G. Zacharakis, H. Kambara, H. Shih, J. Ripoll, J. Grimm, Y. Saeki, R.
Weissleder, and V. Ntziachristos, “Volumetric tomography
of fluorescent proteinsthrough small animals in vivo”, PNAS 102, 18252 – 18257
(2005)
Abstract: Volumetric detection and accurate
quantification of fluorescent proteins in entire animals would greatly enhance
our ability to monitor biological processes in vivo. Here we present a quantitative tomographic technique for visualization
of superficial and deep-seated (>2–3 mm) fluorescent protein activity in vivo. We demonstrate noninvasive imaging of lung
tumor progression in a murine model, as well as imaging of gene delivery using
a herpes virus vector. This technology can significantly improve imaging
capacity over the current state of the art and should find wide in vivo imaging applications in drug discovery,
immunology, and cancer research.
G. Zacharakis, J. Ripoll, R.
Weissleder, and V. Ntziachristos, "Fluorescent protein tomography scanner
for small animal imaging," IEEE Trans Med Imaging 24(7), 878-885 (2005).
Abstract: Microscopy of fluorescent
proteins has enabled unprecedented insights into visualizing gene expression in
living systems. Imaging deeper into animals, however, has been limited due to
the lack of accurate imaging methods for the visible. We present a novel system
designed to perform tomographic imaging of fluorescent proteins through whole
animals. The tomographic method employed a multiangle, multiprojection
illumination scheme, while detection was achieved using a highly sensitive
charge-coupled device camera with appropriate filters. Light propagation was
modeled using a modified solution to the diffusion equation to account for the
high absorption and high scattering of tissue at the visible wavelengths. We
show that the technique can quantitatively detect fluorescence with sub
millimeter spatial resolution both in phantoms and in tissues. We conclude that
the method could be applied in tomographic imaging of fluorescent proteins for
in vivo targeting of different diseases and abnormalities.
K. Marias, J. Ripoll, H. Meyer, V.
Ntziachristos, and S. Orphanoudakis, "Image analysis for assessing
molecular activity changes in time-dependent geometries," IEEE Trans Med
Imaging 24(7), 894-900 (2005).
Abstract: In vivo fluorescence
molecular imaging and tomography has facilitated monitoring of genomics and
proteomics over time and on the same animal. A highly important issue, however,
has been the robust registration of animals imaged at different time points to
obtain accurate description of activity and location. This paper presents a
method for aligning temporal data of small animals based on surface anatomical
features and improving the accuracy of monitoring fluorophore distribution. The
method can account for differences in the positioning and compression of small
animals and can be extended to three-dimensional as well as to other imaging
modalities.
V. Ntziachristos, J. Ripoll, L. V.
Wang, and R. Weissleder, "Looking and listening to light: the evolution of
whole-body photonic imaging," Nat Biotechnol 23(3), 313-320 (2005).
Abstract: Optical imaging of live
animals has grown into an important tool in biomedical research as advances in
photonic technology and reporter strategies have led to widespread exploration
of biological processes in vivo. Although much attention has been paid to
microscopy, macroscopic imaging has allowed small-animal imaging with larger
fields of view (from several millimeters to several centimeters depending on
implementation). Photographic methods have been the mainstay for fluorescence
and bioluminescence macroscopy in whole animals, but emphasis is shifting to
photonic methods that use tomographic principles to noninvasively image optical
contrast at depths of several millimeters to centimeters with high sensitivity
and sub-millimeter to millimeter resolution. Recent theoretical and
instrumentation advances allow the use of large data sets and multiple
projections and offer practical systems for quantitative, three-dimensional
whole-body images. For photonic imaging to fully realize its potential,
however, further progress will be needed in refining optical inversion methods
and data acquisition techniques.
A. Soubert, J. Ripoll, and V.
Ntziachristos, "Accuracy of Fluorescent Tomography in the presence of
heterogeneities: Study of the Normalized Born Ratio," IEEE Trans. Med.
Imag. In press(2005).
Abstract: We study the performance
of three-dimensional fluorescence tomography of diffuse media in presence of
heterogeneities. Experimental measurements were acquired using an imaging
system consisting of a parallel plate-imaging chamber and a lens coupled CCD
camera, which enables conventional planar imaging as well as fluorescence
tomography. To simulate varying degree of background heterogeneity we employed
phantoms made of a fluorochrome tube surrounded by several absorbers in
different combinations of absorption distribution. We show that the normalized
Born approach accurately retrieves the position and shape of the fluorochrome
even at high background heterogeneity. We also demonstrate that quantification
is insensitive to a varying degree of heterogeneity and background optical
properties. Findings are further contrasted to images obtained with the
standard Born expansion and with a normalized approach that divides the
fluorescent field with excitation measurements through a homogeneous medium.
G. M. Turner, G. Zacharakis, A.
Soubret, J. Ripoll, and V. Ntziachristos, "Complete-angle projection
diffuse optical tomography by use of early photons," Opt Lett 30(4),
409-411 (2005).
Abstract: We present the first, to
our knowledge, experimental images of complex-shaped phantoms embedded in
diffuse media by use of optical tomography. Imaging is based on a
complete-angle projection tomographic technique that utilizes transmitted early
photons. Results are contrasted with measurements obtained at later gates as
well as pseudocontinuous-wave data. The scanning system developed employs
noncontact illumination and detection technologies that allow for high spatial
sampling of transmitted photons. Combining this system with complete-angle
illumination is found to be an important strategy toward improved imaging
performance, resulting in a better-posed inversion problem. The appropriateness
of reconstruction algorithms similar to those employed in x-ray computed
tomography are showcased, and suggestions for model improvements are provided.
H. Bahlouli, A. D. Alhaidari, and A. Al Zahrani, E. N. Economou, “Electromagnetic
wave propagation in an active medium and the equivalent chrödinger equation
with an energy-dependent complex potential” Phys. Rev. B 72, 094304 (2005)
ABSTRACT: We study the massless limit of the
Klein-Gordon (K-G) equation in 1+1 dimensions with
static complex potentials in order to provide an alternative, but equivalent,
representation of plane electromagnetic (em) wave propagation in an active medium. In the case of a dispersionless em
medium, the analogy dictates that the potential in the K-G equation is complex
and energy dependent. We study also the nonrelativistic Schrödinger equation
with a potential that has the same energy dependence as that of the K-G
equation. The behavior of the solutions of this Schrödinger equation is
compared with those found elsewhere in the literature for the propagation of
electromagnetic plane waves in a uniform active medium with complex dielectric
constant. In particular, both equations exhibit a discrepancy between the
time-dependent and stationary results; our study attributes this discrepancy to
the appearance of time-growing bound eigenstates corresponding to poles in the
transmission and reflection amplitudes located in the upper half of the
wave-number plane. The omission of these bound states in the expansion in
stationary states leads to the observed discrepancy. Furthermore, it was
demonstrated that there is a frequency- (energy) -and-size-dependent gain threshold above which this discrepancy appears.
