Surface Modes In Photonic Crystals Research Articles

Photonic Crystal Surface Mode Real-Time Imaging of RAD51 DNA Repair Protein Interaction with the ssDNA Substrate.

Photonic crystals (PCs) are promising tools for label-free sensing in drug discovery screening, diagnostics, and analysis of ligand-receptor interactions. Imaging of PC surface modes has emerged as a novel approach to the detection of multiple binding events at the sensor surface. PC surface modification and decoration with recognition units yield an interface providing the highly sensitive detection of cancer biomarkers, antibodies, and oligonucleotides. The RAD51 protein plays a central role in DNA repair via the homologous recombination pathway. This recombinase is essential for the genome stability and its overexpression is often correlated with aggressive cancer. RAD51 is therefore a potential target in the therapeutic strategy for cancer. Here, we report the designing of a PC-based array sensor for real-time monitoring of oligonucleotide-RAD51 recruitment by means of surface mode imaging and validation of the concept of this approach. Our data demonstrate that the designed biosensor ensures the highly sensitive multiplexed analysis of association-dissociation events and detection of the biomarker of DNA damage using a microfluidic PC array. The obtained results highlight the potential of the developed technique for testing the functionality of candidate drugs, discovering new molecular targets and drug entities. This paves the way to further adaption and bioanalytical use of the biosensor for high-content screening to identify new DNA repair inhibitor drugs targeting the RAD51 nucleoprotein filament or to discover new molecular targets.

Photonic Crystal Surface Modes for Trapping and Waveguiding of Ultracold Atoms.

The design of a photonic system for the trapping and waveguiding of ultracold atoms far above a dielectric surface is proposed and analyzed. The system consists of an optical rib waveguide deposited on a planar one-dimensional photonic crystal, which sustains two wavelengths of photonic crystal surface modes tuned in the red and blue sides relative to the atomic transition of the neutral atom. The addition of a third blue-tuned wavelength to the system allows the neutral atoms to be stabilized in the lateral dimension above the rib waveguide. Trapping atoms at relatively large distances, more than 600 nm above the dielectric surface, allows to reduce the influence of Casimir-Polder forces in this system. The detailed design methodology and specifications of the photonic system are provided. The presented design can be employed in atomic chips and quantum sensors.

Dendrimer-Based Coatings on a Photonic Crystal Surface for Ultra-Sensitive Small Molecule Detection.

We propose and demonstrate dendrimer-based coatings for a sensitive biochip surface that enhance the high-performance sorption of small molecules (i.e., biomolecules with low molecular weights) and the sensitivity of a label-free, real-time photonic crystal surface mode (PC SM) biosensor. Biomolecule sorption is detected by measuring changes in the parameters of optical modes on the surface of a photonic crystal (PC). We describe the step-by-step biochip fabrication process. Using oligonucleotides as small molecules and PC SM visualization in a microfluidic mode, we show that the PAMAM (poly-amidoamine)-modified chip's sorption efficiency is almost 14 times higher than that of the planar aminosilane layer and 5 times higher than the 3D epoxy-dextran matrix. The results obtained demonstrate a promising direction for further development of the dendrimer-based PC SM sensor method as an advanced label-free microfluidic tool for detecting biomolecule interactions. Current label-free methods for small biomolecule detection, such as surface plasmon resonance (SPR), have a detection limit down to pM. In this work, we achieved for a PC SM biosensor a Limit of Quantitation of up to 70 fM, which is comparable with the best label-using methods without their inherent disadvantages, such as changes in molecular activity caused by labeling.

Label-Free Multiplexed Microfluidic Analysis of Protein Interactions Based on Photonic Crystal Surface Mode Imaging.

High-throughput protein assays are crucial for modern diagnostics, drug discovery, proteomics, and other fields of biology and medicine. It allows simultaneous detection of hundreds of analytes and miniaturization of both fabrication and analytical procedures. Photonic crystal surface mode (PC SM) imaging is an effective alternative to surface plasmon resonance (SPR) imaging used in conventional gold-coated, label-free biosensors. PC SM imaging is advantageous as a quick, label-free, and reproducible technique for multiplexed analysis of biomolecular interactions. PC SM sensors are characterized by a longer signal propagation at the cost of a lower spatial resolution, which makes them more sensitive than classical SPR imaging sensors. We describe an approach for designing label-free protein biosensing assays employing PC SM imaging in the microfluidic mode. Label-free, real-time detection of PC SM imaging biosensors using two-dimensional imaging of binding events has been designed to study arrays of model proteins (antibodies, immunoglobulin G-binding proteins, serum proteins, and DNA repair proteins) at 96 points prepared by automated spotting. The data prove feasibility of simultaneous PC SM imaging of multiple protein interactions. The results pave the way to further develop PC SM imaging as an advanced label-free microfluidic assay for the multiplexed detection of protein interactions.

