We created nanometer-scale transmembrane channels in lipid bilayers using self-assembled DNA-based nanostructures. Scaffolded DNA origami was used to create a stem that penetrates and spans a lipid membrane, and a barrel-shaped cap that adheres to the membrane in part via 26 cholesterol moieties. In single-channel electrophysiological measurements, we find similarities to the response of natural ion channels, such as conductances on the order of 1 nS and channel gating. More pronounced gating was seen for mutations in which a single DNA strand of the stem protruded into the channel. In single-molecule translocation experiments, we highlight one of many potential applications of the synthetic channels, namely as single DNA molecule sensing devices.

Synthetic nanopores have been used to study individual biomolecules in high thoroughput but their performance as sensors does not match biological ion channels. Controlling the translocation times of single-molecule analytes and their non-specific interaction with pore walls remain a challenge. Inspired by the olfactory sensilla of the insect antenna, here we show that coating nanopores with fluid bilayer lipids allows the pore diameters to be fine-tuned in sub-nanometre increments. Incorporation of mobile ligands in the lipid conferred specificity and slowed down the translocation of targeted proteins sufficiently to time-resolve translocation events of individual proteins. The lipid coatings also prevented pores from clogging, eliminated non-specific binding and enabled the translocation of amyloid-beta (Aβ) oligomers and fibrils. Through combined analysis of translocation time, volume, charge, shape and ligand affinity, different proteins were identified.

The motion of peritrichously flagellated bacteria close to surfaces is relevant to understanding the early stages of biofilm formation and of pathogenic infection. This motion differs from the random-walk trajectories of cells in free solution. Individual Escherichia coli cells swim in clockwise, circular trajectories near planar glass surfaces. On a semi-solid agar substrate, cells differentiate into an elongated, hyperflagellated phenotype and migrate cooperatively over the surface, a phenomenon called swarming. We have developed a technique for observing isolated E. coli swarmer cells moving on an agar substrate and confined in shallow, oxidized poly(dimethylsiloxane) (PDMS) microchannels. Here we show that cells in these microchannels preferentially 'drive on the right', swimming preferentially along the right wall of the microchannel (viewed from behind the moving cell, with the agar on the bottom). We propose that when cells are confined between two interfaces--one an agar gel and the second PDMS--they swim closer to the agar surface than to the PDMS surface (and for much longer periods of time), leading to the preferential movement on the right of the microchannel. Thus, the choice of materials guides the motion of cells in microchannels.

Progress towards the integration of technology into living organisms requires electrical power sources that are biocompatible, mechanically flexible, and able to harness the chemical energy available inside biological systems. Conventional batteries were not designed with these criteria in mind. The electric organ of the knifefish Electrophorus electricus (commonly known as the electric eel) is, however, an example of an electrical power source that operates within biological constraints while featuring power characteristics that include peak potential differences of 600 volts and currents of 1 ampere. Here we introduce an electric-eel-inspired power concept that uses gradients of ions between miniature polyacrylamide hydrogel compartments bounded by a repeating sequence of cation- and anion-selective hydrogel membranes. The system uses a scalable stacking or folding geometry that generates 110 volts at open circuit or 27 milliwatts per square metre per gel cell upon simultaneous, self-registered mechanical contact activation of thousands of gel compartments in series while circumventing power dissipation before contact. Unlike typical batteries, these systems are soft, flexible, transparent, and potentially biocompatible. These characteristics suggest that artificial electric organs could be used to power next-generation implant materials such as pacemakers, implantable sensors, or prosthetic devices in hybrids of living and non-living systems.

Biological protein pores and pore-forming peptides can generate a pathway for the flux of ions and other charged or polar molecules across cellular membranes. In nature, these nanopores have diverse and essential functions that range from maintaining cell homeostasis and participating in cell signaling to activating or killing cells. The combination of the nanoscale dimensions and sophisticated – often regulated – functionality of these biological pores make them particularly attractive for the growing field of nanobiotechnology. Applications range from single-molecule sensing to drug delivery and targeted killing of malignant cells. Potential future applications may include the use of nanopores for single strand DNA sequencing and for generating bio-inspired, and possibly, biocompatible visual detection systems and batteries. This article reviews the current state of applications of pore-forming peptides and proteins in nanomedicine, sensing, and nanoelectronics.

