Directed Self-Assembly Driven Mesoscale Lithography Using Laser-Induced and Manipulated Microbubbles: Complex Architectures and Diverse Applications

Dimension Evolution of Self-Assembled Organic Microcrystal for Laser and Polarization-Rotation Function

Multidimensional integrated micro/nanostructures are vitally important for the implementation of versatile photonic functionalities, whereas current material structures still suffer undesired surface defects and contaminations in either multistep micro/nanofabrications or extreme synthetic conditions. Herein, the dimension evolution of organic self-assembled structures 2D microrings and 3D microhelixes for multidimensional photonic devices is realized via a protic/aprotic solvent-directed molecular assembly method based on a multiaxial confined-assisted growth mechanism. The 2D microrings with consummate circle boundaries and molecular-smooth surfaces function as high-quality whispering-gallery-mode microcavities for dual-wavelength energy-influence-dependent switchable lasing. Moreover, the 3D microhelixes with smooth surfaces and natural twistable characteristics act as active photon-transport materials and polarization rotators. These results will broaden the horizon of constructing multidimensional microstructures for integrated photonic circuits.

Biologically Active Micropatterns of Biomolecules and Living Matter Using Microbubble Lithography

In situ patterning of biomolecules and living organisms while retaining their biological activity is extremely challenging, primarily because such patterning typically involves thermal stresses that could be substantially higher than the physiological thermal or stress tolerance level. Top-down patterning approaches are especially prone to these issues, while bottom-up approaches suffer from a lack of control in developing defined structures and the time required for patterning. A microbubble generated and manipulated by optical tweezers (microbubble lithography) is used to self-assemble and pattern living organisms in continuous microscopic structures in real-time, where the material thus patterned remains biologically active due to their ability to withstand elevated temperatures for short exposures. Successful patterns of microorganisms (Escherichia coli, Lactococcus. lactis and the Type A influenza virus) are demonstrated, as well as reporter proteins such as green fluorescent protein (GFP) on functionalized substrates with high signal-to-noise ratio and selectivity. Together, the data presented herein may open up fascinating possibilities in rapid in situ parallelized diagnostics of multiple pathogens and bioelectronics.

Moving Meniscus-Assisted Template-Free Optothermofluidic Nanoparticle Patterning and Its Application in Optothermoconvective Particle Trapping

Moving meniscus-assisted vertical lifting is a commonly employed particle assembly technique to realize large-area particle patterning for the easy fabrication of colloidal photonic crystals and sensors. Though great success has been achieved for large-area patterning, inscribing desired patterns over the target substrate with precise control over the morphology remains a challenge. The target substrates need to be functionalized (physically or chemically) to realize desired patterns, which increases the complexity and limits their applicability to specific particle-liquid combinations. We demonstrate a new approach for the precise patterning of gold nanoparticles (Au NPs, diameter ∼60 nm) over solid substrates by the synergy of light-induced Marangoni flow and vertical lifting process (moving meniscus), without the requirement of photomasks or templates. The core idea relies on the particle accumulation due to light-induced Marangoni flow near the liquid meniscus in contact with a solid surface (due to plasmonic absorption of the particles) and the controlled lifting of the substrate. We present both the simulation and experimental results of the developed patterning technique. Various patterns such as continuous lines, intermittent lines with varying lengths, patterns with continuously varying widths, cross patterns, etc. are successfully inscribed. Dynamic control over the three-dimensional morphology of the deposited patterns is achieved by varying the lifting velocity, laser irradiation time, and lifting direction during the inscription process. Finally, we show the applicability of the developed plasmonically active surface for the large-area parallel manipulation of nonabsorbing microparticles based on optothermoconvective flow. The major advantage of the developed method compared to the existing light-controlled patterning techniques is its ability to inscribe patterns over large distances (up to several centimeters). We expect that the results presented in this paper will benefit different applications requiring precise particle patterning, such as optical elements, sensors, plasmonic substrates, microfluidic master templates, and electronic circuits.

