Ultrasensitive DNA Detection Using Photonic Crystals

Ultrasensitive Method Enables Liquid Biopsy for the Precise Detection of Circulating MicroRNAs

Due to invasive and serial examinations of bioactive molecules, liquid biopsy (LB) has emerged as a rapid and reliable solution for early disease detection and monitoring. Developing portable devices with high specificity and sensitivity for LB is highly valuable. To realize a generalized approach to increase the sensitivity of LB, we developed an ultrasensitive diagnostic biochip based on the amplification of miRNA by recombinase polymerase amplification and the significant enhancement of fluorescence signals by photonic crystal (PC) materials. The PCs-RPA biochip has a detection limit as low as 0.24 aM, a wide linear range of 8 orders of magnitude, and excellent specificity. Such advantages realize the accurate detection of circulating miRNAs with very low content in clinical serum samples for the precise diagnosis of nonsmall cell lung cancer.

Low-triggering-potential electrochemiluminescence based on mental-organic frameworks encapsulation of ruthenium for synthetic cathinone detection by coupling photonic crystal light-scattering signal amplification of covalent-organic frameworks

Developing effective electrochemiluminescence (ECL) platforms is always an essential concern in highly sensitive bioanalysis. In this work, a low-triggering-potential ECL sensor was designed for detecting synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) based on a dual-signal amplification strategy. Initially, a probe was created by integrating Ruthenium into the hollow porphyrin-based MOF (PCN-222) structure to decrease the excitation potential and enhance ECL performance without external co-reaction accelerators. Additionally, for the first time, photonic crystals (PCs) assembled from covalent organic frameworks (COFs) were employed to amplify the ECL signal, thereby increasing the photon flux and the loading capacity of the ECL emitter to enhance sensitivity of the sensor. In the presence of the target MDPV, the aptamer labeled with Ferrocene (Fc) experienced conformational changes, causing Fc to approach the luminophore and resulting in ECL quenching. This effect was attributed to aptamer's conformational changes induced by the target, directly correlating with the target concentration. The constructed sensor showed good linearity with the target MDPV concentration, covering a dynamic range from 1.0 × 10-14 to 1.0 × 10-6 g/L and achieved an ultra-low detection limit of 4.79 × 10-15 g/L. This work employed dual amplification strategies to enhance ECL signals effectively, providing a novel method for developing highly responsive and bioactive sensors.

A dual-mode biosensor based on silica inverse opal photonic crystals modulated electrochemiluminescence and dye displacement colorimetry for the sensitive detection of synthetic cathinone in water environment

To address the challenges posed by signal capacity limitations and the reliance of sensing methods on single analytical information, this study developed an electrochemiluminescence (ECL) and colorimetric dual-mode sensing platform for the precise detection of 4-chloroethcathinone (4-CEC) in water environments. Firstly, the accurate alignment of the reflection wavelength of appropriately sized silica inverse opal photonic crystals (SIOPCs) with the ECL emission wavelength of luminescent metal-organic frameworks (PCN-224) has been achieved via diameter modulation. This innovative design, which cleverly utilized the band-edge effect, improved the luminous intensity of the ECL sensor, leading to a significant boost in analytical performance. Secondly, the establishment of a colorimetric detection method for confirming the presence of 4-CEC in samples through visual observation of color changes was achieved by employing an aptamer-based dye displacement reaction, utilizing differential binding affinities between the aptamer and both the sulforhodamine B (SRB) and 4-CEC. Under the optimal experimental conditions, the dual-mode sensor demonstrated ECL detection of limits (LOD) of 2.6 × 10-13 g/L and colorimetric LOD of 6.5 ng/L for 4-CEC. These findings highlighted the tremendous potential of developing streamlined and efficient dual-signal readout platforms using ECL aptamer sensors for the precise determination of other Synthetic cathinones (SCs) in water environments.

Label-Free, High-Throughput, Sensitive, and Logical Analysis Using Biomimetic Array Based on Stable Luminescent Copper Nanoclusters and Entropy-Driven Nanomachine

The development of an array for high-throughput and logical analysis of biomarkers is significant for disease diagnosis. DNA-templated copper nanoclusters (CuNCs) have a strong potential to serve as a label-free photoluminescence source in array platforms, but their luminescent stability and sensitivity need to be improved. Herein, we report a facile, sensitive, and robust biomimetic array assay by integrating with stable luminescent CuNCs and entropy-driven nanomachine (EDN). In this strategy, the luminescent stability of CuNCs was improved by adding fructose in CuNCs synthesis to offer a reliable label-free signal. Meanwhile, the DNA template for CuNCs synthesis was introduced into EDN with excellent signal amplification ability, in which the reaction triggered by target miRNA would cause the blunt/protruding conformation change of 3'-terminus accompanied by the production or loss of luminescence. In addition, a biomimetic array fabricated by photonic crystals (PCs) physically enhanced the emitted luminescent signal of CuNCs and achieved high-throughput signal readout by a microplate reader. The proposed assay can isothermally detect as low as 4.5 pM of miR-21. Moreover, the logical EDN was constructed to achieve logical analysis of multiple miRNAs by "AND" or "OR" logic gate operation. Therefore, the proposed assay has the advantages of label-free property, high sensitivity, flexible design, and high-throughput analysis, which provides ideas for developing a new generation of facile and smart platforms in the fields of biological analysis and clinical application.

