Silicon wire arrays, though attractive materials for use in photovoltaics and as photocathodes for hydrogen generation, have to date exhibited poor performance. Using a copper-catalyzed, vapor-liquid-solid–growth process, SiCl4 and BCl3 were used to grow ordered arrays of crystalline p-type silicon (p-Si) microwires on p+-Si(111) substrates. When these wire arrays were used as photocathodes in contact with an aqueous methyl viologen2+/+ electrolyte, energy-conversion efficiencies of up to 3% were observed for monochromatic 808-nanometer light at fluxes comparable to solar illumination, despite an external quantum yield at short circuit of only 0.2. Internal quantum yields were at least 0.7, demonstrating that the measured photocurrents were limited by light absorption in the wire arrays, which filled only 4% of the incident optical plane in our test devices. The inherent performance of these wires thus conceptually allows the development of efficient photovoltaic and photoelectrochemical energy-conversion devices based on a radial junction platform.

The identification of cell-penetrating peptides (CPPs) as vectors for the intracellular delivery of conjugated molecules such as peptides, proteins, and oligonucleotides has emerged as a significant tool to modulate biological activities inside cells. The mechanism of CPP uptake by the cells is still unclear, and appears to be both endocytotic and non-endocytotic, depending on the CPP and cell type. Moreover, it is also unknown whether cargo sequences have an effect on the uptake and cellular distribution properties of CPP sequences. Here, we combine results from quantitative fluorescence microscopy and binding to lipid membrane models to determine the effect of cargo peptide molecules on the cellular uptake and distribution of the arginine-rich CPPs, R7, and R7W, in live cells. Image analysis algorithms that quantify fluorescence were used to measure the relative amount of peptide taken up by the cell, as well as the extent to which the uptake was endocytotic in nature. The results presented here indicate that fusion of arginine-rich CPPs to peptide sequences reduces the efficiency of uptake, and dramatically changes the cellular distribution of the CPP from a diffuse pattern to one in which the peptides are mostly retained in endosomal compartments.

Degenerately doped N-type Si(111) wafers (0.004 ohm-cm) were thermally oxided to produce a 285 nm oxide film. These wafers were then coated with S1813 photoresist (Microchem), exposed to the pattern (square array of 3 µm holes, 7 µm center Control samples consisted of oxidized wafers that contained patterned openings in the oxide, but no gold was deposited, and wires were not grown on such samples. Photoelectrochemical Measurements

The lithographic-galvanic (LIGA) electrodes analyzed by Neudeck and Dunsch in terms of their cyclic voltammetry behavior are similar to the porous electrodes used in this study (ref 44). The LIGA electrodes are hexagonal arrays of pores with regular pore dimensions and pore-pore spacing. The porous electrodes used in this study, although not regular in pore dimension and spacing, are structurally similar, and therefore their normalized peak current behavior with respect to scan rate can be modeled using the same approach.Derivation of the expression for the peak potential requires several equations that relate the dimensionless radius, p, to the dimensionless potential, , and the dimensionless current , under various conditions. These quantities can be defined as:where r is the radius of the electrode, n is the number of moles of electrons involved in the reaction (n = 1 for Me 2 Fc), F is Faraday's constant, v is the scan rate, R is the gas constant, T is the absolute temperature, D is the diffusion coefficient (measured to be

Cell-penetrating peptides (CPPs), once postulated to cross cell membranes in a non-endocytic, non-energy-dependent process, have since been found to accumulate in vesicles in live mammalian cells. In this study, we show that it is possible to use laser light from a confocal microscope to cause labeled peptide-conjugated CPPs to redistribute from vesicles into the cytoplasm and nucleus of cells. Following redistribution, the cells are found to be biologically responsive, and they retain morphology for several hours. It was possible to initiate redistribution of both fluorescein- and Alexa633-labeled peptides by selective irradiation of one of the fluorophores. These peptides could potentially be used as tracers to selectively deliver cargo biomolecules into cells by laser illumination using a standard fluorescence confocal microscope.