Peak Wavelength Value Research Articles

Nanoimprinting of soda–lime glass using vitreous carbon nanomold for high-temperature stable nanophotonic crystal filter

We demonstrate a cost-effective and high-precision glass nanoimprinting method to fabricate a nanophotonic device on soda-lime glass using a vitreous carbon (VC) mold. The VC mold was obtained by replication of a furan-based thermoset polymer resin, followed by carbonization. In particular, the shrinkage of the nanostructures on the VC mold during carbonization are discussed and confirmed by finite element analysis using the linear gradual shrinkage ratio model. To verify the applicability of the proposed method to a photonic crystal filter, a nanograting with an effective pattern area of 30 × 30 mm2 was fabricated. The measured peak wavelength value of the glass photonic crystal filter was 597 nm, which was in good agreement with the simulated value of 602 nm. The results of thermal stability evaluation demonstrate that the glass photonic crystal filter was stable up to 510 °C. We believe that such high-precision nanophotonic devices fabricated by the proposed method can benefit various optical applications that require superior thermal, mechanical, and chemical durabilities.

Enhanced light absorption in monolayer tungsten disulfide with dielectric Bragg reflector and metallic thin film

A multi-layer structure based on the microcavity effect of a dielectric Bragg reflector (DBR) and metallic thin film to enhance light absorption of monolayer tungsten disulfide (WS2) is proposed. This structure is combined with a cover layer and a spacer layer to adjust the phase-matching condition. The transfer matrix method (TMM) was used to study its optical transport characteristics. It was found that the microcavity effect of DBR and the metallic thin film forms a maximum value of electric field intensity near the monolayer WS2, which effectively promotes the light-matter interaction in monolayer WS2. As the thicknesses of the spacer layer and cover layer were comprehensively optimized, the light absorption of monolayer WS2 at the wavelength of 611 nm reached 94.38 % and the full width at half maximum (FWHM) is only 9 nm. Furthermore, the effect of DBR periodicity and angle of incidence on the light absorption of monolayer WS2 were discussed. The research presented here confirms that changing the above structural parameters can effectively regulate the absorption peak wavelength and maximum value of monolayer WS2. The results of this study provide new ideas for the preparation of high-performance monolayer WS2 photodetectors and other new optoelectronic devices.

High-Sensitivity 3D ZIF-8/PDA Photonic Crystal-Based Biosensor for Blood Component Recognition.

Optical biosensors are sensitive devices used in bioanalytics detection. Analysis of blood constituents is very important for the detection of major diseases and also performs a significant role in the diagnosis of diabetes, various cancers, and cardiovascular disorders. In this work, a three-dimensional photonic crystal-based biosensor composed of zeolitic imidazolate framework-8 (ZIF-8) nanoarrays are placed on polydopamine (PDA) coated on a silicon substrate. This sensor is designed, simulated, and evaluated for various blood components in the wavelength range of 1.1 to 1.5 μm by the finite-difference time-domain (FDTD) method. The proposed biosensor was used for 10 types of blood components such as biotin-streptavidin, bovine serum albumin (BSA), cytop, glucose (40 mg/100 mL), hemoglobin, blood plasma, Sylgard184, white blood compounds, urethane dimethacrylate, and polyacrylamide. The FDTD technique was used for the performance analysis of the biosensor. The design parameters of the radius, the lattice constant, the thickness of the ZIF-8 arrays, and the PDA layer thickness are chosen to optimize the photonic crystal structure. This study indicates that the thickness of the PDA is the most important parameter for peak wavelength value in comparison to the other physical parameters. The factors for optimizing the photonic crystal-based biosensors such as the peak wavelength value (PWV), sensitivity, full width at half-maximum (FWHM), and figure of merit (FOM) are significant in comparison with pertinent works in this field, which evaluated 171 nm/RIU, 7.62 nm, and 22.5 RIU-1, respectively. A change of 0.01 nm in the refractive index of the constituents of the blood leads to a shift of 80 nm in the maximum peak wavelength, therefore acting as a functional biosensor with a high detection limit of 0.004 RIU.

Thermal emission of one-dimensional conjugated photonic crystals heterojunction embedded with graphene

By means of characteristic matrix method, we make a theoretical investigation on the properties of thermal emission from one-dimensional conjugated photonic crystals heterojunction embedded with graphene. We find that the emissivity plots show sharp spectral peaks and narrow antenna-like angular lobes which show the excellent temporal coherence and spatial coherence. By optimizing the parameters, a close-to-unity emissivity can be achieved in our proposed structure. Furthermore, we demonstrate that the emissivity peak wavelength and emissivity values can be tuned by changing the chemical potential of graphene layer and the center wavelength of conjugated photonic crystals. The study shows that our proposed structure may find great application in infrared spectrometers and infrared gas sensors.

