Photonic crystal protein hydrogel sensor materials enabled by conformationally induced volume phase transition

Self-powered optical fiber biosensor integrated with enzymes for non-invasive glucose sensing

To alleviate the discomfort associated with frequent blood glucose detection in diabetic patients, a novel non-invasive tear glucose biosensor has been developed. This involved the design and preparation of a photoelectrochemical probe based on an optical fiber and biological enzymes. One end of the optical fiber connects to a light source, acting as an energy source and imparting, self-powered capability to the biosensor. The opposite end is loaded with nanomaterials and glucose oxidase, designed for insertion into the sample to realize photoelectrochemical sensing. This innovative configuration not only improves the integration of the biosensor but is also suitable for analyzing minuscule voluminal samples. The results show that the proposed biosensor exhibits a linear range from 10 nM to 100 μM, possesses a low detection limit of 4.1 nM and a short response time of 0.7 s. Benefiting from the high selectivity of the enzyme, the proposed biosensor demonstrates excellent resistance to the interference of common tear components. In summary, this work provides a more effective method for non-invasive glucose detection and affords valuable ideas for the design and fabrication of non-invasive and self-powered biosensors.

Research Progress of Bioinspired Structural Color in Camouflage

Bioinspired structural color represents a burgeoning field that draws upon principles, strategies, and concepts derived from biological systems to inspire the design of novel technologies or products featuring reversible color changing mechanisms, with significant potential applications for camouflage, sensors, anticounterfeiting, etc. This mini-review focuses specifically on the research progress of bioinspired structural color in the realm of camouflage. Firstly, it discusses fundamental mechanisms of coloration in biological systems, encompassing pigmentation, structural coloration, fluorescence, and bioluminescence. Subsequently, it delineates three modulation strategies-namely, photonic crystals, film interference, and plasmonic modulation-that contribute to the development of bioinspired structural color materials or devices. Moreover, the review critically assesses the integration of bioinspired structural color materials with environmental contexts, with a particular emphasis on their application in camouflage. Finally, the paper outlines persisting challenges and suggests future development trends in the camouflage field via bioinspired structural color.

Recent Insights into Glucose-Responsive Concanavalin A-Based Smart Hydrogels for Controlled Insulin Delivery

Many efforts are continuously undertaken to develop glucose-sensitive biomaterials able of controlling glucose levels in the body and self-regulating insulin delivery. Hydrogels that swell or shrink as a function of the environmental free glucose content are suitable systems for monitoring blood glucose, delivering insulin doses adapted to the glucose concentration. In this context, the development of sensors based on reversible binding to glucose molecules represents a continuous challenge. Concanavalin A (Con A) is a bioactive protein isolated from sword bean plants (Canavalia ensiformis) and contains four sugar-binding sites. The high affinity for reversibly and specifically binding glucose and mannose makes Con A as a suitable natural receptor for the development of smart glucose-responsive materials. During the last few years, Con A was used to develop smart materials, such as hydrogels, microgels, nanoparticles and films, for producing glucose biosensors or drug delivery devices. This review is focused on Con A-based materials suitable in the diagnosis and therapeutics of diabetes. A brief outlook on glucose-derived theranostics of cancer is also presented.

Biomimetic 3D Color-Changing Hydrogel Actuators Constructed Based on Soft Permeable Photonic Crystals

The integration of photonic crystals and self-shaping actuators is a promising method for constructing powerful biomimetic color-changing actuators. The major barrier is that common photonic crystals generally block the transfer/orientation of monomers/fillers and hence hinder the formation of heterogeneous structures for programmed 3D deformations as well as degrade the deformation capacity and mechanical properties of actuators. Herein, we present the construction of complex and strong 3D color-changing hydrogel actuators by asymmetric photolithography based on soft, permeable photonic crystals. The soft permeable photonic crystals are assembled by hydrogel microspheres with an ultralow volume fraction. During the asymmetric photolithography, the monomers in precursor solutions can thus transfer freely to generate heterogeneous microstructures, spatially patterned internal stresses, and interpenetrating networks for programming the deformation trajectories and initial 3D configurations and enhancing mechanical properties of actuators. Various 3D color-changing hydrogel actuators (e.g., flower and scroll painting) are constructed for applications such as information encryption and display.