Bio-inspired optical structures for enhancing luminescence

Luminescence is an essential signal for many plants, insects, and marine organisms to attract the opposite sex, avoid predators, and so on. Most luminescent living organisms have ingenious optical structures which can help them get high luminescent performances. These remarkable and efficient structures have been formed by natural selection from long-time evolution. Researchers keenly observed the enhanced luminescence phenomena and studied how these phenomena happen in order to learn the characteristics of bio-photonics. In this review, we summarize the optical structures for enhancing luminescence and their applications. The structures are classified according to their different functions. We focus on how researchers use these biological inspirations to enhance different luminescence processes, such as chemiluminescence (CL), photoluminescence (PL), and electroluminescence (EL). It lays a foundation for further research on the applications of luminescence enhancement. Furthermore, we give examples of luminescence enhancement by bio-inspired structures in information encryption, biochemical detection, and light sources. These examples show that it is possible to use bio-inspired optical structures to solve complex problems in optical applications. Our work will provide guidance for research on biomimetic optics, micro- and nano-optical structures, and enhanced luminescence.

A Sensitive Electrochemiluminescence Urea Sensor for Dynamic Monitoring of Urea Transport in Living Cells

A multiple signal-amplified electrochemiluminescence (ECL) urea sensor was designed based on a self-enhanced probe and SiO₂ photonic crystals for dynamic tracking of urea transmembrane transport. The self-enhanced probe (AuNR@Ru-LA) prepared by loading polyethyleneimine (PEI), lactobionic acid (LA), and Ru(dcbpy)₃²⁺ on gold nanorods (AuNRs) generated an initial ECL signal, and then the intensity was multiple-amplified by the enhanced light-scattering effect of SiO₂ photonic crystals and the co-reaction with urea. The as-prepared sensor exhibited excellent performance for the detection of urea in the range of 1.0 × 10^-10 to 1.0 × 10^-4 M with a detection limit of 8.8 × 10^-11 M at (3σ)/S. The AuNR@Ru-LA probes were labeled on HepG2 cells to construct a cytosensor with a detection range of 1.0 × 10³ to 2.0 × 10⁶ cells mL^-1. In addition, the dynamic changes of the extracellular urea concentration were tracked by monitoring the ECL signal of the cytosensor to study urea transmembrane transport. The developed strategy realized the amplification of multiple ECL signals and the tracking of urea transmembrane transport, which provided a novel dynamic detection method for small biomolecules.

Begonia-Inspired Slow Photon Effect of a Photonic Crystal for Augmenting Algae Photosynthesis

Plant photosynthesis is considered to be an environmentally friendly and effective measure for reducing carbon dioxide levels to meet the global objective of carbon neutrality. However, the light energy utilization of photosynthetic pigments is insufficient. Begonia pavonine (B. pavonina) with blue leaves exhibits a photosynthetic quantum yield 10% higher than those of other plants by virtue of their photonic crystal (PC) thylakoids. Inspired by this property, we prepared non-angle-dependent PC hydrogels and assembled them with algae Chlorella pyrenoidosa (C. pyre). The band edge of PC hydrogels matched the absorption peaks of C. pyre, and the resulting slow photon effect increased the interaction time between incident light and photosynthetic pigments, which in turn induced the expression of light-harvesting proteins and the synthesis of pigments, thereby improving the light energy utilization. Further, we introduced an artificial antenna into the assembly, which assisted the slow photon effect in increasing the oxygen evolution and carbon sequestration rate by more than 200%. This method avoids the photobleaching problems faced by methods of synthesizing artificial antenna pigments and the biosafety problems faced by genetically engineered methods of editing pigments or proteins.

Band-Edge Effect-Induced Electrochemiluminescence Signal Amplification Based on Inverse Opal Photonic Crystals for Ultrasensitive Detection of Carcinoembryonic Antigen

Photonic crystals (PCs) have emerged as a promising electrochemiluminescence (ECL) matrix in the domain of immunoassay. Making maximum use of light manipulation properties of PCs is highly desired for improving the sensitivity. In this work, we proposed a band-edge effect-induced ECL enhancement strategy based on silica inverse opal PCs (SIOPCs). By fine-tuning the lattice constant and carefully calibrating the stopband position, we found that the band edge of the stopband exerted significant influences on the ECL intensity and spectral distribution. The high density of states at the blue edge of the photonic band gap increased the radiative transition probability of ECL emitters and enhanced the photon extraction during propagation, giving rise to ∼20-fold ECL signal amplification accompanied by a redistributed ECL spectrum for the Ru(bpy)₃²⁺-TPrA system. In combination with the intrinsic structural superiority, like large specific surface area and interconnected macropores, the developed SIOPC electrode was successfully applied in constructing a sandwich-type immunosensor. The fabricated immunosensor displayed a very low detection limit of 0.032 pg/mL and a wide linear range of 0.1 pg/mL-150 ng/mL for a carcinoembryonic antigen assay, showing its potential application in disease diagnosis.

