T. Cloitre

Selection and mass spectrometry characterization of peptides targeting semiconductor surfaces.

We report on elaboration of 12‐mer peptides that reveal specific recognition for the following semiconductor (SC) surfaces: GaAs(100), InAs(100), GaN(0001), ZnSe(100), ZnTe(100), GaAs(111)A, GaSb(100), CdSe(100). A M13 bacteriophage library was used to screen 109 different 12‐mer peptides against these substrates to finally isolate, in maximum six amplification cycles, peptides that bind to the target surfaces. The specific peptides for the InAs and ZnSe surfaces were obtained. Contrary, for the other SC surfaces several peptides with high affinities have been isolated. Aiming for a better specificity, when the phage display has been conducted through six cycles, the screening procedure got dominated by a phage present in the M13 bacteriophage library and the SVSVGMKPSPRP peptide has been selected for different SCs. The high amplification potential of this phage has been observed previously with different targets. Thus, precaution should be undertaken in defining adhesion peptides with the phage display technique and real affinity of the obtained biolinkers should be studied with other methods. We employed mass spectrometry (MALDI‐TOF/TOF) to demonstrate the preferential attachment (or not) of the SVSVGMKPSPRP peptide to the different SC surfaces. This allows us to define a realistic selection of the expressed peptides presenting affinity for the studied eight SC surfaces. We demonstrate that with increasing the dielectric constants of the employed solvents, adhesion of the SVSVGMKPSPRP peptide onto GaN(0001) is hindered. Biotechnol. Bioeng. 2009; 104: 1121–1131.

MOVPE growth of zincblende magnesium sulphide

Abstract The successful growth of MgS epitaxial layers with the MOVPE technique is reported. The samples were grown on GaAs substrates in a classical horizontal reactor, using bis(methylcyclopentadienyl) magnesium and H 2 S as precursors. The zincblende structure of MgS layers is evidenced by careful X-ray diffraction analysis. The lattice constant is found to be about 5.66 A. The influence of the growth temperature on the morphology and quality of the layers is studied in detail.

Porous Silicon/Photosynthetic Reaction Center Hybrid Nanostructure

The purified photosynthetic reaction center protein (RC) from Rhodobacter sphaeroides R-26 purple bacteria was bound to porous silicon microcavities (PSiMc) either through silane-glutaraldehyde (GTA) chemistry or via a noncovalent peptide cross-linker. The characteristic resonance mode in the microcavity reflectivity spectrum red shifted by several nanometers upon RC binding, indicating the protein infiltration into the porous silicon (PSi) photonic structure. Flash photolysis experiments confirmed the photochemical activity of RC after its binding to the solid substrate. The kinetic components of the intraprotein charge recombination were considerably faster (τ(fast) = 14 (±9) ms, τ(slow) = 230 (±28) ms with the RC bound through the GTA cross-linker and only τ(fast) = 27 (±3) ms through peptide coating) than in solution (τ(fast) = 120 (±3) ms, τ(slow) = 1387 (±2) ms), indicating the effect of the PSi surface on the light-induced electron transfer in the protein. The PSi/RC complex was found to oxidize the externally added electron donor, mammalian cytochrome c, and the cytochrome oxidation was blocked by the competitive RC inhibitor, terbutryne. This fact indicates that the specific surface binding sites on the PSi-bound RC are still accessible to external cofactors and an electronic interaction with redox components in the aqueous environment is possible. This new type of biophotonic material is considered to be an excellent model for new generation applications at the interface of silicon-based electronics and biological redox systems designed by nature.