This threshold corresponds to the value of the gain at which the first pole
crosses the real axis.
J. Zhou, Th.
Koschny, M. Kafesaki, E. N. Economou, J. B. Pendry, and C. M. Soukoulis, “Saturation of the Magnetic Response of Split-Ring Resonators at Optical
Frequencies”, Phys. Rev. Lett. 95,
223902 (2005)
ABSTRACT: We investigate numerically the limits
of the resonant magnetic response with a negative effective permeability μeff
for single-ring
multicut split-ring resonator (SRR) designs up to optical frequencies. We find
the breakdown of linear scaling due to the free electron kinetic energy for
frequencies above_100 THz. Above the linear scaling regime, the
resonance frequency saturates, while the amplitude of theresonant permeability
decreases, ultimately ceasing to reach negative value. The highest
resonancefrequency at which μeff
< 0 increases with the number of cuts in
the SRR. A LC circuit model providesexplanation of the
numerical data.
G. Filippidis, C. Kouloumentas, G. Voglis, F.
Zacharopoulou, T. G. Papazoglou, N. Tavernarakis “Imaging of Caenorhabditis
elegans neurons by Second Harmonic Generation and Two-Photon Excitation
Fluorescence.’’ Journal of Biomedical Optics 10, 024015 (2005)
ABSTRACT: Second-harmonic generation (SHG) and
two-photon excitation fluorescence (TPEF) are relatively new and promising
tools for the detailed imaging of biological samples and processes at the
microscopic level. By exploiting these nonlinear phenomena phototoxicity and
photobleaching effects on the specimens are reduced dramatically. The main
target of this work was the development of a compact inexpensive and reliable
experimental apparatus for nonlinear microscopy measurements. Femtosecond laser
pulses were utilized for excitation. We achieved high-resolution imaging and
mapping of Caenorhabditis elegans (C. elegans) neurons and muscular structures
of the pharynx, at the microscopic level by performing SHG and TPEF
measurements. By detecting nonlinear phenomena such as SHG and TPEF it is
feasible to extract valuable information concerning the structure and the
function of nematode neurons.
G. Filippidis, C. Kouloumentas, D.
Kapsokalyvas, G. Voglis, N. Tavernarakis, T. G. Papazoglou “Imaging
of Caenorhabditis elegans samples and sub-cellular localization of new
generation photosensitizers for Photodynamic Therapy, using non-linear
microscopy.’’ Journal of Physics D: Applied Physics 38, 2625-2632 (2005)
ABSTRACT: Two-photon excitation fluorescence
(TPEF) and second-harmonic generation (SHG) are relatively new promising tools
for the imaging and mapping of biological structures and processes at the
microscopic level. The combination of the two image-contrast modes in a single
instrument can provide unique and complementary information concerning the
structure and the function of tissues and individual cells. The extended
application of this novel, innovative technique by the biological community is
limited due to the high price of commercial multiphoton microscopes. In this
study, a compact, inexpensive and reliable setup utilizing femtosecond pulses
for excitation was developed for the TPEF and SHG imaging of biological
samples. Specific cell types of the nematode Caenorhabditis elegans were imaged. Detection of the endogenous
structural proteins of the worm, which are responsible for observation of SHG
signals, was achieved. Additionally, the binding of different photosensitizers
in the HL-60 cell line was investigated, using non-linear microscopy. The
sub-cellular localization of photosensitizers of a new generation, very
promising for photodynamic therapy (PDT), (Hypericum perforatum L. extracts) was achieved. The sub-cellular
localization of these novel photosensitizers was linked with their photodynamic
action during PDT, and the possible mechanisms for cell killing have been
elucidated.
D. Skalkos, E. Gioti, C.G. Stalikas, H. Meyer, T.G. Papazoglou, G.
Filippidis “Photophysical
Properties of Hypericum Perforatum L. Extracts - Novel Photosensitizers for PDT
’’ Journal of Photochemistry and Photobiology B: Biology 82, 146-151 (2006)
ABSTRACT: We report the preparation of the
methanolic extract (ME), and polar methanolic fraction (PMF) from the plant
Hypericum perforatum L. The extracts contain various photosensitizing
constituents such as naphthodianthrone derivatives (in 1.37% w/w), and
chlorophylls (in 0.08% w/w). Upon light emission these constituents can be
activated, providing photodynamic properties to the extracts, and making them a
potent, new class, natural photosensitizers for use in photodynamic therapy
(PDT), and photodynamic diagnosis (PDD). The absorbance spectra of the extracts
are similar to the spectrum of hypericin, the main naphthodianthrone identified
within, with two major bands at 548 and 590 nm. The fluorescence spectra in
ethanol exhibit two main bands around 595 and 640 nm, in accordance with the
spectrum of pure hypericin. The fluorescence intensity of PMF at 595 nm is only
eight times less than the intensity of pure hypericin at the same wavelength,
even though its hypericin concentration is only 0.57% w/w. The dependence of
the PMF fluorescence signal on the pH of the medium, alone and in comparison
with the signal of hypericin, has been investigated. PMF signal fades steadily,
and smoothly both in acidic, and basic environment.
J. Swartling, J. Svensson, D.
Bengtsson, K. Terike, and S. Andersson-Engels, 2005 Fluorescence spectra
provide information on the depth of fluorescent lesions in tissue, Applied
Optics 44(10), 1934-1941
Abstract: The fluorescence spectrum measured from a
fluorophore in tissue is affected by the absorption and scattering properties
of the tissue, as well as by the measurement geometry. We analyze this effect
with Monte Carlo simulations and by measurements on phantoms. The spectral
changes can be used to estimate the depth of a fluorescent lesion embedded in
the tissue by measurement of the fluorescence signal in different wavelength
bands. By taking the ratio between the signals at two wavelengths, we show that
it is possible to determine the depth of the lesion. Simulations were performed
and validated by measurements on a phantom in the wavelength range 815–930 nm. The depth of a fluorescing layer could be
determined with 0.6-mm accuracy down to at least a depth of 10 mm. Monte Carlo
simulations were also performed for different tissue types of various
composition. The results indicate that depth estimation of a lesion should be
possible with 2–3-mm accuracy, with no assumptions
made about the optical properties, for a wide range of tissues.