Bubble Printing of Layered Silicates: Surface Chemistry Effects and Picomolar Förster Resonance Energy Transfer Sensing

The assembly of nanoparticles on surfaces in defined patterns has long been achieved via template-assisted methods that involve long deposition and drying steps and the need for molds or masks to obtain the desired patterns. Control over deposition of materials on surfaces via laser-directed microbubbles is a nascent technique that holds promise for rapid fabrication of devices down to the micrometer scale. However, the influence of surface chemistry on the resulting assembly using such approaches has so far not been studied. Herein, the printing of layered silicate nanoclays using a laser-directed microbubble was established. Significant differences in the macroscale structure of the printed patterns were observed for hydrophilic, pristine layered silicates compared to hydrophobic, modified layered silicates, which provided the first example of how the surface chemistry of such nanoscale objects results in changes in assembly with this approach. Furthermore, the ability of layered silicates to adsorb molecules at the interface was retained, which allowed the fabrication of proof-of-concept sensors based on Förster resonance energy transfer (FRET) from quantum dots embedded in the assemblies to bound dye molecules. The detection limit for Rhodamine 800 sensing via FRET was found to be on the order of 10-12 M, suggesting signal enhancement due to favorable interactions between the dye and nanoclay. This work sets the stage for future advances in the control of hierarchical assembly of nanoparticles by modification of surface chemistry while also demonstrating a quick and versatile approach to achieve ultrasensitive molecular sensors.

Experimental verification of arcsine laws in mesoscopic nonequilibrium systems

A large number of processes in the mesoscopic world occur out of equilibrium, where the time evolution of a system becomes immensely important since it is driven principally by dissipative effects. Nonequilibrium steady states (NESS) represent a crucial category in such systems, where relaxation timescales are comparable to the operational timescales. In this study, we employ a model NESS stochastic system, which is comprised of a colloidal microparticle optically trapped in a viscous fluid, externally driven by a temporally correlated noise, and show that time-integrated observables such as the entropic current, the work done on the system or the work dissipated by it, follow the three Lévy arcsine laws [A. C. Barato et al., Phys. Rev. Lett. 121, 090601 (2018)0031-900710.1103/PhysRevLett.121.090601], in the large time limit. We discover that cumulative distributions converge faster to arcsine distributions when it is near equilibrium and the rate of entropy production is small, because in that case the entropic current has weaker temporal autocorrelation. We study this phenomenon by changing the strength of the added noise as well as by perturbing our system with a flow field produced by a microbubble at close proximity to the trapped particle. We confirm our experimental findings with theoretical simulations of the systems. Our work provides an interesting insight into the NESS statistics of the meso-regime, where stochastic fluctuations play a pivotal role.

Optically Triggered Nanoscale Plasmonic Dynamite

Photons as energy carriers are clean and abundant, which can be conveniently applied for nanoactuation but the response is usually slow with very low energy efficiency/density. Here, we underpin the concept of robust nanoscale plasmonic dynamite by incorporating fullerene (C₆₀). The Au@C₆₀ core-shell nanoparticles can be triggered to explode in nanoscale with synergy of plasmon-enhanced photochemical and photothermal effects. It is suggested that a sensible amount of CO₂ was generated and pressurized in nanometric volume in an extremely short time scale (∼ns), which triggers the nanoexplosion, rendering the ejection of Au NPs at the speed over 300 m/s. The ejection generates extremely large local forces (∼1 μN) with thermomechanical energy efficiency up to ∼30%, which is demonstrated as a powerful nanoengine for controlled mobilization of micro-objects on solid surfaces. Such nanoscale plasmonic dynamite is highly exploitable for different types of nanomachines, which provides a powerful energy source for nanoactuation and nanomigration.

Bubble-pen lithography: Fundamentals and applications: Nanoscience: Special Issue Dedicated to Professor Paul S. Weiss

Developing on-chip functional devices requires reliable fabrication methods with high resolution for miniaturization, desired components for enhanced performance, and high throughput for fast prototyping and mass production. Recently, laser-based bubble-pen lithography (BPL) has been developed to enable sub-micron linewidths, in situ synthesis of custom materials, and on-demand patterning for various functional components and devices. BPL exploits Marangoni convection induced by a laser-controlled microbubble to attract, accumulate, and immobilize particles, ions, and molecules onto different substrates. Recent years have witnessed tremendous progress in theory, engineering, and application of BPL, which motivated us to write this review. First, an overview of experimental demonstrations and theoretical understandings of BPL is presented. Next, we discuss the advantages of BPL and its diverse applications in quantum dot displays, biological and chemical sensing, clinical diagnosis, nanoalloy synthesis, and microrobotics. We conclude this review with our perspective on the challenges and future directions of BPL.

Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly

In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a power source, bubbles can propel microrobots to swim in liquid under low-Reynolds-number conditions. As a manipulation tool, microbubbles can act as the micromanipulators of microrobots, allowing them to operate upon particles, cells, and organisms. As a microrobot, microbubbles can operate and assemble complex microparts in two- or three-dimensional spaces. This review provides a comprehensive overview of bubble applications in microrobotics including propulsion, micromanipulation, and microassembly. First, we introduce the diverse bubble generation and control methods. Then, we review and discuss how bubbles can play a role in microrobotics via three functions: propulsion, manipulation, and assembly. Finally, by highlighting the advantages and current challenges of this progress, we discuss the prospects of microbubbles in microrobotics.

Conductive Materials with Elaborate Micro/Nanostructures for Bioelectronics

Bioelectronics, an emerging field with the mutual penetration of biological systems and electronic sciences, allows the quantitative analysis of complicated biosignals together with the dynamic regulation of fateful biological functions. In this area, the development of conductive materials with elaborate micro/nanostructures has been of great significance to the improvement of high-performance bioelectronic devices. Thus, here, a comprehensive and up-to-date summary of relevant research studies on the fabrication and properties of conductive materials with micro/nanostructures and their promising applications and future opportunities in bioelectronic applications is presented. In addition, a critical analysis of the current opportunities and challenges regarding the future developments of conductive materials with elaborate micro/nanostructures for bioelectronic applications is also presented.

Programmable fabrication of a miniaturized photodetector with thermal stability via femtosecond laser direct writing

With the ever-increasing sophistication of integration of electronic devices, the problem of heat accumulation has become ever more serious. Here, a miniaturized photodetector with thermal stability was fabricated by combining the excellent characteristics of femtosecond laser direct writing (FsLDW) and silicon (Si). The sensing part of the photodetector is a Si microwire composed of Si nanoparticles and the sensing area is only 300 μm². As a result, the photodetector can work stably at a temperature as high as 100°C and the response speed of the photodetector becomes notably faster at high temperatures. Furthermore, an image sensor was successfully fabricated by integrating 16 photodetectors and the image sensor can also work stably at high temperatures. This work demonstrates the potential for application of photodetectors based on Si microwires prepared by FsLDW under harsh conditions.

Optothermal pulling, trapping, and assembly of colloids using nanowire plasmons

Optical excitation of colloids can be harnessed to realize soft matter systems that are out of equilibrium. In this paper, we present our experimental studies on the dynamics of silica colloids in the vicinity of a silver nanowire propagating surface plasmon polaritons (SPPs). Due to the optothermal interaction, the colloids are directionally pulled towards the excitation point of the nanowire. Having reached this point, they are spatio-temporally trapped around the excitation location. By increasing the concentration of colloids in the system, we observe multi-particle assembly around the nanowire. This process is thermophoretically driven and assisted by the SPPs. Furthermore, we find such an assembly to be sensitive to the excitation polarization at the input of the nanowire. Numerically-simulated temperature distribution around an illuminated nanowire corroborates sensitivity to the excitation polarization. Our study will find relevance in exploration of SPP-assisted optothermal pulling, trapping and assembly of colloids, and can serve as a test-bed of plasmon-driven active matter.

Optically Driven Gold Nanoparticles Seed Surface Bubble Nucleation in Plasmonic Suspension

Photothermal surface bubbles play important roles in applications like microfluidics and biosensing, but their formation on transparent substrates immersed in a plasmonic nanoparticle (NP) suspension has an unknown origin. Here, we reveal NPs deposited on the transparent substrate by optical forces are responsible for the nucleation of such photothermal surface bubbles. We show the surface bubble formation is always preceded by the optically driven NPs moving toward and deposited to the surface. Interestingly, such optically driven motion can happen both along and against the photon stream. The laser power density thresholds to form a surface bubble drastically differ depending on if the surface is forward- or backward-facing the light propagation direction. We attributed this to different optical power densities needed to enable optical pulling and pushing of NPs in the suspension, as optical pulling requires higher light intensity to excite supercavitation around NPs to enable proper optical configuration.