Efficient concentration of trace analyte with ordered hotspot construction for a robust and sensitive SERS platform

Surface-enhanced Raman scattering(SERS)platform,which enables trace analyte detection,has important application prospects.By structuring/modifying the surface of the SERSsubstrate,analyte in highly diluted solutions can be concentrated into localized active areas for highly sensitive detection.However,subject to the difficulty of the fabrication process,itremains challenging to balance hot-spot construction and the concentration capacity of analyte simultaneously.Therefore,preparing SERS substrates with densely ordered hot spots andefficient concentration capacity is of great significance for highly sensitive detection.Herein,we propose an Ag and fluoroalkyl-modified hierarchical armour substrate(Ag/F-HA),which has a double-layer stacking design to combine analyte concentration with hotspot construction.The microarmour structure is fabricated by femtosecond-laser processing to serve as asuperhydrophobic and low-adhesive surface to concentrate analyte,while the anodic aluminium oxide(AAO)template creates a nanopillar array serving as dense and ordered hot spots.Under the synergistic action of hot spots and analyte concentration,Ag/F-HA achieves a detectionlimit down to 10^(-7)M doxorubicin(DOX)molecules with a RSD of 7.69%.Additionally,Ag/F-HA exhibits excellent robustness to resist external disturbances such as liquid splash or abrasion.Based on our strategy,SERS substrates with directional analyte concentrations are further explored by patterning microcone arrays with defects.This work opens a way to the realistic implementation of SERS in diverse scenarios.

High-performance liquid metal electromagnetic actuator fabricated by femtosecond laser

Small-scale electromagnetic soft actuators are characterized by a fast response and simplecontrol,holding prospects in the field of soft and miniaturized robotics.The use of liquid metal(LM)to replace a rigid conductor inside soft actuators can reduce the rigidity and enhance the actuation performance and robustness.Despite research efforts,challenges persist in the flexible fabrication of LM soft actuators and in the improvement of actuation performance.To address these challenges,we developed a fast and robust electromagnetic soft microplate actuator based on a laser-induced selective adhesion transfer method.Equipped with unprecedentedly thin LM circuit and customized low Young’s modulus silicone rubber(1.03 kPa),our actuator exhibits an excellent deformation angle(265.25?)and actuation bending angular velocity(284.66 rad·s^(-1)).Furthermore,multiple actuators have been combined to build an artificial gripper with a wide range of functionalities.Our actuator presents new possibilities for designing small-scaleartificial machines and supports advancements in ultrafast soft and miniaturized robotics.

Femtosecond laser direct writing of functional stimulus-responsive structures and applications

Diverse natural organisms possess stimulus-responsive structures to adapt to the surrounding environment.Inspired by nature,researchers have developed various smart stimulus-responsive structures with adjustable properties and functions to address the demands of ever-changing application environments that are becoming more intricate.Among many fabrication methods for stimulus-responsive structures,femtosecond laser direct writing(FsLDW)has received increasing attention because of its high precision,simplicity,true three-dimensional machining ability,and wide applicability to almost all materials.This paper systematically outlines state-of-the-art research on stimulus-responsive structures prepared by FsLDW.Based on the introduction of femtosecond laser-matter interaction and mainstream FsLDW-based manufacturing strategies,different stimulating factors that can trigger structural responses of prepared intelligent structures,such as magnetic field,light,temperature,pH,and humidity,are emphatically summarized.Various applications of functional structures with stimuli-responsive dynamic behaviors fabricated by FsLDW,as well as the present obstacles and forthcoming development opportunities,are discussed.

