Tunable 2D diffusion of DNA nanostructures on lipid membranes.

DNA nanotechnology facilitates the synthesis of biomimetic models for studying biological systems. This work uses lipid bilayers as platforms for two-dimensional single-particle tracking of the dynamics of DNA nanostructures. Three different DNA origami structures adhere to the membrane through hybridization with cholesterol-modified strands. Their two-dimensional diffusion coefficient is modulated by changing the concentration of monovalent and divalent salts and the number of anchors. In addition, the diffusion coefficient is tuned by targeting cholesterol-modified anchor strands with strand-displacement reactions. We demonstrate a responsive system with changing diffusivity by selectively displacing membrane-bound anchor strands. We also show the programmed release of origami structures from the lipid membranes.

Trends and Innovations in Biosensors for COVID-19 Mass Testing.

Fast and widespread diagnosis is crucial to fighting against the outbreak of COVID-19. This work surveys the landscape of available and emerging biosensor technologies for COVID-19 testing. Molecular diagnostic assays based on quantitative reverse transcription polymerase chain reaction are used in most clinical laboratories. However, the COVID-19 pandemic has overwhelmed testing capacity and motivated the development of fast point-of-care tests and the adoption of isothermal DNA amplification. Antigenic and serological rapid tests based on lateral-flow immunoassays suffer from low sensitivity. Advanced digital systems enhance performance at the expense of speed and the need for large equipment. Emerging technologies, including CRISPR gene-editing tools, benefit from high sensitivity and specificity of molecular diagnostics and the easy use of lateral-flow assays. DNA sequencing and sample pooling strategies are highlighted to bring out the full capacity of the available biosensor technologies and accelerate mass testing.

High-Yield Electrochemical Synthesis of Silver Nanoparticles by Enzyme-Modified Boron-Doped Diamond Electrodes.

We report a novel electrochemical approach for synthesizing colloidal silver in an aqueous phase by a hemoglobin-modified boron-doped diamond electrode. The resulting Ag nanoparticles are within 10 nm in size and highly monodisperse with minimal electrode deposition. We also introduce a method for measuring the yield of synthesized nanoparticles using square-wave voltammetry as an alternative to UV-vis spectroscopy. More than 50% of the transferred electrons contributed directly to the formation of silver nanoparticles. This high yield indicates that such electrochemical synthesis is an efficient one-pot method for producing colloidal silver free of toxic reagents and offers a path toward green metal nanoparticle synthesis in solution. A comparative study using alternative electrodes, modifiers, and surfactants suggests a mechanism for the formation of silver nanoparticles mediated by hemoglobin-modified boron-doped diamond electrodes.

DNA data storage in electrospun and melt-electrowritten composite nucleic acid-polymer fibers.

Incorporating biomolecules as integral parts of computational systems represents a frontier challenge in bio- and nanotechnology. Using DNA to store digital data is an attractive alternative to conventional information technologies due to its high information density and long lifetime. However, developing an adequate DNA storage medium remains a significant challenge in permitting the safe archiving and retrieval of oligonucleotides. This work introduces composite nucleic acid-polymer fibers as matrix materials for digital information-bearing oligonucleotides. We devised a complete workflow for the stable storage of DNA in PEO, PVA, and PCL fibers by employing electrohydrodynamic processes to produce electrospun nanofibers with embedded oligonucleotides. The on-demand retrieval of messages is afforded by non-hazardous chemical treatment and subsequent PCR amplification and DNA sequencing. Finally, we develop a platform for melt-electrowriting of polymer-DNA composites to produce microfiber meshes of programmable patterns and geometries.

Electrokinetic Torque Generation by DNA Nanorobotic Arms Studied via Single-Molecule Fluctuation Analysis.

