Metasurfaces, planer artificial materials composed of subwavelength unit cells, have shown superior abilities to manipulate the wavefronts of electromagnetic waves. In the last few years, ...metasurfaces have been a burgeoning field of research, with a large variety of functional devices, including planar lenses, beam deflectors, polarization converters, and metaholograms, being demonstrated. Up to date, the majority of metasurfaces cannot be tuned postfabrication. Yet, the dynamic control of optical properties of metasurfaces is highly desirable for a plethora of applications including free space optical communications, holographic displays, and depth sensing. Recently, much effort has been made to exploit active materials, whose optical properties can be controlled under external stimuli, for the dynamic control of metasurfaces. The tunability enabled by active materials can be attributed to various mechanisms, including but not limited to thermo‐optic effects, free‐carrier effects, and phase transitions. This short review summarizes the recent progress on tunable metasurfaces based on various approaches and analyzes their respective advantages and challenges to be confronted with. A number of potential future directions are also discussed at the end.
Various mechanisms to achieve dynamic control of metasurfaces enabled by active materials are discussed. Recent works on tunable metasurfaces based on thermo‐optic effects, free carrier effects, and phase transitions are summarized. Their respective advantages and challenges are analyzed and an outlook on the potential development of tunable metasurfaces is presented.
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The results of numerous studies have led to the development of supramolecular (assembled) organic substances for use in biomedical imaging as part of comprehensive approaches to the diagnosis of ...diseases. This review summarizes recent advances that have been made in the design and fabrication of assembled organic dyes for fluorescence and photoacoustic bioimaging.
The results of numerous studies have led to the development of assembled organic substances for fluorescence and photoacoustic bioimaging as part of comprehensive approaches to the diagnosis of diseases.
Actuators that can convert environmental stimuli into mechanical work are widely used in intelligent systems, robots, and micromechanics. To produce robust and sensitive actuators of different ...scales, efforts are devoted to developing effective actuating schemes and functional materials for actuator design. Carbon‐based nanomaterials have emerged as preferred candidates for different actuating systems because of their low cost, ease of processing, mechanical strength, and excellent physical/chemical properties. Especially, due to their excellent photothermal activity, which includes both optical absorption and thermal conductivities, carbon‐based materials have shown great potential for use in photothermal actuators. Herein, the recent advances in photothermal actuators based on various carbon allotropes, including graphite, carbon nanotubes, amorphous carbon, graphene and its derivatives, are reviewed. Different photothermal actuating schemes, including photothermal effect–induced expansion, desorption, phase change, surface tension gradient creation, and actuation under magnetic levitation, are summarized, and the light‐to‐heat and heat‐to‐work conversion mechanisms are discussed. Carbon‐based photothermal actuators that feature high light‐to‐work conversion efficiency, mechanical robustness, and noncontact manipulation hold great promise for future autonomous systems.
This review highlights the recent advances in carbon‐based photothermal actuators. Physical properties and light‐to‐heat conversion mechanisms of various carbon‐based functional materials are summarized. Photothermal actuating schemes such as photothermal expansion, desorption, phase change, surface tension effect, and magnetic susceptibility are reviewed. The current challenges and future perspectives of this field are also discussed.
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Azobenzene is a well‐known derivative of stimulus‐responsive molecular switches and has shown superior performance as a functional material in biomedical applications. The results of multiple studies ...have led to the development of light/hypoxia‐responsive azobenzene for biomedical use. In recent years, long‐wavelength‐responsive azobenzene has been developed. Matching the longer wavelength absorption and hypoxia‐response characteristics of the azobenzene switch unit to the bio‐optical window results in a large and effective stimulus response. In addition, azobenzene has been used as a hypoxia‐sensitive connector via biological cleavage under appropriate stimulus conditions. This has resulted in on/off state switching of properties such as pharmacology and fluorescence activity. Herein, recent advances in the design and fabrication of azobenzene as a trigger in biomedicine are summarized.
Azobenzene is a well‐known derivative of stimulus‐responsive molecular switches and has shown superior performance as a functional material in biomedical applications. The results of numerous studies have led to the development of light/hypoxia‐responsive azobenzene for biomedical use. Recent advances in the design and fabrication of azobenzene as a trigger in biomedicine are summarized.
