Efficient spin-light emitting diodes based on InGaN/GaN quantum disks at room temperature: a new self-polarized paradigm.

A well-behaved spin-light emitting diode (LED) composed of InGaN/GaN multiple quantum disks (MQDs), ferromagnetic contact, and Fe3O4 nanoparticles has been designed, fabricated, and characterized. The degree of circular polarization of electroluminescence (EL) can reach up to a high value of 10.9% at room temperature in a low magnetic field of 0.35 T, which overcomes a very low degree of spin polarization in nitride semiconductors due to the weak spin-orbit interaction. Several underlying mechanisms play significant roles simultaneously in this newly designed device for the achievement of such a high performance. Most of all, the vacancy between nanodisks can be filled by half-metal nanoparticles with suitable energy band alignment, which enables selective transfer of spin polarized electrons and holes and leads to the enhanced output spin polarization of LED. Unlike previously reported mechanisms, this new process leads to a weak dependence of spin relaxation on temperature. Additionally, the internal strain in planar InGaN/GaN multiple quantum wells can be relaxed in the nanodisk formation process, which leads to the disappearance of Rashba Hamiltonian and enhances the spin relaxation time. Our approach therefore opens up a new route for the further research and development of semiconductor spintronics.

Three-dimensional structural imaging of starch granules by second-harmonic generation circular dichroism.

Chirality is one of the most fundamental and essential structural properties of biological molecules. Many important biological molecules including amino acids and polysaccharides are intrinsically chiral. Conventionally, chiral species can be distinguished by interaction with circularly polarized light, and circular dichroism is one of the best-known approaches for chirality detection. As a linear optical process, circular dichroism suffers from very low signal contrast and lack of spatial resolution in the axial direction. It has been demonstrated that by incorporating nonlinear interaction with circularly polarized excitation, second-harmonic generation circular dichroism can provide much higher signal contrast. However, previous circular dichroism and second-harmonic generation circular dichroism studies are mostly limited to probe chiralities at surfaces and interfaces. It is known that second-harmonic generation, as a second-order nonlinear optical effect, provides excellent optical sectioning capability when combined with a laser-scanning microscope. In this work, we combine the axial resolving power of second-harmonic generation and chiral sensitivity of second-harmonic generation circular dichroism to realize three-dimensional chiral detection in biological tissues. Within the point spread function of a tight focus, second-harmonic generation circular dichroism could arise from the macroscopic supramolecular packing as well as the microscopic intramolecular chirality, so our aim is to clarify the origins of second-harmonic generation circular dichroism response in complicated three-dimensional biological systems. The sample we use is starch granules whose second-harmonic generation-active molecules are amylopectin with both microscopic chirality due to its helical structure and macroscopic chirality due to its crystallized packing. We found that in a starch granule, the second-harmonic generation for right-handed circularly polarized excitation is significantly different from second-harmonic generation for left-handed one, offering excellent second-harmonic generation circular dichroism contrast that approaches 100%. In addition, three-dimensional visualization of second-harmonic generation circular dichroism distribution with sub-micrometer spatial resolution is realized. We observed second-harmonic generation circular dichroism sign change across the starch granules, and the result suggests that in thick biological tissue, second-harmonic generation circular dichroism arises from macroscopic molecular packing. Our result provides a new method to visualize the organization of three-dimensional structures of starch granules. The second-harmonic generation circular dichroism imaging method expands the horizon of nonlinear chiroptical studies from simplified surface/solution environments to complicated biological tissues.

Chiral imaging of collagen by second-harmonic generation circular dichroism.

We provide evidence that the chirality of collagen can give rise to strong second-harmonic generation circular dichroism (SHG-CD) responses in nonlinear microscopy. Although chirality is an intrinsic structural property of collagen, most of the previous studies ignore that property. We demonstrate chiral imaging of individual collagen fibers by using a laser scanning microscope and type-I collagen from pig ligaments. 100% contrast level of SHG-CD is achieved with sub-micrometer spatial resolution. As a new contrast mechanism for imaging chiral structures in bio-tissues, this technique provides information about collagen morphology and three-dimensional orientation of collagen molecules.

Novel insight into the inflammatory and cellular responses following experimental glaucoma surgery: a roadmap for inhibiting fibrosis.

