determine the LR asymmetry in morphogenesis. [2] For example, chirality has been found in Xenopus egg cortex before fertilization, [1] and can be passed down to more differentiated cells that establish LR body axis of animal body plan, [7] organ distribution, [8-10] and epithelial movement that leads to axial torsion and overall handedness of hindgut. [11,12] For specialized adult cells derived from somatic tissue, footprints of cell chirality can still be seen by their ability of generating cellular torque, [6,13] migration with LR bias, [14-16] or forming specific alignment in the multicellular level. [15,17,18] Through cell-cell communication, the chiral behavior causes LR-biased cell assembly of multicellular structure [15] and regulates permeability of intercellular junctions. [19] Clearly, cell chirality can be manifested in diverse forms and coordinate different morphogenic dynamics, resulting in distinct forms of tissue and organ architecture. Actin cytoskeleton plays an important role in cell chirality. When cultured on micropatterned substrate, the accumulation of actomyosin stress fibers at micropattern boundary is essential to activate the LR bias in cell migration and orientation. [15,17] Molecular studies suggest helical motion of actin filament as the underlying mechanism for the chirality at cellular level. [20,21] Functioning as a built-in machinery, actomyosin cytoskeleton allows chiral nucleus rotation of single cell [21] and generation of cellular torque with rotational bias. [13] Through a series of amplification process, the actin chirality ultimately determines the symmetry breaking in early embryonic development, [1,7,22] cardiac looping, [4,8,23] and organ laterality [9] in vivo. To give rise to such diverse forms of cell chirality, cell differentiation should play a role. [13,15,17] Cell differentiation is a process coupling with chemical [24] and physical factors. [25-27] Based on variation of key proteins in cytoskeleton, [28] cytoskeleton can be changed at early stage of cell differentiation, as shown by upregulation of cytoskeletal contractility [29] and cell morphological features, which can even forecast the cell lineage fate. [28] It suggests that cytoskeletal components, particularly actin, may early respond to the induction of cell differentiation and then actively participate the signal cascades to engage cell fate. Evidences can be found by regulation of cell differentiation via changed cell shape and cell spreading by physical cues [30-38]

Lead contamination in drinking water is a primary concern in public health, but it is difficult to monitor by end-users. Here, we provide a rapid and power-free microfluidic particle dam which enables visual quantification of lead ions (Pb2+) by the naked eye. GR-5 DNAzyme with extended termini can connect magnetic microparticles (MMPs) and polystyrene microparticles (PMPs) by DNA hybridization, forming “MMPs-GR-5-PMPs”. When Pb2+ is present, GR-5 is cleaved, resulting in an increasing number of free PMPs. To visually count the free PMPs, the solution is loaded to a capillary-driven microfluidic device that consists of a magnetic separator to remove the MMPs-GR-5-PMPs, followed by a particle dam that traps and accumulates the free PMPs into a visual bar with growing length proportional to the concentration of lead. The device achieved a limit of detection at 2.12 nM (0.44 ppb), high selectivity (>20,000-fold) against other metal ions, high tolerance to different pH and water hardness, and is compatible with tap water with a high recovery rate, enabling visual quantification and user-friendly interface for rapid screening of water safety.

Various COVID-19 vaccines are currently deployed, but their immunization varies and decays with time. Antibody level is a potent correlate to immune protection, but its quantitation relies on intensive laboratory techniques. Here, we report a decentralized, instrument-free microfluidic device that directly visualizes SARS-CoV-2 antibody levels. Magnetic microparticles (MMPs) and polystyrene microparticles (PMPs) can bind to SARS-CoV-2 antibodies simultaneously. In a microfluidic chip, this binding reduces the incidence of free PMPs escaping from magnetic separation and shortens PMP accumulation length at a particle dam. This visual quantitative result enables use in either sensitive mode [limit of detection (LOD): 13.3 ng/ml; sample-to-answer time: 70 min] or rapid mode (LOD: 57.8 ng/ml; sample-to-answer time: 20 min) and closely agrees with the gold standard enzyme-linked immunosorbent assay. Trials on 91 vaccinees revealed higher antibody levels in mRNA vaccinees than in inactivated vaccinees and their decay in 45 days, demonstrating the need for point-of-care devices to monitor immune protection.