Bioinspired micro/nanostructured surfaces prepared by femtosecond laser direct writing for multi-functional applications

manufacturing of biomimetic micro/nanostructures due to its specific advantages including high precision,simplicity,and compatibility for diverse materials in comparison with other methods(e.g.ion etching,sol-gel process,chemical vapor deposition,template method,and self-assembly).These biomimetic micro/nanostructured surfaces are of significant interest for academic and industrial research due to their wide range of potential applications,including self-cleaning surfaces,oil-water separation,and fog collection.This review presents the inherent relationship between natural organisms,fabrication methods,micro/nanostructures and their potential applications.Thereafter,we throw a list of current fabrication strategies so as to highlight the advantages of FLDW in manufacturing bioinspired microstructured surfaces.Subsequently,we summarize a variety of typical bioinspired designs(e.g.lotus leaf,pitcher plant,rice leaf,butterfly wings,etc)for diverse multifunctional micro/nanostructures through extreme femtosecond laser processing technology.Based on the principle of interfacial chemistry and geometrical optics,we discuss the potential applications of these functional micro/nanostructures and assess the underlying challenges and opportunities in the extreme fabrication of bioinspired micro/nanostructures by FLDW.This review concludes with a follow up and an outlook of femtosecond laser processing in biomimetic domains.

Magnetically responsive manipulation of droplets and bubbles

Droplets and bubbles have a wide range of applications in industry,agriculture,and daily life,and their controllable manipulation is of significant scientific and technological importance.Versatile magnetically responsive manipulation strategies have been developed to achieve precise control over droplets and bubbles.To manipulate nonmagnetic droplets or bubbles with magnetic fields,the presence of magnetic medium is indispensable.Magnetic additives can be added to the surface or interior of droplets and bubbles,allowing for on-demand manipulation by direct magnetic actuation.Alternatively,magnetically responsive elastomer substrates can be used to actuate droplets and bubbles by controlling the deformation of microstructures on the substrates through magnetic stimulation.Another strategy is based on untethered magnetic devices,which enables free mobility,facilitating versatile manipulation of droplets and bubbles in a flexible manner.This paper reviews the advances in magnetically responsive manipulation strategies from the perspective of droplets and bubbles.An overview of the different classes of magnetic medium,along with their respective corresponding droplet/bubble manipulation methods and principles,is first introduced.Then,the applications of droplet/bubble manipulation in biomedicine,microchemistry,and other fields are presented.Finally,the remaining challenges and future opportunities related to regulating droplet/bubble behavior using magnetic fields are discussed.

Rapid fabrication of reconfigurable helical microswimmers with environmentally adaptive locomotion

Artificial helical microswimmers with shape-morphing capacities and adaptive locomotion have great potential for precision medicine and noninvasive surgery.However,current reconfigurable helical microswimmers are hampered by their low-throughput fabrication and limited adaptive locomotion.Here,a rotary holographic processing strategy(a helical femtosecond laser beam)is proposed to produce stimuli-responsive helical microswimmers(<100μm)rapidly(<1 s).This method allows for the easy one-step fabrication of various microswimmers with controllable sizes and diverse bioinspired morphologies,including spirulina-,Escherichia-,sperm-,and Trypanosoma-like shapes.Owing to their shape-morphing capability,the helical microswimmers undergo a dynamic transition between tumbling and corkscrewing motions under a constant rotating magnetic field.By exploiting adaptive locomotion,helical microswimmers can navigate complex terrain and achieve targeted drug delivery.Hence,these microswimmers hold considerable promise for diverse precision treatments and biomedical applications.

Three-dimensional chiral microstructures fabricated by structured optical vortices in isotropic material

Optical vortices,a type of structured beam with helical phase wavefronts and‘doughnut’-shaped intensity distributions,have been used to fabricate chiral structures in metals and spiral patterns in anisotropic polarization-dependent azobenzene polymers.However,in isotropic polymers,the fabricated microstructures are typically confined to non-chiral cylindrical geometry due to the two-dimensional‘doughnut’-shaped intensity profile of the optical vortices.Here we develop a powerful strategy to realize chiral microstructures in isotropic material by coaxial interference of a vortex beam and a plane wave,which produces threedimensional(3D)spiral optical fields.These coaxial interference beams are generated by designing contrivable holograms consisting of an azimuthal phase and an equiphase loaded on a liquid-crystal spatial light modulator.In isotropic polymers,3D chiral microstructures are achieved under illumination using coaxial interference femtosecond laser beams with their chirality controlled by the topological charge.Our further investigation reveals that the spiral lobes and chirality are caused by interfering patterns and helical phase wavefronts,respectively.This technique is simple,stable and easy to perform,and it offers broad applications in optical tweezers,optical communications and fast metamaterial fabrication.

