Local Dielectric Environment Research Articles

Tuning Exchange Coupling in a New Family of Nanocrystal-Based Granular Multiferroics Using an Applied Electric Field.

In this work, we demonstrate an experimental realization of a granular multiferroic composite, where the magnetic state of a nanocrystal array is modified by tuning the interparticle exchange coupling using an applied electric field. Previous theoretical models of a granular multiferroic composite predicted a unique magnetoelectric coupling mechanism, in which the magnetic spins of the ensemble are governed by interparticle exchange. The extent of these exchange interactions can be controlled by varying the local dielectric environment between grains. We specifically utilize the strong dielectric dependence of ferroelectric materials to modify the interparticle coupling of closely spaced magnetic nanoparticles using either a change in temperature or an electric field. This coupling modifies the ensemble magnetic coercivity and thus the superparamagnetic-to-ferromagnetic phase transition temperature. Through the use of two different ferroelectrics, our results suggest that this magnetoelectric coupling mechanism could be generalized as a new class of multiferroic material, applicable to a broad range of ferroelectric/magnetic nanocrystal composites.

Acid-Base Equilibrium and Dielectric Environment Regulate Charge in Supramolecular Nanofibers.

Peptide amphiphiles are a class of molecules that can self-assemble into a variety of supramolecular structures, including high-aspect-ratio nanofibers. It is challenging to model and predict the charges in these supramolecular nanofibers because the ionization state of the peptides are not fixed but liable to change due to the acid-base equilibrium that is coupled to the structural organization of the peptide amphiphile molecules. Here, we have developed a theoretical model to describe and predict the amount of charge found on self-assembled peptide amphiphiles as a function of pH and ion concentration. In particular, we computed the amount of charge of peptide amphiphiles nanofibers with the sequence C 16 − V 2 A 2 E 2. In our theoretical formulation, we consider charge regulation of the carboxylic acid groups, which involves the acid-base chemical equilibrium of the glutamic acid residues and the possibility of ion condensation. The charge regulation is coupled with the local dielectric environment by allowing for a varying dielectric constant that also includes a position-dependent electrostatic solvation energy for the charged species. We find that the charges on the glutamic acid residues of the peptide amphiphile nanofiber are much lower than the same functional group in aqueous solution. There is a strong coupling between the charging via the acid-base equilibrium and the local dielectric environment. Our model predicts a much lower degree of deprotonation for a position-dependent relative dielectric constant compared to a constant dielectric background. Furthermore, the shape and size of the electrostatic potential as well as the counterion distribution are quantitatively and qualitatively different. These results indicate that an accurate model of peptide amphiphile self-assembly must take into account charge regulation of acidic groups through acid–base equilibria and ion condensation, as well as coupling to the local dielectric environment.

Molding 2D Exciton Flux toward Room Temperature Excitonic Devices

AbstractDevices operating with excitons have promising prospects for overcoming the dilemma of response time and integration in current generation of electron‐ or/and photon‐based elements and devices. In combination with the advantages of emerging twistronics and valleytronics, the atomically thin transition metal dichalcogenide semiconductors open up new opportunities for pursuing practical excitonic devices, where the strong exciton binding energy enables operating exciton at room temperature. The essential and foremost step toward exciton devices is the control of spatiotemporal exciton flux, which is density‐dependent and affected by the complex many‐body interactions. It can be effectively controlled by the strain, electric field, electron‐doping, and local dielectric environment. Intriguingly, exotic phenomena such as exciton condensation, electron‐hole liquid, exciton Hall effects, and exciton halo effects can be occurred in 2D exciton system, providing new possibilities for excitonic devices. Up to now, the proof‐of‐principle of room temperature exciton devices, including excitonic switching and transistor, exciton guides, and excitonic nanolaser, have been realized. Here the authors review the recent advances in molding 2D exciton flux from basic principle, manipulation, exotic phenomena to promising applications and discuss the opportunities and challenges in pushing the frontiers of room temperature excitonic devices.

