Effective energy coupling and preservation in a surface plasmon-light emitter coupling system on a metal nanostructure

The simulation results of the coupling of a radiation dipole with a surface plasmon (SP), which is induced on a metal/dielectric interface of a single groove (SG) plus a grating structure, are demonstrated. With the SG structure, the dipole can effectively couple energy into an SP feature, which has a mixed nature of localized surface plasmon (LSP) and surface plasmon polariton (SPP). The SPP energy is confined by a grating structure with a well designed grating period and position. With such a cavity configuration, the SPP energy can be well preserved. Both the dipole-SP coupling behaviors in the frequency and time domains are numerically illustrated. The results are useful for designing a metal/dielectric interface nanostructure for implementing a SPASER (surface plasmon amplification by stimulated emission of radiation) system.

Study on the decay mechanisms of surface plasmon coupling features with a light emitter through time-resolved simulations

The transient behaviors of the dipole coupling with surface plasmon (SP) features in an Ag/dielectric-interface grating structure in order to understand the characteristics of those dipole-coupling features are demonstrated. In particular, the major decay mechanisms of those coupling features can be identified. For comparison, the time-resolved behaviors of the resonant surface plasmon polariton (SPP) coupling feature on a flat interface are also illustrated. Among the three major grating-induced SP-dipole coupling features, two of them are identified to be localized surface plasmons (LSPs). The third one is a grating-assisted SPP, which shows two decay components, corresponding to the first stage of SPP in-plane propagation and the second stage of coupling system decay. In all the dipole coupling features, metal dissipation can dominate the energy relaxation process, depending on the assumption of damping factor. All the dissipation rates are proportional to the assumed damping factor in the Drude model of the metal. The dissipation rates of the LSP and resonant SPP features are about the same as the damping rate, implying their local electron oscillation natures. The dissipation rate of the grating-assisted SSP feature is consistent with theoretical calculation. In the LSP features under study, dielectric-side emission is prominent. The coupled energy in the grating-assisted SPP feature can be efficiently stored in the coupling system due to its low emission efficiency and effective energy confinement through grating diffraction.

Effective indicators for diagnosis of oral cancer using optical coherence tomography

A swept-source optical coherence tomography system is used to clinically scan oral precancer and cancer patients for statistically analyzing the effective indicators of diagnosis. Three indicators are considered, including the standard deviation (SD) of an A-mode scan signal profile, the exponential decay constant (alpha) of an A-mode-scan spatial-frequency spectrum, and the epithelium thickness (T) when the boundary between epithelium and lamina propria can still be identified. Generally, in abnormal mucosa, the standard deviation becomes larger, the decay constant of the spatial-frequency spectrum becomes smaller, and epithelium becomes thicker. The sensitivity and specificity of the three indicators are discussed based on universal and individual relative criteria. It is found that SD and alpha are good diagnosis indicators for moderate dysplasia and squamous cell carcinoma. On the other hand, T is a good diagnosis indicator for epithelia hyperplasia and moderate dysplasia.

Effective indicators for diagnosis of oral cancer using optical coherence tomography

A swept-source optical coherence tomography system is used to clinically scan oral precancer and cancer patients for statistically analyzing the effective indicators of diagnosis. Three indicators are considered, including the standard deviation (SD) of an A-mode scan signal profile, the exponential decay constant (alpha) of an A-mode-scan spatial-frequency spectrum, and the epithelium thickness (T) when the boundary between epithelium and lamina propria can still be identified. Generally, in abnormal mucosa, the standard deviation becomes larger, the decay constant of the spatial-frequency spectrum becomes smaller, and epithelium becomes thicker. The sensitivity and specificity of the three indicators are discussed based on universal and individual relative criteria. It is found that SD and alpha are good diagnosis indicators for moderate dysplasia and squamous cell carcinoma. On the other hand, T is a good diagnosis indicator for epithelia hyperplasia and moderate dysplasia.

