Nanoplasmonic interferometric imagers successfully detect MMP-9 in supernatant, demonstrating the potential for multiplexed sensing for cell function analysis.

We developed a nanoplasmonic sensor employing extraordinary optical properties of 30nm-thick ultrathin Ag nanogratings. An order-of-magnitude improvement in the temporal and spatial resolutions was achieved relative to state-of-the-art nanoplasmonic sensors, for comparable detection resolutions.

We present a nanoplasmonic interferometric sensor platform that can differentiate the adsorption of a thin protein layer on the sensor surface from bulk refractive index changes, exploiting the different penetration depths of multiple SPPs.

We systematically investigate the optical and electrical properties of ultrathin two-dimensional (2D) Ag nanogratings (NGs), and explore their use as plasmonic transparent conducting electrodes in molecular organic photovoltaics (OPVs). A large broadband and polarization-insensitive optical absorption enhancement in the CuPc (copper phthalocyanine): PTCBI (perylene tetracarboxylic bisbenzimidazole) active light-harvesting layers is demonstrated using ultrathin 2D Ag NGs, and is attributed to the excitation of surface plasmon resonances and plasmonic cavity modes.

Label-free biosensing based on extraordinary optical transmission (EOT) through metallic nanoaperture arrays is a highly promising application of nanoplasmonics. The optical properties of these nanostructures, however, are complex due to the coupling between propagating and localized plasmon resonances, and some important features of the sensing mechanism have not been fully exploited. In this paper, in contrast to most previous studies that focused on the optimization of sensor response to bulk refractive index changes, we investigate the sensor response upon biomolecule bindings at different sensor positions inside or outside the nanoapertures. By properly tuning the geometric parameters of a gold nanoslit array, we show that the enhanced optical field in this EOT-based sensor can be spatially tailored to increase its interaction volume with the binding target biomolecules and improve the sensor performance. The results presented deepen the current understanding of the EOT-based sensor properties and open up new opportunities to further optimize their sensing performance.

The optical and electrical properties of optically-thin one-dimensional (1D) Ag nanogratings and two-dimensional (2D) Ag nanogrids are studied, and their use as transparent electrodes in organic photovoltaics are explored. A large broadband and polarization-insensitive optical absorption enhancement in the organic light-harvesting layers is theoretically and numerically demonstrated using either single-layer 2D Ag nanogrids or two perpendicular 1D Ag nanogratings, and is attributed to the excitation of surface plasmon resonances and plasmonic cavity modes. Total photon absorption enhancements of 150% and 200% are achieved for the optimized single-layer 2D Ag nanogrids and double (top and bottom) perpendicular 1D Ag nanogratings, respectively.

Label-free biomolecular sensing is by far the most common and successful application area in the emerging field of nanoplasmonics. This review paper highlights the latest progress and achievements made in this area. Key aspects of the nanoplasmonic sensor development, including performance enhancement, efforts to increase multiplexing capacity, and the progress in sensor integration and miniaturization, are discussed.

The optical and electrical properties of optically thin one-dimensional (1-D) Ag nanogratings and two-dimensional (2-D) Ag nanogrids are studied, and their use as transparent electrodes in organic photovoltaics is explored. A large broadband and polarization-insensitive optical absorption enhancement in the organic light-harvesting layers is theoretically and numerically demonstrated using either single-layer 2-D Ag nanogrids or two perpendicular 1-D Ag nanogratings, and is attributed to the excitation of surface plasmon resonances and plasmonic cavity modes. Total photon absorption enhancements of 150% and 200% are achieved for the optimized single-layer 2-D Ag nanogrids and double (top and bottom) perpendicular 1-D Ag nanogratings, respectively. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

This article summarized our recent progress in theoretical designs for achieving super absorption in ultra-thin organic photovoltaic (OPV) films based on various planar OPV-on-metal and metal-OPV-metal structures. Three different structures were numerically simulated to demonstrate strongly enhanced optical absorption in ultra-thin OPV layers, which is polarization-independent and occurs over a wide range of incident angles in visible regime. Physical mechanisms associated with these super absorptive ultra-thin layers are analyzed and validated using numerical and analytical modeling.

Broadband light absorption enhancement is numerically investigated for the active light harvesting layer of an organic photovoltaic (OPV), which consists of a blend of poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). Periodic plasmonic nanostructures placed above and below the active layer incorporate Ag, Al, Au, or a combination of two different metals. Three dimensional (3D) full-field electromagnetic simulations are applied to determine the effect of varying the metal employed in the plasmonic nanostructures on the absorption enhancement of the OPV. In addition, the geometric parameters (e.g., film thickness, period, and diameter) of the symmetrically distributed top and bottom metal (Ag, Al, or Au) nanostructures were varied to optimize the device structure and delineate the mechanism(s) leading to the absorption enhancement. A spectrally broadband, polarization-insensitive, and wide-angle absorption enhancement is obtained using a double plasmonic nanostructure and is attributed to the combined excitation of localized and single-interface surface plasmon polariton modes. The total photon absorption of the OPV with the optimized double plasmonic Ag nanostructures was found to be enhanced by as much as 82.8% and 80.4% under normal (0°) and 60° light incidence, respectively.