Laser induced fluorescence resonance energy transfer for detection of arsenic in water

Ingestion of arsenic by the human body through drinking water induces numerous diseases. Therefore, detection and estimation of arsenic concentration in water, especially in groundwater, is important to protect the human world from its toxicity. In this work we demonstrate a laser induced fluorescence resonance energy transfer (LIFRET) method for the determination of the arsenic concentration in water. The fluorescence resonance energy transfer (FRET) is observed in an aqueous solution of 1, 8-naphthalimide and rhodamine-B by exciting it with a laser radiation of wavelength 405 nm. It is observed that if arsenic contaminated water is added to the pure solution of 1, 8-naphthalimide and rhodamine-B the wavelength of the peak in its FRET spectrum shifts from its pure value at 632.45 nm (peak position of the FRET spectrum of a pure solution of 1, 8-naphthalimide and rhodamine-B). These shifts of wavelengths are towards the lower wavelength side, corresponding to an increase in the concentration of arsenic added to the solution. In the present work, based on the shifting of the peak wavelength value of the FRET spectra corresponding to different concentrations of arsenic, we have described a method for the estimation of arsenic in water up to a lowest limit of 0.000 01 gm l−1 (the maximum permissible limit of arsenic in water according to the World Health Organisation). The LIFRET method described in this work is portable, relatively cost effective, more convenient and has the potential for any in situ measurement of arsenic in the ground water of arsenic contaminated areas.

Direct light written holographic volume grating as a novel optical platform for sensing characterization of solution

We proposed a novel photosensitive hydrogel based holographic sensor for the detection of hydrogel swelling and hence the chemical concentrations, which formed by thermally polymerizing 2-hydroxyethyl methacrylate. Holographic volume grating recorded in the hydrogel as an optical sensing platform was employed in response to the hydrogel deformation induced by target molecules. Co-monomer methacrylic acid with carboxyl groups functionalized the polymer matrix for improving the selectivity. Peak wavelength shift of the diffraction spectrum was a significant parameter in sensing the pH value of the buffer. The extracted time constant of the wavelength shift curve evaluated the sensitivity of the novel holographic sensor. There were good exponential relations between peak wavelength and pH value with various thicknesses. The novel sensor could be considered as an effective platform for sensing the analytes concentration of solution. The reversible measurement experimentally demonstrated the repeatability of the holographic sensor. The novel photosensitive hydrogel and its sensor provided a probability for sensing the performance of solution and accelerating the development of water resistant holographic sensor based on polymer hydrogel.

Novel pH-sensitive photopolymer hydrogel and its holographic sensing response for solution characterization

Optical sensor based on pH-sensitive hydrogel has important practical applications in medical diagnosis and bio-sensor areas. This report details the experimental and theoretical results from a novel photosensitive polymer hydrogel holographic sensor, which formed by thermal polymerization of 2-hydroxyethyl methacrylate, for the detection of pH in buffer. Volume grating recorded in the polymer hydrogel was employed in response to the performance of solution. Methacrylic acid with carboxyl groups was selected as the primary co-monomer to functionalize the matrix. Peak diffraction spectrum of holographic grating determined as a primary sensing parameter was characterized to reflect the change in pH. The extracted linear relation between peak wavelength and pH value provided a probability for the practical application of holographic sensor. To explore the sensing mechanism deeply, a theoretical model was used to describe the relevant holographic processes, including grating formation, dark diffusional enhancement, and final fringe swelling. Numerical result further showed all of the dynamic processes and internal sensing physical mechanism. These experimental and numerical results provided a significant foundation for the development of novel holographic sensor based on polymer hydrogel and improvement of its practical applicability.

A Nanofluidic Biosensor Based on Nanoreplica Molding Photonic Crystal.

