Photonic Crystals : A Review as Promising Tool for the Selective Detection of Toxic Gases

Muhammad Shahzeb Khan ¹ , Muhammad Ibrar Asif ² , Shahid Hussain?? ³ , Syeda Shan E Zehra ¹ , Mobashar Hassan?? ³ , Muhammad Kashif Aslam ⁴ , Muhammad Khurram Tufail ⁵ , Jesse Nii Okai Amudarko ³ , Amjad Ali ³

1 Department of Chemistry and Technology of Functional Materials, Faculty of Chemistry, Gdansk University of Technology, Gdansk, 80-233, Poland

2 Department of Biological and Environmental Sciences and Technologies, University DEL Salento, Italy

3 School of Materials Science and Engineering, Jiangsu University, Zhenjiang, 212013, P.R. China

4 School of Energy and Power Engineering, Ministry of Education, Nanjing University of Science and Technology, Nanjing, 210094, China

5 College of Material Science and Engineering, Qingdao University, Shandong, Qingdao, 266071, P. R. China

Abstract

Photonic crystals (PhCs) based sensing nanotechnology has gained a lot of attention because of its unique structural and morphological characteristics. With the potential utility, these PhC materials are promising as sensitive, selective, economical, portable, and visually detectable gas/vapor sensors for environment quality monitoring. This review focuses on current progress in the natural and artificial PhCs for gas sensing. We will discuss different PhCs including morpho butterfly wings and their nanostructure mimics, porous silicon, Bragg stacks, and colloidal crystals. Moreover, their fabrication techniques for PhCs sensing materials, structural modifications, and sensing mechanisms will be analyzed. In this review article, we highlighted the problem and solution as emerging trends for recent advances in PhCs-based sensors and their applications in environmental monitoring and pollution control. Furthermore, this study envisions new methodologies for PhCs-based sensors that will be highly advanced and effective.

^*

Keywords

Photonic crystals, Gas sensing, Morpho wings, Porous silicon, Bragg stacks, Colloidal crystals

INTRODCUTION

Photonic crystals (PhCs) are specialized periodic optical structures that trap light. PhCs have a bandgap in which a specific wavelength of light is entrapped and the diffraction grating phenomenon occurs.^1-6 PhCs have a specified periodic array of atoms that’s why these are classified into 1 dimensional (1D), 2 dimensional (2D), and 3 dimensional (3D) on the base of their structure as shown in Figure 1.⁷ The simplest PhCs are 1D because these comprise of alternating layers of substances with various dielectric constants. Light with a frequency of definite array acts as Braggs mirror in 1D PhCs.^8,9 2D PhCs are those having a variable refractive index in two directions. Etching, spin coating, or confined convective assembly techniques are used to synthesize 2D PhCs.^10-12 3D PhCs have spatial 3 dimensional; opal and inverse opal are substantial examples of 3D structures. The main synthetic route to preparing PhCs is bottom-up self-assembly including gravity or vertical deposition. These consist of nanometer or sub-micrometer size spheres such as poly(methyl methacrylate), polystyrene, or silica.^13-16

Figure 1: 1D, 2D, and 3D photonic crystals representation.⁷

Various colors exhibit materials with different dielectric constants. The motion of photons can be affected by these materials similar to the effect of electrons motion in semiconductor crystals. The periodic arrangement of arrays in dielectric substances develops a photonic bandgap that is specified for propagation to certain frequencies or wavelengths of light while another light is permissible to move. These light controlling properties insert excellent properties in PhCs that made them the ideal optics ^17-20. Therefore, PhCs are very important substances because of their application diversity in every field of life.

PhCs are one of the promising tools in gas sensing due to their large surface area, and unique optical and structural properties. These have great advantages over traditional sensing devices including sensitivity, portability, constancy, and online monitoring of results ^21-23. As discussed earlier, PhCs is the dielectric material having periodicity in their periodic lattice. Light propagation and reflection through the holes produce various colors. Bragg’s law explains the diffraction mechanism of PhCs that was proposed by Yablonovitch and John:^24-26

2ndsinθ=mλ

In this equation, n is the refractive index, d is spacing between lattice plates, ‘m’ is diffraction order, λ shows the wavelength of the incident light, and θ is the glancing angle of the material.^27,28 PhCs enhance the sensitivity, selectivity, and fluorescence due to photonic bandgap within a specified wavelength that’s why these are the most advanced sensor for vapor/gas sensing.

PHOTONIC CRYSTALS FOR GAS SENSING

Volatile organic compounds (VOCs) and other toxic gases are contaminating the environment through various emission sources and have become a major concern of air pollution. These vapors affect human health and cause human diseases such as cancer, nausea, skin irritation, memory impairment, and visual disorders.^29-32

Figure 2: Working principle of a photonic crystal for sensing vapor/gas.

epresents various VOCs profiles related to air quality. There are some traditional sensors present to detect the gas/vapor but these have some disadvantages including less sensitivity, and selectivity, and do not bear environmental conditions. In contrast to traditional sensors, optical sensors are very fast, selective, and have a long lifetime that’s why optical sensors have commercialization potential but there is a marketable difficulty because of their expensiveness.^33,34 The optical sensor converts light signals into analytical useful signals. Optical sensors have diverse applications in the field of environmental safety, agriculture, diagnostics, and energy ^35-37. There is a necessity for a longer interaction path for the conventional optical sensor. This longer interaction path needs more space and volume that’s why its size becomes large. This problem is solved by incorporating a mirror that multiplies the interaction between the gas and radiation. In this way, the size of the optical device decreased. However, its cost is high and restricted to following a hard fabrication process. PhCs replaced the traditional optical sensors due to their small size, low cost, high sensitivity, selectivity, robustness, and easy manufacturing process. The size of a PhC-based optical sensor is less than 1 cm which provides a platform for portability and on spot detection of the analytes ^33,38,39 as shown in Figure 2. We will review various PhC-based optical sensors for gas/vapor sensing including morpho butterfly wing nanostructure, porous silicon, multilayer films, and colloidal array PhCs.

Table 1: VOCs profile regarding air quality caused by the anthropogenic emissions in atmospheric environment.^40,41

Morpho butterfly wing and their mimic nanostructure

PhCs are natural architecture present in stones, birds, and animals. The color of butterfly wings and chameleons is one of the major examples of the PhCs. These natural PhCs are low-cost and selective in their response. The color of butterfly wings is due to the diffraction of light between photonic multilayers and pigmentation (in some species). When the angle of incident light changes, color also changes which gives evidence of the nanostructure network. Morpho butterfly structure consisted of different layers of chitin and air with varying refractive indexes.^42-44 Kim et al. used rigorous coupled-wave analysis to calculate diffraction efficiencies of the morpho butterfly wings. Other structural variations were also studied including thickness, material index, and grating width to evaluate optical properties as shown in Figure 3.⁴⁵

Figure 3: Schematic diagram of Morpho photonic structures for calculation purposes. ⁴⁵

There is also a biological pattern associated with morpho butterfly that functionalizes the surface. This photonic security of the butterfly made it responsive to different analytes that’s why morpho wings have wide applications in gas sensing. When volatile compounds come in contact with the wing’s structure the color changes occur. That is why it is used in different optical sensing devices. When vapors entrap into the nanoarchitecture, the capillary condensation mechanism of the vapors explains its optical response.^46-48 Couple-wave analysis method analyzes the diffraction efficiencies of the wings. Different parameters are also evaluated to analyze optical performance. Membrane thickness of closely packed grating nanoarchitecture shows color changes in response to environmental changes (vapors presence).^49,50