Advantages and Prospective Implications of Smart Materials in Tissue Engineering: Piezoelectric, Shape Memory, and Hydrogels

Conventional biomaterial is frequently used in the biomedical sector for various therapies, imaging, treatment, and theranostic functions. However, their properties are fixed to meet certain applications. Smart materials respond in a controllable and reversible way, modifying some of their properties because of external stimuli. However, protein-based smart materials allow modular protein domains with different functionalities and responsive behaviours to be easily combined. Wherein, these "smart" behaviours can be tuned by amino acid identity and sequence. This review aims to give an insight into the design of smart materials, mainly protein-based piezoelectric materials, shape-memory materials, and hydrogels, as well as highlight the current progress and challenges of protein-based smart materials in tissue engineering. These materials have demonstrated outstanding regeneration of neural, skin, cartilage, bone, and cardiac tissues with great stimuli-responsive properties, biocompatibility, biodegradability, and biofunctionality.

Aptamer-linked photonic crystal hydrogel sensor for rapid point-of-care detection of human immuno-deficiency virus-1 (HIV-1)

The detection of the human immunodeficiency virus-1 (HIV) at an early stage is vital and could be realized through its cell surface glycoprotein-120 (gp120) without virus preprocessing. Here, we present an ssDNA-aptamer-linked photonic crystal (APC) hydrogel sensor for HIV detection which is comprised of photonic crystals (PCs) made of polystyrene nanoparticles embedded in the polyacrylamide hydrogel. ssDNA aptamers specific for gp120 are crosslinked in the hydrogel which can selectively bind to gp120 by hydrogen bonding increasing the PCs particle spacing and swelling of the hydrogel. The binding response can be visually monitored as a color change due to the diffraction of light from PCs and can eventually be measured (1-1000 ng mL^-1 of gp120) and 10⁰ to 10⁸ VP mL^-1 of HIV by the Debye's ring diameter or a UV/Vis spectrometer. APC-hydrogel can be regenerated by Tris-HCl and EDTA washing buffer system. The sensor demonstrates LOD of 7.1 ± 1.55 ng mL^-1 for gp120 and 4 VP mL^-1 for the whole HIV, a rapid response of 5 min, reusability up to 70 % (in fifth use), and recovery of 95.4 ± 0.1 % to 99.0 ± 0.2 % in plasma samples. The sensor is cost-effect and stable compared to antibody-based sensors and can be utilized to develop point-of-care testing (POCT) devices for HIV diagnosis.

Supramolecular Photonic Hydrogel for High-Sensitivity Alkaline Phosphatase Detection via Synergistic Driving Force

Structurally-colored photonic hydrogels which are fabricated by introducing hydrogels into thin films or photonic crystal structures are promising candidates for biosensing. Generally, the design of photonic hydrogel biosensors is based on the sensor-analyte interactions induced charge variation within the hydrogel matrix, or chemically grafting binding sites onto the polymer chains, to achieve significant volume change and color variation of the photonic hydrogel. However, relatively low anti-interference capability or complicated synthesis hinder the facile and low-cost fabrication of high-performance photonic hydrogel biosensors. Here, a facilely prepared supramolecular photonic hydrogel biosensor is developed for high-sensitivity detection of alkaline phosphatase (ALP), which is an extensively considered clinical biomarker for a variety of diseases. Responding to ALP results in the broken supramolecular crosslinking and thus increased lattice distancing of the photonic hydrogel driven by synergistic repulsive force between nanoparticles embedded in photonic crystal structure and osmotic swelling pressure. The biosensor shows sensitivity of 7.3 nm spectral shift per mU mL^-1 ALP, with detection limit of 0.52 mU mL^-1 . High-accuracy colorimetric detection can be realized via a smartphone, promoting point-of-care sensing and timely diagnosis of related pathological conditions.

Smart Nanostructured Materials for SARS-CoV-2 and Variants Prevention, Biosensing and Vaccination

The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has raised great concerns about human health globally. At the current stage, prevention and vaccination are still the most efficient ways to slow down the pandemic and to treat SARS-CoV-2 in various aspects. In this review, we summarize current progress and research activities in developing smart nanostructured materials for COVID-19 prevention, sensing, and vaccination. A few established concepts to prevent the spreading of SARS-CoV-2 and the variants of concerns (VOCs) are firstly reviewed, which emphasizes the importance of smart nanostructures in cutting the virus spreading chains. In the second part, we focus our discussion on the development of stimuli-responsive nanostructures for high-performance biosensing and detection of SARS-CoV-2 and VOCs. The use of nanostructures in developing effective and reliable vaccines for SARS-CoV-2 and VOCs will be introduced in the following section. In the conclusion, we summarize the current research focus on smart nanostructured materials for SARS-CoV-2 treatment. Some existing challenges are also provided, which need continuous efforts in creating smart nanostructured materials for coronavirus biosensing, treatment, and vaccination.

