Crossover between Weak Antilocalization and Weak Localization of Bulk States in Ultrathin Bi2Se3 Films

We report transport studies on the 5 nm thick Bi2Se3 topological insulator films which are grown via molecular beam epitaxy technique. The angle-resolved photoemission spectroscopy data show that the Fermi level of the system lies in the bulk conduction band above the Dirac point, suggesting important contribution of bulk states to the transport results. In particular, the crossover from weak antilocalization to weak localization in the bulk states is observed in the parallel magnetic field measurements up to 50 Tesla. The measured magneto-resistance exhibits interesting anisotropy with respect to the orientation of B// and I, signifying intrinsic spin-orbit coupling in the Bi2Se3 films. Our work directly shows the crossover of quantum interference effect in the bulk states from weak antilocalization to weak localization. It presents an important step toward a better understanding of the existing three-dimensional topological insulators and the potential applications of nano-scale topological insulator devices

In vivo photoacoustic imaging of breast cancer tumor with HER2-targeted nanodiamonds

Radiation-damaged nanodiamonds (NDs) are ideal optical contrast agents for photoacoustic (PA) imaging in biological tissues due to their good biocompatibility and high optical absorbance in the near-infrared (NIR) range. Acid treated NDs are oxidized to form carboxyl groups on the surface, functionalized with polyethylene glycol (PEG) and human epidermal growth factor receptor 2 (HER2) targeting ligand for breast cancer tumor imaging. Because of the specific binding of the ligand conjugated NDs to the HER2-overexpressing murine breast cancer cells (4T1.2 neu), the tumor tissues are significantly delineated from the surrounding normal tissue at wavelength of 820 nm under the PA imaging modality. Moreover, HER2 targeted NDs (HER2-PEG-NDs) result in higher accumulation in HER2 positive breast tumors as compared to non-targeted NDs after intravenous injection (i.v.). Longer retention time of HER-PEG-NDs is observed in HER2 overexpressing tumor model than that in negative tumor model (4T1.2). This demonstrates that targeting moiety conjugated NDs have great potential for the sensitive detection of cancer tumors and provide an attractive delivery strategy for anti-cancer drugs

Target Nanodiamonds as Phenotype Specific Photoacoustic Contrast Agents for Breast Cancer

AIM: The aim is to develop irradiated nanodiamonds (INDs) as a molecularly-targeted contrast agent for high resolution and phenotype-specific detection of breast cancer with photoacoustic (PA) imaging. MATERIALS & METHODS: The surface of acid treated radiation-damaged nanodiamonds was grafted with polyethylene glycol (PEG) to improve its stability and circulation time in blood, followed by conjugation to an anti-Human epidermal growth factor receptor-2 (HER2) peptide (KCCYSL) with a final nanoparticle size of ca. 92 nm. Immunocompetent mice bearing orthotopic HER2 positive or negative tumors were administered INDs and PA imaged using an 820-nm near infrared laser. RESULTS: PA images demonstrated that INDs accumulate in tumors and completely delineated the entire tumor within 10 hours. HER2 targeting significantly enhanced imaging of HER2-positive tumors. Pathological examination demonstrated INDs are non-toxic. CONCLUSIONS: PA technology is adaptable to low-cost bedside medicine, and with new contrast agents described herein, PA can achieve high resolution (sub-mm) and phenotype specific monitoring of cancer growth

Electron interaction-driven insulating ground state in Bi2Se3 topological insulators in the two dimensional limit

We report a transport study of ultrathin Bi2Se3 topological insulators with thickness from one quintuple layer to six quintuple layers grown by molecular beam epitaxy. At low temperatures, the film resistance increases logarithmically with decreasing temperature, revealing an insulating ground state. The sharp increase of resistance with magnetic field, however, indicates the existence of weak antilocalization, which should reduce the resistance as temperature decreases. We show that these apparently contradictory behaviors can be understood by considering the electron interaction effect, which plays a crucial role in determining the electronic ground state of topological insulators in the two dimensional limit.Comment: 4 figure

