Single-molecule DNA logic nanomachines based on origami

Nowadays,it is a truism that chemists,bioengineers and others must be schooled in cell and molecular biology,including knowledge of the cellular,elemental and molecular building blocks of living systems.Inspired by exquisite and efficient biomolecular machines in living cells,such as ATPases that catalyze the decomposition of ATP into ADP and free phosphate ion,researchers representing multiple disciplines are actively engaged in developing artificial nanostructures with well-defined geometry and nanoscale addressability.A successful outcome of these studies could lead to the development and clinical application of smart molecular machines for the drug delivery of theranostics in vivo.

Dual-enzyme-propelled unbounded DNA walking nanomachine for intracellular imaging of lowly expressed microRNA

Despite the progress on the analysis of miRNA either in vitro or in vivo,intracellular imaging of lowly expressed microRNA remains a challenge.Here we develop a novel dual-enzyme-propelled DNA walking nanomachine,which is tailored to accomplish this mission.The nanomachine is constructed with nanoparticles-loaded DNA tracks,on which the targeted miRNA working as a single-foot DNA walker can move autonomously under the catalysis of two cooperative enzymes.Cleavage of the DNA tracks like a "burnt-bridge" mechanism is thereafter triggered,resulting in an amplified fluorescent signal.After the comprehensive study and optimization of the DNA nanomachine,miR-892b,a significantly down-regulated miRNA in breast cancer cells,is selected as a model target.Sensitivity detection in vitro is achieved with a superior detection limit of 4 pM.While being delivered into cells,the DNA nanomachine is available for the imaging of the lowly expressed microRNA,which is totally missing using the conventional fluorescence in situ hybridization (FISH) method.Up-regulation or down-regulation of the miRNA by exogenous regulatory factors can be also well evaluated.This DNA nanomachine provides a competitive approach for the analysis of miRNA,and has the potential to be extended to some other biomolecules.

Fabrication of Periodic Nanostructures Using AFM Tip-Based Nanomachining:Combining Groove and Material Pile-Up Topographies

This paper presents an atomic force microscopy(AFM)tip-based nanomachining method to fabricate periodic nanostructures.This method relies on combining the topography generated by machined grooves with the topography resulting from accumulated pile-up material on the side of these grooves.It is shown that controlling the distance between adjacent and parallel grooves is the key factor in ensuring the quality of the resulting nanostructures.The presented experimental data show that periodic patterns with good quality can be achieved when the feed value between adjacent scratching paths is equal to the width between the two peaks of material pile-up on the sides of a single groove.The quality of the periodicity of the obtained nanostructures is evaluated by applying one-and two-dimensional fast Fourier transform(FFT)algorithms.The ratio of the area of the peak part to the total area in the normalized amplitude–frequency characteristic diagram of the cross-section of the measured AFM image is employed to quantitatively analyze the periodic nanostructures.Finally,the optical effect induced by the use of machined periodic nanostructures for surface colorization is investigated for potential applications in the fields of anti-counterfeiting and metal sensing.

The Effect of Interatomic Potentials on the Molecular Dynamics Simulation of Nanometric Machining

One of the major tasks in a molecular dynamics （MD） simulation is the selection of adequate potential functions, from which forces are derived. If the potentials do not model the behaviour of the atoms correctly, the results produced from the simulation would be useless. Three popular potentials, namely, Lennard-Jones （L J）, Morse, and embedded-atom method （EAM） potentials, were employed to model copper workpiece and diamond tool in nanometric machining. From the simulation results and further analysis, the EAM potential was found to be the most suitable of the three potentials. This is because it best describes the metallic bonding of the copper atoms; it demonstrated the lowest cutting force variation, and the potential energy is most stable for the EAM.

Intermolecular and surface forces in atomic-scale manufacturing

Atomic and close-to-atomic scale manufacturing(ACSM)aims to provide techniques for manufacturing in various fields,such as circuit manufacturing,high energy physics equipment,and medical devices and materials.The realization of atomic scale material manipulation depending on the theoretical system of classical mechanics faces great challenges.Understanding and using intermolecular and surface forces are the basis for better designing of ACSM.Transformation of atoms based on scanning tunneling microscopy or atomic force microscopy(AFM)is an essential process to regulate intermolecular interactions.Self-assemble process is a thermodynamic process involving complex intermolecular forces.The competition of these interaction determines structure assembly and packing geometry.For typical nanomachining processes including AFM nanomachining and chemical mechanical polishing,the coupling of chemistry and stress(tribochemistry)assists in the removal of surface atoms.Furthermore,based on the principle of triboelectrochemistry,we expect a further reduction of the potential barrier,and a potential application in high-efficiency atoms removal and fabricating functional coating.Future fundamental research is proposed for achieving high-efficiency and high-accuracy manufacturing with the aiding of external field.This review highlights the significant contribution of intermolecular and surface forces to ACSM,and may accelerate its progress in the in-depth investigation of fundamentals.

Research on the influence of machining introduced sub-surface defects and residue stress upon the mechanical properties of single crystal copper

Large scale molecular dynamics simulations of nanomachining and stretching of single crystal copper are performed to analyze the machining process’ influence on the material’s mechanical properties. The simulation results show that the machining process will introduce interfacial defects inside the specimen and enhance the compressive stress beneath the surface. Gener- ally speaking, interfacial defects lead to the decrease of the strength limit, while residue compressive stress can enhance the elastic limit and even the strength limit. Various machining parameters are adopted to investigate their influence on the me- chanical behavior of machined specimen. Lower cutting speed and smaller cutting depth lead to less defects and greater residue compressive stress, which brings about better mechanical properties. The elastic limit increases by 36.8% under the cutting depth of 0.73 nm and decreases by 21.1% under the cutting depth of 1.46 nm. The strength limit increases by 7.7% under the cutting speed of 100 m/s and decreases by 28.2% under the cutting speed of 300 m/s.

Tip-Based Nanomachining on Thin Films:A Mini Review

As one of the most widely used nanofabrication methods,the atomic force microscopy(AFM)tip-based nanomachining technique offers important advantages,including nanoscale manipulation accuracy,low maintenance cost,and flexible experimental operation.This technique has been applied to one-,two-,and even three-dimensional nanomachining patterns on thin films made of polymers,metals,and two-dimensional materials.These structures are widely used in the fields of nanooptics,nanoelectronics,data storage,super lubrication,and so forth.Moreover,they are believed to have a wide application in other fields,and their possible industrialization may be realized in the future.In this work,the current state of the research into the use of the AFM tip-based nanomachining method in thin-film machining is presented.First,the state of the structures machined on thin films is reviewed according to the type of thin-film materials(i.e.,polymers,metals,and two-dimensional materials).Second,the related applications of tip-based nanomachining to film machining are presented.Finally,the current situation of this area and its potential development direction are discussed.This review is expected to enrich the understanding of the research status of the use of the tip-based nanomachining method in thin-film machining and ultimately broaden its application.