Microfluidic paper-based analytical devices (μPADs) have experienced rapid growth over the past decade due to their simple design, low cost, minimal sample requirement, and good sensitivity, ...selectivity and accuracy. While designed originally for point-of-care medical diagnostics, biological, and food safety applications, μPADs are now used increasingly for environmental monitoring purposes. This review provides a detailed overview of the μPADs developed over the past ten years for the environmental analysis of soil, air, ecology (pesticides) and river water. The review commences by introducing the fabrication techniques and detection methods used in μPAD technology. A detailed description of the main μPAD frameworks proposed in the past decade for environmental monitoring is then provided. The review concludes by examining the challenges facing μPADs for environmental monitoring and identifying probable avenues of future research.
We explore the skyrmion formation and control possibilities in two-dimensional (2D) magnets from the ubiquitous moiré pattern in vdW heterostructures. Using the example of a ferromagnetic monolayer ...on an antiferromagnetic substrate, we demonstrate a new origin of skyrmions in the 2D magnets from the lateral modulation of interlayer magnetic coupling by the locally different atomic registries in moiré. The moiré skyrmions are doubly degenerate with opposite topological charge and trapped at an ordered array of sites with the moiré periodicity that can be dramatically tuned by strain and interlayer translation. At relatively strong interlayer coupling, the ground states are skyrmion lattices, where magnetic field can switch the skyrmion vorticity and location in the moiré. At weak interlayer coupling limit, we find metastable skyrmion excitations on the ferromagnetic ground state that can be deterministically moved between the ordered moiré trapping sites by current pulses. Our results point to potential uses of moiré skyrmions both as information carriers and as drastically tunable topological background of electron transport.
The discharge of excessive metal ions and anions into water bodies leads to the serious pollution of water and environment, which in turn has a certain impact on industry, agriculture, and human ...life. Because of the unique advantages of luminescent metal-organic frameworks (LMOFs), they have been successfully explored as various fluorescent probes to quickly and effectively detect these pollutants. This perspective not only introduces the design strategy and classification of LMOFs, especially the construction methods of water-stable LMOFs, but also reports the latest progresses in some LMOFs between 2016 and 2020 as well as expounds the mechanisms of LMOFs for detecting anions and cations. Moreover, the luminescence properties of LMOFs are related to the selection of metal ions, the structure of organic ligands, the pore size, and the interaction of guest molecules. Finally, the further development of LMOFs is summarized and prospected in this field.
This work mainly reviews the recent progresses in luminescent metal-organic frameworks (LMOFs) as sensors for detecting various metal ions and anions in aqueous solutions.
This paper presents a review of the current state-of-the-art in micropumping technology for biomedical applications. The review focuses particularly on the actuation schemes, flow directing methods ...and liquid chamber configurations used in the devices proposed over the past five years. A comparative study is presented of the various mechanical and non-mechanical micropumps proposed for biomedical applications. The performance of the various devices is compared in terms of their actuation voltage, power consumption, operating frequency range, flow rate, backpressure, and so forth. The basic operating principles and advantages of each method are introduced, and their limitations described where appropriate. The review provides a useful source of reference for selecting micropumping schemes capable of meeting the specific flow rate requirements of different biomedical applications. In general, the review is expected to be of interest to both seasoned researchers and practitioners in the micropumping and biomedical technology fields and those entering the field for the first time.
•Micropumps are one of the most powerful approaches for biomedical applications.•The review focuses on proposals for operating principles and performance of two types of micropump.•A comprehensive review of the main applications of micropumps over the past five years.
Discoveries of intrinsic two-dimensional (2D) ferromagnetism in van der Waals (vdW) crystals provide an interesting arena for studying fundamental 2D magnetism and devices that employ localized ...spins1–4. However, an exfoliable vdW material that exhibits intrinsic 2D itinerant magnetism remains elusive. Here we demonstrate that Fe3GeTe2 (FGT), an exfoliable vdW magnet, exhibits robust 2D ferromagnetism with strong perpendicular anisotropy when thinned down to a monolayer. Layer-number-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanied by a fast drop of the Curie temperature (TC) from 207 K to 130 K in the monolayer. For FGT flakes thicker than ~15 nm, a distinct magnetic behaviour emerges in an intermediate temperature range, which we show is due to the formation of labyrinthine domain patterns. Our work introduces an atomically thin ferromagnetic metal that could be useful for the study of controllable 2D itinerant ferromagnetism and for engineering spintronic vdW heterostructures5.