DNA nanotechnology has enabled the creation of supramolecular machines, whose shape and function are inspired from traditional mechanical engineering as well as from biological examples. As DNA inherently is a highly charged biopolymer, the external application of electric fields provides a versatile, computer-programmable way to control the movement of DNA-based machines. However, the details of the electrohydrodynamic interactions underlying the electrical manipulation of these machines are complex, as the influence of their intrinsic charge, the surrounding cloud of counterions, and the effect of electrokinetic fluid flow have to be taken into account. In this work, we identify the relevant effects involved in this actuation mechanism by determining the electric response of an established DNA-based nanorobotic arm to varying design and operation parameters. Borrowing an approach from single-molecule biophysics, we determined the electrical torque exerted on the nanorobotic arms by analyzing their thermal fluctuations when oriented in an electric field. We analyze the influence of various experimental and design parameters on the "actuatability" of the nanostructures and optimize the generated torque according to these parameters. Our findings give insight into the physical processes involved in the actuation mechanism and provide general guidelines that aid in designing and efficiently operating electrically driven nanorobotic devices made from DNA.

Single DNA Origami Detection by Nanoimpact Electrochemistry.

DNA has emerged as the material of choice for producing supramolecular building blocks of arbitrary geometry from the 'bottom up'. Characterisation of these structures via electron or atomic force microscopy usually requires their surface immobilisation. In this work, we developed a nanoimpact electrochemistry platform to detect DNA self-assembled origami structures in solution, using the intercalator methylene blue as a redox probe. Here, we report the electrochemical detection of single DNA origami collisions at Pt microelectrodes. Our work paves the way towards the characterisation of DNA nanostructures in solution via nanoimpact electrochemistry.

Self-Propulsion Strategies for Artificial Cell-Like Compartments.

Reconstitution of life-like properties in artificial cells is a current research frontier in synthetic biology. Mimicking metabolism, growth, and sensing are active areas of investigation; however, achieving motility and directional taxis are also challenging in the context of artificial cells. To tackle this problem, recent progress has been made that leverages the tools of active matter physics in synthetic biology. This review surveys the most significant achievements in designing motile cell-like compartments. In this context, strategies for self-propulsion are summarized, including, compartmentalization of catalytically active particles, phoretic propulsion of vesicles and emulsion droplet motion driven by Marangoni flows. This work showcases how the realization of motile protocells may impact biomedical engineering while also aiming at answering fundamental questions in locomotion of prebiotic cells.

Self-propulsion of catalytic nanomotors synthesised by seeded growth of asymmetric platinum-gold nanoparticles.

Asymmetric bimetallic nanomotors are synthesised by seeded growth in solution, providing a convenient and high-throughput alternative to the usual top-down lithographic fabrication of self-propelled catalytic nanoparticles. These synthetic nanomotors catalyse H2O2 decomposition and exhibit enhanced diffusion that depends on fuel concentration, consistent with their chemical propulsion.

Observation of nanoimpact events of catalase on diamond ultramicroelectrodes by direct electron transfer.

We report electrochemical detection of single-catalase collisions at diamond ultramicroelectrodes and show the operative mechanism involves direct enzyme-mediated charge transfer between electrode and solution. Hydrogen peroxide increases the collision frequency, which fluorescence correlation spectroscopy diffusion measurements suggest stems from an increase in the diffusion rate as the underlying cause.

Ordering Gold Nanoparticles with DNA Origami Nanoflowers.

Nanostructured materials, including plasmonic metamaterials made from gold and silver nanoparticles, provide access to new materials properties. The assembly of nanoparticles into extended arrays can be controlled through surface functionalization and the use of increasingly sophisticated linkers. We present a versatile way to control the bonding symmetry of gold nanoparticles by wrapping them in flower-shaped DNA origami structures. These "nanoflowers" assemble into two-dimensonal gold nanoparticle lattices with symmetries that can be controlled through auxiliary DNA linker strands. Nanoflower lattices are true composites: interactions between the gold nanoparticles are mediated entirely by DNA, and the DNA origami will fold into its designed form only in the presence of the gold nanoparticles.