Photonic Crystal Microspheres Research Articles

Smart Window with Reversible and Instantaneous Photoluminescence based on Microsphere Structure.

A smart window that dynamically regulates light transmittance is crucial for modern life end-users and promising for on-demand optical devices. The advent of three-dimensional (3D) photonic crystal microspheres has enriched the functions of a smart window. However, the smart window formed by polymer microspheres encounters poor mechanical strength and microstructural defects. Herein, to solve this limitation, we report the microsphere-based smart window composed of tightly packed cross-linked polymer microspheres (as a precursor) containing organic photochromic dyes, followed by compression under a high elastic state. When excited under an ultraviolet supply, our smart window showed a rapid and reversible fluorescent photoluminescence without fatigue (50 cycles). Moreover, the bulk devices with a microsphere cross-linked network structure enable excellent mechanical strength (hardness reached 0.158 GPa) and visible-light transparency. Interestingly, a QR code can be recognized under visible light exposure but not under ultraviolet light exposure because of photoluminescence of the smart window. Our method generally provided a paradigm for various amorphous polymers, which can be regarded as a simple and effective approach to build a versatile strategy to introduce an ideal marketplace with economic and community benefits.

Photonic crystal microspheres: Synthesis, characterization, and applications in colored contact lenses

Structural colors arise from the interaction between light and ordered structural materials, making them the ideal choice for colored contact lenses. This study utilized a fast, large-scale synthesis method for silica photonic crystal microspheres, introducing carbon black to enhance the structural coloring effect. The sintering process strengthened the cohesion between particles, increasing their strength and expanding their range of applications. This approach successfully prepared SiO2 photonic crystal inks with structural colors to produce contact lenses through a pad printing technique. In particular, the coloration is solely achieved using SiO2 and carbon black without other organic species. The resulting structural color blue contact lenses exhibit high light transmittance and vivid structural colors. Furthermore, the following necessary properties were me: oxygen transmittance, visible light transmittance, hydrophilicity, and lipid and protein adsorption of the contact lenses. Cell viability experiments indicate that contact lenses made from this material are biocompatible. The results illustrated that these as-prepared lenses are promising candidates for traditional colored contact lenses.

Rapid multiplex assay of SARS-CoV-2 antigens based on magnetic Janus photonic barcodes

SARS-CoV-2 has been causing severe impacts on all aspects of society for more than three years. Antigen immunoassay is the main detection method of SARS-CoV-2 at present. Here, a magnetic photonic crystal microsphere with a Janus structure is designed for synchronous detection of SARS-CoV-2-associated antigens. One hemisphere of the Janus microsphere is a photonic crystal assembled by silica nanoparticles, where the structural color serves as the encoding basis for multiplex detection and the surface is functionalized with the capture antibodies. The other hemisphere of the Janus microsphere is assembled by magnetic nanoparticles, allowing the controlled movement of the microspheres in a magnetic field, thereby enhancing antigen capture efficiency. It is demonstrated that this ingeniously designed detection platform can rapidly and simultaneously detect spike protein and nucleocapsid protein of SARS-CoV-2 based on a double-antibody sandwich immunoassay strategy. The limit of detection (LOD) is 0.478 ng/mL for spike protein and 0.255 ng/mL for nucleocapsid protein. Hence, the Janus photonic barcodes provide a new avenue for multiplex detection of SARS-CoV-2-associated antigens and have the potential to be utilized in the assay of other disease-related biomarkers.

Novel SiO2 photonic crystal microspheres as inorganic pigments for structural color contact lenses

Traditional contact lenses patterns are mostly colored with organic pigments, but they suffered a pigment leakage risk after long-term wearing, which causes corneal inflammation and ulceration. To solve this issue, the structural color is applied to contact lenses because it has color and pigment free. Herein, we reported the application of SiO2 photonic crystal microspheres in contact lenses. We successfully prepared SiO2 photonic crystal ink with structural color and fabricated contact lenses by ink transfer printing, and these contact lenses also contain patterns and pupil areas that are the same as the traditional pigment one. In addition, in vitro cytotoxicity test, physicochemical property test, and optical property test were carried out to verify the performance of the prepared structural color lenses. All results suggested it has great potential to replace traditional organic pigment contact lenses.

