposed in the 1990s as eﬀective for destroying liver
tumors. Limitations, however, included the requirement for
invasive needle placement, accuracy of image guidance, tumor
size, and collateral damage to non-tumorous liver parenchyma
and adjacent structures, the occurrence of learning curves and
relatively high local tumor recurrence. Thus a non-invasive
technique has very recently been reported for tumor ablation
using a variable power (0–2 kW) RF signal (13.56 MHz) by
direct injection of citrate-AuNPs into the tumor to focus the
radiowave for selective heating both in vitro and in vivo
(rat exposure at 35 W).
Human cell lines were also exposed
to a 13.56 MHz RF ﬁeld, and the resulting induced heat was
lethal to these cancer cells bearing AuNPs in vitro.
6.3 Angiogenesis therapy
Angiogenesis is the formation of new blood vessels from
existing ones, and ‘‘abnormal’’ angiogenesis was shown to
play an important role in the growth and spread of cancer, due
to the feed of cancer cells by the new blood vessels with oxygen
and nutrients. Mukherjee et al. discovered than AuNPs inhibit
angiogenesis and recently published a review article on this
The authors showed that addition of AuNPs
profoundly inhibited phosphorylation of the proteins
responsible for angiogenesis in a dose-dependent manner,
almost complete inhibition being observed at concentrations
of 335–670 nM. It was suggested that the responsible
inhibition mechanism involves AuNPs direct binding to
heparin-binding growth factors presumably through cysteine
residues of the heparin-binding domain (Fig. 19).
6.4 Rheumatoid arthritis therapy
AuNPs have been used in the treatment of rheumatoid
arthritis for a very long time, and medical treatment dates
Fig. 19 Eﬀect of nanogold on angiogenesis in vivo in the ears of nude mice. Gross appearance of angiogenesis 7 days after injection of nanogold
only (a), Ad-VEGF only (b), nanogold and Ad-VEGF (c). Eﬀect of nanogold on permeability, Ad-VEGF only (d), nanogold and Ad-VEGF (e).
Reprinted with permission of the American Association for Cancer Research (ref. 152, Mukherjee’s group).
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from the 1920s. Recently, it was shown that 13-nm AuNPs
prepared by the citrate reduction method inhibited prolifera-
tion and migration of the protein responsible for angiogenesis.
Angiogenesis plays a key role in the formation and
maintenance of rheumatoid arthritis. Furthermore, animal
testing by intradermal injection of these AuNPs for 7 and
10 days resulted in a signiﬁcant reduction of joint inﬂamma-
tion, and immunohistochemical staining revealed a signiﬁcant
decrease in macrophage inﬁltration into the synovium of rats.
This is important, because rheumatoid arthritis is still
currently essentially incurable. Photoacoustic tomography of
joints aided by an Etanercept-conjugated AuNR contrast
agent was shown to visualize the AuNR-drug conjugate down
to 1 pM in phantoms or 10 pM in biological tissues.
6.5 Anti-bacterial therapy
Strong laser-induced overheating eﬀects accompanied by the
bubble-formation phenomena around clustered AuNPs cause
bacterial damage, and this nanotechnology was used for
selective killing of the Gram-positive Staphylococcus aureus
by targeting bacteria surface using 10-, 20- and 40-nm AuNPs
conjugated with anti-protein A antibodies.
6.6 Drug vectorization
Therapeutic vectors carry drugs, genes and imaging agents
into living cells and tissues.
The drugs vectors should
also be stable in the circulatory system, yet become labile
under appropriate conditions when the targeted organ is
reached. The drug vectors carry the drug by encapsulation
or more or less strong binding (covalent, coordination or
supramolecular bond). The potential vectors include micelles,
liposomes, steroids, folate, peptides, hyaluronic acid, fatty
acids, antigens, polymers, dendrimers, nanotubes, and nano-
AuNPs have recently been considered as excellent
drug-delivery systems due to their biocompatibility, optical
properties and excellent abilities to bind (bioconjugation)
biological ligands, DNA and small interfering RNA (siRNA)
(noncovalent interaction) and drugs through AuNP surface
Speciﬁc applications can be classiﬁed in
targeted drug delivery and mediated gene delivery. Targeted
drug delivery has been achieved by endocytosis through a
transmembrane receptor. For this purpose, AuNPs are con-
jugated to a ligand that speciﬁcally recognizes the receptor.