Failure after glaucoma filtration surgery is attributed to fibrosis at the operated site. To understand the wound healing process after glaucoma filtration surgery, we have developed a mouse model for glaucoma filtration surgery which closely mimics the clinical response. In this study, we describe a systematic analysis of the wound healing response in vivo. Our data revealed that the post-surgical tissue response was separable into two distinguishable phases. The early "acute inflammatory" phase was characterized by significantly increased transcript expression of Vegfa, Cxcl1, Cxcl5, Ccl2, Ccl3, Ccl4, Gmcsf and specific Mmps as well as greater infiltration of monocytes/macrophages and T cells. The late "fibrotic" phase was characterized by an increased expression of Tgfb2 and extracellular matrix genes as well as a notable reduction of infiltrating inflammatory cells. Significantly, more mitotic cells were observed at both time points post-surgery. Subconjunctival fibroblasts may be involved in both phases since they have the capacity to reiterate the in vivo gene expression profiles upon either pro-inflammatory or pro-fibrotic cytokine stimulation. Given that the cellular and molecular targets that govern the early and late phases of wound healing are distinct and time sensitive, a multi-targeted therapeutic approach to sequentially inhibit inflammation and fibrogenesis at the critical time point may lead to improved surgical outcomes in glaucoma filtration surgery.

Synthesis and characterization of multifunctional periodic mesoporous organosilica from diureidophenylene bridged organosilica precursor.

This paper reports the periodic mesoporous organosilicas (PMOs) functionalised with newly synthesized bis-silylated (1,1(1,4-phenylene (bis-3-(3-triethoxysilylpropyl)urea)(BSBDA)) organosilica with 1,2-bis(triethoxysilyl) ethane (BTSE) using a co-condensation process. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen adsorption-desorption, NMR (proton, 13C and 29Si) spectra, and MALDI-TOF were used to characterise and evaluate the structural properties. The results showed that BSBDA is linked covalently to the mesochannel of the PMO frameworks. The pore size and overall structural properties in the functionalised PMOs were found to depend on the loading amounts of BSBDA. The overall results suggested that the highly functionalised PMOs could be tuned even at high BSBDA loadings (25 wt%).

Nonlinear bio-photonic crystal effects revealed with multimodal nonlinear microscopy.

Highly optically active nonlinear bio-photonic crystalline and semicrystalline structures in living cells were studied by a novel multimodal nonlinear microscopy. Numerous biological structures, including stacked membranes and aligned protein structures are highly organized on a nanoscale and have been found to exhibit strong optical activities through second-harmonic generation (SHG) interactions, behaving similarly to man-made nonlinear photonic crystals. The microscopic technology used in this study is based on a combination of different imaging modes including SHG, third-harmonic generation, and multiphoton-induced fluorescence. With no energy release during harmonic generation processes, the nonlinear-photonic-crystal-like SHG activity is useful for investigating the dynamics of structure-function relationships at subcellular levels and is ideal for studying living cells, as minimal or no preparation is required.

Multiphoton confocal microscopy using a femtosecond Cr:forsterite laser.

With its output wavelength covering the infrared penetrating window of most biological tissues at 1,200-1,250 nm, the femtosecond Cr:forsterite laser shows high potential to serve as an excellent excitation source for the multiphoton fluorescence microscope. Its high output power, short optical pulse width, high stability, and low dispersion in fibers make it a perfect replacement for the currently widely used Ti:sapphire laser. In this paper, we study the capability of using a femtosecond Cr:forsterite laser in multiphoton scanning microscopy. We have performed the multiphoton excited photoluminescence spectrum measurement on several commonly used bioprobes using the 1,230 nm femtosecond pulses from a Cr:forsterite laser. Efficient fluorescence can be easily observed in these bioprobes through two-photon or three-photon excitation processes. These results will assist in the selection of dichroic beam splitter and band pass filters in a multiphoton microscopic system. We have also performed the autofluorescence spectrum measurement from chlorophylls in live leaves of the plant Arabidopsis thaliana excited by 1,230 nm femtosecond pulses from the Cr:forsterite laser. Bright luminescence from chlorophyll, centered at 673 and 728 nm, respectively, can be easily observed. Taking advantage of the bright two-photon photoluminescence from chlorophyll, we demonstrated the two-photon scanning paradermal and cross-sectional images of palisade mesophyll cells in live leaves of Arabidopsis thaliana.

Mapping piezoelectric-field distribution in gallium nitride with scanning second-harmonic generation microscopy.