High-performance molecularly imprinted polymers grafted magnetic photonic crystal microspheres for selective enrichment of ochratoxin a

Development of selective enrichment materials for the accurate analysis of ochratoxin a (OTA) in environmental and food samples is an effective way to protect human health. Here, a molecularly imprinted polymer (MIP) known as plastic antibody was synthesized onto the magnetic inverse opal photonic crystal microsphere (MIPCM) using a low-cost dummy template imprinting strategy targeting OTA. The MIP@MIPCM exhibited ultrahigh selectivity with an imprinting factor of 130, high specificity with cross-reactivity factors of 3.3–10.5, and large adsorption capacity of 60.5 μg/mg. Such MIP@MIPCM was used for selective capture of OTA in real samples which was quantified in combination with high-performance liquid chromatography, giving a wide linear detection range of 5–20,000 ng/mL, a detection limit of 0.675 ng/mL, and good recovery rates of 84–116%. Moreover, the MIP@MIPCM can be produced simply and rapidly and is very stable under different environmental conditions and easy to store and transport, so it is an ideal substitute of biological antibody modified materials for the selective enrichment of OTA in real samples.

Thermochromic Photonic Crystal Microspheres with Uniform Color Display and Wide Coloration Range.

Thermochromic microspheres based on poly(N-isopropylacrylamide) attract much attention in detection and sensor due to the noticeable color response and fast response rate. However, some issues such as uneven color display and narrow coloration range still limit their practical applications. Herein, novel thermochromic microspheres with homogeneous color displays and wide thermochromic range are designed by combining the microfluidic technology with the magnetically-induced self-assembly technique and copolymerizing acrylamide (AM) with N-isopropylacrylamide. The photonic crystal structure with especially even colors is fast and conveniently constructed by magnetic assembly. The addition of AM makes the microspheres more hydrophilic and thus leading to a broader coloration range. The relationship between the structural color display and both the microstructures of photonic crystals and the thermo-responsive properties of gel matrix are elucidated. The detectable temperature of microspheres rises to as high as 60°C, and displays bright iridescent color variations from orange to blue-violet in the heating process. Importantly, their shrinking or swelling equilibrium can be reached in 80 and 105 s. Such microspheres are successfully used to visually indicate the appropriate temperature of enzymatic reaction, and have great potential in practical applications such as visual temperature detection and efficiency monitoring of chemical reactions.

Label-Free Fluorescence Quantitative Detection Platform on Plasmonic Silica Photonic Crystal Microsphere Array.

We have demonstrated the proof-of-concept of a label-free fluorescence quantitative detection platform based on gold nanoparticle (AuNP) enhancement intrinsic fluorescence of protein on the silica photonic crystal microsphere (SPCM) array. The label-free one-step competitive fluorescence immunoassay protocol has been proposed on the surface of the SPCM. Aflatoxin B1 (AFB1) as a model molecule was detected by the newly established method. AFB1-bovine serum albumin and monoclonal antibodies (Abs) of anti-AFB1 have been immobilized on the surfaces of SPCMs and AuNPs, respectively. AuNPs remarkably enhanced the intrinsic fluorescence of artificial antigens on the surface of the SPCM at near UV excitation. The simulation of electric field distribution showed that the maximum value of the near-field enhancement |E/E0| of the SPCM with AuNPs could reach 20. The label-free fluorescence enhancement effect comes from the synergistic effects of photonic crystal effect and AuNP plasmon effect. Such a label-free fluorescence detection method can provide a linear detection range from 0.1 to 10 ng/mL with a limit of detection of 0.025 ng/mL and good specificity for AFB1. The recovery rates in the spiked cereal samples were measured in the range of 84.07 ± 5.71%-101.02 ± 5.13%, which were consistent with that of the traditional enzyme linked immunosorbent assay method. The label-free detection platform displays great application potential in biology, medicine, agriculture, food industry, chemical industry, energy source, and environmental protection.