Photonic Crystal Surface Mode Imaging for Multiplexed Real-Time Detection of Antibodies, Oligonucleotides, and DNA Repair Proteins

Sensors based on photonic crystal (PC) surface mode imaging are promising tools for label-free drug screening and discovery, diagnostics, and analysis of ligand–receptor interactions. Imaging of PC surface modes has been demonstrated to allow simultaneous real-time detection of multiple events at the sensor surface. Here, we report the engineering of a lateral-flow microfluidic assay where PC surface mode imaging is used for multiplexed detection of biomolecular targets (antibodies, oligonucleotides, and a DNA repair protein), as well as kinetic data on their interactions obtained without additional labelling or signal amplification. Our data demonstrate the suitability of the biosensing platform designed for ultrasensitive, quick, and low-cost detection and monitoring of interactions between different biomolecules.

The Elaboration of Effective Coatings for Photonic Crystal Chips in Optical Biosensors.

Here, we propose and study several types of quartz surface coatings designed for the high-performance sorption of biomolecules and their subsequent detection by a photonic crystal surface mode (PC SM) biosensor. The deposition and sorption of biomolecules are revealed by analyzing changes in the propagation parameters of optical modes on the surface of a photonic crystal (PC). The method makes it possible to measure molecular and cellular affinity interactions in real time by independently recording the values of the angle of total internal reflection and the angle of excitation of the surface wave on the surface of the PC. A series of dextrans with various anchor groups (aldehyde, carboxy, epoxy) suitable for binding with bioligands have been studied. We have carried out comparative experiments with dextrans with other molecular weights. The results confirmed that dextran with a Mw of 500 kDa and anchor epoxy groups have a promising potential as a matrix for the detection of proteins in optical biosensors. The proposed approach would make it possible to enhance the sensitivity of the PC SM biosensor and also permit studying the binding process of low molecular weight molecules in real time.

Physical factors affecting the propagation length of Bloch surface modes in one-dimensional photonic crystals

In this work we present a detailed study of the propagation length of Bloch modes along the surface between a bulk medium and a one-dimensional truncated photonic crystal and how this quantity is affected by different parameters like the number of periods composing the photonic crystal, absorption of materials, the leak of energy due to the intrinsic structure of the system, and the roughness of involved surfaces that is inherently present depending on the manufacturing method and the materials themselves. To analyze the influence of different factors affecting the propagation length, we use essentially three different methods: the characteristic matrix for systems composed of smooth surfaces, along with the numerical fitting of a Lorentz curve around the resonance; the boundary integral method based on the Green function for two-dimensional systems that include random rough surfaces; and the numerical analysis of the energy propagation along the surface when a Gaussian beam impinges on it. We have found that the propagation length can vary from a few nanometers to some millimeters depending on the different mentioned factors, along with the relative position of the modes within the bandgaps. Bloch modes located at the center of bandgaps propagate longer distances than those residing near the edges. Absorption and roughness provoke a drastic decreasing of the propagation length as they increase at small rates. Finally, the number of periods composing the structure also produces an increase of the propagation length reaching a maximum and then dropping almost suddenly to zero when it grows at a constant pace.

Photonic crystal surface mode imaging for multiplexed and high-throughput label-free biosensing

A photonic crystal surface mode imaging (PCSMi) technique is implemented for the simultaneous detection of antibody binding with specific antigens in arrays containing 96- and 384-spots. Like the surface plasmon resonance imaging (SPRi) technique, the presented approach is label-free and permits interrogating an analyte by hundreds of different ligands immobilized in small spots. The adsorption kinetics is recorded with a sub-picogram resolution at every spot simultaneously. Possible implementations of this technique for multiplexed and high-throughput biosensing are discussed.

Enhanced third-harmonic generation via s- and p-polarized optical surface modes of 1D photonic crystal structure

Generation of third-harmonic radiation, visible to the naked eye as a collimated green beam, is obtained via femtosecond excitation of the optical surface modes (SMs) propagating along a one-dimensional (1D) photonic crystal (PC) for s- and p-polarizations separately. For both polarizations, the PC SMs exist at the fundamental and third-harmonic frequencies, which allows efficient nonlinear conversion at the phase-matching points. The pattern of the third-harmonic surface wave scattering is detected and modeled, and it is shown that this pattern reveals the mode structure of the PC. Applications of the studied 1D PC structure for the experimental testing of 2D nonlinear materials are discussed.

