Quantum dots (QDs) are semiconductor nanocrystals with extensive imaging and diagnostic capabilities, including the
potential for single molecule tracking. Commercially available QDs offer distinct advantages over organic fluorophores,
such as increased photostability and tunable emission spectra, but their cadmium selenide (CdSe) core raises toxicity
concerns. For this reason, replacements for CdSe-based QDs have been sought that can offer equivalent optical
properties. The spectral range, brightness and stability of InP QDs may comprise such a solution. To this end,
LANL/CINT personnel fabricated moderately thick-shell novel InP QDs that retain brightness and emission over time in
an aqueous environment. We are interested in evaluating how the composition and surface properties of these novel QDs
affect their entry and sequestration within the cell. Here we use epifluorescence and transmission electron microscopy
(TEM) to evaluate the structural properties of cultured Xenopus kidney cells (A6; ATCC) that were exposed either to
commercially available CdSe QDs (Qtracker® 565, Invitrogen) or to heterostructured InP QDs (LANL). Epifluorescence
imaging permitted assessment of the general morphology of cells labeled with fluorescent molecular probes (Alexa
Fluor® ® phalloidin; Hoechst 33342), and the prevalence of QD association with cells. In contrast, TEM offered unique
advantages for viewing electron dense QDs at higher resolution with regard to subcellular sequestration and
compartmentalization. Preliminary results show that in the absence of targeting moieties, InP QDs (200 nM) can
passively enter cells and sequester nonspecifically in cytosolic regions whereas commercially available targeted QDs
principally associate with membranous structures within the cell. Supported by: NIH 5R01GM084702.
Localized surface plasmons (LSPs) are charge density oscillations caused by an interaction of the external
electromagnetic waves with the interface between metallic nanostructures (e.g. noble metal nanoparticles) and a
dielectric medium. Intensity and frequency of the resulting SP absorption bands are characteristic for the type of material
and depends on the size, shape and surrounding environments of the nanostructures. We have designed core/shellnanostructures
with a defined Au-core and increasing Ag-shell thickness as previously described . We have used
AFM measurement and dark-field microscopy to characterize the nanoparticles, which were immobilized via silane
chemistry on glass substrates. The plasmon band of selected particles was investigated by single particle spectroscopy
(SPS) in transmission and reflection mode. Their potential as optical biosensor was demonstrated by immobilization of a
protein and a protein specific antibody leading to a refractive index change in the local environment of metal
nanoparticles, which causes a characteristic shift of the SP absorption band maximum.
Use of gold nanoparticles (NPs) as a contrast agent for medical imaging is shown to improve the efficiency of optoacoustic signal generation; this signal enhancement allows differentiation between different tissue types. This aspect of medical imaging is important when concerned early cancer detection. The present paper presents the results on the interaction process between the laser light and gold NPs, providing valuable information necessary for improved and more efficient NP synthesis. The attenuation of laser is studied for NP solutions of different geometrical characteristics and concentrations where the study is based on both optical and optoacoustic characterization techniques. First results show that the absorption and scattering are correlated by increasing the size of the nanoparticles between 5nm and 60nm. The optoacoustic signals we have been obtained demonstrate similar behavior for gold NP diameters of 5nm to 12nm.
Apertures with diameters below the wavelength of light represent a nanoscale structure with interesting novel
properties. They are usually discussed in an array setting leading to integral optical (spectroscopic) effects. We present
here results obtained by a combination of such apertures (but investigated as an individual structure) with metal
nanoparticles. These nanoparticles are known to exhibit surface plasmon resonance. The optical effect resulting from the
combination of both structures were studied by a complementary ultra structural (AFM, SEM) and spectroscopic
characterization on the single aperture level, yielding insights into this promising novel nanophotonic element.
