Inverse silica opal photonic crystals for optical sensing applications

Self-Similarity Properties of Complex Quasi-Periodic Fibonacci and Cantor Photonic Crystals

In this paper, the influence of structural modifications on basic quasi-periodic (QP) photonic crystals (PhC’s) on self-similarity feature in their spectral responses is examined. Investigated crystals are chosen based on a present knowledge on the QP crystals, and are classified according to their structure. One of the QP crystals considered for the calculations is a concatenation, Fibonacci structure. It characterizes with a self-similar spectra for its different orders, which means, that the spectral shape repeats itself and can be partially identical for a different orders of the Fibonacci QP crystal. The calculations were also performed for the fractal structure, based on a Cantor QP crystal. Just as for the case of the Fibonacci structure, it characterizes with a self-similar spectra for different orders of the structure. Considered photonic devices are next put through simple modification operations by multiplication, conjugation or mirror reflection. Resulting, modified structures are used for the calculations of their spectral response. Results show, that the self-similarity of the spectra is not affected by performed modifications, and thus spectral response of QP PhC can be designed without losing this feature. Moreover the regular expansion of the repeated central part of the spectrum that appears in higher-order Fibonacci QP PhC spectra (due to the self-similarity) with the increase Fibonacci crystal order is presented here for the first time.

State-of-the-Art Optical Devices for Biomedical Sensing Applications—A Review

Optical sensors for biomedical applications have gained prominence in recent decades due to their compact size, high sensitivity, reliability, portability, and low cost. In this review, we summarized and discussed a few selected techniques and corresponding technological platforms enabling the manufacturing of optical biomedical sensors of different types. We discussed integrated optical biosensors, vertical grating couplers, plasmonic sensors, surface plasmon resonance optical fiber biosensors, and metasurface biosensors, Photonic crystal-based biosensors, thin metal films biosensors, and fiber Bragg grating biosensors as the most representative cases. All of these might enable the identification of symptoms of deadly illnesses in their early stages; thus, potentially saving a patient’s life. The aim of this paper was not to render a definitive judgment in favor of one sensor technology over another. We presented the pros and cons of all the major sensor systems enabling the readers to choose the solution tailored to their needs and demands.

Photonic crystal based biosensors: Emerging inverse opals for biomarker detection

Photonic crystal (PC)-based inverse opal (IO) arrays are one of the substrates for label-free sensing mechanism. IO-based materials with their advanced and ordered three-dimensional microporous structures have recently found attractive optical sensor and biological applications in the detection of biomolecules like proteins, DNA, viruses, etc. The unique optical and structural properties of IO materials can simplify the improvements in non-destructive optical study capabilities for point of care testing (POCT) used within a wide variety of biosensor research. In this review, which is an interdisciplinary investigation among nanotechnology, biology, chemistry and medical sciences, the recent fabrication methodologies and the main challenges regarding the application of (inverse opals) IOs in terms of their bio-sensing capability are summarized.

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The recent main challenges regarding the application of inverse opals (IOs) in the detection of biomolecules are reviewed.

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Sensing mechanisms of biomolecules including glucose, proteins, DNA, viruses were summarized.

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IO materials with their ordered 3D microporous structures have found attractive optical biosensor applications.

Photonic Crystal Stimuli-Responsive Chromatic Sensors: A Short Review

Photonic crystals (PhC) are spatially ordered structures with lattice parameters comparable to the wavelength of propagating light. Their geometrical and refractive index features lead to an energy band structure for photons, which may allow or forbid the propagation of electromagnetic waves in a limited frequency range. These unique properties have attracted much attention for both theoretical and applied research. Devices such as high-reflection omnidirectional mirrors, low-loss waveguides, and high- and low-reflection coatings have been demonstrated, and several application areas have been explored, from optical communications and color displays to energy harvest and sensors. In this latter area, photonic crystal fibers (PCF) have proven to be very suitable for the development of highly performing sensors, but one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) PhCs have been successfully employed, too. The working principle of most PhC sensors is based on the fact that any physical phenomenon which affects the periodicity and the refractive index of the PhC structure induces changes in the intensity and spectral characteristics of the reflected, transmitted or diffracted light; thus, optical measurements allow one to sense, for instance, temperature, pressure, strain, chemical parameters, like pH and ionic strength, and the presence of chemical or biological elements. In the present article, after a brief general introduction, we present a review of the state of the art of PhC sensors, with particular reference to our own results in the field of mechanochromic sensors. We believe that PhC sensors based on changes of structural color and mechanochromic effect are able to provide a promising, technologically simple, low-cost platform for further developing devices and functionalities.

