Ultraviolet-Visible Chiroptical Activity of Aluminum Nanostructures

Ultraviolet (UV)-resonant metals (e.g., aluminum) typically have low melting point to cause a fabrication difficulty in helical sculpture to generate plasmons with chiroptical activity in the UV region. In this work, using glancing angle deposition (GLAD), two new methods are devised to generate crystalline chiral Al nanostructures that have stable chiroptical response in the UV-visible region originating from intrinsic helical structures. One approach involves fast substrate rotation during GLAD to fabricate Al nanoparticles (AlNPs) with hidden helicity; another is to deposit an achiral Al thin film on a host of plasmonic chiral NPs, such that the helical structures are duplicated from the chiral host to the achiral guest of Al nanocappings. The host@guest helicity duplication is a new GLAD methodology to generate chiroptically active plasmons, which can be generally adapted to diverse plasmonic metals for tailoring plasmonic chiroptical activity flexibly in the UV-visible region. More importantly, this work offers those two new methods to generate UV-active plasmonic chiral substrates, which can markedly enhance chiroptical activity of biomolecules. It would open a door to develop surface-enhanced chiroptical spectroscopies for sensitively monitoring stereobiochemical information, which is of prominent interest in understanding a wide range of homochirality-determined biological phenomena.

Analyzing intrinsic plasmonic chirality by tracking the interplay of electric and magnetic dipole modes

Plasmonic chirality represents significant potential for novel nanooptical devices due to its association with strong chiroptical responses. Previous reports on plasmonic chirality mechanism mainly focus on phase retardation and coupling. In this paper, we propose a model similar to the chiral molecules for explaining the intrinsic plasmonic chirality mechanism of varies 3D chiral structures quantitatively based on the interplay and mixing of electric and magnetic dipole modes (directly from electromagnetic field numerical simulations), which forms mixed electric and magnetic polarizability.

Fabricating chiroptical starfruit-like Au nanoparticles via interface modulation of chiral thiols

The surface/interface matters as the size of materials enters the nanoscale. Control of surface/interface, therefore, plays an important role in creating novel nanostructures with unusual properties and in obtaining devices with high performance. Herein, we demonstrate unique interface regulation in fabricating nanostructures with strong plasmonic circular dichroism (PCD). With chiral cysteine (Cys) as surface-modulating molecules, starfruit-like Au nanoparticles (NPs) with high PCD responses are obtained via Au overgrowth on Au nanorods (AuNRs). Pre-incubation of the AuNRs with Cys is vital in achieving strong and reproducible PCD responses. Instead of contributing to PCD signals, the pre-adsorbed Cys molecules are found to play a major role in manipulating the Au growth mode and thus the formation of hotspots within the shell. Strong PCD signal mainly comes from the entrapped Cys molecules within the hotspots and is enhanced via local field effect. The distinct roles of the same ligands at different surfaces/interfaces are elucidated. Furthermore, our findings contribute to the strategy of utilizing interface modulation to fabricate complex nanostructures with novel properties.

Excitons in gyrotropic quantum-dot supercrystals

We use quantum theory of molecular crystals to study collective excitations (excitons) of gyrotropic quantum-dot (QD) supercrystals with complex lattices consisting of two or more sublattices of semiconductor QDs. We illustrate the potentials of our approach by applying it to analytically calculate the linear permittivity tensor of supercrystals with two QDs per unit cell. The spatial dispersions of exciton energy bands and permittivity tensor components are examined in detail for two-dimensional supercrystals with a square lattice, which are relatively easy to fabricate in practice. Our results provide a systematic and versatile framework for the engineering of dispersion properties of gyrotropic QD supercrystals and for the analysis of their absorption and circular dichroism spectra.

Amplification of the molecular chiroptical effect by low-loss dielectric nanoantennas

We report here the chiroptical amplification effect occurring in the hybrid systems consisting of chiral molecules and Si nanostructures. Under resonant excitation of circularly polarized light, the hybrid systems show strong CD induction signals at the optical frequency, which arise from both the electric and magnetic responses of the Si nanostructures. More interestingly, the induced CD signals from Si-based dielectric nanoantennas are always larger than that from Au-based plasmonic counterparts. The related physical origin was disclosed. Furthermore, compared to the Au-based high-loss plasmonic nanoantennas, Si-based low-loss structures would generate negligible photothermal effect, which makes Si nanoantennas an optimized candidate to amplify molecular CD signals with ultralow thermal damage. Our findings may provide a guideline for the design of novel chiral nanosensors, which are applicable in the fields of biomedicine and pharmaceutics.