Low pressure metalorganic vapour-phase epitaxy growth of ZnTe using triethylamine dimethyl zinc adduct

Abstract We present for the first time a detailed investigation of the growth of ZnTe layers deposited on GaAs substrates by low pressure metalorganic vapour-phase epitaxy using the new triethylamine dimethyl zinc adduct in combination with diisopropyl telluride as zinc and tellurium precursors respectively. The influence of the growth temperature ( T g ), the VI/II molar ratio, and the overall growth pressure ( P ) are studied. The successful growth of ZnTe is demonstrated at temperatures as low as 300°C. For growth temperatures ranging between 300 and 450°C, the growth rate is limited by the kinetics at the growing interface, and we measure an activation energy of 28 kcal/mol. At T g = 375°C, we found a linear variation of the growth rate with the overall growth pressure on the one hand, and with both zinc and telluride molar flows on the other hand. Low temperature reflectance and photoluminescence measurements were performed to characterize all the samples and are used to determine the optimal growth conditions: T g = 350°C, VI/II = 2, with P = 40 Torr. The stress experienced by the epilayers is investigated using the reflectance measurements. The relative intensity of the arsenic related bound exciton emission at 2.367 eV decreases as T g decreases. On the other hand, the I 1 b unknown acceptor related bound exciton emission at 2.356 eV decreases linearly with the growth rate.

Assembly of Purple Membranes on Polyelectrolyte Films

The membrane protein bacteriorhodopsin in its native membrane bound form (purple membrane) was adsorbed and incorporated into polyelectrolyte multilayered films, and adsorption was in situ monitored by optical waveguide light-mode spectroscopy. The formation of a single layer or a double layer of purple membranes was observed when adsorbed on negatively or positively charged surfaces, respectively. The purple membrane patches adsorbed on the polyelectrolyte multilayers were also evidenced by atomic force microscopy images. The driving forces of the adsorption process were evaluated by varying the ionic strength of the solution as well as the purple membrane concentration. At high purple membrane concentration, interpenetrating polyelectrolyte loops might provide new binding sites for the adsorption of a second layer of purple membranes, whereas at lower concentrations only a single layer is formed. Negative surfaces do not promote a second protein layer adsorption. Driving forces other than just electrostatic ones, such as hydrophobic forces, should play a role in the polyelectrolyte/purple membrane layering. The subtle interplay of all these factors determines the formation of the polyelectrolyte/purple membrane matrix with a presumably high degree of orientation for the incorporated purple membranes, with their cytoplasmic, or extracellular side toward the bulk on negatively or positively charged polyelectrolyte, respectively. The structural stability of bacteriorhodopsin during adsorption onto the surface and incorporation into the polyelectrolyte multilayers was investigated by Fourier transform infrared spectroscopy in attenuated total reflection mode. Adsorption and incorporation of purple membranes within polyelectrolyte multilayers does not disturb the conformational majority of membrane-embedded alpha-helix structures of the protein, but may slightly alter the structure of the extramembraneous segments or their interaction with the environment. This high stability is different from the lower stability of the predominantly beta-sheet structures of numerous globular proteins when adsorbed onto surfaces.

Three-dimensional spatial resolution of the nonlinear photoemission from biofunctionalized porous silicon microcavity

Infiltration of biomacromolecules into porous silicon photonic architectures results in biofunctionalized structures with unique properties. Characterization of their optical response and performance optimization in biomacromolecular detection and biophotonic application require a combination of optical and structural studies. Nonlinear optical microscopy is applied to study porous silicon microcavities with and without infiltrated glucose oxidase. The infiltrated protein acts as an internal two-photon-excited fluorescence emitter and second harmonic generator, enabling the in-depth visualization of the porous structure. Enhanced second harmonic generation and fluorescence emission by the porous silicon structure is experimentally associated with the defect layer.

Multiphoton imaging of the dentine-enamel junction.