Consensus Receptor-Binding Domain-Targeted Aptamer Selection and Designing of a Photonic Crystal-Decorated Aptasensor for SARS-CoV-2

The frequent emergence of variants of concern (VOC) of SARS-CoV-2 necessitates a sensitive and all-inclusive detection platform that remains viable despite the virus mutations. In this context, we targeted the receptor-binding domain (RBD) of glycoprotein (S-protein) of all VOC and constructed a consensus RBD (cRBD) based on the conserved amino acids. Then, we selected a high-affinity ssDNA novel aptamer specific for the cRBD by an in silico approach. The selected aptamer is utilized to fabricate a photonic crystal (PC)-decorated aptasensor (APC-sensor), which consists of polystyrene nanoparticles polymerized within a polyacrylamide hydrogel. cRBD-responsive ssDNA aptamers are crosslinked in the hydrogel network, which selectively bind to the cRBD and SARS-CoV-2 in saliva samples. The binding response can be visually monitored by swelling of the hydrogel and color generation by diffraction of light from PCs and can be quantified by the diffraction ring diameter or a spectrometer. The sensor delivers a LOD of 12.7 ± 0.55 ng mL-1 for the cRBD and 3 ± 18.8 cells mL-1 for SARS-CoV-2 in saliva samples, with a rapid response of 5 min. The sensor can be stored and regenerated without loss of activity. It can be utilized as a point-of-care testing (POCT) for SARS-CoV-2 diagnosis.

Emerging Theranostic Nanomaterials in Diabetes and Its Complications

Diabetes mellitus (DM) refers to a group of metabolic disorders that are characterized by hyperglycemia. Oral subcutaneously administered antidiabetic drugs such as insulin, glipalamide, and metformin can temporarily balance blood sugar levels, however, long-term administration of these therapies is associated with undesirable side effects on the kidney and liver. In addition, due to overproduction of reactive oxygen species and hyperglycemia-induced macrovascular system damage, diabetics have an increased risk of complications. Fortunately, recent advances in nanomaterials have provided new opportunities for diabetes therapy and diagnosis. This review provides a panoramic overview of the current nanomaterials for the detection of diabetic biomarkers and diabetes treatment. Apart from diabetic sensing mechanisms and antidiabetic activities, the applications of these bioengineered nanoparticles for preventing several diabetic complications are elucidated. This review provides an overall perspective in this field, including current challenges and future trends, which may be helpful in informing the development of novel nanomaterials with new functions and properties for diabetes diagnosis and therapy.

Bio-inspired structural colors and their applications

Structural colors, generated by the interaction of interference, diffraction, and scattering between incident light and periodic nanostructured surfaces with features of the same scale with incident visible light wavelengths, have recently attracted intense interest in a wide range of research fields, due to their advantages such as various brilliant colors, long-term stability and environmental friendliness, low energy consumption, and mysterious biological functions. Tremendous effort has been made to design structural colors and considerable progress has been achieved in the past few decades. However, there are still significant challenges and obstacles, such as durability, portability, compatibility, recyclability, mass production of structural-color materials, etc., that need to be solved by rational structural design and novel manufacturing strategies. In this review, we summarize the recent progress of bio-inspired structural colors and their applications. First, we introduce several typical natural structural colors displayed by living organisms from fundamental optical phenomena, including interference, diffraction grating, scattering, photonic crystals effects, the combination of different phenomena, etc. Subsequently, we review recent progress in bio-inspired artificial structural colors generated from advanced micro/nanoscale manufacturing strategies to relevant biomimetic approaches, including self-assembly, template methods, phase conversion, magnetron sputtering, atomic layer deposition, etc. Besides, we also present the current and potential applications of structural colors in various fields, such as displays, anti-counterfeiting, wearable electronics, stealth, printing, etc. Finally, we discuss the challenges and future development directions of structural colors, aiming to push forward the research and applications of structural-color materials.

