Smart colloidal photonic crystal sensors.

Smart colloidal photonic crystals (PCs) with stimuli-responsive periodic micro/nano-structures, photonic bandgaps, and structural colors have shown unique advantages (high sensitivity, visual readout, wireless characteristics, etc.) in sensing by outputting diverse structural colors and reflection signals. In this review, smart PC sensors are summarized according to their fabrications, structures, sensing mechanisms, and applications. The fabrications of colloidal PCs are mainly by self-assembling the well-defined nanoparticles into the periodical structure (supersaturation-, polymerization-, evaporation-, shear-, interaction-, and field-induced self-assembly process). Their structures can be divided into two groups: closely packed and non-closely packed nano-structures. The sensing mechanisms can be explained by Bragg's law, including the change in the effective refractive index, lattice constant, and the order degree. The sensing applications are detailly introduced according to the analytes of the target, including solvents, vapors, humidity, mechanical force, temperature, electrical field, magnetic field, pH, ions/molecules, and so on. Finally, the corresponding challenges and the future potential prospects of artificial smart colloidal PCs in the sensing field are discussed.

Metal-organic framework photonic crystals with bidisperse particles-based brilliant structural colors and high optical transparency for elaborate anti-counterfeiting.

Photonic crystals (PCs) have attracted great interest and wide applications in displays, printing, anti-counterfeiting, etc. However, two main challenges significantly hinder their applications: 1) the tradeoff between high optical transparency across the whole visible range and brilliant colors requiring a large refractive index contrast (Δn), and 2) the way of regulating structural colors by altering tens of different sizes. To address these issues, a new type of metal-organic framework (MOF)-based transparent photonic crystal (TPC) has been fabricated through self-assembling MOF particles into three-dimensional ordered structures which were then infiltrated by polydimethylsiloxane (PDMS). Compared to conventional PCs, these TPCs exhibit 1) both brilliant forward iridescent structural colors and high transmittance (>75 %) across the whole visible spectra range, and 2) conveniently adjustable colors based on bidisperse particles. The unique color-generating mechanism of the light diffraction by each plane lattice and the small Δn between MOF particles and PDMS are the keys to TPCs' characteristics. Moreover, the prepared invisible anti-counterfeit labels can reversibly hide-reveal patterns with elaborate and exchangeable color contrast in a non-destructive way, showing potential applications in anti-counterfeiting, information encryption, and optical devices.

Mechanochromic and Solvomechanochromic Fluorescent Photonic Crystals for Dual-Mode Modulating Fluorescence and Multilevel Anticounterfeiting.

Fluorescent photonic crystals (FPCs) are ideal candidates for regulating dyes' fluorescence through their unique photonic band gaps (PBGs). However, challenges, including the lack of dynamic regulation of fluorescence, dye release in solvents, and instability, dramatically limit their practical applications. Here, we report mechanochromic and solvomechanochromic rhodamine B (RhB)-based FPCs with dynamic regulation of photoluminescence (PL) by stretching and swelling, brilliant fluorescent and structural colors, and no release of the RhB in solvents. The FPCs with force/solvent-responsive nonclose-packing structures were fabricated by (1) preparing RhB-silica particles by combining click chemistry and cohydrolysis processes and (2) self-assembling these particles in poly(ethylene glycol) phenyl ether acrylate followed by a photopolymerization. Maximal PL inhibition (37%, stretching strain of 6.8%) and enhancement (150%, swelling time of 8 min) were gained when PBGs and their blue edges are precisely adjusted to the PL peak position, respectively. Compared with stretching, PL regulation is more efficient by swelling. These characteristics benefit from the rational design and combination of unique compositions, chemical bonds, nonclosely packed micro/nanostructures, and solvents for swelling. Moreover, these FPCs have been used to encrypt photonic patterns, which display background/strain/angle/UV-dependent color contrasts, showing their potential applications in multilevel anticounterfeiting, optical devices, wireless sensors, etc.

Lattice Transformation-Induced Retroreflective Structural Colors.

