Nanomechanics of the formation of DNA self-assembled monolayers and hybridization on microcantilevers

Biomolecular interactions over the surface of a microcantilever can produce its bending motion via changes of the surface stress, which is referred to nanomechanical response. Here, we have studied the interaction forces responsible for the bending motion during the formation of a self-assembled monolayer of thiolated 27-mer single-stranded DNA on the gold-coated side of a microcantilever and during the subsequent hybridization with the complementary nucleic acid. The immobilization of the single-stranded DNA probe gives a mean surface stress of 25 mN/m and a mean bending of 23 nm for microcantilevers with a length and thickness of about 200 microm and 0.8 microm, respectively. The hybridization with the complementary sequence could not be inferred from the nanomechanical response. The nanomechanical response was compared with data from well-established techniques such as surface plasmon resonance and radiolabeling, to determine the surface coverage and study the intermolecular forces between neighboring DNA molecules anchored to the microcantilever surface. From both techniques, an immobilization surface density of 3 x 10(12) molecules/cm(2) and a hybridization efficiency of 40% were determined. More importantly, label-free hybridization was clearly detected in the same conditions with a conventional sensor based on surface plasmon resonance. The results imply that the nanomechanical signal during the immobilization process arises mainly from the covalent attachment to the gold surface, and the interchain interactions between neighboring DNA molecules are weak, producing an undetectable surface stress. We conclude that detection of nucleic acid hybridization with nanomechanical sensors requires reference cantilevers to remove nonspecific signals, more sensitive microcantilever geometries, and immobilization chemistries specially addressed to enhance the surface stress variations.     

Site-specific DNA-programmed growth of fluorescent and functional silver nanoclusters

Precise organization of metallic nanoclusters on DNA scaffolds holds great interest for nanopatterned materials that may find uses in electronics, sensors, medicine, and many other fields. Herein, we report the site-specific growth of fluorescent silver nanoclusters by using a mismatched double-stranded DNA template. Few-atom, molecular-scale Ag clusters are found to localize at the mismatched site and the metallized DNA retains its integrity. The DNA-encapsulated nanoclusters can be utilized as functional biological probes to identify single-nucleotide polymorphisms by taking advantage of the very bright fluorescence and excellent photostability of the nanoclusters. This approach offers the possibility of constructing novel DNA-based nanomaterials and nanomechanical devices with more sophisticated functions and will be highly beneficial in future biochemical, pharmaceutical, nanomechanical, and electronic applications.     

Monitoring the hydration of DNA self-assembled monolayers using an extensional nanomechanical resonator

We have fabricated an ultrasensitive nanomechanical resonator based on the extensional vibration mode to weigh the adsorbed water on self-assembled monolayers of DNA as a function of the relative humidity. The water adsorption isotherms provide the number of adsorbed water molecules per nucleotide for monolayers of single stranded (ss) DNA and after hybridization with the complementary DNA strand. Our results differ from previous data obtained with bulk samples, showing the genuine behavior of these self-assembled monolayers. The hybridization cannot be inferred from the water adsorption isotherms due to the low hybridization efficiency of these highly packed monolayers. Strikingly, we efficiently detect the hybridization by measuring the thermal desorption of water at constant relativity humidity. This finding adds a new nanomechanical tool for developing a label-free nucleic acid sensor based on the interaction between water and self-assembled monolayers of nucleic acids.     