Ultrasensitive multiplex SERS immunoassay based on porous Au–Ag alloy nanoparticle–amplified Raman signal probe and encoded photonic crystal beads

An ultrasensitive multiplex surface-enhanced Raman scattering (SERS) immunoassay was developed using porous Au-Ag alloy nanoparticles (p-AuAg NPs) as Raman signal amplification probe coupling with encoded photonic crystal microsphere. p-AuAg NPs were synthesized and modified with the second antibody (Ab2) and Raman tag (mercaptobenzoic acid, MBA) to prepare aRaman signal-amplified probe. The high porosity of the p-AuAg NPs enables significant coupling of the localized surface plasmon resonance and thus abundant inherent hotspots for Raman signal enhancement. 3D-ordered silver nanoparticles-coated silica photonic crystal beads (Ag/SPCBs) were prepared as encoded SERS substrate for multiplex detection using their reflection peaks. Thesignal-amplified probe was used for multiplex detection of tumor markers carcinoembryonic antigen (CEA) and alpha fetoprotein (AFP). The wide linear ranges of 10-7-103ng/mL for CEA and 10-4-103ng/mL for AFP with detection limits of 1.22 × 10-8ng/mL and 2.47 × 10-5ng/mL for CEA and AFP at asignal-to-noise ratio of 3 were obtained. The proposed multiplex SERS immunoassay method displays ultrahigh sensitivity, wide linear range, and excellent specificity, which can be successfully applied to measure clinical serum samples with satisfactory results. The research provides a novel SERS signal enhancement strategy for the multiplex bioassay.

Three-Dimensional Ordered Macroporous Magnetic Inverse Photonic Crystal Microsphere-Based Molecularly Imprinted Polymer for Selective Capture of Aflatoxin B1.

Development of an efficient detection method to monitor residual mycotoxins in food is very important to ensure food safety, but the complex food matrix seriously affects the detection sensitivity and accuracy. Here, using a three-dimensional ordered macroporous magnetic inverse photonic crystal microsphere (MPCM) as the supporting material, a molecularly imprinted polymer (MIP) that can selectively recognize aflatoxin B1 (AFB1) was synthesized through the dummy template imprinting strategy. The MPCM@MIP prepared by employing 5,7-dimethoxycoumarin as the template and methacrylic acid as the functional monomer displayed selectivity toward AFB1 (imprinting factor of 1.5) and could be used as a solid-phase extraction material. By coupling with high-performance liquid chromatography, an analytical method targeting AFB1 was established and displayed a wide linear range of 5-1000 ng/mL with a low detection limit of 0.4 ng/mL. The method showed a good recovery rate of 73-92% in AFB1-spiked soy sauce and vinegar samples. Moreover, the MPCM@MIP could be separated from the sample solution easily because of its magnetic performance, displaying a promising future not only in the enrichment of AFB1 to improve the detection sensitivity and accuracy but also in the removal of AFB1 from food and environmental samples.

Highly sensitive SERS detection for Aflatoxin B1 and Ochratoxin A based on aptamer-functionalized photonic crystal microsphere array

A highly sensitive surface-enhanced Raman spectroscopy (SERS) aptasensor for multiplex mycotoxins detection was developed based on aptamer-functionalized photonic microsphere array. Gold nanoparticles (AuNPs) were grafted covalently onto the silica photonic crystal microsphere (SPCM) to fabricate the SERS active substrate, on which the near-field enhancement can reach to 20 times analyzed by the simulation electric field distribution. Two dyes of 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB) and nile blue A (NBA) were employed to make the SERS nanotags on AuNPs that were modified with corresponding anti-aptamer sequences. A SERS assay system was established based on the competitive reaction between the anti-aptamer on SERS nanotags and the target mycotoxin towards the aptamer on SPCM. The developed method showed a linear relationship in the range of 0.01–100 ng/mL for aflatoxin B1 (AFB1) and 0.001–10 ng/mL for ochratoxin A (OTA), and a low limit of detection of 0.36 pg/mL for AFB1 and 0.034 pg/mL for OTA. The accuracy of such method was confirmed by its good recovery ratio and high repeatability, and further verified by the classic enzyme-linked immunosorbent assay using naturally mycotoxins contaminated edible samples. The established method has a great application potential for screening mycotoxins rapidly with high sensitivity, low-cost and high throughput in the fields of food and traditional Chinese herb.

Bioinspired Perovskite Nanocrystals-Integrated Photonic Crystal Microsphere Arrays for Information Security.