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Visual detection of nucleic acids provides simple and rapid screening for infectious diseases or environmental pathogens. However, sensitivity is the current bottleneck, which may require enzymatic amplification for targets in low abundance and make them incompatible with detection at resource-limited sites. Here we report an enzyme-free amplification that provides a sensitive visual detection of ssDNA/RNA oligonucleotides on the basis of nano "sticky balls". When target oligonucleotides are present, magnetic microparticles (MMPs) and gold nanoparticles (AuNPs) were linked together, allowing the collection of AuNPs after magnetic attraction. Subsequently, the collected AuNPs, which carry many oligonucleotides, were used as the sticky balls to link a second pair of MMPs and polymer microparticles (PMPs). Thus, because the magnetic field can attract the MMPs as well as the linked PMPs to the sidewall, the reduction of suspended PMPs yields a change of light transmission visible by the naked eye. Our results demonstrate that the limit of detection is 10 amol for ssDNAs (228 fM in 45 μL) and 75 amol for ssRNAs (1.67 pM in 45 μL). This method is also compatible with the serum environment and detection of a microRNA, miR-155, derived from human breast cancer cells. With significantly improved sensitivity for visual detection, it provides great potential for point-of-care applications at resource-limited sites.

We demonstrate a microfluidic bead trap capable of forming a dipstick-type bar visible to the naked eye for simple and quantitative detection of oligonucleotides. We use magnetic microparticles (MMPs) and polystyrene microparticles (PMPs) that are connected and form MMPs-targets-PMPs when target oligonucleotides are present, leaving free PMPs with a number inversely proportional to the amount of targets. Using a capillary flow-driven microfluidic circuitry consisting of a magnetic separator to remove the MMPs-targets-PMPs, the free PMPs can be trapped at the narrowing nozzle downstream, forming a visual bar quantifiable based on the length of PMP accumulation. Such a power-free and instrument-free platform enables a limit of detection at 13 fmol (0.65 nM in 20 μl, S/N = 3) of oligonucleotides and is compatible with single-nucleotide polymorphisms and operation in a complex bio-fluid. Moreover, using DNAzyme as the target oligonucleotide that catalyzes a specific hydrolytic cleavage in the presence of lead ions, we demonstrate a model application that detects lead ions with a limit of detection of 12.2 nM (2.5 μg l), providing quantitative and visual detection of lead contamination at resource-limited sites.

Topographical cues have been widely used to facilitate cell fusion in skeletal muscle formation. However, an unexpected yet consistent chiral orientation of myotube deviating from the groove boundaries is commonly observed but has long been unattended. In this study, we report a method to guide the formation of skeletal myotubes into scalable and controlled patterns. By inducing C2C12 myoblasts on the groove patterns with different widths (from 0.4 to 200 μm), we observed an enhanced chiral orientation of cells developed on wide grooves (50 and 100 μm of width) since the first day of induction. Active chiral nematics of cells involving cell migration and chiral rotation of cell nucleus subsequently led to a unified chiral orientation of the myotubes. Importantly, those chiral myotubes were formed with enhanced length, diameter, and contractility on wide grooves. Treatment of latrunculin A (Lat A) suppressed the chiral rotation and migration of cells as well as the myotube formation, suggesting the essence of chiral numtatics of cells for myogenesis. Finally, by arranging wide groove/stripe patterns with corresponding compensation angles to synergize microtopographic cues and chiral nematics of cells, intricate and scalable patterns of myotubes are formed, providing a strategy for engineering skeletal muscle tissue formation.