Emerging biosensing and transducing techniques for potential applications in point-of-care diagnostics

With the deepening of our understanding in life science, molecular biology, nanotechnology, optics, electrochemistry and other areas, an increasing number of biosensor design strategies have emerged in recent years, capable of providing potential practical applications for point-of-care (POC) diagnosis in various human diseases. Compared to conventional biosensors, the latest POC biosensor research aims at improving sensor precision, cost-effectiveness and time-consumption, as well as the development of versatile detection strategies to achieve multiplexed analyte detection in a single device and enable rapid diagnosis and high-throughput screening. In this review, various intriguing strategies in the recognition and transduction of POC (from 2018 to 2021) are described in light of recent advances in CRISPR technology, electrochemical biosensing, and optical- or spectra-based biosensing. From the perspective of promoting emerging bioanalytical tools into practical POC detecting and diagnostic applications, we have summarized key advances made in this field in recent years and presented our own perspectives on future POC development and challenges.

Unclonable Photonic Crystal Hydrogels with Controllable Encoding Capacity for Anticounterfeiting

Inspired by the formation of random sparkling microcrystallines in naturally precious opals, we develop a new strategy to produce a class of unclonable photonic crystal hydrogels (UPCHs) induced by the electrostatic interaction effect, which further achieve unclonable encoding/decoding and random high-encrypted patterns along with an ultrahigh and controllable encoding capacity up to ca. 2 × 10¹⁶⁶⁰⁵⁵. Owing to the randomness of colloidal crystals in the self-assembly process, UPCHs with randomly distributed sparkling spots are endowed with unpredictable/unrepeatable characteristics. This, coupled with the water response of UPCHs with angle dependence and robustness, can upgrade the encryption level and address some limitations of easy fading, limited durability, and high cost in practical uses of existing unclonable materials. Interestingly, UPCHs can be readily patterned to exhibit reliable and rapid authentication by utilizing artificial intelligence (AI) deep learning, which can find broad applications in developing unbreakable and portable information storage/steganography systems not limited to anticounterfeiting.

Dual photonic bandgap hollow sphere colloidal photonic crystals for real-time fluorescence enhancement in living cells

To overcome the problems of refractive index matching and increased disorder when working with traditional heterostructure colloidal photonic crystals (CPCs) with dual or multiple photonic bandgaps (PBGs) for fluorescence enhancement in water, we propose the use of a chemical heterostructure in hollow sphere CPCs (HSCPCs). A partial chemical modification of the HSCPC creates a large contrast in wettability to induce the heterostructure, while the hollow spheres increase the refractive index difference when used in aqueous environment. With the platform, fluorescence enhancement reaches around 160 times in solution, and 72 times (signal-to-background ratio ~7 times) in cells during proof-of-concept live cardiomyocyte contractility experiments. Such photonic platform can be further exploited for chemical sensing, bioassays, and environmental monitoring. Moreover, the introduction of chemical heterostructures provides new design principles for functionalized photonic devices.

Bottom-Up Assembled Photonic Crystals for Structure-Enabled Label-Free Sensing

Photonic crystals (PhCs) display photonic stop bands (PSBs) and at the edges of these PSBs transport light with reduced velocity, enabling the PhCs to confine and manipulate incident light with enhanced light-matter interaction. Intense research has been devoted to leveraging the optical properties of PhCs for the development of optical sensors for bioassays, diagnosis, and environmental monitoring. These applications have furthermore benefited from the inherently large surface area of PhCs, giving rise to high analyte adsorption and the wide range of options for structural variations of the PhCs leading to enhanced light-matter interaction. Here, we focus on bottom-up assembled PhCs and review the significant advances that have been made in their use as label-free sensors. We describe their potential for point-of-care devices and in the review include their structural design, constituent materials, fabrication strategy, and sensing working principles. We thereby classify them according to five sensing principles: sensing of refractive index variations, sensing by lattice spacing variations, enhanced fluorescence spectroscopy, surface-enhanced Raman spectroscopy, and configuration transitions.

From colloidal particles to photonic crystals: advances in self-assembly and their emerging applications

Over the last three decades, photonic crystals (PhCs) have attracted intense interests thanks to their broad potential applications in optics and photonics. Generally, these structures can be fabricated via either "top-down" lithographic or "bottom-up" self-assembly approaches. The self-assembly approaches have attracted particular attention due to their low cost, simple fabrication processes, relative convenience of scaling up, and the ease of creating complex structures with nanometer precision. The self-assembled colloidal crystals (CCs), which are good candidates for PhCs, have offered unprecedented opportunities for photonics, optics, optoelectronics, sensing, energy harvesting, environmental remediation, pigments, and many other applications. The creation of high-quality CCs and their mass fabrication over large areas are the critical limiting factors for real-world applications. This paper reviews the state-of-the-art techniques in the self-assembly of colloidal particles for the fabrication of large-area high-quality CCs and CCs with unique symmetries. The first part of this review summarizes the types of defects commonly encountered in the fabrication process and their effects on the optical properties of the resultant CCs. Next, the mechanisms of the formation of cracks/defects are discussed, and a range of versatile fabrication methods to create large-area crack/defect-free two-dimensional and three-dimensional CCs are described. Meanwhile, we also shed light on both the advantages and limitations of these advanced approaches developed to fabricate high-quality CCs. The self-assembly routes and achievements in the fabrication of CCs with the ability to open a complete photonic bandgap, such as cubic diamond and pyrochlore structure CCs, are discussed as well. Then emerging applications of large-area high-quality CCs and unique photonic structures enabled by the advanced self-assembly methods are illustrated. At the end of this review, we outlook the future approaches in the fabrication of perfect CCs and highlight their novel real-world applications.