Potyrailo et al. fabricated a multivariable photonic sensor based on morpho scales to sense different gases. Photonic sensors were fabricated by using photolithography and chemical etching techniques. This is a new development in this field to develop artificial sensors after getting inspiration from natural species.⁴⁶ Blue butterflies have a quasi-ordered nanocomposite structure with embedded air holes and these nanostructures lead to the detection of different volatile organic compounds (VOCs) with high selectivity. The exposure of different VOCs changes the bandgap of the cavities and capillary condensation occurs. Pitzer et al. designed a vapor-mixing setup and spectral changes were evaluated. They reported a direct relation between spectral shift and vapor concentration. The sensitivity and selectivity are altered by the modification of the surface through atomic layer deposition and ethanol pretreatment.⁵¹

The composite of different metals and metal oxide with morpho butterfly wings enhances their response towards the analyte. Jiaqing He et al. synthesized a modified photonic structural framework of Morpho wing scales with Pd nanostrips. The coupling of plasmonic and optical resonant coupling modes in Pd nanostrips produced a sharp reflectance peak and enhanced the light-matter interaction. The reflectance of the Pd-modified butterfly wing increased after the exposure to H_2. Figure 4 explained the structural medication of the morpho wing after Pd insertion. Pd nanostrips-biophotonic structural framework achieved a detection limit of less than 10 ppm for H_2. ⁵²

Yang et al. used the self-deposition sintering method to fabricate an amorphous/nanocrystal hybrid TiO₂-based butterfly wing structure (ANH-TiO₂-BW). Original nanoarchitecture was established due to a hybrid configuration. ANH-TiO₂-BW configuration-based sensor was very conductive toward the acetone vapors because of its structural morphologies. The lowest detection limit for the acetone was 5 ppm at room temperature. The structural porosity made it very fast towards the acetone vapors.⁵³ First time, Silver et al. reported modified morpho wings from nano-structured phosphor materials to investigate the optical properties of photonic structures. The morpho wings were filled with two types of phosphor solutions; Y₂O₃:Eu³⁺ phosphor or TiO₂:Eu³⁺ phosphor. The sample was dried at 100 ^oC followed by annealing. Morpho butterfly pleides were synthesized with two different phosphors materials.⁵⁴

Figure 4: Structural modification in Morpho butterfly wing before and after Pd insertion. (a) Morpho butterfly (b) Optical microscopy image of the stacked scales (c) SEM image of stacked scales (d) Top SEM view of photonic structure (e) TEM image for scale ridges with lamella structures (f) TEM image of modified Pd nanostrips coated lamella.⁵²

The hypodermal process was used to fabricate 3D microporous Co₃O₄@C and butterfly wings were taken as templates. The combination of nanoarchitecture with Co₃O₄ and Carbon skeleton enhance the sensitivity. Different characterization tools were used to understand the structural morphologies. The sensor exhibited excellent response towards VOCs at low temperature.⁵⁵ The microfabrication of morpho-wing based nanoarchitecture in atomic layer was performed to study the vapor response towards artificial photonic nanostructures. Two structures were developed: one was obtained by the combination of TiO₂ and Al₂O₃, and the second combining HfO₂ and Al₂O₃. First time, an ALD-Morpho like structure was reported to detect the vapors.⁵⁶ There are different metal oxides with morpho wings including ZnO⁵⁷, SiO₂ ⁵⁸, and SnO₂ ⁵⁹ was also fabricated for different applications.

The coloring polymers were also combined with Morpho wings to investigate their optical response. Zhang and Chen reported the nanofabrication and coloration studies of artificial morpho wings. The artificial nanoarchitecture framework was based on electron beam lithography combined with LOR dissolution and aligned with color polymers (lamellae multilayers). Maxwell’s equations were used to understand the relationship between coloration and genomic dimensions. Spectral measurements were taken carefully for characterization purposes.⁶⁰ First time, natural photonic crystals response was evaluated towards trace chemical warfare agents (CWAs). Dimethyl methylphosphonate (a nerve agent simulant) and dichloropentane (a mustard gas simulant) were detected through modified nanostructured wings of the morpho butterfly. PhCs response was evaluated under visible light. It was also suggested that there are several parameters including material selection, spacing, functionalization, and structure of PhCs which affect the response of the sensor towards the CWA stimulants.⁶¹

Porous silicon Photic crystals

Porous silicon (PSi) PhCs are very significant optical sensors because of their unique sensing characteristics and large surface area. Different size pores have different morphology and characteristics. PSi PhC is one of the ideal optical sensors because the fabrication of such sensing structures is not applicable in other porous material. PSi PhCs have been used for the detection of different VOCs because absorbance of VOCs on the surface of PSi changes the refractive index. The ultimate result of these changes gives a reflection peak and response is evaluated.^62-65 Kumeria et al. fabricated a colorimetric sensor based on PSi PhC through electrochemical anodization technique. The sensor exhibited color changes when it was exposed to alcohol.⁶⁶ Chun and Miskelly monitored a specified PSi PhCs film by hyperspectral and color imaging when it was exposed to different organic vapors. The response was recorded in the concentration range of 100 to 3,000 mgm³. Different solvents were discriminated through hyperspectral imaging, while specificity was not attained from color camera data as shown in Figure 5.⁶⁷

In a new study, colorimetric pSi PhCs was synthesized with two rest bands, one is appropriate activated indicator dye with corresponding optical absorbance and other clear spectral section that specifies a reference. Octadecylsilane was added to modify the inner pore walls and indicator dye was embedded into PhC mesoporous matrix. Various indicator dyes were used for different analyte of interests and results were evaluated by measuring the reflectance spectrum of white light that exhibited colorimetric variations with the detection limit of 14ppm, 5 ppm, and 114ppb for HF, HCN, and, DFP respectively.⁶⁸

Figure 5: SEM image of porous Silicon (a) Oxidized side (b) Methylated side (c) False color map of porous silicon (wavelength of maximum rugate reflectance band).⁶⁷

Different nanocomposites of PSi with metals, metal oxides, and hybrids were produced to enhance the response of PSi PhCs. Ahmed and Mehaney fabricated Porous silicon one-dimensional photonic crystals (PSi-1DPCs) for sensing purpose on the base of changes in refractive indices. Various metals (Al, Ag, Au, and Pt) were attached to PSi-1DPCs structure to enhance the Tamm/Fano resonances. First time, Tamm/Fano resonances were achieved in the PSi-1DPCs simultaneously. Transfer matrix method (TMM) and Bruggeman’s effective medium approximation (BEMA) were used to calculate the reflection spectra of the PSi-1DPCs. Among different metals, Ag/PSi-1DPC based sensor exhibited the highest response with the sensitivity of 5018 nm/RIU.⁶⁹ Finite differential time-domain (FDTD) tools were used to examine periodical lattice of silver-porous silicon (Ag-PSi). Different characteristics like porosity, layering and reflection, absorption, transmission were evaluated in the range of 400-750 nm. The reflection was directly proportional to porosity while it was inversely proportional to the number of layers. There was an inverse relationship between the reflection and number of layers. The results also revealed that transmission had an inverse relation to porosity ⁷⁰. Fecteau and Frechette reported a modified sensor by deposition of Au film on 1D PhC based mesoporous silicon. A high-quality tamm structure was observed with the confirmation of a singularity in the ellipsometric angles.⁷¹