Recent advances in molecular organic photovoltaics (OPVs) have brought 10% power conversion efficiency (PCE) for single-junction cells, placing them in direct competition with amorphous silicon solar cells. Incorporation of plasmonic nanostructures for light trapping in these thin-film devices offers an attractive means to realize higher-efficiency OPVs with PCE>>10%, as reviewed by Zakya H. Kafafi, Qiaoqiang Gan, and Filbert J. Bartoli on page 2385. The cover image conceptually highlights the design of plasmonic-assisted OPV architectures using periodic metallic patterns and randomly distributed nanoparticles.

Recent advances in molecular organic photovoltaics (OPVs) have shown 10% power conversion efficiency (PCE) for single-junction cells, which put them in direct competition with PVs based on amorphous silicon. Incorporation of plasmonic nanostructures for light trapping in these thin-film devices offers an attractive solution to realize higher-efficiency OPVs with PCE >> 10%. This article reviews recent progress on plasmonic-enhanced OPV devices using metallic nanoparticles, and one-dimensional (1D) and two-dimensional (2D) patterned periodic nanostructures. We discuss the benefits of using various plasmonic nanostructures for broad-band, polarization-insensitive and angle-independent absorption enhancement, and their integration with one or two electrode(s) of an OPV device.

We present the design and demonstration of ultra-thin plasmonic color filters, providing a powerful approach for subtractive color filtering with high spatial resolution and ultra-compact architectures on sub-micrometer scales.

We report novel circular plasmonic interferomers for refractometric sensing with detection limit of 8.7×10-7 RIU using a multispectral sensing method. The efficient light suppression through destructive interference also allows low-background intensity-based detection with FOM* exceeding 140.

We report a novel plasmonic interferomer for intensity-based sensing with high FOMs* exceeding 140. This is achieved by means of destructive SPP-light interference, which provides near-perfect light cancellation for sensitive low-background detection.

We report a plasmonic interferometric biosensor based on a simple slit-groove metallic nanostructure that monitors the phase changes of surface plasmon polaritons resulting from biomolecular adsorptions. The proposed sensing scheme integrates the strengths of miniaturized plasmonic architectures with sensitive optical interferometry techniques. Sensing peak linewidths as narrow as 7 nm and refractive index resolutions of 1 × 10(-5) RIU were experimentally measured from a miniaturized sensing area of 10 × 30 µm(2) using a collinear transmission setup and a low-cost compact spectrometer. A high-density array of such interferometric sensors was also fabricated to demonstrate its potential for real-time multiplexed sensing using a CCD camera for intensity interrogation. A self-referencing method was introduced to increase the sensitivity and reduce sensor noise for multiplexing measurements. The enhanced sensing performance, small sensor footprint, and simple instrumentation and optical alignment suggest promise to integrate this platform into low-cost label-free biosensing devices with high multiplexing capabilities.

A plasmonic interferometric biosensor that consists of arrays of circular aperture-groove nanostructures patterned on a gold film for phase-sensitive biomolecular detection is demonstrated. The phase and amplitude of interfering surface plasmon polaritons (SPPs) in the proposed device can be effectively engineered by structural tuning, providing flexible and efficient control over the plasmon line shape observed through SPP interference. Spectral fringes with high contrast, narrow linewidth, and large amplitude have been experimentally measured and permit the sensitive detection of protein surface coverage as low as 0.4 pg mm(-2). This sensor resolution compares favorably with commercial prism-based surface plasmon resonance systems (0.1 pg mm(-2)) but is achieved here using a significantly simpler collinear transmission geometry, a miniaturized sensor footprint, and a low-cost compact spectrometer. Furthermore, we also demonstrate superior sensor performance using the intensity interrogation method, which can be combined with CCD imaging to upscale our platform to high-throughput array sensing. A novel low-background interferometric sensing scheme yields a high sensing figure of merit (FOM*) of 146 in the visible region, surpassing that of previous plasmonic biosensors and facilitating ultrasensitive high-throughput detection.

Plasmonic color filters employing a single optically-thick nanostructured metal layer have recently generated considerable interest as an alternative to colorant-based color filtering technologies, due to their reliability, ease of fabrication, and high color tunability. However, their relatively low transmission efficiency (~30%) needs to be significantly improved for practical applications. The present work reports, for the first time, a novel plasmonic subtractive color filtering scheme that exploits the counter-intuitive phenomenon of extraordinary low transmission (ELT) through an ultrathin nanostructured metal film. This approach relies on a fundamentally different color filtering mechanism than that of existing plasmonic additive color filters, and achieves unusually high transmission efficiencies of 60 ~ 70% for simple architectures. Furthermore, owing to short-range interactions of surface plasmon polaritons at ELT resonances, our design offers high spatial resolution color filtering with compact pixel size close to the optical diffraction limit (~λ/2), creating solid applications ranging from imaging sensors to color displays.