Photonic Crystal of Polystyrene Nanomembrane: Signal Amplification and Low Triggered Potential Electrochemiluminescence for Tetracycline Detection

In this work, a low triggered potential electrochemiluminescence strategy based on gold-filled photonic crystals (GPCs) electrodes composed of photonic crystals self-assembled with polystyrene spheres and gold nanoparticles embedded in the gaps of the photonic crystals was proposed. The GPCs electrodes served as the detection platform to bind antigen, and Ru(bpy)₃²⁺-COOH as a luminophore was labeled on the antibody (Ab). Then, Ru(bpy)₃²⁺-COOH/Ab was connected to the immobilized antigen on the surface of the photonic crystals by the immunoreaction to avoid direct contact with the gold nanoparticles surface. ECL emission can only be initiated by electrochemical oxidation of tripropylamine (TPrA) since Ru(bpy)₃²⁺-COOH cannot be oxidized directly on the electrode surface. The TPrA^·+ and TPrA^· radicals generated by the oxidation of TPrA can spread to the vicinity of Ru(bpy)₃²⁺-COOH over a short distance and react with the Ru(bpy)₃²⁺-COOH, eventually producing ECL emission. The potential of ECL emission caused by TPrA oxidation was about 300 mV lower than that caused by Ru(bpy)₃²⁺-COOH oxidation because the oxidation potential of TPrA (0.95 V vs SCE) was lower than Ru(bpy)₃²⁺-COOH (1.25 V vs SCE). Furthermore, the photonic crystals nanomembrane has the capability to enhance electrochemiluminescence. Thereafter, tetracycline antibiotic as a model compound was successfully detected via competitive immunoassay on GPCs electrodes with a detection limit of 0.075 pg/mL (S/N = 3), which has broad application prospects in the field of analysis and detection.

Biomimetic design of photonic materials for biomedical applications

Photonic crystal (PC) materials with bio-inspired structure colors have drawn increasing attention as their potentials have been rapidly progressed in the field of biomedicine. After elaborate integration with smart materials or preparations through advanced techniques, PC materials have shown significant advantages in biosensing, bio-probing, bio-screening, tissue engineering, and so forth. In this review, we first introduced the fundamentals of PC materials as well as their fabrication strategies with different dimensional outputs. Based on these diversified PC materials, their biomedical potentials as biosensing elements, cell carriers, drug delivery systems, screening methods, cell scaffolds for tissue engineering, cell imaging probes, as well as the monitoring means for biological processes were then highlighted. In addition to these, we finally listed and discussed some emerging applications of PCs integrated with functional materials and newly developed material engineering technologies. In short, this review will provide a panoramic view of PCs-based biomedicines, and moreover, the progressive discussions from fundamentals to advanced applications in this review may also encourage researchers to innovate PC materials or devices for broader biomedical applications.

Highly Efficient Detection of Homologues and Isomers by the Dynamic Swelling Reflection Spectrum

Precise and efficient detection of solvents with similar refractive index is highly desired but remains a big challenge for the conventional opal because the shift of its reflection wavelength only depends on the refractive index of the solvent to be detected. Here, homologues (alcohols, acids, alkalis, esters, and aromatic hydrocarbons), isomers, and other solvents with similar refractive index and structures were precisely distinguished through the dynamic swelling reflection spectrum (DSRS) pattern based on the different swelling behavior of swellable photonic paper in solvents. The one reflection signal of photonic paper will split into two reflection peaks, which then tend to merge together during the swelling process. The variation of the reflection signals and merging time are highly sensitive to the polarity and refractive index of the solvent, and the differences can be significantly amplified in DSRS, resulting in the distinction of the solvent from its unique geometric pattern. Moreover, the variation tendency of the reflectance provides an additional parameter in recognition of the solvent, which can be explained by calculation and comparison of the practical volume ratio of the solvent swelled into the photonic paper and the corresponding critical volume ratio of the solvent determined by its refractive index.

Bioinspired MXene-integrated colloidal crystal arrays for multichannel bioinformation coding

Information coding strategies are becoming increasingly crucial due to the storage demand brought by the information explosion. In particular, bioinformation coding has attracted great attention for its advantages of excellent storage capacity and long lifetime. Herein, we present an innovative bioinspired MXene-integrated photonic crystal (PhC) array for multichannel bioinformation coding. PhC arrays with similar structure to Stenocara beetle's back are utilized as the substrate, exhibiting properties of high throughput and stability. MXene nanosheets are further integrated on the PhC array's substrate with the assistance of the adhesion capacity of mussel-inspired dopamine (DA). Benefitting from their fluorescence resonance energy transfer effect, MXene nanosheets can quench the fluorescence signals of quantum dot (QD) modified DNA probes unless the corresponding targets exist. Additionally, these black MXene nanosheets can enhance the contrast of structural color. In this case, the encrypted information can be easily read out by simply observing the fluorescence signal of DNA probes. It is demonstrated that this strategy based on bioinspired MXene-integrated PhC arrays can realize high-throughput information encoding and encryption, which opens a chapter of bioinformation coding.