Retroreflective structural colors can usually be achieved based on interference combined with a total internal reflection mechanism or diffraction of a monolayer hexagonal two-dimensional (2D) colloidal array. Here, a novel retroreflective structural color was generated based on a hexagonal-parallelogram lattice transformation by stretching 3D photonic crystals with nonclosely packed long-range order. Compared to previous retroreflective colors, this new retroreflective color exhibits two unique off/on color switches: (1) a strain-dependent off/on color switch along the stretching direction and (2) a sample horizontal rotation angle-dependent off/on color switch under the fixed strain. These strain-responsive retroreflective colors are ideal candidates for visually sensing kinesio tapes' strain in practical applications and anticounterfeiting. This work reveals a new structural color regulation mechanism and will advance potential applications in anticounterfeiting, sensing, displays, etc.

Hollow mesoporous cubic silica self-assembling into photonic crystals with rhombohedral lattices and vivid structural colors for anti-counterfeiting.

Colloidal photonic crystals (PCs) feature face-centered cubic (FCC) lattices since spherical particles are usually used as building blocks; however, constructing structural colors originating from PCs with non-FCC lattices is still a big challenge due to the difficulty in preparing non-spherical particles with tunable morphologies, sizes, uniformity, and surface properties and assembling them into ordered structures. Here, uniform, positively charged, and hollow mesoporous cubic silica particles (hmc-SiO2) with tunable sizes and shell thicknesses prepared by a template approach are used to self-assemble into PCs with rhombohedral lattice. The reflection wavelengths and structural colors of the PCs can be controlled by altering the sizes or the shell thicknesses of the hmc-SiO2. Additionally, photoluminescent PCs have been fabricated by taking the advantage of the click chemistry between amino silane and isothiocyanate of a commercial dye. The PC pattern achieved by a hand-writing way with the solution of the photoluminescent hmc-SiO2 instantly and reversibly shows the structural color under visible light but a different photoluminescent color under UV illumination, which is useful for anticounterfeiting and information encryption. The non-FCC structured and photoluminescent PCs will upgrade the basic understanding of the structural colors and facilitate their applications in optical devices, anti-counterfeiting, and so forth.

Stimulus-responsive nonclose-packed photonic crystals: fabrications and applications.

Stimulus-responsive photonic crystals (PCs) possessing unconventional nonclosely packed structures have received growing attention due to their unique capability of mimicking the active structural colors of natural organisms (for example, chameleons' mechanochromic properties). However, there is rarely any systematic review regarding the progress of nonclose-packed photonic crystals (NPCs), involving their fabrication, working mechanisms, and applications. Herein, a comprehensive review of the fundamental principles and practical fabrication strategies of one/two/three-dimensional NPCs is summarized from the perspective of designing nonclose-packed structures. Subsequently, responsive NPCs with exciting functions and working mechanisms are sorted and delineated according to their diverse responses to physical (force, temperature, magnetic, and electric fields), chemical (ions, pH, vapors, and solvents), and biological (glucose, organophosphate, creatinine, and bacteria) stimuli. We then systematically introduced and discussed the applications of NPCs in sensors, printing, anticounterfeiting, display, optical devices, etc. Finally, the current challenges and development prospects for NPCs are presented. This review not only concludes the design principle for NPCs but also provides a significant basis for the exploration of next-generation NPCs.

Bio-Inspired Highly Brilliant Structural Colors and Derived Photonic Superstructures for Information Encryption and Fluorescence Enhancement.