连续流动式聚合酶链式反应生物芯片/微装置中脱氧核糖核酸样品的驱动控制技术进展

介绍国内外连续流动式聚合酶链式反应生物芯片／微装置中脱氧核糖核酸样品的驱碧控制技术进展，主要包括恒流泵（注射泵驱动和蠕动泵驱动）、旋转泵驱动、磁流体动力驱动以及自然对流驱动等。并对这几种驱动方式的优缺点作简要的讨论（引用文献43篇）。     

Wireless Coupling of Conducting Polymer Actuators with Light Emission

Combining the actuation of conducting polymers with additional functionalities is an interesting fundamental scientific challenge and increases their application potential. Herein we demonstrate the possibility of direct integration of a miniaturized light emitting diode (LED) in a polypyrrole (PPy) matrix in order to achieve simultaneous wireless actuation and light emission. A light emitting diode is used as a part of an electroactive surface on which electrochemical polymerization allows direct incorporation of the electronic device into the polymer. The resulting free-standing polymer/LED hybrid can be addressed by bipolar electrochemistry to trigger simultaneously oxidation and reduction reactions at its opposite extremities, leading to a controlled deformation and an electron flow through the integrated LED. Such a dual response in the form of actuation and light emission opens up interesting perspectives in the field of microrobotics.     

Large Deformation of a DNA‐Origami Nanoarm Induced by the Cumulative Actuation of Tension‐Adjustable Modules

Making use of the programmability and structural flexibility of the DNA molecule, a DNA‐origami nanoarm capable of undergoing large deformation is constructed. This DNA‐origami nanoarm comprised serially repeated tension‐adjustable modules, the cumulative actuation of which resulted in a large deformation of the arm structure, which transformed from a linear shape into an arched shape. Combining atomic force microscopy and theoretical analyses based on the mechanics of materials, we demonstrate that the degree of deformation can be systematically controlled by merely replacing a set of strands that is required for the actuation of the module. Moreover, by employing a G‐quadruplex‐forming sequence for the actuation, we could achieve reversible ion‐induced contraction and relaxation of the nanoarm. The adjustability and scalability of this design could enable the production of DNA nanodevices that exhibit large deformation in response to external stimuli.     

An Autonomously Reciprocating Transmembrane Nanoactuator

Biological molecular machines operate far from equilibrium by coupling chemical potential to repeated cycles of dissipative nanomechanical motion. This principle has been exploited in supramolecular systems that exhibit true machine behavior in solution and on surfaces. However, designed membrane‐spanning assemblies developed to date have been limited to simple switches or stochastic shuttles, and true machine behavior has remained elusive. Herein, we present a transmembrane nanoactuator that turns over chemical fuel to drive autonomous reciprocating (back‐and‐forth) nanomechanical motion. Ratcheted reciprocating motion of a DNA/PEG copolymer threaded through a single α‐hemolysin pore was induced by a combination of DNA strand displacement processes and enzyme‐catalyzed reactions. Ion‐current recordings revealed saw‐tooth patterns, indicating that the assemblies operated in autonomous, asymmetric cycles of conformational change at rates of up to one cycle per minute.     

Photoactuation from a carbon nanotube-nafion bilayer composite

A bilayer composite of single walled carbon nanotubes (SWNTs) deposited onto Nafion exhibits substantial mechanical motion upon exposure to visible or near-infrared light. The magnitude of the actuation parallels the absorption spectrum of the SWNTs in the near-infrared, but the actuation diminishes in the visible and disappears in the UV portions of the spectrum. In the near-infrared region, the photoactuation is linear with respect to the light intensity. The photoactuation also appears to be associated with a photocurrent across the nanotube/Nafion interface. The proposed mechanism for the actuation is that band bending of the semiconducting SWNTs induces polarization of mobile hydrogen ions at the Nafion interface, which then causes swelling of the polymer.     

Control of the length of microfibers

Uniform polymeric microfibers of prescribed lengths were synthesized in microfluidic devices using two different approaches--valve actuation and pulses of ultraviolet (UV) light. The more versatile valve approach was employed to demonstrate control of the length of the microfiber as a function of the frequency of valve actuation.     

DNA: beyond the double helix

Reciprocal exchange can be used to produce DNA motifs based on branching at the level of secondary structure. These motifs can be combined by sticky-ended cohesion to produce a variety of structures. Stick polyhedra and nanomechanical devices have been produced by self-assembly from motifs based on branched DNA. Periodic arrays with tunable surface features has also been produced; aperiodic arrangements have been used for DNA-based computation.     

