Bidirectional Transport of Nanoparticles and Cells with a Bio‐Conveyor Belt

Xiaoshuai Liu, You Wu, Xiaohao Xu, Yuchao Li, Yao Zhang, Baojun Li

The bidirectional transport of nanoparticles and biological cells is of great significance in efficient biological assays and precision cell screening, and can be achieved with optical conveyor belts in a noncontact and noninvasive manner. However, implantation of these belts into biological systems can present significant challenges owing to the incompatibility of the artificial materials. In this work, an optical conveyor belt assembled from natural biological cells is proposed. The diameter of the belt (500 nm) is smaller than the laser wavelength (980 nm) and, therefore, the evanescent wave stably traps the nanoparticles and cells on the belt surface. By adjusting the relative power of the lasers injected into the belt, the particles or cells can be bidirectionally transported along the bio‐conveyor belt. The experimental results are numerically interpreted and the transport velocities are investigated based on simulations. Further experiments show that the bio‐conveyor belt can also be assembled with mammalian cells and then applied to dynamic cell transport in vivo. The bio‐conveyor belt might provide a noninvasive and biocompatible tool for biomedical assays, drug delivery, and biological nanoarchitectonics.

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Single‐Cell Biodetection by Upconverting Microspinners

Elisa Ortiz‐Rivero,  Katarzyna Prorok,  Michal Skowickł,  Dasheng Lu,  Artur Bednarkiewicz,  Daniel Jaque,  Patricia Haro‐González

Near‐infrared‐light‐mediated optical tweezing of individual upconverting particles has enabled all‐optical single‐cell studies, such as intracellular thermal sensing and minimally invasive cytoplasm investigations. Furthermore, the intrinsic optical birefringence of upconverting particles renders them light‐driven luminescent spinners with a yet unexplored potential in biomedicine. In this work, the use of upconverting spinners is showcased for the accurate and specific detection of single‐cell and single‐bacteria attachment events, through real‐time monitoring of the spinners rotation velocity of the spinner. The physical mechanisms linking single‐attachment to the angular deceleration of upconverting spinners are discussed in detail. Concomitantly, the upconversion emission generated by the spinner is harnessed for simultaneous thermal sensing and thermal control during the attachment event. Results here included demonstrate the potential of upconverting particles for the development of fast, high‐sensitivity, and cost‐effective systems for single‐cell biodetection.

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DNA Nanotechnology as an Emerging Tool to Study Mechanotransduction in Living Systems

Victor Pui‐Yan Ma,  Khalid Salaita

The ease of tailoring DNA nanostructures with sub‐nanometer precision has enabled new and exciting in vivo applications in the areas of chemical sensing, imaging, and gene regulation. A new emerging paradigm in the field is that DNA nanostructures can be engineered to study molecular mechanics. This new development has transformed the repertoire of capabilities enabled by DNA to include detection of molecular forces in living cells and elucidating the fundamental mechanisms of mechanotransduction. This Review first describes fundamental aspects of force‐induced melting of DNA hairpins and duplexes. This is then followed by a survey of the currently available force sensing DNA probes and different fluorescence‐based force readout modes. Throughout the Review, applications of these probes in studying immune receptor signaling, including the T cell receptor and B cell receptor, as well as Notch and integrin signaling, are discussed.

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Transformation of the Nonprocessive Fast Skeletal Myosin II into a Processive Motor

Mamta Amrute‐Nayak Arnab Nayak Walter Steffen Georgios Tsiavaliaris Tim Scholz Bernhard Brenner

Myosin family motors play diverse cellular roles. Precise insights into how the light chains contribute to the functional variabilities among myosin motors, however, remain unresolved. Here, it is demonstrated that the fast skeletal muscle myosin II isoform myosin heavy chain (MHC‐IID) can be transformed into a processive motor, by simply replacing the native regulatory light chain MLC2f with the regulatory light chain variant MLC2v from the slow muscle myosin II. Single molecule kinetic analyses and optical trapping measurements of the hybrid motor reveal marked changes such as increased association rate of myosin toward adenosine triphosphate (ATP) and actin by more than twofold. The direct consequence of high adenosine diphosphate (ADP) affinity and increased actin rebinding is the altered overall actomyosin association time during the cross‐bridge cycle. The data indicate that the MLC2v influences the duty ratio in the hybrid motor, suggestive of promoting interhead communication and enabling processive movement. This finding establishes that the regulatory light chain fine‐tunes the motor's mechanical output that may have important implications under physiological conditions. Furthermore, the success of this approach paves the way to engineer motors from a known motor protein element to assemble highly specialized biohybrid machines for potential applications in nano‐biomedicine and engineering.