GoldHelix: Gold Nanoparticles Forming 3D Helical Superstructures with Controlled Morphology and Strong Chiroptical Property

Plasmonic nanoparticles, particularly gold nanoparticles (GNPs) hold a great potential as structural and functional building blocks for three-dimensional (3D) nanoarchitectures with specific optical applications. However, a rational control of their assembly into nanoscale superstructures with defined positioning and overall arrangement still remains challenging. Herein, we propose a solution to this challenge by using as building blocks: (1) nanometric silica helices with tunable handedness and sizes as a matrix and (2) GNPs with diameter varying from 4 to 10 nm to prepare a collection of helical GNPs superstructures (called Goldhelices hereafter). These nanomaterials exhibit well-defined arrangement of GNPs following the helicity of the silica template. Strong chiroptical activity is evidenced by circular dichroism (CD) spectroscopy at the wavelength of the surface plasmon resonance (SPR) of the GNPs with a anisotropy factor (g-factor) of the order of 1 × 10^-4, i.e., 10-fold larger than what is typically reported in the literature. Such CD signals were simulated using a coupled dipole method which fit very well the experimental data. The measured signals are 1-2 orders of magnitude lower than the simulated signals, which is explained by the disordered GNPs grafting, the polydispersity of the GNPs, and the dimension of the nanohelices. These Goldhelices based on inorganic templates are much more robust than previously reported organic-based chiroptical nanostructures, making them good candidates for complex hierarchical organization, providing a promising approach for light management and benefits in applications such as circular polarizers, chiral metamaterials, or chiral sensing in the visible range.

Optically active quantum-dot molecules

Chiral molecules made of coupled achiral semiconductor nanocrystals, also known as quantum dots, show great promise for photonic applications owing to their prospective uses as configurable building blocks for optically active structures, materials, and devices. Here we present a simple model of optically active quantum-dot molecules, in which each of the quantum dots is assigned a dipole moment associated with the fundamental interband transition between the size-quantized states of its confined charge carriers. This model is used to analytically calculate the rotatory strengths of optical transitions occurring upon the excitation of chiral dimers, trimers, and tetramers of general configurations. The rotatory strengths of such quantum-dot molecules are found to exceed the typical rotatory strengths of chiral molecules by five to six orders of magnitude. We also study how the optical activity of quantum-dot molecules shows up in their circular dichroism spectra when the energy gap between the molecular states is much smaller than the states' lifetime, and maximize the strengths of the circular dichroism peaks by optimizing orientations of the quantum dots in the molecules. Our analytical results provide clear design guidelines for quantum-dot molecules and can prove useful in engineering optically active quantum-dot supercrystals and photonic devices.

Analytic Optimization of Near-Field Optical Chirality Enhancement

We present an analytic derivation for the enhancement of local optical chirality in the near field of plasmonic nanostructures by tuning the far-field polarization of external light. We illustrate the results by means of simulations with an achiral and a chiral nanostructure assembly and demonstrate that local optical chirality is significantly enhanced with respect to circular polarization in free space. The optimal external far-field polarizations are different from both circular and linear. Symmetry properties of the nanostructure can be exploited to determine whether the optimal far-field polarization is circular. Furthermore, the optimal far-field polarization depends on the frequency, which results in complex-shaped laser pulses for broadband optimization.

Cooperative expression of atomic chirality in inorganic nanostructures

Cooperative chirality phenomena extensively exist in biomolecular and organic systems via intra- and inter-molecular interactions, but study of inorganic materials has been lacking. Here we report, experimentally and theoretically, cooperative chirality in colloidal cinnabar mercury sulfide nanocrystals that originates from chirality interplay between the crystallographic lattice and geometric morphology at different length scales. A two-step synthetic scheme is developed to allow control of critical parameters of these two types of handedness, resulting in different chiral interplays expressed as observables through materials engineering. Furthermore, we adopt an electromagnetic model with the finite element method to elucidate cooperative chirality in inorganic systems, showing excellent agreement with experimental results. Our study enables an emerging class of nanostructures with tailored cooperative chirality that is vital for fundamental understanding of nanoscale chirality as well as technology applications based on new chiroptical building blocks.

Raman optical activity (ROA) and surface-enhanced ROA (SE-ROA) of (+)-(R)-methyloxirane adsorbed on a Ag20cluster

Chirality is ubiquitous in nature and plays an important role in biochemistry because biological function is largely dependent on the handedness of chiral molecules.