Segregated Protein-Cucurbit[7]uril Crystalline Architectures via Modulatory Peptide Tectons

One approach to protein assembly involves water-soluble supramolecular receptors that act like glues. Bionanoarchitectures directed by these scaffolds are often system-specific, with few studies investigating their customization. Herein, the modulation of cucurbituril-mediated protein assemblies through the inclusion of peptide tectons is described. Three peptides of varying length and structural order were N-terminally appended to RSL, a β-propeller building block. Each fusion protein was incorporated into crystalline architectures mediated by cucurbit[7]uril (Q7). A trimeric coiled-coil served as a spacer within a Q7-directed sheet assembly of RSL, giving rise to a layered material of varying porosity. Within the spacer layers, the coiled-coils were dynamic. This result prompted consideration of intrinsically disordered peptides (IDPs) as modulatory tectons. Similar to the coiled-coil, a mussel adhesion peptide (Mefp) also acted as a spacer between protein-Q7 sheets. In contrast, the fusion of a nucleoporin peptide (Nup) to RSL did not recapitulate the sheet assembly. Instead, a Q7-directed cage was adopted, within which disordered Nup peptides were partially "captured" by Q7 receptors. IDP capture occurred by macrocycle recognition of an intrapeptide Phe-Gly motif in which the benzyl group was encapsulated by Q7. The modularity of these protein-cucurbituril architectures adds a new dimension to macrocycle-mediated protein assembly. Segregated protein crystals, with alternating layers of high and low porosity, could provide a basis for new types of materials.

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.

Optical Devices Constructed From Responsive Microgels for Polyphenols Detection

Polyphenols are used as antioxidants in various foods and beverages, which are considered to be a health benefit. The measurement of polyphenols contents is of great interest in food chemistry and health science. This work reported a microgels based photonic device (etalon) to detect polyphenols. Dopamine was used as a model compound of polyphenols. Herein, we proposed a “block” concept for dopamine detection. The dopamine was oxidized and formed dopamine films catalyzed by tyrosinase on the surface of etalon. As the etalon was immersed in ZnCl₂, the dopamine films blocked the ZnCl₂ diffusion into etalon that caused optical property changes. The film thickness is associated with the concentration of dopamine which can be readout via optical signals.

Optical biosensors: an exhaustive and comprehensive review

Optical biosensors have exhibited worthwhile performance in detecting biological systems and promoting significant advances in clinical diagnostics, drug discovery, food process control, and environmental monitoring. Without complexity in their pretreatment and probable influence on the nature of target molecules, these biosensors have additional advantages such as high sensitivity, robustness, reliability, and potential to be integrated on a single chip. In this review, the state of the art optical biosensor technologies, including those based on surface plasmon resonance (SPR), optical waveguides, optical resonators, photonic crystals, and optical fibers, are presented. The principles for each type of biosensor are concisely introduced and particular emphasis has been placed on recent achievements. The strengths and weaknesses of each type of biosensor have been outlined as well. Concluding remarks regarding the perspectives of future developments are discussed.

Glycated albumin based photonic crystal sensors for detection of lipopolysaccharides and discrimination of Gram-negative bacteria

We present two types of two-dimensional (2D) photonic crystals (PC) hydrogel sensors based on glycated albumin (G-alb) as a proof-of-concept for utilizing recognition between G-alb and bacterial cell surface lipopolysaccharides (LPS) to detect and discriminate Gram-negative bacteria. The G-alb functionalized PC-G-alb hydrogel provides recognition of different LPS via hydrogen bonding and can discriminate different Gram-negative bacteria based on their LPS types. The hydrogel delivered LOD of 0.87 ng mL^-1 for E.coli LPS, 153 CFU mL^-1 for E.coli, 1.22 ng mL^-1 for P.aeruginosa LPS and 225 CFU mL^-1 for P.aeruginosa. On the other hand, LPS bioimprinted hydrogel (PC-G-alb-LPS_imp) provides selective recognition of E.coli LPS with LOD 0.76 ng mL^-1 and for E.coli 58 CFU mL^-1, via generation of flexible specific cavities for E.coli and its LPS. The two hydrogels showed remarkable recoveries for both LPS and Gram-negative bacteria in the relevant samples of milk, orange juice, river water, and serum with a short response time of 6-12 min. In the binding process, the hydrogels shrink, and 2D PC particle spacing decreases with diffraction shift from green to blue. The diffraction shifts can be visually observed, measured through Debye's diffraction ring diameter by a laser pointer or determined from a spectrometer.

Hydrogel-Based Colloidal Photonic Crystal Devices for Glucose Sensing

Diabetes, a common epidemic disease, is increasingly hazardous to human health. Monitoring body glucose concentrations for the prevention and therapy of diabetes has become very important. Hydrogel-based responsive photonic crystal (PC) materials are noninvasive options for glucose detection. This article reviews glucose-sensing materials/devices composed of hydrogels and colloidal photonic crystals (CPCs), including the construction of 2D/3D CPCs and 2D/3D hydrogel-based CPCs (HCPCs). The development and mechanisms of glucose-responsive hydrogels and the achieved technologies of HCPC glucose sensors were also concluded. This review concludes by showing a perspective for the future design of CPC glucose biosensors with functional hydrogels.