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Selective Localization of Hierarchically Assembled Particles to Plasma Membranes of Living Cells

Asish C. Misra,  Tae‐Hong Park,  Randy P. Carney,  Giulia Rusciano,  Francesco Stellacci,  Joerg Lahann

Particles that preferentially partition to a specific cellular subunit, such as the nucleus, mitochondria, or the cytoskeleton, are of relevance to a number of applications, including drug delivery, genetic manipulation, or self‐assembly. Here, hierarchical assemblies of fully synthetic particles that selectively localize to the plasma membrane of mammalian cells are presented. A multimodal approach is used to create assemblies of polymer‐based carrier particles with amphiphilic gold nanoparticles immobilized on one hemisphere. These assemblies persist in the plasma membrane of cells for several days and undergo rearrangements and clustering, typically considered to be hallmarks of membrane‐bound receptors.

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Patterned Optoelectronic Tweezers: A New Scheme for Selecting, Moving, and Storing Dielectric Particles and Cells

Shuailong Zhang Nika Shakiba Yujie Chen Yanfeng Zhang Pengfei Tian Jastaranpreet Singh M. Dean Chamberlain Monika Satkauskas Andrew G. Flood Nazir P. Kherani Siyuan Yu Peter W. Zandstra Aaron R. Wheeler
Optical micromanipulation has become popular for a wide range of applications. In this work, a new type of optical micromanipulation platform, patterned optoelectronic tweezers (p‐OET), is introduced. In p‐OET devices, the photoconductive layer (that is continuous in a conventional OET device) is patterned, forming regions in which the electrode layer is locally exposed. It is demonstrated that micropatterns in the photoconductive layer are useful for repelling unwanted particles/cells, and also for keeping selected particles/cells in place after turning off the light source, minimizing light‐induced heating. To clarify the physical mechanism behind these effects, systematic simulations are carried out, which indicate the existence of strong nonuniform electric fields at the boundary of micropatterns. The simulations are consistent with experimental observations, which are explored for a wide variety of geometries and conditions. It is proposed that the new technique may be useful for myriad applications in the rapidly growing area of optical micromanipulation.

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Photothermal Convection Lithography for Rapid and Direct Assembly of Colloidal Plasmonic Nanoparticles on Generic Substrates

Chang Min Jin, Wooju Lee, Dongchoul Kim, Taewook Kang, Inhee Choi

Controlled assembly of colloidal nanoparticles onto solid substrates generally needs to overcome their thermal diffusion in water. For this purpose, several techniques that are based on chemical bonding, capillary interactions with substrate patterning, optical force, and optofluidic heating of light‐absorbing substrates are proposed. However, the direct assembly of colloidal nanoparticles on generic substrates without chemical linkers and substrate patterning still remains challenging. Here, photothermal convection lithography is proposed, which allows the rapid placement of colloidal nanoparticles onto the surface of diverse solid substrates. It is based on local photothermal heating of colloidal nanoparticles by resonant light focusing without substrate heating, which induces convective flow. The convective flow, then, forces the colloidal nanoparticles to assemble at the illumination point of light. The size of the assembly is increased by either increasing the light intensity or illumination time. It is shown that three types of colloidal gold nanoparticles with different shapes (rod, star, and sphere) can be uniformly assembled by the proposed method. Each assembly with a diameter of tens of micrometers can be completed within a minute and its patterned arrays can also be achieved rapidly.

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Impact of Lanthanide Nanomaterials on Photonic Devices and Smart Applications

Jiajia Zhou,  Julius L. Leaño Jr.,  Zhenyu Liu,  Dayong Jin,  Ka‐Leung Wong,  Ru‐Shi Liu, Jean‐Claude G. Bünzli

Half a century after its initial emergence, lanthanide photonics is facing a profound remodeling induced by the upsurge of nanomaterials. Lanthanide‐doped nanomaterials hold promise for bioapplications and photonic devices because they ally the unmatched advantages of lanthanide photophysical properties with those arising from large surface‐to‐volume ratios and quantum confinement that are typical of nanoobjects. Cutting‐edge technologies and devices have recently arisen from this association and are in turn promoting nanophotonic materials as essential tools for a deeper understanding of biological mechanisms and related medical diagnosis and therapy, and as crucial building blocks for next‐generation photonic devices. Here, the recent progress in the development of nanomaterials, nanotechnologies, and nanodevices for clinical uses and commercial exploitation is reviewed. The candidate nanomaterials with mature synthesis protocols and compelling optical uniqueness are surveyed. The specific fields that are directly driven by lanthanide doped nanomaterials are emphasized, spanning from in vivo imaging and theranostics, micro‐/nanoscopic techniques, point‐of‐care medical testing, forensic fingerprints detection, to micro‐LED devices.