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Compared with thin‐film morphology, 1D perovskite structures such as micro/nanowires with fewer grain boundaries and lower defect density are very suitable for high‐performance photodetectors with ...higher stability. Although the stability of perovskite microwire‐based photodetectors has been substantially enhanced in comparison with that of photodetectors based on thin‐film morphology, practical applications require further improvements to the stability before implementation. In this study, a template‐assisted method is developed to prepare methylammonium lead bromide (MAPbBr3) micro/nanowire structures, which are encapsulated in situ by a protective hydrophobic molecular layer. The combination of the protective layer, high crystalline quality, and highly ordered microstructures significantly improve the stability of the MAPbBr3 single‐crystal microwire arrays. Consequently, these MAPbBr3 single‐crystal microwire‐array‐based photodetectors exhibit significant long‐term stability, maintaining 96% of the initial photocurrent after 1 year without further encapsulation. The lifetime of such photodetectors is hence approximately four times longer than that of the most stable previously reported perovskite micro/nanowire‐based photodetector; this is thought to be the most stable perovskite photodetector reported thus far. Furthermore, this work should contribute further toward the realization of perovskite 1D structures with long‐term stability.
MAPbBr3 single‐crystal microwire arrays with designable shape, controllable size, and high crystalline quality are fabricated. The combination of the hydrophobic molecular protective layer, high crystalline quality, and highly ordered microstructures, improve the intrinsic stability of MAPbBr3 single‐crystal microwire arrays. Thus, a flexible photodetector with long‐term performance stability of more than 1 year is achieved.
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Diarylethene (DAE) photoswitch is a new and promising family of photochromic molecules and has shown superior performance as a smart trigger in stimulus‐responsive materials. During the past few ...decades, the DAE family has achieved a leap from simple molecules to functional molecules and developed toward validity as a universal switching building block. In recent years, the introduction of DAE into an assembly system has been an attractive strategy that enables the photochromic behavior of the building blocks to be manifested at the level of the entire system, beyond the DAE unit itself. This assembly‐based strategy will bring many unexpected results that promote the design and manufacture of a new generation of advanced materials. Here, recent advances in the design and fabrication of diarylethene as a trigger in materials science, chemistry, and biomedicine are reviewed.
Diarylethenes are a new type of photochromic molecules with attractive photofatigue resistance and reversibility. The result of a lot of effort has led to the rapid development of photoresponsive diarylethylenes for smart material applications. The recent advances in the design and assembly of diarylethylene as a multifunctional photoresponsive trigger unit are reviewed.
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The subgingival crevice harbors diverse microbial communities. Shifts in the composition of these communities occur with the development of gingivitis and periodontitis, which are considered as ...successive stages of periodontal health deterioration. It is not clear, however, to what extent health‐ and gingivitis‐associated microbiota are protective, or whether these communities facilitate the successive growth of periodontitis‐associated taxa. To further our understanding of the dynamics of the microbial stimuli that trigger disruptions in periodontal homeostasis, we reviewed the available literature with the aim of defining specific microbial signatures associated with different stages of periodontal dysbiosis. Although several studies have evaluated the subgingival communities present in different periodontal conditions, we found limited evidence for the direct comparison of communities in health, gingivitis, and periodontitis. Therefore, we aimed to better define subgingival microbiome shifts by merging and reanalyzing, using unified bioinformatic processing strategies, publicly available 16S ribosomal RNA gene amplicon datasets of periodontal health, gingivitis, and periodontitis. Despite inherent methodological differences across studies, distinct community structures were found for health, gingivitis, and periodontitis, demonstrating the specific associations between gingival tissue status and the subgingival microbiome. Consistent with the concept that periodontal dysbiosis is the result of a process of microbial succession without replacement, more species were detected in disease than in health. However, gingivitis‐associated communities were more diverse than those from subjects with periodontitis, suggesting that certain species ultimately become dominant as dysbiosis progresses. We identified the bacterial species associated with each periodontal condition and prevalent species that do not change in abundance from one state to another (core species), and we also outlined species co‐occurrence patterns via network analysis. Most periodontitis‐associated species were rarely detected in health but were frequently detected, albeit in low abundance, in gingivitis, which suggests that gingivitis and periodontitis are a continuum. Overall, we provide a framework of subgingival microbiome shifts, which can be used to generate hypotheses with respect to community assembly processes and the emergence of periodontal dysbiosis.