Stimuli-Responsive Pure Protein Organogel Sensors and Biocatalytic Materials

Utilizing protein chemistry in organic solvents has important biotechnology applications. Typically, organic solvents negatively impact protein structure and function. Immobilizing proteins via cross-links to a support matrix or to other proteins is a common strategy to preserve the native protein function. Recently, we developed methods to fabricate macroscopic responsive pure protein hydrogels by lightly cross-linking the proteins with glutaraldehyde for chemical sensing and enzymatic catalysis applications. The water in the resulting protein hydrogel can be exchanged for organic solvents. The resulting organogel contains pure organic solvents as their mobile phases. The organogel proteins retain much of their native protein function, i.e., protein-ligand binding and enzymatic activity. A stepwise ethylene glycol (EG) solvent exchange was performed to transform these hydrogels into organogels with a very low vapor pressure mobile phase. These responsive organogels are not limited by solvent/mobile phase evaporation. The solvent exchange to pure EG is accompanied by a volume phase transition (VPT) that decreases the organogel volume compared to that of the hydrogel. Our organogel sensor systems utilize shifts in the particle spacing of an attached two-dimensional photonic crystal (2DPC) to report on the volume changes induced by protein-ligand binding. Our 2DPC bovine serum albumin (BSA) organogels exhibit VPT that swell the organogels in response to the BSA binding of charged ligands like ibuprofen and fatty acids. To our knowledge, this is the first report of a pure protein organogel VPT induced by protein-ligand binding. Catalytic protein organogels were also fabricated that utilize the enzyme organophosphorus hydrolase (OPH) to hydrolyze toxic organophosphate (OP) nerve agents. Our OPH organogels retain significant enzymatic activity. The OPH organogel rate of OP hydrolysis is ∼160 times higher than that of un-cross-linked OPH monomers in a 1:1 ethylene glycol/water mixture.

Chameleon-Inspired Strain-Accommodating Smart Skin

Stimuli-responsive color-changing hydrogels, commonly colored using embedded photonic crystals (PCs), have potential applications ranging from chemical sensing to camouflage and anti-counterfeiting. A major limitation in these PC hydrogels is that they require significant deformation (>20%) in order to change the PC lattice constant and generate an observable chromatic shift (∼100 nm). By analyzing the mechanism of how chameleon skin changes color, we developed a strain-accommodating smart skin (SASS), which maintains near-constant size during chromatic shifting. SASS is composed of two types of hydrogels: a stimuli-responsive, PC-containing hydrogel that is patterned within a second hydrogel with robust mechanical properties, which permits strain accommodation. In contrast to conventional "accordion"-type PC responsive hydrogels, SASS maintains near-constant volume during chromatic shifting. Importantly, SASS materials are stretchable (strain ∼150%), amenable to patterning, spectrally tunable, and responsive to both heat and natural sunlight. We demonstrate examples of using SASS for biomimicry. Our strategy, to embed responsive materials within a mechanically matched scaffolding polymer, provides a general framework to guide the future design of artificial smart skins.

Phagocyte-Inspired Smart Microcapsules

Phagocytes protect the organism by ingesting harmful foreign particles and cells. We use mesoscale computer simulations to design a phagocyte-inspired active microcapsule that is capable of selectively capturing nanoparticles dispersed in solvent. Our fully synthetic microdevice is actuated by a temperature-sensitive microgel enclosed inside a perforated spherical shell. The shell pores are decorated with a copolymer brush that regulates the transport of solutes into the capsule interior. When exposed to an external stimulus, the microgel swells, expanding through the shell pores to make contact with the nanoparticle-rich solution surrounding the capsule. Upon removal of the external stimulus, the gel retracts back into the shell, bringing along with it captured nanoparticles. We probe how periodic application of the stimulus combined with nanoparticle-microgel adhesion enable selectivity and enhance capturing efficiency of our nature-inspired microdevice.

