A luminescent cocrystal system is reported to undergo crystal‐to‐crystal phase transformation from yellow‐emitting polymorph I to green‐emitting polymorph II, triggered by THF fuming or heating, and ...the green emission can recover to the initial yellow emission by grinding. The established spectroscopic and crystallographic analyses demonstrate that the phase transition occurred and benefits from the combined effect of similar molecular arrange sequence and unique alteration of intermolecular interactions from halogen/hydrogen bonds in I to π–π stacking in II. Furthermore, I and II exhibit red‐shift emission under hydrostatic pressure. The emission of I and II shows a red‐shift and recovers towards the initial emission upon acid–base fuming. This is a rare example of reversible luminescent switching of cocrystal based upon crystal‐to‐crystal phase transition, and provides an alternative strategy to develop multi‐stimuli responsive materials.
A luminescent cocrystal exhibits reversible luminescent switching, responding to THF‐vapor/thermal stimuli and mechanical grinding. The crystal‐to‐crystal phase transition between two different cocrystal polymorphs under the external stimuli was demonstrated, enabling an in‐depth understanding of the luminescent switching of organic luminescent materials.
Polymer carbon dots (PCDs) are proposed as a new class of room‐temperature phosphorescence (RTP) materials. The abundant energy levels in PCDs increase the probability of intersystem crossing (ISC) ...and their covalently crosslinked framework structures greatly suppress the nonradiative transitions. The efficient methods allow the manufacture of PCDs with unique RTP properties in air without additional metal complexation or complicated matrix composition. They thus provide a route towards the rational design of metal‐free RTP materials that may be synthesized easily. Furthermore, we find that RTP is associated with a crosslink‐enhanced emission (CEE) effect, which provides further routes to design improved PCDs with diverse RTP performance. Our results show the potential of PCDs as a universal route to achieve effective metal‐free RTP.
Room‐temperature phosphorescence: Polymer carbon dots (PCDs) showing metal‐free room‐temperature phosphorescence (RTP) have been constructed by using a facile method. The contribution of the cross‐link‐enhanced emission effect to the generation of RTP is verified and proposed as a guideline to forecast and synthesize a series of PCDs with diverse RTP performance (ISC=intersystem crossing).
A surface-enhanced Raman scattering (SERS)-microfluidic droplet platform for the rapid, ultrasensitive and simultaneous detection of vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8) ...secreted by a single cell is presented. The high-throughput water-in-oil droplets containing an individual cell along with four kinds of immune-particles (antibody-conjugated silver nanoparticles or magnetic beads, AgNPs@Ab1 and MNs@Ab2) in each were achieved by a cross-typed microfluidic chip, and then they were captured by a collection channel array for SERS measurements. In the appearance of cytokines secreted by one cell, AgNPs@Ab1 can be linked onto the surface of MNs@Ab2 through the immune-recognition to form an immune-sandwich, which makes the “turn on” SERS signal of the Raman reporters previously laid on the surface of MNs due to the adjacent AgNPs. Furthermore, the second SERS signal amplification is from the magnetic field-induced spontaneous collection effect, which brings 75 times enhancement for SERS signal. Additionally, the encapsulation of cytokines in an isolated droplet permits an accumulation effect of targets with time. Owing to the dual signal enhancement and the accumulation effect, such few cytokines secreted by a single cell become detectable and a limit of detection is achieved as 1.0 fg/mL in one droplet. By using this ultrasensitive SERS-microdroplet method, the VEGF and IL-8 secretions from several cells in one droplet were explored and the data show that the cell–cell interaction may promote angiogenesis of cancer cells through the up-regulation of VEGF and IL-8.
Luminescent mechanochromism (e.g., shearing force and hydrostatic pressure) has been intensively studied in recent years. However, there are few reported studies on the difference of the molecular ...configuration changes induced by these stresses. In this study, we chose triphenylamine, C18H6N (TPA), as a model molecule to study different molecular configuration changes under shearing force and hydrostatic pressure. Triphenylamine is an organic optoelectric functional molecule with a propeller-shaped configuration, a large conjugate structure, and a single molecular fluorescence material. Fluorescence and Raman spectra of TPA were recorded in situ under different pressures (0–1.9 GPa) produced by the mechanical grinding or using a diamond anvil cell (DAC). Our results show that the crystal phase of TPA transformed to the amorphous phase by grinding, whereas no obvious phase transition was observed under hydrostatic pressure up to 1.9 GPa, indicating the stability of TPA. Hydrostatic pressure by DAC induces molecular conformation changes, and the pressure-induced emission enhancement phenomenon of TPA is observed. By analyzing the Raman spectra at high pressure, we suggest that the molecular conformation changes under pressure are caused by the twisted dihedral angle between the benzene and the nitrogen atom, which is different from the phase transformation induced by the shearing force of grinding.