Structural Color Materials for Optical Anticounterfeiting

The counterfeiting of goods is growing worldwide, affecting practically any marketable item ranging from consumer goods to human health. Anticounterfeiting is essential for authentication, currency, and security. Anticounterfeiting tags based on structural color materials have enjoyed worldwide and long-term commercial success due to their inexpensive production and exceptional ease of percept. However, conventional anticounterfeiting tags of holographic gratings can be readily copied or imitated. Much progress has been made recently to overcome this limitation by employing sufficient complexity and stimuli-responsive ability into the structural color materials. Moreover, traditional processing methods of structural color tags are mainly based on photolithography and nanoimprinting, while new processing methods such as the inkless printing and additive manufacturing have been developed, enabling massive scale up fabrication of novel structural color security engineering. This review presents recent breakthroughs in structural color materials, and their applications in optical encryption and anticounterfeiting are discussed in detail. Special attention is given to the unique structures for optical anticounterfeiting techniques and their optical aspects for encryption. Finally, emerging research directions and current challenges in optical encryption technologies using structural color materials is presented.

A Self-Assembled Plasmonic Substrate for Enhanced Fluorescence Resonance Energy Transfer

Fluorescence resonance energy transfer (FRET) has found widespread uses in biosensing, molecular imaging, and light harvesting. Plasmonic metal nanostructures offer the possibility of engineering photonic environment of specific fluorophores to enhance the FRET efficiency. However, the potential of plasmonic nanostructures to enable tailored FRET enhancement on planar substrates remains largely unrealized, which are of considerable interest for high-performance on-surface bioassays and photovoltaics. The main challenge lies in the necessitated concurrent control over the spectral properties of plasmonic substrates to match that of fluorophores and the fluorophore-substrate spacing. Here, a self-assembled plasmonic substrate based on polydopamine (PDA)-coated plasmonic nanocrystals is developed to effectively address this challenge. The PDA coating not only drives interfacial self-assembly of the nanocrystals to form closely packed arrays with customized optical properties, but also can serve as a tailored nanoscale spacer between the fluorophores and plasmonic nanocrystals, which collectively lead to optimized fluorescence enhancement. The biocompatible plasmonic substrate that allows convenient bioconjugation imparted by PDA has afforded improved FRET efficiency in DNA microarray assay and FRET imaging of live cells. It is envisioned that the self-assembled plasmonic substrates can be readily integrated into fluorescence-based platforms for diverse biomedical and photoconversion applications.

Metal-Free Photoinduced Atom Transfer Radical Polymerization for Highly Sensitive Detection of Lung Cancer DNA

Convenient and sensitive detection of biomolecules is of great significance to disease diagnosis. In this work, a metal-free photoinduced atom transfer radical polymerization (photoATRP) by a reductive quenching pathway as a novel strategy is applied to achieve lung cancer DNA detection. Thiolated PNA is exploited to specifically recognize target DNA, and the initiator of photoATRP is linked to the electrode surface via phosphate-Zr⁴⁺ -carboxylate. Under the excitation of blue light, the reductive quenching pathway is activated with eosin Y (EY) as photoredox catalyst and N,N,N',N'',N'-pentamethyldiethylenetriamine (PMDETA) as electron donor, and numerous polymeric chains are formed. Under optimal conditions, the linear range of this strategy is from 0.1 pm to 10 nm (R² =0.989) with a limit of detection (LOD) of 1.4 fm (14 zmol in 10 μL). The variety of possible light sources for photoATRP and simple operation endow this biosensor with great potential for practical applications.

Emission Enhancement of Fluorescent Molecules by Antireflective Arrays

Traditional fluorescence enhancement based on a match of the maximum excitation or emission of fluorescence molecule with the spectra of the nanostructure can hardly enhance blue and red fluorescent molecules. Here, an enhanced method which is a new strategy based on the antireflective array has been developed to enhance the emission of blue and red fluorescent molecules. The fluorescence emission is enhanced by increasing the absorption at excitation wavelengths of the fluorescent molecules and reducing the fluorescent energy dissipation with an antireflective array. By introducing the antireflective arrays, the emission enhancement of blue and red fluorescent molecules is, respectively, up to 14 and 18 fold. It is a universal and effective strategy for enhancing fluorescence emission, which could be applied to enhance the intensity of organic LED and imaging.

P-Glycoprotein Antibody Decorated Porous Hydrogel Particles for Capture and Release of Drug-Resistant Tumor Cells

Multidrug resistance is one of the leading causes of chemotherapy failure in cancer patients. Early detection and capture of drug-resistant tumor cells can facilitate the monitoring of the therapy process and improve the prognosis of patients. In this study, novel P-glycoprotein (P-gp) antibody modified porous hydrogel particles are proposed for drug-resistant tumor cells capture. The hydrogel particles employ a highly biocompatible hydrogel, methacrylate gelatin (GelMA), as the carrier and replicate from the silica colloidal crystal beads. By the modification of P-gp antibody probes on their surfaces, the hydrogel particles are endowed with the ability to capture drug-resistant tumor cells, which overexpress specific components of P-gp on their membranes. Additionally, the acquired ordered porous nanostructure of the particles can provide not only more surface area for antibody immobilization but also a nanopatterned platform for highly efficient target cell capture. The above advantages make the porous hydrogel particles ideal for efficient capture and detection of the drug-resistant tumor cells, which can be expected to facilitate the point-of-care pharmacotherapy and promisingly improve the patient outcomes.