Circular Dichroism Studies on Plasmonic Nanostructures

In recent years, optical chirality of plasmonic nanostructures has aroused great interest because of innovative fundamental understanding as well as promising potential applications in optics, catalysis and sensing. Herein, state-of-the-art studies on circular dichroism (CD) characteristics of plasmonic nanostructures are summarized. The hybrid of achiral plasmonic nanoparticles (NPs) and chiral molecules is explored to generate a new CD response at the plasmon resonance as well as the enhanced CD intensity of chiral molecules in the UV region, owing to the Coulomb static and dynamic dipole interactions between plasmonic NPs and chiral molecules. As for chiral assembly of plasmonic NPs, plasmon-plasmon interactions between the building blocks are found to induce generation of intense CD response at the plasmon resonance. Three-dimensional periodical arrangement of plasmonic NPs into macroscale chiral metamaterials is further introduced from the perspective of negative refraction and photonic bandgap. A strong CD signal is also discerned in achiral planar plasmonic nanostructures under illumination of circular polarized plane wave at oblique incidence or input vortex beam at normal incidence. Finally perspectives, especially on future investigation of time-resolved CD responses, are presented.

Mixing of quantum states: A new route to creating optical activity

The ability to induce optical activity in nanoparticles and dynamically control its strength is of great practical importance due to potential applications in various areas, including biochemistry, toxicology, and pharmaceutical science. Here we propose a new method of creating optical activity in originally achiral quantum nanostructures based on the mixing of their energy states of different parities. The mixing can be achieved by selective excitation of specific states or via perturbing all the states in a controllable fashion. We analyze the general features of the so produced optical activity and elucidate the conditions required to realize the total dissymmetry of optical response. The proposed approach is applicable to a broad variety of real systems that can be used to advance chiroptical devices and methods.

Nanoscale chirality in metal and semiconductor nanoparticles

The field of chirality has recently seen a rejuvenation due to the observation of chirality in inorganic nanomaterials. The advancements in understanding the origin of nanoscale chirality and the potential applications of chiroptical nanomaterials in the areas of optics, catalysis and biosensing, among others, have opened up new avenues toward new concepts and design of novel materials. In this article, we review the concept of nanoscale chirality in metal nanoclusters and semiconductor quantum dots, then focus on recent experimental and theoretical advances in chiral metal nanoparticles and plasmonic chirality. Selected examples of potential applications and an outlook on the research on chiral nanomaterials are additionally provided.

DNA Scaffolds for the Dictated Assembly of Left-/Right-Handed Plasmonic Au NP Helices with Programmed Chiro-Optical Properties

Within the broad interest of assembling chiral left- and right-handed helices of plasmonic nanoparticles (NPs), we introduce the DNA-guided organization of left- or right-handed plasmonic Au NPs on DNA scaffolds. The method involves the self-assembly of stacked 12 DNA quasi-rings interlinked by 30 staple-strands. By the functionalization of one group of staple units with programmed tether-nucleic acid strands and additional staple elements with long nucleic acid chains, acting as promoter strands, the promoter-guided assembly of barrels modified with 12 left- or right-handed tethers is achieved. The subsequent hybridization of Au NPs functionalized with single nucleic acid tethers yields left- or right-handed structures of plasmonic NPs. The plasmonic NP structures reveal CD spectra at the plasmon absorbance, and the NPs are imaged by HR-TEM. Using geometrical considerations corresponding to the left- and right-handed helices of the Au NPs, the experimental CD spectra of the plasmonic Au NPs are modeled by theoretical calculations.

Heat-enhanced symmetry breaking in dynamic gold nanorod oligomers: the importance of interface control

We reported a surprisingly strong plasmonic circular dichroism (PCD) response in side-by-side (SS) oligomers of gold nanorods (GNRs) just by a simple heat treatment. The maximal anisotropic (g) factor achieved was up to 0.065, one of the largest reported for plasmon-enhanced chiral nanostructures based on a bottom-up strategy. The introduction of chiral thiolated molecules is suggested to guide the symmetry breaking of GNR assemblies and heat treatment provides the necessary energy to assist this process, and thus produces a huge PCD. Furthermore, we first demonstrated the critical role of the non-chiral component (surfactant layer) on the gold nanorod surface in mediating symmetry breaking. Our findings highlight the importance of interface control in the formation of chiral configuration for a plasmonic nanoparticle system. It offers new possibilities for fabricating nanostructures with strong chiroptical activity by the rational design of interface layers.