Light Scattering by Noble Metallic Nanoparticles for Performance of Compound Solar Cells Enhancement

Light scattering by noble metallic nanoparticles are of interest for a variety of applications due to the large electromagnetic field enhancement that occurs in the vicinity of the metal surface, and the dependence of the resonance photon energy on the nanoparticle size, shape, local dielectric environment, and material. Here, the influences of electromagnetic scattering by Au and Ag nanoparticles placed atop compound solar cells on optical absorption and photocurrent generation were investigated based on the variation in the noble nanoparticle densities. The results indicated that the short-circuit current and power conversion efficiency were strongly affected by the density and material of the noble nanoparticles. The great improvement of 28% in power conversion efficiency can be obtained with Au nanoparticle density of 2\(\times\)108 cm-2. This improvement can be attributed to light scattering, light trapping, and surface roughness by noble nanoparticles. Furthermore, Au nanoparticles showed more efficient in solar cell power conversion efficiency improvement than Ag nanoparticles did although density of Au nanoparticle was lower than that of Ag nanoparticles.

Kinetics and thermodynamics of enzymatic decarboxylation of α,β-unsaturated acid: a theoretical study.

Enzymatic decarboxylation of α,β-unsaturated acid through ferulic acid decarboxylase (FDC1) has been of interest because this reaction has been anticipated to be a promising, environmentally friendly industrial process for producing styrene and its derivatives from natural resources. Because the local dielectric constant at the active site is not exactly known, enzymatic decarboxylation to generate β-methylstyrene (β-MeSt) was studied under two extreme conditions (ε = 1 and 78 in the gas phase and aqueous solution, respectively) using the B3LYP/DZP method and transition state theory (TST). The model molecular clusters consisted of an α-methylcinnamate (Cin) substrate, a prenylated flavin mononucleotide (PrFMN) cofactor and all relevant residues of FDC1. Analysis of the equilibrium structures showed that the FDC1 backbone does not play the most important role in the decarboxylation process. The potential energy profiles confirmed that the increase in the polarity of the solvent could lead to significant changes in the energy barriers, especially for the transition states that involve proton transfer. Analysis of the rate constants confirmed the low/no quantum mechanical tunneling effect in the studied temperature range and that inclusion of the fluctuation of the local dielectric environment in the mechanistic model was essential. Because the computed rate constants are not compatible with the time resolution of the stopped-flow spectrophotometric experiment, the direct route for generating β-MeSt after CO2 elimination (acid catalyst (2)) is unlikely to be utilized, thereby confirming that indirect cycloelimination in a low local dielectric environment is the rate determining step. The thermodynamic results showed that the elementary reactions that involve charge (proton) transfer are affected by solvent polarity, thereby leading to the conclusion that overall, the enzymatic decarboxylation of α,β-unsaturated acid is thermodynamically controlled at high ε. The entropy changes due to the generation of molecules in the active site appeared more pronounced than that due to only covalent bond breaking/formation or structural reorientation. This work examined in detail for the first time the scenarios in each elementary reaction and provided insight into the effect of the fluctuations in the local dielectric environment on the enzymatic decarboxylation of α,β-unsaturated acids. These results could be used as guidelines for further theoretical and experimental studies on the same and similar systems.