Peng et al. used electrochemical corrosion to fabricate macro-porous silicon (MPS) for gas detection. WO₃ nanofilms were deposited on MPS. The resulted WO₃/MPS sensor was used to investigate gases at room temperature. WO₃/MPS exhibited a good response towards NO₂ gas with the detection limit of 1 ppm. This experiment revealed that the addition of metal oxide with MPS PhC increases the sensitivity of the sensor. The sensor response towards ethanol vapors was also recorded which was lower than the NO₂ because of the selectivity of the WO₃/MPS towards NO₂ gas.⁷² Similarly, tungsten oxide (WO₃) nanowires/porous silicon (PS) sensor-loaded nanoparticles of gold (Au) were developed. The sensor exhibited a good response against NO₂ gas. The sputtering method was used to synthesize Au-loaded WO₃ nanowires on a porous silicon substrate. The lowest detection limit of Au-loaded WO₃ nanowires/Psi-based sensor was recorded at 0.2 ppm–5 ppm at 25 ^oC.⁷³ Abed et al. incorporated nanoparticles of CuO mixed SnO₂ into the PSi layer. SnO₂ and CuO nanoparticles were attached to the PSi surface through chemical spray pyrolysis. Laser-assisted etching technique was used to synthesize SnO₂/CuO/Psi nanocomposite and morphological properties of the SnO₂: CuO nanoparticles changed with the content of CuO. An increase in the content of CuO produced various shapes of SnO₂ and SnO₂:CuO on the PSi surface. SnO₂(70%)/CuO(30%)/porous silicon nanocomposites sensor detected the NH₃ gas detected with high sensitivity (88%).⁷⁴ In a similar manner, various PSi metal oxide nanocomposites were synthesized such as ZnO ⁷⁵, ZrO₂ ⁷⁶, and Al₂O_3. ⁷⁷

Carbon nanomaterials have unique characteristics that enhance the sensitivity of the sensing material.⁷⁸ Sailor et al. patented nanocomposites of Carbon and Silicon materials to evaluate the photonic response.⁷⁹ C-dots nanostructures within various PSi Bragg reflectors contained optical properties. C-dots emission spectral features could be tuned and their fluorescence emission enhanced due to the overlapping of PSi high reflection band with the peak wavelength of C-dots ⁸⁰. The precursor of Poly (furfuryl alcohol) (PFA) in PSi was used to fabricate Carbon/porous silicon composite films. A glassy carbon layer was coated into the internal structure of PSi. C₂ hydrocarbon gases were examined by the C/PSi composite-based optical sensor. The electrochemical anodization of moderate or high doped p-type silicon was performed to synthesize porous silicon templates. The reflectance spectrum and sensitivity varied with the carbon percentage in the photonic structure. The large surface area of the C/PSi composite enhanced the sensitivity of the sensor. 0.2% (v/v) was the lowest detection limit recorded for the C₂ hydrocarbons in a nitrogen carrier gas ⁸¹.

Figure 6: Reflection spectra of the PSiO₂ Bragg’s reflector before and after the fabrication of C-dots and the 3D projection image of the PSiO₂ Bragg reflector/C-dots hybrid. (A) Reflection spectra of the PSi (before and after the fabrication of C-dots); (B) Photoluminescence of the PSiO₂; (C) Fluorescence signal (C-dots); (D) A, B combined view (C-dots within a porous layer).⁸⁰

Multilayer photonic crystals

A combination of two different dielectric materials gives rise to a novel substance having unique electromagnetic properties and additional periodicity in bandgap structures. These multilayer systems have enhanced optical properties and can be used for controlled propagation of light. 1D photonic layers are easy to fabricate as structural modification leads to directional changes in a single dimension.^82-86 Development of porous photonic stacks gained a lot of interest in the mid-nineties. Different methods like vapor deposition and sputtering were used due to their simplicity and performance stability.^87,88 Modern techniques like electrochemical etching, chemical and physical vapor deposition, wet deposition methods, and spin coating have enabled the controlled fabrication of nanoparticles, polymer, colloidal crystals, and metal oxide-based multilayer photonic crystals (MPhCs). Their porous structure, large surface area, vides optical response, and binding ability proved them very efficient in gas and vapor sensing.^89-93

Polymer nanoparticles based photonic crystals are a modern type of photonic crystals (PhCs) developed by using spin coating or self-assembly technique. These techniques have the special advantage of controlled nanoparticle size achieved by mixing different ratios of monomers and cross-linkers. Desired chemical properties can be attained by the introduction of specific functional groups that react with gas molecules.⁹⁴ Burratti et al. fabricated a multilayer PhCs-based colorimetric sensor for alcoholic vapor detection through self-assembled polystyrene nanospheres with an average diameter of 250 nm. The drop-casting technique was applied to introduce samples on the surface of a glass substrate. Thin films exhibited an excellent reflectance band and maximum reflection was observed at 600 nm. Adsorption of vapors resulted in swelling of polystyrene nanospheres. Change in reflectance peak (red shift) as time function was observed in the presence of ethanol, n-butanol, isopropanol, and n-propanol vapors. Water vapors did not show any change in reflection because of the hydrophobic properties of polystyrene. The sensor proved to be highly selective for VOC detection with a detection limit of 1167 ppm.⁹⁵ A multilayer PhC-based on stacks of organic and inorganic layers was fabricated for the detection of organic vapors. Different layers were generated by alternate assembly of organic (polystyrene-acrylic acid) and inorganic (TiO₂) nanoparticles for visual detection of toxic hydrocarbons (benzene, toluene, and xylene) with a very fast response time of 1.5 seconds. The sensor was examined with a smartphone-based colorimetric study program that enabled optical detection and analysis of different hydrocarbons ⁹⁶.

Figure 7: Response curves of multichannel silica nanolayer for altered concentrations of (a) benzene, (b) toluene, (c) chlorobenzene, (d) ethanol, (e) acetone, (f) ethane, and n-hexane. Related concentrations in the ppm range are marked on the top of the response curve.⁹⁷ Reproduced with permission from ref 97. Copyright 2018 ACS publications.

Distributed Brag’s reflectors (DBRs) are another type of polymer used as photonic crystals. These are fabricated through alternative thin films of different dielectric materials.⁹⁸ Paola et al. fabricated a multilayer stack of ZnO-polystyrene nanocomposites for the detection of toluene vapors. The proposed sensor was 10-fold more sensitive than the bare polystyrene reflector because of the enhanced optical response of the functionalized surface.⁹⁹ The same group also proposed a Flory-Huggins sensor reflector for sensing VOCs. Alternative layers of inert cellulose acetate and active polystyrene modified with salinized ZnO nanoparticles formed a multilayer stack. Affinity-based attractions led to a change in UV-Visible optical response after the exposure of toluene, benzene, o-dichlorobenzene and CCL₄ vapors.¹⁰⁰ Kuchyanove et al. used multilayer porous silica films that formed hydrogen bonds between the silane group and ammonia leading to greater variations in optical properties. The proposed sensor was highly sensitive with a very low detection limit of 1 to 10⁵ ppm.¹⁰¹ Some materials such as multilayer porous silicon PhCs have the ability to concentrate gas molecules or vapors with micro-capillary condensation phenomena.¹⁰² 1D multilayer porous thin film of mixed metal hydro-oxides (MMO) and TiO₂ were used as PhC-based sensors for the detection of various VOCs with relative humidity. Alternate layers of TiO₂ and double-layered metal hydro-oxides (LDH) were deposited by spin coating and calcination was performed to convert LDH into porous structured MMO. The variation in the thickness of the TiO₂ and MMO layer changes the reflection spectrum in the visible region. Unique color band variations were observed with the absorbance of VOCs on the surface of mesoporous holes.¹⁰³ A photonic multilayer nanochannel membrane of silica was fabricated by generating layer-bilayer stacks of nanometer thickness. The regular arrangement of ultra-thin channels with a diameter of 2.3 nm resulted in very high density (1012 cm^-2) and a large surface area available for the attachment of molecules. Highly porous structures are reflected light in a constructive and destructive pattern of a specific wavelength. The attachment of vapors shifted the reflectometric interference spectrum to a higher wavelength. The lowest detection limit of the sensor was in the ppb range as shown in Figure 7.⁹⁷

Colloidal array photonic crystals

Colloidal crystals are highly ordered closely packed spheres that structurally resemble natural gemstone opal. These have a unique sub-micrometer diameter that enables light diffraction in the visible or near-infrared region. The diffraction wavelength can be altered by varying the assembly and diameter of colloidal arrays.^104-106 Accumulation of vapors on the colloidal surface leads to a change in optical properties, resulting in structural color changes. Therefore, these have been widely used for gas sensing applications.^107-109 Ling et al. fabricated a highly sensitive hybrid mesoporous PhC-based sensor by using florescent dye for qualitative and quantitative analysis of chemical vapors and gas mixtures. A change in color was observed by recording the fluorescence spectra of the excitation light.¹¹⁰

Figure 8: (A) Color changes of SMPCF sensor on glass rubber in response to (a) air, (b) methanol, and (c) acetonitrile. (B) Reflection spectrum of SMPCF sensor in response to different organic solvents.¹²⁷ Reproduced with permission from ref 127. Copyright 2019 ACS publications.

