Coupling hCG-based protease sensors with a commercial pregnancy test strip for simple analyses of protease activities.

Proteases play an essential role in many cellular processes, and consequently, abnormalities in their activities are related to various diseases. Methods have been developed to measure the activity of these enzymes, but most involve sophisticated instruments or complicated procedures, which hampers the development of a point-of-care test (POCT). Here, we propose a strategy for developing simple and sensitive methods to analyze protease activity using commercial pregnancy test strips that detect human chorionic gonadotropin (hCG). hCG was engineered to have site-specific conjugated biotin and a peptide sequence, which can be cleaved by a target protease, between hCG and biotin. hCG protein was immobilized on streptavidin-coated beads, resulting in a protease sensor. The hCG-immobilized beads were too large to flow through the membrane of the hCG test strip and yielded only one band in the control line. When the peptide linker was hydrolyzed by the target protease, hCG was released from the beads, and the signal appeared in both the control and test lines. Three protease sensors for matrix metalloproteinase-2, caspase-3, and thrombin were constructed by replacing the protease-cleavable peptide linker. The combination of the protease sensors and a commercial pregnancy strip enabled the specific detection of each protease in the picomolar range, with a 30-min incubation of the hCG-immobilized beads and samples. The modular design of the protease sensor and simple assay procedure will facilitate the development of POCTs for various protease disease markers.

Plasmon-Enhanced Surface Photovoltage of ZnO/Ag Nanogratings.

We investigated the surface photovoltage (SPV) behaviors of ZnO/Ag one-dimensional (1D) nanogratings using Kelvin probe force microscopy (KPFM). The grating structure could couple surface plasmon polaritons (SPPs) with photons, giving rise to strong light confinement at the ZnO/Ag interface. The larger field produced more photo-excited carriers and increased the SPV. SPP excitation influenced the spatial distribution of the photo-excited carriers and their recombination processes. As a result, the SPV relaxation time clearly depended on the wavelength and polarization of the incident light. All of these results suggested that SPV measurement using KPFM should be very useful for studying the plasmonic effects in nanoscale metal/semiconductor hybrid structures.

Wafer-scale nanoconical frustum array crystalline silicon solar cells: promising candidates for ultrathin device applications.

A high photocurrent of 36.96 mA cm(-2) was achieved for wafer-scaled crystalline Si solar cells with hexagonal nanoconical frustum arrays at the surface. Optical simulations showed that the expected photocurrent of 10 µm thick nanostructured cells could slightly exceed the Lambertian limit.

Polarization-independent light emission enhancement of ZnO/Ag nanograting via surface plasmon polariton excitation and cavity resonance.

In this study, we observed that the photoluminescence (PL) intensity of ZnO/Ag nanogratings was significantly enhanced compared with that of a planar counterpart under illumination of both transverse magnetic (TM) and transverse electric (TE)-mode light. In the TM mode, angle-resolved reflectance spectra exhibited dispersive dips, indicating cavity resonance as well as grating-coupled surface plasmon polariton (SPP) excitation. In the TE mode, cavity resonance only was allowed, and broad dips appeared in the reflectance spectra. Strong optical field confinement in the ZnO layers, with the help of SPP and cavity modes, facilitated polarization-insensitive PL enhancement. Optical simulation results were in good agreement with the experimental results, supporting the suggested scenario.

Surface-plasmon-enhanced visible-light emission of ZnO/Ag grating structures.

We investigated the optical properties of ZnO/Ag grating structures fabricated by sputtering and nanoimprint lithography. The grating structures exhibited multiple peak features in broad visible-range photoluminescence (PL) spectra. The PL intensity of the grating was larger than that of a planar thin film by up to two orders of magnitude. The surface plasmon (SP) dispersion relation suggested excitation of SPs with various energies of the grating, explaining the broad PL emission. The spectral dependence of the PL intensity was also well supported by the experimental reflectance spectra and the simulated electric field distribution at the ZnO/Ag interface.