Coupled external cavity photonic crystal enhanced fluorescence

We report a fundamentally new approach to enhance fluorescence in which surface adsorbed fluorophore‐tagged biomolecules are excited on a photonic crystal surface that functions as a narrow bandwidth and tunable mirror of an external cavity laser. This scheme leads to ～10× increase in the electromagnetic enhancement factor compared to ordinary photonic crystal enhanced fluorescence. In our experiments, the cavity automatically tunes its lasing wavelength to the resonance wavelength of the photonic crystal, ensuring optimal on‐resonance coupling even in the presence of variable device parameters and variations in the density of surface‐adsorbed capture molecules. We achieve ～10⁵× improvement in the limit of detection of a fluorophore‐tagged protein compared to its detection on an unpatterned glass substrate. The enhanced fluorescence signal and easy optical alignment make cavity‐coupled photonic crystals a viable approach for further reducing detection limits of optically‐excited light emitters that are used in biological assays. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A label-free photonic crystal biosensor imaging method for detection of cancer cell cytotoxicity and proliferation

A label-free method for detecting the attachment of human cancer cells to a biosensor surface for rapid screening for biological activity is described, in which attachment of a cell results in highly localized increase of the resonant reflected wavelength of a photonic crystal narrowband reflectance filter incorporated into a standard 96-well microplate. An imaging detection instrument is used to determine the spatial distribution of attached cells by mapping the shift in reflected resonant wavelength as a function of position. The method enables monitoring of cancer cell attachment, cell proliferation, and cell detachment that is induced by exposure of the cells to drug compounds. We demonstrate the efficacy of this method as an early screening technique for the rapid quantification of the rate of cancer cell proliferation on the sensor surface, and subsequently as a means for quantifying cell detachment resulting from apoptosis that is induced by exposure of the cells to cytotoxic chemicals.     

Highly effective protein detection for avidin-biotin system based on colloidal photonic crystals enhanced fluoroimmunoassay

There has been immense interest in both instruments and methods to enhance fluorescence signal and achieve highly sensitive fluoroimmunoassay (FIA). In this paper, we present a facile, low-cost and general method of biotinylated colloidal photonic crystal (PC) to improve the FIA of avidin (avidin FIA). The fluorescence signal intensity of the avidin FIA on the colloidal PC can be enhanced over two orders of magnitude relative to the control sample, attributed to the large surface area, resonance field and coherent scattering effect of the colloidal PC. The detection limit is shrunk to 1/69 of that of the control sample. Furthermore, the signal to interference ratio (S/I ratio) is increased because the band-edge induced fluorescence enhancement is wavelength-selective. The interference fluorescence does not go up proportionally while the signal is significantly enhanced by the colloidal PCs. It is believed that the colloidal PC modified with biotin can act as an effective material for a general and sensitive fluoroimmunoassay.     

Large and Ultrafast Optical Response of a One-Dimensional Plasmonic–Photonic Cavity

The resonant coupling of a localized surface plasmon mode and a cavity mode in a photonic crystal has been recently shown to strongly tailor the stationary optical response of gold nanoparticles. Here, we demonstrate that this can be further exploited for controlling light on an ultrashort time scale. The stationary and ultrafast optical responses of such a plasmonic–photonic cavity are investigated numerically. We show that the transient photo-induced change of the optical transmittance of a bare nanocomposite thin film can be amplified up to 60 times once resonantly coupled to the cavity mode in the hybrid device, despite the degradation of this mode due to absorption losses. In addition, different all-optical, ultrafast, efficient, and reversible photonic functions (increase or decrease of the signal intensity, transient spectral shift of the cavity mode) can be achieved depending on the spectral position of the transmitted mode tuned by varying the angle of incidence. The transient modification of the signal intensity is predicted to reach about 300 % after a subpicosecond rise time when the defect mode matches the plasmon resonance.     

