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This work presents a sensitive handheld refractometer using a tapered fiber tip, a multimode fiber, and a tiny mirror. The taper fiber tip was made using a modified wet etching method. The angular intensity distribution of the transmission light from the tapered fiber is sensitive to the refractive index of the surrounding solution. The low angular wave was reflected and collected by a multimode fiber. By setting a small collection angle and 10-mm distance between the fibers and the mirror, the maximum intensity sensitivity reaches up to 7.8 × 105%/RIU (refractive index unit). The sensor resolution of the sensor probe can achieve 8.7 × 10−5 RIU under 0.25% laser intensity stability. The simple handheld refractometer can be used to determine the properties of various liquids. For the glucose solution measurement under handheld condition, 0 to 50 °Bx can be distinguished by monitoring the intensity change. Considering the hand vibration and environmental disturbance, the sensor resolution was 1.22 °Bx.

A tapered fiber sensor was developed to detect the presence of condensed water and frost. The rough surface of the tapered fiber efficiently scattered the light propagating through the tapered fiber. The scattering loss is selective to the medium surrounding the tapered region of the fiber. Compared to the transmission intensity in the air, liquid water on the tapered fiber causes a 40% increase in transmission, whereas the presence of frost decreases the light transmission by 15%. Frost induces roughness on the surface of the tapered fiber and as a result increases light scattering and transmission losses. In contrast, liquid water uniformly covers the tapered fiber surface and reduces the light scattering. Furthermore, the amount of frozen water on the tapered surface is related to the duration of the transmission intensity peak during the defrosting process. The proposed detection scheme based on a rough tapered fiber can be utilized in real-time remote monitoring systems of the frost formation in large refrigeration systems.

Surface plasmon resonance (SPR) is an important technique for real-time and label-free detection of specific binding biomolecules. However, conventional SPR signals come from both the surface binding biomolecules and the variation in the bulk refractive index. This work demonstrates that Fano resonance in an aluminum capped nanoslit array has the ability to remove the signal of bulk refractive index changes from the SPR signal. As compared to gold nanostructures, the aluminum nanostructure provides an asymmetrical Fano resonance with clear peak and dip wavelengths. The peak wavelength is close to the grating resonance condition. The evanescent depth at the peak wavelength is up to several microns. The dip wavelength comes from the SPR effect. The evanescent depth at the dip wavelength is about 300 nm. By simultaneously measuring the shifts of peaks and the dip wavelengths, the variation in the bulk refractive index can be removed and only the biolayer thickness is measured. The finite-difference time-domain calculation shows that the 470 nm-period nanoslit array with 90 and 70 nm slit depths has the optimal thickness sensitivity. In this experiment, a simple multispectral imaging system is developed for multiple bio-interaction measurements. The measured results verify that the bulk refractive index changes can be removed and the surface biomolecular interactions can be directly obtained without the need of a reference channel.

Surface plasmon resonance (SPR) nanowire array chips with a microfluidic system are an effective detection method for a rapid test device. This study investigated a capped gold nanowire array and a microfluidic test platform to provide a fundamental understanding of the kinetic binding of SPR nanowires and the surface gold refractive index. The device sensitivity of the SPR nanowire array was 485 nm RIU-1 and the detection limit was 4.1 × 10-5 RIU. Moreover, a kinetic binding analysis also indicated that a peak shift resulted from a specific hybridization of the target molecule with the immobilized probe on the gold nanostructures. The peak shift (red-shift) value of latent membrane protein 1 (LMP1) DNA was 2.21 nm. The results demonstrated that this new method had high sensitivity to detect amplified DNA products without labeling or complex sample treatment. The SPR nanowire chip can detect the PCR products at lower cycle numbers compared to gel electrophoresis due to probe and DNA specificity. Furthermore, the mechanisms of SPR nanowire array fabrication and the detection of the LMP1 gene were studied. The findings can assist in improving the biosensing of DNA-amplified products and in developing rapid detection devices with a small-footprint nanostructured SPR chip.

A compact imaging smartphone spectrometer utilizing a lightweight aspheric concave blazed-grating is presented for multichannel spectral detection. The lightweight concave diffraction grating is fabricated on a plastic substrate using a two-step thermal-embossing method in a cost-effective and mass-productive way, which enables a large-area, smooth and aspheric concave surface while preserving a blazed-grating structure. The blazed-grating serves as a key single element for aberration-free light focusing and highly-efficient light diffraction. It thus eliminates extra moving optics in the spectrometer and improves the optical characteristics and system integration, which are proven by both simulation and experiments. Spectral linewidth of 1 nm is achieved by combining the concave grating with a smartphone camera. This compact imaging smartphone spectrometer is only about the size of a match-box. Spectra can be obtained directly from the detected images using a developed application (APP) interface. High-throughput plasmonic resonance sensing using microfluidic silver nanoslit arrays under various glycerin environments is demonstrated, and the detected resonance wavelength response is comparable with that detected by a commercial compact spectrometer.