Effect and mechanism of exogenous selenium on selenium content and quality of fresh tea leaves

To study the effect and mechanism of selenium sources on the selenium content and quality of fresh tea leaves, tea seedlings (Camellia sinensis (L.) O. Kuntze) were the research object. A solution of 100 mg/L sodium selenate (Na2SeO4), sodium selenite (Na2SeO3), and selenium yeast (selenium yeast) were applied on the leaves surface of 5-week-old tea plants, and the selenium levels in the leaves, roots, and stems were determined at 20 weeks of age. The effects of different selenium sources on the mineral nutrient content, antioxidant enzyme activity, and quality parameters content in leaves were analyzed. The mechanism was analyzed by detecting the expression levels of related genes. The results showed that the three selenium sources can increase the growth of tea seedlings and the selenium content in leaves and stems, and the selenium yeast treatment had the most significant effect. Selenium spraying promoted the absorption of mineral nutrients such as nitrogen, phosphorus, and potassium, but had no significant impact on the absorption of calcium and magnesium. Spraying the three selenium sources dramatically increased the activities of APX, POD, and SOD antioxidant enzymes, among which the selenium yeast treatment had the most significant effect. However, there was no significant impact on the MDA level in this study. Selenium sources markedly increased leaves total amino acid levels, accompanied by up-regulation the genes of amino acid synthetic enzymes (CsGS, CsGOGAT, and CsGDH). Leaves glucose, tea polyphenol, total soluble protein, catechin, flavonoid contents, and sucrose were higher in selenium sources treatments than in control treatment seedlings. Moreover, selenium sources up-regulated expression of CsHMGR, CsAPX, and CsTCS1 genes. selenium yeast had the best comprehensive effect of the three selenium sources. These results confirmed that selenium sources play a positive role on the selenium content and quality of tea by increasing the antioxidant capacity of leaves, the absorption rate of mineral nutrients, and regulating expression of related genes in Camellia sinensis

Lymphotoxin-β regulates periderm differentiation during embryonic skin development

Lymphotoxin-beta (LTbeta) is a key regulator of immune system development, but also affects late stages in hair development. In addition, high expression of LTbeta at an early stage in epidermis hinted at a further function in hair follicle induction or epithelial development. We report that hair follicles were normally induced in LTbeta(-/-) skin, but the periderm detached from the epidermis earlier, accompanied by premature appearance of keratohyalin granules. Expression profiling revealed dramatic down-regulation of a gene cluster encoding periderm-specific keratin-associated protein 13 and four novel paralogs in LTbeta(-/-) skin prior to periderm detachment. Epidermal differentiation markers, including small proline-rich proteins, filaggrins and several keratins, were also affected, but transiently in LTbeta(-/-) skin at the time of abnormal periderm detachment. As expected, Tabby mice, which lack the EDA gene, the putative upstream regulator of LTbeta in skin, showed similar though milder periderm histopathology and alterations in gene expression. Overall, LTbeta shows a primary early function in periderm differentiation, with later transient effects on epidermal and hair follicle differentiation

Photoacoustic contrast imaging of biological tissues with nanodiamonds fabricated for high near-infrared absorbance

This is the publisher's version, also available electronically from http://biomedicaloptics.spiedigitallibrary.org/article.aspx?articleid=1619539Radiation-damaged nanodiamonds (DNDs) are potentially ideal optical contrast agents for photoacoustic (PA) imaging in biological tissues due to their low toxicity and high optical absorbance. PA imaging contrast agents have been limited to quantum dots and gold particles, since most existing carbon-based nanoparticles, including fluorescent nanodiamonds, do not have sufficient optical absorption in the near-infrared (NIR) range. A new DND by He+ ion beam irradiation with very high NIR absorption was synthesized. These DNDs produced a 71-fold higher PA signal on a molar basis than similarly dimensioned gold nanorods, and 7.1 fmol of DNDs injected into rodents could be clearly imaged 3 mm below the skin surface with PA signal enhancement of 567% using an 820-nm laser wavelength