Label-Free Flow Multiplex Biosensing via Photonic Crystal Surface Mode Detection

Circulating cancer markers are metabolic products found in body fluids of cancer patients, which are specific for a certain type of malignant tumors. Cancer marker detection plays a key role in cancer diagnosis, treatment, and disease monitoring. The growing need for early cancer diagnosis requires quick and sensitive analytical approaches to detection of cancer markers. The approach based on the photonic crystal surface mode (PC SM) detection has been developed as a label-free high-precision biosensing technique. It allows real-time monitoring of molecular and cellular interactions using independent recording of the total internal reflection angle and the excitation angle of the PC surface wave. We used the PC SM technique for simultaneous detection of the ovarian cancer marker cancer antigen 125 and two breast cancer markers, human epidermal growth factor receptor 2 and cancer antigen 15-3. The new assay is based on the real-time flow detection of specific interaction between the antigens and capture antibodies. Its particular advantage is the possibility of multichannel recording with the same chip, which can be used for multiplexed detection of several cancer markers in a single experiment. The developed approach demonstrates high specificity and sensitivity for detection of all three biomarkers.

Imaging biosensor based on planar optical waveguide

A biosensing technique with a two-dimensional spatial resolution based on a planar optical waveguide is presented. The thickness of the waveguide is chosen such that the wavelength of the waveguide mode is located between the maxima of the blue and green pixels of a color camera. A prism based Kretschmann-like configuration is used for waveguide excitation. The prism is placed between crossed polarizers to obtain the waveguide resonance peak. The spectral shift of the resonance peak is determined through the normalized differences in intensities of the blue and green pixels at each point of the color camera. The spatial distribution of resonance wavelength shifts across the camera reflects the spatial distribution of changes in the thickness of the adsorbate over the sample. The sensitivity, dynamic range, and simplicity of practical implementation of this biosensor are compared with those of an imaging biosensor based on photonic crystal surface mode.

Многопараметрическая детекция бактериального обсеменения с помощью анализа изменений распространения поверхностных волн в фотонных кристаллах

Conventional techniques for food and water quality control and environmental monitoring in general have a number of drawbacks. Below we propose a label-free highly accurate analytical technique for multiplex detection of biomarkers based on the analysis of propagation of Bloch waves on the surface of a photonic crystal. The technique can be used to measure molecular and cell affinity interactions in real time by recording critical and excitation angles of the surface wave on the surface of a photonic crystal. Based on the analysis of photonic crystal surface modes, we elaborated a protocol for the detection of the exotoxin A of Pseudomonas aeruginosa and the heat-labile toxin LT of Escherichia coli. The protocol exploits detection of affinity interactions between antigens pumped through a microfluidic cell and detector antibodies conjugated to the chemically activated silica chip. The proposed technique is highly sensitive, cheap and less time-consuming in comparison with surface plasmon resonance.

Photonic crystal surface mode imaging biosensor based on wavelength interrogation of resonance peak

A novel biosensing technique with a two-dimensional (2D) visualization, which is based on photonic crystal surface modes (PC SMs), is presented. The 2D image of the surface with picometer thickness resolution can be obtained when the PC chip under study is placed between crossed polarizers to convert a PC SM resonance dip into a resonance peak. The PC chip is designed so that the PC SM resonance peak is located between the maxima of the blue and green pixels of a color camera. The spectral shift of the resonance peak is determined by balancing of the intensities of the blue and green pixels at each point in the color camera. The spatial distribution of resonance wavelength shifts across the camera reflects the spatial distribution of changes in the thickness of the adsorbate over the sample. The spatial resolution of the resulting 2D image is determined by the propagation length of the PC surface wave.

Wide-angle resonance of a photonic crystal surface mode under a surface termination and its influence on imaging

We have developed a semi-analytical approach to the modulation transfer function (MTF) for negative-index flat lenses based on photonic crystals (PhCs). Contributions of various PhC modes to the MTF have been identified and analyzed. With a certain surface termination, a high-order PhC surface mode can be tamed to produce a broad angular resonance. As such, the isotropy of the image field can be significantly enhanced, resulting in an ideal image formation with nearly perfect outgoing circular wavefronts. Ray-optics analysis has also been utilized to assist the design of a negative-index flat lens. Finite-difference time domain simulations confirm the effectiveness of PhC lens designed by this semi-analytic approach to the MTF.

Phase-matched third-harmonic generation via doubly resonant optical surface modes in 1D photonic crystals.