Nanostructure-based surface plasmon resonance biosensors have attracted considerable attention since the phenomenon of extraordinary light transmission in metallic nanohole arrays was discovered. However, the mass production of uniform metallic nanostructures with a low-cost, rapid, and high-throughput fabrication process remains a key issue for various multiplex sensing applications. We successfully utilized injection compression molding to mass fabricate transmission-type Fano resonance biochips with a feature size of 60 nm for multiplex sensing applications. Two types of metallic nanostructures, aluminum nanoslits and capped aluminum nanoslits with 24 sensing arrays, were made on polycarbonate substrates. The bulk sensitivity and uniformity of the nanostructure arrays were tested. A Fano resonance with a full-width at half-maximum bandwidth of 8 nm was observed in the visible light region for 470-nm-period capped aluminum nanoslit arrays. The refractive index sensitivity was 460 nm/RIU, and a figure of merit of 58 was achieved. Moreover, aluminum nanoslits had a dip resonance with a bandwidth of 25 nm and a refractive index sensitivity of 463 nm/RIU. The coefficients of variation of the refractive index sensitivities for 24 arrays on a biochip and 10 biochips from different fabrication batches were both below 3%, which indicates that uniform nanostructures can be fabricated by injection compression molding and that the reproducibility is controllable. In addition, the multiplex sensing capability of the aluminum nanostructure arrays was demonstrated by simultaneously monitoring 24 water/glycerin solutions with a hyperspectral imaging system. Protein–protein interactions between bovine serum albumin and anti-bovine serum albumin demonstrated proof of concept of the biological detection capability of the chips. To benefit various multiplex sensing applications such as clinical disease diagnosis, drug screening, and protein biomarker discovery, 96-array aluminum nanoslit biochips the same size as a standard 96-well plate were successfully fabricated. Such a nanostructure-based plasmonic biochip produced by a low-cost, rapid, and high-throughput fabrication method can benefit commercial applications.

Surface plasmon resonance imaging (SPRi) is capable of real-time, label-free, and high-throughput detection for many sensing applications. The conventional prism-based SPRi system is operated with ...

A simple design for shifting the resonance wavelength of silver nanoslits using an electrowetting-on-dielectric (EWOD) cell is proposed. The EWOD cell comprises a polycarbonate (PC) substrate with Teflon-coated silver nanoslits and a glass substrate with Teflon-coated electrodes. A glycerol droplet is placed between the two substrates, and out of the path of a probe beam at zero electric field. Application of an electric field smaller than 0.3 V/µm on the electrodes moves the glycerol droplet into the path of the probe beam, shifting the resonance wavelength of the silver nanoslits by 135 nm. A change (0.33) in the refractive index of the effective medium that is adjacent to the silver nanoslits causes a large shift in the resonance wavelength. The spectral shift of the silver nanoslits is repeatable by the electric field. This simple design is a great achievement for high-performance electro-optical devices with large wavelength shift ranges such as optical switches, variable optical attenuators, and sensor applications.

Controlling circularly polarized (CP) states of light is critical to the development of functional devices for key and emerging applications such as display technology and quantum communication, and the compact circular polarization-tunable photon source is one critical element to realize the applications in the chip-scale integrated system. The atomic layers of transition metal dichalcogenides (TMDCs) exhibit intrinsic CP emissions and are potential chiroptical materials for ultrathin CP photon sources. In this work, we demonstrated CP photon sources of TMDCs with device thicknesses approximately 50 nm. CP photoluminescence from the atomic layers of tungsten diselenide (WSe2) was precisely controlled with chiral metamolecules (MMs), and the optical chirality of WSe2 was enhanced more than 4 times by integrating with the MMs. Both the enhanced and reversed circular dichroisms had been achieved. Through integrations of the novel gain material and plasmonic structure which are both low-dimensional, a compac...

We present a design method and fabrication technique for enhancing detection sensitivity of gold nanostructure-based surface plasmon resonance (SPR) biosensors. In this case, the nanostructure geometry is arbitrary and the optimal design parameters are determined using a microgenetic algorithm integrated with three-dimensional finite-difference time-domain (3D-FDTD) electromagnetic simulations. The corresponding device is fabricated using hot embossing nanoimprint lithography. Two experimental configurations are used to evaluate the device performance: one is the atomic layer deposition and the other is the protein–protein interaction. The performances of the optimal SPR biosensors are superior to the ones with conventional simple structures under both configurations. The improvements in terms of the fitness function are respectively up to 179% and 128% for the 3D-FDTD simulation and the experimental results. The calculated optical fields indicate that the improvement of the fitness function results from ...

Plasmonic hot-carriers, which are induced by plasmons at metal surfaces, can be used to convert photon energy into excited carriers over a subwavelength region and provide a new means to realize photodetection within the sub-band-gap region of semiconductor materials. However, the barrier height of the metal–semiconductor junction affects the behavior of the plasmon-induced hot-carriers and limits the electrical response of photodetection. High electrical responsivity, achieved by manipulating the barrier height using plasmon-induced hot electrons, is desired to broaden the possible applications. Here we report a plasmonic channel-coupled nanogap structure, where the barrier height of the metal–semiconductor junction is altered upon the excitation of plasmon-induced hot-carriers. The structure consists of semiconductor channels and metal slabs forming nanogaps, which sustain coupled plasmons and confine light to the semiconductor–metal interfaces. In contrast to conventional Schottky barriers and ohmic co...