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Three-dimensional (3D) laser nanoprinting allows maskless manufacturing of diverse nanostructures with nanoscale resolution. However, 3D manufacturing of inorganic nanostructures typically requires ...nanomaterial-polymer composites and is limited by a photopolymerization mechanism, resulting in a reduction of material purity and degradation of intrinsic properties. We developed a polymerization-independent, laser direct writing technique called photoexcitation-induced chemical bonding. Without any additives, the holes excited inside semiconductor quantum dots are transferred to the nanocrystal surface and improve their chemical reactivity, leading to interparticle chemical bonding. As a proof of concept, we printed arbitrary 3D quantum dot architectures at a resolution beyond the diffraction limit. Our strategy will enable the manufacturing of free-form quantum dot optoelectronic devices such as light-emitting devices or photodetectors.
Photoprinting nanoparticles
Nanoparticle assembly often requires tailored selection of the ligands so that they can selectively bond, as with complementary DNA strands. Alternately, they can be linked together at specified locations using photopolymerization to connect ligands at desired places. However, this process adds to the complexity of making the nanoparticles and is limited by the fidelity of the ligand attachment. Liu
et al
. show that light can be used to desorb surface thiolate ligands from cadmium selenide/zinc sulfide core shell quantum dots (see the Perspective by Pan and Talapin). The resulting trapped holes drive bonding between the particles through the remaining surface ligands. The authors reveal photoprinting of arbitrary three-dimensional architectures at a resolution beyond the diffraction limit and for a range of nanocrystals. Printing can be optically selected based on the size and/or bandgap of the quantum dots. —MSL
Photoexcitation-induced chemical bonding enables high-resolution three-dimensional printing of semiconductor quantum dots.
Entry into cells is necessary for many nanomaterial applications, and a common solution is to functionalize nanoparticles (NPs) with cell-penetrating ligands. Despite intensive studies on these ...functionalized NPs, little is known about their effect on cellular activities to engulf other cargo from the nearby environment. Here, we use NPs functionalized with TAT (transactivator of transcription) peptide (T-NPs) as an example to investigate their impact on cellular uptake of bystander cargo. We find that T-NP internalization enables cellular uptake of bystander NPs, but not common fluid markers, through a receptor-dependent macropinocytosis pathway. Moreover, the activity of this bystander uptake is stimulated by cysteine presence in the surrounding solution. The cargo selectivity and cysteine regulation are further demonstrated ex vivo and in vivo. These findings reveal another mechanism for NP entry into cells and open up an avenue of studying the interplay among endocytosis, amino acids, and nanomaterial delivery.
Reported here is a bioinspired fabrication of superhydrophobic graphene surfaces by means of two‐beam laser interference (TBLI) treatment of graphene oxide (GO) films. Microscale grating‐like ...structures with tunable periods and additional nanoscale roughness are readily created on graphene films due to laser induced ablation effect. Synchronously, abundant hydrophilic oxygen‐containing groups (OCGs) on GO sheets can be drastically removed after TBLI treatment, which lower its surface energy significantly. The synergistic effect of micro‐nanostructuring and the OCGs removal endows the resultant graphene films with unique superhydrophobicity. Additionally, dual TBLI treatment with 90° rotation is implemented to fabricate superhydrophobic graphene films with two‐dimensional grating‐like structures that can effectively avoid the anisotropic hydrophobicity originated from the grooved structures. Moreover, the superhydrophobic graphene films become conductive due to the laser reduction effect. Unique optical characteristics including transmission diffraction and brilliant structural color are also observed due to the presence of periodic microstructures. As a mask‐free, chemical‐free, and cost‐effective method, the TBLI processing of GO may open up a new way to biomimetic graphene surfaces, and thus hold great promise for the development of novel graphene‐based microdevices.
A bioinspired fabrication of superhydrophobic graphene surfaces by means of laser holographic treatment of graphene oxide (GO) films is presented. Microscale grating‐like structures with nanoscale roughness are created on graphene films, and hydrophilic oxygen groups on GO sheets are drastically removed. The synergistic effect endows the resultant graphene films with unique superhydrophobicity and unique optical properties that mimic butterfly wings.
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