Nanoantenna-Microcavity Hybrids with Highly Cooperative Plasmonic-Photonic Coupling

Nanoantennas offer the ultimate spatial control over light by concentrating optical energy well below the diffraction limit, whereas their quality factor (Q) is constrained by large radiative and dissipative losses. Dielectric microcavities, on the other hand, are capable of generating a high Q-factor through an extended photon storage time but have a diffraction-limited optical mode volume. Here we bridge the two worlds, by studying an exemplary hybrid system integrating plasmonic gold nanorods acting as nanoantennas with an on-resonance dielectric photonic crystal (PC) slab acting as a low-loss microcavity and, more importantly, by synergistically combining their advantages to produce a much stronger local field enhancement than that of the separate entities. To achieve this synergy between the two polar opposite types of nanophotonic resonant elements, we show that it is crucial to coordinate both the dissipative loss of the nanoantenna and the Q-factor of the low-loss cavity. In comparison to the antenna-cavity coupling approach using a Fabry-Perot resonator, which has proved successful for resonant amplification of the antenna's local field intensity, we theoretically and experimentally show that coupling to a modest-Q PC guided resonance can produce a greater amplification by at least an order of magnitude. The synergistic nanoantenna-microcavity hybrid strategy opens new opportunities for further enhancing nanoscale light-matter interactions to benefit numerous areas such as nonlinear optics, nanolasers, plasmonic hot carrier technology, and surface-enhanced Raman and infrared absorption spectroscopies.Comment: Revised version after acceptanc

Growth of Large-Area and Highly Crystalline MoS2 Thin Layers on Insulating Substrates

The two-dimensional layer of molybdenum disulfide (MoS2) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high quality and large-area MoS2 atomic thin layers is still rare. Here we report that the high temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS2 thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS2 sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS2 layer is comparable with those of the micromechanically exfoliated thin sheets from MoS2 crystals. This synthetic approach is simple, scalable and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.Comment: manuscript submitted on 11-Dec-2011, revision submitted on 16-Feb-201

Hollow and Porous Plasmonic Nanostructures for Highly Efficient Chemical and Biological Sensing

Localized surface plasmon resonance (LSPR) involves the collective and coherent oscillation of dielectrically confined conduction electrons. The LSPR wavelength of noble metal nanoparticles (such as gold, silver and copper), which falls into the visible and near infrared range of the electromagnetic spectrum, is sensitive to the composition, size, shape, dielectric properties of the surrounding medium, and proximity to other nanostructures (plasmon coupling). Based on the sensitivity of the surface plasmon resonance to the changes in the dielectric properties of the surrounding medium and the enhancement of the electromagnetic (EM) field in proximity of metal nanostructures, two important classes of plasmonic sensors have evolved: refractometric LSPR and surface enhanced Raman scattering (SERS) sensors. SERS involves the large enhancement of the Raman scattering from analytes adsorbed on or in close proximity to a nanostructured metal surface. Most of the SERS substrates based on individual nanostructures offer modest SERS enhancement. On the other hand, interstitial sites between assembled or lightly aggregated nanostructures, often termed as electromagnetic hotspots, offer large SERS signal enhancements, enabling the single molecule detection under ideal conditions. Although the assemblies of nanostructures are highly SERS-active, the SERS response is very sensitive to the assembly state, thus making it challenging to realize uniform and reproducible SERS substrates with high density of EM hotspots based on such traditional assemblies. Furthermore, the fabrication of SERS substrates based on the controlled assemblies of nanostructures involves either complex chemical methods or expensive lithographic techniques. Therefore, it is desirable to engineer nanostructures with inherent EM hotspots, which can significantly enhance the EM field and enable the sensitive detection of analytes using SERS. Hollow and porous metal nanostructures are a novel class of plasmonic nanostructures that exhibit extraordinary optical and catalytic properties compared to their solid counterparts, due to a higher surface to volume ratio and the facile tunability of the LSPR wavelength over a broad range from visible to parts of near infrared. In this work, we design, synthesize, and comprehensively characterize the optical properties of hollow nanostructures including plasmonic nanocages and nanorattles comprised of gold nanostructures as cores and porous gold cube as shells. We demonstrate that hollow and porous plasmonic nanostructures exhibit a significantly higher refractive index sensitivity compared to other solid nanostructures of similar size, leading to LSPR sensors with higher sensitivity and lower limit-of-detection compared to biosensors based on solid counterparts. Furthermore, we demonstrate that plasmonic nanorattles host electromagnetic hotspots between the core and the shell, offering significantly higher SERS enhancement as compared to other solid nanostructures of similar size. Through a systematic study, we unveil the influence of size, shape and orientation of the plasmonic nanorattles on the optical properties and SERS enhancement. The work described here provides guidelines for the design of hollow plasmonic nanostructures for various sensing applications

Spirit-Quieting Traditional Chinese Medicine May Improve Survival in Prostate Cancer Patients with Depression