An osmium-coated lensed fiber (OLF) probe combined with a silver-coated black silicon (SBS) substrate was used to generate a dielectrophoretic (DEP) force that traps bacteria and enables Raman signal detection from bacteria. The lensed fiber coated with a 2-nm osmium layer was used as an electrode for the DEP force and also as a lens to excite Raman signals. The black silicon coated with a 150-nm silver layer was used both as the surface-enhanced Raman scattering (SERS) substrate and the counter electrode. The enhanced Raman signal was collected by the same OLF probe and further analyzed with a spectrometer. For Raman measurements, a drop of bacterial suspension was placed between the OLF probe and the SBS substrate. By controlling the frequency of an AC voltage on the OLF probe and SBS substrate, a DEP force at 1 MHz concentrated bacteria on the SBS surface and removed the unbound micro-objects in the solution at 1 kHz. A bacteria concentration of 6 × 104 CFU/mL (colony forming units per mL) could be identified in less than 15 min, using a volume of only 1 μL, by recording the variation of the Raman peak at 740 cm−1.

The studies of nanostructure-based aluminum sensors have attracted huge attention because aluminum is a more cost-effective plasmonic material. However, the intrinsic properties of the aluminum metal, having a large imaginary part of the dielectric function and a longer electromagnetic field decay length and problems of poor long-term chemical stability, limit the surface-sensing capability and applicability of nanostructures. We propose the combination of capped aluminum nanoslits and a thin-capped dielectric layer to overcome these limitations. We show that the dielectric layer can positively enhance the wavelength sensitivities of the Wood's anomaly-dominant resonance and asymmetric Fano resonance in capped aluminum nanoslits. The maximum improvement can be reached by a factor of 3.5. Besides, there is an optimal layer thickness for the surface sensitivity because of the trade-off relationship between the refractive index sensitivity and decay length. We attribute the enhanced surface sensitivity to a reduced evanescent length, which is confirmed by the finite difference time-domain calculations. The protein-protein interaction experiments verify the high-surface sensitivity of the structures, and a limit of quantification (LOQ) of 1 pg/mL anti-bovine serum albumin is achieved. Such low-cost, highly sensitive aluminum-based nanostructures can benefit various sensing applications.

In this study, a multiplex detection system was proposed by integrating a localized surface plasmon resonance (LSPR) sensing array and parallel microfluidic channels. The LSPR sensing array was fabricated by nanoimprinting and gold sputter on a polycarbonate (PC) substrate. The polydimethylsiloxane (PDMS) microfluidic channels and PC LSPR sensing array were bound together through (3-aminopropyl)triethoxysilane (APTES) surface treatment and oxygen plasma treatment. The resonant spectrum of the LSPR sensing device was obtained by broadband white-light illumination and polarized wavelength measurements with a spectrometer. The sensitivity of the LSPR sensing device was measured using various ratios of glycerol to water solutions with different refractive indices. Multiplex detection was demonstrated using human immunoglobulin G (IgG), IgA, and IgM. The anti-IgG, anti-IgA, and anti-IgM were separately modified in each sensing region. Various concentrations of human IgG, IgA, and IgM were prepared to prove the concept that the parallel sensing device can be used to detect different targets.

A chip-based ultrasensitive surface plasmon resonance (SPR) sensor in a checkerboard nanostructure on plastic substrates is presented for digital detection. The sensing elements on the checkerboard are composed of silver-capped nanoslit arrays, which were fabricated using the thermal-embossing nanoimprint method, to meet the demand for low-cost and rapid fabrication. Sharp Fano resonances in the optimized nanoslit arrays provide high-intensity sensitivities (20,000% per refractive index unit), with an element size of 12.5µm. The polarization-dependent transmission in the checkerboard pattern produces optical isolation between sensing elements and results in a crosstalk lower than 1%. Protein-antibody experiments demonstrated that the digital detection limit was up to 1pg/mL, which is approximately 1000 times lower than that of conventional analog detection. For a 140µm×140µm checkerboard pattern, the dynamic range was approximately 100 times higher than that of conventional surface plasmon resonance measurements. This new digital detection method is very useful for detecting ultralow concentrations of analytes with a nonuniform distribution on the sensor surface.

We presented a surface plasmon resonance (SPR) sensor with an angular sensitivity up to 440 deg/RIU by using (±1,∓1) mode on a hexagonal gold nanohole array. The large-area gold nanohole arrays were fabricated by thermal-annealing template-stripping method with 180-nm-hole diameter and 600-nm period. A flat dispersion curve deviated from Bragg condition for (±1,∓1) mode occurred when incident angle was larger than 20°. The finite-difference time-domain calculations verified that plasmonic mode changed from surface plasmon mode to cavity mode in nanoholes. Such mode transition resulted in the large change of dispersion curve. The angular sensitivity of the (±1,∓1) mode near the transition band was 6.2 times higher than surface plasmon mode under Bragg condition and 4.5 times higher than prism-based SPR sensors at 850 nm wavelength. Biosensing experiments for antigen-antibody interactions verified the surface binding sensitivity was higher than prism-based SPR machine.

Periodic aluminum-capped nanoslit arrays were produced on a polycarbonate plastic substrate by rapid hot embossing nanoimprint lithography and thermal evaporation, and they were used as a transparent window for blue-emitting polymer light-emitting diodes (PLEDs). The external quantum efficiency of blue-emitting PLEDs was enhanced by the surface plasmon polaritons of the periodic aluminum-capped nanoslit arrays. A maximum current efficiency of 4.84 cd/A was achieved for the proposed PLED, which was over 2.2 times that of the reference PLED (2.18 cd/A). These results demonstrate that periodic nanostructure can assist in the simple and low-cost fabrication of high-performance polymer optoelectronic devices.