•Based on the measurement of pressure and volume, the transient temperature of air is obtained.•The heat transfer behaviour of water spray and air is investigated.•With injection of water spray, the ...compression efficiency is improved.
Compressed air energy storage (CAES) has emerged as an effective large-scale energy storage technology. This storage system can have many urban applications based on the time-dependent price of electricity. In China, the electric power companies employ batteries to store electricity when the price drops and generate electricity when the price increases. When compared with storage batteries, CAES systems have larger storage capacity (100 MWh, battery < 10 MWh), are more environmentally friendly (no heavy metals pollution), and have longer service life. However, the major limitation that restricts the application of such systems is its poor (<60%) turnaround efficiency (electricity to electricity). Most CAES systems are based on adiabatic compression. Approximately half of the electricity is transformed into heat and exhausted due to the poor heat transfer from the air to environment. Most of the previous research focused on enhancing the heat transfer to achieve quasi-isothermal compression. In this study, a contact heat transfer method is used to cool the compressed air by injecting micron-sized (10–100 μm) water spray into the compressed air. A transient temperature measurement method is developed to investigate the heat transfer behaviour between air and water. The measurements showed the spray-air heat transfer rate to lie in the range of 10–120 W·m−2·K−1. When the compression ratio is two in a compression chamber of 0.94 L, the compression power is reduced from 73.8 J/cycle (adiabatic) to 69.0 J/cycle, using water injection of 0.416 g/cycle. The achieved compression efficiency is improved from 86.7% (adiabatic) to 92.4%.
•A multifunctional single cell analysis platform for microoperation, microspectroscopy and microimaging was built.•We use the characteristic and controllable modification method of the laser induced ...deposition on the surface of fiber tip.•Cancer cell has a higher intracellular pH than the extracellular pH while the normal cell has a contrary trend.
The accurate detection of intracellular and extracellular microenvironment at single cell is important for deep understanding of complicated cellular physiological activities, such as exploring organelle structures, and revealing the spatial heterogeneity of intracellular chemical components. Here, we built a single cell analysis platform by using a silver nanoparticles decorated optical fiber tip (diameter less than 500 nm) integrated with microoperation, microspectroscopy and microimaging, working for light propagation, sensing, cell manipulation, and in-situ spectroscopy and imaging, especially for exploring the subcellular microenvironment of a single cell. In view of the flexibility of fiber tip, the silver nanoparticles and the pH sensitive Raman reporters were both modified on the fiber tip surface by the one-step laser-induced Ag deposition method, and this optical fiber sensor was used for the accurate intracellular and extracellular pH detections by the surface-enhanced Raman spectroscopy (SERS) method. Cell heterogeneity according to their different pH microenvironments was disclosed by this optical fiber-based single cell analysis platform and it is also promising in learning biological processes within single cell, as well as monitoring intracellular responses during various external stimuli and therapies.
A surface-enhanced Raman scattering (SERS) measurement of 3,3′,4,4′-tetrachlorobiphenyl (PCB77) with aptamer capturing in a microfluidic device was demonstrated. To construct the microfluidic chip, ...an ordered Ag nanocrown array was fabricated over a patterned polydimethylsiloxane (PDMS) that was achieved by replicating an anodic aluminum oxide (AAO) template. The patterned PDMS sheet was covered with another PDMS sheet having two input channel grooves to form a close chip. The Ag nanocrown array was used for the SERS enhancement area and the detection zone. PCB 77 aptamers were injected into one channel and the other allows for analytes (PCBs). The mercapto aptamers captured the targets in the mixed zone and were immobilized to the SERS detection zone via S–Ag bonds so as to further improve both the SERS sensitivity and selectivity of PCB77. Such an aptamer-based microfluidic chip realized a rapid SERS detection. The lowest detectable concentration of 1.0 × 10–8 M was achieved for PCB77. This work demonstrates that the aptamer-modified SERS microfluidic sensor can be utilized for selective detections of organic pollutants in the environment.