This communication describes a small redox fuel cell fabricated using a design that omits the membrane normally used to separate anodic and cathodic compartments. This design exploits the laminar flow 1 that occurs in liquids flowing at low Reynolds number (Re) to eliminate convective mixing of fuels. Two separate streamsone oxidizing and one reducing -flow parallel to one another through the channel, and no membrane is needed to separate these streams (only diffusive exchange occurs across the interface between them). We demonstrate this concept by operating a millimeter-scale redox fuel cell that uses the redox couples V(V)/V(IV) (cathodic compartment) and V(III)/V(II) (anodic compartment) [2][3][4][5] and that presents no added mechanical nor electrical resistance between the two aqueous solutions.Previous work on fuel cells that do not require a membrane has used selective catalysts or enzymes to restrict reactions of oxidant and reductant present in a mixture to the appropriate electrode. [6][7][8][9][10][11] An example from Dyer 6 used a mixture of O 2 and H 2 ; another, by Willner et al., 9,10 was a biofuel cell with enzymes as catalysts. Figure 1 shows a schematic representation of a single cell. We used soft lithography to fabricate a channel with two inlets and one outlet either in poly(dimethylsiloxane) (PDMS) using soft lithography (for thick channels: h ≈ 200 µm) or in SU-8 photoresist using conventional lithography (for thin channels: h ≈ 50 µm); 12,13 details of fabrication are given in the Supporting Information. We used graphite rather than metals as the electrodes to reduce electrolysis of water during the operation of the cell. 14 The vanadium system has two redox couples with a large difference in formal potentials, ∼1.0 V/NHE for V(V)/V(IV) (as VO 2 + /VO 2+ ) and -0.25 V/NHE for V(III)/V(II). 15 We prepared these two redox species by electrolyzing an ∼1 M solution of VOSO 4 in 25% H 2 SO 4 in two half-cells separated by a Nafion membrane. (The concentrations used in the fluidic fuel cell were ∼1 M for both V(V) and V(II), and 10 -3 M for V(III) and V(IV)). When the V(V) and V(II) solutions were flowing at 25 µL s -1 in the channel, the cell generated a maximum open-circuit voltage (i.e., the potential when no net current was flowing) of 1.52 V in a 200-µm thick membraneless structure; it generated 1.59 V in a 50-µm thick system at a flow rate of 0.07 µL s -1 . 16 These voltages are approximately 90% of the experimental value (1.67 V) obtained using two platinum wires separated by a membrane in a twoelectrode configuration. The permeation of O 2 through the PDMS slab is sufficiently slow, as compared to the residence time of the solution in the channel, that it does not affect the open-circuit potential.As the two half-cells of the fuel cell are not physically separated by a membrane, they are defined only by the laminar flow of the two streams of fuel. For two fluids with the same viscosity (the case for our two solutions) and flow rate, the interface between the two miscible aqueous ...

It is difficult to harness the power generated by biological motors to carry out mechanical work in systems outside the cell. Efforts to capture the mechanical energy of nanomotors ex vivo require in vitro reconstitution of motor proteins and, often, protein engineering. This study presents a method for harnessing the power produced by biological motors that uses intact cells. The unicellular, biflagellated algae Chlamydomonas reinhardtii serve as ''microoxen.'' This method uses surface chemistry to attach loads (1-to 6-m-diameter polystyrene beads) to cells, phototaxis to steer swimming cells, and photochemistry to release loads. These motile microorganisms can transport microscale loads (3-m-diameter beads) at velocities of Ϸ100 -200 m⅐sec ؊1 and over distances as large as 20 cm.biological motors ͉ Chlamydomonas ͉ phototaxis ͉ microfluidics ͉ microspheres T his study demonstrates the biological propulsion of microscale loads by the unicellular photosynthetic algae Chlamydomonas reinhardtii (CR). We exploit the chemistry of the algal cell wall to attach single 1-to 6-m polymer beads to CR. Cells with these ''loads'' attached swim at velocities as high as 100-200 m⅐sec Ϫ1 , approximately the velocity of unmodified cells. CR is phototactic and can be guided by using visible light ( Ϸ 500 nm); we have used this phototaxis to control the transport of microscale loads. A photocleavable linker between the surface of the bead and the cell wall allows us to release loads from the surface of the cell photochemically. We have combined these processes to pick up, transport, guide, and drop off beads by using motile cells.There are many examples of nanometer-scale motors in nature. Within the cell, linear motors, including DNA and RNA polymerase, dyneins, kinesins, and myosin, play a critical role in transcription, mitosis, meiosis, muscle contraction, and transporting organelles and synaptic vesicles (1-5). In eukaryotic mitochondria, a rotary motor, ATP synthase, produces ATP by harnessing the flow of protons down an electrochemical proton gradient (6, 7). Outside of the cell, ciliary dyneins drive the beating of eukaryotic flagella and cilia. In bacteria, a complex of Ϸ20 proteins makes up the remarkable rotary motor that powers the motion of flagella (8).Interest in biological motors is based on both their transduction of energy and their small size and hence their possible relevance to micro͞nanotechnology; the remarkable work of Walker, Vale, Kinosita, Hirokawa, Yanagida and others (9-17) has transformed our understanding of molecular motors. One outcome has been the design and fabrication of new synthetic motors composed entirely of biological molecules (18, 19); another outcome has been the integration of components onto recombinant biological motors (20)(21)(22).Here, we use biological motors intact in cells that use flagella (23). An advantage of this strategy over that using isolated and reconstituted motors is its simplicity. It (i) avoids purification and reconstitution of individual motor proteins, (ii) takes...

This paper describes a method to form giant liposomes in solutions of physiologic ionic strength, such as phosphate buffered saline (PBS) or 150 mM KCl. Formation of these cell-sized liposomes proceeded from hybrid films of partially dried agarose and lipids. Hydrating the films of agarose and lipids in aqueous salt solutions resulted in swelling and partial dissolution of the hybrid films and in concomitant rapid formation of giant liposomes in high yield. This method did not require the presence of an electric field or specialized lipids; it generated giant liposomes from pure phosphatidylcholine lipids or from lipid mixtures that contained cholesterol or negatively charged lipids. Hybrid films of agarose and lipids even enabled the formation of giant liposomes in PBS from lipid compositions that are typically problematic for liposome formation, such as pure phosphatidylserine, pure phosphatidylglycerol, and asolectin. This paper discusses biophysical aspects of the formation of giant liposomes from hybrid films of agarose and lipids in comparison to established methods and shows that gentle hydration of hybrid films of agarose and lipids is a simple, rapid, and reproducible procedure to generate giant liposomes of various lipid compositions in solutions of physiologic ionic strength without the need for specialized equipment.