J. Svensson and S.
Andersson-Engels, 2005, Modeling of spectral changes for depth localization of
fluorescent inclusion, Optics Express 13(11), 4263-4274
Abstract: We have performed modeling
of fluorescence signals from inclusions inside turbid media to investigate the
influence of a limited fluorescence contrast and how accurately the depth can
be determined by using the spectral information. The depth was determined by
forming a ratio of simulated fluorescence intensities at two wavelengths. The
results show that it is important to consider the background autofluorescence
in determining the depth of a fluorescent inclusion. It is also necessary to
know the optical properties of the tissue to obtain the depth. A 20% error in
absorption or scattering coefficients yields an error in the determined depth
of approximately 2-3 mm (relative error of 10-15%) in a 20 mm thick tissue
slab.
J. Svensson, J. Axelsson, A.
Garofalakis, H. Meyer, S. Andersson-Engels, 2005, Fluorescence spectroscopy in
tissue phantoms for depth estimation in tissue imaging, Submitted to Journal of
Biomedical Optics
Abstract: One way of determining
the depth of a fluorescent inclusion is to detect fluorescent light that has
propagated through the medium at two different wavelength bands, in which case
a ratio can be calculated between the corresponding intensities. The wavelength
regions should be chosen such that there is a difference in the attenuation in
the medium. The method could be used to determine the depth of deep-lying
tumors marked with a fluorescent compound. The depth information obtained by
the ratio could be used as a complement to other methods, for example to
tomography, due to its straightforward implementation. In this study we have
performed phantom measurements to determine the depth of a fluorescent object
inside a tissue phantom. Fluorescence at multiple wavelengths was measured and
a ratio of yellow to red fluorescence was calculated for different depths of a
fluorescent inclusion in a 2.5 cm thick liquid phantom. The ratio showed a
clear dependence on the depth of the object. In order to verify the performance
of the method in a realistic situation, measurements were also performed in
tissue, where autofluorescence is superimposed on the fluorescence from the
inclusion, yielding encouraging results.
M. Schweiger, S. Arridge, O.Dorn, A. Zacharopoulos, V.
Kolehmainen,Reconstructing absorption and diffusion shape profiles in optical
tomography using a level set technique, Optics Letters, (in press), 2005.
J. Sikora, A. Zacharopoulos, A.
Douiri, M. Schweiger, L. Horesh, S.R. Arridge and J. Ripoll, Photon propagation
in multilayered Geometries, Physics in
Medicine and Biology (in press), 2005.
Paper published in Invest Radiolgy
40(6): 321-7 (2005), Optical imaging of spontaneous breast tumors using
protease sensing smart optical contrast agents
Abstract: Objectives:To determine
if spontaneous breast cancer lesions can be detected by fluorescence
reflectance imaging (FRI) and fluorescence mediated tomography (FMT) using
protease-sensing optical probes.
Materials and Methods: Transgenic
(FVB/N-TgN (WapHRAS)69Lin YSJL)) mice that spontaneously develop carcinomas of
the breast were i.v. injected with a cathepsin-sensing fluorescent probe. FRI
and FMT were performed 24 hrs after contrast injection and region of interest
(ROI) analysis was performed. MR images were acquired for anatomical
co-registration with the FMT data. Moreover, correlative immunohistochemistry
and fluorescence microscopy were performed. Results: All tumor nodules were
clearly delineated by FRI showing an average signal intensity of 380 +- 106 AU.
Fluorescence of the animal could be clearly localized to the tumor by FMT. In accordance
with the imaging findings immunohistochemistry confirmed cathepsin-B expression
of the tumors and fluorescence microscopy revealed a strong Cy 5.5. deposition
in the tissue.
Conclusions: FRI and FMT using ‘smart’ protease sensing probes allow to detect experimental
spontaneous breast cancers. Since the expression levels of various proteases
correlate with patient outcome this technique may not only help to detect but
also to differentiate breast cancers non-invasively.
Paper submitted to Radiology: In
vivo quantification of avβ3-expression using fluorescence mediated
tomography
Abstract: Purpose: To
non-invasively image and quanitfy the expression of the integrin av?3- as a
molecular marker of tumor angiogensis using planar and tomographic optical
methods.
Material and Methods: An
av?3-targeted peptide was labeled with the cyanine dye Cy 5.5. Binding of the
optical tracer was tested on human melanoma (M21), HT-1080 fibrosarcoma and
MCF-7 adenocarcinoma cells. M21 tumor bearing mice were i.v. injected with
either unmodified Cy 5.5 or RGD-Cy 5.5. For competition studies 250 nmol of the
non-labeled RGD-peptide were administered prior to the injection of RGD-Cy 5.5.
All optical imaging studies were performed using 2-d planar fluorescence reflectance
imaging (FRI) technology and 3-d fluorescence mediated tomography (FMT).
Results: In vitro the peptide-dye
conjugate showed clear binding affinity to av?3-positive cells (M21, HT-1080)
while av?3-negative cells (MCF-7) and pre-dosing of M21 cells with the free
RGD-peptide revealed little to no fluorescence. In vivo M21 xenografts were
clearly visualized by FRI up to 24 h after i.v. injection of RGD-Cy 5.5
revealing an up to 40% higher target-to-background ratio as compared to the
non-modified dye. FMT allowed to quantitatively analyze fluorochrome
distribution in deeper tissue sections showing an average fluorochrome
concentration of 102 nM in the target tissue. Competition with the free peptide
resulted in a significant reduction of fluorochrome concentration in the tumor
tissue (appr. 41 nM) suggesting binding specificity of the probe in vivo.
Conclusion: RGD-Cy 5.5 combined
with novel tomographic optical imaging methods allows to non-invasively image
and quantify av?3-expression in vivo and may thus be a promising strategy for
sensitive tumor detection.
R. Pierrat, J.-J. Greffet, R.
Carminati and R. Elaloufi, 2005, "Spatial coherence in strongly scattering
media", J. Opt. Soc. Am. A vol. 22, 2329-2337.
Abstract : We study the spatial
coherence of an optical beam in a strongly scattering medium confined in a slab
geometry. Using the radiative transfer equation, we study numerically the
behavior of the transverse spatial coherence length in the different transport
regimes. Transitions from the ballistic to the diffusive regimes are clearly
identified.