Hollow Colloid Assembled Photonic Crystal Clusters as Suspension Barcodes for Multiplex Bioassays

Barcode particles have a demonstrated value for multiplexed high-throughput bioassays. Here, a novel photonic crystal (PhC) barcode is presented that consists of hollow colloidal nanospheres assembled through microfluidic droplet templates. Due to their gas-filled core, the resultant barcode particles not only show increased refractive index contrast, but also remain in suspension by adjusting the overall density of the PhC to match that of a detection solution. In addition, magnetic nanoparticles can be integrated to give the barcodes a magnetically controllable motion ability. The encoding ability of the barcodes is demonstrated in microRNA detection with high specificity and sensitivity, and the excellent features of the barcodes make them potentially very useful for biomedical applications.

Ramachandran A, Mohamed AP, Pillai S. Photonic band gap effect and dye-encapsulated cucurbituril-triggered enhanced fluorescence using monolithic colloidal photonic crystals

Enhanced fluorescence was achieved by tuning the photonic band gaps in colloidal photonic crystals and host–guest chemistry.

Bio-inspired photonic crystals for naked eye quantification of nucleic acids

The quantitative detection of nucleic acids by the naked eye was achieved based on structural color.

Detection of Homologue and Isomer Vapors through Dynamic Reflection Spectra of Hollow Mesoporous Silica Sphere Photonic Crystals

Vapors of homologues and isomers with very similar refractive indices can be easily distinguished by using dynamic reflection spectra (DRS) of hollow mesoporous silica sphere (HMSS) photonic crystals (PCs). Different diffusion behaviors render the HMSS PCs with a distinct response to different chemicals vapors, leading to diversity in the evolution of the reflection spectra and their DRS patterns. Therefore, by studying the geometric characteristics and color changes of color-filled contour maps, as well as the reflection peak shift speeds at different stages, even isomers such as n-butanol and iso-butanol, with a refractive index difference of only 0.001, can be recognized. The reflection peak shift speed depends on both the refractive index and the diffusion speed of chemicals. The proposed strategy provides a convenient, accurate, and low-cost method to detect vapors of homologues and isomers.

Manipulating Luminescence of Light Emitters by Photonic Crystals

The modulation of luminescence is essential because unwanted spontaneous-emission modes have a negative effect on the performance of luminescence-based photonic devices. Photonic crystals are promising materials for the control of light emission because of the variation in the local density of optical modes within them. They have been widely investigated for the manipulation of the emission intensity and lifetime of light emitters. Several groups have achieved greatly enhanced emission by depositing emitters on the surface of photonic crystals. Herein, the different modulating effects of photonic crystal dimensions, light-emitter positions, photonic crystal structure type, and the refractive index of photonic crystal building blocks are highlighted, with the aim of evaluating the fundamental principles that determine light propagation. The applications of using photonic crystals to manipulate spontaneous emission in light-emitting diodes and sensors are also reviewed. In addition, potential future challenges and improvements in this field are presented.

Biomimetic enzyme cascade reaction system in microfluidic electrospray microcapsules

Mimicking subcellular compartments containing enzymes in organisms is considered a promising approach to substitute for missing or lost cellular functions. Inspired by the multicompartment structures of cellular architectures, we present a novel multienzyme system based on hollow hydrogel microcapsules with flexible enzymatic inverse opal particles. Benefiting from the precise operation capability of the microfluidic electrospray and the remarkable structural color marks in the inverse opal particles, we developed a multienzyme system with controllable number, type, and spatial arrangement of the encapsulated enzymes. The hydrogel shells also could improve enzyme stability against proteolysis in the system. The multienzyme system containing alcohol oxidase and catalase could act as a cascade biocatalyst and reduce alcohol levels in media, providing an alternative antidote and prophylactic for alcohol intoxication. These features indicated that our strategy provides an ideal enzyme cascade reaction system for complex biocatalysis and biomimetic functions of some organelles or organs.

Multi-functional organosilane-polymerized carbon dot inverse opals

This paper demonstrates multi-functional optical properties of organosilane-polymerized carbon dot inverse opals, such as tricolor-fluorescence, fluorescence enhancement, multi-color micro-patterns for anti-fake applications and a thermally-induced blueshift of bandgaps. It is of significance for the design and fabrication of novel optical devices.

A two-color fluorescence enhanced dot-blot assay for revealing co-operative expression of chemokine receptors in cells

A highly sensitive two-color dot-blot assay has been developed to simultaneously detect co-operative expression of chemokine receptors in cells.

