Interference-Induced Broadband Absorption Enhancement for Plasmonic-Metal@Semiconductor Microsphere as Visible Light Photocatalyst

A fundamental study is performed on the surface plasmon resonance (SPR) of metal@semiconductor microsphere photocatalyst to uncover its broadband absorption mechanism over the visible wavelength region. Finite element method studies show that an interference pattern is uniquely generated inside the semiconductor microsphere due to the optical reflection and refraction at the interface between the microsphere and the catalytic medium. By embedding plasmonic nanoparticles (NPs) into the microsphere, an interference-induced broadband absorption enhancement over the entire visible region can be achieved as compared to other plasmonic structures. Based on the properties of the interference, the broadband absorption enhancement can be obtained everywhere inside the microsphere and is particularly large at the microsphere hot-zone. Studies also show that microsphere consisting of higher refractive index semiconductor can maximize the interference-induced broadband absorption enhancement. Besides, NPs with different materials can be mixed to tune the overall absorption band for flexible energy harvesting and enhanced selectivity. At the same time, the evanescent nature of the SPR near field could be better exploited to enhance the catalytic rate if locating the NPs close to the microsphere surface. Our findings could help experimentalists to design optimized metal@semiconductor microsphere photocatalyst to more efficiently utilize the solar power to drive chemical transformation

Metal–Dielectric Hybrid Dimer Nanoantenna: Coupling between Surface Plasmons and Dielectric Resonances for Fluorescence Enhancement

Dimers made of noble metal particles possess extraordinary field enhancements but suffer from large dissipation, whereas low-loss dielectric dimers are limited by relatively weak optical confinement. Hybrid systems could take advantages from both worlds. In this contribution, we study the mode coupling in a hybrid dimer with rigorous dipole–dipole interaction theory and explore its potential in fluorescence enhancement. We first discovered that the direct coupling between metal surface–plasmon resonance and dielectric electric–dipole mode creates a hybridized mode due to the strong electric–electric dipole–dipole interaction between the constituent nanoparticles, whereas the dielectric magnetic–dipole mode can only indirectly couple to the plasmons on the basis of the induced electric–magnetic dipole–dipole interaction. When an electric/magnetic quantum emitter couples to the hybrid dimer, the emitter selectively excites the electric/magnetic (magnetic/electric) resonant modes of the dimer for emitter orientation parallel (perpendicular) to the dimer axis. Our study shows that the hybrid dimer simultaneously possesses high field enhancement and low-loss features, which demonstrates a fluorescence excitation rate 40% higher than that of the pure dielectric dimer and an average quantum yield 30% higher than that of the pure metallic dimer. On top of that, the unique asymmetrical structure of the hybrid dimer directs 20% more radiation toward the dielectric side, hence improving the directivity of the dimer as an antenna

Toward the Long-Term Stability of Cobalt Benzoate Confined Highly Dispersed PtCo Alloy Supported on a Nitrogen-Doped Carbon Nanosheet/Fe₃C Nanoparticle Hybrid as a Multifunctional Catalyst for Zinc-Air Batteries

This work reports a new type of platinum-based heterostructural electrode catalyst that highly dispersed PtCo alloy nanoparticles (NPs) confined in cobalt benzoate (Co-BA) nanowires are supported on a nitrogen-doped ultra-thin carbon nanosheet/Fe3C hybrid (PtCo@Co-BA-Fe3C/NC) to show high electrochemical activity and long-term stability. One-dimensional Co-BA nanowires could alleviate the shedding and agglomeration of PtCo alloy NPs during the reaction so as to achieve satisfactory long-term durability. Moreover, the synergistic effect at the interface optimizes the surface electronic structure and prominently accelerates the electrochemical kinetics. The oxygen reduction reaction half-wave potential is 0.923 V, and the oxygen evolution reaction under the condition of 10 mA•cm–2 is 1.48 V. Higher power density (263.12 mW•cm–2), narrowed voltage gap (0.49 V), and specific capacity (808.5 mAh•g–1) for PtCo@Co-BA-Fe3C/NC in Zn-air batteries are achieved with long-term cycling measurements over 776 h, which is obviously better than the Pt/C + RuO2 catalyst. The interfacial electronic interaction of PtCo@Co-BA-Fe3C/NC is investigated, which can accelerate electron transfer from Fe to Pt. Density functional theory calculations also indicate that the interfacial potential regulates the binding energies of the intermediates to achieve the best performance