Inverse Opal Photonic Crystals as an Optofluidic Platform for Fast Analysis of Hydrocarbon Mixtures

Most of the reported optofluidic devices analyze liquid by measuring its refractive index. Recently, the wettability of liquid on various substrates has also been used as a key sensing parameter in optofluidic sensors. However, the above-mentioned techniques face challenges in the analysis of the relative concentration of components in an alkane hydrocarbon mixture, as both refractive indices and wettabilities of alkane hydrocarbons are very close. Here, we propose to apply volatility of liquid as the key sensing parameter, correlate it to the optical property of liquid inside inverse opal photonic crystals, and construct powerful optofluidic sensors for alkane hydrocarbon identification and analysis. We have demonstrated that via evaporation of hydrocarbons inside the periodic structure of inverse opal photonic crystals and observation of their reflection spectra, an inverse opal film could be used as a fast-response optofluidic sensor to accurately differentiate pure hydrocarbon liquids and relative concentrations of their binary and ternary mixtures in tens of seconds. In these 3D photonic crystals, pure chemicals with different volatilities would have different evaporation rates and can be easily identified via the total drying time. For multicomponent mixtures, the same strategy is applied to determine the relative concentration of each component simply by measuring drying time under different temperatures. Using this optofluidic sensing platform, we have determined the relative concentrations of ternary hydrocarbon mixtures with the difference of only one carbon between alkane hydrocarbons, which is a big step toward detailed hydrocarbon analysis for practical use.

Two-Dimensional Organic-Inorganic Hybrid Perovskite Photonic Films

Organic-inorganic hybrid perovskites have created enormous expectations for low-cost and high-performance optoelectronic devices. In prospect, future advancements may derive from reaping novel electrical and optical properties beyond pristine perovskites through microscopic structure design and engineering. Herein, we report the successful preparation of two-dimensional inverse-opal perovskite (IOP) photonic films, featuring unique nanostructures and vivid colors. Further compositional and structural managements promise optical property and energy level tunability of the IOP films. They are further functionalized in solar cells, resulting in colorful devices with respectable power conversion efficiency. Such concept has not been previously applied for perovskite-based solar cells, which could open a route for more versatile optoelectronic devices.

A humidity sensitive two-dimensional tunable amorphous photonic structure in the bivalve ligament of Meretrix linnaeus

A humidity sensitive two-dimensional tunable amorphous photonic structure (2D TAPS) in the bivalve ligament of Meretrix linnaeus (LML) was reported in this paper. The structural color and microstructure of LML were investigated by reflection spectra and scanning electron microscopy, respectively. The results indicate that the LML has complex structural colors from blue to orange in the wet state from ventral to dorsal, which are derived from the aragonite fiber diameter increases continuously from ventral to dorsal of the ligament. The reflection peak wavelength of the wet LML can blue-shift from 522 nm to 480 nm with the air drying time increased from 0 to 60 min, while the reflectivity decreases gradually and only a weak reflection peak at last, relevant color changes from green to light blue. The structural color in the LML is produced by a two-dimensional amorphous photonic structure consists of aligned aragonite fibers and proteins, in which the diameters of the aragonite fiber and the inter-fiber spacing are 104±11 nm and 126±16 nm, respectively. Water can reversibly tune the reflection peak wavelength and reflectivity of this photonic structure, and the regulation achieved through dynamically tune the degree of order and lattice constant of the ligament in the different wet states.

A humidity sensitive two-dimensional tunable amorphous photonic structure in the outer layer of bivalve ligament from Sunset Siliqua

A humidity sensitive two-dimensional tunable amorphous photonic structure (2D TAPS) in the outer layer of bivalve ligament from Sunset Siliqua (OLLS) was reported in this paper. The structural color and microstructure of OLLS were investigated by reflection spectra and scanning electron microscopy, respectively. The results indicate that the reflection peak wavelength of the wet OLLS blue-shifts from 454 nm to 392 nm with the increasing of air drying time from 0 to 40 min, while the reflectivity decreases gradually and vanishes at last, relevant color changes from blue to black background color. The structural color in the OLLS is produced by a two-dimensional amorphous photonic structure consisting of aligned protein fibers, in which the diameter of protein fiber and the inter-fiber spacing are 101 ± 12 nm. Water can reversibly tune the reflection peak wavelength and reflectivity of this photonic structure, and the regulation achieved through dynamically tuning the interaction between inter-fiber spacing and average refractive index.