Quantitatively analyzing the mechanism of giant circular dichroism in extrinsic plasmonic chiral nanostructures by tracking the interplay of electric and magnetic dipoles

Plasmonic chirality has drawn much attention because of tunable circular dichroism (CD) and the enhancement for chiral molecule signals. Although various mechanisms have been proposed to explain the plasmonic CD, a quantitative explanation like the ab initio mechanism for chiral molecules, is still unavailable. In this study, a mechanism similar to the mechanisms associated with chiral molecules was analyzed. The giant extrinsic circular dichroism of a plasmonic splitting rectangle ring was quantitatively investigated from a theoretical standpoint. The interplay of the electric and magnetic modes of the meta-structure is proposed to explain the giant CD. We analyzed the interplay using both an analytical coupled electric-magnetic dipole model and a finite element method model. The surface charge distributions showed that the circular current yielded by the splitting rectangle ring causes the ring to behave like a magneton at some resonant modes, which then interact with the electric modes, resulting in a mixing of the two types of modes. The strong interplay of the two mode types is primarily responsible for the giant CD. The analysis of the chiral near-field of the structure shows potential applications for chiral molecule sensing.

Enhancing the plasmonic circular dichroism by entrapping chiral molecules at the core–shell interface of rod-shaped Au@Ag nanocrystals

When Ag is coated on the Cys-modified Au nanorods, some Cys molecules are embedded at the core–shell interface, which induce strong PCD signals.

Formation of Enhanced Uniform Chiral Fields in Symmetric Dimer Nanostructures

Chiral fields with large optical chirality are very important in chiral molecules analysis, sensing and other measurements. Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals. However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications. Plasmonic helical nanostructures and blocked squares have been proved to provide uniform chiral near-fields, but structure fabrication is a challenge. In this paper, we show that very simple plasmonic dimer structures can provide uniform chiral fields in the gaps with large enhancement of both near electric fields and chiral fields under linearly polarized light illumination with polarization off the dimer axis at dipole resonance. An analytical dipole model is utilized to explain this behavior theoretically. 30 times of volume averaged chiral field enhancement is gotten in the whole gap. Chiral fields with opposite handedness can be obtained simply by changing the polarization to the other side of the dimer axis. It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.

Understanding complex chiral plasmonics

Chiral nanoplasmonics exhibits great potential for novel nanooptical devices due to the generation of a strong chiroptical response within nanoscale metallic structures. Recently, a number of different approaches have been utilized to create chiral nanoplasmonic structures. However, particularly for tailoring nanooptical chiral sensing devices, the understanding of the resulting chiroptical response when coupling chiral and achiral structures together is crucial and has not been completely understood to date. Here, we present a thorough and step-by-step experimental study to understand the intriguing chiral-achiral coupling scheme. We set up a hybrid plasmonic system, which bears resemblance to the 'host-guest' system in supramolecular chemistry to analyze and explain the complex chiral response both at the chiral and achiral plasmonic resonances. We also provide an elegant and simple analytical model, which can describe, predict, and comprehend the chiroptical spectra in detail. Our study will shed light on designing well-controlled chiral-achiral coupling platforms for reliable chiral sensing.

Optically tunable chiral nematic mesoporous cellulose films

Demand for sustainable functional materials has never been larger. The introduction of functionality into pure cellulose might be one step forward in this field as it is one of the most abundant natural biopolymers. In this paper, we demonstrate a straightforward and scalable way to produce iridescent, mesoporous cellulose membranes with tunable colors and porosity. Concomitant assembly of cellulose nanocrystals (CNCs) and condensation of silica precursors results in CNC-silica composites with chiral nematic structures and tunable optical properties. Removal of the stabilizing silica matrix by alkaline or acid treatment gives access to novel chiral nematic mesoporous cellulose (CNMC) films. Importantly, the optical properties and the mesoporosity can be controlled by either varying the silica-to-CNC ratio, or by varying the substrate used during the evaporation-induced self-assembly process. In order to introduce additional functionality, CNMC has been used to stabilize gold nanoparticles with three different concentrations by wet impregnation. These materials are stable in water and can potentially function in sensors, tissue engineering or functional membranes.

Chiral nematic cellulose–gold nanoparticle composites from mesoporous photonic cellulose

Nearly monodisperse gold nanoparticles with chiroptical properties are prepared by the in situ reduction of Au³⁺ inside mesoporous photonic cellulose.

Chiral assembly and plasmonic response of silver nanoparticles in a three-dimensional blue-phase nanostructure template

Three-dimensional chiral assembly of Ag-NPs in a BP polymer template was demonstrated where the hybrid architecture exhibited optical activity at Ag-NP plasmonic wavelengths as well as showed the ability to respond to the dielectric environment.

