232 research outputs found
Singular-phase nanooptics: towards label-free single molecule detection
Non-trivial topology of phase is crucial for many important physics phenomena
such as, for example, the Aharonov-Bohm effect 1 and the Berry phase 2. Light
phase allows one to create "twisted" photons 3, 4 , vortex knots 5,
dislocations 6 which has led to an emerging field of singular optics relying on
abrupt phase changes 7. Here we demonstrate the feasibility of singular
visible-light nanooptics which exploits the benefits of both plasmonic field
enhancement and non-trivial topology of light phase. We show that properly
designed plasmonic nanomaterials exhibit topologically protected singular phase
behaviour which can be employed to radically improve sensitivity of detectors
based on plasmon resonances. By using reversible hydrogenation of graphene 8
and a streptavidin-biotin test 9, we demonstrate areal mass sensitivity at a
level of femto-grams per mm2 and detection of individual biomolecules,
respectively. Our proof-of-concept results offer a way towards simple and
scalable single-molecular label-free biosensing technologies.Comment: 19 pages, 4 figure
Nanofabrication with Pulsed Lasers
An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser–matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics
Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Virtually Unlimited Sensitivity
Due to the absence of labels and fast analyses, optical biosensors promise
major advances in biomedical diagnostics, security, environmental and food
safety applications. However, sensitivity of the most advanced plasmonic
biosensor implementations has a fundamental limitation caused by losses in the
system and or geometry of biochips. Here, we report a scissor effect in
topologically dark metamaterials which is capable of providing virtually
unlimited bona fide sensitivity to biosensing thus solving the bottleneck
sensitivity limitation problem. We explain how the scissor effect can be
realized via a proper design of topologically dark metamaterials and describe
strategies for their fabrication. To validate the applicability of this effect
in biosensing, we demonstrate the detection of folic acid (vitamin important
for human health) in the wide 3-log linear dynamic range with the limit of
detection of 0.125 nM, which is orders of magnitude better than previously
reported for all optical counterparts. Our work opens possibilities for
designing and realising plasmonic, semiconductor and dielectric metamaterials
with ultra-sensitivity to binding events.Comment: 22 pages, 4 figure
Topological photonics with scattering media
Scattering media, being ubiquitous in nature and critically important for
assessments (e.g., biological tissues), are often considered as nuisance in
optics. Here we show that it is not always the case and scattering media could
be essential in providing elements of topological photonics. We demonstrate
that topological darkness can be realised in the presence of scattering media
due to the transverse nature of electromagnetic waves and the hairy ball
theorem. We describe realizations of topological darkness in a scattering
medium comprising composite gold nanostructures produced by a low-cost
technique of laser structuring of thin metal films. Our results can be useful
for a variety of tasks, including topological nanophotonics, optical label-free
biosensing, and biomedical photonics
Boosting the Figure Of Merit of LSPR-based refractive index sensing by phase-sensitive measurements
Localized surface plasmon resonances possess very interesting properties for
a wide variety of sensing applications. In many of the existing applications
only the intensity of the reflected or transmitted signals is taken into
account, while the phase information is ignored. At the center frequency of a
(localized) surface plasmon resonance, the electron cloud makes the transition
between in- and out-of-phase oscillation with respect to the incident wave.
Here we show that this information can experimentally be extracted by
performing phase-sensitive measurements, which result in linewidths that are
almost one order of magnitude smaller than those for intensity based
measurements. As this phase transition is an intrinsic property of a plasmon
resonance, this opens up many possibilities for boosting the figure of merit
(FOM) of refractive index sensing by taking into account the phase of the
plasmon resonance. We experimentally investigated this for two model systems:
randomly distributed gold nanodisks and gold nanorings on top of a continuous
gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5
for the respective nanoparticles
Biocompatibility of Bare Nanoparticles Based on Silicon and Gold for Nervous Cells
This work aimed to investigate the biocompatibility of bare (ligand-free) lasersynthesized nanoparticles (NPs) based on silicon (Si) and gold (Au) with primary hippocampal cultures. 1%, 5% and 7% of culture medium were replaced by 0.1 mg/mL NP solution on day 14 of culture development in vitro. Our studies revealed that the NPs caused a dose-dependent cytotoxic effect, which was manifested by an increase the number of dead cells and a decrease of the spontaneous functional calcium activity of neural networks. Au NPs revealed less pronounced cytotoxic effect than Si ones and it can be explained by larger size and better solubility of Si NPs.