BIOSENSOR PROPERTIES OF PLASMONIC SILVER NANOPARTICLES PRODUCED BY PLD

Plasmonic metal nanoparticles (NPs), such as Ag, Au, Cu NPs, attracts a lot of interest due to their notable applications in biological, and chemical sensing. Researchers have studied on plasmonic metal NPs which have exceptional optical properties in a large spectral region. Metal NPs form a unique surface plasmon resonance (SPR) peak that is in the electromagnetic spectrum’s visible part. The peak of SPR firmly depends on the NP’s size, shape, dielectric constant, and medium that the particle is in. Light interacts with nanoparticles that are smaller than the wavelength of incident light in localized surface resonance. That leads Localised Surface Plasmon Resonance (LSPR) in which an oscillating local plasma around NP with a certain frequency form. LSPR detection is the most common method for wavelength shift measurement. Analyte absorption causes a change in the local dielectric constant and thus LSPR peak shifts. Biological molecules such as proteins and antibodies can sensitively be detected as they change the local dielectric environment. Therefore, Ag or Au metal NPs can be used as sensor by employing LSPR wavelength shift technique. Among the metal NPs, Ag has a relatively higher refractive index sensitivity. Since Ag NPs have a shaper LSPR peak, they generate more precise measurements. In our work, we have produced plasmonic Ag NPs with various sizes and spherical shapes by employing Pulsed Laser Deposition (PLD). We investigated the LSPR peaks of produced plasmonic Ag NPs by UV-Vis spectroscopy. Moreover, biosensor properties of plasmonic Ag NPs are investigated by binding Protein A molecules to surface of the NPs. That produced a LSPR wavelength shift of around 100 nm/RIU.

The Grotthuss mechanism for bifunctional proton transfer in poly(benzimidazole).

Poly(benzimidazole) (PBI) has received considerable attention as an effective high-temperature polymer electrolyte membrane for fuel cells. In this work, the Grotthuss mechanism for bifunctional proton transfer in PBI membranes was studied using density functional theory and transition state theory. This study focused on the reaction paths and kinetics for bifunctional proton transfer scenarios in neutral ([PBI]2), single (H+[PBI]2) and double-protonated (H2+[PBI]2) dimers. The theoretical results showed that the energy barriers and strength for H-bonds are sensitive to the local dielectric environment. For [PBI]2 with ε = 1, the uphill potential energy curve is attributed to extraordinarily strong ion-pair H-bonds in the transition structure, regarded as a ‘dipolar energy trap’. For ε = 23, the ion-pair charges are partially neutralized, leading to a reduction in the electrostatic attraction in the transition structure. The dipolar energy trap appears to prohibit interconversion between the precursor, transition and proton-transferred structures, which rules out the possibility for [PBI]2 to be involved in the Grotthuss mechanism. For H+[PBI]2 and H2+[PBI]2 with ε = 1, the interconversion involves a low energy barrier, and the increase in the energy barrier for ε = 23 can be attributed to an increase in the strength of the protonated H-bonds in the transition structure: the local dielectric environment enhances the donor–acceptor interaction of the protonated H-bonds. Analysis of the rate constants confirmed that the quantum effect is not negligible for the N–H+ … N H-bond especially at low temperatures. Agreement between the theoretical and experimental data leads to the conclusion that the concerted bifunctional proton transfer in H2+[PBI]2 in a high local dielectric environment is ‘the rate-determining scenario’. Therefore, a low local dielectric environment can be one of the required conditions for effective proton conduction in acid-doped PBI membranes. These theoretical results provide insights into the Grotthuss mechanism, which can be used as guidelines for understanding the fundamentals of proton transfers in other bifunctional H-bond systems.

Improve the Effective Resonance Light Scattering of Three-Layered Plasmonic Au@Dielectric@Ag Bimetallic Nanoshells

The strong light scattering from SPR has received an extraordinary attention due to the useful applications in photodetectors and cell and biomedical imaging. However, the applications using light scattering require a high scattering cross-section along with low absorption losses near the resonance wavelength. In this paper, effective plasmonic scattering of three-layered Au–Ag bimetallic nanoshells with a dielectric separate layer has been studied using the quasi-static approximation of classical electrodynamics. Because of the surface plasmon resonance (SPR)-induced intense light absorption, the effective scattering intensity is much weaker than that of scattering cross-section. However, the effective scattering intensity could be improved by tuning the geometric dimension and local dielectric environment of the nanostructure. It has been found that the greatest effective scattering takes place when the outer Ag nanoshell has a thick thickness or the dielectric separate layer has a small dielectric constant. The effective scattering also depends on the inner Au sphere radius and outer surrounding dielectric constant. Because of the mode transformation of the SPR, the effective scattering could also be greatly improved when the inner Au sphere has a very small or large size. However, the effective scattering intensity changes non-monotonously as the surrounding dielectric constant increases. The greatest effective scattering could be obtained when the surrounding dielectric constant has an intermediate value. This tunable effective plasmonic scattering of Au@Ag three-layered nanoshells presents a potential for design and fabrication of plasmonic optical nanodevice based on resonance light scattering.