Metal oxides provide highly selective interactions, rigidity, and gas absorbing properties.¹¹¹ Yun et al. reported tin oxide (SnO₂) nanospheres for the sensing of ethanol vapors. Different structural spheres were synthesized using different growth models and their sensitivity was checked at different ethanol concentrations. Results revealed that nanocones are more sensitive than hollow and amorphous core structures due to better changes in the diffraction of light.¹¹² Applying metal oxides to a heat-generating system increases their sensitivity and recovery time which is necessary for in-situ gas detection.^113-115 2D colloidal array of SnO₂ was fabricated on a selective surface of a micro-heater for the formaldehyde vapors detection. Monolayer self-assembly and thermal decomposition were used for homogenous chemical deposition of the SnO₂ metal layer. The sensor was selective with a very low detection limit of 6.5 ppb and a recovery time of 5.4 seconds.¹¹⁶ He et al. reported a porosity-controlled SnO₂ sphere for acetone detection. The electrostatic spraying method was applied for the fabrication of homogenous porous spheres while 3D polystyrene beads were developed by colloidal templating of polystyrene beads. Different characterization tools were used to understand the composition and morphology of the sensing material. The sensor exhibited a very low detection limit of 5 ppm with high selectivity.¹¹⁷

Polymer colloidal photonic crystals have found great interest in colloidal PhCs because of their high flexibility, functionalities, and unique optical properties.^118,119 Zhang et al. developed polymer infiltrated silicon dioxide (SiO₂) inverse opal photonic crystal (IOPhC) to detect xylene vapors in air. The polymer was developed on the Inverse opal SiO₂ layer with 4-vinylbenzyl chloride-co-methyl MAA functional monomer. A resemblance in solubility parameters resulted in a higher affinity of polymer surface towards xylene vapors. The sensor exhibited a color change from green to red when exposed to the analyte with the detection limit of 0.51, 0.41, and 0.17 μg mL⁻¹ for ortho, para, and meta-xylene vapors.¹²⁰ Polymeric hydroxyethyl 2-Methacrylate film was used for the detection of carbohydrates and polyhydric alcohols. The film was fabricated with a self-assembly method followed by rinsing of deionized water to attain swelling equilibrium. A redshift in wavelength from 520-780 nm was observed with the attachment of analyte molecules.¹²¹ Li et al. fabricated IOPhC film on SiO₂ nanosphere by using hydroxyethyl methacrylate as a monomer and Ethylene glycol dimethacrylate (EGDMA) as a cross-linker. The sensor selectively responded with a color change from green to red when exposed to different concentrations of p-Nitrophenol vapors.¹²² In another study, Chang et al. reported a colloidal photonic crystal-polydimethylsiloxane (PDMS) composite for VOCs detection. Nanoscale easy net process (NET) was used for the construction of colloidal crystal-PDMS composite. The sensor detected VOCs vapors with high sensitivity and color changes were observed in the visible region.¹²³

Silk/cellulose fibers have found a recent application as a matrix for photonic materials due to mechanical strength, degradation ability, and low cost.^124,125 An opal and inverse opal 2D and 3D cellulose photonic film (CPCF) was fabricated by using 2D and 3D PMMA arrays into carboxymethyl cellulose (CMC). The wavelength of diffracted light was controlled by changing the size and diameter of nanoparticles. A visible color change from violet to red was observed by exposing the fabricated CPCF to VOCs.¹²⁶ With an extension in PhCs technology, Dan et al. synthesized a wearable silk and cellulose composite, the composite was first dyed then its surface was functionalized with 3D polystyrene and polymethyl methaacrylate (PMMA) nanostructured colloidal arrays. The Resulted inverse opal silk methylcellulose photonic crystal film (SMPCF) was highly flexible. A redshift in wavelength with a color change from green to red was observed by exposing the sensor to different VOC vapors. The SMPCF sensor integrated on a rubber glove also exhibited excellent sensitivity and selectivity towards organic solvents including methanol, ethanol, acetonitrile, toluene, and acetone as shown in Figure 8.¹²⁷

CONCLUSIONS

Recent advances in photonic sensors have enhanced their applications in environmental monitoring and pollution control. Their fast response time, high sensitivity, and lower detection limit have proved them more attractive than other sensing devices. In this review, we have discussed recent advances in different types of photonic structures and improvements in their gas sensing properties. The sensitivity of the sensor mainly depends upon the change in the refractive index induced by gas or vapor adsorption. Recent modifications have led to the enhanced optical and gas adsorbing ability of photonic crystals making them an attractive tool for gas sensing in the environment. Two and Three-dimensional nanostructures have the ability to refract light in the visual region and color changes observe with the naked eye. Furthermore, in the future, key technologies of PhC-based sensors will explore new design methodologies for highly advanced and effective gas sensors.

References

1. Joannopoulos, J D, Villeneuve, Pierre R & Fan, Shanhui . 1997. Photonic crystals: putting a new twist on light. Nature 386(6621):143–149.

2. Sibilia, C, Benson, T M, Marciniak, M & Szoplik, T . 2008. Photonic crystals: physics and technology. Springer

3. Prather, D W, Shi, S, Sharkawy, A, Murakowski, J & Schneider, G . 2009. Photonic crystals. Theory, Aplications and Fabrication.

4. Lourtioz, J.-M, Benisty, H, Berger, V, Gerard, J.-M, Maystre, D & A., Tchelnokov, . 2005. Photonic crystals. Towards Nanoscale Photonic Devices. Springer

5. Wei, L, Pavin, S, Zhao, X & Lu, M . 2021. In Nanophotonics in Biomedical Engineering .

6. Dong, Jian-Wen, Chen, Xiao-Dong, Zhu, Hanyu, Wang, Yuan & Zhang, Xiang . 2017. Valley photonic crystals for control of spin and topology. Nature Materials 16(3):298–302.

7. Wan, Bowei, Zhu, Lianqing, Ma, Xin, Li, Tianshu & Zhang, Jian . Characteristic Analysis and Structural Design of Hollow-Core Photonic Crystal Fibers with Band Gap Cladding Structures. Sensors 21(1):284.

8. Baghbadorani, H K & Barvestani, J . 2021. Sensing improvement of 1D photonic crystal sensors by hybridization of defect and Bloch surface modes. Applied Surface Science 537:147730.

9. Lova, Paola, Manfredi, Giovanni & Comoretto, Davide . 2018. Advances in Functional Solution Processed Planar 1D Photonic Crystals. Advanced Optical Materials 6(24):1800730.

10. Butt, M, Khonina, S & Kazanskiy, N . 2021. 2D-Photonic crystal heterostructures for the realization of compact photonic devices. Photonics and Nanostructures-Fundamentals and Applications 44:100903.

11. Askarian, A . 2021. Design and analysis of all optical half subtractor in 2D photonic crystal platform. Optik 228:166126.