Keywords: bare nanoparticles, primary hippocampal cultures, neurotoxicit
Concave Plasmonic Particles: Broad-Band Geometrical Tunability in the Near Infra-Red
Optical resonances spanning the Near and Short Infra-Red spectral regime were
exhibited experimentally by arrays of plasmonic nano-particles with concave
cross-section. The concavity of the particle was shown to be the key ingredient
for enabling the broad band tunability of the resonance frequency, even for
particles with dimensional aspect ratios of order unity. The atypical
flexibility of setting the resonance wavelength is shown to stem from a unique
interplay of local geometry with surface charge distributions
Analysis of the structure, configuration, and sizing of Cu and Cu oxide nanoparticles generated by fs laser ablation of solid target in liquids
We report on the analysis of structure, configuration, and sizing of Cu and Cu oxide nanoparticles (Nps) produced by femtosecond (fs) laser ablation of solid copper target in liquids. Laser pulse energy ranged between 500 µJ and 50 µJ. Water and acetone were used to produce the colloidal suspensions. The study was performed through optical extinction spectroscopy using Mie theory to fit the full experimental spectra, considering free and bound electrons size dependent contributions to the metal dielectric function. Raman spectroscopy and AFM technique were also used to characterize the sample. Considering the possible oxidation of copper during the fabrication process, two species (Cu and Cu2O) arranged in two structures (bare core or core-shell) and in two configuration types (Cu-Cu2O or Cu2O-Cu) were considered for the fitting depending on the laser pulse energy and the surrounding media. For water at high energy, it can be observed that a Cu-Cu2O configuration fits the experimental spectra of the colloidal suspension, while for decreasingenergy and below a certain threshold, a Cu2O-Cu configuration needs to be included for theoptimum fit. Both species coexist for energies below 170 µJ for water. On the other hand, for acetone at high energy, optimum fit of the full spectrum suggests the presence a bimodal Cu-Cu2O core-shell Nps distribution while for decreasing energy and below a 70 µJ threshold energy value, Cu2O-Cu core-shell Nps must be included, together with the former configuration, for the fit of the full spectrum. We discuss possible reasons for the changes in the structural configuration of the core-shell Nps.Fil: Schinca, Daniel Carlos. Universidad Nacional de la Plata. Facultad de Cs.exactas. Instituto de Fisica de la Plata; ArgentinaFil: Videla, Fabian Alfredo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico la Plata. Centro de Investigaciones Opticas (i); ArgentinaFil: Fernández van Raap, Marcela Beatriz. Universidad Nacional de la Plata. Facultad de Ingenieria; ArgentinaFil: Scaffardi, Lucia Beatriz. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico la Plata. Centro de Investigaciones Opticas (i); ArgentinaFil: Santillán, Jesica MarĂa JosĂ©. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico la Plata. Centro de Investigaciones Opticas (i); Argentin
Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics
Recent developments in the area of resonant dielectric nanostructures have created attractive opportunities for concentrating and manipulating light at the nanoscale and the establishment of the new exciting field of all-dielectric nanophotonics. Transition metal dichalcogenides (TMDCs) with nanopatterned surfaces are especially promising for these tasks. Still, the fabrication of these structures requires sophisticated lithographic processes, drastically complicating application prospects. To bridge this gap and broaden the application scope of TMDC nanomaterials, we report here femtosecond laser-ablative fabrication of water-dispersed spherical TMDC (MoS2 and WS2) nanoparticles (NPs) of variable size (5 to 250 nm). Such NPs demonstrate exciting optical and electronic properties inherited from TMDC crystals, due to preserved crystalline structure, which offers a unique combination of pronounced excitonic response and high refractive index value, making possible a strong concentration of electromagnetic field in the NPs. Furthermore, such NPs offer additional tunability due to hybridization between the Mie and excitonic resonances. Such properties bring to life a number of nontrivial effects, including enhanced photoabsorption and photothermal conversion. As an illustration, we demonstrate that the NPs exhibit a very strong photothermal response, much exceeding that of conventional dielectric nanoresonators based on Si. Being in a mobile colloidal state and exhibiting superior optical properties compared to other dielectric resonant structures, the synthesized TMDC NPs offer opportunities for the development of next-generation nanophotonic and nanotheranostic platforms, including photothermal therapy and multimodal bioimaging
Resonances On-Demand for Plasmonic Nano-Particles
A method for designing plasmonic particles with desired resonance spectra is
presented. The method is based on repetitive perturbations of an initial
particle shape while calculating the eigenvalues of the various quasistatic
resonances. The method is rigorously proved, assuring a solution exists for any
required spectral resonance location. Resonances spanning the visible and the
near-infrared regimes, as designed by our method, are verified using
finite-difference time-domain simulations. A novel family of particles with
collocated dipole-quadrupole resonances is designed, demonstrating the unique
power of the method. Such on-demand engineering enables strict realization of
nano-antennas and metamaterials for various applications requiring specific
spectral functions
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