Highly Sensitive SPR Sensor Based on D-shaped Photonic Crystal Fiber Coated with Indium Tin Oxide at Near-Infrared Wavelength

A surface plasmon resonance (SPR) sensor based on D-shaped photonic crystal fiber (PCF) coated with indium tin oxide (ITO) film is proposed and numerically investigated. Thanks to the adjustable complex refractive index of ITO, the sensor can be operated in the near-infrared (NIR) region. The wavelength sensitivity, amplitude sensitivity, and phase sensitivity are investigated with different fiber structure parameters. Simulation results show that ～6000 nm/refractive index unit (RIU), ～148/RIU, and ～1.2?×?10⁶ deg/RIU/cm sensitivity can be achieved for wavelength interrogation, amplitude interrogation, and phase interrogation, respectively, when the environment refractive index varies between 1.30 and 1.31. It is noted that the wavelength sensitivity and phase sensitivity are more pronounced with larger refractive index. The proposed SPR sensor can be used in various applications, including medicine, environment, and large-scale targets detection.     

Highly sensitive SERS detection of cancer proteins in low sample volume using hollow core photonic crystal fiber

Enzyme-linked immunosorbent assays (ELISA) are commonly used for detecting cancer proteins at concentration in the range of about ng-μg/mL. Hence it often fails to detect tumor markers at the early stages of cancer and other diseases where the amount of protein is extremely low. Herein, we report a novel photonic crystal fiber (PCF) based surface enhanced Raman scattering (SERS) sensing platform for the ultrasensitive detection of cancer proteins in an extremely low sample volume. As a proof of concept, epidermal growth factor receptors (EGFRs) in a lysate solution from human epithelial carcinoma cells were immobilized into the hollow core PCF. Highly sensitive detection of protein was achieved using anti-EGFR antibody conjugated SERS nanotag. This SERS nanotag probe was realized by anchoring highly active Raman molecules onto the gold nanoparticles followed by bioconjugation. The proposed sensing method can detect low amount of proteins at ～100 pg in a sample volume of ～10 nL. Our approach may lead to the highly sensitive protein sensing methodology for the early detection of diseases.     

Optical Channel Drop Filter Design Based on PCRR and Micro Cavity Resonator

Optical channel drop filter (OCDF) plays a key role in optical communication networks for filtering the individual wavelength among the group of channels in wavelength division multiplexing systems. There are several channel drop filters with different design mechanisms available in the literature, but those structure dimensions are not compact enough for the photonic integrated applications. Hence, in this paper, a compact and efficient OCDF is developed in the triangular lattice PC structure based on diamond-shaped photonic crystal ring resonator (PCRR) mechanism combined with micro cavity resonator (MCR). The developed OCDF is analysed for different operating wavelengths by considering the different positions of MCR around the main PCRR. Based upon the position of the MCR around PCRR, the three dropping wavelengths such as 1540 nm, 1550 nm, and 1570 nm are observed at the output waveguides with 100% dropping efficiency. Then the structural and performance parameter comparison is done between the proposed and existing structures in terms of device dimension, dropping efficiency, and quality factor. It is depicted through the results that the quality factor and the device dimension are better than that of the existing structures for 1550-nm wavelength.

     

All-Optical Tunable Wavelength-Division Multiplexing Based on Colloidal Crystal Coated Silver Film

An all-optical tunable nanoscale wavelength-division multiplexing device is realized theoretically based on a plasmonic microstructure, which is composed of a silver film coated with a monolayer colloidal crystal made of cholesteryl iodide-doped polystyrene. The physical mechanism is attributed to the variation of surface plasmon polariton modes and guided modes caused by pump-laser-induced refractive index change of cholesteryl iodide. An up to 90-nm shift in the resonant wavelength of optical channels can be reached under excitation of a 500?mJ/cm² pump laser. The number of optical channels can be tuned by adjusting the structure parameters of the monolayer colloidal crystal. This may open a new way for the study of integrated photonic devices.     

Silicon photonic crystal nanocavity-coupled waveguides for error-corrected optical biosensing

A photonic crystal (PhC) waveguide based optical biosensor capable of label-free and error-corrected sensing was investigated in this study. The detection principle of the biosensor involved shifts in the resonant mode wavelength of nanocavities coupled to the silicon PhC waveguide due to changes in ambient refractive index. The optical characteristics of the nanocavity structure were predicted by FDTD theoretical methods. The device was fabricated using standard nanolithography and reactive-ion-etching techniques. Experimental results showed that the structure had a refractive index sensitivity of 10(-2) RIU. The biosensing capability of the nanocavity sensor was tested by detecting human IgG molecules. The device sensitivity was found to be 2.3±0.24×10(5) nm/M with an achievable lowest detection limit of 1.5 fg for human IgG molecules. Additionally, experimental results demonstrated that the PhC devices were specific in IgG detection and provided concentration-dependent responses consistent with Langmuir behavior. The PhC devices manifest outstanding potential as microscale label-free error-correcting sensors, and may have future utility as ultrasensitive multiplex devices.     