Manganese porphyrin decorated on DNA networks as quencher and mimicking enzyme for construction of ultrasensitive photoelectrochemistry aptasensor

In this work, the manganese porphyrin (MnPP) decorated on DNA networks could serve as quencher and mimicking enzyme to efficiently reduce the photocurrent of photoactive material 3,4,9,10-perylene tetracarboxylic acid (PTCA), which was elaborately used to construct a novel label-free aptasensor for ultrasensitive detection of thrombin (TB) in a signal-off manner. The Au-doped PTCA (PTCA-PEI-Au) with outstanding membrane-forming and photoelectric property was modified on electrode to acquire a strong initial photoelectrochemistry (PEC) signal. Afterward, target binding aptamer Ι (TBAΙ) was modified on electrode to specially recognize target TB, which could further combine with TBAII and single-stranded DNA P1-modified platinum nanoparticles (TBAII-PtNPs-P1) for immobilizing DNA networks with abundant MnPP. Ingeniously, the MnPP could not only directly quench the photocurrent of PTCA, but also acted as hydrogen peroxide (HRP) mimicking enzyme to remarkably stimulate the deposition of benzo-4-chlorhexidine (4-CD) on electrode for further decreasing the photocurrent of PTCA, thereby obtaining a definitely low photocurrent for detection of TB. As a result, the proposed PEC aptasensor illustrated excellent sensitivity with a low detection limit down to 3 fM, exploiting a new avenue about intergrating two functions in one substance for ultrasensitive biological monitoring.

Patterned Colloidal Photonic Crystals

Colloidal photonic crystals (PCs) have been well developed because they are easy to prepare, cost-effective, and versatile with regards to modification and functionalization. Patterned colloidal PCs contribute a novel approach to constructing high-performance PC devices with unique structures and specific functions. In this review, an overview of the strategies for fabricating patterned colloidal PCs, including patterned substrate-induced assembly, inkjet printing, and selective immobilization and modification, is presented. The advantages of patterned PC devices are also discussed in detail, for example, improved detection sensitivity and response speed of the sensors, control over the flow direction and wicking rate of microfluidic channels, recognition of cross-reactive molecules through an array-patterned microchip, fabrication of display devices with tunable patterns, well-arranged RGB units, and wide viewing-angles, and the ability to construct anti-counterfeiting devices with different security strategies. Finally, the perspective of future developments and challenges is presented.

Responsive photonic barcodes for sensitive multiplex bioassay

Barcodes have a demonstrated value for multiplex high-throughput bioassays. The tendency of this technology is to pursue high sensitivity target screening. Herein, we presented a new type of inverse opal-structured poly(N-isopropylacrylamide) (pNIPAM) hydrogel photonic crystal (PhC) barcodes with the function of fluorescent signal self-amplification for the detection. During the bio-reaction process at body temperature, the pNIPAM hydrogel barcodes kept swelling, and their inverse opal structure with interconnected pores provided unblocked channels for the targets to diffuse into the voids of the barcodes and react. During the detection process, the barcodes were kept at a volume phase transition temperature (VPTT) to shrink their volume; this resulted in an obvious increase in the density of fluorescent molecules and signal amplification. It was demonstrated that the responsive barcodes could achieve the limits of detection (LOD) of α-fetoprotein (AFP) and carcinoembryonic antigen (CEA) at 0.623 ng mL^-1 and 0.492 ng mL^-1, respectively. In addition, the proposed barcodes showed good multiplex detection capacity with acceptable cross-reactivity, accuracy, and reproducibility, and the results were consistent with those of common clinical laboratory methods for the detection of clinical samples. These features of the inverse opal-structured responsive hydrogel barcodes indicate that they are ideal technology for high-sensitive multiplex bioassays.

Transpiration-Inspired Fabrication of Opal Capillary with Multiple Heterostructures for Multiplex Aptamer-Based Fluorescent Assays

In this work we report a method for the fabrication of opal capillary with multiple heterostructures for aptamer-based assays. The method is inspired by plant transpiration. During the fabrication, monodisperse SiO₂ nanoparticles (NPs) self-assemble in a glass capillary, with the solvent gradually evaporating from the top end of the capillary. By a simple change of the colloid solution that wicks through the capillary, multiple heterostructures can be easily prepared inside the capillary. On the surface of the SiO₂ NPs, polydopamine is coated for immobilization of aminomethyl-modified aptamers. The aptamers are used for fluorescent detection of adenosine triphosphate (ATP) and thrombin. Owing to fluorescence enhancement effect of the photonic heterstructures, the fluorescent signal for detection is amplified up to 40-fold. The limit of detection is 32 μM for ATP and 8.1 nM for thrombin. Therefore, we believe this method is promising for the fabrication of analytical capillary devices for point-of-care testing.

Simultaneous Visualization and Quantitation of Multiple Steroid Hormones Based on Signal-Amplified Biosensing with Duplex Molecular Recognition

The simultaneous quantitation of multiple steroid hormones in real time is of great importance in medical diagnosis. In this study, a portable hormone biosensor based on duplex molecular recognition coupled with a signal-amplified substrate was successfully developed for the simultaneous visualization and quantitation of multiple steroid hormones. Aptamer-functionalized upconversion nanoparticles (UCNPs) with different emission peaks are immobilized on the photonic crystal (PC) substrate as the nanoprobes, leading to the specific and simultaneous assay of multiple steroid hormones. Coupled with the luminescence-enhanced effect of the PC substrate, nanomolar quantification limits of multiple hormones are achieved. This well-designed biosensor is also promising in the quantification of multiple hormones in serum samples. The amplified luminescence signals can be visualized with the naked eye and captured by an unmodified phone camera. This hormone quantitation biosensor exhibits the advantages of multi-detection, visualization, high sensitivity, and selectivity for potential applications in clinical disease diagnosis.