Temperature Tuning of Coherent Mixing between States Driving Singlet Fission in a Spiro-Fused Terrylenediimide Dimer.

The excited-state dynamics of a spiro-fused terrylene-3,4:11,12-bis(dicarboximide) (TDI) dimer (sTDI2) in toluene and 2-methyltetrahydrofuran (mTHF) were investigated as a function of temperature using femtosecond- and nanosecond-transient absorption spectroscopy, as well as two-dimensional electronic spectroscopy. The spiro conjugation and the corresponding geometry of this compound guarantee a short intermonomer distance along with a partial orbital overlap between the orthogonal TDI π-electron systems, providing electronic coupling between the TDIs. Photoexcitation of sTDI2 in toluene, a low dielectric solvent, at 295 K, results in the ultrafast formation of a state composed of a coherent mixture of singlet 1(S1S0), multiexciton 1(T1T1), and charge-transfer (CT) electronic characters. This mixed species decays to decorrelated triplet states on the nanosecond timescale, completing the process of intramolecular singlet fission (SF) in sTDI2. Upon decreasing the temperature from 295 to 200 K, the contribution of the 1(T1T1) state to the mixed species decreases concurrently with an increase in the CT state character. We attribute this behavior to the variation in the vibrational energy level alignment between the states comprising the mixture due to changes in the temperature and hence the local dielectric environment. In contrast, photoexcitation of sTDI2 in more polar mTHF at 295 K results in the formation of a mixed singlet and CT state before undergoing symmetry-breaking charge separation, owing to the increased stabilization of the CT state in the medium. However, in glassy mTHF at 85 K, photoexcited sTDI2 exhibits discernible multiexciton character, comparable to that observed in toluene at 200 K, which we rationalize by the similarity of the dielectric constants under these two sets of conditions. These observations of mixed states of varying diabatic contributions over the range of experimental conditions show that the temperature and the static dielectric constant can directly control the composition of the electronically mixed excited state of sTDI2 and thus the fate of the SF process.

Gas Sensors Based on Localized Surface Plasmon Resonances: Synthesis of Oxide Films with Embedded Metal Nanoparticles, Theory and Simulation, and Sensitivity Enhancement Strategies

This work presents a comprehensive review on gas sensors based on localized surface plasmon resonance (LSPR) phenomenon, including the theory of LSPR, the synthesis of nanoparticle-embedded oxide thin films, and strategies to enhance the sensitivity of these optical sensors, supported by simulations of the electromagnetic properties. The LSPR phenomenon is known to be responsible for the unique colour effects observed in the ancient Roman Lycurgus Cup and at the windows of the medieval cathedrals. In both cases, the optical effects result from the interaction of the visible light (scattering and absorption) with the conduction band electrons of noble metal nanoparticles (gold, silver, and gold–silver alloys). These nanoparticles are dispersed in a dielectric matrix with a relatively high refractive index in order to push the resonance to the visible spectral range. At the same time, they have to be located at the surface to make LSPR sensitive to changes in the local dielectric environment, the property that is very attractive for sensing applications. Hence, an overview of gas sensors is presented, including electronic-nose systems, followed by a description of the surface plasmons that arise in noble metal thin films and nanoparticles. Afterwards, metal oxides are explored as robust and sensitive materials to host nanoparticles, followed by preparation methods of nanocomposite plasmonic thin films with sustainable techniques. Finally, several optical properties simulation methods are described, and the optical LSPR sensitivity of gold nanoparticles with different shapes, sensing volumes, and surroundings is calculated using the discrete dipole approximation method.

