Non-centrosymmetric nanostructures consisting of multiple functional subunits represents an emerging class of hybrid nanostructures that can possess dramatic difference in property and functionality from concentric core-shell configuration. Here we develop a general synthetic method to achieve hierarchical control of high-order non-centrosymmetric hybrid nanostructures. The key is to employ a common intermedium for sequential conversion to all distinct predesigned subunits under similar growth condition, thus facilitating manifold control of a hybrid nanostructure. This advancement leads to an optimally designed plasmon-mediated photocatalytic nanostructure with 14.8-fold enhancement of photocatalytic efficiency as compared with conventional photocatalysts. Mechanistic study involving theoretical modelling and ultrafast time-resolved optical measurement uncovers a hot plasmonic electron-driven photocatalysis mechanism with an identified electron transfer pathway. This study may represent an important step towards high-level control of artificial nanostructures with new horizons for fundamental and technological applications.
Nanocomposites of colloidal quantum dots (QDs) integrated into conjugated polymers (CPs) are key to hybrid optoelectronics, where engineering the excitonic interactions at the nanoscale is crucial. For such excitonic operation, it was believed that exciton diffusion is essential to realize nonradiative energy transfer from CPs to QDs. In this study, contrary to the previous literature, efficient exciton transfer is demonstrated in the nanocomposites of dense QDs, where exciton transfer can be as efficient as 80% without requiring the assistance of exciton diffusion. This is enabled by uniform dispersion of QDs at high density (up to ?70 wt%) in the nanocomposite while avoiding phase segregation. Theoretical modeling supports the experimental observation of weakly temperature dependent nonradiative energy transfer dynamics. This new finding provides the ability to design hybrid light-emitting diodes that show an order of magnitude enhanced external quantum efficiencies.
Strong epidemiologic evidence supports correlation between lower urinary tract symptoms due to benign prostatic hyperplasia (LUTS/BPH) and erectile dysfunction (ED). The link has biologic plausibility given phosphodiesterase type 5 (PDE5) expression in pelvic structures. PDE5 inhibitors target pathophysiologic processes implicated in LUTS/BPH.
Inflammation has been suggested to be involved in the pathogenesis of benign prostatic hyperplasia (BPH). We studied the prevalence of inflammation and BPH in Asian and Caucasian men on prostate glands (n=320) obtained during autopsy in Moscow, Russia (Caucasian men, n=220), and Tokyo, Japan (Asian men, n=100). We correlated the presence and grade of acute inflammation (AI) or chronic inflammation (CI) and BPH. AI, CI, and histologic BPH were analyzed in a blinded fashion using a grading system (0-3). We used the Cochran-Armitage test for associations between the degree of BPH and clinical variables and proportional odds logistic regression models in multivariable analysis. Histologic BPH was observed in a similar proportion of Asian and Caucasian men (p=0.94). CI was found in>70% of men in both the Asian and Caucasian groups (p>0.05). Higher BPH scores were associated with more CI (p<0.001). In multivariate analyses, individuals with CI were 6.8 times more likely to have a higher BPH score than individuals without (p<0.0001). Men included in this study presented at the hospital and their symptomatic status was not known. The prevalence of CI and BPH on autopsy is similar in Asian and Caucasian men despite very different diet and lifestyle. CI is strongly associated in both groups with BPH.
A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules.
The phase transformation properties of liquid water to vapor is characterized by optical excitation of the lithographically fabricated single gold nanowrenches and contrasted to the phase transformation properties of gold nanoparticles located and optically excited in a bulk solution system [two and three dimensions]. The 532 nm continuous wave excitation of a single gold nanowrench results in superheating of the water to the spinodal decomposition temperature of 580 ± 20 K with bubble formation below the spinodal decomposition temperature being a rare event. Between the spinodal decomposition temperature and the boiling point liquid water is trapped into a metastable state because a barrier to vapor nucleation exists that must be overcome before the thermodynamically stable state is realized. The phase transformation for an optically heated single gold nanowrench is different from the phase transformation of optically excited colloidal gold nanoparticles solution where collective heating effects dominates and leads to the boiling of the solution exactly at the boiling point. In the solution case, the optically excited ensemble of nanoparticles collectively raises the ambient temperature of water to the boiling point where liquid is converted into vapor. The striking difference in the boiling properties of the single gold nanowrench and the nanoparticle solution system can be explained in terms of the vapor-nucleation mechanism, the volume of the overheated liquid, and the collective heating effect. The interpretation of the observed regimes of heating and vaporization is consistent with our theoretical modeling. In particular, we explain with our theory why the boiling with the collective heating in a solution requires 3 orders of magnitude less intensity compared to the case of optically driven single nanowrench.