Real-Time Fluorescence Detection in Aqueous Systems by Combined and Enhanced Photonic and Surface Effects in Patterned Hollow Sphere Colloidal Photonic Crystals

Hollow sphere colloidal photonic crystals (HSCPCs) exhibit the ability to maintain a high refractive index contrast after infiltration of water, leading to extremely high-quality photonic band gap effects, even in an aqueous (physiological) environment. Superhydrophilic pinning centers in a superhydrophobic environment can be used to strongly confine and concentrate water-soluble analytes. We report a strategy to realize real-time ultrasensitive fluorescence detection in patterned HSCPCs based on strongly enhanced fluorescence due to the photonic band-edge effect combined with wettability differentiation in the superhydrophobic/superhydrophilic pattern. The orthogonal nature of the two strategies allows for a multiplicative effect, resulting in an increase of two orders of magnitude in fluorescence.

Photonic crystals: emerging biosensors and their promise for point-of-care applications

Biosensors are extensively employed for diagnosing a broad array of diseases and disorders in clinical settings worldwide. The implementation of biosensors at the point-of-care (POC), such as at primary clinics or the bedside, faces impediments because they may require highly trained personnel, have long assay times, large sizes, and high instrumental cost. Thus, there exists a need to develop inexpensive, reliable, user-friendly, and compact biosensing systems at the POC. Biosensors incorporated with photonic crystal (PC) structures hold promise to address many of the aforementioned challenges facing the development of new POC diagnostics. Currently, PC-based biosensors have been employed for detecting a variety of biotargets, such as cells, pathogens, proteins, antibodies, and nucleic acids, with high efficiency and selectivity. In this review, we provide a broad overview of PCs by explaining their structures, fabrication techniques, and sensing principles. Furthermore, we discuss recent applications of PC-based biosensors incorporated with emerging technologies, including telemedicine, flexible and wearable sensing, smart materials and metamaterials. Finally, we discuss current challenges associated with existing biosensors, and provide an outlook for PC-based biosensors and their promise at the POC.

Biomimetic superwettable materials with structural colours

This review aims at offering a comprehension elaboration of the mechanism, recent biomimetic research and applications of biomimetic superwettable materials with structural colours. Futhermore, this review will provide significant insight into the design, fabrication and application of biomimetic superwettable materials with structural colours.

Naked eye detection of multiple tumor-related mRNAs from patients with photonic-crystal micropattern supported dual-modal upconversion bioprobes

We have designed a biochip-based mRNA detection device by combining a hydrophilic–hydrophobic micropattern with upconversion luminescence (UCL) probes.

Development of a portable device for the detection of multiple mRNAs is a significant need in the early diagnosis of cancer. We have designed a biochip-based mRNA detection device by combining a hydrophilic–hydrophobic micropattern with upconversion luminescence (UCL) probes. The device achieves highly sensitive detection, using the naked eye, of multiple mRNAs among patient samples. The high sensitivity is attributed to enrichment of the target concentration and a fluorescence enhancement effect. In addition, since the photonic crystal (PC) dot biochip is functionalized with dual-wavelength excitation UCL probes, two kinds of mRNAs in the heterogeneous biological samples are detected simultaneously, and the corresponding luminescence signals are captured using an unmodified camera phone. The biochip-based mRNA detection device reported here demonstrates that multiple mRNAs extracted from patient samples can be simultaneously and sensitively detected in a visual way without sophisticated instrumentation. Therefore, this device is promising for real-time detection of multiple biomarkers in patient samples, and it is anticipated that it will provide a powerful tool for convenient early diagnosis of cancer.

Short-range ordered photonic structures of lamellae-forming diblock copolymers for excitation-regulated fluorescence enhancement

Photonic crystals can be represented by periodic nanostructures with alternating refractive indices, which create artificial stop bands with the appearance of colors. In this regard, nanodomains of block copolymers and the corresponding structural colors have been intensively studied in the past. However, the practical application of photonic crystals of block copolymers has been limited to a large degree because of the presence of large defects and grain boundaries in the nanodomains of block copolymers. The present study focuses on the alternative opportunity of short-range ordered nanodomains of block copolymers for fluorescence enhancement, which also has a direct relevance to the development of fluorescence sensors or detectors. The enhancement mechanism was found to be interconnected with the excitation process rather than the alternation of the decay kinetics. In particular, we demonstrate that randomly oriented, but regular grains of lamellae of polystyrene-block-polyisoprene, PS-b-PI, diblock copolymers and their blend with PS homopolymers can behave as Bragg mirrors to induce multiple reflections of the excitation source inside the photonic structures. This process in turn significantly increases the effective absorption of the given fluorophores inside the polymeric photonic structures to amplify the fluorescence signal.