飞秒激光诱导钛表面可控微纳结构用于水下气泡操纵

针对典型金属材料钛,利用自主搭建的飞秒激光振镜扫描加工系统,加工了具有特定形貌特征的多尺度微纳结构.在此基础上对多尺度微纳结构的可逆润湿性及水下气泡操纵特性进行了实验探究,并从微观界面化学的角度阐释了可逆润湿性的调谐机理.研究结果表明:在飞秒激光烧蚀挤压作用下,钛表面诱导的多尺度微纳结构对原始表面的润湿性具有放大效应,固液接触角减小,水下气泡接触角增大;在辅助加热条件下,固液接触角增大,水下气泡接触角同时减小,气泡在表面完全铺展;随后将超疏水表面置于紫外灯下曝光,多尺度微纳结构上的液体接触角又开始减小,并最终实现了超疏水到超亲水性以及水下超亲气到超疏气的可逆调谐.另外,液体接触角与水下气泡接触角的可逆调谐特性呈现相反的变化趋势,这与固液气三相接触线的移动机制密切相关.本文对实现钛表面微纳结构设计与调控,提高具有可逆润湿性的金属表面在水下气泡操纵与收集,以及污水处理等领域的应用都具有重要意义.

Quasi-phase-matching-division multiplexing holography in a three-dimensional nonlinear photonic crystal

Nonlinear holography has recently emerged as a novel tool to reconstruct the encoded information at a new wavelength,which has important applications in optical display and optical encryption.However,this scheme still struggles with low conversion efficiency and ineffective multiplexing.In this work,we demonstrate a quasi-phasematching(QPM)-division multiplexing holography in a three-dimensional(3D)nonlinear photonic crystal(NPC).3D NPC works as a nonlinear hologram,in which multiple images are distributed into different Ewald spheres in reciprocal space.The reciprocal vectors locating in a given Ewald sphere are capable of fulfilling the complete QPM conditions for the high-efficiency reconstruction of the target image at the second-harmonic(SH)wave.One can easily switch the reconstructed SH images by changing the QPM condition.The multiplexing capacity is scalable with the period number of 3D NPC.Our work provides a promising strategy to achieve highly efficient nonlinear multiplexing holography for high-security and high-density storage of optical information.

Efficient full-path optical calculation of scalar and vector diffraction using the Bluestein method

Efficient calculation of the light diffraction in free space is of great significance for tracing electromagnetic field propagation and predicting the performance of optical systems such as microscopy,photolithography,and manipulation.However,existing calculation methods suffer from low computational efficiency and poor flexibility.Here,we present a fast and flexible calculation method for computing scalar and vector diffraction in the corresponding optical regimes using the Bluestein method.The computation time can be substantially reduced to the sub-second level,which is 105 faster than that achieved by the direct integration approach(~hours level)and 102 faster than that achieved by the fast Fourier transform method(~minutes level).The high efficiency facilitates the ultrafast evaluation of light propagation in diverse optical systems.Furthermore,the region of interest and the sampling numbers can be arbitrarily chosen,endowing the proposed method with superior flexibility.Based on these results,full-path calculation of a complex optical system is readily demonstrated and verified by experimental results,laying a foundation for real-time light field analysis for realistic optical implementation such as imaging,laser processing,and optical manipulation.

Dynamic Airy imaging through high_efficiency broadband phase microelements by femtosecond laser direct writing