R. Pierrat, J.-J. Greffet, R.
Carminati, 2005, "Photon diffusion coefficient in scattering and absorbing
media", J. Opt. Soc. Am. A, accepted for publication.
Abstract : We present a unified
derivation of the photon diffusion coefficient for both steady-state and
time-dependent transport in disordered absorbing media. The derivation is based
on a modal analysis of the time-dependent radiative transfer equation. This
approach confirms that the dynamic diffusion coefficient is given by the random-walk result D=1/3 c
l*, where l* is the transport mean-free path and c is the energy velocity,
independently on the level of absorption. It also shows that the diffusion
coefficient for steady-state transport, often used in biomedical optics,
depends on absorption, in agreement with recent theoretical and experimental
works. These two results resolve a recurrent controversy in light propagation
and imaging in scattering media.
R. Carminati, C. Henkel, J.-J. Greffet
and J.M. Vigoureux, 2005, "Radiative and non-radiative decay of a single
molecule close to a metallic nanoparticle", Opt. Commun., accepted for
publication.
Abstract : We study the spontaneous
emission of a single emitter close to a metallic nanoparticle, with the aim to
clarify the distance dependence of the radiative and non-radiative decay rates.
We derive analytical formulas based on a dipole-dipole model, and show that the
non-radiative decay rate follows a R^-6 dependence at short distance, where R
is the distance between the emitter and the center of the nanoparticle, as in
F?rster's energy transfer. The distance dependence of the radiative decay rate
is more subtle. It is chiefly dominated by a R^-3 dependence, a R^-6 dependence
being visible at plasmon resonance. The latter is a consequence of radiative
damping in the effective dipole polarisability of the nanoparticle. The different distance behavior of the
radiative and non-radiative decay rates implies that the apparent quantum yield
always vanishes at short distance. Moreover, non-radiative decay is strongly
enhanced when the emitter radiates at the plasmon-resonance frequency of the
nanoparticle.
M. Laroche, R. Carminati and J.-J.
Greffet, 2005, "Resonant optical transmission through a photonic crystal
in the forbidden gap", Phys. Rev. B vol. 71, 155113.
Abstract : We show that a slab of a
photonic crystal whose thickness is 3.5 ?m can transmit 100% of an incident
beam whose frequency lies in the forbidden gap. This phenomenon is not linked
to a volume defect but to the resonant coupling of leaky surface modes at both
interfaces.
M. Laroche, C. Arnold, F. Marquier,
R. Carminati, J.-J. Greffet, S. Collin, N. Bardou and J.-L. Pelouard, 2005,
"Highly directional radiation generated by a tungsten thermal
source", Opt. Lett. vol. 30, 2623-2625.
Abstract : We report the design of
a tungsten thermal source with extraordinarily high directivity in the near
infrared, comparable to the directivity of a CO2 laser. This high directivity
is the signature of the long-range correlation of the electromagnetic field in
the source plane. This phenomenon is due to the resonant thermal excitation of
surface-plasmon polaritons.
M. Thomas, J.-J. Greffet and R.
Carminati, 2005, "Single-molecule fluorescence enhancement using a
metallic nanoantenna", manuscript in preparation.
Abstract : The spontaneous emission
of a single molecule is substantially modified close to a nanostructure. We
study numerically the spectral behavior of the radiative and non-radiative
decay rates, of the local-field factor and the apparent quantum yield in the
vicinity of a metallic nano-antenna. We study the competition between
fluorescence enhancement and quenching versus the experimental parameters
(transition dipole orientation, emission spectrum, distance to the
nano-antenna, etc).
G. Cwilich, L.S. Froufe-Perez and
J.J. Saenz (2005), Spatial wave intensity correlations in quasi-one-dimensional
wires, Physical Review Letters, Submitted)
Abstract : Spatial intensity
correlations between waves transmitted through random media are analyzed within
the framework of the random matrix theory of transport. Assuming that the
statistical distribution of transfer matrices is isotropic, we found that the
spatial correlation function can be expressed as the sum of three terms, with
distinctive spatial dependences. This result coincides with the one obtained in
the diffusive regime from perturbative calculations, but holds all the way from
quasi-ballistic transport to localization. While correlations are positive in
the diffusive regime, we predict a transition to negative correlations as the
length of the system decreases.
G. M. Sacha, A. Verdaguer, J.
Mart?nez, J. J. Saenz, D. F. Ogletree, and M. Salmeron (2005), Effective tip
radius in electrostatic force microscopy, Applied Physics Letters 86, 123101
Abstract : A method to determine
the effective electrostatic tip radius of arbitrarily shaped conducting tips in
atomic force microscopy is presented. The method is based on the finding that
for conductive samples, the electrostatic force can be separated into two
contributions: one from a constant background that depends only on the
macroscopic shape of the tips cone or pyramid and cantilever, and another that
depends only on the radius of curvature of the tip apex. Based on a simple
theoretical expression derived from the generalized image charge method, we
show that the tip radius can be directly determined from experimental
force-distance characteristics. For irregular tip shapes, we show that the
measured tip radius is the average of two principal curvatures, in agreement
with tip shape images obtained by scanning electron microscopy.
Jeong Young Park, G. M. Sacha, M.
Enachescu, D. F. Ogletree, R. A. Ribeiro, P. C. Canfield, C. J. Jenks, P. A.
Thiel, J. J. Saenz, and M. Salmeron., Sensing Dipole Fields at Atomic Steps
with Combined Scanning Tunneling and Force Microscopy, Physical Review Letters
95, 136802 (2005)
Abstract : The electric field of
dipoles localized at the atomic steps of metal surfaces due to the Smoluchowski
effect were measured from the electrostatic force exerted on the biased tip of
a scanning tunnelling microscope. By varying the tip-sample bias the
contribution of the step dipole was separated from changes in the force due to
van der Waals and polarization forces. Combined with electrostatic
calculations, the method was used to determine the local dipole moment in steps
of different heights on Au(111) and on the twofold surface of an Al-Ni-Co
decagonal quasicrystal.
F. J. Garcia de Abajo and J. J.
Saenz, Electromagnetic Surface Modes in Structured Perfect-Conductor Surfaces,
Physical Review Letters 95, 233901 (2005)
Abstract : Surface-bound modes in metamaterials forged by
drilling periodic hole arrays in perfect-conductor surfaces are investigated by
means of both analytical techniques and rigorous numerical solution of Maxwell’s equations. It is shown that these metamaterials cannot
be described in general by local, frequency-dependent permittivities and permeabilities
for small periods compared to the wavelength, except in certain limiting cases
that are discussed in detail. New related metamaterials are shown to exhibit
exciting optical properties that are elucidated in the light of our simple
analytical approach.