A nanostructure-based plasmonic biochip with the same size as standard 96-well plates for backside reflection-type biosensing was proposed and validated through analyses of biological interactions. The capped gold nanoslit arrays were fabricated on a polycarbonate plastic film using a rapid hot embossing nanoimprint lithography process. The optical properties of capped gold nanoslits with different structure parameters in backside reflection geometry were studied; their refractive index (bulk) and surface (thickness) sensitivities were verified. By changing the cavity length, the coupling between a broadband cavity resonance and a narrowband surface plasmon resonance mode results in an asymmetric Fano resonance in the reflection spectra. The coupling mode is able to enhance the thickness sensitivity by a factor of 2.4 with wavelength interrogation. The bulk and thickness sensitivities were 454 nm/RIU and 1.14 nm/nm, respectively. The protein-protein interaction experiments verified the sensing capabilities and high sensitivity of the capped nanostructures; a limit of detection (LOD) of 2 ng/mL IgA was achieved. Such a multi-well plate with backside reflection-type geometry, decoupling the optical paths, allows for sensing with opaque, bubbly or highly scattering liquids and benefits multiple sensing applications in the biotechnology and agricultural products.

© 2015 Elsevier B.V. Plasmonic hot spots located among closely dispersed plasmonic nanoparticles (NPs) are intensively studied for efficient conversion of solar to chemical or electrical energy applications. Here, a successful method to synthesize high-density unaggregated plasmonic Ag or Au NPs (AgNPs or AuNPs) onto nanostructured semiconductors with 3D densely organized NPs is demonstrated. The densely dispersed plasmonic AgNPs or AuNPs are assembled chemically on the entire surface of the ZnO nanorods through bifunctional thioctic acid bridging linkers. The fabricated NPs possessing small interparticle gaps generate numerous plasmonic hot spots which boost catalytic activities of the photocatalysts. As depicted by exact 3D finite-difference time domain simulations, the electromagnetic fields are magnified exponentially among interparticle gaps, hot spots, due to the plasmonic coupling effects of the neighboring AgNPs. The electromagnetic fields are strengthened by decreasing the interparticle spacing of coupled AgNPs. It is consistent with the result that the photocatalytic reaction rate increases non-linearly with the Ag content under full-spectrum light irradiation. Using the spectral characterizations and electromagnetic field simulations, we unambiguously confirm the enhancement of photoactivity due to coupling of plasmonic hot spot effect to nanostructured semiconductors. Moreover, diverse heterostructures based on the plasmonic NPs on various ZnO nanostructures (films, nanorod arrays, branched nanowires, and mesoporous structures) or functional materials (CuInGaSe2absorber films, multiferroic BiFeO3films, visible-light photoactive Cu2S and CdS nanorods) are successfully fabricated using the present synthesis methodology.

We propose a method and optical design for direct visualization of label-free detection. The system, similar to a tiny spectral analyzer, is composed of a nanostructure-based surface plasmon resonance chip, linear polarizer and 532 nm laser light source. The full-width-at-half-maximum bandwidths of the enhanced surface plasmon resonances are about 5 nm. The distribution of the transmitted light from these arrays comprises a spectral image on the chip. The qualitative and quantitative analyses of the analyte can be conducted by observing the spot shift on the chip. We tested the sensing capability of the chip. The detectable surface mass density with the naked eye is about 0.476 μg cm(-2). In addition, antigen-antibody interaction experiments are conducted to verify the surface binding measurements. A monolayer protein attached on the chip can be directly observed and the concentration levels of the analyte can be estimated with the naked eye. Such plasmonic biochips can benefit sensing applications in point-of-care diagnostics.

A Si channel-separated interdigitated Au grating structure is demonstrated to achieve spectrally selective photodetection in the C-band (1530–1565 nm) in this work. The measured full width at half-maximum of the structure reaches as narrow as 23 nm, and the measured responsivity reaches 804 nA/mW at the resonant wavelength of 1550 nm and the bias voltage of 0.08 V. The responsivity represents a large variation of 59% when the light wavelength is varied by only 20 nm (from 1550 to 1530 nm). A theoretical model is also performed to quantify the photocurrent response in terms of the optical and electrical properties of the structure. The strongly resonant and narrowband photocurrent response and readily tunable resonant wavelength not only enable the structure to achieve spectrally selective photodetection in the near-infrared region but also make it amenable to the application of sensing devices, imaging devices, and other optoelectronic devices working in the sub-bandgap regime of semiconductor materials.

Photodetection based on hot electrons is attracting interest due to its capability of enabling photodetection at sub-bandgap energies of semiconductor materials. Si-based photodetectors incorporating hot electrons have emerged as one of the most widely studied devices used for near infrared (NIR) photodetection. However, most reported Si-based NIR photodetectors have broad bandwidths with responsivities that change slowly with the target wavelength, limiting their practicality as spectrally selective photodetectors. This paper reports a Si channel-separated Au grating structure that exhibits the spectrally selective photodetection in the C-band (1530–1565 nm). The measured responsivity of the structure drops from 64.5 nA mW−1 at 1530 nm to 19.0 nA mW−1 at 1565 nm, representing a variation of 70.5% over the C-band. The narrowband, ease of tuning the resonant wavelength, and spectral selectivity of the device not only help bridge the gap between the optical and electrical systems for photodetection but are also beneficial in other potential applications, such as sensing, imaging, and communications systems.