Photonic crystals for chemical sensing and biosensing

This Review covers photonic crystals (PhCs) and their use for sensing mainly chemical and biochemical parameters, with a particular focus on the materials applied. Specific sections are devoted to a) a lead-in into natural and synthetic photonic nanoarchitectures, b) the various kinds of structures of PhCs, c) reflection and diffraction in PhCs, d) aspects of sensing based on mechanical, thermal, optical, electrical, magnetic, and purely chemical stimuli, e) aspects of biosensing based on biomolecules incorporated into PhCs, and f) current trends and limitations of such sensors.

Photonic bandgap of inverse opals prepared from core-shell spheres

In this study, we synthesized monodispersed polystyrene (PS)-silica core-shell spheres with various shell thicknesses for the fabrication of photonic crystals. The shell thickness of the spheres was controlled by various additions of tetraethyl orthosilicate during the shell growth process. The shrinkage ratio of the inverse opal photonic crystals prepared from the core-shell spheres was significantly reduced from 14.7% to within 3%. We suspected that the improvement resulted from the confinement of silica shell to the contraction of PS space during calcination. Due to the shell effect, the inverse opals prepared from the core-shell spheres have higher filling fraction and larger wavelength of stop band maximum.

Lasing with well-defined cavity modes in dye-infiltrated silica inverse opals

Lasing in dye solution-embedded inverse silica opal structures was investigated. The opal films were prepared by sedimentation of polystyrene microspheres on a cover glass. The polystyrene structures were inverted using sol-gel infiltration of silica and subsequent removal of polystyrene. Photoluminescence of rhodamine (rhodamine B, 6G and sulfo-rhodamine 101) dye solutions embedded into the inverse silica opal structures exhibited clear signatures of the lasing via a distributed feedback (DFB) and gain modulation. The refractive index contrast between the dye and the inverse opal was small enough (approximately 0.03%) for the formation of refractive index coupling between the lasing modes. The lasing spectrum exhibited a highly regular periodic structure of modal peaks, rather than the chaotic superposition of peaks reported in previous studies. Lasing modes having a spectral width of about 0.25 nm and a free spectral range of about 0.75 nm appeared at the position of the maximum gain (the maximum fluorescence of the dye).

Influence of imperfections on the insulating and guiding properties of finite Si-inverted opal crystals

The stability of the photonic properties of Si-infiltrated opals for fabrication disorder is tested with following models of applied imperfections: deviations in radii of spheres, deviations in spheres positions and both of them. The deviations are assumed to be distributed accordingly to the normal law and to the skewed distribution experimentally observed in the process of production of polymer self-assembled crystals. The criteria for the photonic crystals tolerances are evaluated versus the quality of photonic insulation provided by films or bulk spheres of finite thicknesses. In addition the stability of the photonic crystal waveguides in inverted opals is tested versus the imperfections strength.

Tunable single-mode photonic lasing from zirconia inverse opal photonic crystals

Lasing from zirconia inverse opal photonic crystal structures infiltrated by solutions of rhodamine dyes was found to exhibit single-mode lasing peaks with spectral width less than 1 nm and quality factor in excess of 4000. The lasing occurs within the approximate range of high-reflectance spectral region associated with photonic stop band along [111] crystallographic direction, but its wavelength is not fixed to the corresponding Bragg wavelength of the periodic structure, and depends on the spectral position of the gain band. This lasing regime can be useful for realizing tunable single-mode photonic crystal lasers.

Refractive index sensing utilizing a cw photonic crystal nanolaser and its array configuration

We demonstrate refractive index sensing using photonic crystal point shift nanolasers. These lasers operate continuously at room temperature by photopumping in a liquid, and exhibit a 50-dB peak intensity over the background level and a spectral linewidth of < 26 pm, the resolution limit of the present experiment. The lasing wavelength shifts by soaking in different liquids; the wavelength to index sensitivity was 350 nm/RIU, the highest value recorded to date for nanocavity- based sensors. An index resolution of 9.0 x 10(-5) was thus confirmed, leading to an expectation of a resolution of < 10(-6). We propose and demonstrate a spectrometer-free sensor based on nanolasers in an array configuration. These will be disposable sensors with very simple optical I/O. They are anticipated to be integrated with biochips and used for label-free single molecule detection.