“Multidimensional Fluorescence
Imaging”,
“Multidimensional Fluorescence
Imaging Applied to Biological Tissue” Daniel S. Elson, Neil Galletly, Clifford
Talbot, Jose Requejo-Isidro, James McGinty, Christopher Dunsby, Peter M. P.
Lanigan, Ian Munro, Richard K. P. Benninger, Mark A. A. Neil, John Lever,
Gordon W. Stamp, and Paul M. W. French /
Accepted for publication as a chapter in Annual Reviews in Fluorescence 2006
“Wide-Field Optically-Sectioned
Fluorescence Lifetime Imaging using a Nipkow Disk Microscope and a Tunable
Ultrafast Continuum Excitation Source” D. M. Grant, D. S. Elson, D. Schimpf, C.
Dunsby, J. Requejo-Isidro, I. Munro, M. A. A. Neil and P. M. W. French, E. Nye
and G. Stamp, P. Courtney Accepted for
publication in Optics Letters
van Munster, E.B. and Gadella Jr.,
T.W.J. (2005) Fluorescence lifetime imaging microscopy (FLIM) in Microscopic
techniques (ed. Rietdorf J.) of the series Advances in Biochemical
engineering/biotechnology vol 95 (series ed. Scheper, T.), Springer Verlag,
Heidelberg, pp 143-175.
Abstract: Fluorescence lifetime
imaging microscopy (FLIM) is a technique to map the spatial distribution of
nanosecond excited state lifetimes within microscopic images. FLIM systems have
been implemented both in the frequency domain, using sinusoidally
intensity-modulated excitation light and modulated detectors, and in the time
domain, using pulsed excitation sources and time-correlated or time-gated
detection. In this review we describe the different modes in which both
frequency-domain and time-domain FLIM instruments have been constructed in
wide-field and in point-scanning (confocal) microscopes. Also novel additional
strategies for constructing FLIM-instruments are discussed. In addition to technical implementation this
chapter gives an overview of the application of FLIM in cell biological en
biomedical studies. Especially for in situ protein-protein interaction studies
using fluorescence resonance energy transfer (FRET), FLIM has proven to be a
robust and established technique in modern cell biology. Other application
areas including usage of lifetime contrast for ion-imaging, quantitative
imaging, tissue characterization and medical applications are discussed.
van Munster, E., Kremers, G.-J.,
Adjobo-Hermans, M., Gadella Jr., T.W.J.
(2005) Fluorescence resonance energy transfer (FRET) measurement by
gradual acceptor photobleaching, J. Microsc. 218: 253-262.
Abstract: Fluorescence resonance
energy transfer (FRET) is an extremely effective tool to detect molecular
interaction at suboptical lresolutions. One of the techniques for measuring
FRET is acceptor photobleaching: the increase in donor fluorescence after
complete acceptor photobleaching is a measure of the FRET efficiency. However,
in wide-field microscopy, complete acceptor photobleaching is difficult due to
the low excitation intensities. In addition, the method is sensitive to
inadvertent donor bleaching, autofluorescence and bleed-through of excitation
light. In the method introduced in this paper, donor and acceptor intensities are
monitored continuously during acceptor photobleaching. Subsequently, curve
fitting is used to determine the FRET efficiency. The method was demonstrated
on cameleon (YC2.1), a FRET-based Ca 2 + indicator, and on a CFP-YFP fusion
protein expressed in HeLa cells. FRET efficiency of cameleon in the presence of
1 mM Ca2+ was 31 ± 3%. In the absence of Ca2+ a FRET efficiency of 15 ± 2% was
found. A FRET efficiency of 28% was found for the CFP-YFP fusion protein in
HeLa cells. Advantages of the method are that it does not require complete
acceptor photobleaching, it includes correction for spectral cross-talk, donor
photobleaching and autofluorescence, and is relatively simple to use on a
normal wide-field microscope.
Schultz, C., Schleifenbaum, A.,
Goedhart, J. and Gadella Jr., T.W.J. (2005) Multiparameter imaging for the
analysis of intracellular signaling, Chem. Biochem. 6: 1323-1330.
Abstract: In biological
experimentation and especially in drug discovery there is a trend towards more
complex test systems. Cell-based assays are replacing conventional binding or
enzyme assays more and more. This development is strongly driven by novel
fluorescent probes that give insight into cellular processes. Target proteins
are studied in their natural environment; this gives much more realistic test
results, especially with respect to enzyme location and kinetics. However, in
the complex environment of cells, many parameters contribute to the performance
of the protein of interest. Therefore, it would be desirable to monitor
simultaneously as many of the relevant cellular processes as possible. Here, we
discuss the possibilities and limitations provided by multiparameter monitoring
of cellular events with fluorescent probes. Some novel examples of the use of
fluorescent probes and multiparameter imaging are shown.
Cremazy, F, Manders, E.M.M.,
Bastiaens, P.I.H., Kramer, G., Hager, G.L., van Munster, E.B., Verschure, P.J.,
Gadella Jr., T.W.J., and van Driel, R. (2005) Imaging in situ protein-DNA
interactions in the cell nucleus using FRET-FLIM, Exp. Cell Res. 309, 390-396.
Abstract: Although the distribution
of DNA-binding proteins inside the cell nucleus can be analyzed by
immunolabeling or by tagging proteins with GFP, we cannot establish whether the
protein is bound to DNA or not. Here, we describe a novel approach that allows
imaging of the in situ interaction between a GFP-fusion protein and DNA in the
cell nucleus, using fluorescence resonance energy transfer (FRET). We used
fluorescence lifetime imaging microscopy (FLIM) as a reliable tool to detect
protein in contact with DNA. The method was successfully applied to the
DNA-binding proteins histone H2B and the glucocorticoid receptor and to the
heterochromatin-associated proteins HP1? and HP1?.