An axicon fiber tip combined with a camera device is developed to sensitively detect refractive indexes in solutions. The transparent axicon tips were made by etching optical fibers through a wet end-etching method at room temperature. When the axicon fiber tip was immersed in various refractive index media, the angular spectrum of the emitted light from the axicon fiber tip was changed. Using a low numerical aperture lens to collect the directly transmitted light, a high intensity sensitivity was achieved when the tip cone angle was about 35 to 40 degrees. We combined the axicon fiber tip with a laser diode and a smartphone into a portable refractometer. The front camera of the smartphone was used to collect the light emitted from the axicon fiber tip. By analyzing the selected area of the captured images, the refractive index can be distinguished for various solutions. The refractive index sensitivity was up to 56,000%/RIU, and the detection limit was 1.79 &times, 10&minus, 5 RIU. By measuring the refractive index change via the axicon fiber tip, the concentration of different mediums can be sensitively detected. The detection limits of the measurement for sucrose solutions, saline solutions, and diluted wine were 8.86 &times, 3 &deg, Bx, 0.12&permil, and 0.35%, respectively.

A spectral integration combined with a threshold method for the analysis of spectral scanning surface plasmon resonance (SPR) images can significantly increase signal recognition at low concentration of antibody solution. The 12-well SPR sensing plates consisted of gold-capped nanowire arrays with 500-nm period, 80-nm linewidth and 50-nm gold thickness which were used for generating multiple SPR images. A threshold method is introduced to eliminate background noises in spectral scanning images. Combining spectral integration and the threshold method, the detection limit of antibody concentration was 1.23 ng/mL. Using multiple-well SPR sensing plates and the proposed analytical method, multiple kinetic responses with spectral and spatial information on different sensing areas can be sensitively measured.

We propose a spectral contrast method to map the transmission images of surface plasmon resonance (SPR) in metallic nanostructures. Comparing the intensities between two neighboring wavelength bands near the SPR wavelength, the signal-to-noise ratio for biosensing applications obtained using the proposed method is found to be ten times higher than that obtained by conventional intensity analysis and 1.6 times better than that obtained by peak-wavelength fitting. The dynamic range and linearity of the refractive index are comparable to the peak-wavelength shift measurement. Based on the detection method, a spectral modulation system for the optical microscope is developed, combined with a gold-capped nanowire array, to measure the biointeractions in microfluidic devices. The experimental results show that the proposed method obtained multiple detections with a detection limit of 1.04 × 10−5 refractive index units. Two types of analysis methods for SPR images are used to study the protein-antibody interactions. The region-of-interest analysis supports multiplexing detections in a compact microfluidic sensor. The effective pixel analysis eliminates low-response pixels and enhances the signal-to-noise ratios for sensitive label-free detection.

Improving surface sensitivities of nanostructure-based plasmonic sensors is an important issue to be addressed. Among the SPR measurements, the wavelength interrogation is commonly utilized. We proposed using blue-shifted surface plasmon mode and Fano resonance, caused by the coupling of a cavity mode (angle-independent) and the surface plasmon mode (angle-dependent) in a long-periodicity silver nanoslit array, to increase surface (wavelength) sensitivities of metallic nanostructures. It results in an improvement by at least a factor of 4 in the spectral shift as compared to sensors operated under normal incidence. The improved surface sensitivity was attributed to a high refractive index sensitivity and the decrease of plasmonic evanescent field caused by two effects, the Fano coupling and the blue-shifted resonance. These concepts can enhance the sensing capability and be applicable to various metallic nanostructures with periodicities.

A circularly polarized light source with ultrathin geometry were demonstrated by integrating the WSe 2 atomic layers with plasmonic chiral metasurfaces. The intrinsic chiral emission of WSe2 was manipulated by chiral metasurfaces to achieve emission circular dichroism more than 25%.

We propose a position-sensitive measurement method for tracking resonant signals of surface plasmon resonance (SPR) in periodic metallic nanostructures. Compared with conventional measurement methods, such as wavelength interrogation, intensity interrogation and spectral integration, this approach provides superior noise reduction and simple calculation process. Experimental results show that the limit of detection reaches to 5.88 × 10−6 RIU by using a portable spectrometer with a spectral resolution of 0.4 nm. The relationship between shot noise and signal noise was theoretically compared. The superior noise reduction of the resonant position tracking method is useful for the smartphone-based SPR measurement. The protein-antibody interactions using the smartphone and gold nanoslit arrays as the SPR sensor are demonstrated. It verifies that a smartphone can be used for sensitive measurement of binding-kinetics of the proteins.

We demonstrate the synthesis of heterostructured photocatalysts that comprise high-density unaggregated plasmonic Ag nanoparticles (AgNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNRs) that were grown on graphene (GR)-containing solid substrates to form ordered heterostructures without agglomeration. The photocatalysts provide the capability to monolithically integrate the photocatalytic functionality of AgNPs, ZNRs, and GR, which significantly enhances solar light absorption, suppresses charge recombination, and provides an ultrahigh density of catalytic reaction centers. Surprisingly, the AgNPs–ZNRs–GR heterostructures exhibit a photocatalytic reaction rate 13.8 times higher than that recorded for the bare ZNRs under solar light illumination. As depicted by geometric characterization, ultraviolet photoelectron spectroscopy, photoluminescence spectroscopy, and electromagnetic field simulation, the extraordinary photocatalytic performance could be attributed to the synergetic effect of electronic and plasmonic coupling, as well as the unique geometry.