Multiphoton microscopy has been used to reveal structural details of dentine and enamel at the dentin-enamel junction (DEJ) based on their 2-photon excited fluorescence (2PEF) emission and second harmonic generation (SHG). In dentine tubule 2PEF intensity varies due to protein content variation. Intertubular dentin produces both SHG and 2PEF signals. Tubules are surrounded by a thin circular zone with a lower SHG signal than the bulk dentine and the presence of collagen fibers perpendicular to the tubule longitudinal axis is indicated by strong SHG responses. The DEJ appears as a low intensity line on the 2PEF images and this was never previously reported. The SHG signal is completely absent for enamel and aprismatic enamel shows a homogeneous low 2PEF signal contrary to prismatic enamel. The SHG intensity of mantle dentine is increasing from the dentine-enamel junction in the first 12 μm indicating a progressive presence of fibrillar collagen and corresponding to the more external part of mantle dentine where matrix metallo-proteases accumulate. The high information content of multiphoton images confirms the huge potential of this method to investigate tooth structures in physiological and pathological conditions.

Optical properties and thermal transport of carriers in (Zn,Cd)Se-ZnSe heterostructures

We report a detailed optical study of ZnSe-based graded index separate confinement heterostructures. These structures were grown by metalorganic vapor phase epitaxy and are composed of either one or two Zn0.79Cd0.21Se central well(s) embedded between two ZnCdSe barriers which cadmium composition varies linearly from 5% near the wells to 0% at the end of the barriers. 2K photoreflectance and reflectivity experiments allow the observation of excitonic transitions involving the third electron and heavy hole confined states. The temperature dependence of the photoluminescence lines under in-well resonant excitation conditions (Eexc = 2.661 eV) shows that the thermal quenching of the photoluminescence line is ruled by nonradiative recombinations on defects localized at the heterointerfaces at low temperature and by the thermal escape of the minority carriers at higher temperatures. Under above-barrier excitation conditions (Eexc=3.814 eV), the temperature dependence of the photoluminescence line from the well shows a strong influence of the mechanism of diffusion of the carriers from the barriers to the well.

Sensing by Means of Nonlinear Optics with Functionalized GaAs/AlGaAs Photonic Crystals

We report on specific functionalization of GaAs/AlGaAs photonic structures for molecular sensing via the optical second harmonic generation signal in the visible range exhibited by these nanostructures. Functionalization has been achieved by peptides selected by the phage display technology, revealing specific recognition for semiconducting surfaces. These small peptides when biotinylated serve for controlled placement of biotin onto the substrate to capture then streptavidin. Functionalization (with biotinylated peptide) and molecular recognition (of streptavidin) events both result in enhancing the nonlinear optical response of the samples. Adsorption and infiltration of biomolecules into the GaAs/AlGaAs photonic structure were monitored by atomic force and scanning electron microscopy combined with Energy Dispersive X-ray spectroscopy. We demonstrate that once functionalized with specific peptides, photonic structures could be used as miniature biosensors down to femtomolar detection sensitivity, by monitoring changes in the second harmonic signal when molecules are captured. Our results prove the outstanding sensitivity of the nonlinear approach in biosensing with photonic crystal waveguides as compared to linear absorption techniques on the same samples. The present work is expected to pioneer development of a new class of extremely small affinity-based biosensors with high sensitivity and demonstrates that photonic structures support device functionality that includes strongly confined and localized nonlinear radiation emission and detection processes.

Interactions at the Peptide/Silicon Surfaces: Evidence of Peptide Multilayer Assembly

Selective deposition of peptides from liquid solutions to n- and p-doped silicon has been demonstrated. The selectivity is governed by peptide/silicon adhesion differences. A noninvasive, fast characterization of the obtained peptide layers is required to promote their application for interfacing silicon-based devices with biological material. In this study we show that spectroscopic ellipsometry-a method increasingly used for the investigation of biointerfaces-can provide essential information about the amount of adsorbed peptide material and the degree of coverage on silicon surfaces. We observed the formation of peptide multilayers for a strongly binding adhesion peptide on p-doped silicon. Application of the patterned layer ellipsometric evaluation method combined with Sellmeier dispersion led to physically consistent results, which describe well the optical properties of peptide layers in the visible spectral range. This evaluation allowed the estimation of surface coverage, which is an important indicator of adsorption quality. The ellipsometric findings were well supported by atomic force microscopy results.