Highly Sensitive Plasmonic Temperature Sensor Based on Photonic Crystal Surface Plasmon Waveguide

We propose a highly sensitive temperature sensor based on photonic crystal surface plasmon waveguides comprising different plasmonic active metals such as gold, silver, and aluminum, utilizing surface plasmon resonance phenomenon. We found that the resonance wavelength can be easily and substantially tuned over a broad spectral range by changing the temperature and also by judiciously choosing the different plasmonic metals. Employing coupled mode theory, we found that the proposed sensor can be used in harsh environment with sensitivity as high as ～70 pm/K around telecommunication window.     

Radiative decay engineering 6: Fluorescence on one-dimensional photonic crystals

During the past decade the interactions of fluorophores with metallic particles and surfaces has become an active area of research. These near-field interactions of fluorophores with surface plasmons have resulted in increased brightness and directional emission. However, using metals has some disadvantages such as quenching at short fluorophore–metal distances and increased rates of energy dissipation due to lossy metals. These unfavorable effects are not expected in dielectrics. In this article, we describe the interactions of fluorophores with one-dimensional (1D) photonic crystals (PCs), which have alternating layers of dielectrics with dimensions that create a photonic band gap (PBG). Freely propagating light at the PBG wavelength will be reflected. However, similar to metals, we show that fluorophores within near-field distances of the 1DPC interacts with the structure. Our results demonstrate that these fluorophores can interact with both internal modes and Bloch surface waves (BSWs) of the 1DPC. For fluorophores on the surface of the 1DPC, the emission dominantly occurs through the 1DPC and into the substrate. We refer to these two phenomena together as Bragg grating-coupled emission (BGCE). Here we describe our preliminary results on BGCE. 1DPCs are simple to fabricate and can be handled and reused without damage. We believe that BGCE provides opportunities for new formats for fluorescence detection and sensing.     

Ag/Au bi-metallic film based color surface plasmon resonance biosensor with enhanced sensitivity, color contrast and great linearity

In wavelength surface plasmon resonance (SPR) biosensor, the manipulation of SPR dispersion relation by Ag/Au bi-metallic film was first time implemented. Due to the enhanced resonant wavelength shift and the sharper SPR slope of using Ag/Au bi-metallic film, the illuminated color of reflection shows one order of magnitude greater contrast than conventional SPR biosensors. Such an Ag/Au bi-metallic film based color SPR biosensor (CSPRB) allows the detail bio-interactions, for example 100 nM streptavidin, to be distinguished by directly observing the color change of reflection through naked eyes rather than the analysis of spectrometer. In addition to the enhanced sensitivity and color contrast, this CSPRB also possesses a great linear detection range up to 0.0254 RIU, which leading to the application of point-of-care tests.     

Ultra-high Sensitivity Plasmonic Nanosensor Based on Multiple Fano Resonance in the MDM Side-Coupled Cavities

We propose a compact plasmonic structure comprising a metal-dielectric-metal (MDM) waveguide coupled with a side cavity and groove resonators. The proposed system is investigated by the finite element method. Simulation results show that the side-coupled cavity supports a local discrete state and the groove provides a continuous spectrum, the interaction between them, gives rise to the Fano resonance. The asymmetrical line shape and the resonant wavelength can be easily tuned by changing the geometrical parameters of the structure. Moreover, we can extend this plasmonic structure by the double side-coupled cavities to gain the multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of ～1900 nm/RIU and a figure of merit of about ～3.8?×?10⁴, which can find wide applications for nanosensors.     

Photonic crystal nanostructures for optical biosensing applications

We present the design, fabrication and optical investigation of photonic crystal (PhC) nanocavity drop filters for use as optical biosensors. The resonant cavity mode wavelength and Q-factor are studied as a function of the ambient refractive index and as a function of adsorbed proteins (bovine serum albumin) on the sensor surface. Experiments were performed by evanescent excitation of the cavity mode via a PhC waveguide. This in turn is coupled to a ridge waveguide that allows the introduction of a fluid flow cell on a chip. A response of ∂λ/∂c=(4.54±0.66)×10⁵ nm/M is measured leading to a measured detection limit as good as  fg or  pg/mm²in the sensitive area.     