A nanofluidic biosensor based on nanoreplica molding photonic crystal (PC) was proposed. UV epoxy PC was fabricated by nanoreplica molding on a master PC wafer. The nanochannels were sealed between the gratings on the PC surface and a taped layer. The resonance wavelength of PC-based nanofluidic biosensor was used for testing the sealing effect. According to the peak wavelength value of the sensor, an initial label-free experiment was realized with R6g as the analyte. When the PC-based biosensor was illuminated by a monochromatic light source with a specific angle, the resonance wavelength of the sensor will match with the light source and amplified the electromagnetic field. The amplified electromagnetic field was used to enhance the fluorescence excitation result. The enhancement effect was used for enhancing fluorescence excitation and emission when matched with the resonance condition. Alexa Fluor 635 was used as the target dye excited by 637-nm laser source on a configured photonic crystal enhanced fluorescence (PCEF) setup, and an initial PCEF enhancement factor was obtained.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1644-x) contains supplementary material, which is available to authorized users.

Higher-order mode photonic crystal based nanofluidic sensor

A higher-order photonic crystal (PC) based nanofluidic sensor, which worked at 532nm, was designed and demonstrated. A systematical and detailed method for sculpturing a PC sensor for a given peak wavelength value (PWV) and specified materials was illuminated. It was the first time that the higher order mode was used to design PC based nanofluidic sensor, and the refractive index (RI) sensitivity of this sensor had been verified with FDTD simulation software from Lumerical. The enhanced electrical field of higher order mode structure was mostly confined in the channel area, where the enhance field is wholly interacting with the analytes in the channels. The comparison of RI sensitivity between fundamental mode and higher order mode shows the RI variation of higher order mode is 124.5nm/RIU which is much larger than the fundamental mode. The proposed PC based nanofluidic structure pioneering a novel style for future optofluidic design.

High-throughput detection of human salivary cortisol using a multiple optical probe based scanning system with micro-optics and nanograting coupled label-free microarray

We demonstrate the use of a parallel detection system with a nanograting-based microarray to accomplish high-throughput analysis of bio-molecular interactions in a label-free manner. Well-type label-free microarrays were fabricated to eliminate the risk of cross-contamination and to minimize sample volumes. Parallel analysis without the use of spectrometer arrays or a moving platform was accomplished by using scanning multiple optical probes generated by a spatial light modulator and microlens array. Additionally, multiple optical probe spots focused by the microlens array reduced detection errors while enhancing the signal-to-noise ratio within a high-density microarray. Finally, we verified the feasibility of the parallel detection system by analyzing the peak wavelength value (PWV) shift of human salivary cortisol and anti-cortisol in a competitive binding experiment.

Evaluation of Indoor Daylight Parameters during Long–Term Observations in the Rooms Equipped with Intensive Coloured Surfaces

Examination, design and control of internal light conditions belong to important actual architectural issues. In most cases the reason is increasingly growing interest in non-visual response of human on the ambient light properties. Sick Building Syndrome (SBS) is assumed to be caused by complex of inappropriate indoor environment circumstances. Unsuitable light conditions are regarded to be one of them. This paper deals with comparison of internal light parameters such as photopic illuminance level EV, Spectral Power Distribution (SPD) and definition of peak wavelength value recorded in tested office rooms, which were scaled down to models for easier handling. Models are equipped with different selected colored wallpapers and flooring materials, whereby one model remains with all surfaces in neutral colors. The outputs of measured parameters are compared with each other and also with outdoor levels of the same light properties. There is also defined filtration efficacy of blue light component assumed to be most effective for controlling of non-visual sensoring system of human body. This observation may provide more complex overview on selection of internal surfaces colors in long-term occupied spaces, taking health and wellbeing into consideration.

Emission decay rate of a light emitter on thin metal films

We theoretically study the emission decay rate of a light emitter on thin Au films based on a semiclassical point-dipole model. The complex dielectric functions of Au films determined by spectroscopic ellipsometry are used in this calculation model. We investigate the dependences of the decay rate on the metal thickness, distance between emitter and metal, and emitted-light wavelength. It is found that the decay rate shows a peak at the surface plasmon resonance wavelength. It is also shown that its peak wavelength, width, and peak value are strongly dependent on the Au layer thickness. The peak value in the decay rate versus wavelength curves for the Au film of 10 nm thickness is also found to be higher than for the bulk Au metal. These results are due to the metal-thickness-dependent plasmon effects on the emission decay rates.