Localized surface plasmon-induced emission enhancement of a green light-emitting diode

The output enhancement of a green InGaN/GaN quantum-well (QW) light-emitting diode (LED) through the coupling of a QW with localized surface plasmons (LSPs), which are generated on Ag nanostructures on the top of the device, is demonstrated. The suitable Ag nanostructures for generating LSPs of resonance energies around the LED wavelength are formed by controlling the Ag deposition thickness and the post-thermal-annealing condition. With a 20 mA current injected onto the LED, enhancements of up to 150% in electroluminescence peak intensity and of 120% in integrated intensity are observed. By comparing this with a similar result for a blue LED previously published, it is confirmed that surface plasmon coupling for emission enhancement can be more effective for an InGaN/GaN QW of lower crystal quality, which normally corresponds to the emission of a longer wavelength.

Delineation of an oral cancer lesion with swept-source optical coherence tomography

We demonstrate the ex vivo imaging of an oral cancerous sample with a swept-source optical coherence tomography (SS-OCT) system. With the axial resolution of 8 microm in free space and system sensitivity of 108 dB, we can well distinguish the normal and abnormal tissue portions in a sample. In particular, we analyze the lateral variation of A-scan profiles to show two parameters of SS-OCT signal for delineating an oral cancer lesion. One of the parameters is the decay constant in the exponential fitting of the SS-OCT signal intensity along depth. This decay constant decreases as the A-scan point moves laterally across the margin of a lesion. The other parameter is the standard deviation of the SS-OCT signal intensity fluctuation in an A-scan. This parameter increases significantly when the A-scan point is moved across the transition region between the normal and abnormal portions. Such parameters are useful for determining the margins of oral cancer.

Measurement of the hemoglobin oxygen saturation level with spectroscopic spectral-domain optical coherence tomography

We report the measurement of the hemoglobin (Hb) oxygen saturation level in human blood with a spectroscopic spectral-domain optical coherence tomography (SSD-OCT) system based on the crossover behavior of Hb and oxyhemoglobin (HbO(2)) absorption coefficients around 800 nm. By calculating the ratio of the exponential decay constant of A-mode scan signal in the long-wavelength range (>800 nm) over that in the short-wavelength range (<800 nm), the relative oxygen saturation level of Hb can be calibrated. Such a relative level can be used for practical diagnosis application after a golden standard is built by comparing the variation of the OCT result with that of a conventional method, such as the use of a blood gas analyzer. In our experiment, the variation curve based on the SSD-OCT measurement, which has the advantages of noninvasive, real-time, and high-resolution measurements, is coincident with that of using a commercial blood gas analyzer.

Fabrication of high-aspect-ratio Fresnel zone plates by e-beam lithography and electroplating

The fabrication of gold Fresnel zone plates, by a combination of e-beam lithography and electrodeposition, with a 30 nm outermost zone width and a 450 nm-thick structure is described. The e-beam lithography process was implemented with a careful evaluation of applied dosage, tests of different bake-out temperatures and durations for the photoresist, and the use of a developer without methylisobutylketone. Electrodeposition with a pulsed current mode and with a specially designed apparatus produced the desired high-aspect-ratio nanostructures. The fabricated zone plates were examined by electron microscopy and their performances were assessed using a transmission X-ray microscope. The results specifically demonstrated an image resolution of 40 nm.

Recent progress in the development of inhibitors of human immunodeficiency virus (HIV) integrase for the management of HIV infection

Current therapy of acquired immune deficiency syndrome (AIDS) involves the use of a combination of at least three antiviral drugs to inhibit Human immunodeficiency virus 1 and 2 (HIV-1 and 2, in short HIV) replication via targeting of viral reverse transcriptase and protease. However, all anti-HIV drugs give rise to the new retroviral resistant strains. Therefore, new therapeutic agents against the emerging resistant HIV strains without secondary effects are very much needed. In HIV infection, the integration of viral DNA obtained from RNA genome into the chromosome of the host cell by viral integrase (IN) is essential for an effective viral replication. Moreover, no cellular IN has been found in the cells suggesting that viral IN appears to be one of the best candidates for the development of an antiviral drug. In recent years, promising results have proved that IN inhibitors are useful for treatment of retroviral infections. In this review, we briefly introduce IN and summarize potential inhibitors of IN, which are classified into several groups according to their origin and chemical structure. The resistance to the IN inhibitors is also discussed. Currently, several IN inhibitors are either being used in the clinical treatment or tested in clinical trials. Nevertheless, a great effort must be made to elicit wide knowledge with respect to the design of better viral inhibitors and the synthesis of new chemical derivatives with an anti-HIV activity.