Depression is associated with higher mortality in prostate cancer. However, whether traditional Chinese medicine (TCM) for depression improves outcomes in patients with prostate cancer is unclear. This retrospective cohort study evaluated the association between TCM for depression and mortality in patients with prostate cancer. During the period 1998⁻2012, a total of 248 prostate cancer patients in Taiwan with depression were enrolled and divided into three groups: TCM for depression (n = 81, 32.7%), TCM for other purposes (n = 53, 21.3%), and no TCM (n = 114, 46.0%). During a median follow-up of 6.2 years, 12 (14.8%), 13 (24.5%), and 36 (31.6%) deaths occurred in the TCM for depression, TCM for other purposes, and no TCM groups, respectively. After adjusting age at diagnosis, urbanization, insured amount, comorbidity disease, and prostate cancer type, TCM for depression was associated with a significantly lower risk of overall mortality based on a multivariate-adjusted Cox proportional-hazards model (hazard ratio 0.42, 95% confidence interval: 0.21⁻0.85, p = 0.02) and Kaplan⁻Meier survival curve (log-rank test, p = 0.0055) compared to no TCM. In conclusion, TCM for depression may have a positive association with the survival of prostate cancer patients with depression

Highly Flexible MoS₂ Thin-Film Transistors with Ion Gel Dielectrics

Molybdenum disulfide (MoS₂) thin-film transistors were fabricated with ion gel gate dielectrics. These thin-film transistors exhibited excellent band transport with a low threshold voltage (<1 V), high mobility (12.5 cm²/(V·s)) and a high on/off current ratio (10⁵). Furthermore, the MoS₂ transistors exhibited remarkably high mechanical flexibility, and no degradation in the electrical characteristics was observed when they were significantly bent to a curvature radius of 0.75 mm. The superior electrical performance and excellent pliability of MoS₂ films make them suitable for use in large-area flexible electronics

Wood–Graphene Oxide Composite for Highly Efficient Solar Steam Generation and Desalination

Solar steam generation is a highly promising technology for harvesting solar energy, desalination and water purification. We introduce a novel bilayered structure composed of wood and graphene oxide (GO) for highly efficient solar steam generation. The GO layer deposited on the microporous wood provides broad optical absorption and high photothermal conversion resulting in rapid increase in the temperature at the liquid surface. On the other hand, wood serves as a thermal insulator to confine the photothermal heat to the evaporative surface and to facilitate the efficient transport of water from the bulk to the photothermally active space. Owing to the tailored bilayer structure and the optimal thermo-optical properties of the individual components, the wood–GO composite structure exhibited a solar thermal efficiency of ∼83% under simulated solar excitation at a power density of 12 kW/m². The novel composite structure demonstrated here is highly scalable and cost-efficient, making it an attractive material for various applications involving large light absorption, photothermal conversion and heat localization

Influence of Surface Charge of the Nanostructures on the Biocatalytic Activity

The physicochemical properties of abiotic nanostructures determine the structure and function of biological counterparts in biotic–abiotic nanohybrids. A comprehensive understanding of the interfacial interactions and the predictive capability of their structure and function is paramount for virtually all fields of bionanotechnology. In this study, using plasmonic nanostructures as a model abiotic system, we investigate the effect of the surface charge of nanostructures on the biocatalytic reaction kinetics of a bound enzyme. We found that the surface charge of nanostructures profoundly influences the structure, orientation, and activity of the bound enzyme. Furthermore, the interactions of the enzyme with nanoparticles result in stable conjugates that retain their functionality at elevated temperatures, unlike their free counterparts that lose their secondary structure and biocatalytic activity

Depression Negatively Impacts Survival of Patients with Metastatic Prostate Cancer

The prevalence of depression in patients with cancer is high, especially for patients with advanced cancer. In this study, we evaluated the prevalence of depression in prostate cancer patients in Taiwan and the association between depression and mortality in prostate cancer. This study included 1101 newly diagnosed patients with prostate cancer. We tracked the medical information of these patients from diagnosis until the end of 2012. Patients were divided into two groups according to presence or absence of depression diagnosis, and were further divided into three stages by initial treatments: localized or locally advanced, metastatic, and castration-resistant prostate cancer. Of 1101 participants, 267 (24.3%) had depression. By the end of the follow-up period (M = 8.30 &plusmn; 3.12 years), 77 (28.8%) patients in the depression group and 194 (23.3%) in the non-depressed group died. Depression was associated with higher mortality risk, (aHR 1.37; 95% CI [ 1.04&ndash;1.80]; p value 0.01). Patients in the metastatic prostate cancer group with depression had a significantly higher mortality risk compared to the non-depressed group, (aHR, 1.49; 95% CI [1.05&ndash;2.11]; p value 0.02). The impact of depression on mortality risk was not significant in either the localized or locally advanced or the castration-resistant prostate cancer groups. Our study showed that depression is related to an increased mortality risk for patients with prostate cancer, especially for metastatic prostate cancer. These results indicate that urologists should pay attention to the mood and psychiatric disorders of patients with prostate cancer