Taking advantage of the electric field-enhanced second-harmonic generation effect in bulk gallium nitride (GaN) and indium gallium nitride (InGaN) quantum wells, we demonstrated the piezoelectric field distribution mapping in bulk GaN and InGaN multiple-quantum-well (MQW) samples using scanning second-harmonic generation (SHG) microscopy. Scanning SHG microscopy and the accompanying third-harmonic generation (THG) microscopy of the bulk GaN sample were demonstrated using a femtosecond Cr:forsterite laser at a wavelength of 1230 nm. Taking advantage of the off-resonant electric field-enhanced SHG effect and the bandtail state-resonance THG effect, the second- and third-harmonic generation microscopic images obtained revealed the piezoelectric field and bandtail state distributions in a GaN sample. Combined with 720 nm wavelength excited two-photon fluorescence microscopy in the same sample, the increased defect density around the defect area was found to suppress bandedge photoluminescence, to increase yellow luminescence, to increase bandtail state density, and to decrease residue piezoelectric field intensity. Scanning SHG microscopy of the InGaN MQW sample was resonant excited with 800 nm femtosecond pulses from a Ti:sapphire laser in order to suppress SHG contribution from the bulk GaN substrate. Taking advantage of the strong piezoelectric field inside the InGaN quantum well, the wavelength resonant effect, and the electric field-enhanced SHG effect of InGaN quantum wells, resonant scanning SHG microscopy revealed the piezoelectric field distribution inside the wells. Combined with accompanying three-photon fluorescence microscopy from the bulk GaN substrate underneath the quantum wells, the direct correspondence between the piezoelectric field strength inside the quantum well and the substrate quality can be obtained. According to our study, the GaN substrate area with bright bandedge luminescence corresponds to the area with strong SHG signals indicating a higher stained-induced piezoelectric field. These scanning harmonic generation microscopies exhibit superior images of the piezoelectric field and defect state distributions in GaN and InGaN MQWs not available before. Combining with scanning multiphoton fluorescence microscopy, these techniques open new ways for the physical property study of this important material system and can provide interesting details that are not readily available by other microscopic techniques.

Multimodal nonlinear spectral microscopy based on a femtosecond Cr:forsterite laser.

We demonstrate a novel multimodal nonlinear spectral microscopy based on a femtosecond Cr:forsterite laser at 1230 nm. By acquiring the whole nonlinear spectrum in the visible and near-NIR region, this novel technique allows a combination of different imaging modalities, including second-harmonic generation, third-harmonic generation, and multiple-photon fluorescence. Combined with the selected excitation wavelength, which is located in the IR transparency window, this microscopic technique can provide high penetration depth with reduced damage and is ideal for studying living cells.

Induction of glutathione depletion, p53 protein accumulation and cellular transformation by tetrachlorohydroquinone, a toxic metabolite of pentachlorophenol.

Glutathione (GSH) conjugate formation with tetrachlorohydroquione (TCHQ) and the GSH content in vivo were measured by capillary zone electrophoresis. A more than 60% depletion of GSH content was found in liver tissue of mice treated with TCHQ. In addition, p53 protein accumulation and DNA fragmentation was induced by TCHQ. A two-stage model of chemical transformation of mouse embryonic fibroblasts was used to elucidate the transformation activity of TCHQ in vitro, and a 33% foci formation efficiency was found at the concentration of 5 microM. GSH depletion caused by TCHQ could abolish the protective ability of the cell against reactive oxygen species provided by GSH. When DNA was damaged, p53 protein accumulated in the nucleus and, in the case of severe damage, initiated apoptosis. TCHQ's ability to cause GSH depletion and DNA damage may play a role in the cytotoxic and genotoxic properties of its metabolic precursor, PCP.

Developmental differences in the expression of the cholera toxin sensitive subunit (Gs alpha) of adenylate cyclase in the rat small intestine.

BACKGROUND: The stimulatory guanosine triphosphate (GTP) binding protein alpha subunit (Gs alpha) of adenylate cyclase is the target protein for cholera toxin. AIMS/METHODS: The expression of this signal transducer was analysed in the small intestine of developing rats by RNA transfer (northern blot) analysis by immunoblotting, and by ADP-ribosylation of membrane proteins. RESULTS: Intestinal Gs alpha mRNA (about 1.9 kb) was increased in the neonate compared with the adult rat. Two isoforms of Gs alpha proteins, a 45,000 and a 52,000 form, were expressed in the small intestinal epithelial cell and both were ADP-ribosylated by cholera toxin. A significant increase in the larger isoform (52,000) and in its ribosylation was noted in the 2 week old suckling compared with post-weaned older animals. The protein content or ribosylation of the smaller form (45,000) did not significantly change with age. CONCLUSION: These data show that a developmental decline of intestinal Gs alpha expression seems to be, in part, regulated at the mRNA level. An increased Gs alpha expression in the immature intestine may help to explain a previously reported, dose dependent increased adenylate cyclase response and an increase in fluid secretion to cholera toxin in neonates compared with adults.

Development of the mucosal barrier: bacterial toxin interaction with the immature enterocyte.

The microvillus surface of the enterocyte has been studied extensively to determine if compositional differences in pre- and postweaned animals can account for the increased incidence of immunologic and infectious intestinal disease states in newborns. The interaction of cholera toxin with the developing enterocyte was studied with respect to receptor-effector response. In previous studies, we have reported that more toxin binds to the preweaned animal gut than to the postweaned. More recently we have shown that toxin causes an increased cAMP response and decreased Na+-K1+ATPase response, suggesting that the enhanced response to toxin by the immature enterocyte may contribute to increased toxigenic diarrhea in newborns.

myo-inositol action on gerbil intestine: alterations in alkaline phosphatase activity upon phosphatidylinositol depletion and repletion in vivo.