Modern technology is founded on the intimate understanding of how to utilize and control electrons. Next to electrons, nature uses phonons, quantized vibrations of an elastic structure, to carry energy, momentum and even information through solids. Phonons permeate the crystalline components of modern technology, yet in terms of technological utilization phonons are far from being on par with electrons. Here we demonstrate how phonons can be employed to render a single quantum dot pair optically transparent. This phonon-induced transparency is realized via the formation of a molecular polaron, the result of a Fano-type quantum interference, which proves that we have accomplished making typically incoherent and dissipative phonons behave in a coherent and non-dissipative manner. We find the transparency to be widely tunable by electronic and optical means. Thereby we show amplification of weakest coupling channels. We further outline the molecular polaron's potential as a control element in phononic circuitry architecture.
A reconfigurable plasmonic nanosystem combines an active plasmonic structure with a regulated physical or chemical control input. There have been considerable efforts on integration of plasmonic nanostructures with active platforms using top-down techniques. The active media include phase-transition materials, graphene, liquid crystals and carrier-modulated semiconductors, which can respond to thermal, electrical and optical stimuli. However, these plasmonic nanostructures are often restricted to two-dimensional substrates, showing desired optical response only along specific excitation directions. Alternatively, bottom-up techniques offer a new pathway to impart reconfigurability and functionality to passive systems. In particular, DNA has proven to be one of the most versatile and robust building blocks for construction of complex three-dimensional architectures with high fidelity. Here we show the creation of reconfigurable three-dimensional plasmonic metamolecules, which execute DNA-regulated conformational changes at the nanoscale. DNA serves as both a construction material to organize plasmonic nanoparticles in three dimensions, as well as fuel for driving the metamolecules to distinct conformational states. Simultaneously, the three-dimensional plasmonic metamolecules can work as optical reporters, which transduce their conformational changes in situ into circular dichroism changes in the visible wavelength range.
Several reports have shown that patients who undergo minimally invasive radical prostatectomy have a lower chance of undergoing pelvic lymph node dissection (PLND), irrespective of the disease characteristics.
3D plasmonic chiral colloids are synthesized through deterministically grouping of two gold nanorod AuNRs on DNA origami. These nanorod crosses exhibit strong circular dichroism (CD) at optical frequencies which can be engineered through position tuning of the rods on the origami. Our experimental results agree qualitatively well with theoretical predictions.
We study phonon-assisted Förster resonance energy transfer (FRET) into an indirect band-gap semiconductor using nanoemitters. The unusual temperature dependence of this energy transfer, which is measured using the donor nanoemitters of quantum dot (QD) layers integrated on the acceptor monocrystalline bulk silicon as a model system, is predicted by a phonon-assisted exciton transfer model proposed here. The model includes the phonon-mediated optical properties of silicon, while considering the contribution from the multimonolayer-equivalent QD film to the nonradiative energy transfer, which is derived with a d(-3) distance dependence. The FRET efficiencies are experimentally observed to decrease at cryogenic temperatures, which are well explained by the model considering the phonon depopulation in the indirect band-gap acceptor together with the changes in the quantum yield of the donor. These understandings will be crucial for designing FRET-enabled sensitization of silicon based high-efficiency excitonic systems using nanoemitters.
Chirality of plasmonic films can be strongly enhanced by three-dimensional (3D) out-of-plane geometries. The complexity of lithographic methods currently used to produce such structures and other methods utilizing chiral templates impose limitations on spectral windows of chiroptical effects, the size of substrates, and hence, further research on chiral plasmonics. Here we demonstrate 3D chiral plasmonic nanostructures (CPNs) with high optical activity in the visible spectral range based on initially achiral nanopillars from ZnO. We made asymmetric gold nanoshells on the nanopillars by vacuum evaporation at different inclination and rotation angles to achieve controlled symmetry breaking and obtained both left- and right-rotating isomers. The attribution of chiral optical effects to monolithic enantiomers made in this process was confirmed by theoretical calculations based on their geometry established from scanning electron microscope (SEM) images. The chirality of the nanoshells is retained upon the release from the substrate into a stable dispersion. Deviation of the incident angle of light from normal results in increase of polarization rotation and chiral g-factor as high as -0.3. This general approach for preparation of abiological nanoscale chiral materials can be extended to other out-of plane 3D nanostructures. The large area films made on achiral nanopillars are convenient for sensors, optical devices, and catalysis.
