Protein detection is universal and vital in biological study and medical diagnosis (e.g., cancer detection). Fluorescent immunoassay is one of the most widely used and most sensitive methods in protein detection (Giljohann, D. A.; Mirkin, C. A. Nature2009, 462, 461-464; Yager, P.; et al. Nature2006, 442, 412-418). Improvements of such assays have many significant implications. Here, we report the use of a new plasmonic structure and a molecular spacer to enhance the average fluorescence of an immunoassay of Protein A and human immunoglobulin G (IgG) by over 7400-fold and the immunoassay's detection sensitivity by 3,000,000-fold (the limit of detection is reduced from 0.9 × 10(-9) to 0.3 × 10(-15) molar (i.e., from 0.9 nM to 300 aM), compared to identical assays performed on glass plates). Furthermore, the average fluorescence enhancement has a dynamic range of 8 orders of magnitude and is uniform over the entire large sample area with a spatial variation ±9%. Additionally, we observed that, when a single molecule fluorophore is placed at a "hot spot" of the plasmonic structure, its fluorescence is enhanced by 4 × 10(6)-fold, thus indicating the potential to further significantly increase the average fluorescence enhancement and the detection sensitivity. Together with good spatial uniformity, wide dynamic range, and ease to manufacture, the giant enhancement in immunoassay's fluorescence and detection sensitivity (orders of magnitude higher than previously reported) should open up broad applications in biology study, medical diagnosis, and others.

Three of central challenges in solar cells are high light coupling into solar cell, high light trapping and absorption in a sub-absorption-length-thick active layer, and replacement of the indium-tin-oxide (ITO) transparent electrode used in thin-film devices. Here, we report a proposal and the first experimental study and demonstration of a new ultra-thin high-efficiency organic solar cell (SC), termed "plasmonic cavity with subwavelength hole-array (PlaCSH) solar cell", that offers a solution to all three issues with unprecedented performances. The ultrathin PlaCSH-SC is a thin plasmonic cavity that consists of a 30 nm thick front metal-mesh electrode with subwavelength hole-array (MESH) which replaces ITO, a thin (100 nm thick) back metal electrode, and in-between a polymer photovoltaic active layer (P3HT/PCBM) of 85 nm thick (1/3 average absorption-length). Experimentally, the PlaCSH-SCs have achieved (1) light coupling-efficiency/absorptance as high as 96% (average 90%), broad-band, and Omni acceptance (light coupling nearly independent of both light incident angle and polarization); (2) an external quantum efficiency of 69% for only 27% single-pass active layer absorptance; leading to (3) a 4.4% power conversion efficiency (PCE) at standard-solar-irradiation, which is 52% higher than the reference ITO-SC (identical structure and fabrication to PlaCSH-SC except MESH replaced by ITO), and also is among the highest PCE for the material system that was achievable previously only by using thick active materials and/or optimized polymer compositions and treatments. In harvesting scattered light, the Omni acceptance can increase PCE by additional 81% over ITO-SC, leading to a total 175% increase (i.e. 8% PCE). Furthermore, we found that (a) after formation of PlaCSH the light reflection and absorption by MESH are reduced by 2 to 6 fold from the values when it is alone; and (b) the sheet resistance of a 30 nm thick MESH is 2.2 ohm/sq or less-4.5 fold or more lower than the best reported value for a 100 nm thick ITO film, giving a lowest reflectance-sheet-resistance product. Finally, fabrication of PlaCSH has used nanoimprint on 4" wafer and is scalable to roll-to-roll manufacturing. The designs, fabrications, and findings are applicable to thin solar cells in other materials.

6329wileyonlinelibrary.com or metal mirrors) [3][4][5][7][8][9][11][12][13][14][15][16][17][18][19][20][36][37][38][39] often signifi cantly increase the ambient light refl ection, hence degrading the contrast. Such ambient light refl ection problem is particularly serious in OLEDs (which use metallic high-refl ective backplanes) [22][23][24] or high light extraction inorganic LEDs (fl ip-chip with metallic high refl ectivemirror).[ 10 ] All current methods for good contrast uses the methods that absorb the ambient light (e.g., circular polarizers, light absorbing layers, destructive-interference buffer layers, and low light refl ection black cathode) [22][23][24][26][27][28][29][30][31][32][33][34] but also degrade the light extraction substantially. The light extraction degradation is often as large as a factor of 2 (i.e., lossing a half of the total light that is otherwise being extracted). In other words, the most current LED structures cannot have high light extraction and high ambient light absorption (i.e., low ambient light refl ection) at the same time; they are either a good light radiator or a good ambient light absorber, but not both. Resonant-cavity LEDs with dielectric mirrors can be a good light radiator and absorber, but only in a few nanometer wavelength range and in a particular direction, [ 37,40 ] hence suffering similar low contrast and large glare as other LED structures in display applications. Moreover, in conventional LEDs, the viewing angle is fi xed by the Lambertian radiation pattern unless using lenses or resonant cavities; [ 41 ] and the ambient light refl ection often follows Fresnel's law, hence having large glare.Metals have many unique properties over dielectric counterparts. One of them is the generation of surface plasmon polariton (SPP), which can, under certain conditions, enhance the light radiation rate (Purcell Effect), alter the radiation intensity and pattern, and improve the light extraction. [ 42,43,55,56 ] Yet, the implementation into LEDs with a single layer of metallic (plasmonic) structures (either nanostructures or a planar thinfi lm) [ 44 ] or two layers of planar metallic thin-fi lms has achieved only limited improvements in LED light extraction. [ 36 ] The general concept of using a plasmonic microcavity with nanoperforated metal cladding for improving light extraction was fi rst proposed and discussed theoretically by Barnes, [ 43 ] and was implemented experimentally, with limited enhancements, to the optical pumped inorganic LEDs with a metal nanograting One central challenge in LEDs is to increase light extraction; but for display applications, other factors may have equal signifi cance, such as ambientlight absorption, contrast, viewing angle, image sharpness, brightness, and low-glare. However, current LED structures enhance only some of the factors, while degrading the others. Here, a new organic LED (OLED) structure is proposed and demonstrated, with a novel plasmonic nanocavity, termed "plasmonic cavity with subwavelength hole-array" (PlaCSH), and exhib...

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