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Piconewton-Scale Analysis of Ras-BRaf Signal Transduction with Single-Molecule Force Spectroscopy

Chae-Seok Lim, Cheng Wen, Yanghui Sheng, Guangfu Wang, Zhuan Zhou, Shiqiang Wang, Huaye Zhang, Anpei Ye, J. Julius Zhu

Intermolecular interactions dominate the behavior of signal transduction in various physiological and pathological cell processes, yet assessing these interactions remains a challenging task. Here, this study reports a single-molecule force spectroscopic method that enables functional delineation of two interaction sites (≈35 pN and ≈90 pN) between signaling effectors Ras and BRaf in the canonical mitogen-activated protein kinase (MAPK) pathway. This analysis reveals mutations on BRaf at Q257 and A246, two sites frequently linked to cardio-faciocutaneous syndrome, result in ≈10−30 pN alterations in Ras[BOND]BRaf intermolecular binding force. The magnitude of changes in Ras[BOND]BRaf binding force correlates with the size of alterations in protein affinity and in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-sensitive glutamate receptor (-R)-mediated synaptic transmission in neurons expressing replacement BRaf mutants, and predicts the extent of learning impairments in animals expressing replacement BRaf mutants. These results establish single-molecule force spectroscopy as an effective platform for evaluating the piconewton-level interaction of signaling molecules and predicting the behavior outcome of signal transduction.

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Effective Light Directed Assembly of Building Blocks with Microscale Control

Ngoc-Duy Dinh, Rongcong Luo, Maria Tankeh Asuncion Christine, Weikang Nicholas Lin, Wei-Chuan Shih, James Cho-Hong Goh, Chia-Hung Chen

Light-directed forces have been widely used to pattern micro/nanoscale objects with precise control, forming functional assemblies. However, a substantial laser intensity is required to generate sufficient optical gradient forces to move a small object in a certain direction, causing limited throughput for applications. A high-throughput light-directed assembly is demonstrated as a printing technology by introducing gold nanorods to induce thermal convection flows that move microparticles (diameter = 40 µm to several hundreds of micrometers) to specific light-guided locations, forming desired patterns. With the advantage of effective light-directed assembly, the microfluidic-fabricated monodispersed biocompatible microparticles are used as building blocks to construct a structured assembly (≈10 cm scale) in ≈2 min. The control with microscale precision is approached by changing the size of the laser light spot. After crosslinking assembly of building blocks, a novel soft material with wanted pattern is approached. To demonstrate its application, the mesenchymal stem-cell-seeded hydrogel microparticles are prepared as functional building blocks to construct scaffold-free tissues with desired structures. This light-directed fabrication method can be applied to integrate different building units, enabling the bottom-up formation of materials with precise control over their internal structure for bioprinting, tissue engineering, and advanced manufacturing.

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Targeted Nanoparticle Thermometry: A Method to Measure Local Temperature at the Nanoscale Point Where Water Vapor Nucleation Occurs

Arwa A. Alaulamie, Susil Baral, Samuel C. Johnson, Hugh H. Richardson

An optical nanothermometer technique based on laser trapping, moving and targeted attaching an erbium oxide nanoparticle cluster is developed to measure the local temperature. The authors apply this new nanoscale temperature measuring technique (limited by the size of the nanoparticles) to measure the temperature of vapor nucleation in water. Vapor nucleation is observed after superheating water above the boiling point for degassed and nondegassed water. The average nucleation temperature for water without gas is 560 K but this temperature is lowered by 100 K when gas is introduced into the water. The authors are able to measure the temperature inside the bubble during bubble formation and find that the temperature inside the bubble spikes to over 1000 K because the heat source (optically-heated nanorods) is no longer connected to liquid water and heat dissipation is greatly reduced.

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Single Upconversion Nanoparticle–Bacterium Cotrapping for Single-Bacterium Labeling and Analysis

Hongbao Xin, Yuchao Li, Dekang Xu, Yueli Zhang, Chia-Hung Chen, Baojun Li

Detecting and analyzing pathogenic bacteria in an effective and reliable manner is crucial for the diagnosis of acute bacterial infection and initial antibiotic therapy. However, the precise labeling and analysis of bacteria at the single-bacterium level are a technical challenge but very important to reveal important details about the heterogeneity of cells and responds to environment. This study demonstrates an optical strategy for single-bacterium labeling and analysis by the cotrapping of single upconversion nanoparticles (UCNPs) and bacteria together. A single UCNP with an average size of ≈120 nm is first optically trapped. Both ends of a single bacterium are then trapped and labeled with single UCNPs emitting green light. The labeled bacterium can be flexibly moved to designated locations for further analysis. Signals from bacteria of different sizes are detected in real time for single-bacterium analysis. This cotrapping method provides a new approach for single-pathogenic-bacterium labeling, detection, and real-time analysis at the single-particle and single-bacterium level.