Efficient nonlinear conversion requires that interacting optical waves maintain a consistent phase relationship when traveling in a medium despite its dispersion. Birefringent phase-matching, which is often used to compensate for the dispersion, is not applicable to optically isotropic nonlinear materials. Here, we present a one-dimensional photonic crystal structure that allows the propagation of optical surface waves, both at the fundamental and third-harmonic frequencies, as an efficient medium for phase-matched third-harmonic generation. A unique advantage of this structure is that the effective refractive indices for the surface waves are similar to the refractive index of air at both frequencies. This allows phase-matching between the first and third harmonics, and a visible collinear beam of the third harmonic is produced at the prism-coupled output. Moreover, these optical surface waves propagate over long distances even if a lossy nonlinear nanofilm is deposited onto the photonic crystal surface. We provide experimental results for third-harmonic generation at a wavelength of 410 nm for a bare dielectric Ta2O5/SiO2 multilayer structure and for the same structure coated with a 15-nm GaAs film.

Coupling of photonic crystal–photonic crystal interface and guided modes in two-dimensional heterostructures

In this work, we propose a two-dimensional photonic crystal–photonic crystal heterostructure that possesses the requirements for exciting an electromagnetic interface mode and investigate its interaction with photonic crystal waveguide modes. To study the interaction and coupling of both types of modes, the proper conditions to excite them are analyzed. Photonic crystal guided modes can appear in nearly any band gap when the photonic crystal has a line of defects within its lattice. Photonic crystal–photonic crystal surface modes can be excited at the junction of two different photonic crystals that share translation symmetry along the interface direction and have overlapped frequency band gaps. When this condition is met, dispersion relations of photonic crystal–photonic crystal surface modes will lie in the common region of both band gaps. Once the proper conditions are provided to excite these two modes, an interaction between them is possible. In the resulting calculations, a symmetric supercell and a plane wave basis are defined to numerically solve the wave equation.

Self-collimated 1×2 TM-polarized beam splitter based on photonic crystal surface mode

We design a self-collimated surface mode photonic crystal (PhC) W1 waveguide, and integrate it with an improved PhC T-junction to generate a self-collimated 1×2 TM-polarized beam splitter. On the basis of the detailed study of the surface mode of PhC without corrugations and with corrugations, the physical mechanism of self-collimated effect using periodic corrugated PhC is explained. As far as we know, this is the first time that such kind of device is presented. We further validate the self-collimated effect using the finite difference time domain method. From its far field, no beaming is observed, and the half width angle is as low as 3.68 degree which demonstrates the self-collimated phenomena of our designed device. Furthermore, our design demonstrates the possibility of integration of different PhC devices, and can be easily extended to other TM-polarized beam splitters.

Ultracompact 1×4 TM-polarized beam splitter based on photonic crystal surface mode

We provide an improved surface-mode photonic crystal (PhC) T-junction waveguide, combine it with an improved PhC bandgap T-junction waveguide, and then provide an ultracompact 1×4 TM-polarized beam splitter. The energy is split equally into the four output waveguides. The maximal transmission ratio of each output waveguide branch equals 24.7%, and the corresponding total transmission ratio of the ultracompact 1×4 beam splitter equals 98.8%. The normalized frequency of maximal transmission ratio is 0.397(2πc/a), and the bandwidth of the ultracompact 1×4 TM-polarized beam splitter is 0.0106(2πc/a). To the best of our knowledge, this is the first time such a high-efficiency 1×4 beam splitter exploiting the nonradiative surface mode as a guided mode has been proposed. Although we only employed a 1×4 beam splitter, our design can easily be extended to other 1×n beam splitters.

Various photonic crystal bio-sensor configurations based on optical surface modes

We design a new bio-sensor concept that incorporates photonic crystal (PC) surface modes to sense small refractive index changes. The initial attempt creates optical surface modes by first enlarging and then perforating the radii of rods residing along the end surface of the square-lattice PC. The strongly confined mode which decays both evanescently along transverse to propagation direction interacts with the substance while propagating along the PC-air interface. Due to index change of the ambient medium, the transmission spectrum experiences linear shift with a large dynamic range. The relocation of the surface defects enhances the sensitivity of bio-sensor from ∼8 to ∼93nm/RIU. The second type of investigated PC structure is based on triangular-lattice PC and it provides a surface state bio-sensor with a sensitivity of 117nm/RIU. In addition to these designs, we propose a final structure that incorporates air slot along one side of triangular-lattice PC. We succeeded to obtain a new sensitivity value of 396nm/RIU. The investigation shows that even higher sensitivities can be achieved. The different RIU values are reminiscent of group velocity of the relevant modes which can be extracted from the dispersion analysis. Compact, sensitive and label-free optical sensors based on surface modes may become part of the important applications in opto-fluidic technology and lab-on-a-chip.

Erratum: Photonic-crystal surface modes found from impedances [Phys. Rev. A82, 053840 (2010)

Erratum: Photonic-crystal surface modes found from impedances [Phys. Rev. A82, 053840 (2010)