The protein transferin has been conjugated to AuNPs,
because many tumors cells overexpress transferin receptors,
and uptake of AuNP-transferin by tumor cells has been
characterized by AFM and confocal scanning laser microscopy.
PEG chains were anchored by thiotic acid and folic acid
on opposite ends and conjugated to 10-nm AuNPs that proved
to be stable in the pH 2–12 range and NaCl concentrations up
to 0.5 M and could be taken up by folate-receptor-positive
tumor cells. Cellular uptake was demonstrated by TEM of
KB cells that actively express folate receptors on their
In a rare example of in vivo study, 26-nm
AuNPs conjugated with the tumor-necrosis factor (TNF)
were injected into tumor-bearing mice. They preferentially
accumulated in the tumor and diminished the tumor mass
more eﬀectively than free TNF.
Enhanced eﬃcacy of such
AuNPs with a thiolated paclitaxel was also shown.
A TEM study of 16-nm AuNPs conjugated with human
ﬁbroblast cells shows control of the uptake mechanism either
via delivery of AuNPs by liposomes or by surface modiﬁcation
of the AuNPs with cell-penetrating peptides.
entrapped AuNPs showed enhanced uptake by Chinese
Hamster Ovary cells compared to liposome-free AuNPs
AuNPs were conjugated with transferrin mole-
cules for imaging and therapy of breast cancer cells (Hs578T,
ATCC). The transferrin/transferrin-receptor mediated cellular
uptake of the AuNPs was six times of that in the absence of
this interaction. The cellular uptake was only one fourth of
that by the cancerous cells.
Tumor necrosis factor-a is a
potent cytokine with anticancer eﬃcacy, but it is systemically
toxic, thereby needing selective delivery. Thus, the Paciotti
group reported that PEG-33-nm AuNPs with incorporated
TNF-a payload (several hundred TNF-a per AuNP) maximize
tumor damage and minimize exposure to TNF-a.
delivery is very promising, but common viral vectors raise
cytotoxicity and immune response problems. Thus AuNP-
based DNA-delivery vectors have been developed by Rotello’s
group ﬁrst using cationic ligands, then with amphiphilic
ligands that were more eﬃcient on transfection.
Fig. 20 Cellular uptake and distribution of liposome entrapped gold
nanoparticles in CHO cells. Images were taken after 1, 2, 4 and 6 h
(A to D) incubation with liposome entrapped gold nanoparticles.
Images E and F were taken after 1 and 2 h incubation when plain
gold nanoparticles were used. Reprinted with permission of Elsevier
(ref. 165, Devi’s group).
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The Royal Society of Chemistry 2009
Klibanov’s group also reported the transfection eﬃciency of
AuNP-PEI conjugates into kidney (Cos-7) cells.
et al. showed the use of AuNPs conjugated to negatively-
charged oligodeoxynucleotide for gene therapy,
Rotello’s group showed that intracellular concentrations of
glutathione can trigger the restoration of DNA from cationic
AuNP-NDA conjugate with potential applications in
the creation of transfection vectors and gene-regulation
Rotello et al. also reported photolabile AuNPs
that provide light-regulated control over DNA-AuNP inter-
actions, which is evidenced by a high level of DNA-transcrip-
tion recovery in vitro and signiﬁcant nuclear localization of
DNA in cells.
The techniques that are available to char-
acterize cell uptake by AuNPs carriers and intracellular probes
are essentially luminescent imaging (including barcoding),
AFM and TEM. Multiplexed screening of cellular uptake
has been demonstrated with laser-ionization mass
(Fig. 21) and time-of-ﬂight secondary ion
mass spectrometry (TOF-SIMS).
Adding polyelectrolyte-coated AuNRs to three-dimensional
constructs composed of collagen and cardiac ﬁbroblasts
reduced contraction and altered the expression of mRNA
encoding g-actin, a-smooth muscle actin and collagen type 1.
These data show that AuNRs can modulate cell-mediated
matrix remodeling and suggest that the targeted delivery of
AuNRs can be applied for antiﬁbrotic therapies.
AuNP-sensors are also based on refractive-index change.