Use of gold nanoparticles (GNPs) as a contrast agent for medical imaging is shown to improve the efficiency of
optoacoustic signal generation; signal enhancement allows differentiation between different tissue types. This aspect of
medical imaging is important when concerned with early cancer detection. The present paper presents a comparative
analysis of two different optical techniques, optical transmission and optoacoustics, to define the different components
associated with the attenuation of light in GNPs. This attenuation of light is first studied for a pure absorber where the
results are shown to be in agreement for both optical methods, thus showing the effectiveness of the measurement
technique. A comparative analysis is also carried out on spherical GNPs which have been synthesized to have peak
absorption at the laser wavelength.
Metal (especially gold) nanoparticles exhibit unique electronic, optical, and catalytic properties. In order to utilize these
properties, an integration of the particles into technical setups such as a chip surface is helpful. We develop techniques to
use (bio) molecular tools in order to address and control the positioning of particles on microstructured chips. These
techniques are utilized for novel DNA detection schemes using optical or electrical principles. Plasmonic properties of
the particles and the combination of nano-apertures with particles are promising fields for further bioanalytical
On the other hand, methods for defined positioning of single molecules or molecular constructs in parallel approaches
are under development, in order to provide needed defined nanostructures for applications in nanoelectronics.
Connecting DNA with nanoparticles, metallization of DNA or positioning of individual DNA-structures over
microstructured electrode gap including subsequent metal particle binding are important steps in this direction. The
utilization of (bio) molecular tools and principles based on highly specific binding and self-assembly represent a
promising development in order to realize novel nanoparticle-based devices for bioanalytics, nano-optics and - electronics.
Based on their various interesting properties metal nanoparticles show the potential as analytical tool in electronic,
optical, and catalytical applications. The different properties depending on composition, shape, and size of the single
particles were utilized in many different approaches such as optics, magnetics and laser technology<sup>1</sup>.
We present a way for enzymatic deposition of silver nanoparticles and a bioanalytical application in DNA microarray
technology for this method. The technology consists of a microstructured chip with 10&mgr;m broad electrode gaps on the
surface and specially designed readout device<sup>2</sup>. In principle we immobilize gold nanoparticle-labelled DNA in a gap
between two electrodes. Afterwards a silver deposition on the bound gold nanoparticles generates a conductive layer
between the electrodes. The measured drop in the resistance serves as signal for the chip-based electrical detection of
To further optimize this system the gold nanoparticles as seed are replaced by the enzyme horseradish peroxidase. For a
better understanding of the enzymatically silver deposition process the formed silver particles were analyzed by
spectroscopic characterization on a single particle level. Further investigations of these particles by AFM and SEM
should give a hint to the connection between size/shape and the plasmonic properties at individual particles.
Chemical approaches allow for the synthesis of highly defined metal heterostructures, such as core-shell nanoparticles.
As the material of metal nanoparticles determines the plasmon resonance-induced absorption band, the control of
particle composition results in control of the absorption maximum position.
Metal deposition on gold or silver nanoparticles was used to prepare core-shell particles with modified optical properties
with respect to monometal nanoparticles. UV-vis spectroscopy on solution-grown and immobilized particles was
conducted as ensemble measurements, complemented by single particle spectroscopy of selected structures. Increasing
layers of a second metal, connected to a dominant contribution of the shell material to the extinction spectrum, lead to a
shift in the absorption band. The extent of shell growth could be controlled by reaction time or the concentration of
either the metal salt or the reducing agent. Additional to the optical characterization, the utilization of AFM, SEM and
TEM yielded important information about the ultrastructure of the nanoparticle complexes.
Small metal nanostructures, especially gold and silver nanoparticles, are known for their interesting optical properties
caused by plasmons. Isotropic or anisotropic, homogeneous or heterogeneous metal nanoparticles provide a platform for
different highly defined functional units with interesting optical properties for applications such as waveguides or (in
combination with molecular parts) molecular beacons. We combined such nanoparticles with sub-wavelengths apertures
in metal films, and studied the effect of the presence of particles in these nanocavities on the topography as well as on
the optical behavior. Therefore, methods were developed that allow for a correlation of topography and optical
properties. The transmission through the holes was clearly influenced by the presence of nanoparticles. Combined with
the potential of designing the plasmonic properties of particles by customized diameters as well as composition using
core-shell techniques, this approach promises an interesting novel class of plasmonic nanostructures.