Synthesis of Anisotropic Concave Gold Nanocuboids with Distinctive Plasmonic Properties

Gold nanoparticles have attracted considerable attention owing to their appealing plasmonic properties that have found applications in sensing, imaging, and energy harvesting. In the present article, we report the synthesis of anisotropic concave Au nanocuboids using a seeded growth method controlled by a seed concentration. Unlike conventional nonconcave counterparts which typically present two fundamental plasmonic modes (transverse and longitudinal modes), our experimental measurements and theoretical analysis show that the anisotropic concave Au nanocuboid has three plasmonic resonances. Theoretical calculations based on a finite element method confirm that the third resonance is a transverse “edge” mode, which is enhanced by the sharpened edges of the concave surfaces. This third resonance is found to be separated from the conventional broad transverse mode band. Because of the separation of the resonance mode, the quality-factor of the original transverse mode shows nearly a 3-fold enhancement

Hybrid Mushroom Nanoantenna for Fluorescence Enhancement by Matching the Stokes Shift of the Emitter

Nanoantenna-enhanced fluorescence is a promising method in many emergent applications, such as single molecule detection. The excitation and emission wavelengths of emitters can be well separated depending on the corresponding Stokes shifts, preventing optimal fluorescence enhancement by a rudimentary nanoantenna. We illustrate a hybrid mushroom nanoantenna that can achieve overall enhancements (e.g., excitation rate, quantum yield, fluorescence enhancement) in fluorescence emission. The nanoantenna is made of a plasmonic metal stipe and a dielectric cap, and the resonances can be flexibly and independently controlled to match the Stokes shift of the emitter. By fully leveraging the advantages of the large field enhancement from the metal and the low loss feature from the dielectric, a fluorescence enhancement factor (far field intensity) twice (20 times) as high as that from a pure metallic antenna can be attained, accompanied by improved directivity. Approximately 70% of the overall radiation was directed toward the mushroom cap via coupling to the dielectric resonance, which could benefit the collection efficiency. This hybrid concept introduces a way to build high-performance nanoantennas for fluorescence enhancement applications

Aromatic Ring Fluorination Patterns Modulate Inhibitory Potency of Fluorophenylhydroxamates Complexed with Histone Deacetylase 6

Bavarostat (EKZ-001) is a selective inhibitor of histone deacetylase 6 (HDAC6) that contains a meta-fluorophenylhydroxamate Zn2+-binding group. The recently determined crystal structure of its complex with HDAC6 from Danio rerio (zebrafish) revealed that the meta-fluoro substituent binds exclusively in an aromatic crevice defined by F583 and F643 rather than being oriented out toward solvent. To explore the binding of inhibitor C–F groups in this fluorophilic crevice, we now report a series of 10 simple fluorophenylhydroxamates bearing one or more fluorine atoms with different substitution patterns. Inhibitory potencies against human and zebrafish HDAC6 range widely from 121 to >30,000 nM. The best inhibitory potency is measured for meta-difluorophenylhydroxamate (5) with IC50 = 121 nM against human HDAC6; the worst inhibitory potencies are measured for ortho-fluorophenylhydroxamate (1) as well as fluorophenylhydroxamates 4, 7, 9, and 10, although there are some variations in activity trends against human and zebrafish HDAC6. These studies show that aromatic ring fluorination at the meta position(s) does not improve inhibitory activity against human HDAC6 relative to the nonfluorinated parent compound phenylhydroxamate (IC50 = 120 nM), but meta-fluorination does not seriously compromise inhibitory activity either. Crystal structures of selected zebrafish HDAC6–fluorophenylhydroxamate complexes reveal that the fluoroaromatic ring is uniformly accommodated in the F583–F643 aromatic crevice, so ring fluorination does not perturb the inhibitor binding conformation. However, hydroxamate–Zn2+ coordination is bidentate for some inhibitors and monodentate for others. These studies will inform design strategies underlying the design of 18F-labeled HDAC6 inhibitors intended for positron emission tomography