Nanostructured Optical Photonic Crystal Biosensor for HIV Viral Load Measurement

Detecting and quantifying biomarkers and viruses in biological samples have broad applications in early disease diagnosis and treatment monitoring. We have demonstrated a label-free optical sensing mechanism using nanostructured photonic crystals (PC) to capture and quantify intact viruses (HIV-1) from biologically relevant samples. The nanostructured surface of the PC biosensor resonantly reflects a narrow wavelength band during illumination with a broadband light source. Surface-adsorbed biotarget induces a shift in the resonant Peak Wavelength Value (PWV) that is detectable with <10 pm wavelength resolution, enabling detection of both biomolecular layers and small number of viruses that sparsely populate the transducer surface. We have successfully captured and detected HIV-1 in serum and phosphate buffered saline (PBS) samples with viral loads ranging from 104 to 108 copies/mL. The surface density of immobilized biomolecular layers used in the sensor functionalization process, including 3-mercaptopropyltrimethoxysilane (3-MPS), N-gamma-Maleimidobutyryl-oxysuccinimide ester (GMBS), NeutrAvidin, anti-gp120, and bovine serum albumin (BSA) were also quantified by the PC biosensor.

Design Optimization of Structural Parameters for Highly Sensitive Photonic Crystal Label-Free Biosensors

The effects of structural design parameters on the performance of nano-replicated photonic crystal (PC) label-free biosensors were examined by the analysis of simulated reflection spectra of PC structures. The grating pitch, duty, scaled grating height and scaled TiO2 layer thickness were selected as the design factors to optimize the PC structure. The peak wavelength value (PWV), full width at half maximum of the peak, figure of merit for the bulk and surface sensitivities, and surface/bulk sensitivity ratio were also selected as the responses to optimize the PC label-free biosensor performance. A parametric study showed that the grating pitch was the dominant factor for PWV, and that it had low interaction effects with other scaled design factors. Therefore, we can isolate the effect of grating pitch using scaled design factors. For the design of PC-label free biosensor, one should consider that: (1) the PWV can be measured by the reflection peak measurement instruments, (2) the grating pitch and duty can be manufactured using conventional lithography systems, and (3) the optimum design is less sensitive to the grating height and TiO2 layer thickness variations in the fabrication process. In this paper, we suggested a design guide for highly sensitive PC biosensor in which one select the grating pitch and duty based on the limitations of the lithography and measurement system, and conduct a multi objective optimization of the grating height and TiO2 layer thickness for maximizing performance and minimizing the influence of parameter variation. Through multi-objective optimization of a PC structure with a fixed grating height of 550 nm and a duty of 50%, we obtained a surface FOM of 66.18 RIU−1 and an S/B ratio of 34.8%, with a grating height of 117 nm and TiO2 height of 210 nm.

Surface Morphological Effects on Subwavelength Filter of Nanoscale Grating for Near Infrared Biosensing

We modeled the effects of surface roughness (SR) on a near-infrared guided-mode resonance (GMR) biosensor. A power spectral density function was used to describe the SR with spatial autocorrelation integration through a rigorous coupled-wave analysis (RCWA), and a peak wavelength value (PWV) shift in reflectance was observed under transverse electric (TE) and transverse magnetic (TM) polarization. Sub-nanometer SR caused significant PWV shifts, leading to invalid spectral recognition. In addition to random roughness, we studied the PWV reflectance shift for SR models such as sinusoidal, rectangular, and effective medium types. All SR models showed a larger PWV shift for TM polarization than for TE polarization. Owing to SR, PWV reflectance decreased abruptly for TM polarization at small angular deviations from normal incidence. However, the symmetrically splitting of the reflectance spectra for TE polarization implied a high angular tolerance to fabrication errors. Compared to vertical sidewall roughness in our prior work, the SR is much more deleterious for GMR biosensing and should be appropriately controlled.

Effects of vertical sidewall roughness on near-UV biosensing nanoresonant gratings

The effects of vertical sidewall roughness (VSR) were investigated for a nanoresonant grating designed to have enhanced surface-to-bulk sensitivity for biosensing when illuminated by a near-ultraviolet source. Rigorous coupled wave analysis (RCWA) was applied to design a grating with an ultra-narrow spectral full width at half maximum (FWHM) through the examination of virtual biosamples. We assumed a power spectral density function consisting of only the correlation length ξ and roughness deviation σ to describe the VSR superimposed on the grating. For the designed wavelength, the reflectance on the ξ–σ diagram revealed a deviation from the peak value that formed bandgap-like striped areas resembling the bandgaps in the band diagram of a photonic crystal. We defined the concept of a process window in the ξ–σ diagram and the parameter η to quantify the probability of the bandgap-like peak-value stripes that appeared in the process window. η was only >50% when σ and ξ were less than 3 and 100 nm, respectively, which means that there is a >50% probability of bandgap-like stripes for which the roughness can be tolerated under severe nanofabrication limitations compared to the near-IR case. On the other hand, within the process window but outside the bandgap-like stripes, even a small σ of less than a nanometer necessitates accurate calibration of the peak wavelength value (PWV) shift due to the VSR effect on the nanoresonant biosensor. When η = 90%, the process window is narrower and almost the same for near-UV and near-IR cases. However, there is less need to calibrate the PWV shift at the expense of a more severe fabrication limit.