Chemical approaches allow for the synthesis of highly defined metal hetero-nanostructures, such as core-shell nanospheres. Because the material of metal nanoparticles determines the plasmon resonance-induced absorption band, the control of particle composition results in control of the position of the absorption band. Metal deposition on gold or silver nanoparticles yielded core-shell particles with modified optical properties. Besides the optical characterization, the utilization of AFM and TEM yielded important information about the morphology of the nanoparticle complexes. UV-vis spectroscopy on solution-grown and surface-grown particles was conducted as ensemble measurements in solution. Increasing layers of a second metal lead to a shift in the absorption band, and a shell diameter comparable to the original particle diameter leads to a predominant influence of the shell material. The extent of shell growth could be controlled by reaction time or the concentration of either the metal salt or the reducing agent.
Manipulation of material by optical means represents an emerging field with numerous applications. Especially in biology and medicine, the flexible and powerful potential of laser utilization holds great promises. For many applications, the resolution of the induced effects is essential. Besides focusing of the beam by various means, the use of sub-wavelengths nanoantenna could overcome this problem. The optical absorption of certain nanostructures is based on plasmon effects. We present studies of the use of metal (homogeneous gold or gold/silver core/shell systems) nanoparticles as antennas that convert the incident laser light into irreversible destructive effects. Based on the established field of DNA-conjugated nanoparticles, we investigated the sequence-specific attachment of DNA-nanoparticle complexes onto DNA with complementary sequences, in the state of double-stranded either isolated or metaphase chromosomal DNA. Important points were the adjustment of the absorption properties of the nanoparticles by control of their material composition (e.g., by addition of a silver layer to a gold core) and diameter. Another group of experiments studied chromosome-conjugated particles before and after laser treatment, in order to reveal the lateral extension of damages as well as the underlying mechanism.
Metal nanoparticles represent an interesting tool for bioanalytics. Due to their small size, attachment to biomolecules does not interfere significantly with specific molecular binding. Therefore particles can be applied as label in affinity assays (e.g., DNA hybridization), using setups with high parallelization. Beside this rather passive use of nanoparticles, these structures can also be utilized as 'nano antenna' for the conversion of laser light pulses into heat. Using DNA-modified particles sequence-specific bound to DNA, a novel restriction technique is in development that applies this conversion for local DNA destruction. Metal nanoparticles combine the ability for highly precise positioning (due to specific molecular binding) with the possibility of optical access in a bright-field mode. They exhibit an interesting potential for spanning the gap between the macroscopic technical environment and the molecular scale, thereby enabling a true integration of nanoscale constructs with today’s technology.
DNA restriction is a basic method in today’s molecular biology. Besides application for DNA manipulation, this method is used in DNA analytics for 'restriction analysis'. Thereby DNA is digested by sequence specific restriction enzymes, and the length distribution of the resulting fragments is detected by gel electrophoresis. Differences in the sequence lead to different restriction patterns. A disadvantage of this standard method is the limitation to a small set of fixed sequences, so that the assay can not be adapted to any sequence of interest (e.g. SNP). We designed a scheme for DNA restriction in order to provide access to any desired sequence, based on laser light conversion on sequence-specific positioned metal nanoparticles. Especially gold nanoparticles are known for their interesting optical properties caused by plasmon resonance. The resulting absorption can be used to convert laser light pulses into heat, resulting in nanoparticle destruction. We work on the combination of this principle with DNA-modification of nanoparticles and the sequence-specific binding (hybridization) of these DNA-nanoparticle complexes along DNA molecules. Different mechanisms of light-conversion were studied, and the destructive effect of laser light on the nanoparticles and DNA is demonstrated.