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Detection and identification of low abundance biomarker proteins is frequently based on various types of membrane-based devices. Lowering of the protein detection limits is vital in commercial applications such as lateral flow assays and in Western blots widely used in proteomics. These currently suffer from insufficient detection sensitivity and low retention for small 2-5 kDa proteins. In this study, we report the deposition of two types of metal nanoparticles: gold colloids (50-95 nm diameter) and silver fractals onto a range of commonly used types of membranes including polyvinylidene fluoride (PVDF). Due to strong affinity of proteins to noble metals, such modified membranes have the potential to effectively capture trace proteins preventing their loss. The membranes modified by metal particles were characterized optically and by SEM. The membrane performance in protein dot blots was evaluated using the protein-fluorophore conjugates Deep Purple-bovine serum albumin and fluorescein-human serum albumin. We found that the metal nanoparticles increase light extinction by metals, which is balanced by increased fluorescence, so that the effective fluorescence signal is unchanged. This feature combined with the capture of proteins by the nanoparticles embedded in the membrane increases the detection limit of membrane assays. [ABSTRACT FROM AUTHOR]

Molecular beam epitaxy was used for the first time to grow novel GaAs/GaSb heterostructures with ultrathin (0.8-3 monolayers) GaAs layers embedded in GaSb. These structures were studied by X-ray diffraction, transmission electron microscopy, and photoluminescence. By contrast to known structures with selfassembled quantum dots, GaAs layers in GaAs/GaSb structures are subject to elastic tensile stresses due to 7% lattice mismatch. The structures exhibit intense photoluminescence in the 2 µm region at low temperatures. Quantum-dimensional islands are formed in the structure at a nominal GaAs layer thickness exceeding 1.5 monolayers. The band alignment of the structures is of type II. [ABSTRACT FROM AUTHOR]

An efficient combined numerical-analytical technique is developed for calculating states of the continuum spectrum in systems with quantum wells (QWs) with an arbitrary potential shape, described by a system of coupled Schrödinger equations, e.g., hole states in semiconductor QWs. Continuum-spectrum states are found exactly using the approach similar to the scattering theory. Scattering states (the in/out-solutions) and the S-matrix for the case of multichannel scattering in one-dimensional systems with QWs are constructed, and their symmetry is determined and analyzed. The method is applied to studying the hole scattering by GaInAs-InGaAsP QWs with strained layers. The hole transmission and reflection coefficients and the delay-time energy dependence are calculated in relation to parameters of the structures and values of the transversal momentum components. In the energy range in which the channel with heavy hole conversion into a propagating light hole is closed, scattering of the heavy hole on a QW has a resonant nature. [ABSTRACT FROM AUTHOR]

AlxGa1−xSb films in the regime 0×0.25 have been grown by metalorganic chemical vapor deposition on GaAs and GaSb substrates using TMAl, TMGa, and TMSb precursors. We report growth conditions and film properties, including the effect of V/III ratio and growth temperature on electrical and optical properties. Growth temperatures in the range of 520°C and 680°C and V/III ratios from 1 to 5 have been investigated. All epilayers grown exhibit p-type behavior. The mobility decreases and the carrier concentration increases sharply when a small amount of Al is incorporated into GaSb. The sharp cutoff and Fabry-Perot oscillations of the transmission spectra of the AlGaSb layers confirm the high quality of the films. The principle photoluminescence features observed are attributed to bound exciton and donor-acceptor transitions with FWHM comparable to the best values reported elsewhere. [ABSTRACT FROM AUTHOR]

We present results of photoluminescence and cathodoluminescence measurements of strained undoped In0.15Ga0.85As/GaAs and In0.15Ga0.85As/Al0.15Ga0.85As quantum well structures, designed to throw light on the current controversy over light-hole band alignment at low In content. We compare these data with theoretical calculations of the confined state energies within the eight band effective mass approximation. Our analysis shows that for In0.15Ga0.85As/GaAs, the observed two transitions are consistent with either type I or type II alignment of the light hole band for band offset ratios within the accepted range. In the case of In0.15Ga0.85As/Al0.15Ga0.85As, however, our results clearly indicate type II alignment for the light hole band. We derive the band offset ratio Q, defined here as Q = δEc/δEg where δEc is the conduction band offset and δEg is the bandgap difference between the quantum well and the barrier in the presence of strain, for the In0.15Ga0.85As/Al0.15Ga0.85As system to be Q = 0.83 and discuss it in the context of the common anion rule. [ABSTRACT FROM AUTHOR]