‘‘Gellan gum’’, widely used in food as a thickening and
gelling agent, has been used in the reductive synthesis and
stabilization of AuNPs that were applied to load anthracyclin
Fig. 21 Schematic illustration of the analysis of the AuNPs in cell lysates by LDI-MS; (a) Multiplexed LDI mass spectrum of COS-1 cell lysate
with the four cationic AuNPs 1–4. m/z 422, m/z 436, m/z 492, and m/z 465 correspond to AuNP 1, AuNP 2, AuNP 3, and AuNP 4, respectively.
The symbol key is the same as in Fig. 3. (b) Relative amounts of AuNPs 1–4 obtained from LDI-MS. The AuNP amounts are normalized to that of
AuNP 1. Reprinted with permission of Elsevier (ref. 174, Rotello’s group).
Fig. 22 Schematic diagram showing anionic gellan gum gold nanoparticles and subsequent loading of cationic doxorubicin HCl on gellan gum
capped gold nanoparticles. Reprinted with permission of Wiley InterScience (ref. 178, Prasad’s group).
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The Royal Society of Chemistry 2009 Chem. Soc. Rev., 2009, 38, 1759–1782 | 1775
ring antibiotic doxorubicin hydrochloride. Such drug loading
showed enhanced cytotoxic eﬀects on human glioma cell lines
LN-18 and LN-229 (Fig. 22).
The Paciotti group has reported cryosurgery. The cytokine
adjuvant TNF-a can be used to achieve complete cancer
destruction at the periphery of an iceball (0 to 40 1C).
Although both surgery alone or TNF treatment alone caused
only a minimal damage to the tumor tissues, the combination
of TNF and cryosurgery produced a signiﬁcant damage to the
The surfactant dodecylcysteine hydro-
chloride was reported to improve the antitumor activity of
AuNPs in a cell line of the Ehrlich ascites carcinoma.
Hyperthermia of cancer cells using AuNPs appears essential
to ﬁght against intratumoral hypoxia that is a key mediator of
the resistance of tumor cells to radiation therapy. Thus, an
integrated antihypoxic and localized vascular disrupting
therapeutic strategy was developed using tumor-vasculature-
focused eﬀects mediated by perivascularly sequestered AuNSs
Carbonic anhydrase inhibitors coated AuNPs
were shown to selectively inhibit the tumor-associated isoform
IX over the cytosolic isozymes I and II (Fig. 24).
The long history of (almost legendary) gold colloid use for
therapeutic purposes suggests that AuNPs should be bio-
compatible. The considerable potential use of AuNPs in
nanomedicine, especially for imaging, diagnostic and therapy
requires, however, their toxicity to be thoroughly examined
with maximum care and accuracy. The cytotoxicity of AuNPs,
i.e. their cellular toxicity, has indeed been examined by several
research groups and reviewed.
Since everything is toxic
at high dose, the important question is whether AuNPs are
toxic at the concentration at which they will be used, believed
to be in the range of 1–100 AuNPs per cell.
7.1 Cytotoxicity in vitro
Some AuNPs can transfect cells. Rotello has shown that
cationically functionalized alkylthiolate-AuNPs containing
trimethylammonium ligand termini mediate DNA transloca-
tion across cell membranes in mammalian cells at a high level.
Toxicity of these AuNPs was observed at concentrations only
2-fold higher than that found for maximal transfection
activity. In fact, it is essential to distinguish between the
toxicity of the AuNP core and that due to the ligands of the
AuNP. In this case, it was shown that, whereas these cationic
AuNPs are moderately toxic, the same alkylthiolate-AuNPs
containing carboxylate termini are quite non-toxic.
Accordingly, concentration-dependent lysis mediated by
electrostatic binding was observed in dye release studies using
lipid vesicles, suggesting the operating mechanism for the
Fig. 23 Immunoﬂuorescence staining of control, hyperthermia,
radiation, and thermoradiotherapy treated tumors showing hypoxia,
cell proliferation (a–d), and hypoxia, perfusion in tumor periphery
(e–h), and tumor core (i–l), respectively. Red, blue, and green ﬂuores-
cence represents cell proliferation, perfusion, and hypoxic regions in
tumors. Patchy hypoxic region seen in (l) is attributed to the vascular
disruption eﬀect induced by gold nanoshell-mediated thermo-
radiotherapy. Scale bars are represented in the bottom image of each
column. Reprinted with permission of the American Chemical Society
(ref. 182, Krishnan’s group).
Fig. 24 Synthesis of AuNPs coated with sulfonamide CAI, of type GNP-1 and GNP-2. Reprinted with permission of the American Chemical
Society (ref. 183, Supuran’s group).