•This study proposes an isothermal piston formed with a gas-solid-liquid three-layer heat transfer structure.•The porous medium works as a medium to enhance the heat transfer from air to ...environment.•The isothermal piston could improve the compression efficiency.•Dimensionless parameters Ka and Xu is obtained to analyze the system.
Currently, Compressed Air Energy Storage systems mainly use adiabatic compression. Compared with isothermal compression, approximately twice the electricity is transformed into heat. Twice the heat passed into heat exchange mediums leads to twice the heat transfer losses. Enhancement of the heat transfer between air and environment to achieve isothermal compression is an effective approach to improve the turnaround efficiency of CAES systems. An isothermal piston structure is proposed to do isothermal compression. One end of the isothermal piston is connected to a traditional piston, and the other end dips into a liquid medium in the bottom of a cylinder. This forms a gas–solid–liquid three-layer heat transfer structure. A porous medium is used to enhance the heat transfer from the air to the liquid. As the heat capacity of the liquid is much greater than that of the air, the temperature of the liquid remains unchanged as well as the compressed air. A new method is proposed to look at the thermodynamics of the compressor with two dimensionless parameters Ka and Xu. Ka describes the extent of the compressor approaching isothermal. When Ka is over 80, the temperature of the air is reduced by 80% compared with adiabatic condition. In the case of using an aluminum porous medium, the compression efficiency increases by 11% at the compression ratio of 7 and the speed of 1200 r/min.
Elastic organic single crystals with light‐emitting and multi‐faceted bending properties are extremely rare. They have potential application in optical materials and have attracted the extensive ...attention of researchers. In this paper, we reported a structurally simple barbituric derivative DBDT, which was easily crystallized and gained long needle‐like crystals (centimeter‐scale) in DCM/CH3OH (v/v=2/8). Upon applying or removing the mechanical force, both the (100) and (040) faces of the needle‐like crystal showed reversible bending behaviour, showing the nature of multi‐faceted bending. The average hardness (H) and elastic modulus (E) were 0.28±0.01 GPa and 4.56±0.03 GPa for the (040) plane, respectively. Through the analysis of the single crystal data, it could be seen that the van der waals (C−H⋅⋅⋅π and C−H⋅⋅⋅C), H‐bond (C−H⋅⋅⋅O) and π⋅⋅⋅π interactions between molecules were responsible for the generation of the crystal elasticity. Interestingly, elastic crystals exhibited optical waveguide characteristics in straight or bent state. The optical loss coefficients measured at 627 nm were 0.7 dBmm−1 (straight state) and 0.9 dBmm−1 (bent state), while the optical loss coefficient (α) were 1.5 dBmm−1 (straight state) and 1.8 dBmm−1 (bent state) at 567 nm. Notably, the elastic organic molecular crystal based on barbituric derivative could be used as the candidate for flexible optical devices.
The D‐π‐A molecule (DBDT) was synthesized by a simple one‐step reaction, and the centimeter‐scale needle‐like crystals were prepared by slow volatilization in DCM/CH3OH (v/v=2/8). Upon applying or removing the mechanical force, both the (100) and (040) faces of the needle‐like crystal showed reversible bending behaviour, showing the nature of multi‐faceted bending. Fortunately, the elastic crystals also exhibited optical waveguide characteristics in straight or bent state.
With the significant increase in demand for artificial intelligence, environmental map reconstruction has become a research hotspot for obstacle avoidance navigation, unmanned operations, and virtual ...reality. The quality of the map plays a vital role in positioning, path planning, and obstacle avoidance. This review starts with the development of SLAM (Simultaneous Localization and Mapping) and proceeds to a review of V-SLAM (Visual-SLAM) from its proposal to the present, with a summary of its historical milestones. In this context, the five parts of the classic V-SLAM framework—visual sensor, visual odometer, backend optimization, loop detection, and mapping—are explained separately. Meanwhile, the details of the latest methods are shown; VI-SLAM (Visual inertial SLAM) is reviewed and extended. The four critical techniques of V-SLAM and its technical difficulties are summarized as feature detection and matching, selection of keyframes, uncertainty technology, and expression of maps. Finally, the development direction and needs of the V-SLAM field are proposed.
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