Circular dichroism spectra of naturally occurring molecules and also of synthetic chiral arrangements of plasmonic particles often exhibit characteristic bisignate shapes. Such spectra consist of peaks next to dips (or vice versa) and result from the superposition of signals originating from many individual chiral objects oriented randomly in solution. Here we show that by first aligning and then toggling the orientation of DNA-origami-scaffolded nanoparticle helices attached to a substrate, we are able to reversibly switch the optical response between two distinct circular dichroism spectra corresponding to either perpendicular or parallel helix orientation with respect to the light beam. The observed directional circular dichroism of our switchable plasmonic material is in good agreement with predictions based on dipole approximation theory. Such dynamic metamaterials introduce functionality into soft matter-based optical devices and may enable novel data storage schemes or signal modulators.
Substantial geographical differences in prostate cancer (PCa) incidence and mortality exist, being lower among Asian (ASI) men compared with Caucasian (CAU) men. We prospectively compared PCa prevalence in CAU and ASI men from specific populations with low penetrance of prostate-specific antigen screening.
One of the most intriguing structural properties, chirality, is often exhibited by organic and bio-organic molecular constructs. Chiral spectral signatures, typically appearing in the UV range for organic materials and known as circular dichroism (CD), are widely used to probe a molecular stereometry. Such probing has an increasingly broad importance for biomedical and pharmacological fields due to synthesis/separation/detection of homochiral species, biological role of chiral organization, and structural response to environmental conditions and enantiomeric drugs. Recent theoretical and experimental works demonstrated that the CD signal from chiral organic molecules could appear in the plasmonic (typically, visible) band when they coupled with plasmonic particles. However, the magnitude of this CD signal, induced by discrete nonchiral plasmonic particles, and its native molecular analog were found to be comparable. Here we show that shaped nonchiral nanoparticles, namely, gold/silver core/shell nanocubes, can act as plasmonic reporters of chirality for attached molecules by providing a giant, 2 orders of magnitude CD enhancement in a near-visible region. Through the experimental and theoretical comparison with nanoparticles of other shapes and materials, we demonstrate a uniqueness of silver nanocube geometry for the CD enhancement. The discovered phenomenon opens novel opportunities in ultrasensitive probing of chiral molecules and for novel optical nanomaterials based on the chiral elements.
This paper reviews the recent advances in experiment and theory of the induction of chiroptical effects, primarily circular dichroism (CD), at the plasmonic and excitonic resonances of achiral inorganic nanocrystals (NCs) capped and/or formed with chiral molecules. It also addresses stronger chiroptical effects obtained in intrinsically chiral inorganic nanostructures obtained from growing enantiomeric excess of intrinsically chiral NCs or arranging achiral plasmonic particles in chiral configurations. The accumulated experimental data and theory on various CD induction mechanisms provide an extended set of tools to properly analyze and understand the electromagnetic influence of chiral molecules on inorganic particles and obtain new general insights into the interaction of capping molecules with inorganic NCs. Among the field-induced CD mechanisms developed recently one can name the Coulomb (near-field, dipolar) mechanism for nanostructures much smaller than the wavelength, and for larger nanostructures, the electromagnetic (effective chiral medium), and intrinsically chiral plasmonic mechanisms.
DNA nanotechnology is a rapidly developing research area in nanoscience. It includes the development of DNA machines, tailoring of DNA nanostructures, application of DNA nanostructures for computing, and more. Different DNA machines were reported in the past and DNA-guided assembly of nanoparticles represents an active research effort in DNA nanotechnology. Several DNA-dictated nanoparticle structures were reported, including a tetrahedron, a triangle or linear nanoengineered nanoparticle structures; however, the programmed, dynamic reversible switching of nanoparticle structures and, particularly, the dictated switchable functions emerging from the nanostructures, are missing elements in DNA nanotechnology. Here we introduce DNA catenane systems (interlocked DNA rings) as molecular DNA machines for the programmed, reversible and switchable arrangement of different-sized gold nanoparticles. We further demonstrate that the machine-powered gold nanoparticle structures reveal unique emerging switchable spectroscopic features, such as plasmonic coupling or surface-enhanced fluorescence.