Information security occupies an important position in the era of big data. Attempts to improve the security performance tend to impart them with more additional encryption strategies. Herein, inspired by the wettability feature of Stenocara beetle elytra and signal model of traffic light, a novel array of perovskite nanocrystals (PNs)‐integrated PhC microsphere for information security is presented. The photoluminescent PNs are encapsulated in angle‐independent PhC microspheres to impart them with binary optical signals as coding information. Through the multimask superposition approach, PNs‐integrated PhC microspheres with different codes are placed into fluorosilane‐treated PDMS substrate to form different arrays. These arrays could converge moisture on PhC microspheres in wet environment, which avoids the ions loss of the PNs and effectively prevented mutual contamination. In addition, the fluorescence of the PNs inside PhC microspheres could reversibly quench or recover in response to the environmental moisture. Based on these features, it is demonstrated that the PNs‐integrated PhC microsphere arrays could realize various information encryption modes, which indicate their excellent values in information security fields.

Rapid fabrication of SiO2-PHEMA photonic crystal hydrogel composite microspheres

Traditional photonic crystal microspheres have internal pores and can only be fabricated by self-assembly of colloidal nanoparticles. Therefore, their internal vulnerability to contamination and poor structural stability limit their further application. Therefore, we proposed a new method of photonic crystal composite microsphere fabrication by combining polymerisation with the self-assembly process. The droplets composed of colloidal nanoparticles, monomer, and initiator in continuous phase are obtained by a Shirasu porous glass (SPG) membrane emulsification undergo polymerised and self-assembled to obtain organic-inorganic photonic crystal composite microspheres. Since the self-assembled colloidal nanoparticles are immobilized in the polymer cross-linked network, the composite microspheres exhibit high structural stability. Based on this, we fabricated SiO2-PHEMA photonic crystal composite microspheres by polymerisation and self-assembly process. Compared with the pure SiO2 photonic crystal microspheres fabricated by the same method, the composite microspheres exhibit high structural stability, color saturation, and good hydrophobicity due to the self-curling of the material driven by hydrogen bonding during polymerisation. In addition to the potential applications as dyes, biosensors, and in light, these composite microspheres overcome the difficulty of bulk generation of traditional photonic crystal microspheres and have the potential for industrialized mass production.

A highly sensitive and reproducible multiplex mycotoxin SERS array based on AuNPs-loaded inverse opal silica photonic crystal microsphere

A highly sensitive and reproducible multiplex mycotoxin SERS array has been established based on gold nanoparticles (AuNPs)-loaded inverse opal silica photonic crystal microsphere (SIPCM). Three types of Raman nanotags were synthesized by covalently grafting different antibodies and non-covalently loading different organic dyes onto the AuNPs for coding corresponding mycotoxins. To enhance Raman signal, AuNPs were loaded on the surface of SIPCM to create hot-spots once the Raman nanotags came closely. The maximal electric field enhancing effect in SIPCM with AuNP dimer could reach to 8 times. The assay principle was based on the competition immunoassay between the mycotoxins in sample and the artificial antigens immobilized on the surface of SIPCM. The three Raman nanotags could be integrated into an array to qualitatively and quantitatively detect multiplex mycotoxins in a sample. Such SERS-based assay displayed wide linear detection ranges of 0.001–10 ng/mL for ochratoxin A (OTA), 0.001–10 ng/mL for fumonisin B1 (FB1), and 0.1–1000 ng/mL for deoxynivalenol (DON), and low limits of detection (LOD) of 2.46 pg/mL for OTA, 0.20 pg/mL for FB1, and 68.98 pg/mL for DON. The recovery rates of the new method were measured to be 77.68–104.69% for OTA, 76.39–117.73% for FB1, and 70.95–113.16% for DON, in agreement with that of the classical ELISA method. The SERS-based method shows obvious advantages over fluorescence label or enzyme catalytic chemiluminescence methods, having a great application potential in rapidly screening multiplex mycotoxins in real samples.

Modular Assembly of Mechanoresponsive Color‐Changing Materials from Hydrogel‐Based Photonic Crystal Microspheres

Mechanoresponsive, soft, photonic materials with tunable structural coloration represent a class of materials that have potential benefits for a wide range of applications. While many lab‐scale fabrication approaches afford control over the nano‐ and microscale morphology of these materials, upscaling their manufacture remains a challenge. Herein, a scalable fabrication concept is proposed that centers on the modular assembly of color‐changing materials from microscale building blocks. The building blocks consist of hydrogel‐based spherical photonic crystals. They are formed through a water‐in‐oil emulsification of nanoscale colloidal particles suspended in the aqueous phase. Once formed, the photonic crystal microspheres are then assembled into macroscale photonic materials, such as stretchable fibers or sheets. The resulting materials respond to a mechanical deformation with a reversible, dynamic change in color. Fabricated via a scalable, modular‐assembly approach, these mechanoresponsive photonic fibers and sheets, in turn, form a valuable building block for sensing systems or visual communication in healthcare, architecture, and consumer product design.

