Capillary pumping independent of the liquid surface energy and viscosity

Capillary pumping is an attractive means of liquid actuation because it is a passive mechanism,i.e.,it does not rely on an external energy supply during operation.The capillary flow rate generally depends on the liquid sample viscosity and surface energy.This poses a problem for capillary-driven systems that rely on a predictable flow rate and for which the sample viscosity or surface energy are not precisely known.Here,we introduce the capillary pumping of sample liquids with a flow rate that is constant in time and independent of the sample viscosity and sample surface energy.These features are enabled by a design in which a well-characterized pump liquid is capillarily imbibed into the downstream section of the pump and thereby pulls the unknown sample liquid into the upstream pump section.The downstream pump geometry is designed to exert a Laplace pressure and fluidic resistance that are substantially larger than those exerted by the upstream pump geometry on the sample liquid.Hence,the influence of the unknown sample liquid on the flow rate is negligible.We experimentally tested pumps of the new design with a variety of sample liquids,including water,different samples of whole blood,different samples of urine,isopropanol,mineral oil,and glycerol.The capillary filling speeds of these liquids vary by more than a factor 1000 when imbibed to a standard constant cross-section glass capillary.In our new pump design,20 filling tests involving these liquid samples with vastly different properties resulted in a constant volumetric flow rate in the range of 20.96–24.76μL/min.We expect this novel capillary design to have immediate applications in lab-on-a-chip systems and diagnostic devices.

Soft metamaterial with programmable ferromagnetism

Magnetopolymers are of interest in smart material applications;however,changing their magnetic properties post synthesis is complicated.In this study,we introduce easily programmable polymer magnetic composites comprising 2D lattices of droplets of solid-liquid phase change material,with each droplet containing a single magnetic dipole particle.These composites are ferromagnetic with a Curie temperature defined by the rotational freedom of the particles above the droplet melting point.We demonstrate magnetopolymers combining high remanence characteristics with Curie temperatures below the composite degradation temperature.We easily reprogram the material between four states:(1)a superparamagnetic state above the melting point which,in the absence of an external magnetic field,spontaneously collapses to;(2)an artificial spin ice state,which after cooling forms either;(3)a spin glass state with low bulk remanence,or;(4)a ferromagnetic state with high bulk remanence when cooled in the presence of an external magnetic field.We observe the spontaneous emergence of 2D magnetic vortices in the spin ice and elucidate the correlation of these vortex structures with the external bulk remanence.We also demonstrate the easy programming of magnetically latching structures.

Reaction injection molding of hydrophilicin-hydrophobic femtolitre-well arrays

Patterning of micro-and nanoscale topologies and surface properties of polymer devices is of particular importance for a broad range of life science applications,including cell-adhesion assays and highly sensitive bioassays.The manufacturing of such devices necessitates cumbersome multiple-step fabrication procedures and results in surface properties which degrade over time.This critically hinders their wide-spread dissemination.Here,we simultaneously mold and surface energy pattern microstructures in off-stoichiometric thiol-ene by area-selective monomer selfassembly in a rapid micro-reaction injection molding cycle.We replicated arrays of 1,843,650 hydrophilic-inhydrophobic femtolitre-wells with long-term stable surface properties and magnetically trapped beads with 75%and 87.2%efficiency in single-and multiple-seeding events,respectively.These results form the basis for ultrasensitive digital biosensors,specifically,and for the fabrication of medical devices and life science research tools,generally.

Efficient DNA-assisted synthesis of trans-membrane gold nanowires

Whereas electric circuits and surface-based(bio)chemical sensors are mostly constructed in-plane due to ease of manufacturing,3D microscale and nanoscale structures allow denser integration of electronic components and improved mass transport of the analyte to(bio)chemical sensor surfaces.This work reports the first out-of-plane metallic nanowire formation based on stretching of DNA through a porous membrane.We use rolling circle amplification(RCA)to generate long single-stranded DNA concatemers with one end anchored to the surface.The DNA strands are stretched through the pores in the membrane during liquid removal by forced convection.Because the liquid–air interface movement across the membrane occurs in every pore,DNA stretching across the membrane is highly efficient.The stretched DNA molecules are transformed into trans-membrane gold nanowires through gold nanoparticle hybridization and gold enhancement chemistry.A 50 fM oligonucleotide concentration,a value two orders of magnitude lower than previously reported for flat surface-based nanowire formation,was sufficient for nanowire formation.We observed nanowires in up to 2.7% of the membrane pores,leading to an across-membrane electrical conductivity reduction from open circuit to <20Ω.The simple electrical read-out offers a high signal-to-noise ratio and can also be extended for use as a biosensor due to the high specificity and scope for multiplexing offered by RCA.

Off-stoichiometry improves the photostructuring of thiol-enes through diffusion-induced monomer depletion

Thiol–enes are a group of alternating copolymers with highly ordered networks and are used in a wide range of applications.Here,“click”chemistry photostructuring in off-stoichiometric thiol–enes is shown to induce microscale polymeric compositional gradients due to species diffusion between non-illuminated and illuminated regions,creating two narrow zones with distinct compositions on either side of the photomask feature boundary:a densely cross-linked zone in the illuminated region and a zone with an unpolymerized highly off-stoichiometric monomer composition in the non-illuminated region.Using confocal Raman microscopy,it is here explained how species diffusion causes such intricate compositional gradients in the polymer and how offstoichiometry results in improved image transfer accuracy in thiol–ene photostructuring.Furthermore,increasing the functional group off-stoichiometry and decreasing the photomask feature size is shown to amplify the induced gradients,which potentially leads to a new methodology for microstructuring.

Correction to:Efficient DNA-assisted synthesis of trans-membrane gold nanowires

Figure 2 and the descriptive text in the Section“SEM characterization of synthesized nanowires”of the previously published version of this Article were erroneous.The authors would like to replace Fig.2 and section“SEM characterization of synthesized nanowires”with the figure and text below.