The influence of phosphatidylinositol (PI) on intestinal alkaline phosphatase activity was studied in myo-inositol deficient gerbils. A reduction of membrane PI in intestinal mucosa to 30-40% of the control was produced by feeding female gerbils a myo-inositol-deficient diet containing coconut oil for 2 weeks. As expected, the animals developed typical intestinal lipodystrophy with abnormal fat accumulation. In the PI-depleted animal, intestinal alkaline phosphatase activity was reduced to 20-30% of the control group. The levels of both membranous and soluble enzymes in intestinal mucosa were affected, but there were no changes in liver, kidney and plasma levels. When the lipodystrophic gerbils were given dietary myo-inositol, the complete repletion of intestinal membrane PI to the control level occurred 36 h later, whereas membrane-bound alkaline phosphatase activity in intestine was not restored to the control level until 72 h later. Administration of cycloheximide or actinomycin D did not block this enzyme induction. Lymphatic output of triacylglycerol into the bloodstream was stimulated 10-fold at 18 h of myo-inositol repletion, but there was no parallel increase in the activity of alkaline phosphatase in plasma during this early phase of intestinal recovery. Thus, these data suggest a possible regulatory role of PI in the processing and/or turnover of alkaline phosphatase in vivo, but a negative role of alkaline phosphatase in lipid transport across gerbil intestine.

myo-Inositol action on gerbil intestine. Association of phosphatidylinositol metabolism with lipid clearance.

The synthesis and turnover of phosphatidylinositol as well as clearance were studied in the intestines of lipodystrophic gerbils treated with or without an intraperitoneal dose of myo-inositol by monitoring the incorporation of 32Pi and the retention of absorbed [1-14C] palmitic acid. 1. myo-Inositol deficiency produced an intestinal lipodystrophy with a large lipid accumulation and a decreased level of phosphatidylinositol. Upon myo-inositol repletion, the intestinal phosphatidylinositol rapidly returned to the control level by h, at which time the removal of excess lipid still remained in a lag phase. 2. myo-Inositol injection caused an increase in the incorporation of 32Pi into phosphatidylinositol mainly due to an increased phosphatidylinositol synthesis de novo. As a result, the turnover of phosphatidylinositol molecules might increase because of an expanded pool size. 3. The stimulation of phosphatidylinositol synthesis was then followed by an enhanced clearance of absorbed [14C] palmitate and by an intestinal recovery which was monitored by the loss of accumulated triacylglycerol. 4. This study indicates that myo-inositol availability appears to regulate the in vivo biosynthesis of phosphatidylinositol which, in turn, may play a crucial role in normal lipid transport across gerbil intestine.

Lymph fatty acid composition during constant infusion of saturated fats of different chain lengths in the rat.

The fatty acid composition of intestinal lymph in the rat was determined during constant intraduodenal infusion of a single saturated fatty acid with chain length ranging from C8 to C18 in the form of mixed mono- and diglycerides. The appearance of the infused fatty acid in lymph triglycerides depended on the chain length with the optimum at 14 and 16. Fatty acids with chain length less than 14 were not significantly incorporated into lymph phospholipid and cholesterol ester. Lymph phospholipids had the highest specificity toward stearic acid and cholesterol esters toward palmitic acid. Feeding hydrogenated coconut oil to the rat diminished the essential fatty acids and induced eicosatrienoic acid (20:3 omega 9) present in lymph lipids with no change in the appearance of infused saturated fatty acids except an increase in the infused lauric acid in lymph triglyceride. This study also suggested that the rat intestine probably could synthesize and export triglycerides containing almost entirely myristic and palmitic acids, but unsaturated fatty acids apparently were required for the synthesis of other lipoprotein lipids to transport saturated fatty acids via the lymphatic pathway.

The relationship of plasma arginine and kidney arginase activity to arginine degradation in chickens.

Experiments were carried out to study urea excretion during arginine or ornithine infusion into wing veins of hens previously fed diets that induced different arginase levels in their kidneys. Urea excretion was found to increase as plasma arginine increased. Hens with high levels of arginase activity in their kidneys had a greater increase in urea excretion than hens with low kidney arginase activity. Arginine degradation was also dependent on both the kidney arginase activity and on the plasma level of arginine. Ornithine infusion did not inhibit urea excretion even when high levels of plasma ornithine were reached. Even though ornithine was an in vitro inhibitor of arginase, no evidence was obtained of in vivo inhibition.