A nanostructured back reflective electrode with nanobowl-shaped 2D nanohole arrays made from a polystyrene (PS) nanosphere template was developed for enhancing the efficiency of top-illuminated organic solar cells with MoOx (10 nm)/Ag (10 nm)/MoOx (25 nm) stacks as transparent electrodes. The high-performance top electrode with a transmittance of 88.05% at 550 nm and a sheet resistance of 5.93 Ω sq−1 reached an extremely high figure of merit (σdc/σopt = 484). Incorporating plasmonic-assisted electrodes into a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) blend system increased the cell efficiency from 2.91% to 3.35% compared with devices using a planar back electrode. We attributed the efficiency enhancement to the substantial scattering of back-reflected light and enhanced near-field absorption in the proximity of nanoholes.

In this paper, a facile fabrication technique called nanosphere lithography combining with two-step reactive ion etching method for patterning honeycomb metallic electrode with high transparency and excellent uniformity is demonstrated. The patterning silver electrode with 15-nm film thickness and 68.6% fill-factor was used as the organic light-emitting diode (OLED) anode, which showed an average transmittance of 77.4% and sheet resistance of 30.7 Ω/□. The current efficiency is 8.35 cd/A for the OLED with patterned silver anode under 100 cd/m2 operation brightness, which was 47% higher than the device with indium tin oxide (ITO) anode. After applying the polystyrene nanosphere to form a photonic crystal array onto the device, the extracted light from organic mode can be further coupled out from device substrate mode. The overall luminous enhancement of the device with the combination of internal honeycomb metallic anode and external photonic crystal array is 115% higher than the traditional ITO-based OLED.

Nanostructure-based surface plasmon resonance (SPR) sensors are capable of sensitive, real-time, label-free, and multiplexed detection for chemical and biomedical applications. Recently, the studies of nanostructure-based aluminum sensors have attracted a large attention. However, the intrinsic properties of aluminum metal, having a large imaginary part of the dielectric function and a longer electromagnetic field decay length, limit nanostructure’s surface sensing capability. To improve the surface sensitivity, a nearly guided wave SPR sensor has been proposed, which enables the surface plasmons to spread along the dielectric layer and increases the interaction volume. Here we proposed the combination between Fano resonances in capped nanoslits and a thin nanodielectric top layer to develop highly sensitive nanostructure-based aluminum sensors. We studied the effects of an Al 2 O 3 protection layer on the optical properties, bulk and surface (wavelength and intensity) sensitivities of capped aluminum nanoslits. We found the top layer can enhance the sensitivities of the Wood’s anomaly-dominant resonance or asymmetric Fano resonance in capped aluminum nanoslits. The maximum improvement can be reached by a factor of 16. The maximum wavelength and intensity sensitivities are 6.8 nm/nm and 150 %/nm, respectively. With 1.71 % intensity change (3 times of noise level), the limit of detection of Al 2 O 3 film thickness was 0.018 nm. We attributed the enhanced surface sensitivity for capped aluminum nanoslits to a reduced evanescent length and sharp slope of the asymmetric profile caused by the capped oxide layer and Fano coupling. The protein-protein interaction experiments verified the high sensitivity of the Al 2 O 3 -aliminum capped nanoslits.

We performed experimental measurements and theoretical simulation based on an efficient half-space Green’s function method to investigate the diffraction patterns of light scattered from the biological structure on 1D reflection grating made of metal and polymer. The 1D grating provides higher-order reflected light, which can boost the image signal for off-specular reflection. This can facilitate the micro-ellipsometry imaging experiment when an incident angle of light is at a large angle, while the detection camera is placed at the upright position. The micro-ellipsometry images for s- and p-polarized reflectance and their phase difference (Rs, Rp, and Δ) was taken by a modified Optrel MULTISKOP system with rotating compensator configuration for various angles of incidence and wavelengths ranging from 450nm to 750nm. By using an 80X objective lens, the pixel size for our image is around 164nm. We can further increase the magnification and the numerical aperture by using a substrate collocated with a homemade acrylic resin lens, and the pixel size can be reduced to 50 nm. Based on the above, we study the optical properties of metallic/dielectric nanostructures and nearby biological systems including bacteria, and cancer cells via an imaging micro-ellipsometer combined with detailed theoretical modeling. By using specular and off-specular micro-ellipsometry imaging, we can achieve sufficient sensitivity to collect signals from a small area (around 10μm X 10μm and obtain a 3D image mapping of the morphology and dielectric properties of the biological system of interest.

We present a convenient and low-cost method to fabricate large-area polycarbonate AR nanostructures to improve the luminous intensity and image clarity of a commercial 2.0-inch OLED display panel in bright condition. The polycarbonate AR nanostructures were nanoimprinted by the graded-density nanoporous silicon template with nanoparticle-catalyzed etching. After attaching on the display panel to reduce the light reflection on the substrate, the brightness enhancement and decrease of ambient light reflection were observed. Due to the enhancement of contrast ratio, the quality index of the Lena image test was improved from 0.85 to 0.92 under strong ambient illumination.