12. Wang, Xiaoting, Cui, Yu, Li, Tao, Lei, Ming, Li, Jingbo & Wei, Zhongming . 2019. Recent Advances in the Functional 2D Photonic and Optoelectronic Devices. Advanced Optical Materials 7(3):1801274.

13. Cersonsky, Rose K, Antonaglia, James, Dice, Bradley D & Glotzer, Sharon C . 2021. The diversity of three-dimensional photonic crystals. Nature Communications 12(1):1.

14. Boyle, Bret M, French, Tracy A, Pearson, Ryan M, Mccarthy, Blaine G & Miyake, Garret M . 2017. Structural Color for Additive Manufacturing: 3D-Printed Photonic Crystals from Block Copolymers. ACS Nano 11(3):3052–3058.

15. Men, Dandan, Liu, Dilong & Li, Yue . 2016. Visualized optical sensors based on two/three-dimensional photonic crystals for biochemicals. Science Bulletin 61(17):1358–1371.

16. Shen, Huaizhong, Wang, Zhanhua, Wu, Yuxin & Yang, Bai . 2016. One-dimensional photonic crystals: fabrication, responsiveness and emerging applications in 3D construction. RSC Advances 6(6):4505–4520.

17. Nucara, Luca, Greco, Francesco & Mattoli, Virgilio . Electrically responsive photonic crystals: a review. Journal of Materials Chemistry C 3(33):8449–8467.

18. Collins, Gillian, Armstrong, Eileen, Mcnulty, David, O’hanlon, Sally, Geaney, Hugh & O’dwyer, Colm . 2016. 2D and 3D photonic crystal materials for photocatalysis and electrochemical energy storage and conversion. Science and Technology of Advanced Materials 17(1):563–582.

19. Maldovan, M . 2015. Phonon wave interference and thermal bandgap materials. Nature Materials 14(7):667–674.

20. Sani, Mojtaba Hosseinzadeh, Ghanbari, Ashkan & Saghaei, Hamed . High-sensitivity biosensor for simultaneous detection of cancer and diabetes using photonic crystal microstructure. Optical and Quantum Electronics 2022(1):1.

21. Sizova, Svetlana, Shakurov, Ruslan, Mitko, Tatiana, Shirshikov, Fedor, Solovyeva, Daria, Konopsky, Valery, Alieva, Elena, Klinov, Dmitry, Bespyatykh, Julia & Basmanov, Dmitry . The Elaboration of Effective Coatings for Photonic Crystal Chips in Optical Biosensors. Polymers 14(1):152.

22. Rashidnia, Ali, Pakarzadeh, H, Hatami, Mohsen & Ayyanar, Natesan . Photonic Crystal-Based Biosensor for Detection of Human Red Blood Cells Parasitized by Plasmodium Falciparum. Optical and Quantum Electronics 2022(1):1.

23. Kaur, Baljinder, Kumar, Santosh & Kaushik, Brajesh Kumar . 2022. Recent advancements in optical biosensors for cancer detection. Biosensors and Bioelectronics 197:113805.

24. Yablonovitch, E, Gmitter, T J, Meade, R D, Rappe, A M, Brommer, K D & Joannopoulos, J D . 1991. Donor and acceptor modes in photonic band structure. Physical Review Letters 67(24):3380–3383.

25. Yablonovitch, E . 1994. Photonic Crystals. Journal of Modern Optics 41(2):173–194.

26. John, S . 1987. Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters 58(23):2486–2489.

27. Bond, W L . 1960. Precision lattice constant determination. Acta Crystallographica 13(10):814–818.

28. Lopez, C . 2003. Materials aspects of photonic crystals. Advanced Materials 15(20):1679.

29. He, Xiaohong, Che, Xiang, Gao, Song, Chen, Xi, Pan, Miaoting, Jiang, Minzi, Zhang, Shuwei, Jia, Haohao & Duan, Yusen . 2022. Volatile organic compounds emission inventory of organic chemical raw material industry. Atmospheric Pollution Research 13(1):101276.

30. Sapuan, S, Ilyas, R & Asyraf, M . Emission of Hazardous Air Pollution in the Composite Production. Safety and Health in Composite Industry 2022. 35

31. Manisalidis, Ioannis, Stavropoulou, Elisavet, Stavropoulos, Agathangelos & Bezirtzoglou, Eugenia . Environmental and Health Impacts of Air Pollution: A Review. Frontiers in Public Health 8:14.

32. Rouf, Z, Dar, I Y, Javaid, M, Dar, M Y & Jehangir, A . In Ecological and Health Effects of Building Materials 2022.

33. Xu, Hua, Wu, Pin, Zhu, Chu, Elbaz, Abdelrahman & Gu, Zhong Ze . 2013. Photonic crystal for gas sensing. Journal of Materials Chemistry C 1(38):6087.

34. Goyal, Amit Kumar, Dutta, Hemant Sankar & Pal, Suchandan . 2017. Recent advances and progress in photonic crystal-based gas sensors. Journal of Physics D: Applied Physics 50(20):203001.

35. Hassan, Md Mehedi, Xu, Yi, Zareef, Muhammad, Li, Huanhuan, Rong, Yawen & Chen, Quansheng . 2021. Recent advances of nanomaterial-based optical sensor for the detection of benzimidazole fungicides in food: a review. Critical Reviews in Food Science and Nutrition 1:1–22.

36. Joe, H.-E, Yun, H, Jo, S.-H, Jun, M B & Min, B.-K . 2018. A review on optical fiber sensors for environmental monitoring. International journal of precision engineering and manufacturing-green technology 5:173.

37. Huang, Chang, Chen, Yun, Zhang, Shiqiang & Wu, Jianping . 2018. Detecting, Extracting, and Monitoring Surface Water From Space Using Optical Sensors: A Review. Reviews of Geophysics 56(2):333–360.

38. Law, Cheryl Suwen, Lim, Siew Yee, Abell, Andrew D, Voelcker, Nicolas H & Santos, Abel . 2018. Nanoporous Anodic Alumina Photonic Crystals for Optical Chemo- and Biosensing: Fundamentals, Advances, and Perspectives. Nanomaterials 8(10):788.

39. Zhao, Yong, Zhang, Ya-Nan & Wang, Qi . 2011. Research advances of photonic crystal gas and liquid sensors. Sensors and Actuators B: Chemical 160(1):1288–1297.

40. Tomi?, Milena, Šetka, Milena, Vojk?vka, Lukaš & Vallejos, Stella . VOCs Sensing by Metal Oxides, Conductive Polymers, and Carbon-Based Materials. Nanomaterials 11(2):552.

41. Hanna, George B, Boshier, Piers R, Markar, Sheraz R & Romano, Andrea . Accuracy and Methodologic Challenges of Volatile Organic Compound–Based Exhaled Breath Tests for Cancer Diagnosis. JAMA Oncology 5(1):e182815.

42. Barhoum, A, García-Betancourt, M L, Jeevanandam, J, Hussien, E A, Mekkawy, S A, Mostafa, M, Omran, M M, Abdalla, M & Bechelany, M . Review on Natural, Incidental, Bioinspired, and Engineered Nanomaterials: History, Definitions, Classifications, Synthesis, Properties, Market, Toxicities, Risks, and Regulations 2022:177.

43. Dong, Zhengqiong, Zhao, Hang, Nie, Lei, Tang, Shaokang, Li, Chenyang & Wang, Xuanze . Effects of Measurement Configurations on the Sensitivity of Morpho Butterfly Scales Based Chemical Biosensor. Frontiers in Physics 9:792.

44. Cao, Xiaobao, Du, Ying, Guo, Yujia, Hu, Guohang, Zhang, Ming, Wang, Lu, Zhou, Jiangtao, Gao, Quan, Fischer, Peter, Wang, Jing, Stavrakis, Stavros & Demello, Andrew . 2022. Replicating the Cynandra opis Butterfly's Structural Color for Bioinspired Bigrating Color Filters. Advanced Materials 34(9):2109161.

