Thermal effects on electron-phonon interaction in silicon nanostructures

Raman spectra from silicon nanostructures, recorded using excitation laser power density of 1.0 kW/cm^2, is employed here to reveal the dominance of thermal effects at temperatures higher than the room temperature. Room temperature Raman spectrum shows only phonon confinement and Fano effects. Raman spectra recorded at higher temperatures show increase in FWHM and decrease in asymmetry ratio with respect to its room temperature counterpart. Experimental Raman scattering data are analyzed successfully using theoretical Raman line-shape generated by incorporating the temperature dependence of phonon dispersion relation. Experimental and theoretical temperature dependent Raman spectra are in good agreement. Although quantum confinement and Fano effects persists, heating effects start dominating at higher temperatures than room tempaerature.Comment: 9 Pages, 3 Figures and 1 Tabl

Spectroscopic investigation of quantum confinement effects in ion implanted silicon-on-sapphire films

Crystalline Silicon-on-Sapphire (SOS) films were implanted with boron (B$^+$) and phosphorous (P$^+$) ions. Different samples, prepared by varying the ion dose in the range $10^{14}$ to 5 x $10^{15}$ and ion energy in the range 150-350 keV, were investigated by the Raman spectroscopy, photoluminescence (PL) spectroscopy and glancing angle x-ray diffraction (GAXRD). The Raman results from dose dependent B$^+$ implanted samples show red-shifted and asymmetrically broadened Raman line-shape for B$^+$ dose greater than $10^{14}$ ions cm$^{-2}$. The asymmetry and red shift in the Raman line-shape is explained in terms of quantum confinement of phonons in silicon nanostructures formed as a result of ion implantation. PL spectra shows size dependent visible luminescence at $\sim$ 1.9 eV at room temperature, which confirms the presence of silicon nanostructures. Raman studies on P$^+$ implanted samples were also done as a function of ion energy. The Raman results show an amorphous top SOS surface for sample implanted with 150 keV P$^+$ ions of dose 5 x $10^{15}$ ions cm$^{-2}$. The nanostructures are formed when the P$^+$ energy is increased to 350 keV by keeping the ion dose fixed. The GAXRD results show consistency with the Raman results.Comment: 9 Pages, 6 Figures and 1 Table, \LaTex format To appear in SILICON(SPRINGER

The role of tumour-derived iNOS in tumour progression and angiogenesis

BACKGROUND: Progressive tumour growth is dependent on the development of a functional tumour vasculature and highly regulated by growth factors and cytokines. Nitric oxide (NO) is a free radical, produced both by tumour and host cells, and functions as a signalling molecule downstream of several angiogenic factors. Both pro-and antitumourigenic properties have been attributed to NO. METHODS: The expression of the inducible isoform of NO synthase (iNOS) was knocked down in the C6 glioma cell line using constitutive expression of antisense RNA, and the effect of tumour-derived NO on tumour progression and angiogenesis was investigated. RESULTS: Tumours in which iNOS expression was decreased displayed significantly reduced growth rates compared with tumours derived from parental C6 cells. Quantitative non-invasive magnetic resonance imaging and fluorescence microscopy of tumour uptake of Hoechst 33342, and haematoxylin and eosin staining, revealed significantly impaired vascular development and function in antisense iNOS tumours compared with control in vivo, primarily associated with the more necrotic tumour core. Decreased iNOS expression had no effect on tumour VEGF expression. CONCLUSION: Nitric oxide derived from tumour iNOS is an important modulator of tumour progression and angiogenesis in C6 gliomas and further supports the therapeutic strategy of inhibiting iNOS for the treatment of cancer. British Journal of Cancer (2011) 104, 83-90. doi:10.1038/sj.bjc.6606034 www.bjcancer.com Published online 7 December 2010 (C) 2011 Cancer Research U