Inspired by the brilliant and tunable structural colors based on the large refractive index contrast (Δn) and non-close-packing structures of chameleon skins, ZnS-silica photonic crystals (PCs) with highly saturated and adjustable colors are fabricated. Due to the large Δn and non-close-packing structure, ZnS-silica PCs show 1) intense reflectance (maximal: 90%), wide photonic bandgaps, and large peak areas, 2.6-7.6, 1.6, and 4.0 times higher than those of silica PCs, respectively; 2) tunable colors by simply adjusting the volume fraction of particles with the same size, more convenient than the conventional way of altering particle sizes; and 3) a relatively low threshold of PC's thickness (57 µm) possessing maximal reflectance compared to that (>200 µm) of the silica PCs. Benefiting from the core-shell structure of the particles, various derived photonic superstructures are fabricated by co-assembling ZnS-silica and silica particles into PCs or by selectively etching silica or ZnS of ZnS-silica/silica and ZnS-silica PCs. A new information encryption technique is developed based on the unique reversible "disorder-order" switch of water-responsive photonic superstructures. Additionally, ZnS-silica PCs are ideal candidates for enhancing fluorescence (approximately tenfold), approximately six times higher than that of silica PC.

LSD1 in beige adipocytes protects cardiomyocytes against oxygen and glucose deprivation.

Objectives: Epicardial adipose tissue (EpAT) is known for its role in supporting the cardiomyocytes. Lysine-specific demethylase 1 (LSD1), a typical lysine demethylase, is an essential regulator for the maintenance of beige adipocytes. However, the effect of LSD1 in the adipogenic differentiation of beige adipocytes in EpAT, and its function on oxygen and glucose deprivation (OGD)-injured cardiomyocytes remain unclear. Materials and Methods: Heart tissues from young mice and elder mice were collected for immunohistochemical staining. LSD1 in 3T3-L1 cells was knocked down by LSD1-shRNA lentivirus infection. The qRT-PCR, western blotting, and Oil Red O staining were employed to detect the adipogenic differentiation of 3T3-L1 cells and formation of beige adipocytes. The cardiomyocytes co-cultured with beige adipocytes were used for OGD treatment. Cell apoptosis was analyzed by flow cytometry. The lactate dehydrogenase (LDH) and superoxide dismutase (SOD) activity were analyzed using commercially available kits. Results: The decrease of LSD1 was related to the age-dependent loss of beige adipocytes in mice EpAT. LSD1 knockdown inhibited the adipogenic differentiation of 3T3-L1 cells and formation of beige adipocytes. The down-regulation of LSD1 in 3T3-L1 cells decreased the protective effect of mature adipocytes on OGD-injured cardiomyocytes. Conclusion: The decreased expression of LSD1 in mice EpAT was associated with age-dependent ablation of beige adipocytes. The protective effect of beige adipocytes on OGD-injured cardiomyocytes is reduced by knockdown of LSD1 in adipocytes. The present study provided exciting insights into establishing novel therapies against age-dependent cardiac diseases.

Precisely sensing hydrofluoric acid by photonic crystal hydrogels.

It is a great challenge to detect hydrofluoric acid (HF) with high precision, good selectivity, and visual readouts characteristics. Herein, a new photonic crystal (PC) hydrogel HF sensor based on the "selective etching-induced swelling" mechanism has been developed. This HF sensor consisting of silica/water/hydroxyethyl acrylate and non-closely packed structures was fabricated through simple non-close-assembling, photopolymerization, and water swelling processes. Silica slightly etched by HF induces the swelling of PC hydrogel, leading to the variation of reflection wavelength and structural colors, thereby realizing visually and spectrally sensing HF (0-10 mM). The unique structure and compositions of PC hydrogel are the keys to the high sensing precision, outstanding selectivity, and low detection limit (0.1 mM). Furthermore, the sensor possesses tailorable, portable, easy-to-operation, and low-cost (<0.01 $/sensor) advantages. This work provides an efficient and convenient tool for sensing and recognizing HF in the aqueous solution for practical applications and upgrades the basic understanding of the photonic sensing mechanism.

Reconfigurable Mechanochromic Patterns into Chameleon-Inspired Photonic Papers.

