Digital Assembly of Colloidal Particles for Nanoscale Manufacturing

Abhay Kotnala, Yuebing Zheng

From unravelling the most fundamental phenomena to enabling applications that impact our everyday lives, the nanoscale world holds great promise for science, technology, and medicine. However, the extent of its practical realization relies on manufacturing at the nanoscale. Among the various nanomanufacturing approaches being investigated, the bottom‐up approach involving assembly of colloidal nanoparticles as building blocks is promising. Compared to a top‐down lithographic approach, particle assembly exhibits advantages such as smaller feature size, finer control of chemical composition, less defects, lower material wastage, and higher scalability. The capability to assemble colloidal particles one by one or “digitally” has been heavily sought as it mimics the natural method of making matter and enables construction of nanomaterials with sophisticated architectures. An insight into the tools and techniques for digital assembly of particles, including their working mechanisms and demonstrated particle assemblies, is provided. Examples of nanomaterials and nanodevices are presented to demonstrate the strength of digital assembly in nanomanufacturing.

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Emergent Upconversion Sustainable Micro‐Optical Trapping Device

Kuan Bo Lin, Ting Wei Shen, Yen Hsun Su

Ultrathin‐thickness single‐junction Si‐based solar cells can be developed to enhance photoelectric conversion efficiency (PECE) approaching to Shockley–Queisser limit. However, loss of short circuit current is a crucial factor that dramatically affects PECE improvement. Even though many studies have focused on rare reflector architecture for facilitating near‐infrared radiation absorption, PECE is still constraint due to its fabrication cost. Herein, an upconversion sustainable micro‐optical trapping device is reported. Using a systematic procedure, a high upconversion performance core–shell‐nanoparticles (CSNPs) structure is synthesized. Accordingly, silica diatom microporous frustule is a good electromagnetic field localization chamber, upon which CSNPs are embedded through a microassemble synthesis. This emerging device can be support on ultrathin‐thickness single‐junction Si‐based solar cells as a rare absorber with its low preparation cost. In the experiment, CSNPs upconversion optical density by surface plasmon resonance of Au nanoparticle's enhancement can be increased five‐time greater than NaYF4 without SiO2 coating. A finite difference time domain simulation and real color luminescence images in this study are also demonstrated.

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Optical Force Sensing with Cylindrical Microcontainers

Robert Meissner, Neus Oliver, Cornelia Denz

Quantitative force sensing reveals essential information for the study of biological systems. Forces on molecules, cells, and tissues uncover functioning conditions and pathways. To analyze such forces, spherical particles are trapped and controlled inside an optical tweezers (OT) trap. Although these spherical particles are well‐established sensors in biophysics, elongated probes are envisioned for remote force sensing reducing heat damage caused by OT. There is thus a growing demand for force metrology with OT using complexly shaped objects, e.g., sac‐like organelles or rod‐like bacteria. Here, the employment of Zeolite‐L crystals as cylindrical force sensing probes inside a single optical trap is investigated. It is shown that cylindrical objects can be used as force probes since existing calibration assays can be performed with suitable corrections. Forces of active driving assays are compared with passive calibration methods. Finally, the investigations are extended to direct force measurements based on momentum calibration, in which the influence of rotation due to torque in a single optical trap is unveiled. Simulations reveal the relation between torque and the position of equilibrium in the trap. The results highlight the functionality of Zeolite‐L crystals as probes for force sensing, while opening perspectives for enhanced, accurate force metrology in biophotonics.

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Optomechanically Assisted Assembly of Surface‐Functionalized Zeolite‐L‐Based Hybrid Soft Matter

Álvaro Barroso, Tim Buscher, Katrin Ahlers, Armido Studer, Cornelia Denz

Nanoporous particles are particularly interesting for the assembly of functional nano‐ and microsystems because they provide hierarchical supramolecular organization of a large variety of guest molecules. In this work, arbitrary nanoarchitectures consisting of nanoporous zeolite‐L crystals are assembled by combining holographic optical tweezers (HOT) with polymer brush functionalized particles to overcome the limitations of 1D and restricted self‐assembly of zeolite‐L crystals. Readily prepared and functionalized polymer shells allow for controlled, instant, and highly efficient particle–particle and particle–surface adhesion without the need for an external trigger. In contrast to earlier studies, these assemblies remain permanently stable after release out of the HOT system. This novel strategy can be used to fabricate either motile units or locally grounded 1D, 2D, and 3D microconstructions, which can be further utilized as microtools in microfluidic and nanophotonic applications.