Tissue birefringence of hypercholesterolemic rat liver measured with polarization-sensitive optical coherence tomography

We measure in vitro tissue birefringence in the liver of hypercholesterolemic rats with polarization-sensitive optical coherence tomography. Tissue birefringence is determined by measuring the phase retardation as a function of tissue depth. The birefringence of such a sample is usually due to the narrow fibrous structures that cannot be resolved by a standard optical coherence tomography system. Anisotropic structures are formed in the hypercholesterolemic rat liver, which is quite different from the isotropic nature of healthy liver. Birefringence is evaluated to give an order of magnitude of 4.48x10(-4) at 790 nm in hypercholesterolemic rat liver. The infiltration of macrophages and increased collagen deposition should be major causes for tissue birefringence in hypercholesterolemic liver.

Merging molecular and anatomical information: A feasibility study on rodents using microPET and MRI

OBJECTIVE

The use of the micro positron emission tomography (microPET) technique provides a powerful means for molecular imaging on small animals, while its inferior spatial resolution offers insufficient anatomical information which impedes the interpretations of the scans. To improve this limitation, it often relies on a clinical magnetic resonance imaging (MRI) for providing anatomical details. In this study, we designed and developed a new image co-registration platform which contains a stereotactic frame and external fiducial markers for microPET and MRI studies. The image co-registration accuracies were also validated by this new platform using various imaging protocols for microPET and MRI.

METHODS

The microPET images were reconstructed by filtered back-projection (FBP) and ordered subset expectation maximization (OSEM) methods. Two MRI pulse sequences, two-dimensional T1-weighted fast spin-echo (FSE) and three-dimensional spoiled gradient recalled (SPGR), were employed in the studies. Two MRI scanning protocols were proposed for small animal imaging: the whole-body high-speed mode and the partial high-resolution mode.

RESULTS

Reconstructed images from two different modalities were integrated by point-to-point registration via the external fiducials. Four inter-modality matched co-registration pairs (FBP-FSE, FBP-SPGR, OSEM-FSE, OSEM-SPGR) were obtained for both the high speed and high resolution modes. Co-registration accuracy was given as the average fiducial registration error (FRE) between the centroids of six markers from the registered images. The overall systemic FREs were about 0.50 mm.

CONCLUSIONS

From the inter-modality FRE comparison, MRI imaging with FSE performed better than that with SPGR sequence, due to its higher signal-to-noise ratio and less magnetic susceptibility effects. In the microPET perspective, the OSEM was superior to the FBP, as a result of fewer image artifacts.

28-Day oral toxicity study of the aqueous extract from spider brake (Pteris multifida Poiret) in rats

Spider brake (Pteris multifida Poiret) is a very important folk herb and a constituent in most of the traditional herbal beverage formulas in Taiwan; however, little toxicological information is available regarding the safety following repeated exposure. The present study was conducted to evaluate the toxicity of aqueous extract from spider brake (SB) in Sprague-Dawley rats on dietary oral gavage at concentrations of 100, 500, and 1000 mg/kg b.w. day for 28 days. There were no adverse effects on general condition, growth, feed and water consumption, feed conversion efficiency, red blood cell and clotting potential parameters, clinical chemistry values, and organ weights except for neutrophils and lymphocytes being slightly diminished in male and female rats at the highest dose, respectively. Necropsy and histopathology findings revealed no treatment-related changes in any of the organs. The results obtained in this study allowed us to conclude that the SB properly utilized in the traditional oral administration could be devoid of any toxic risk.