Ultrathin Photonic Polymer Gel Films Templated by Non-Close-Packed Monolayer Colloidal Crystals to Enhance Colorimetric Sensing

Responsive polymer-based sensors have attracted considerable attention due to their ability to detect the presence of analytes and convert the detected signal into a physical and/or chemical change. High responsiveness, fast response speed, good linearity, strong stability, and small hysteresis are ideal, but to gain these properties at the same time remains challenging. This paper presents a facile and efficient method to improve the photonic sensing properties of polymeric gels by using non-close-packed monolayer colloidal crystals (ncp MCCs) as the template. Poly-(2-vinyl pyridine) (P2VP), a weak electrolyte, was selected to form the pH-responsive gel material, which was deposited onto ncp MCCs obtained by controlled O₂ plasma etching of close-packed (cp) MCCs. The resultant ultrathin photonic polymer gel film (UPPGF) exhibited significant improvement in responsiveness and linearity towards pH sensing compared to those prepared using cp MCCs template, achieving fast visualized monitoring of pH changes with excellent cyclic stability and small hysteresis loop. The responsiveness and linearity were found to depend on the volume and filling fraction of the polymer gel. Based on a simple geometric model, we established that the volume increased first and then decreased with the decrease of template size, but the filling fraction increased all the time, which was verified by microscopy observations. Therefore, the responsiveness and linearity of UPPGF to pH can be improved by simply adjusting the etching time of oxygen plasma. The well-designed UPPGF is reliable for visualized monitoring of analytes and their concentrations, and can easily be combined in sensor arrays for more accurate detection.

Polysulfide microspheres with chemical modification for generation of interfaces with macroscopic colour variation and biomimetic superhydrophobicity

Both superwettability and structural colours have attracted considerable attention in recent years. In addition, the combination of structural colours and superwettability could endow materials with broader application prospects. The combination provides a new strategy to design novel functional materials, and there are many studies pertaining to these materials that have been reported in recent years. Herein, a polysulfide (PSF) superhydrophobic coating was synthesized successfully. The PSF superhydrophobic coating possesses excellent superhydrophobicity, oleophobicity for diesel and macroscopic structural colour variation when wetted. The colour is changed when the coating is wetted and it returns to its original colour after drying. In addition, the surface presents better reusability and thermostability which satisfies various daily needs. The PSF superhydrophobic coating can be considered as an excellent candidate for designing wetting responsive materials, and it has enormous application potential in the fields of detection, sensing, anti-counterfeiting and security. For the first time, we present a novel and low-cost strategy to fabricate materials with both superhydrophobicity and structural colour, offering significant insights into the practical application of these functional materials.

Separation-cooperated assembly of liquid photonic crystals from polydisperse particles

Easy and cost-effective production of high-quality photonic crystals (PCs) remains challenging but attractive, not just because they are a type of gemstone but more for their scientific applications (e.g., serving as lossless waveguides, visual sensors, novel pigments and novel separation media). Herein presented is a separation-cooperated assembly (SCA) strategy able to organize cheap polydisperse particles into PCs. Its feasibility was validated through sink-induced SCA of poorly disperse (size variation up to 56%) particles into iridescent liquid PCs in 3 days or more. Strikingly, with a sharp photonic band gap down to 10 nm (ca. 1/7 of the reported 66 nm), the liquid PCs are able to cyclically recover their iridescent color in ca 20 s after agitation, and keep their structural order after dryness, making them practicable to write and paint directly. Also significant is that SCA yielded uniform particles with size variation down to 0.7%. It is thus an easy way to isolate homogeneous particles from disperse ones.

Chiral Photonic Crystalline Microcapsules with Strict Monodispersity, Ultrahigh Thermal Stability, and Reversible Response

Tunable photonic crystals (TPCs) reflecting selected wavelengths of visible light and responding to external stimuli are widely applied to fabricate smart optical devices. Chiral nematic liquid crystals (CNLCs) possessing response to temperature, electric field, and magnetic field are considered as one-dimensional TPCs. The encapsulation of CNLCs provides responsive photonic devices with stand-alone macroscopic structure and excellent processability. However, when CNLCs as cores are wrapped by polymeric shells to form core-shell structured microcapsules, the polydispersity of microcapsule size, the irregular spatial geometry, and the low thermal stability inevitably result in a deterioration of the optical performance and limited application at high temperatures. Herein, a combination of microfluidic emulsification and interfacial polymerization is employed to fabricate polymer wrapped photonic crystalline microcapsules (PWPCMs). The sizes and reflected colors of PWPCMs can be simultaneously controlled by adjusting the flow rates in the microfluidic chips. PWPCMs possess strictly monodispersed sizes with coefficients of variation less than 1%. The free-standing PWPCMs have high thermal stability. The deformation temperature of PWPCMs is as high as 210 °C. The colored PWPCMs also exhibit a reversible thermochromic property between the chiral nematic phase and the isotropic phase. The highly stable and tunable PWPCMs provide new opportunities for a wide range of photonic applications, including smart optical window, tunable microlasers, responsive microsensors, and various photonic devices.