Selective Decrosslinking in Liquid Crystal Polymer Actuators for Optical Reconfiguration of Origami and Light‐Fueled Locomotion

The ability to optically reconfigure an existing actuator of a liquid crystal polymer network (LCN) so that it can display a new actuation behavior or function is highly desired in developing materials for soft robotics applications. Demonstrated here is a powerful approach relying on selective polymer chain decrosslinking in a LCN actuator with uniaxial LC alignment. Using an anthracene‐containing LCN, spatially controlled optical decrosslinking can be realized through photocleavage of anthracene dimers under 254 nm UV light, which alters the distribution of actuation (crosslinked) and non‐actuation (decrosslinked) domains and thus determines the actuation behavior upon order‐disorder phase transitions. Based on this mechanism, a single actuator having a flat shape can be reconfigured in an on‐demand manner to exhibit reversible shape transformation such as self‐folding into origami three‐dimensional structures. Moreover, using a dye‐doped LCN actuator, a light‐fueled microwalker can be optically reconfigured to adopt different locomotion behaviors, changing from moving in the laser scanning direction to moving in the opposite direction.     

Large Deformation of a DNA-Origami Nanoarm Induced by the Cumulative Actuation of Tension-Adjustable Modules

Making use of the programmability and structural flexibility of the DNA molecule, a DNA-origami nanoarm capable of undergoing large deformation is constructed. This DNA-origami nanoarm comprised serially repeated tension-adjustable modules, the cumulative actuation of which resulted in a large deformation of the arm structure, which transformed from a linear shape into an arched shape. Combining atomic force microscopy and theoretical analyses based on the mechanics of materials, we demonstrate that the degree of deformation can be systematically controlled by merely replacing a set of strands that is required for the actuation of the module. Moreover, by employing a G-quadruplex-forming sequence for the actuation, we could achieve reversible ion-induced contraction and relaxation of the nanoarm. The adjustability and scalability of this design could enable the production of DNA nanodevices that exhibit large deformation in response to external stimuli.     

电机械聚合物人工肌肉材料的研究进展

模拟肌肉组织进行信息传递、能量转换、传动的人工肌肉驱动器成为新材料研发焦点。智能聚合物可以对外界刺激发生响应,产生形变,是制备人工肌肉的良好材料,已被广泛地用于机器人与智能机械系统,成为众多肌肉驱动器中的研究重点。本文主要总结电机械聚合物人工肌肉材料的研究进展,论述了静电作用、电热驱动、水/湿度驱动三种驱动方式的工作机理和研究进展,分析了聚合物人工肌肉材料驱动器发展过程中受到限制的关键因素,并对未来人工肌肉材料研究提出展望。     

Nucleic Acid Nanostructures and Topology

Knots, polyhedra, and Borromean rings with specific structural and topological features can be made from DNA. Biotechnologists have been exploiting the programmability of DNA intermolecular associations for a quarter of a century. These operations have now been applied successfully to branched DNA species to produce complex target structures (for example, the cube shown in the picture) and a nanomechanical device. The assembly of two-dimensional crystals with programmed topographic characteristics demonstrates the simplicity of translating design into surface structures.     

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

Arbitrary shape (re)programming is appealing for fabricating untethered shape‐morphing photo‐actuators with intricate configurations and features. We present re‐programmable light‐responsive thermoplastic actuators with arbitrary initial shapes through spray‐coating of polyethylene terephthalate (PET) with an azobenzene‐doped light‐responsive liquid crystal network (LCN). The initial geometry of the actuator is controlled by thermally shaping and fixing the thermoplastic PET, allowing arbitrary shapes, including origami‐like folds and left‐ and right‐handed helicity within a single sample. The thermally fixed geometries can be reversibly actuated through light exposure, with fast, reversible area‐specific actuation such as winding, unwinding and unfolding. By shape re‐programming, the same sample can be re‐designed and light‐actuated again. The strategy presented here demonstrates easy fabrication of mechanically robust, recyclable, photo‐responsive actuators with highly tuneable geometries and actuation modes.     