Development of In Vivo Nanosensors Using Organic Color Centers

Covalent bonding of organic functional groups to the sp2 carbon lattice of single-walled carbon nanotubes produces tunable sp3 quantum defects that fluoresce brightly in the second near-infrared region (NIR-II, 1000-1700 nm). Such synthetic defects, also known as organic color centers (OCCs), provide a molecular focal point that sensitively and selectively responds to the local dielectric environments. To take advantage of these unique electronic and optical properties of OCCs for biomedical applications, we discuss a new method that controls the biological interactions/biocompatibility of OCC-based nanosensors via their supramolecular interactions with polymers and other excipients. The resulting nanosensor sensitively detects local intracellular environments in live cells and in vivo. We assess the utility of the nanosensor for cancer research.

Ultrahigh surface sensitivity of deposited gold nanorod arrays for nanoplasmonic biosensing

The biosensing performance of plasmonic nanostructures critically depends on detecting changes in the local refractive index near the sensor surface, which is referred to as surface sensitivity. For biosensing applications at solid-liquid interfaces, recent efforts to boost surface sensitivity have narrowly focused on laterally isotropic nanostructures, while there is an outstanding need to explore laterally anisotropic nanostructures such as nanorods that have distinct plasmonic properties. Herein, we report the development of plasmonic gold nanorod (AuNR) arrays that exhibit ultrahigh surface sensitivity to detect various classes of biomacromolecular interactions with superior biosensing performance. A colloidal deposition strategy was devised to fabricate AuNR-coated glass substrates, along with experimental measurements and analytical calculations to investigate how nanorod dimensions and local dielectric environment affect plasmonic properties. To validate the sensing concept, real-time biosensing experiments involving protein adsorption and peptide-induced vesicle rupture were conducted and revealed that rationally tuning nanorod dimensions could yield AuNR arrays with the highest reported degree of surface sensitivity compared to a wide range of plasmonic nanostructures tested in past studies. We discuss plasmonic factors that contribute to this ultrahigh surface sensitivity and the measurement capabilities developed in this study are broadly extendable to a wide range of biosensing applications.

Improve the Local Electric Field Enhancement of Au Cylindrical Nanohole by Pt Coating

Local electric field enhancement in a long cylindrical Au nanohole with Pt coating has been theoretically studied based on quasi-static model. Calculation results show that both the peak wavelength and local field factor in the nanohole are greatly dependent on the Pt coating thickness. Because of the Pt coating, a new local surface plasmon resonance (LSPR) band takes place in the ultraviolet wavelength below 400 nm, which also results in intense local electric field enhancement in the nanohole. As the Pt coating thickness is increased, the local field factor peak corresponding to the Pt shell red shifts and gets intense rapidly, which is much greater than that of Au shell. However, the increasing Pt thickness can also leads to the decrease of the local field factor when the dielectric constant of inner hole is much greater than that of outer environment. The local field factor in Pt shell is also sensitive to the Pt thickness and local dielectric environment. At the inner surface of the Pt shell, the increasing Pt thickness results in non-monotonic change of the local field factor when the dielectric constant of inner hole is equal or smaller than that of outer environment. Whereas at the outer surface of the Pt shell, the increasing Pt thickness always results in monotonic decrease of the local field factor, which is independent on the difference of the dielectric constant between inner hole and outer surrounding. This Pt coating-controlled local field enhancement in cylindrical Au@Pt nanohole presents design criteria and synthetic strategies toward local field effect-induced surface-enhanced Raman scattering (SERS), surface-enhanced fluorescence, and biosensing applications.