45. Kim, Hyun Myung, Kim, Sang Hyeok, Lee, Gil Ju, Kim, Kyujung M & Song, Young Min . 2015. Parametric Studies on Artificial Morpho Butterfly Wing Scales for Optical Device Applications. Journal of Nanomaterials 2015:1–7.

46. Potyrailo, Radislav A, Karker, Nicholas, Carpenter, Michael A & Minnick, Andrew . 2018. Multivariable bio-inspired photonic sensors for non-condensable gases. Journal of Optics 20(2):024006.

47. Tripathy, Ashis, Nine, Md Julker, Losic, Dusan & Silva, Filipe Samuel . 2021. Nature inspired emerging sensing technology: Recent progress and perspectives. Materials Science and Engineering: R: Reports 146:100647.

48. Potyrailo, R A, Brewer, J, Cheng, B, Carpenter, M A, Houlihan, N & Kolmakov, A . 2020. Bio-inspired gas sensing: boosting performance with sensor optimization guided by “machine learning”. Faraday Discussions 223:161–182.

49. Krishna, Anirudh, Nie, Xiao, Briscoe, Adriana D & Lee, Jaeho . 2021. Air temperature drives the evolution of mid-infrared optical properties of butterfly wings. Scientific Reports 11(1):1.

50. Yang, Bo, Cheng, Hua, Chen, Shuqi & Tian, Jianguo . Structural colors in metasurfaces: principle, design and applications. Materials Chemistry Frontiers 3(5):750–761.

51. Piszter, Gábor, Kertész, Krisztián, Bálint, Zsolt & Biró, László P . 2016. Pretreated Butterfly Wings for Tuning the Selective Vapor Sensing. Sensors 16(9):1446.

52. He, Jiaqing, Villa, Nicolò Simone, Luo, Zhen, An, Shun, Shen, Qingchen, Tao, Peng, Song, Chengyi, Wu, Jianbo, Deng, Tao & Shang, Wen . Integrating plasmonic nanostructures with natural photonic architectures in Pd-modified Morpho butterfly wings for sensitive hydrogen gas sensing. RSC Advances 8(57):32395–32400.

53. Yang, Guiqin, Zhang, Meng, Dong, Decheng, Pan, Xiaofang, Zhou, Ye, Han, Su-Ting, Xu, Zongxiang, Wang, Wanlin & Yan, Yan . TiO2 based sensor with butterfly wing configurations for fast acetone detection at room temperature. Journal of Materials Chemistry C 7(36):11118–11125.

54. *, J Silver, Withnall*, R, Ireland, T G & Fern, G R . 2005. Novel nano-structured phosphor materials cast from natural Morpho butterfly scales. Journal of Modern Optics 52(7):999–1007.

55. Zhang, Jiujie, Liang, Yanqin, Mao, Jing, Yang, Xianjin, Cui, Zhenduo, Zhu, Shengli & Li, Zhaoyang . 2016. 3D microporous Co3O4-carbon hybrids biotemplated from butterfly wings as high performance VOCs gas sensor. Sensors and Actuators B: Chemical 235:420–431.

56. Poncelet, Olivier, Tallier, Guillaume, Mouchet, Sébastien R, Crahay, André, Rasson, Jonathan, Kotipalli, Ratan, Deparis, Olivier & Francis, Laurent A . 2016. Vapour sensitivity of an ALD hierarchical photonic structure inspired by Morpho. Bioinspiration & Biomimetics 11(3):036011.

57. Rodríguez, R E, Agarwal, S P, An, S, Kazyak, E, Das, D, Shang, W, Skye, R, Deng, T & Dasgupta, N P . 2018. Biotemplated Morpho butterfly wings for tunable structurally colored photocatalysts. ACS applied materials & interfaces 10(5):4614.

58. Han, Zhiwu, Mu, Zhengzhi, Li, Bo, Wang, Ze, Zhang, Junqiu, Niu, Shichao & Ren, Luquan . 2016. Active Antifogging Property of Monolayer SiO2 Film with Bioinspired Multiscale Hierarchical Pagoda Structures. ACS Nano 10(9):8591–8602.

59. Xu, Guogang, Zhang, Xueying, Cui, Hongzhi, Chen, Zhiwei, Ding, Jianxu & Zhan, Xiaoyuan . 2016. Preparation of mesoporous SnO 2 by solvothermal method using Stahlianthus involucratus leaves and application to n-butanol sensor. Powder Technology 302:283–287.

60. Zhang, Sichao & Chen, Yifang . 2015. Nanofabrication and coloration study of artificial Morpho butterfly wings with aligned lamellae layers. Scientific Reports 5(1):1.

61. Kittle, Joshua D, Fisher, Benjamin P, Esparza, Anthony J, Morey, Aimee M & Iacono, Scott T . 2017. Sensing Chemical Warfare Agent Simulants via Photonic Crystals of the Morpho didius Butterfly. ACS Omega 2(11):8301–8307.

62. Bouachma, Soraya, Ayouz-Chebout, Katia, Kechouane, Mouhamed, Manseri, Amar, Yaddadene, Chafiaa, Menari, Hamid & Gabouze, Noureddine . 2022. Synthesis of PSi-n/CuO-p/Cu2O-n heterostructure for CO2 gas sensing at room temperature. Applied Physics A 128(1):1.

63. Ramirez-Gutierrez, Cristian Felipe, Martinez-Hernandez, Harol David, Lujan-Cabrera, Ivan Alonso & Rodriguez-García, Mario Enrique . 2019. Design, fabrication, and optical characterization of one-dimensional photonic crystals based on porous silicon assisted by in-situ photoacoustics. Scientific Reports 9(1):1.

64. Bui, Huy, Pham, Van Hoi, Pham, Van Dai, Hoang, Thi Hong Cam, Pham, Thanh Binh, Do, Thuy Chi, Ngo, Quang Minh & Nguyen, Thuy Van . 2019. Determination of low solvent concentration by nano-porous silicon photonic sensors using volatile organic compound method. Environmental Technology 40(26):3403–3411.

65. Moore, T J & Sharma, B . 2018. Volatile Organic Compound Detection using Porous-Silicon-Oxide Coated Disc-on-Pillar Arrays. SeTu4E.4.

66. Kumeria, Tushar, Wang, Joanna, Chan, Nicole, Harris, Todd J & Sailor, Michael J . 2018. Visual Sensor for Sterilization of Polymer Fixtures Using Embedded Mesoporous Silicon Photonic Crystals. ACS Sensors 3(1):143–150.

67. Chun, Soohyun & Miskelly, Gordon M . 2018. Hyperspectral and Color Imaging of Solvent Vapor Sorption Into Porous Silicon. Frontiers in Chemistry 6:610.

68. Lu, Yi-Sheng, Vijayakumar, Sanahan, Chaix, Arnaud, Pimentel, Brian R, Bentz, Kyle C, Li, Sheng, Chan, Adriano, Wahl, Charlotte, Ha, James S, Hunka, Deborah E, Boss, Gerry R, Cohen, Seth M & Sailor, Michael J . 2021. Remote Detection of HCN, HF, and Nerve Agent Vapors Based on Self-Referencing, Dye-Impregnated Porous Silicon Photonic Crystals. ACS Sensors 6(2):418–428.

69. Ahmed, Ashour M & Mehaney, Ahmed . 2019. Ultra-high sensitive 1D porous silicon photonic crystal sensor based on the coupling of Tamm/Fano resonances in the mid-infrared region. Scientific Reports 9(1):1.

70. Min-Dianey, K A A, Zhang, H.-C, Brohi, A A, Yu, H & Xia, X . 2018. Optical spectra of composite silver-porous silicon (Ag-pSi) nanostructure based periodical lattice. Superlattices and Microstructures 115:168.