Mechano-Based Transductive Sensing for Wearable Healthcare

Wearable healthcare presents exciting opportunities for continuous, real-time, and noninvasive monitoring of health status. Even though electrochemical and optical sensing have already made great advances, there is still an urgent demand for alternative signal transformation in terms of miniaturization, wearability, conformability, and stretchability. Mechano-based transductive sensing, referred to the efficient transformation of biosignals into measureable mechanical signals, is claimed to exhibit the aforementioned desirable properties, and ultrasensitivity. In this Concept, a focus on pressure, strain, deflection, and swelling transductive principles based on micro-/nanostructures for wearable healthcare is presented. Special attention is paid to biophysical sensors based on pressure/strain, and biochemical sensors based on microfluidic pressure, microcantilever, and photonic crystals. There are still many challenges to be confronted in terms of sample collection, miniaturization, and wireless data readout. With continuing efforts toward solving those problems, it is anticipated that mechano-based transduction will provide an accessible route for multimode wearable healthcare systems integrated with physical, electrophysiological, and biochemical sensors.

Non-dye cell viability monitoring by using pH-responsive inverse opal hydrogels

Recent advances in the field of drug screening focus on accurate, rapid and high-throughput screening methods. In our work, hydrogel inverse opal photonic crystal microspheres (HPCMs) were fabricated through a templating method and exhibited a robust and reversible response to temperature and pH. The response performance was tested under various temperature (25-55 °C) and pH (1.5-7.5) conditions and the reflective peak shifted noticeably within the visible wavelength range. Furthermore, HPCMs were used as drug delivery carriers and not only displayed high doxorubicin (DOX) drug loading but also presented thermo/pH-induced drug release properties. More importantly, these carriers were shown to be good reporters for monitoring cell viability due to their tunable colour variation. This capability was applied to H460 cell cultures with or without DOX. The structure colour of HPCMs varied in different cell culture microenvironments, and cell apoptosis was able to be distinguished. In this way, this fast, non-dyeing method for reporting cell viability in tumour cytotoxicity assays has potential in the field of drug screening and may give new insights into the use of structural colour to report results in drug screening systems.

Nanocomposite Microgels for the Selective Separation of Halogen Compounds from Aqueous Solution

Nanocomposite microgels that selectively adsorb and release halogen compounds were developed. These nanocomposite microgels consist of poly(2-methoxyethyl acrylate) (pMEA) and a poly(oligo ethylene glycol methacrylate) hydrogel matrix. Therefore, the methoxy groups of the former are crucial for the halogen bonding, while the presence of the latter adds colloidal stability and allows controlled uptake/release of the halogen compounds. Such nanocomposite microgels may not only be used as dispersed carriers, but also in films and columnar formations. Thus, these unprecedented polymer/polymer nanocomposite microgels resolve a variety of problems associated with, e.g., the removal of halogen compounds from wastewater, or with the delivery of halogen-containing drugs.

Applications and developments of on-chip biochemical sensors based on optofluidic photonic crystal cavities

Photonic crystal (PC) cavities, which possess the advantages of compactness, flexible design, and suitability for integration in a lab-on-a-chip system, are able to distinguish slight variations in refractive index with only a small amount of analyte. Combined with the newly proposed optofluidic technology, PC-cavity devices stimulate an emerging class of miniaturized and label-free biochemical sensors. In this review, an overview of optofluidic PC cavities based biochemical sensors is presented. First, the basic properties of the PC, as well as the sensing principle of the PC cavity, are discussed. Second, the applications of the sensors in detecting gas, liquid, and biomolecule concentrations are reviewed, with a focus on their structures, sensing principles, sensing properties, advantages, and disadvantages. Finally, the current challenges and future development directions of optofluidic PC-cavity-based biochemical sensors are discussed.