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The Royal Society of Chemistry 2009
observed toxicity of these cationic AuNPs.
evidence of the key role of AuNP ligands, large AuNPs
conjugated with biotin, cysteine, citrate, and glucose did not
appear to be toxic in human leukemia (K562) cells at concen-
trations up to 250 mM in contrast to HAuCl
was found to be 90% toxic.
AuNP cytotoxicity may also eventually more or less depend
on the cell lines, although this point is somewhat controversial,
because diﬀerences observed might perhaps be due to
variation of ligands (Fig. 25).
No physiological complica-
tion were found either in mice with AuNSs in another study.
Dose-dependent cytotoxicity was found with Au–Cu–NSs
with 100% viability at low dose in mice, but 67% viability
at high dose.
With AuNRs, strong cytotoxicity was asso-
ciated with a low concentration of CTAB-stabilized AuNRs,
and free CTAB was proposed to cause the toxicity.
Phosphatidylcholine was reported to reduce the cytotoxicity
of CTAB-coated AuNRs.
It was pointed out that
non-cytotoxic AuNPs can eventually cause cell damage, and
abnormal ﬁlaments formation was produced by such 13-nm
AuNRs coated with layer-by-layer poly-
electrolytes such as the common poly(diallyldimethylammonium
chloride)-poly(4-styrenylsulfonic acid) showed low toxicity
and were considered as well suited for therapeutic applications.
The cytotoxicity of AuNPs conjugated with PEGylated
biotin-PEG-poly(e-caprolactone) copolymers towards Caco-2
cells in culture was shown to be negligible.
7.2 Cytotoxicity in vivo
The full potential of innovations in terms of AuNP medical
use can only be achieved with the concomitant realization of
in vivo proﬁles for pharmacological intervention.
routes of administration can result in various eﬀects on the
biodistribution of drug carriers.
muscular or topical administration of colloidal drug carriers
generally results in retention of the drug carrier for longer time
than free drug, and these drug carriers are mainly retained by
local lymph nodes.
In vivo distribution subsequent to
administration largely depends on NP size, surface charge and
The inﬂuence of these factors on
the uptake of NPs by the mononuclear phagocyte system has
The presence of biocompatible amphiphilic
chains on NP surface decreases phagocytosis of the NPs by the
non-parenchymal cells of the liver, allowing longer circulation
time in blood.
Permeation of small AuNPs through skin
and intestine was found to be size dependent.
distribution of various sizes (15, 50, 100 and 200 nm) of
AuNPs on intravenous administration in mice was investi-
gated and revealed that AuNPs of all sizes were mainly
accumulated in liver, lung and spleen, whereas accumulation
in various tissues depended on AuNP size. High amounts of
15-nm AuNPs were found in all tissues including blood, liver,
lung, spleen, kidney, and stomach and were able to pass the
blood-brain barrier, as 50-nm AuNPs also did. On the other
hand, only minute amount of 200-nm AuNPs were found in
blood, brain, stomach and pancreas.
another study, rats intravenously injected with AuNPs of
10-, 50-, 100- and 250-nm diameters were shown to contain
the 10-nm AuNPs in the various organs, whereas larger
AuNPs were only detected in blood, liver and spleen.
Paciotti group reported that the tumor-necrosis factor (TNF)-
conjugated AuNPs show similar antitumor eﬀects to TNF
alone, but with less systeic toxicity in mice.
biodistribution of 1.4-nm and 1.8-nm AuNPs that were
administrated by intravenous injection or intratracheal instil-
lation in rats indicated that the 1.4-nm AuNPs can be trans-
located through the air/blood barrier of the respiratory tract in
signiﬁcant amounts, whereas the 1.8-nm AuNPs are almost
completely trapped in the lungs. Additionally, there is evi-
dence that the AuNPs are modiﬁed during the translocation
In a study of pharmacokinetics and biodistribution
in nude mice of PEG-coated AuNPs, AuNPs coated with
thioctic acid-anchored PEG exhibited higher colloidal stability
in phosphate-buﬀered saline in the presence of dithiothreitol
than did AuNPs coated with monothiol-anchored PEG.