Size- and shape-controlled synthesis of copper chalcogenide nanocrystals (NCs) is of paramount importance for a careful engineering and understanding of their optoelectronic properties and, thus, for their exploitation in energy- and plasmonic-related applications. From the copper chalcogenide family copper telluride NCs have remained fairly unexplored as a result of a poor size-, shape-, and monodispersity control that is achieved via one-step syntheses approaches. Here we show that copper telluride (namely Cu(2-x)Te) NCs with well-defined morphologies (spheres, rods, tetrapods) can be prepared via cation exchange of preformed CdTe NCs while retaining their original shape. The resulting copper telluride NCs are characterized by pronounced plasmon bands in the near-infrared (NIR), in analogy to other copper-deficient chalcogenides (Cu(2-x)S, Cu(2-x)Se). We demonstrate that the extinction spectra of the as-prepared NCs are in agreement with theoretical calculations based on the discrete dipole approximation and an empirical dielectric function for Cu(2-x)Te. Additionally we show that the Drude model does not appropriately describe the complete set of Cu(2-x)Te NCs with different shapes. In particular, the low-intensity longitudinal plasmon bands for nanorods and tetrapods are better described by a modified Drude model with an increased damping in the long-wavelength interval. Importantly, a Lorentz model of localized quantum oscillators describes reasonably well all three morphologies, suggesting that holes in the valence band of Cu(2-x)Te cannot be described as fully free particles and that the effects of localization of holes are important. A similar behavior for Cu2-xS and Cu(2-x)Se NCs suggests that the effect of localization of holes can be a common property for the whole class of copper chalcogenide NCs. Taken altogether, our results represent a simple route toward copper telluride nanocrystals with well-defined shapes and optical properties and extend the understanding on vacancy-doped copper chalcogenide NCs with NIR optical resonances.
Chiral molecules are shown to induce circular dichroism (CD) at surface plasmon resonances of gold nanostructures when in proximity to the metal surface without direct bonding to the metal. By changing the molecule-Au separation, we were able to learn about the mechanism of plasmonic CD induction for such nanostructures. It was found that even two monolayers of chiral molecules can induce observable plasmonic CD, while without the presence of the plasmonic nanostructures their own CD signal is unmeasurable. Hence, plasmonic arrays could offer a route to enhanced sensitivity for chirality detection.
Coherently coupled plasmons and excitons give rise to new optical excitations--plexcitons--due to the strong coupling of these two oscillator systems. Time-resolved studies of J-aggregate-Au nanoshell complexes when the nanoshell plasmon and J-aggregate exciton energies are degenerate probe the dynamical behavior of this coupled system. Transient absorption of the interacting plasmon-exciton system is observed, in dramatic contrast to the photoinduced transmission of the pristine J-aggregate. An additional, transient Fano-shaped modulation within the Fano dip is also observable. The behavior of the J-aggregate-Au nanoshell complex is described by a combined one-exciton and two-exciton state model coupled to the nanoshell plasmon.
Nature is remarkable at tailoring the chirality of different biomolecules to suit specific functions. Chiral molecules can impart optical activity to achiral materials in the form of the particles electronic transition frequency. Herein, we used peptides of differing secondary structures (random coil and ?-helix) to artificially create optically active chiral gold nanoparticles through peptide-nanoparticle interactions as observed by circular dichroism (CD) spectroscopy. This interaction produces a CD signal at the plasmon resonance frequency (?520 nm) of the chiral peptide-nanoparticle complex. Aggregation of the peptide-coated nanoparticles using metal ions results in a red-shifted plasmonic CD response. Our results suggest that chiroptical properties of nanomaterials can be engineered using peptides.
We describe from the theoretical point of view a plasmonic mechanism of optical activity in chiral complexes composed of metal nanoparticles (NPs). In our model, the circular dichroism (CD) signal comes from the Coulomb interaction between NPs. We show that the CD spectrum is very sensitive to the geometry and composition of a chiral complex and also has typically both positive and negative bands. In our calculations, the strongest CD signals were found for the helix geometry resembling helical structures of many biomolecules. For chiral tetramers and pyramids, the symmetry of a frame of a complex is very important for the formation of a strong CD response. Chiral natural molecules (peptides, DNA, etc.) often have strong CD signals in the UV range and typically show weak CD responses in the visible range of photon energies. In contrast to the natural molecules, the described mechanism of plasmonic CD is able to create strong CD signals in the visible wavelength range. This plasmonic mechanism offers a unique possibility to design colloidal and other nanostructures with strong optical chirality.