Interplaying Role of Particle Size and Polymer Layer Thickness on the Large Tunable Optical Response of Polymer-coated Silver Nanostructures

The interplaying role of particle size and polymer layer thickness on the tunable optical response of polymer-coated Ag nanoparticles (NPs) has been studied experimentally and theoretically. A large redshift ( $$\sim$$ 38 nm) of surface plasmon resonance (SPR) peak position has been observed experimentally for Ag NPs of sizes in the range of 8−18 nm synthesized by polyol process with the varying concentration of metal precursor (AgNO $$_{3}$$ ) and using a surfactant (PVP) as a stabilizer. The observed large redshift of the SPR peak position of Ag NPs coated with PVP has been argued due to mainly change of NP size as well as change of local dielectric environment in the vicinity of the Ag NPs. The experimentally observed SPR peak shift has been explained by considering the system as a metal-core polymer-shell nanostructure. The change of local dielectric environment of the surrounding of the NPs is due to the change in the PVP layer on the NPs. Such observation has been confirmed through the theoretical studies considering the changes of NP size as well as the effective thickness of the PVP layers on the NPs. The SPR peak of the system with core-shell nanostructure has been found to vary linearly with the increase in radius of core and thickness of shell together. However, it changes exponentially with particle size alone. It has been found from a detailed study that the change in the ratio of radius of core and thickness of the shell is responsible for the observed redshift. Thus, the redshift of SPR peak position of Ag NPs cannot be justified by only considering the increase in particle size. Rather shell thickness has been found to play a prominent role in the SPR peak shift. This study can be used to understand the optical response of noble metal NPs coated with organic polymers.

Extracting the Infrared Permittivity of SiO2 Substrates Locally by Near-Field Imaging of Phonon Polaritons in a van der Waals Crystal.

Layered materials in which individual atomic layers are bonded by weak van der Waals forces (vdW materials) constitute one of the most prominent platforms for materials research. Particularly, polar vdW crystals, such as hexagonal boron nitride (h-BN), alpha-molybdenum trioxide (α-MoO3) or alpha-vanadium pentoxide (α-V2O5), have received significant attention in nano-optics, since they support phonon polaritons (PhPs)―light coupled to lattice vibrations― with strong electromagnetic confinement and low optical losses. Recently, correlative far- and near-field studies of α-MoO3 have been demonstrated as an effective strategy to accurately extract the permittivity of this material. Here, we use this accurately characterized and low-loss polaritonic material to sense its local dielectric environment, namely silica (SiO2), one of the most widespread substrates in nanotechnology. By studying the propagation of PhPs on α-MoO3 flakes with different thicknesses laying on SiO2 substrates via near-field microscopy (s-SNOM), we extract locally the infrared permittivity of SiO2. Our work reveals PhPs nanoimaging as a versatile method for the quantitative characterization of the local optical properties of dielectric substrates, crucial for understanding and predicting the response of nanomaterials and for the future scalability of integrated nanophotonic devices.

The Effect of Local Dielectric Environment on the Fluorescence Quenching Efficiency of Gold Nanoshell

By using the theory of quasi-static electrodynamics and fluorescence resonance energy transfer (FRET), local dielectric constant-dependent fluorescence quenching of gold nanoshell has been studied. Because the bonding plasmon coupling mode has stronger resonance light absorption, the bonding plasmon coupling mode-induced FRET has a greater quenching efficiency than that of anti-bonding plasmon coupling mode. Both the bonding and anti-bonding plasmon coupling mode-induced fluorescence quenching are greatly dependent on the local dielectric constant. The quenching efficiency corresponding to anti-bonding plasmon coupling mode increases as the inner core dielectric constant is increased, whereas the quenching efficiency corresponding to bonding plasmon coupling mode increases as the outer surrounding dielectric constant is increased. The corresponding physical origin could be illustrated as follows. The anti-bonding and bonding plasmon coupling modes are primarily composed of the cavity and surface plasmon, respectively. As the result of the increasing outer surrounding/inner core dielectric constant-induced shifting and widening of bonding/anti-bonding plasmonic absorption peak, the corresponding wavelength region with high quenching efficiency value also red shifts and broadens as the dielectric constant of outer surrounding/inner core is increased. Thus, the fluorescence quenching efficiency of gold nanoshell could be fine tuned by altering the local dielectric environment.