Surface Morphological Effects on Subwavelength Filter of Nanoscale Grating for Near Infrared Biosensing

We modeled the effects of surface roughness (SR) on a near-infrared guided-mode resonance (GMR) biosensor. A power spectral density function was used to describe the SR with spatial autocorrelation integration through a rigorous coupled-wave analysis (RCWA), and a peak wavelength value (PWV) shift in reflectance was observed under transverse electric (TE) and transverse magnetic (TM) polarization. Sub-nanometer SR caused significant PWV shifts, leading to invalid spectral recognition. In addition to random roughness, we studied the PWV reflectance shift for SR models such as sinusoidal, rectangular, and effective medium types. All SR models showed a larger PWV shift for TM polarization than for TE polarization. Owing to SR, PWV reflectance decreased abruptly for TM polarization at small angular deviations from normal incidence. However, the symmetrically splitting of the reflectance spectra for TE polarization implied a high angular tolerance to fabrication errors. Compared to vertical sidewall roughness in our prior work, the SR is much more deleterious for GMR biosensing and should be appropriately controlled.

Ultrasensitive guided-mode resonance biosensors superimposed with vertical-sidewall roughness

In this paper, we present our investigations of the effects of vertical-sidewall roughness (VSR) on guided-mode resonance (GMR) filters made of subwavelength grating for applications to ultrasensitive biosensors operated under IR illumination. We designed the spectral FWHM of the grating filter to be as narrow as possible in order to emphasize the sensitivity and VSR effects. Three types of VSR morphologies on the grating-in terms of the correlation length ξ and the rms of the maximum roughness deviation σ-were considered and evaluated. Rigorous coupled-wave analysis was then implemented to quantify the shifts in the reflective resonance peak wavelength value (PWV) of the grating filter. Our simulations show that for specific ξ values, the PWVs remain constant even if σ becomes as large as 10 nm; this indicates dramatic bandgaplike stripes, which are similar to the bandgaps observed in the band diagrams of photonic crystals in the ξ-σ diagram that we have proposed in this study. In other words, the effects of VSR on the GMR biosensor performance are insignificant when ξ is located at certain bands; therefore, this type of roughness is highly tolerable even if the linewidth of the filter is decreased to only a few tens of nanometers.

Design of a Novel Left-Handed Photonic Crystal Sensor Operating in Aqueous Environment

In this letter, we theoretically propose a biosensor based on a two-dimensional left-handed photonic crystal coupled to an M-shaped resonator. The sensor is optimized to operate in an aqueous environment. By controlling the radius of the air cylinder defect, a strong interaction between light and biomolecules in aqueous solution is achieved. We demonstrate numerically that by confining the biomolecular into the region of interest, a high sensitivity is reached. It is shown that shifts in the peak wavelength values are strongly related to the refractive index changes.

Detection of growth factor binding to gelatin and heparin using a photonic crystal optical biosensor

Drug–carrier interactions are important to protein controlled release systems to protect the protein from denaturation and ensure properly timed release. A novel photonic crystal biosensor was used to investigate a gelatin–protein controlled release system to determine the amount of protein bound to the carrier at physiological conditions. The Biomolecular Interaction Detection (BIND) system reflects a narrow band of wavelengths when white light is shone incident to the grating. As mass is deposited onto the surface, the peak wavelength value is shifted due to changes in the optical density of the biosensor. The BIND system was used to detect the binding of growth factors onto acidic gelatin, basic gelatin, and heparin on the sensor surface. Through a series of experiments, including functionalizing the sensor, adjusting the ionic strength of the solution, adjusting the substrate concentration, and minimizing non-specific signal, the adsorption of the gelatins and heparin on the sensor was enhanced. The binding interaction of recombinant human transforming growth factor (rhTGF)-β1 and bone morphogenetic protein (rhBMP)-2 with the two types of gelatin and heparin were investigated. The strength of the interaction between rhTGF-β1 and the substrates is in the following order: heparin > acidic gelatin > basic gelatin. RhBMP-2 bound to the substrates but with less intensity than TGF-β1: heparin > basic gelatin > acidic gelatin. This work provides support for the controlled release mechanism through degradation of the gelatin carrier.