A
bstract
Analysis of EDGES data shows an absorption signal of the redshifted 21-cm line of atomic hydrogen at
z
∼ 17 which is stronger than expected from the standard ΛCDM model. The absorption ...signal interpreted as brightness temperature
T
21
of the 21-cm line gives an amplitude of
−
500
−
500
+
200
mK at 99% C.L. which is a 3.8
σ
deviation from what the standard ΛCDM cosmology gives. We present a particle physics model for the baryon cooling where a fraction of the dark matter resides in the hidden sector with a U(1) gauge symmetry and a Stueckelberg mechanism operates mixing the visible and the hidden sectors with the hidden sector consisting of dark Dirac fermions and dark photons. The Stueckelberg mass mixing mechanism automatically generates a millicharge for the hidden sector dark fermions providing a theoretical basis for using millicharged dark matter to produce the desired cooling of baryons seen by EDGES by scattering from millicharged dark matter. We compute the relic density of the millicharged dark matter by solving a set of coupled equations for the dark fermion and dark photon yields and for the temperature ratio of the hidden sector and the visible sector heat baths. For the analysis of baryon cooling, we analyze the evolution equations for the temperatures of baryons and millicharged dark matter as a function of the redshift. We exhibit regions of the parameter space which allow consistency with the EDGES data. We note that the Stueckelberg mechanism arises naturally in strings and the existence of a millicharge would point to its string origin.
Polyelectrolyte complex nanoparticles (PEC NPs) were fabricated via electrostatic interactions between positively charged heat-denatured lactoferrin (LF) particles and negatively charged pectin. The ...obtained PEC NPs were then utilized as curcumin carriers. PEC NPs were prepared by mixing 1.0 mg/mL solutions of heat-denatured LF and pectin at a mass ratio of 1:1 (w/w) in the absence of NaCl at pH 4.50. PEC NPs that were prepared under optimized conditions were spherical in shape with a particle size of ∼208 nm and zeta potential of ∼−32 mV. Hydrophobic curcumin was successfully encapsulated into LF/pectin PEC NPs with high encapsulation efficiency (∼85.3%) and loading content (∼13.4%). The in vitro controlled release and prominent antioxidant activities of curcumin from LF/pectin PEC NPs were observed. The present work provides a facile and fast method to synthesize nanoscale food-grade delivery systems for the improved water solubility, controlled release, and antioxidant activity of hydrophobic curcumin.
Organic dye based NIR‐II fluorescent probes, owing to their high signal‐to‐background ratio and deeper penetration, are highly useful for deep‐tissue high‐contrast imaging in vivo. However, it is ...still a challenge to design activatable NIR‐II fluorescent probes. Here, a novel class of polymethine dyes (NIRII‐RTs), with bright (quantum yield up to 2.03 %), stable, and anti‐solvent quenching NIR‐II emission, together with large Stokes shifts, was designed. Significantly, the novel NIR‐II dyes NIRII‐RT3 and NIRII‐RT4, equipped with a carboxylic acid group, can serve as effective NIR‐II platforms for the design of activatable bioimaging probes with high contrast. As a proof of concept, a series of target‐activatable NIRII‐RT probes (NIRII‐RT‐pH, NIRII‐RT‐ATP and NIRII‐RT‐Hg) for pH, adenosine triphosphate (ATP), and metal‐ion detection, were synthesized. By applying the NIRII‐RT probe, the real‐time monitoring of drug‐induced hepatotoxicity was realized.
The presented work reports a new class of polymethine dyes (NIRII‐RTs) with bright, stable, and anti‐quenching NIR‐II emissions together with large Stokes shifts. Importantly, by introducing the carboxylic acid functional group, the novel dyes NIRII‐RT3 and NIRII‐RT4 can serve as effective NIR‐II platforms for the design of activatable bioimaging probes with high contrast.
We show that topological order and vibrational edge modes can exist in a classical mechanical system consisting of a two-dimensional honeycomb lattice of masses and springs. The band structure shows ...the existence of Dirac cones and unconventional edge states that are similar to the vibrational modes in graphene. Interestingly, as the system is placed on a constantly rotational coordinate system, the Coriolis force resulting from the non-inertial reference frame introduces time-reversal symmetry breaking and leads to topologically nontrivial band gaps. The nontrivial topological orders are further verified by the calculation of Chern numbers for corresponding bands.
Anion-exchange membrane fuel cells (AEMFCs) are promising energy storage and conversion devices that provide opportunities and advantages in the application of low-cost transition metal oxide ...(TMO)-based catalysts. However, the oxygen reduction reaction (ORR) activity of these catalysts is still greatly inferior to that of Pt-based catalysts. In this review, the key factors to develop high performance TMO-based catalysts have been carefully detailed, including strategies to enhance their electrical conductivity, recent advances in the understanding of their intrinsic activity, and their morphology and structure design. Finally, we discussed the existing challenges and future research directions for further development of TMO-based ORR catalysts.
Recent advances in the electrical conductivity, intrinsic activity and morphology design of transition-metal-oxide-based oxygen reduction catalysts are summarized.
PDF