Microsphere Photolithography Patterned Nanohole Array on an Optical Fiber

Microsphere Photolithography (MPL) is a nanopatterning technique that utilizes a self-assembled monolayer of microspheres as an optical element to focus incident radiation inside a layer of photoresist. The microspheres produces a sub-diffraction limited photonic-jet on the opposite side of each microsphere from the illumination. When combined with pattern transfer techniques such as etching/lift-off, MPL provides a versatile, low-cost fabrication method for producing hexagonal close-packed metasurfaces. This article investigates the MPL process for creating refractive index (RI) sensors on the cleaved tips of optical fiber. The resonant wavelength of metal elements on the surface is dependent on the local dielectric environment and allows the refractive index of an analyte to be resolved spectrally. A numerical study of hole arrays defined in metal films shows that the waveguide mode provides good sensitivity to the analyte refractive index. This can be readily tuned by adjusting the MPL exposure and the simulation results guide the fabrication of a defect tolerant refractive index sensor on the tip of a fiber tip with a sensitivity of 613 nm/RIU. The conformal nature of the microsphere monolayer simplifies the fabrication process and provides a viable alternative to direct-write techniques such as Focused Ion Beam (FIB) milling.

Real-Time, In Vivo Monitoring of Pharmacodynamics in Solid Tumors Using Organic Color Centers

Covalent bonding of organic functional groups to the sp2 carbon lattice can produce tunable sp3 quantum defects that fluoresce brightly in the second near-infrared (NIR-II, 1000-1700 nm). Such synthetic defects, or ‘organic color centers’ (OCCs), provide a molecular focal point that sensitively and selectively responds to the local dielectric environments. To benefit from the unique electronic and optical properties of OCCs in biomedical applications, we present a new method that controls the biological interactions/biocompatibility of OCC-based nanosensors via their supramolecular interactions with polymers and other excipients. The resultig OCC-based nanosensor measures endolysosomal pH in live cells and in vivo. We discuss the utility of the nanosensor to real-time monitor the pharmacodynamics of anticancer drugs in solid tumors.

Extreme sensitivity of plasmon drag to surface modification

Giant enhancement of photocurrents in plasmonic structures (plasmon drag effect) provides opportunities for compact electric monitoring of plasmonic effects, and thus is promising for plasmonic-based sensing applications. In the experiment, we measure photoinduced electric signals in flat and profile-modulated systems, and test their sensitivity to small changes of the local dielectric environment, such as a presence of Langmuir–Blodgett monolayers at the metal surface. We show that the addition of a stearic acid monolayer leading to a small shift in plasmon resonance conditions can be ultimately resolved with electrical measurements as the switching in the photovoltage polarity.

Observation of Fano resonance in silver nanocube–nanosphere dimer

In this paper, we perform a theoretical investigation of the plasmon coupling in silver (Ag) nanocube–nanosphere dimer using finite difference time domain (FDTD) technique. Due to plasmonic Fano resonance, we observe a pronounced dip in the absorption spectrum, which is induced by the destructive interference between the bright dipole mode from the Ag nanocube and the dark quadrupole mode from the Ag nanosphere. We study the effects on the Fano resonance by varying the dimensions of the nanocube and nanosphere, as well as the inter-surface gap distance between them. In addition, we vary the local dielectric environment surrounding the dimer and find a wide tuning in the Fano resonance line-shape. We calculate the localised surface plasmon resonance (LSPR) sensitivity of the nanocube–nanosphere dimer to the surrounding environment and find a high figure of merit (FOM) of 32.23, which indicates its promising potential as a plasmonic biosensor.