At the crossroads of chemistry, biology, and materials: structural DNA nanotechnology

Structural DNA nanotechnology consists of combining unusual DNA motifs by specific structurally well-defined cohesive interactions (primarily sticky ends) to produce target materials with predictable 3D structures. This effort has generated DNA polyhedral catenanes, robust nanomechanical devices, and a variety of periodic arrays in two dimensions. The system has been used to produce specific patterns on the mesoscale through designing and combining specific DNA strands, which are then examined by atomic force microscopy. The combination of these constructions with other chemical components is expected to contribute to the development of nanoelectronics, nanorobotics, and smart materials. The organizational capabilities of structural DNA nanotechnology are just beginning to be explored, and the field is expected ultimately to be able to organize a variety of species that will lead to exciting and possibly revolutionary materials.     

Localised Actuation in Composites Containing Carbon Nanotubes and Liquid Crystalline Elastomers

A liquid crystalline elastomer–carbon nanotube (LCE‐CNT) composite displays a reversible shape change property in response to light. The development of some systems such as tactile devices requires localised actuation of this material. A method is reported that combines mechanical stretching and thermal crosslinking of an LCE‐CNT for creating sufficiently well‐aligned liquid crystal units to produce localised actuation. The method demonstrates that it is feasible to optically drive a LCE‐CNT film within a localised area, since only the walls of the stretched parts of the film contain aligned LC domains.     

Near-Infrared Light Triggered-Release in Deep Brain Regions Using Ultra-photosensitive Nanovesicles

Remote and minimally-invasive modulation of biological systems with light has transformed modern biology and neuroscience. However, light absorption and scattering significantly prevents penetration to deep brain regions. Herein, we describe the use of gold-coated mechanoresponsive nanovesicles, which consist of liposomes made from the artificial phospholipid Rad-PC-Rad as a tool for the delivery of bioactive molecules into brain tissue. Near-infrared picosecond laser pulses activated the gold-coating on the surface of nanovesicles, creating nanomechanical stress and leading to near-complete vesicle cargo release in sub-seconds. Compared to natural phospholipid liposomes, the photo-release was possible at 40 times lower laser energy. This high photosensitivity enables photorelease of molecules down to a depth of 4 mm in mouse brain. This promising tool provides a versatile platform to optically release functional molecules to modulate brain circuits.     

Protein-Controlled Actuation of Dynamic Nucleic Acid Networks by Using Synthetic DNA Translators**

Integrating dynamic DNA nanotechnology with protein-controlled actuation will expand our ability to process molecular information. We have developed a strategy to actuate strand displacement reactions using DNA-binding proteins by engineering synthetic DNA translators that convert specific protein-binding events into trigger inputs through a programmed conformational change. We have constructed synthetic DNA networks responsive to two different DNA-binding proteins, TATA-binding protein and Myc-Max, and demonstrated multi-input activation of strand displacement reactions. We achieved protein-controlled regulation of a synthetic RNA and of an enzyme through artificial DNA-based communication, showing the potential of our molecular system in performing further programmable tasks.     

Hydrophobic Actuation of a DNA Origami Bilayer Structure

Amphiphilic compounds have a strong tendency to form aggregates in aqueous solutions. It is shown that such aggregation can be utilized to fold cholesterol‐modified, single‐layered DNA origami structures into sandwich‐like bilayer structures, which hide the cholesterol modifications in their interior. The DNA bilayer structures unfold after addition of the surfactant Tween 80, and also in the presence of lipid bilayer membranes, with opening kinetics well described by stretched exponentials. It is also demonstrated that by combination with an appropriate lock and key mechanism, hydrophobic actuation of DNA sandwiches can be made conditional on the presence of an additional molecular input such as a specific DNA sequence.