Manipulating Airy beams to symmetric Airy beams(SABs)with abruptly autofocusing and self accelerating properties has attracted much attention.With such a particular propagation dynamic,SABs may provide great potential in dynamic signal imaging.On the other hand,the generation of SABs by spatial light modulators suffers from the limitations of phase gradient accuracy,low optical efficiency(<40%),and a bulky footprint.Therefore,exploring imaging applications and optimal generation methods of these Airy-type beams deserves further research.Here,based on the coordinate transformation of SAB,an asymmetric Airy beam(AAB)is realized.Symmetric/asymmetric cubic phase microplates(SCPPs/ACPPs)are designed and fabricated for generating SAB/AAB.The SCPP/ACPP demonstrates superior performance:compact construction(60μm × 60μm × 1.1μm),continuous variation of phase,high efficiency(~81%at 532 nm),and broadband operation from 405 to 780 nm.Dynamic imaging under monochromatic and polychromatic lights is realized by the SAB/AAB,indicating various results at different propagation distances with a certain initial signal.Further investigation reveals that the SCPP on a soft substrate maintains its physical dimensions and optical properties unchanged during stretching.Our work enables wide potential applications in integrated optics,beam manipulation,and imaging.

Reply to Comments on “Efficient full-path optical calculation of scalar and vector diffraction using the Bluestein method”

Dear Editor,In ref.we present an efficient full-path optical calculation by using the Bluestein method.A real optical apparatus for laser processing,imaging,or optical tweezing normally involves diverse optical lenses with different physical and numerical apertures(NA).In such applications,the optical path is usually tortuous and long.To assist in the design,evaluation,and alignment of optical instruments,it is advantageous to retrieve the optical field in an arbitrary position along the entire optical path,which is termed the full-path calculation in our paper,with sufficient accuracy and efficiency.In particular,high flexibility is required to accommodate the mismatch between optical apertures of different components in the optical path.We present a fullpath optical calculation method by adopting the Bluestein method to address this realistic demand.

Multilayered skyscraper microchipsfabricated by hybrid “all-in-one”femtosecond laser processing

Multilayered microfluidic channels integrated with functional microcomponents are the general trend of future biochips,which is similar to the history of Si-integrated circuits from the planer to the three-dimensional(3D)configuration,since they offer miniaturization while increasing the integration degree and diversifying the applications in the reaction,catalysis,and cell cultures.In this paper,an optimized hybrid processing technology is proposed to create true multilayered microchips,by which“all-in-one”3D microchips can be fabricated with a successive procedure of 3D glass micromachining by femtosecond-laser-assisted wet etching(FLAE)and the integration of microcomponents into the fabricated microchannels by two-photon polymerization(TPP).To create the multilayered microchannels at different depths in glass substrates(the top layer was embedded at 200μm below the surface,and the underlying layers were constructed with a 200-μm spacing)with high uniformity and quality,the laser power density(13~16.9 TW/cm^(2))was optimized to fabricate different layers.To simultaneously complete the etching of each layer,which is also important to ensure the high uniformity,the control layers(nonlaser exposed regions)were prepared at the upper ends of the longitudinal channels.Solvents with different dyes were used to verify that each layer was isolated from the others.The high-quality integration was ensured by quantitatively investigating the experimental conditions in TPP,including the prebaking time(18~40 h),laser power density(2.52~3.36 TW/cm2)and developing time(0.8~4 h),all of which were optimized for each channel formed at different depths.Finally,the eightlayered microfluidic channels integrated with polymer microstructures were successfully fabricated to demonstrate the unique capability of this hybrid technique.

How the electron-deficient Cp ligand facilitates Rh-catalyzed annulations with alkynes

The mechanism and origin of the Cp^(X) ligand effects on Rh-catalyzed annulations with alkynes were inves-tigated using DFT calculations and the approach of energy decomposition analysis(EDA).The results reveal that the alkyne migratory insertion is the rate-determining step for the reactions with both acetanilide and 2-phenyl-2-propanol substrates.

Origins of regio-and stereoselectivity in Cu-catalyzed alkyne difunctionalization with CO_(2) and organoboranes

The mechanism and origins of regio-and stereoselectivities of Cu-catalyzed alkyne difunctionalization with CO_(2) and trialkyl boranes were computationally investigated.The results show that the vicinal addition to alkyne is disfavored due to the kinetical inertness of the alkyl copper intermediate.The favored geminal addition proceeds through the cationic Cu-mediated stereoselective 1,2-migration pathway.The energy decomposition analysis indicates that theσ)(πPauli repulsion is the dominant factor for controlling the stereoselectivity.