A Novel Multiplex Mycotoxin Surface-Enhanced Raman Spectroscopy Immunoassay Using Functional Gold Nanotags on a Silica Photonic Crystal Microsphere Biochip.

A novel multiplex mycotoxin surface-enhanced Raman spectroscopy (SERS) immunoassay was established for the first time on different artificial antigen-modified silica photonic crystal microspheres (SPCMs), which can be integrated into a biochip array to achieve multiplex detection using corresponding antibody-functionalized gold nanoparticles (AuNPs) as the SERS nanotag. The unique optical structure of SPCMs is helpful to find the detection spots easily, accommodate a large amount of probe molecules, and enhance the Raman signal intensity. Such enhancement was confirmed by the simulation result, showing the electric field enhancing effect in SPCMs with AuNPs being 7 times. A competitive SERS immunoassay was established using antigen-modified SPCMs and mycotoxins to compete for binding antibody-functionalized SERS nanotags, displaying broad linear detection ranges of 0.001-0.1 ng/mL for aflatoxin B1 (AFB1), 0.01-10 ng/mL for ochratoxin A (OTA), and 0.001-0.1 ng/mL for zearalenone (ZEN) and low detection limits of 0.82 pg/mL for AFB1, 1.43 pg/mL for OTA, and 1.00 pg/mL for ZEN. In the spiked cereal samples, recovery rates of the method were measured in the range of 70.35-118.04% for the three mycotoxins, which was in agreement with that of the traditional enzyme-linked immunosorbent assay method. The SERS immunoassay for mycotoxin detection also showed high specificity and good repeatability and reproducibility. The new microsphere-based SERS immunoassay biochip only requires a one-step reaction and overcomes the disadvantages of fluorescence and chemiluminescence background signals. The work paves the way for further developing SERS-based microsphere suspension arrays for new targets.

A capillary device made by aptamer-functionalized silica photonic crystal microspheres for the point-of-care detection of Ochratoxin A

Abstract Ochratoxin A (OTA) is one of the mycotoxins widely found in various cereals, development of a simple, low-cost, and point-of-care detection technique is urgently needed to protect human from OTA threat by food chains. Here, a point-of-care analytical device targeting OTA was developed based on a capillary column packed with silica photonic crystal microspheres (SPCMs). The SPCMs were modified with fluorophore-labeled aptamers for the specific recognition of OTA. A monolithic plunger in the capillary column was made and could improve the detection sensitivity and accuracy. The designed capillary device was able to automatically extract target molecules based on capillary force, and could realize the point-of-care detection through the fluorescence detection on column directly. Moreover, the capillary device could achieve repeated tests at one time in a single column. Finally, the point-of-care device was successfully applied for the OTA detection in cereals, giving a broad linear detection range of 1–100 ng/mL and a high-quality recovery rate of 86–108 %, and just requiring a small sample volume of 2 μL per SPCM. The point-of-care analytical device could also be expanded for the multiple target molecules screening detection by using SPCMs that were modified with different mycotoxins aptamers.

Responsive Photonic Crystal Microcapsules of Block Copolymers with Enhanced Monochromaticity.

Self-assembly of block copolymers (BCPs) has been developed as a promising approach for constructing photonic crystal (PC) microspheres for dynamic optical modulation. However, high curvature in the center of microspheres usually distorts the periodic core structure, leading to an inconsistency of photonic bandgap and poor monochromaticity of structural color. Herein, we report a simple yet robust strategy for fabricating responsive PC microcapsules of polystyrene-b-poly(2-vinylpyridine) through self-emulsification strategy. Interestingly, the microcapsules exhibit bright structural color with significantly enhanced monochromaticity, compared to their solid counterpart, since the microcapsules have no irregular cores. The structural colors of the PC microcapsules not only exhibit a variability through binary mixing of BCPs but also show a responsiveness to pH value. As a colored microcarrier, the PC microcapsules show a potential for visualizing the pH-dependent release behavior of encapsulated hydrophilic cargos on account of pH-responsive structural color.

