Electron transfer (ET) through proteins, a fundamental element of many biochemical reactions, is studied intensively in aqueous solutions. Over the past decade, attempts were made to integrate proteins into solid-state junctions in order to study their electronic conductance properties. Most such studies to date were conducted with one or very few molecules in the junction, using scanning probe techniques. Here we present the high-yield, reproducible preparation of large-area monolayer junctions, assembled on a Si platform, of proteins of three different families: azurin (Az), a blue-copper ET protein, bacteriorhodopsin (bR), a membrane protein-chromophore complex with a proton pumping function, and bovine serum albumin (BSA). We achieve highly reproducible electrical current measurements with these three types of monolayers using appropriate top electrodes. Notably, the current-voltage (I-V) measurements on such junctions show relatively minor differences between Az and bR, even though the latter lacks any known ET function. Electron Transport (ETp) across both Az and bR is much more efficient than across BSA, but even for the latter the measured currents are higher than those through a monolayer of organic, C18 alkyl chains that is about half as wide, therefore suggesting transport mechanism(s) different from the often considered coherent mechanism. Our results show that the employed proteins maintain their conformation under these conditions. The relatively efficient ETp through these proteins opens up possibilities for using such biomolecules as current-carrying elements in solid-state electronic devices.

A new design of dye-sensitized solar cells involves colloidal semiconductor quantum dots that serve as antennas, funneling absorbed light to the charge separating dye molecules via nonradiative energy transfer. The colloidal quantum dot donors are incorporated into the solid titania electrode resulting in high energy transfer efficiency and significant improvement of the cell stability. This design practically separates the processes of light absorption and charge carrier injection, enabling us to optimize each of these separately. Incident photon-to-current efficiency measurements show a full coverage of the visible spectrum despite the use of a red absorbing dye, limited only by the efficiency of charge injection from the dye to the titania electrode. Time resolved luminescence measurements clearly relate this to Forster resonance energy transfer from the quantum dots to the dye. The presented design introduces new degrees of freedom in the utilization of quantum dot sensitizers for photovoltaic cells. In particular, it opens the way toward the utilization of new materials whose band offsets do not allow direct charge injection.

The optical diffraction limit imposes a bound on imaging resolution in classical optics. Over the last twenty years, many theoretical schemes have been presented for overcoming the diffraction barrier in optical imaging using quantum properties of light. Here, we demonstrate a quantum superresolution imaging method taking advantage of nonclassical light naturally produced in fluorescence microscopy due to photon antibunching, a fundamentally quantum phenomenon inhibiting simultaneous emission of multiple photons. Using a photon counting digital camera, we detect antibunching-induced second and third order intensity correlations and perform subdiffraction limited quantum imaging in a standard wide-field fluorescence microscope.

Plasmonic antennas are key elements to control the luminescence of quantum emitters. However, the antenna's influence is often hidden by quenching losses. Here, the luminescence of a quantum dot coupled to a gold dimer antenna is investigated. Detailed analysis of the multiply excited states quantifies the antenna's influence on the excitation intensity and the luminescence quantum yield separately

D ye-sensitized solar cells (DSSCs) are a promising low-cost alternative to existing crystalline silicon and thin-film photovoltaic technologies. 1 Photoconversion efficiencies higher than 11.5% have been reported for DSSCs based on nanoporous TiO 2 electrodes. 2 In these cells, titania crystallites are covered with dye molecules, and the mesoporous film architecture is interpenetrated with a liquid electrolyte. The crystallite network is the recipient of injected electrons from optically excited dye molecules and provides a conductive pathway to the transparent back contact. The redox species in the electrolyte transport the holes from the oxidized dyes to the counter electrode.Despite the current performance, widespread use of DSSCs requires higher efficiencies with preference to a solid version of the redox mediator. Solid mediators seem to be more appropriate for large-scale fabrication and less sensitive to cell sealing. Moreover, the desired photovoltage increase in DSSCs (>800 mV) is mostly observed in solid mediator based cells. 3 The traditional absorbers in DSSCs are rutheniumbased complexes (for example, N719 and N3) that have fairly broad absorption spectra (Δλ = 350 nm) but low molar extinction coefficients (5000À20 000 M À1 cm À1 ), requiring the use of high-surface-area electrodes. 2,4 However, most solid electrolytes do not operate well in the thick nanoporous electrodes that provide the necessary surface area. Therefore, a key to improving the efficiency of DSSCs is to increase the sensitizer extinction while extending the spectral response region of the sensitizer to the near-IR region. 5 Many efforts have been made to increase the absorption extinction coefficient and to widen the spectral response of the photosensitizers. New organic dyes and organometallic complexes were synthesized and optimized for efficient light harvesting. 6 Dye cocktails or cosensitizers that broaden the absorption spectrum were tested, 7,8 and bisensnitizer layers that lead to a much higher sensitizer surface concentration were developed. 9 Similar geometries using inorganic semiconductor sensitizers (nanocrystals, quantum dots, thin layers) have been proposed. 10À17 For example, monodispersed semiconductor quantum dots (QDs) such as CdTe, CdS, CdSe, PbS, and InP have exceptionally high extinction coefficients. The optical and electronic properties of the QDs can be tailored by controlling their size and by engineering of the heterostructures. 18À21 Surface chemistry permits adjustment of their surface function. 22À27 In contrast with the Semiconductor quantum dot donors can enable broadening of the spectral response and increased optical density of the cell, thus increasing the current while potentially decreasing the electrode thickness.ABSTRACT: The use of F€ orster resonant energy transfer (FRET) has recently shown promise for significant improvement in various aspects of photoelectrochemical cells.Considering the particular case of semiconductor quantum dot donors, we show that they can enable broadening of the sp...