Dhonukshe, P., Mathur, J.,
H?lskamp, M. and Gadella Jr, T.W.J., (2005) Microtubule plus-ends reveal
essential links between intracellular polarization and localized modulation of
endocytosis during division-plane establishment in plant cells, BMC Biology 3,
11. Published on internet http://www.biomedcentral.com/1741-7007/3/11
Abstract: Background: A key event
in plant morphogenesis is the establishment of a division plane. A plant- specific microtubular preprophase band (PPB)
accurately predicts the line of cell division, whereas the phragmoplast, another plant-specific
array, executes cell division by maintaining this predicted line. Although establishment of these
specific arrays apparently involves intracellular repolarization events that focus cellular resources to a
division site, it still remains unclear how microtubules position the cell division planes. Here we
study GFP-AtEB1 decorated microtubule plus-ends to dissect events at the division plane.
Results: Early mitotic events
included guided growth of endoplasmic microtubules (EMTs) towards the PPB site and their coincident
localization with endocytic vesicles. Consequently, an endosomal belt lay in close proximity to the
microtubular PPB at its maturation and was maintained during spindle formation. During cytokinesis,
EMTs radiated from the former spindle poles in a geometrical conformation correlating with
cell-plate navigation and tilt-correction.
Naphthylphtalamic acid (NPA), an inhibitor of polar auxin efflux, caused
abnormal PPBs and shifted division
planes.
Conclusion: Our observations reveal
a spatio-temporal link between microtubules and
intracellular polarization essential for localized endocytosis and
precise establishment of the division
plane in plants. Additionally, they implicate the growth regulator, auxin, in
this important cellular event.
Dhonukshe, P., Baluška, F.,
Schlicht, M., Hlavacka, A., Šamaj, J., Friml, J. and Gadella (2005) Endocytosis
of cell surface material mediates cell plate formation during plant
cytokinesis. Dev. Cell, accepted
Abstract: Dividing plant cells
perform a remarkable task of building a new cell wall within the cytoplasm in a
matter of minutes. A long standing paradigm claims that this primordial cell
wall, known as the cell plate, is generated by delivery of newly synthesised material from Golgi
apparatus-originated secretory vesicles. Here we show that in diverse plant
species cell surface material including
plasma membrane proteins, cell wall components and exogenously applied
endocytic tracers, are rapidly delivered to the forming cell plate.
Importantly, this occurs even when de novo protein synthesis is blocked. In
addition, cytokinesis-specific syntaxin KNOLLE as well as PM-resident proteins
localize to endosomes which aggregate to initiate the cell plate. Furthermore,
the rate of endocytosis is strongly enhanced during cell plate formation and
its genetic or pharmacological inhibition leads to cytokinesis defects. Our
results reveal that endocytic delivery of cell surface material significantly
contributes to cell plate formation during plant cytokinesis.
Goedhart, J. & Gadella Jr.,
T.W.J. (2005) Analysis of oligonucleotide annealing by electrophoresis in
agarose gels using sodium borate conductive medium. Anal. Biochem.
343:186-187.
Abstract: Annealed oligonucleotides are often used to
insert short DNA sequences of 10–60 base pairs into
a plasmid. In this way, short tags such as FLAG tags and oligohistidine tags,
as well as user-deWned multiple cloning sites, can be created. The insertion of
oligonucleotides is also of interest for creating plasmids that encode short
hairpin RNA (shRNA)1 to knock-down genes
Schultz, C., Schleifenbaum, A.,
Goedhart, J., Gadella, T. W. J. (2005) Multiparameter imaging for the analysis
of intracellular signaling. ChemBioChem 6, 1323-1330.
In biological experimentation and
especially in drug discovery there is a trend towards more complex test
systems. Cell-based assays are more and more replacing conventional binding or
enzyme assays. This development is strongly driven by novel fluorescent probes
that are giving insight into cellular processes. Target proteins are studied in
their natural environment, which gives much more realistic test results,
especially with respect to enzyme location and kinetics. However, in the
complex environment of the cell, many parameters are contributing to the
performance of the protein of interest. Therefore, it would be desirable to
monitor as many of the relevant cellular processes as possible simultaneously.
Here, we discuss the possibilities and limitations provided by multiparameter
monitoring of cellular events with the help of fluorescent probes. Some novel
examples using fluorescent probes and multiparameter imaging are shown.
Wichmann, O., Wittbrodt, J.,
Schultz, C. (2005) A small molecule FRET probe to monitor PLA2 activity in
cells and organisms, Angew. Chem. Int. Ed. Engl., in press.
Watching live: The FRET reporter
PENN/SATE (FRET=fluorescence resonance energy transfer) is membrane-permeant
and enters cells and small organisms by using a prodrug approach. Once inside
cells the reporter is cleaved by phospholipases, which results in a 30-fold
change in the emission ratio.
Brumbaugh, J., Schleifenbaum, A.,
Gasch, A., Sattler, M., Schultz, C. (2005) A dual parameter FRET probe for
measuring PKC and PKA activity in living cells. J. Am. Chem. Soc., accepted.
Cell function is regulated by
complex and often interdependent networks of signaling molecules. To accurately
describe these networks, it is important to monitor multiple signals in
parallel. To this end we have developed a genetically encoded, FRET-based probe
that independently monitors both protein kinase A (PKA) and protein kinase C
(PKC) activity in vivo. Artificial, as well as physiological stimulants
produced a negative or positive change in FRET efficiency following PKA or PKC
activation respectively. Mutations of the phosphate accepting amino acids of
the PKC substrate yielded a probe that was sensitive to PKA activation alone.
Black, S. L., Stanley, W. A.,
Filipp, F. V., Bhairo, M., Verma, A., Wichmann, O., Sattler, M., Wilmanns, M.,
Schultz, C. (2005) Probing lipid and drug binding domains with fluorescent
dyes. J. Med. Chem., submitted.
Abstract: A series of 2- and 3-OH Nile red dyes was
prepared in order to generate water-soluble probes that could be used to probe
lipid binding to proteins. Various substitutions in positions 2-/3-, 6-, and
7-, shifted wavelengths while maintaining the environmental sensitivity of Nile
red. In order to increase the solubility of the dyes in aqueous solutions, we
attached butyric acid groups to the 2- or 3-OH position. In addition,
phenothiazine dyes, which exhibited particularly long excitation properties,
were synthesized and tested for the first time. All dyes showed Stoke’s shifts of 70-100 nm and changes in excitation and
emission of over 100 nm, depending on the hydrophobicity of the environment.
Binding studies with bovine serum albumin and the non-specific lipid transfer
protein SCP2, revealed emission changes of more than 30 nm upon binding to the
protein and a five-fold increase in emission intensity. Titration of the
dye-loaded proteins with various lipids or drugs replaced the dye and thereby
reversed the shift in wavelength intensity. This allowed us to estimate the
lipid binding affinity of the investigated proteins. For SCP2, isothermal
calorimetry (ITC) data verified the titration experiments. NMR titration
experiments of SCP2 with 1a revealed that the dye is bound within the lipid
binding pocket and competes with lipid ligands for this binding site. These
results give valuable insight into lipid and drug transport by proteins outside
and inside cells.