Self-organization of plasmonic and excitonic nanoparticles into resonant chiral supraparticle assemblies

Chiral nanostructures exhibit strong coupling to the spin angular momentum of incident photons. The integration of metal nanostructures with semiconductor nanoparticles (NPs) to form hybrid plasmon-exciton nanoscale assemblies can potentially lead to plasmon-induced optical activity and unusual chiroptical properties of plasmon-exciton states. Here we investigate such effects in supraparticles (SPs) spontaneously formed from gold nanorods (NRs) and chiral CdTe NPs. The geometry of this new type of self-limited nanoscale superstructures depends on the molar ratio between NRs and NPs. NR dimers surrounded by CdTe NPs were obtained for the ratio NR/NP = 1:15, whereas increasing the NP content to a ratio of NR/NP = 1:180 leads to single NRs in a shell of NPs. The SPs based on NR dimers exhibit strong optical rotatory activity associated in large part with their twisted scissor-like geometry. The preference for a specific nanoscale enantiomer is attributed to the chiral interactions between CdTe NP in the shell. The SPs based on single NRs also yield surprising chiroptical activity at the frequency of the longitudinal mode of NRs. Numerical simulations reveal that the origin of this chiroptical band is the cross talk between the longitudinal and the transverse plasmon modes, which makes both of them coupled with the NP excitonic state. The chiral SP NR-NP assemblies combine the optical properties of excitons and plasmons that are essential for chiral sensing, chiroptical memory, and chiral catalysis.

Pyramidal sensor platform with reversible chiroptical signals for DNA detection

A heterogeneous chiral sensor for DNA detection is demonstrated by post-assembly system reconfiguration for two types of NPs pyramids. In the presence of target DNA, two types of NPs pyramids undergo dynamic reconfiguration or dissociation process which functions as an off-on or on-off switch towards CD signals changes. Under optimized conditions, the detection limit of this approach can reach to 3.4 aM with no involvement of amplification process.

Shell-programmed Au nanoparticle heterodimers with customized chiroptical activity

Chiral plasmonic assemblies with strong and tunable chiroptical activity are emerging materials yet challenging to fabricate. Moreover, shell-programmed chiroptical regulation is really rare. Here, the chiroptical activity of core-shell (CS) nanoparticles (NPs) heterodimers (HDs) with different types and thicknesses of the shell but featuring the same gap was exploited. It was found that the type of shell guided the position of the chiral peaks, and the shell thickness tuned the intensity but also moderately affected the wavelength shift at invariable interparticle distance. Shell deposition intensified the hot-spot chirality, and evidently guided the enantiomorphous chiral configuration, resulting in a startlingly intense, asymmetric, dipolar coupling strength. The magnitude of the chiroptical activity showed an 8-10 fold enhancement with a maximum anisotropy factor (g-factor) of 1.5 × 10(-2) . Shell-driven chiroptical regulation opens new avenues to feasibly fabricate chiroptically active materials with desired chiroptical response for the development of switchable recognition units for sensitive and various target detections.

3D plasmonic chiral colloids

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.

Wafer scale fabrication of porous three-dimensional plasmonic metamaterials for the visible region: chiral and beyond

We report on a wafer scale fabrication method of a three-dimensional plasmonic metamaterial with strong chiroptical response in the visible region of the electromagnetic spectrum. The system was comprised of metallic nanoparticles arranged in a helical fashion, with high degree of flexibility over the choice of the underlying material, as well as their geometrical parameters. This resulted in exquisite control over the chiroptical properties, most importantly the spectral signature of the circular dichroism. In spite of the large variability in the arrangement, as well as the size and shape of the constituent nanoparticles, the average chiro-optical response of the material remained uniform across the wafer, thus confirming the suitability of this system as a large area chiral metamaterial. By simply heating the substrate for a few minutes, the geometrical properties of the nanoparticles could be altered, thus providing an additional handle towards tailoring the spectral response of this novel material.

Discrete nanocubes as plasmonic reporters of molecular chirality

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.

Amplification of chiroptical activity of chiral biomolecules by surface plasmons

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.

Formation of chiral fields in a symmetric environment

Chiral fields, i. e., electromagnetic fields with nonvanishing optical chirality, can occur next to symmetric nanostructures without geometrical chirality illuminated with linearly polarized light at normal incidence. A simple dipole model is utilized to explain this behavior theoretically. Illuminated with circularly polarized light, the chiral near-fields are still dominated by the distributions found for the linear polarization but show additional features due to the optical chirality of the incident light. Rotating the angle of linear polarization introduces more subtle changes to the distribution of optical chirality. Using our findings, we propose a novel scheme to obtain chiroptical far-field response using linearly polarized light, which could be utilized for applications such as optical enantiomer sensing.

Plasmonic chiroptical response of silver nanoparticles interacting with chiral supramolecular assemblies

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.