Photonic crystal (PC) patterns have shown wide applications in optical devices, information encryption, anticounterfeiting, etc. Unfortunately, it is still a great challenge to reconfigure the PC patterns once fabricated. Herein, a new strategy is presented to reconfigure self-recordable PC patterns by printing local patterns into the chameleon-inspired PC papers using the phase change material (PCM) as ink and then erasing the patterns in ethanol. Multicolor and high-resolution (25 and 75 µm for dot and lines, respectively) patterns can be efficiently and repeatedly reconfigured. In addition, the photonic patterns based on the PC paper and PCM combinations are gifted with mechanochromic characteristics and can show programmable and reversible color change under pressure. The high melting point of the ink, nonclosely packed structures of the PC paper, and the similar solubility parameter of PC paper, PCM, and ethanol are the keys for all these characteristics. This work offers a simple, flexible, efficient way to reconfigure PC patterns with mechanochromic properties and could open up exciting applications for novel hand-operation-based anticounterfeiting and optical devices.

LSD1 regulates the expressions of core cardiogenic transcription factors and cardiac genes in oxygen and glucose deprivation injured mice fibroblasts in vitro.

Cardiac reprogramming has emerged as a novel therapeutic approach to regenerating the damaged heart by directly converting endogenous cardiac fibroblasts (CFs) into induced cardiomyocytes (iCMs). Cardiac reprogramming requires the activation of the cardiogenic transcriptional program in concert with the repression of the fibroblastic transcriptional program. Lysine-specific demethylase 1 (LSD1) plays an instrumental role in many physiological processes such as cell growth, differentiation and metabolism. The epigenetic modifications of histones are essential for the accurate expression of genes in cardiomyocytes and the normal functioning of the heart. However, the effect of LSD1 in regulating the cardiogenic transcriptional program under myocardial ischemia/reperfusion (I/R) injury remains unclear. Thus, mice I/R injury was induced by 4 and 24 h reperfusion after 1-h occlusion of the left anterior descending coronary artery. The primary CFs and CMs were exposed under oxygen and glucose deprivation (OGD) to mimic I/R injury. The expression of LSD1 significantly decreased in I/R injured heart tissue and OGD-injured primary CFs and CM, and methylated histone presented a notable increase in OGD-injured primary CFs. Overexpression of LSD1 inhibited the injury of primary CFs induced by OGD, but showed limited inhibition on injured primary CMs. Under the OGD condition, LSD1 overexpression significantly increased cell viability, decreased cell apoptosis and reactive oxygen species (ROS) production of primary CFs. The expression of core cardiogenic transcription factors and cardiac genes were significantly decreased in OGD injured primary CFs, whereas LSD1 overexpression reversed the decrease of transcription factors and cardiac genes under the OGD condition. In conclusion, the overexpression of LSD1 has a protective role in I/R injury by inhibiting the histone methylation of primary CFs and regulates the expressions of core cardiogenic transcription factors and cardiac genes, which can prove to be a potential approach for direct cardiac reprogramming.

Tetramethylpyrazine Improves Monocrotaline-Induced Pulmonary Hypertension through the ROS/iNOS/PKG-1 Axis.

Background: Tetramethylpyrazine (TMP), a potent anti-free radical and anti-inflammations substance, has been demonstrated to possess a direct vessel relaxation property. This study aimed to evaluate the effect of TMP treatment in pulmonary hypertension (PH) and test the hypothesis that TMP prevents or reverses the process of PH. Methods: Rats (n = 36) injected with 50 mg/kg of monocrotaline (MCT) subcutaneously 4 weeks to develop PH were then randomized to TMP (5 mg/kg per day) for another 4 weeks. Hemodynamics was evaluated via the right ventricle. Pulmonary vessels structural remodeling and inflammation were examined by histologic and transmission electron microscopy observation. The expression of inducible nitric oxide synthase (iNOS) and cGMP-dependent protein kinases 1 (PKG-1) was detected by immunohistochemical staining and Western blot. Generation of reactive oxygen species (ROS) and antioxidation species was measured by biochemical analyses. Results: MCT increased PH and right ventricle hypertrophy. TMP alleviated pulmonary arterial pressure elevation, leukocyte infiltration, and structural remodeling of pulmonary arterials induced by MCT successfully. TMP treatment significantly increased the PKG-1 expression and suppressed the iNOS expression. The activity of superoxide dismutase (SOD), glutathione peroxidase (GSH), and catalase (CAT) was significantly higher than control group, while malondialdehyde (MDA) levels were lower compared with MCT group. Conclusion: TMP can suppress established MCT-induced PH through the ROS/iNOS/PKG axis. The underlying mechanisms may be associated with its anti-inflammatory, antioxidant, and antiproliferative properties in pulmonary arterial.