The photosystem I (PS I) protein is one of natures most efficient light harvesting complexes and exhibits outstanding optoelectronic properties. Here we demonstrate how metal nanoparticles which act as artificial antennas can enhance the light absorption of the protein. This hybrid system shows an increase in light absorption and of circular dichroism over the entire absorption band of the protein rather than at the specific plasmon resonance wavelength of spherical metal nanoparticles (NPs). This is explained by broad-resonant and nonresonant field enhancements caused by metal NP aggregates, by the high dielectric constant of the metal, and by NP-PS I-NP antenna junctions which effectively enhance light absorption in the PS I.
Our calculations show that a nonchiral nanocrystal is able to dramatically change the circular dichroism (CD) of a chiral molecule when the nanocrystal and molecule form a complex and couple via dipole and multipole Coulomb interactions. Plasmon resonances of metal nanocrystals in the nanocrystal-molecule complex result in both the resonant enhancement of CD signals of molecules and the appearance of new spectral structures. Two mechanisms, in which a nanocrystal can influence the CD effect, have been identified. The first mechanism is the plasmon-induced change in the electromagnetic field inside the chiral molecule. The second is the optical absorption of the nanocrystal-molecule complex due to the chiral currents inside the metal nanocrystal induced by the dipole of the chiral molecule. The first mechanism creates a change in the angle between the effective electric and magnetic dipoles of the molecule. This mechanism can lead to symmetry breaking and to a plasmon-induced CD signal of the nonchiral molecule. Both mechanisms create interesting Fano-like shapes in the CD spectra. Importantly, the second mechanism gives the main contribution to the CD signal at the plasmon frequency when the absorption band of the chiral molecule is far from the plasmon resonance. This may happen in many cases since many biomolecules are optically active in the UV range, whereas plasmon resonances in commonly used nanometals are found at longer wavelengths. As concrete examples, the paper describes alpha-helix and calixarene ligand molecules coupled with metal nanocrystals. The above results are also applied to complexes incorporating semiconductor nanocrystals. The results obtained here can be used to design a variety of hybrid nanostructures with enhanced and tailored optical chirality in the visible wavelength range.
The 6th Meeting of the European Society of Oncological Urology (chaired by Vincent Ravery, Paris, France) was held in Istanbul, Turkey, on 16-18 January 2009 and gathered more than 600 participants from 44 countries. Topics encompassed a number of uro-oncological issues, including prostatic carcinoma and bladder, renal and testicular cancers. The conference, in addition to its exciting scientific program and contribution from a highly prestigious international faculty, also included a series of debates and interactive voting dealing with the latest surgical and medical developments in the field of oncological urology.
We perform a set of experiments on photoheating in a water droplet containing gold nanoparticles (NPs). Using photocalorimetric methods, we determine efficiency of light-to-heat conversion (eta) which turns out to be remarkably close to 1, (0.97 < eta < 1.03). Detailed studies reveal a complex character of heat transfer in an optically stimulated droplet. The main mechanism of equilibration is due to convectional flow. Theoretical modeling is performed to describe thermal effects at both nano- and millimeter scales. Theory shows that the collective photoheating is the main mechanism. For a large concentration of NPs and small laser intensity, an averaged temperature increase (at the millimeter scale) is significant (approximately 7 degrees C), whereas on the nanometer scale the temperature increase at the surface of a single NP is small (approximately 0.02 degrees C). In the opposite regime, that is, a small NP concentration and intense laser irradiation, we find an opposite picture: a temperature increase at the millimeter scale is small (0.1 degrees C) but a local, nanoscale temperature has strong local spikes at the surfaces of NPs (approximately 3 degrees C). These studies are crucial for the understanding of photothermal effects in NPs and for their potential and current applications in nano- and biotechnologies.
Silver nanoparticles were prepared in aqueous solutions of chiral supramolecular structures made of chiral molecular building blocks. While these chiral molecules display negligible circular dichroism (CD) as isolated molecules, their stacking produced a significant CD response at room temperature, which could be eliminated by heating to 80 °C due to disordering of the stacks. The chiral stack-plasmon coupling has induced CD at the surface plasmon resonance absorption band of the silver nanoparticles. Switching between two plasmonic CD induction mechanisms was observed: (1) Small Ag nanoparticles coated with large molecular stacks, where the induced plasmonic CD decayed together with the UV molecular CD bands on heating the solution, indicating some type of electromagnetic or dipole coupling mechanism. (2) Larger Ag nanoparticles coated with about a monolayer of molecules exhibited induced plasmonic CD that was temperature-independent. In this case it is estimated that the low chiroptical response of a molecular monolayer is incapable of inducing such a large chiroptical effect, and a model calculation shows that the plasmonic CD response may be the result of a slight chiral shape distortion of the silver nanoparticles.