Cancer Detection with Surface Plasmon Resonance-Based Photonic Crystal Fiber Biosensor

Plasmonics - In this study, early cancer detection of a single living cell is investigated by employing a surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) biosensor structure. The...     

Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators ^1,2. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials.Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides ³, asymmetric split-ring resonators ⁴, and photonic band gap structures integrated into parallel-plate waveguides ⁵. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc.The sensor design we use here is based on a simple parallel-plate waveguide ^6,7. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE₁) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove ^6,8. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index ⁹.Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves ¹⁰. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.     

Compatibility of Temperature Sensor and Polarization Filter Based on Au Film and Glycerin Selectively Infilling Photonic Crystal Fibers

The Au film and glycerin selectively infilling photonic crystal fibers are analyzed by the finite element method. One cladding air hole is coated with Au film and infiltrated with glycerin to form a defect core. The simulation results show that both of the defect core modes formed on the glycerin and Au film can inspire resonance with core modes. The maximum sensitivity can reach to 2.50 nm/ ^°C in x polarized direction and 2.00 nm/ ^°C in y polarized direction for the temperature sensor, respectively. Furthermore, we obtain that the confinement losses of the photonic crystal fibers (PCFs) can meet with 321.442 dB/cm and 445.958 dB/cm at a short wavelength band (1460 ～1530 nm) and an extended wavelengths band (1360 ～1460 nm) for x polarized direction and y polarized direction respectively, which can be applied in many polarization filter devices as well. The compatibility of temperature sensor and polarization filter based on an identical structure can be realized at different wavelengths.     

Design Analysis of Multisample Single-Analyte Surface Plasmon Resonance Biosensor Based on D-Shape Photonic Crystal Fibers

Plasmonics - This paper dealt with the analysis of a surface plasmon resonance (SPR)-based D-shape photonic crystal fiber (PCF) biosensor for the detection of multimolecules present in a single...     

Simultaneous Detection of Fenitrothion and Chlorpyrifos-Methyl with a Photonic Suspension Array

A technique was developed for simultaneous detection of fenitrothion (FNT) and chlorpyrifos-methyl (CLT) using a photonic suspension array based on silica colloidal crystal beads (SCCBs). The SCCBs were encoded with the characteristic reflection peak originating from the stop-band of colloidal crystal. This approach avoids the bleaching, fading or potential interference seen when encoding by fluorescence. SCCBs with a nanopatterned surface had increased biomolecule binding capacity and improved stability. Under optimal conditions, the proposed suspension array allowed simultaneous detection of the selected pesticides in the ranges of 0.25 to 1024 ng/mL and 0.40 to 735.37 ng/mL, with the limits of detection (LODs) of 0.25 and 0.40 ng/mL, respectively. The suspension array was specific and had no significant cross-reactivity with other chemicals. The mean recoveries in tests in which samples were spiked with target standards were 82.35% to 109.90% with a standard deviation within 9.93% for CLT and 81.64% to 108.10% with a standard deviation within 8.82% for FNT. The proposed method shows a potentially powerful capability for fast quantitative analysis of pesticide residues.     

Integrated Tunable Optofluidics Optical Filter Based on MIM Side-Coupled-Cavity Waveguide

A tunable wavelength filter based on plasmonic metal?Cdielectric?Cmetal waveguide with optofluidics pump system has been proposed and numerically investigated. The finite difference time domain method with perfectly matched layer-absorbing boundary condition is adopted to simulate and study their properties. An analytical solution to the resonant condition of the structure is derived by means of the cavity theory. It is found that the resonant wavelength of the filter is easily tuned in a broadband by manipulating the fluid filled in the cavity. Both analytical and simulative results reveal that the resonant wavelengths are proportional to the volume and refractive index of liquid in the cavity and are related to the structure of the filter. The resonant wavelengths of this structure can be changed from 1,106 to around 1,800?nm in this paper. The waveguide filter may become a choice for the design of devices in highly integrated optical circuits.