71. Juneau-Fecteau, Alexandre & Fréchette, Luc G . 2018. Tamm plasmon-polaritons in a metal coated porous silicon photonic crystal. Optical Materials Express 8(9):2774.

72. Sun, Peng, Hu, Ming, Li, Mingda & Ma, Shuangyun . 2012. Nano-WO3 film modified macro-porous silicon (MPS) gas sensor. Journal of Semiconductors 33(5):054012.

73. Wang, Deng-Feng, Liang, Ji-Ran, Li, Chang-Qing, Yan, Wen-Jun & Hu, Ming . 2016. Room temperature NO2 gas sensing of Au-loaded tungsten oxide nanowires/porous silicon hybrid structure. Chinese Physics B 25(2):028102.

74. Abed, Husam R, Alwan, Alwan M, Yousif, Ali A & Habubi, Nadir F . 2019. Efficient SnO2/CuO/porous silicon nanocomposites structure for NH3 gas sensing by incorporating CuO nanoparticles. Optical and Quantum Electronics 51(10):1.

75. Zhang, Hongyan & Jia, Zhenhong . 2017. Application of porous silicon microcavity to enhance photoluminescence of ZnO/PS nanocomposites in UV light emission. Optik 130:1183–1190.

76. Zamani, Mehdi & Hocini, Abdesselam . 2016. Large Faraday rotation in magnetophotonic crystals containing SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles. Optical Materials 58:306–309.

77. Bueno, Priscila, Pagnan Furlan, Kaline, Hotza, Dachamir & Janssen, Rolf . High-temperature stable inverse opal photonic crystals via mullite-sol-gel infiltration of direct photonic crystals. Journal of the American Ceramic Society 2019(2):686.

78. Mutyala, S, Charan, P H K, Rajaram, R & Mahesh, K N . 2022. Functionalized carbon nanomaterials in electrochemical detection. In: Functionalized Nanomaterial-Based Electrochemical Sensors. (pp. 2022) Elsevier

79. Sailor, M J & Kelly, T . 2016. Carbon and carbon/silicon composite nanostructured materials and casting formation method. US Patent No. 9499407B2. Google Patents

80. Massad-Ivanir, Naama, Bhunia, Susanta Kumar, Jelinek, Raz & Segal, Ester . 2018. Porous Silicon Bragg Reflector/Carbon Dot Hybrids: Synthesis, Nanostructure, and Optical Properties. Frontiers in Chemistry 6:574.

81. Chan, Danny Yuan, Sega, Adrian Garcia, Lee, Jessica Y, Gao, Ting, Cunin, Frèderique, Renzo, Francesco Di & Sailor, Michael J . 2014. Optical detection of C 2 hydrocarbons ethane, ethylene, and acetylene with a photonic crystal made from carbonized porous silicon. Inorganica Chimica Acta 422:21–29.

82. Gowdhami, D, Balaji, V R, Murugan, M, Robinson, S & Hegde, Gopalkrishna . 2022. Photonic crystal based biosensors: an overview. ISSS Journal of Micro and Smart Systems 11(1):147–167.

83. Belhadj, Walid, Timoumi, Abdelmajid, Dakhlaoui, Hassen & Alhashmi Alamer, Fahad . Design and Optimization of One-Dimensional TiO2/GO Photonic Crystal Structures for Enhanced Thermophotovoltaics. Coatings 12(2):129.

84. Trabelsi, Y, Belhadj, W, Ali, B, Aly, A H & Photonics, . 2021.

85. Panda, Abinash, Pukhrambam, Puspa Devi, Wu, Feng & Belhadj, Walid . 2021. Graphene-based 1D defective photonic crystal biosensor for real-time detection of cancer cells. The European Physical Journal Plus 136(8):1.

86. Panda, A & Pukhrambam, P D . Micro and Nanoelectronics Devices 2022.

87. Liu, W, Ma, H & Walsh, A . 2019. Advance in photonic crystal solar cells. Renewable and Sustainable Energy Reviews 116:109436.

88. Castillo-Gallardo, V, Puente-Díaz, Luis Eduardo, Ariza-Flores, D, Pérez-Aguilar, Héctor, Mochán, W Luis & Agarwal, V . 2021. Optimization of wide-band quasi-omnidirectional 1-D photonic structures. Optical Materials 117:111202.

89. Noah, N M . 2020. Design and Synthesis of Nanostructured Materials for Sensor Applications. Journal of Nanomaterials 2020:1–20.

90. Sui, Xiaoyu, Downing, Julia R, Hersam, Mark C & Chen, Junhong . 2021. Additive manufacturing and applications of nanomaterial-based sensors. Materials Today 48:135–154.

91. Meng, Zheng, Stolz, Robert M, Mendecki, Lukasz & Mirica, Katherine A . 2019. Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials. Chemical Reviews 119(1):478–598.

92. Yu, Jie, Lei, Juying, Wang, Lingzhi, Zhang, Jinlong & Liu, Yongdi . 2018. TiO2 inverse opal photonic crystals: Synthesis, modification, and applications - A review. Journal of Alloys and Compounds 769:740–757.

93. Paternò, G M, Moscardi, L, Kriegel, I, Scotognella, F & Lanzani, G . 2018. Electro-optic and magneto-optic photonic devices based on multilayer photonic structures. Journal of Photonics for Energy 8(3):32201.

94. Edrington, A C, Urbas, A M, Derege, P, Chen, C X, Swager, T M, Hadjichristidis, N, Xenidou, M, Fetters, L J, Joannopoulos, J D, Fink, Y & Thomas, E L . 2001. Polymer?Based Photonic Crystals. Advanced Materials 13(6):421–425.

95. Burratti, L, De Matteis, F, Casalboni, M, Francini, R, Pizzoferrato, R & Prosposito, P . 2018. Polystyrene photonic crystals as optical sensors for volatile organic compounds. Materials Chemistry and Physics 212:274–281.

96. Kou, Donghui, Zhang, Yongce, Zhang, Shufen, Wu, Suli & Ma, Wei . 2019. High-sensitive and stable photonic crystal sensors for visual detection and discrimination of volatile aromatic hydrocarbon vapors. Chemical Engineering Journal 375:121987.

97. Wang, Yafeng, Yang, Qian, Zhao, Meijiao, Wu, Jianmin & Su, Bin . 2018. Silica-Nanochannel-Based Interferometric Sensor for Selective Detection of Polar and Aromatic Volatile Organic Compounds. Analytical Chemistry 90(18):10780–10785.

98. Lin, Dongqing, Liu, Jin'an A, Zhang, He, Qian, Yue, Yang, Hao, Liu, Lihui A, Ren, Ang, Zhao, Yongsheng, Yu, Xiang, Wei, Ying, Hu, Shu, Li, Lianjie, Li, Shifeng, Sheng, Chuanxiang, Zhang, Wenhua, Chen, Shufen, Shen, Jianping, Liu, Huifang A, Feng, Quanyou, Wang, Shasha, Xie, Linghai & Huang, Wei . 2022. Gridization?Driven Mesoscale Self?Assembly of Conjugated Nanopolymers into Luminescence?Anisotropic Photonic Crystals. Advanced Materials 34(11):2109399.

99. Lova, Paola . Polymer distributed Bragg reflectors for label-free vapor sensing. Acs Photonics 2015(4):537.

100. Lova, P . Selective Polymer Distributed Bragg Reflector Vapor Sensors. Polymers 10(10):1161.

101. Kuchyanov, A S, Chubakov, P A, Chubakov, V P & Mikerin, S L . 2019. Nonlinear interaction of silica photonic crystals with ammonia vapor. Results in Physics 15:102726.