Medically Biodegradable Hydrogenated Amorphous Silicon Microspheres

[EN] Hydrogenated amorphous silicon colloids of low surface area (<5 m(2)/g) are shown to exhibit complete in-vitro biodegradation into orthosilicic acid within 10-15 days at 37 degrees C. When converted into polycrystalline silicon colloids, by high temperature annealing in an inert atmosphere, microparticle solubility is dramatically reduced. The data suggests that amorphous silicon does not require nanoscale porosification for full in-vivo biodegradability. This has significant implications for using a-Si:H coatings for medical implants in general, and orthopedic implants in particular. The high sphericity and biodegradability of submicron particles may also confer advantages with regards to contrast agents for medical imaging.This work has been partially supported by the Spanish CICyT projects, FIS2009-07812, Consolider CSD2007-046, MAT2009-010350 and PROMETEO/2010/043.Shabir, Q.; Pokale, A.; Loni, A.; Johnson, DR.; Canham, L.; Fenollosa Esteve, R.; Tymczenko, MK.... (2011). Medically Biodegradable Hydrogenated Amorphous Silicon Microspheres. Silicon. 3(4):173-176. https://doi.org/10.1007/s12633-011-9097-4S17317634Salonen J, Kaukonen AM, Hirvonen J, Lehto VP (2008) J Pharmaceutics 97:632–53Anglin EJ, Cheng L, Freeman WR, Sailor MJ (2008) Adv Drug Deliv Rev 60:1266–77O’Farrell N, Houlton A, Horrocks BR (2006) Int J Nanomedicine 1:451–72Canham LT (1995) Adv Mater 7:1037, PCT patent WO 97/06101,1999Park JH, Gui L, Malzahn G, Ruoslahti E, Bhatia SN, Sailor MJ (2009) Nature Mater 8:331–6Cullis AG, Canham LT, Calcott PDJ (1997) J Appl Phys 82:909–66Canham LT, Reeves CR (1996) Mat Res Soc Symp 414:189–90Edell DJ, Toi VV, McNeil VM, Clark LD (1992) IEEE Trans Biomed Eng 39:635–43Fenollosa R, Meseguer F, Tymczenko M (2008) Adv Mater 20:95Fenollosa R, Meseguer F, Tymczenko M, Spanish Patent P200701681, 2007Pell LE, Schricker AD, Mikulec FV, Korgel BA (2004) Langmuir 20:6546Xifré-Perez E, Fenollosa R, Meseguer F (2011) Opt Express 19:3455–63Fenollosa R, Ramiro-Manzano F, Tymczenko M, Meseguer F (2010) J Mater Chem 20:5210Xifré-Pérez E, Domenech JD, Fenollosa R, Muñoz P, Capmany J, Meseguer F (2011) Opt Express 19–4:3185–92Rodriguez I, Fenollosa R, Meseguer F, Cosmetics & Toiletries 2010;42–49Ramiro-Manzano F, Fenollosa R, Xifré-Pérez E, Garín M, Meseguer F (2011) Adv Mater 23:3022–3025. doi: 10.1002/adma.201100986Iler RK (1979) Chemistry of silica: solubility, polymerization, colloid & surface properties & biochemistry. Wiley, New YorkTanaka K, Maruyama E, Shimado T, Okamoto H (1999) Amorphous silicon. Wiley, New York, NYPatterson AL (1939) Phys Rev 56:978–82Canham LT, Reeves CL, King DO, Branfield PJ, Gabb JG, Ward MC (1996) Adv Mater 8:850–2Iler RK In: Chemistry of silica: solubility, polymerization, colloid & surface properties &Biochemistry. Wiley, New York, NYFinnie KS, Waller DJ, Perret FL, Krause-Heuer AM, Lin HQ, Hanna JV, Barbe CJ (2009) J Sol-Gel Technol 49:12–8Zhao D, Huo Q, Feng J, Chmelka BF, Stucky GD (1998) J Am Chem Soc 120:6024–36Fan D, Akkaraju GR, Couch EF, Canham LT, Coffer JL (2010) Nanoscale 1:354–61Tasciotti E, Godin B, Martinez JO, Chiappini C, Bhavane R, Liu X, Ferrari M (2011) Mol Imaging 10:56–

Connexin channels and phospholipids: association and modulation

<p>Abstract</p> <p>Background</p> <p>For membrane proteins, lipids provide a structural framework and means to modulate function. Paired connexin hemichannels form the intercellular channels that compose gap junction plaques while unpaired hemichannels have regulated functions in non-junctional plasma membrane. The importance of interactions between connexin channels and phospholipids is poorly understood.</p> <p>Results</p> <p>Endogenous phospholipids most tightly associated with purified connexin26 or connexin32 hemichannels or with junctional plaques in cell membranes, those likely to have structural and/or modulatory effects, were identified by tandem electrospray ionization-mass spectrometry using class-specific interpretative methods. Phospholipids were characterized by headgroup class, charge, glycerol-alkyl chain linkage and by acyl chain length and saturation. The results indicate that specific endogenous phospholipids are uniquely associated with either connexin26 or connexin32 channels, and some phospholipids are associated with both. Functional effects of the major phospholipid classes on connexin channel activity were assessed by molecular permeability of hemichannels reconstituted into liposomes. Changes to phospholipid composition(s) of the liposome membrane altered the activity of connexin channels in a manner reflecting changes to the surface charge/potential of the membrane and, secondarily, to cholesterol content. Together, the data show that connexin26 and connexin32 channels have a preference for tight association with unique anionic phospholipids, and that these, independent of headgroup, have a positive effect on the activity of both connexin26 and connexin32 channels. Additionally, the data suggest that the likely in vivo phospholipid modulators of connexin channel structure-function that are connexin isoform-specific are found in the cytoplasmic leaflet. A modulatory role for phospholipids that promote negative curvature is also inferred.</p> <p>Conclusion</p> <p>This study is the first to identify (endogenous) phospholipids that tightly associate with connexin channels. The finding that specific phospholipids are associated with different connexin isoforms suggests connexin-specific regulatory and/or structural interactions with lipid membranes. The results are interpreted in light of connexin channel function and cell biology, as informed by current knowledge of lipid-protein interactions and membrane biophysics. The intimate involvement of distinct phospholipids with different connexins contributes to channel structure and/or function, as well as plaque integrity, and to modulation of connexin channels by lipophilic agents.</p