Shkrob M.A., Yanushevich Y.G.,
Chudakov D.M., Gurskaya N.G., Labas Y.A., Poponov S.Y., Mudrik N.N., Lukyanov
S., Lukyanov K.A. Far-red fluorescent proteins evolved from a blue
chromoprotein from Actinia equina. Biochem. J. 2005, 392, 649-654. Cover
illustration.
Abstract: Proteins of Green
Fluorescent Protein (GFP) family demonstrate a great spectral and phylogenetic
diversity. However, red-shifted GFP-like proteins are still of intense demand
for both basic and applied science. To obtain GFP-like chromoproteins with
red-shifted absorption we performed a broad search in blue-coloured Anthozoa
species. We revealed specimens of Beadlet Anemone Actinia equina exhibiting a
bright blue circle band at the edge of its basal disc. A novel blue
chromoprotein aeCP597 with absorption maximum at 597 nm determining the
colouration of the anemone basal disk was cloned. AeCP597 carries a chromophore
chemically identical to that of well-studied red fluorescent protein DsRed.
Thus, a strong 42-nm bathochromic shift of aeCP597 absorption compared to DsRed
is determined by peculiarities of chromophore environment. Site-directed and
random mutagenesis of aeCP597 resulted in far-red fluorescent mutants with
emission maxima at up to 663 nm. The most bright and stable mutant AQ143
possessed excitation-emission maxima at 595 and 655 nm, respectively. Thus,
aeCP597 and its fluorescent mutants set a new record of red-shifted absorption
and emission maxima among GFP-like proteins.
Lukyanov K.A., Chudakov D.M.,
Lukyanov S., Verkhusha V.V. Photoactivatable fluorescent proteins. Nature
Review Mol. Cell Biol. 2005, 6, 885-891.
Abstract: The fluorescence
characteristics of photoactivatable proteins can be controlled by irradiating
them with light of a specific wavelength, intensity and duration. This provides
unique possibilities for the optical labelling and tracking of living cells,
organelles and intracellular molecules in a spatio-temporal manner. Here, we discuss
the properties of the available photoactivatable fluorescent proteins and their
potential applications.
Chudakov D.M., Lukyanov S.,
Lukyanov K.A. Fluorescent proteins as a toolkit for in vivo imaging. Trends
Biotechnol. 2005, 23, 605-613.
Abstract: Green fluorescent protein
(GFP) from the jellyfish Aequorea victoria, and its mutant variants, are the
only fully genetically encoded fluorescent probes available and they have
proved to be excellent tools for labeling living specimens. Since 1999, numerous
GFP homologues have been discovered in Anthozoa, Hydrozoa and Copepoda species,
demonstrating the broad evolutionary and spectral diversity of this protein
family. Mutagenic studies gave rise to diversified and optimized variants of
fluorescent proteins, which have never been encountered in nature. This article
gives an overview of the GFP-like proteins developed to date and their most
common applications to study living specimens using fluorescence microscopy.
Chudakov D.M., Lukyanov K.A. (2005)
Using photoactivatable GFPs to study protein dynamics and function. In Jorde,
L.B., Little, P.F.R., Dunn, M.J. and Subramaniam, S. (Eds), Encyclopedia of
Genetics, Genomics, Proteomics and Bioinformatics. John Wiley & Sons Ltd:
Abstract: Green Fluorescent Protein
(GFP) from jellyfish Aequorea victoria, its mutants and homologues from other
organisms have become an integral part of modern methodology in cell and
molecular biology. GFP-like proteins represent the only genetically encoded
fluorescent tags that can be widely used to label organisms, cells, organelles,
and proteins. This review is focused on photoactivatable GFP-like proteins,
i.e. proteins capable of many-fold increase of fluorescence intensity at
certain excitation-emission wavelengths in response to irradiation with
specific light. Photoactivatable tags make it possible to "switch-on"
fluorescent signal by a beam of light in precisely chosen part of organism or
cell in order to track movement of the labeled objects. The spectral properties
and mechanisms of the photoactivation for the most experimentally useful
photoconvertible proteins are described in detail. In particular, we discuss GFP and its mutant
PA-GFP, green-to-red convertible protein Kaede from a stony coral Trachyphyllia
geoffroyi, and Kindling Fluorescent Protein (KFP) from a sea anemone Anemonia
sulcata. Considerable progress is still required to enrich the palette of
monomeric photoactivatable GFP-like proteins, that would extend the field of
possible applications.
Bulina M.E., Chudakov D.M.,
Britanova O.V., Yanushevich Y.G., Staroverov D.B., Chepurnykh T.V., Merzlyak
E.M., Shkrob M.A., Lukyanov S., Lukyanov K.A. Genetically encoded
photosensitizer. Nature Biotech. 2005, in press.
Abstract: Photosensitizers are
chromophores that convert light energy into reactive oxygen species (ROS)
production. Photosensitizers are used for the precise protein inactivation in
chromophore-assisted light inactivation (
A. D. Kim and M. Moscoso (2005)
Light transport in two-layered tissues, Journal of Biomedical Optics, 10,
034015.
Abstract: We study theoretically light backscattered by
tissues using the radiative transport equation. In particular we consider a
two-layered medium in which a finite slab is situated on top of a half space.
We solve the one dimensional problem in which a plane wave is incident normally
on the top layer and is the only source of light. The solution to this problem
is obtained formally by imposing continuity between the solutions for the upper
and lower layers. However, we are interested solely in probing the top layer.
Assuming that the optical properties in the lower layer are known, we remove it
from the problem yielding a finite slab problem by prescribing an alternate
boundary condition. This boundary condition is derived using the theory of
Green’s functions and is exact. Hence, one needs only to solve
the transport equation in a finite slab using this alternate boundary
condition. We derive an asymptotic solution for the case when the slab is
optically thin. We extend these results to the three dimensional problem using
Fourier transforms. These results are validated by comparisons with numerical
solutions for the entire two-layered problem.
A. D. Kim and M. Moscoso (2005),
Radiative transport theory for optical molecular imaging, accepted for
publication in “Inverse Problems”
Abstract: We study the inverse
fluorescent source problem for optical molecular imaging. In particular, we
recover key properties of a fluorescent source inside a halfspace composed of a
uniform absorbing and scattering medium from angularly resolved measurements at
the boundary plane. We use the radiative transport equation to model the
multiple scattering of light in tissues.