102. De Stefano, L . 2019. Porous Silicon Optical Biosensors: Still a Promise or a Failure? Sensors 19(21):4776.

103. Dou, Yibo, Han, Jingbin, Wang, Tengli, Wei, Min, Evans, David G & Duan, Xue . 2012. Fabrication of MMO–TiO2 one-dimensional photonic crystal and its application as a colorimetric sensor. Journal of Materials Chemistry 22(28):14001.

104. Li, Fangjie, Luo, Yuning, Feng, Xiaoyi, Guo, Yuqiong, Zhou, Yue, He, Dongxiu, Xie, Zhizhong, Zhang, Haitao & Liu, Yang . 2022. Two-dimensional colloidal crystal of soft microgel spheres: Development, preparation and applications. Colloids and Surfaces B: Biointerfaces 212:112358.

105. Liao, Junlong, Ye, Changqing, Agrawal, Prajwal, Gu, Zhongze & Zhang, Yu Shrike . 2021. Colloidal Photonic Crystals for Biomedical Applications. Small Structures 2(5):2000110.

106. Cai, Zhongyu, Li, Zhiwei, Ravaine, Serge, He, Mingxin, Song, Yanlin, Yin, Yadong, Zheng, Hanbin, Teng, Jinghua & Zhang, Ao . 2021. From colloidal particles to photonic crystals: advances in self-assembly and their emerging applications. Chemical Society Reviews 50(10):5898–5951.

107. Guo, Shuaibing, Yu, Bing, Gao, Fengyuan, Wang, Song, Shen, Youqing & Cong, Hailin . 2021. Research status and development trend of three-dimensional colloidal crystals. Journal of Industrial and Engineering Chemistry 96:34–58.

108. Qi, Fenglian, Meng, Zihui, Xue, Min & Qiu, Lili . 2020. Recent advances in self-assemblies and sensing applications of colloidal photonic crystals. Analytica Chimica Acta 1123:91–112.

109. Pan, , Wang, , Dou, , Zhao, , Xu, , Wang, , Zhang, , Li, , Pan, & Li, . Recent Advances in Colloidal Photonic Crystal-Based Anti-Counterfeiting Materials. Crystals 9(8):417.

110. Bai, Ling, Xie, Zhuoying, Cao, Kaidi, Zhao, Yuanjin, Xu, Hua, Zhu, Cun, Mu, Zhongde, Zhong, Qifeng & Gu, Zhongze . 2014. Hybrid mesoporous colloid photonic crystal array for high performance vapor sensing. Nanoscale 6(11):5680.

111. Kumbhakar, Partha, Chowde Gowda, Chinmayee, Mahapatra, Preeti Lata, Mukherjee, Madhubanti, Malviya, Kirtiman Deo, Chaker, Mohamed, Chandra, Amreesh, Lahiri, Basudev, Ajayan, P M, Jariwala, Deep, Singh, Abhishek & Tiwary, Chandra Sekhar . 2021. Emerging 2D metal oxides and their applications. Materials Today 45:142–168.

112. Kuang, Yun, Chen, Guobing, Lei, Xiaodong, Luo, Liang & Sun, Xiaoming . 2013. Mesoporous assembled SnO2 nanospheres: Controlled synthesis, structural analysis and ethanol sensing investigation. Sensors and Actuators B: Chemical 181:629–636.

113. Mo, Yaowu, Okawa, Yuzo, Tajima, Motoshi, Nakai, Takehito, Yoshiike, Nobuyuki & Natukawa, Kazuki . 2001. Micro-machined gas sensor array based on metal film micro-heater. Sensors and Actuators B: Chemical 79(2-3):175–181.

114. Korotcenkov, G . 2008. The role of morphology and crystallographic structure of metal oxides in response of conductometric-type gas sensors. Materials Science and Engineering: R: Reports 61(1-6):1–39.

115. Mondal, Biplob & Gogoi, Pranjal Kumar . 2022. Nanoscale Heterostructured Materials Based on Metal Oxides for a Chemiresistive Gas Sensor. ACS Applied Electronic Materials 4(1):59–86.

116. Rao, Ameya, Long, Hu, Harley-Trochimczyk, Anna, Pham, Thang, Zettl, Alex, Carraro, Carlo & Maboudian, Roya . 2017. In Situ Localized Growth of Ordered Metal Oxide Hollow Sphere Array on Microheater Platform for Sensitive, Ultra-Fast Gas Sensing. ACS Applied Materials & Interfaces 9(3):2634–2641.

117. Cho, Hee-Jin, Choi, Seon-Jin, Kim, Nam-Hoon & Kim, Il-Doo . 2020. Porosity controlled 3D SnO2 spheres via electrostatic spray: Selective acetone sensors. Sensors and Actuators B: Chemical 304:127350.

118. Yang, Zhaokun, Jin, Huajun, Yu, Ang, Yu, Zhangyong, Shi, Dongjian, Yan, Shengrong, Qin, Liyan, Liu, Shirong & Chen, Mingqing . 2022. Construction of surface molecularly imprinted photonic hydrogel sensors with high sensitivity. Colloids and Surfaces A: Physicochemical and Engineering Aspects 639:128341.

119. Chen, C, Wang, X, Dong, Z, Chen, G, Zhao, X, Zhu, Z, Shih, W.-H & Zhu, Y . 2019. Smart Polymer Catalysts and Tunable Catalysis. Elsevier

120. Zhang, Yuqi, Sun, Yimin, Liu, Jiaqi, Guo, Pu, Cai, Zhongyu & Wang, Ji-Jiang . 2019. Polymer-infiltrated SiO2 inverse opal photonic crystals for colorimetrically selective detection of xylene vapors. Sensors and Actuators B: Chemical 291:67–73.

121. Zhang, Yongli, Tang, Jing, Feng, Keke, Zhao, Huilin, Yan, Weiwei, Sun, Zhiming, Wu, Fuming, Sun, Yu & Gao, Jianping . 2020. Response of photonic crystal hydrogels to carbohydrate and polyhydroxy alcohols. Reactive and Functional Polymers 148:104504.

122. Li, Lu, Meng, Tiantian, Zhang, Wanbin, Su, Ying, Wei, Juan, Shi, Xinwei & Zhang, Guanghua . Selective and Colorimetric Detection of p-Nitrophenol Based on Inverse Opal Polymeric Photonic Crystals. Polymers 12(1):83.

123. Chang, Hyung-Kwan, Chang, Gyu Tae, Thokchom, Ashish K, Kim, Taesung & Park, Jungyul . 2018. Ultra-fast responsive colloidal–polymer composite-based volatile organic compounds (VOC) sensor using nanoscale easy tear process. Scientific Reports 8(1):1.

124. Liu, Qiaoling, Peng, Qianqian, Ma, Cheng, Jiang, Min, Zong, Lu & Zhang, Jianming . 2022. Efficient transition metal dichalcogenides exfoliation by cellulose nanocrystals for ultrabroad-pH/temp stable aqueous dispersions and multi-responsive photonic films. Chemical Engineering Journal 428:132594.

125. Babaei-Ghazvini, Amin, Acharya, Bishnu & Korber, Darren R . 2022. Multilayer photonic films based on interlocked chiral-nematic cellulose nanocrystals in starch/chitosan. Carbohydrate Polymers 275:118709.

126. Yan, Dan, Li, Renbin, Lu, Wei, Piao, Chunmei, Qiu, Lili, Meng, Zihui & Wang, Shushan . Flexible construction of cellulose photonic crystal optical sensing nano-materials detecting organic solvents. The Analyst 144(6):1892–1897.

127. Yan, Dan, Qiu, Lili, Shea, Kenneth J, Meng, Zihui & Xue, Min . 2019. Dyeing and Functionalization of Wearable Silk Fibroin/Cellulose Composite by Nanocolloidal Array. ACS Applied Materials & Interfaces 11(42):39163–39170.