Numerical study on surface plasmon polariton behaviors in periodic metal-dielectric structures using a plane-wave-assisted boundary integral-equation method

A novel hybrid technique based on the boundary integral-equation method is proposed for studying the surface plasmon polariton behaviors in two-dimensional periodic structures. Considering the periodicity property of the problem, we use the plane-wave expansion concept and the periodic boundary condition instead of using the periodic Green's function. The diffraction efficiency can then be readily calculated once the equivalent electric and magnetic currents are solved that avoids invoking the numerical calculation of the radiation integral. The numerical validity is verified with the cases of highly conducting materials and practical metals. Numerical convergence can be easily achieved even in the case of a large incident angle as 80o. Based on the numerical scheme, a metal-dielectric wavy structure is designed for enhancing the transmittance of optical signal through the structure. The excitation of the coupled surface plasmon polaritons for the high transmission is demonstrated.

Formation of various metal nanostructures with thermal annealing to control the effective coupling energy between a surface plasmon and an InGaN/GaN quantum well

We demonstrate the variations of the photoluminescence (PL) spectral peak position and intensity through the surface plasmon (SP) coupling with an InGaN/GaN quantum well (QW) by forming Ag nanostructures of different scale sizes on the QW structure with thermal annealing. By transferring an Ag thin film into a nanoisland structure, we can not only enhance the PL intensity, but also adjust the SP dispersion relation and hence red-shift the effective QW emission wavelength. Such an emission spectrum control can be realized by initially coating Ag films of different thicknesses. Although the screening process of the quantum-confined Stark effect, which can result in PL spectrum blue-shift and intensity enhancement, also contributes to the variations of the emission behaviour, it is found that the SP-QW coupling process dominates in the observed phenomena.

Quasi-Isochoric Superheating of Nanoparticles Embedded in Rigid Matrixes

A thermodynamic model for pressure-induced quasi-isochoric superheating of nanoparticles embedded in rigid matrixes was established quantitatively by introducing the size dependence of melting enthalpy. The accuracy of the developed model was verified with the reported experimental data of Sn and Pb nanoparticles encapsulated in fullerene-like graphitic shells (FGS) as well as Ge nanoparticles embedded in SiO2. The mechanism behind the smaller superheating for Al nanoparticles embedded in Al2O3 was also studied. It was found that the extent of the superheating is determined by the pressure, which is in turn related to the confinement effect and to the size of the nanoparticles. Through the knowledge obtained in this study, it can be concluded that the extreme superheating of nanoparticles can be achieved on the proviso that they are encased in a sufficiently rigid matrix, while the size of nanoparticles is small enough.

Influence of oxygen defects on the crystal structure and magnetic properties of the (Tb1-xNax)MnO3-y (0<or=x<or=0.3) system

The crystallographic and magnetic behaviors of (Tb1-xNax)MnO3-y (0<or=x<or=0.3) have been studied by neutron powder diffraction (NPD), synchrotron X-ray powder diffraction, and Raman spectroscopy techniques. Although Na+ ions have larger ionic radii than Tb3+ ions, analysis of NPD data reveals a decrease in cell volume upon Na-doping, which can be explained solely by the occurrence of oxygen deficiencies and not by the size effect. The Raman spectrum represents the variation in bond length and bond angle, which originates from the balance of ions, asymmetric structure, and defects in the system. Na-doping causes an oxygen deficiency, and consequently, a peak shift is seen in the Raman spectrum because of the structural adjustment resulting from the doping. The observed effective moments decrease with increasing x because of the replacement of Tb3+ ions by Na+ ions. The well-defined peak at approximately 45 K (labeled TMn) of the x=0.3 sample is associated with Mn spin ordering, while the magnetic responses associated with TMn are not clearly present in the x=0.15 and x=0 samples.

Free radical-scavenging activity of aqueous extract of Pteris multifida Poiret

Aqueous extract of Pteris multifida showed scavenging activities on DPPH, hydroxyl radicals and reducing power.