Exploiting Surface-Plasmon-Enhanced Light Scattering for the Design of Ultrasensitive Biosensing Modality

Development of new detection methodologies and amplification schemes is indispensable for plasmonic biosensors to improve the sensitivity for the detection of trace amounts of analytes. Herein, an ultrasensitive scheme for signal enhancement based on the concept of surface-plasmon-resonance-enhanced light scattering (SP-LS) was validated experimentally and theoretically. The SP-LS of gold nanoparticles’ (AuNPs) tags was employed in a sandwich assay for the detection of cardiac troponin I and provided up to 2 orders of magnitude improved sensitivity over conventional AuNPs-enhanced refractometric measurements and 3 orders of magnitude improvement over label-free SPR. Simulations were also performed to provide insights into the physical mechanisms

Molecular Imaging of Alzheimer’s Disease-Related Sigma‑1 Receptor in the Brain <b><i>via</i></b> a Novel Ru-Mediated Aromatic ^<b>18</b>F‑deoxyfluorination Probe

Sigma-1 receptor (σ1R) is an intracellular protein implicated in a spectrum of neurodegenerative conditions, notably Alzheimer’s disease (AD). Positron emission tomography (PET) imaging of brain σ1R could provide a powerful tool for better understanding the underlying pathomechanism of σ1R in AD. In this study, we successfully developed a 18F-labeled σ1R radiotracer [18F]CNY-05 via an innovative ruthenium (Ru)-mediated 18F-deoxyfluorination method. [18F]CNY-05 exhibited preferable brain uptake, high specific binding, and slightly reversible pharmacokinetics within the PET scanning time window. PET imaging of [18F]CNY-05 in nonhuman primates (NHP) indicated brain permeability, metabolic stability, and safety. Moreover, autoradiography and PET studies of [18F]CNY-05 in the AD mouse model found a significantly decreased brain uptake compared to that in wild-type mice. Collectively, we have provided a novel 18F-radiolabeled σ1R PET probe, which enables visualizing brain σ1R in health and neurological diseases

Molecular Imaging of Alzheimer’s Disease-Related Sigma‑1 Receptor in the Brain <b><i>via</i></b> a Novel Ru-Mediated Aromatic ^<b>18</b>F‑deoxyfluorination Probe

Sigma-1 receptor (σ1R) is an intracellular protein implicated in a spectrum of neurodegenerative conditions, notably Alzheimer’s disease (AD). Positron emission tomography (PET) imaging of brain σ1R could provide a powerful tool for better understanding the underlying pathomechanism of σ1R in AD. In this study, we successfully developed a 18F-labeled σ1R radiotracer [18F]CNY-05 via an innovative ruthenium (Ru)-mediated 18F-deoxyfluorination method. [18F]CNY-05 exhibited preferable brain uptake, high specific binding, and slightly reversible pharmacokinetics within the PET scanning time window. PET imaging of [18F]CNY-05 in nonhuman primates (NHP) indicated brain permeability, metabolic stability, and safety. Moreover, autoradiography and PET studies of [18F]CNY-05 in the AD mouse model found a significantly decreased brain uptake compared to that in wild-type mice. Collectively, we have provided a novel 18F-radiolabeled σ1R PET probe, which enables visualizing brain σ1R in health and neurological diseases