Photo-Luminescent Photonic Crystals for Anti-Counterfeiting.

The conventional photonic crystals (PCs) are usually prepared by the self-assembly of silica or polystyrene particles. However, their applications are limited significantly due to the lack of the functions of the building blocks. Here, a new kind of photo-luminescent photonic crystals (PLPCs) with brilliant PL and structural colors were prepared by the self-assembly of dye-doped silica particles. The PL and structural colors of PCs can be well-controlled by altering the species of dyes and the size of the particles, respectively. Based on these advantages, PLPC patterns with encrypted information were fabricated through the combination of PLPCs and PCs with similar structural colors but diverse PL colors. These patterns can reversibly hide and display the encrypted information under sunlight and UV illumination, respectively. This work paves a new way for constructing functional PCs and will promote their applications in anti-counterfeiting, smart labels, and optical devices.

Chameleon-Inspired Brilliant and Sensitive Mechano-Chromic Photonic Skins for Self-Reporting the Strains of Earthworms.

The skins of chameleons have attracted growing interest because they have sensitive mechano-chromic properties and bright colors due to the large surface-to-surface distances (Ds-s) between neighboring particles and contrast of the refractive index (Δn), respectively. Inspired by these, artificial mechano-chromic photonic skins (MPSs) mimicking those of chameleons were fabricated by the large Δn and Ds-s. The fabrication is considerably simple and efficient based on the self-assembly strategy using commercial chemicals and materials. The reflectance of MPSs depends on the value of Δn, which can be greatly increased to 70% with a Δn of 0.035, leading to their brilliant colors. Because of the large Ds-s, the MPSs possess outstanding mechano-chromic performances, including a large maximal (Δλ = 205 nm) and effective (Δλe = 184 nm) tuning range of the reflection wavelength, high sensitivity (368), fast responsiveness (2.2 nm/ms), good stabilities (>1 year), and reversibility (>100 times). Based on these advantages, MPSs have been used for self-reporting the strain of earthworms by outputting diverse colors during the peristaltic process, indicating the great potential of the MPSs as visual sensors and optical coatings.

Alleviation of glucolipotoxicity-incurred cardiomyocyte dysfunction by Z-ligustilide involves in the suppression of oxidative insult, inflammation and fibrosis.

Diabetes mellitus ranks as a major risk cause for disability and death around the world due to its complications, especially diabetic cardiomyopathy (DCM). Glucolipotoxicity is one of the critical causal factors of DCM. Recent finding confirms the beneficial roles of Z-ligustilide in diabetes mellitus. Nevertheless, its efficacy in DCM remains elusive. Here, Z-ligustilide elevated high glucose/high palmitic acid (HG/P)-inhibited cell viability and attenuated HG/P-induced cell apoptosis, caspase-3 activity, pro-apoptotic Bax and anti-apoptotic Bcl-2 protein expression. Furthermore, Z-ligustilide alleviated HG/P-evoked oxidative damage by decreasing HG/P-induced elevation in ROS, lactate dehydrogenase (LDH) and malondialdehyde (MDA) leakage, but increasing antioxidant enzyme-superoxide dismutase (SOD) and glutathione (GSH) levels suppressed by HG/P. Concomitantly, Z-ligustilide attenuated HG/P-induced cardiomyocyte fibrosis by increasing MMP-14 expression and diminishing HG/P-enhanced fibrotic protein expression, including collagen I, collagen II and TGF-ß. Mechanistically, Z-ligustilide offset the adverse effects of HG/P on the activation of the AMPK/GSK-3ß/Nrf2 pathway. Importantly, blocking the AMPK signaling overturned the protective efficacy of Z-ligustilide against HG/P-induced cardiomyocyte oxidative damage, inflammation and fibrosis. Together, these findings highlight that Z-ligustilide may alleviate glucolipotoxicity-induced cardiomyocyte dysfunction by regulating cell oxidative injury, inflammation and fibrosis via the AMPK/GSK-3ß/Nrf2 pathway. Consequently, Z-ligustilide may represent a promising therapeutic agent against DCM by restoring cardiomyocyte dysfunction.