Using Green's function, given as an analytical expansion in plane wave
solutions, we subtract contributions from the measured angular data due to
surface sources yielding a quantity that depends only on the interior
fluorescent source. We analyse this reduced problem and obtain explicit
solutions for a point source and a voxel source. Using the point source and
voxel source solutions, we estimate the locations, size and total strength of a
general source. We perform numerical studies to validate
this theory as well as investigate
modelling errors due to incorrectly asumed optical properties of the medium.
M. Schweiger, S. R. Arridge, O.
Dorn, A. Zacharopoulos, V. Kolehmainen (2005), Reconstructing absorption and
diffusion shape profiles in optical tomography using a level set technique,
accepted by 'Optics Letters'
Abstract: A novel shape
reconstruction algorithm for optical tomography is introduced which uses a
level-set formulation for the
shapes. Evolution laws based on
gradient directions for a cost functional are derived for two different
level-set functions, one
describing the absorption and one
the diffusion parameter, as well as for the parameter values inside these
shapes. Numerical experiments are
presented in 2-D which show that the new method is able to simultaneously
recover shapes and contrast values of absorbing and scattering objects embedded
in a moderately heterogeneous background medium from simulated noisy data.
Schlacher, K., K. Leslie, C. Wyman,
R. Woodgate, M. Cox, and M.F. Goodman. (2005) DNA polymerase V and RecA
protein, a minimal mutasome. Molec.
Cell, 17, p. 561-572.
Abstract: A hallmark of the Escherichia coli SOS response
is the large increase in mutations caused by translesion synthesis (TLS). TLS requires DNA polymerase V (UmuD’2C) and RecA. Here
we show that pol V and RecA interact by two distinct mechanisms. First, pol V binds to RecA through its UmuC
subunit in the absence of DNA and ATP, and second through its UmuD’ subunit in the presence of DNA and ATP, without ATP
hydrolysis. DNA synthesis using RecA
mutants with increased affinity for single-stranded DNA reveals that any
additional RecA bound to DNA inhibits TLS.
Therefore, a RecA nucleoprotein filament is unlikely to be required for
SOS mutagenesis. The activity of polV in
vitro is greatly diminished in the absence of RecA or in the presence of
RecA1730, a mutant defective for pol V mutagenesis in vivo, suggesting that
RecA is an obligate accessory factor that activates pol V for SOS
mutagenesis.
David de Juan,
Hernanz-Falcon, P., Rodriguez-Frade,
JM., Serrano, A., Martinez-A., C. and Mellado, M.
On the dimerization of CCR5. Nat. Immunol. 6:535-536 (2005) .
Juan Luis Garcia-Pomar and Manuel
Nieto-Vesperinas, "Imaging of extended objects by a negative refractive
index slab ". New Journal of
Physics 7, 160 (2005).
Using a finite element method, we
numerically study the imaging of an extended object by slabs of media with
negative refractive index (within an effective medium theory). We analyse the
consequences of possible deviations of the refractive index of the slab from
the archetypal value of n = -1. These variations are obtained by introducing
losses in the material and also by changing the real part of n. In this way, we
show how slight changes in the refractive index from n = -1 affect the
resolution of the image of the extended object.
J. L. Garcia-Pomar and M.
Nieto-Vesperinas, "Waveguiding,
collimation and subwavelength concentration in photonic crystals". Optics Express 13, 7998 (2005).
By means of both finite elements
and FDTD calculations, we demonstrate that a structure of photonic crystal,
constituted by two dimensional arrays of dielectric cylinders in air, or
viceversa, previously proposed as capable of producing negative refraction with
superlensing properties and subsequently proved to lack this characteristic, do
possesses however the property of giving rise to effects of total internal
reflection that allow both waveguiding, bending and collimation with high
intensity subwavelength concentration of wavefronts. This is a consequence of
both the dominant propagation along the ΓM direction due to
diffraction, and of intensity localization in the cylinder regions as a result
of the operating frequency being in the lower part of the bandgap, namely, in
the so-called dielectric band.
P.C. Chaumet, A. Rahmani and M.
Nieto-Vesperinas, "Photonic force spectroscopy on metallic and absorbing
nanoparticles"
PHYSICAL REVIEW B 71, 045425
(2005).
We present a detailed study of the
optical trapping and manipulation of nanoparticles with complex permittivity
using an apertureless near-field probe. We use a three-dimensional,
self-consistent description of the electromagnetic scattering processes that
accounts for retardation and the intricate many-body interaction between the
substrate, the particle, and the probe. We analyze the influence of absorption
on the optical force. For metals we describe how the optical force spectrum is
influenced by the optical response of the metal, and in particular by plasmon
resonances. We find that the optical force spectrum can provide an intrinsic
signature of the particle composition which can be used to achieve a
material-selective trapping and nanomanipulation.
S. E. Sburlan, L. A. Blanco, and M.
Nieto-Vesperinas, "Plasmon excitation in sets of nanoscale cylinders and
spheres", Physical Review B (in press).
By means of the boundary element
method, we calculate and interpret the spectral lineshapes and near field
spatial distributions of sets of a few nanospheres and nanocylinders on
illumination close to the plasmon polariton excitation wavelength. This
collective behavior is studied versus that of one isolated particle.
Comparisons with results from previous experiments are done. As far as cylinders are concerned, our
procedure goes beyond former calculations based on the quasi-electrostatic
approximation and, hence, it is exact. It allows to address mixtures of a few
of these particles with different sizes providing the configuration possesses
axial symmetry. In particular, configurations with nanoantenna behavior are
discussed. Finally, we discuss in terms of the direction of propagation and
polarization of the incident wave, both the spectral and spatial field
distributions of a chain of three self-similar metallic nanospheres whose
plasmon eigenmodes were previously analytically obtained and whose properties
of
nanofocusing were predicted.
S. Ioanid, Ming Bai and N. Garcia,
etc. Light Collimation and focusing by a thin flat metallic slab, Opt. Lett.
30, 2317 (2005)
H. Mathee et. al. (2005),
'Nanostructure of specific chromatin regions and nuclear complexes', Histochem
Cell Biol (online available)
C. Wagner et. al. (2005), 'Beyond
nanosizing: an approach to shape analysis of fluorescent nanostructures by
SMI-microscopy', Optik (in press)