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Bioconjugated Core–Shell Microparticles for High‐Force Optical Trapping

Juan Carlos Cordova Dana N. Reinemann Daniel J. Laky William R. Hesse Sophie K. Tushak Zane L. Weltman Kelsea B. Best Rizia Bardhan Matthew J. Lang

Due to their high spatial resolution and precise application of force, optical traps are widely used to study the mechanics of biomolecules and biopolymers at the single‐molecule level. Recently, core–shell particles with optical properties that enhance their trapping ability represent promising candidates for high‐force experiments. To fully harness their properties, methods for functionalizing these particles with biocompatible handles are required. Here, a straightforward synthesis is provided for producing functional titania core–shell microparticles with proteins and nucleic acids by adding a silane–thiol chemical group to the shell surface. These particles display higher trap stiffness compared to conventional plastic beads featured in optical tweezers experiments. These core–shell microparticles are also utilized in biophysical assays such as amyloid fiber pulling and actin rupturing to demonstrate their high‐force applications. It is anticipated that the functionalized core–shells can be used to probe the mechanics of stable proteins structures that are inaccessible using current trapping techniques.

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Self-Propelled Micro/Nanoparticle Motors

Maria Guix, Sonja M. Weiz, Oliver G. Schmidt, Mariana Medina-Sánch

The growing interest in the design and fabrication of novel autonomous micro- and nanoparticles is motivated by the vast advances in their motion efficiency and their further implementation in both biomedical and environmental fields. The present review covers the motion principle and fabrication procedures of synthetic and hybrid particle-like micromotors reported to date to give a comprehensive view of the key design parameters and different approaches for optimal motor guidance. The applications of self-propelled micro- and nanoparticles in different fields are classified accordingly to clarify not only the latest advances but also the current challenges and constraints in the field. This review aims to provide clues to develop more efficient and biocompatible autonomous microparticles in the future, with advanced multitasking and sensing capabilities while being able to perform cooperative work.

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Bioconjugated Core–Shell Microparticles for High-Force Optical Trapping

Juan Carlos Cordova, Dana N. Reinemann, Daniel J. Laky, William R. Hesse, Sophie K. Tushak, Zane L. Weltman, Kelsea B. Best, Rizia Bardhan, Matthew J. Lang

Due to their high spatial resolution and precise application of force, optical traps are widely used to study the mechanics of biomolecules and biopolymers at the single-molecule level. Recently, core–shell particles with optical properties that enhance their trapping ability represent promising candidates for high-force experiments. To fully harness their properties, methods for functionalizing these particles with biocompatible handles are required. Here, a straightforward synthesis is provided for producing functional titania core–shell microparticles with proteins and nucleic acids by adding a silane–thiol chemical group to the shell surface. These particles display higher trap stiffness compared to conventional plastic beads featured in optical tweezers experiments. These core–shell microparticles are also utilized in biophysical assays such as amyloid fiber pulling and actin rupturing to demonstrate their high-force applications. It is anticipated that the functionalized core–shells can be used to probe the mechanics of stable proteins structures that are inaccessible using current trapping techniques.

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Plasmonic Particles with Unique Optical Interaction and Mechanical Motion Properties

Jiafang Li, Jing Liu, Ximin Tian, Zhi-Yuan Li

Metal nanoparticles have unique localized surface plasmon resonance (SPR) properties due to the strong interaction of localized surface plasmon polariton (SPP) with incident light. This review will cover some of our recent theoretical and experimental studies on exploring the unique optical interaction and mechanical motion properties of plasmonic particles that originate from SPR enhanced light-matter interaction. Firstly, the efficient enhancement of both the fluorescence excitation and emission process of dye molecules by the double SPR modes (longitudinal and transverse modes) in gold nanorods, and surface plasmon amplification in metal nanoparticles with gain is discussed. Secondly, it is theoretically demonstrated that two basic physical processes of molecules interacting with light, i.e., the elastic Rayleigh scattering and inelastic Raman scattering, will strongly intertwine and correlate with each other in many plasmonic surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) nanosystems. Thirdly, it is experimentally shown that SPR can enhance the optical force and torque of nanoparticles embedded within non-intrusive optical tweezers. The work presented in this review shows that plasmonic particles can possess unique optical interaction and mechanical motion properties when their geometries are deliberately controlled.

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Optomagnetically Controlled Microparticles Manufactured with Glancing Angle Deposition

Joseph L. Lawson, Nathan J. Jenness and Robert L. Clark

Optical trapping and magnetic trapping are common micromanipulation techniques for controlling colloids including micro- and nanoparticles. Combining these two manipulation strategies allows a larger range of applied forces and decoupled control of rotation and translation; each of which are beneficial properties for many applications including force spectroscopy and advanced manufacturing. However, optical trapping and magnetic trapping have conflicting material requirements inhibiting the combination of these methodologies. In this paper, anisotropic microscaled particles capable of being simultaneously controlled by optical and magnetic trapping are synthesized using a glancing angle deposition (GLAD) technique. The anisotropic alignment of dielectric and ferromagnetic materials limits the optical scattering from the metallic components which typically prevents stable optical trapping in three dimensions. Compared to the current state of the art, the benefits of this approach are twofold. First, the composite structure allows larger volumes of ferromagnetic material so that larger magnetic moments may be applied without inhibiting the stability of optical trapping. Second, the robustness of the synthesis process is greatly improved. The dual optical and magnetic functionality of the synthesized colloids is demonstrated by simultaneously optically translating and magnetically rotating a magnetic GLAD particle using a custom designed optomagnetic trapping system.

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