Noniridescent structural color from enhanced electromagnetic resonances of particle aggregations and its applications for reconfigurable patterns.

HYPOTHESIS: The conventional noniridescent structural colors refer to the coherent scattering of visible light by the short-range ordered structures assembled from the small colloids (100-250 nm). Our hypothesis is that noniridescent structural color can be generated by the random aggregations of large silica particles through the enhanced electromagnetic resonances. EXPERIMENTS: The random aggregations of large silica particles (350-475 nm) were prepared through the infiltration of silica particles solution with the porous substrate. The mechanism of the structural color is investigated. Reconfigurable patterns are prepared. FINDINGS: Dissimilar to the conventional noniridescent colors, the angle-independent colors of silica aggregations originate from the enhanced electromagnetic resonances due to the random aggregation of the particles. The colors (blue, green, and red) and corresponding reflection peak positions of the particle aggregations can be well controlled by simply altering the size of the silica particles. Compared to the traditional prints with permanent patterns, reconfigurable patterns with large-area and multicolor can be fabricated by the repeatedly selective spray of water on the substrate pre-coated with noniridescent colors. This work provides new insight and greenway for the fabrication of noniridescent structural colors and reconfigurable patterns, and will promote their applications in soft display, green printing, and anti-counterfeiting.

Simple and efficient fabrication of multi-stage color-changeable photonic prints as anti-counterfeit labels.

Color changeable photonic prints (CCPPs) show their potential applications in high-level information storage and anti-counterfeiting, but usually suffer from the complex fabrication process and limited color variation. Here, a simple and efficient method is developed to generate CCPPs with multilevel tunable color contrasts by packing the solvent responsive photonic crystals with diverse cross-linking degrees and desired way. The key to the successful fabrication is to create and control over the optical response of each part of the CCPPs through altering the cross-linking degree of PCs and thus the affinity between the CCPPs and solvents. A CCPPs based anti-fake label with the encrypted information functionality which originates from reversible color change between dried state and swelling with the mixture of acetic acid and ethanol is investigated. Compared with conventional CCPPs, the as-prepared CCPPs can reveal multistage information depending on the volume fraction of ethanol. This work provides a new insight for the simple fabrication of CCPPs and will facilitate their applications in the information protection and high-level anti-counterfeiting.

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.

Highly efficient utilization of light and charge separation over a hematite photoanode achieved through a noncontact photonic crystal film for photoelectrochemical water splitting.

The trade-off problem between light absorption and charge collection under lower band-bending (bias) is extremely difficult to resolve in water splitting on photoelectrodes. Although the use of metallic back-reflectors, antireflection coatings, and textured substrates and light absorbers enable the improvement of light utilization efficiency, these methods still suffer from high cost and complex fabrication process, especially, incompetent separation of photogenerated carriers. Here taking the hematite (α-Fe2O3) photoanode as a model, we report that a noncontact photonic crystal (PC) film composed of silica nanoparticles and ethoxylated trimethylolpropane triacrylate (ETPTA) resin can significantly enhance the photoelectrochemical (PEC) activity of the photoelectrode. Specifically, more than 250 mV cathodic shift in the onset potential and 4 times larger photocurrent at 1.0 V versus a reversible hydrogen electrode (RHE) were achieved over the α-Fe2O3-PC photoanode hybrid system, compared with the pristine α-Fe2O3 photoanode. Our work showed that a PC film not only boosted light absorption of the α-Fe2O3 layer but also improved its charge transfer efficiency under light illumination. These new findings of the synergistic effect will open a new avenue to design high-performance solar energy conversion devices.