Here, a controlled synthesis of remarkable 3D photocatalysts is presented that is composed of ultrahigh-density unaggregated plasmonic Au nanoparticles (AuNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNA) through bifunctional molecular linkers. Experimental probes and electromagnetic simulations of electron transfer and localized plasmonic coupling processes are exploited to gain insight into the underlying light-irradiation-induced interactions in the 3D ZNA–AuNPs photocatalysts. Highly dense AuNPs on ZNA surfaces act as sinks for the storage of UV-generated electrons, which promote the separation of charge carriers and create numerous photocatalytic reaction centers. Furthermore, 3D finite-difference time domain simulation indicates that significant visible light confinement and enhancement around the ZNA–AuNPs interfacial plasmon “hot spots” contribute to efficient conversion of light energy to electron-hole pairs. Significantly, in comparison with the bare ZNA, the 10-nm-sized AuNPs-decorated ZNA exhibits 10.6-fold enhanced photoreaction rate in the entire UV–vis region. Moreover, various novel hybrid structures based on the plasmonic AuNPs and diverse nanostructures (films, powdered nanorods, mesoporous, and nanotubes) or functional materials (multiferroic BiFeO3, CuInGaSe2 absorber layers, and photoactive TiO2) are successfully constructed using the present synthesis methodology. It may stimulate the progress in materials science toward the synthesis of multifunctional plasmonic heterostructures or devices.

A photoactivated ZnO nanomesh with precisely controlled dimensions and geometries is fabricated by using nanosphere lithography process. The nanomesh structures effectively increase the surface-to-volume ratio to improve the sensing response under the same testing gas. And the periodical nanostructures also increase the effective light path and lead to more efficient light activation for gas sensing. With the increase of the photoinduced oxygen ions by UV illumination, a distinguished sensing response is observed at room temperature. In the optimized case, the sensing response (△R/R0) of the ZnO nanomesh at the butanol concentration of 500 ppm is 97.5%, which is 4.54 times higher than the unpatterned one.

In this study, we demonstrate a compact imaging spectroscopic system for high-throughput detection of biomolecular interactions on plasmonic chips, based on a curved grating as the key element of light diffraction and light focusing. Both the curved grating and the plasmonic chips are fabricated on flexible plastic substrates using a gas-assisted thermal-embossing method. A fiber-coupled broadband light source and a camera are included in the system. Spectral resolution within 1 nm is achieved in sensing environmental index solutions and protein bindings. The detected sensitivities of the plasmonic chip are comparable with a commercial spectrometer. An extra one-dimensional scanning stage enables high-throughput detection of protein binding on a designed plasmonic chip consisting of several nanoslit arrays with different periods. The detected resonance wavelengths match well with the grating equation under an air environment. Wavelength shifts between 1 and 9 nm are detected for antigens of various concentrations binding with antibodies. A simple, mass-productive and cost-effective method has been demonstrated on the imaging spectroscopic system for real-time, label-free, highly sensitive and high-throughput screening of biomolecular interactions.

A transparent electrode consists of nanoporous silver thin film and molybdenum oxide was developed for transparent anode with advantages of low cost, large-area processing and room-temperature fabrication. High density nanoporous silver film was fabricated by controlling thickness and deposition rate during thermal evaporation. With silver thickness of 10 nm and 5 A/s deposition rate, the MoO x /nanoporous Ag/MoO x multilayer structure achieved ~9 Ω/sq sheet resistance and ~70% transparency. Compared to the indium—tin-oxide (ITO) anode, the nanoporous anode/SubPc/C 60 /BCP/Al photovoltaic device has an enhanced surface-plasmon absorption and a higher fill factor. Although its transparency is lower than ITO, the nanoporous anode achieved 3.45% power conversion efficiency, comparable to ITO-based devices.

We report a study of a two-layer dielectric-loaded surface plasmon polariton waveguide (TDLSPPW) which consisted of two dielectric layers (high-index/low-index) on a silver film. The discontinuity of the electric field at the interfaces resulted in a concentrated field in the low-index region. It efficiently reduced the propagation loss of the surface plasmon polariton mode. The mode fields and corresponding complex propagation constants were calculated by a vector finite-difference method. The propagation properties were measured by a modified near-field optical microscope. It is confirmed that the propagation length of the proposed TDLSPPW was about 1.6 times longer than conventional single-layer SPP waveguides. In addition, a 90∘ waveguide turn with 3 μm radius showed that the bending loss was smaller than 2 dB.

A novel and efficient light extraction technique of OLEDs by attaching hierarchical micro-pyramid array with antireflective nanostructures was demonstrated. The hierarchical micropyramid arrays were nanoimprinted on polycarbonate films by using silicon concave mold incorporated with micropyramid and nanoporous surface, which were made by alkaline texturing and nanoparticle-catalyzed etching processes respectively. The additional antireflective nanostructures can effectively reduce the loss for the light normally incident at the inclined surface. After applying the subwavelength antireflective surface at the conventional micropyramids, the luminous efficiency enhancement was improved from 37.7% to 84.2%.

The internal and external efficiency of polymer light emitting devices were found can be simultaneously improved by insertion a high refractive index material, titanium oxide (TiOx), to the emission layer and a prism sheet attached to the substrate. The TiOx layer increased the internal efficiency due to a better electron injection and hole confinement. However, it led a wider angular emission profile with more photons trapped in the substrate. By using the prism sheet, those trapped light was efficiently coupled to the air. The extraction efficiency enhancement was increased from 33.1% to 54.4% and the overall current efficiency was improved up to 86%.