Ultrafast pump-probe spectroscopy in the UV-blue range with an extremely broad probe spectrum for the carrier relaxation study in an InGaN thin film with indium-rich nano-clusters

We implement an extremely broad second-harmonic spectrum of about 90 nm in width based on a 7-fs mode-locked Ti:sapphire laser. This broadband second-harmonic signal is used as the probe in a non-degenerate pump-probe experiment to investigate the ultrafast carrier dynamics in wide band-gap semiconductors. To properly calibrate the pump-probe data, the time delays between the pump of a particular wavelength and the probes of various spectral portions are determined through the interferometry measurement and the dispersion calculation. To demonstrate the pump-probe experiment operation, we measure the carrier relaxation process from the excitation levels down to the free-carrier and the localized states in an InGaN thin-film sample, in which indium-rich nano-clusters exist to form the localized states. From the time-resolved differential transmission profiles at various spectral positions of an infinitesimal spectral width and the temporal evolution of probe spectrum, one can observe the following relaxation process: First, once carriers are excited, only a small portion of carriers relaxes into the free-carrier and localized states independently within 1 ps. Then, the major part of carriers starts to relax into the two groups of states not until several ps after excitation. Such a relaxation process does not seem to be cascading, i.e., relaxation into the localized states through the free-carrier states.

Chemical size effect on the magnetic and electrical properties in the (Tb(1-)(x)Eu(x))MnO(3) (0 < or = x < or = 1.0) system

The effect of isovalent chemical substitution of Eu3+ into the Tb3+ sites on the magnetic and electrical properties of (Tb1-xEux)MnO3 (0 </= x </= 1.0) system has been investigated. The orthorhombic structure with space group Pbnm is observed in this series of materials. An increase in Mn-O bond distance with increasing Eu content leads to improvement in the overlap between the Mn 3d and O 2p orbital thereby causing a decrease in activation energy and resistivity. Moreover, as the Eu content increases, the effective moments (mueff) are reduced linearly and an exchange coupling is observed in Tb-Tb, Tb-Eu, and Eu-Eu complexes for x = 0.1 and 0.3 samples. Both these features can be related to the substitution of bigger Eu3+ ions replacing the original Tb-Tb coupling.

Expression of sex-determining genes in human sebaceous glands and their possible role in the pathogenesis of acne

BACKGROUND

The human skin, especially the sebaceous gland, is a steroidogenic organ similar to the gonads and adrenal cortex, possessing all the enzymes required for steroid sex-hormone synthesis and metabolism. Factors regulating cutaneous steroidogenesis associated with disease status remain largely unknown.

OBJECTIVE

We hypothesized that transcription factors involved in sex formation and regulation of steroidogenesis in the classical steroidogenic organs are also expressed in the sebaceous glands. Their possible role in the pathogenesis of acne were investigated.

METHODS

We used reverse transcription polymerase chain reaction (RT-PCR), in situ hybridization and Western blotting to analyse the expression of SF-1, WT-1, SRY, SOX-9 and DAX-1 mRNAs and their proteins in cultured human sebocytes and the facial skin of acne patients.

RESULTS

The in situ hybridization study showed SOX-9 mRNA mainly localized in basal keratinocytes, the basal layer of the sebaceous glands and eccrine glands. Immortalized human sebaceous gland cells (SZ95) expressed mRNA for SOX-9, WT-1 and DAX-1 but not for SF-1 or SRY. The expression of DAX-1 protein was slightly inhibited by 10(-6) m oestradiol (E2) at 6 h but enhanced by 10(-6) m dihydrotestosterone (DHT) at 48 h. The facial expression of SOX-9 seemed to be higher in the acne-prone male patients, while DAX-1 was stronger in subjects without acne, although both were statistically insignificant.

CONCLUSION

Our findings confirm the expression of some sex-determining genes in human sebaceous glands. Further studies on a larger patient population including the normal controls are needed to elucidate the functional significance of these transcription factors in the pathogenesis of acne.

Leukoencephalopathy induced by levamisole alone for the treatment of recurrent aphthous ulcers

We report imaging and clinical findings of leukoencephalopathy occurring after levamisole. The lesions were hypoattenuating on CT and appeared as multifocal oval or elliptical foci in the white matter or along the subependymal veins on MRI. Most lesions resolve after prompt withdrawal of levamisole. Detailed history taking is important for diagnosing levamisole-induced leukoencephalopathy because multiple sclerosis and acute disseminated encephalomyelitis cannot be differentiated by neuroimaging findings alone.