AuNPs coated with 5000-Da PEG were more stable than
those coated with 2000-Da PEG. Of the 20-nm, 40-nm, and
80-nm AuNPs coated with thioctic acid-terminated 5000-Da
PEG, the 20-nm AuNPs exhibited the lowest uptake by
retinoendothelial cells and the lowest clearance by the body,
and showed signiﬁcantly higher tumor uptake and extra-
vasation from the tumor blood vessels than did the 40- and
Although all these studies show the AuNP size distribution,
it would also be of interest in the future to obtain information
on the inﬂuence of other AuNP characteristics such as
morphology, crystallinity, surface defects, charge and reactivity.
Fig. 25 M1 nanoparticles incubated with HeLa cells. After 1 h, nanoparticles were observed by video-enhanced color diﬀerential interference
contrast microscopy (A) and transmission electron microscopy (B) clustered in compartments inside the cytoplasm. After 2 h, nanoparticles were
found accumulated around the nuclear membrane (C). Reprinted with permission of the American Chemical Society (ref. 188, Feldheim’s group).
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7.3 Conclusion on toxicity studies
In conclusion to the toxicity survey, it appears that AuNPs
usually show rather little toxicity, if any, because many
cytotoxicity studies report negative cytotoxicity ﬁnding
results. The cationic ligands of AuNPs, however, clearly cause
moderate toxicity, and some toxicity may also be speciﬁc to
other types of ligands. A systematic toxicity study must be
carried out for each speciﬁc case under precise conditions,
before imaging, diagnosis and therapeutic applications of
AuNPs can be carried out in human. Also, in vivo conditions
are diﬀerent from in vitro results, and in particular more in vivo
studies are called for. Thus, no general conclusion can be
drawn at present. It has been suggested, however, that it could
be applicable to use AuNPs as reference nanoparticles for low
toxicity in the set-up of a nanoparticle toxicity scale, given the
higher toxicity of carbon nanotubes and quantum dots
compared to non-cationic AuNPs. Finally, AuNPs are redox
active and therefore reduce the production of reactive oxygen-
and nitrite species.
The non-cytotoxicity, non-immunogenicity
and biocompatibility of many AuNPs make us relatively
optimistic concerning their future essential applications in
8. Conclusion and outlook
Medically useful AuNPs can be prepared and stabilized
(conjugated) with a large variety of stabilizers (citrate, various
ligands, polymers, dendrimers, surfactants) including bio-
molecules such as oligonucleotides and DNA. The best
stabilizers are thiolates (for instance oligonucleotides modiﬁed
with a thiolate group). New practical stabilizers such as
‘‘gellan gum’’ exemplify this variety.
Thiolated PEGs are
especially useful because they masks AuNPs from the intra-
vascular immune system and help targeting cancer cells due to
the EPR eﬀect.
The surface plasmon absorption of AuNPs provides
outstanding optical properties that can be used with a variety
of techniques for labeling, imaging, sensing leading to both
diagnostics and therapies. This SPB is extremely dependent on
the surface, AuNP shape, inter-AuNP distance, medium
(refractive index) and ligands, which makes the basis for
molecular recognition, imaging and sensing sensitivity. The
most famous example of sensor is Mirkin’s ‘‘Northwestern spot
test’’, a visual record of the inter-AuNP distance-dependent
color change and temperature-dependent disaggregation
(melting) that can detect mismatched DNA.
Modern spectroscopic techniques, such as SERS that
provides a huge enhancement of the Raman signal, by a factor
of ca. 10
, allowing detection at the single molecule
considerably facilitates the diagnostic of cancer and
other diseases (SERS combines elastically scattered visible
light from the AuNP themselves that can be imaged using a
dark-ﬁeld optical microscope with inelastic SERS eﬀect due to
adsorbed molecules providing a Raman spectrum leading to
the identiﬁcation of biomolecules). For instance, antibody-
modiﬁed AuNPs displayed a million-fold higher sensitivity
than conventional ELISA-based assay in the detection of
prostate speciﬁc antigen (PSA).
A number of other useful optical and electrochemical
techniques including ﬂuorescence, Ag staining and electro-
catalytic biosensors have been discussed here. These bio-
sensing techniques allow clinical diagnosis of cancer, Alzheimer,
HIV, hepatitis B, tuberculosis, diabetes and arthritis.