Microfluidic Assembly Synthesis of Magnetic TiO2@SiO2 Hybrid Photonic Crystal Microspheres for Photocatalytic Degradation of Deoxynivalenol

Mycotoxin contamination is a serious threat to food safety and human health. The development of efficient degradation strategies targeting mycotoxins is valuable. In this paper, magnetic TiO2@SiO2 hybrid photonic crystal microspheres (MHPCMs) were designed and prepared by the water-in-oil droplet method through a simple two-phase home-made microfluidic device for the degradation of deoxynivalenol (DON), the most serious mycotoxin contaminating cereals and feeding samples among natural mycotoxins. The morphologies of the synthesized microspheres were investigated by both metallurgical microscope and scanning electronic microscope (SEM), confirming that MHPCMs have a spherical shape and regular photonic crystal nanostructures. In the self-assembly system, TiO2 and Fe3O4 nanoparticles were responsible to form photocatalytic sites and magnet response, respectively. The effect of the TiO2 and Fe3O4 contents in the microspheres on their morphology and photocatalytic degradation activity was studied in detail. Finally, the optimized MHPCM could degrade DON in water under the light irradiation and be recycled easily by magnet.

Three-dimensional ordered macroporous magnetic photonic crystal microspheres for enrichment and detection of mycotoxins (I):Droplet-basedmicrofluidicself-assemblysynthesis.

Ordered porous materials are attracting enormous attention due to their uniform pore structures, particularly the magnetic photonic crystal microspheres (PCMs) which not only possess unique photonic crystal structure but also can achieve separation easily based on magnet. Here, a two-phase microfluidic self-assembly synthetic system was established simply and employed for the preparation of three dimensional PCMs (3DPCMs) by using the emulsion droplet approach. One phase (dispersed phase) was an aqueous emulsion containing Fe3O4, silica (SiO2) and polystyrene (PS) nanoparticles; another phase (continuous phase) was pure silicone oil. The droplets were formed by introducing the dispersed phase into the continuous phase through a tee valve. By heating the droplets, the water would evaporate and the nanoparticles would finally assemble into solid microspheres, which could be changed into macroporous 3DPCMs after removal of the PS nanoparticles by calcination. The contents and particle sizes of Fe3O4, SiO2 and PS nanoparticles in the dispersed phase were investigated in detail and optimized to prepare macroporous magnetic 3DPCMs with high quality. The morphologies, surface crystal structure, magnetic property, particle size distribution, specific surface area and pore size of the macroporous magnetic 3DPCMs were characterized. The expected 3DPCM displayed regular and uniform photonic crystal structure, narrow particle size distribution and strong magnetic property. The macroporous magnetic 3DPCMs grafted with vomitoxin (DON)-antibodies could be applied for selective enrichment of DON in real samples.

Three-dimensional ordered macroporous magnetic photonic crystal microspheres for enrichment and detection of mycotoxins (II): The application in liquid chromatography with fluorescence detector for mycotoxins

Enrichment, separation and purification are very important to accurately analyze mycotoxins in complicated samples. In the work, we developed a new enrichment, purification and high-performance liquid chromatography combined with fluorescence detector (HPLC-FLD) for aflatoxins B1 (AFB1), ochratoxin A (OTA) and Zearalenone (ZEN) assay using the macroporous magnetic 3D photonic crystal microspheres (3DPCMs). The conditions of enrichment and purification for mycotoxins have been optimized, which are as follows: pore size of 3DPCMs at 280 nm, 1:1 methanol:acetonitrile (v/v) as eluent, antibody concentrations at 60 µg/mL,60 µg/mL and 120 µg/mL for OTA, AFB1 and ZEN, respectively. The recovery rates in the rice, wheat and corn samples range from 70.01% to 100.12% and the relative standard deviation (RSD) range from 0.45% to 7.09%. The recovery rates used 3DPCMs are almost tenfold higher than that used non-macroporous PCMs in the same conditions. The developed method is simple, rapid (time including enrichment, purification and detection <2 h) and only requires small volume reagents (≤200 µL).