Responsive Photonic Crystal Carbohydrate Hydrogel Sensor Materials for Selective and Sensitive Lectin Protein Detection

Lectin proteins, such as the highly toxic lectin protein, ricin, and the immunochemically important lectin, jacalin, play significant roles in many biological functions. It is highly desirable to develop a simple but efficient method to selectively detect lectin proteins. Here we report the development of carbohydrate containing responsive hydrogel sensing materials for the selective detection of lectin proteins. The copolymerization of a vinyl linked carbohydrate monomer with acrylamide and acrylic acid forms a carbohydrate hydrogel that shows specific "multivalent" binding to lectin proteins. The resulting carbohydrate hydrogels are attached to 2-D photonic crystals (PCs) that brightly diffract visible light. This diffraction provides an optical readout that sensitively monitors the hydrogel volume. We utilize lactose, galactose, and mannose containing hydrogels to fabricate a series of 2-D PC sensors that show strong selective binding to the lectin proteins ricin, jacalin, and concanavalin A (Con A). This binding causes a carbohydrate hydrogel shrinkage which significantly shifts the diffraction wavelength. The resulting 2-D PC sensors can selectively detect the lectin proteins ricin, jacalin, and Con A. These unoptimized 2-D PC hydrogel sensors show a limit of detection (LoD) of 7.5 × 10^-8 M for ricin, a LoD of 2.3 × 10^-7 M for jacalin, and a LoD of 3.8 × 10^-8 M for Con A, respectively. This sensor fabrication approach may enable numerous sensors for the selective detection of numerous lectin proteins.

AIE-doped poly(ionic liquid) photonic spheres: a single sphere-based customizable sensing platform for the discrimination of multi-analytes

By simultaneously exploiting the unique properties of ionic liquids and aggregation-induced emission (AIE) luminogens, as well as photonic structures, a novel customizable sensing system for multi-analytes was developed based on a single AIE-doped poly(ionic liquid) photonic sphere. It was found that due to the extraordinary multiple intermolecular interactions involved in the ionic liquid units, one single sphere could differentially interact with broader classes of analytes, thus generating response patterns with remarkable diversity. Moreover, the optical properties of both the AIE luminogen and photonic structure integrated in the poly(ionic liquid) sphere provide multidimensional signal channels for transducing the involved recognition process in a complementary manner and the acquisition of abundant and sufficient sensing information could be easily achieved on only one sphere sensor element. More importantly, the sensing performance of our poly(ionic liquid) photonic sphere is designable and customizable through a simple ion-exchange reaction and target-oriented multi-analyte sensing can be conveniently realized using a selective receptor species, such as counterions, showing great flexibility and extendibility. The power of our single sphere-based customizable sensing system was exemplified by the successful on-demand detection and discrimination of four multi-analyte challenge systems: all 20 natural amino acids, nine important phosphate derivatives, ten metal ions and three pairs of enantiomers. To further demonstrate the potential of our spheres for real-life application, 20 amino acids in human urine and their 26 unprecedented complex mixtures were also discriminated between by the single sphere-based array.

Gold Nanoparticles in Photonic Crystals Applications: A Review

This review concerns the recently emerged class of composite colloidal photonic crystals (PCs), in which gold nanoparticles (AuNPs) are included in the photonic structure. The use of composites allows achieving a strong modification of the optical properties of photonic crystals by involving the light scattering with electronic excitations of the gold component (surface plasmon resonance, SPR) realizing a combination of absorption bands with the diffraction resonances occurring in the body of the photonic crystals. Considering different preparations of composite plasmonic-photonic crystals, based on 3D-PCs in presence of AuNPs, different resonance phenomena determine the optical response of hybrid crystals leading to a broadly tunable functionality of these crystals. Several chemical methods for fabrication of opals and inverse opals are presented together with preparations of composites plasmonic-photonic crystals: the influence of SPR on the optical properties of PCs is also discussed. Main applications of this new class of composite materials are illustrated with the aim to offer the reader an overview of the recent advances in this field.

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.

Optical Devices Constructed from Ferrocene-Modified Microgels for H2O2 Sensing

Ferrocene-modified poly(N-isopropylacrylamide)-based microgels were synthesized, characterized, and used to construct optical devices (etalons). The response of the microgels and etalons to H₂O₂ was investigated, and we show that both the microgel diameter and the optical properties of the etalons depend on the solution concentration of H₂O₂ from 0.6 to 35 mM. This behavior is a direct result of the oxidation of ferrocene, which influences the microgel diameter. This was also demonstrated by electrochemical-mediated oxidation/reduction of ferrocene using cyclic voltammetry. We go on to show that these materials could be used to monitor H₂O₂ that is generated from enzymatic reactions. Specifically, we show that the H₂O₂ generated from the oxidation of glucose catalyzed by glucose oxidase could be quantified. Finally, the devices can be reused multiple times via a regeneration process. This investigation illustrates the versatility of the etalon system to detect species of broad relevance and how they could potentially be used to quantify products of biological reactions.