This work presents using a tapered fiber tip coated with thin metallic film to detect small particles in water with high sensitivity. When an AC voltage applied to the Ti/Al coated fiber tip and indium tin oxide (ITO) substrate, a gradient electric field at the fiber tip induced attractive/repulsive force to suspended small particles due to the frequency-dependent dielectrophoresis (DEP) effect. Such DEP force greatly enhanced the concentration of the small particles near the tip. The increase of the local concentration also increased the scattering of surface plasmon wave near the fiber tip. Combined both DEP effect and scattering optical near-field, we show the detection limit of the concentration for 1.36 μm polystyrene beads can be down to 1 particle/mL. The detection limit of the Escherichia coli (E. coli) bacteria was 20 CFU/mL. The fiber tip sensor takes advantages of ultrasmall volume, label-free and simple detection system.

We present an antireflection structure consisted of irregular nanopillars to reduce the substrate surface reflection of OLED/OPV hybrid device, which both the luminous efficiency and energy conversion efficiency had great improvement. The nanopillars were made on flexible polycarbonate substrates by using nanoimprint method with anodized aluminum oxide template. The average reflectivity of the patterned polycarbonate substrate in visible wavelength was reduced to 3.3% in the optimized case. With the antireflection structure, the luminous intensity for OLED was improved 49.8% as compared to the device with flat substrates. The power conversion efficiency for OPV was improved from 0.48% to 0.55%, which had 14.6% enhancement at normal incidence.

We demonstrated a highly efficient color conversion layers (CCLs) by using nanosphere arrays for white organic light-emitting diodes. The introduced periodical nanospheres not only help extract the confined light in devices, but also increase the effective light path to achieve more efficient color conversion. By applying the nanospheres patterned CCL on a PVK-based phosphorescent blue OLED, 137% color conversion ratio had been achieved, which was 2.68 times higher than flat CCL. The resulting luminous efficiency of white device with patterned CCL (20.97 cd/A, 1000 cd/m2) was twice higher than the efficiency of the flat device (10.26 cd/A, 1000 cd/m2).

Nanostructure-based sensors are capable of sensitive and label-free detection for biomedical applications. However, high-throughput and low-cost fabrication techniques are the main issues which should be addressed. In this study, chip-based nanostructures for intensity-sensitive detection were fabricated and tested using a thermal-annealing-assisted template-stripping method. Large-area uniform nanoslit arrays with a 500 nm period and various slit widths, from 30 to 165 nm, were made on plastic films. A transverse magnetic-polarized wave in these gold nanostructures generated sharp and asymmetric Fano resonances in transmission spectra. The full width at half-maximum bandwidth decreased with the decrease of the slit width. The narrowest bandwidth was smaller than 10 nm. Compared to nanoslit arrays on glass substrates using electron-beam lithography, the proposed chip has a higher intensity sensitivity up to 10367%/RIU (refractive index unit) and reaches a figure of merit up to 55. The higher intensity sensitivity for the template-stripped nanostructure is attributed to a smoother gold surface and larger grain sizes on the plastic film, which reduces the surface plasmon propagation loss.

Development of imaging, sensing, and characterization of cells at Research Center for Applied Sciences (RCAS) of Academia Sinica in Taiwan is progressing rapidly. The research on advanced lattice light sheet microscopy for temporal visualization of cells in three dimensions at sub-cellular resolution shows novel imaging results. Label-free observation on filopodial dynamics provides a convenient assay on cancer cell motility. The newly-developed software enables us to track the movement of two types of particles through different channels and reconstruct the co-localized tracks. Surface plasmon resonance (SPR) for detecting urinary microRNA for diagnosis of acute kidney injury demonstrates excellent sensitivity. A fully automated and integrated portable reader was constructed as a home-based surveillance system for post-operation hepatocellular carcinoma. New microfluidic cell culture devices for fast and accurate characterizations prove various diagnosis capabilities.

Nanosphere lithography is used to pattern metallic thin films to form hexagonal nanohole arrays with both high conductivity and good transparency. We fabricated a silver thin film with a transparency of up to 85% and a sheet resistance lower than 35 Ω/□, which is comparable to the commercial ITO electrode. The nanohole array not only increased the transparency but also helped extracting the guided light trapped in organic layers. Compared to the reference device with ITO anodes, Alq 3 -based organic light-emitting devices with the silver nanohole arrays reduced the turn-on voltage by 0.82 V and improved the current efficiency by up to 68.8% due to extraction enhancement.

We present an antireflection structure consisted of tapered nanopillars to simultaneously increase light extraction efficiency and image contrast of flexible organic light-emitting devices. The nanopillars were made by imprinting the anodized aluminum oxide on polycarbonate substrates. The thermal viscosity effect formed the nanopillars with tapered shapes. Such tapered nanopillars show excellent antireflection properties for a wide range of incident angles and wavelengths. The transmittance was greatly improved from 52.8% to 89.1% at 60° incident angle for 150-nm-height nanopillars. With this antireflection structure, the device efficiency was improved 69% as compared to devices with flat substrates. Due to wide-angle antireflection, the ANSI image contrast ratio was also significantly improved.

A near-field coupling method for studying propagation properties of surface plasmon polariton (SPP) in subwavelength dielectric-loaded SPP waveguides (DLSPPWs) is presented. In this method, a tapered fiber probe is employed to generate a nanometer optical spot. When this spot is near the entrance of the DLSPPW with its polarization parallel to the waveguide, a strong guiding wave is observed by a leakage radiation microscope. For DLSPPWs with a dielectric height of about 600 nm, we observed SPP waves with zigzag propagation patterns at 650 nm wavelength. Such zigzag propagation results in a great reduction of propagation loss. In addition, the zigzag wave has a strong optical confinement. The bending loss for an L-bend DLSPPW is only about 0.4 dB.