In the cancer therapy section, it was shown how photo-
thermal AuNP NIR irradiation of cancer cells combines both
diagnosis (imaging) and selective therapy, a technique also
applicable to other diseases. In addition, the discovery that the
SPB can be shifted from the visible region for spherical AuNPs
to the NIR region for AuNRs and AuNSs led the groups of
to introduce a break-
through with the extension of the eﬃcient use of the SPB for
cancer therapy, a non-invasive method with eﬃcient tumor
ablation in the NIR region were blood and tissues are less
absorbing (‘‘biological window’’: 650–900 nm).
Techniques that do not use the SPB, however, such as RF
heating of AuNPs and AuP-targeting with singlet oxygen
therapy are also known. Indeed, the use of AuNPs as vectors
is very general, because it can be directly applied in a non-
invasive way for various therapies including angiogenesis,
anti-bacterial treatments, etc.
Drug delivery (both drugs and DNA) appears as one of the
most promising future applications of AuNPs, as exempliﬁed
by a number of recent reports that were reviewed here. For
instance AuNP-based DNA-delivery vectors have been
developed by Rotello who showed that intracellular concen-
trations of glutathione can trigger the restoration of DNA
with potential applications in the creation of transfection
Mirkin showed the use of AuNPs conjugated to
oligodeoxynucleotide for gene therapy.
The Paciotti group
reported cryosurgery, indicating that the combination of
TNF-a and cryosurgery produced a signiﬁcant damage to
the tumor tissues.
Finally, a very important problem in potential therapy for
human is that of toxicity that must be carefully and precisely
studied. Many groups have reported the non-toxicity of
AuNPs. One must distinguish between the toxicity of the
AuNP core and that of ligands. Cationic ligands including
CTAB appear moderately toxic, and some other ligands also
may be toxic. Many biocompatible ligands including thiolated
PEGs are non-toxic, however. AuNPs appear much less toxic
than other types of nanoparticles, and one should be
reasonably optimistic concerning potential applications. In
conclusion, AuNPs are biocompatible, easily bio-conjugable
and very promising for imaging, diagnostics and therapy
biomedical applications for cancer and a number of other
diseases for human.
List of abbreviations
AFM Atomic force microscopy
ATP Adenosine triphosphate
AuNPs Gold nanoparticles
AuNRs Gold nanorods
AuNSs Gold nanoshells
CCD Charge-coupled device
CCR5 Chemokine CC motif receptor 5
CD Compact disc
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The Royal Society of Chemistry 2009
CEA Carcinoembryonic antigen
CTAB Cetyl trimethylammonium bromide
DIC Diﬀerential interference contrast
DLSS Diﬀerential light-scattering spectroscopy
DNA Deoxyribonucleic acid
ECL Electrogenerated chemiluminescence
EGFR Epithelial growth factor receptor
EIS Electrochemical impedance spectroscopy
ELISA Enzyme-linked immunosorbent assay
FCS Fluorescence correlation spectroscopy
FRET Fluorescence resonance energy transfer
GO Glucose oxidase
HBV Hepatitis B virus
HEK Human embryonic kidney
HER2 Human epidermal growth factor receptor 2
HIV Human immunodeﬁciency virus
HOC Human ovarian cancer
HRS Hyper-Raleigh scattering
HSC Hematopoetic stem cells
Half maximal inhibitory concentration
IgG Immunoglobulin G
MRI Magnetic resonance imaging
mRNA Messenger ribonucleic acid
Nd-YAG Neodymium-doped yttrium aluminium garnet
NIR Near infrared
PCT Photothermal coherence tomography
PCR Polymerase chain reaction
PEG Polyethylene glycol
PEI Polyethylene imine
PLC Phospholipase C
PSA Prostate speciﬁc antigen
RCM Reﬂection contrast microscopy
RNA Ribonucleic acid
ScFv Single-chain variable-fragment
SDC Shielded dynamic complex-gate
SELEX Systematic evolution of ligands by exponential
SERS Surface-enhanced Raman scattering
siRNA Small interfering ribonucleic acid
SNPs Single nucleotide polymorphisms
SPB Surface plasmon band
SPR Surface plasmon resonance
TEM Transmission electron microscopy
TNF Tumor-necrosis factor
TOF-SIMS Time-of-ﬂight secondary mass spectrometry
We are grateful to the Universite
Bordeaux I, the Centre
National de la Recherche Scientiﬁque (CNRS), the Institut
Universitaire de France (IUF, DA) and the Agence Nationale
de la Recherche (ANR) for ﬁnancial support.
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