The life is inherently chiral. Consequently, chirality plays a pivotal role in biochemistry and the evolution of life itself. Optical manifestation of chirality of biomolecules, so-called circular dichroism, is a remarkable but relatively weak effect appearing typically in the UV. In contrast to the biomolecules, plasmonic nanocrystals offer an interesting opportunity to create strong circular dichroism (CD) in the visible spectral range. Here we describe plasmonic properties of single chiral nanocrystals and focus on a new mechanism of optical chirality originating from a chiral shape of a nanocrystal. After careful examination, we found that this CD mechanism is induced by the mixing between different plasmon harmonics and is qualitatively different from the previously described dipolar CD effect in chiral assemblies of spherical nanoparticles. Chiral plasmonic nanocrystals studied here offer a new approach for the creation of nanomaterials with strong chiroptical responses in the visible spectral interval.
Matter structured on a length scale comparable to or smaller than the wavelength of light can exhibit unusual optical properties. Particularly promising components for such materials are metal nanostructures, where structural alterations provide a straightforward means of tailoring their surface plasmon resonances and hence their interaction with light. But the top-down fabrication of plasmonic materials with controlled optical responses in the visible spectral range remains challenging, because lithographic methods are limited in resolution and in their ability to generate genuinely three-dimensional architectures. Molecular self-assembly provides an alternative bottom-up fabrication route not restricted by these limitations, and DNA- and peptide-directed assembly have proved to be viable methods for the controlled arrangement of metal nanoparticles in complex and also chiral geometries. Here we show that DNA origami enables the high-yield production of plasmonic structures that contain nanoparticles arranged in nanometre-scale helices. We find, in agreement with theoretical predictions, that the structures in solution exhibit defined circular dichroism and optical rotatory dispersion effects at visible wavelengths that originate from the collective plasmon-plasmon interactions of the nanoparticles positioned with an accuracy better than two nanometres. Circular dichroism effects in the visible part of the spectrum have been achieved by exploiting the chiral morphology of organic molecules and the plasmonic properties of nanoparticles, or even without precise control over the spatial configuration of the nanoparticles. In contrast, the optical response of our nanoparticle assemblies is rationally designed and tunable in handedness, colour and intensity-in accordance with our theoretical model.
Plasmonic nanocrystals strongly interact with chiral molecular shells through electric and magnetic fields and in this way acquire new chiro-optical properties. Transfer of chirality from biomolecules to the plasmonic resonances is a collective phenomenon and strongly depends on the geometry of nanostructure. Collective effects in a molecular chiral shell may suppress or enhance plasmonic circular dichroism (CD) depending on the geometry of hybrid nanocrystal. In large chiral plasmonic structures, we identify a new electrodynamic mechanism of plasmonic CD that is qualitatively different to the near-field, dipolar mechanism of the plasmonic chirality described by us previously. Our models also show that anisotropic nanocrystals, such as nanorods or oriented molecular shells, have strongly enhanced CD at the plasmonic frequency. A family of chiral plasmonic nanostructures proposed and modeled here can be used for designing new optical media and chiral sensors.
We report a new approach for creating chiral plasmonic nanomaterials. A previously unconsidered, far-field mechanism is utilized which enables chirality to be conveyed from a surrounding chiral molecular material to a plasmonic resonance of an achiral metallic nanostructure. Our observations break a currently held preconception that optical properties of plasmonic particles can most effectively be manipulated by molecular materials through near-field effects. We show that far-field electromagnetic coupling between a localized plasmon of a nonchiral nanostructure and a surrounding chiral molecular layer can induce plasmonic chirality much more effectively (by a factor of 10(3)) than previously reported near-field phenomena. We gain insight into the mechanism by comparing our experimental results to a simple electromagnetic model which incorporates a plasmonic object coupled with a chiral molecular medium. Our work offers a new direction for the creation of hybrid molecular plasmonic nanomaterials that display significant chiroptical properties in the visible spectral region.
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