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Multibuilding Block Janus Synthesized by Seed-Mediated Self-Assembly for Enhanced Photothermal Effects and Colored Brownian Motion in an Optical Trap

Kanokwan Sansanaphongpricha, Michael C. DeSantis, Hongwei Chen, Wei Cheng, Kai Sun, Bo Wen, Duxin Sun

The asymmetrical features and unique properties of multibuilding block Janus nanostructures (JNSs) provide superior functions for biomedical applications. However, their production process is very challenging. This problem has hampered the progress of JNS research and the exploration of their applications. In this study, an asymmetrical multibuilding block gold/iron oxide JNS has been generated to enhance photothermal effects and display colored Brownian motion in an optical trap. JNS is formed by seed-mediated self-assembly of nanoparticle-loaded thermocleavable micelles, where the hydrophobic backbones of the polymer are disrupted at high temperatures, resulting in secondary self-assembly and structural rearrangement. The JNS significantly enhances photothermal effects compared to their homogeneous counterpart after near-infrared (NIR) light irradiation. The asymmetrical distribution of gold and iron oxide within JNS also generates uneven thermophoretic force to display active colored Brownian rotational motion in a single-beam gradient optical trap. These properties indicate that the asymmetrical JNS could be employed as a strong photothermal therapy mediator and a fuel-free nanoscale Janus motor under NIR light.

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Combined Optical and Chemical Control of a Microsized Photofueled Janus Particle

Sabrina Simoncelli, Johannes Summer, Spas Nedev, Paul Kühler, Jochen Feldmann

A Au–silica Janus particle is elevated along the laser beam axis in an optical trap. The propulsion mechanism is based on the local temperature gradient created around the particle due to the photothermal conversion of the gold-coated hemisphere. The height of the particle and its motion-direction are tuned by the nature and the concentration of the electrolytes in the medium.

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Plasmofluidics: Merging Light and Fluids at the Micro-/Nanoscale

Mingsong Wang, Chenglong Zhao, Xiaoyu Miao, Yanhui Zhao, Joseph Rufo, Yan Jun Liu, Tony Jun Huang and Yuebing Zheng

Plasmofluidics is the synergistic integration of plasmonics and micro/nanofluidics in devices and applications in order to enhance performance. There has been significant progress in the emerging field of plasmofluidics in recent years. By utilizing the capability of plasmonics to manipulate light at the nanoscale, combined with the unique optical properties of fluids and precise manipulation via micro/nanofluidics, plasmofluidic technologies enable innovations in lab-on-a-chip systems, reconfigurable photonic devices, optical sensing, imaging, and spectroscopy. In this review article, the most recent advances in plasmofluidics are examined and categorized into plasmon-enhanced functionalities in microfluidics and microfluidics-enhanced plasmonic devices. The former focuses on plasmonic manipulations of fluids, bubbles, particles, biological cells, and molecules at the micro/nanoscale. The latter includes technological advances that apply microfluidic principles to enable reconfigurable plasmonic devices and performance-enhanced plasmonic sensors. The article is concluded with perspectives on the upcoming challenges, opportunities, and possible future directions of the emerging field of plasmofluidics.

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Recent Progress on Man-Made Inorganic Nanomachines

Kwanoh Kim, Jianhe Guo, Xiaobin Xu and D. L. Fan

The successful development of nanoscale machinery, which can operate with high controllability, high precision, long lifetimes, and tunable driving powers, is pivotal for the realization of future intelligent nanorobots, nanofactories, and advanced biomedical devices. However, the development of nanomachines remains one of the most difficult research areas, largely due to the grand challenges in fabrication of devices with complex components and actuation with desired efficiency, precision, lifetime, and/or environmental friendliness. In this work, the cutting-edge efforts toward fabricating and actuating various types of nanomachines and their applications are reviewed, with a special focus on nanomotors made from inorganic nanoscale building blocks, which are introduced according to the employed actuation mechanism. The unique characteristics and obstacles for each type of nanomachine are discussed, and perspectives and challenges of this exciting field are presented.

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Microfluidic Single-Cell Analysis with Affinity Beads

Michael Werner, Raghavendra Palankar, Loïc Arm, Ruud Hovius and Horst Vogel

To investigate functional heterogeneity between individuals in a cell population, affinity beads are transferred into living mammalian cells by H. Vogel and co-workers. On page 2607, beads coated with specific capture agents efficiently bind and up-concentrate cytosolic target proteins on their surface. For single-cell analysis, an optically trapped bead with bound target proteins is extracted from its host cell in a microfluidic device. Compared to classical chemical cytometry, this method has the potential to reach high analytical sensitivity and throughput for single-cell analysis in many biomedical fields.

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Enhancing Optical Forces on Fluorescent Up-Converting Nanoparticles by Surface Charge Tailoring

Héctor Rodríguez-Rodríguez, Paloma Rodríguez Sevilla, Emma Martín Rodríguez, Dirk H. Ortgies, Marco Pedroni, Adolfo Speghini, Marco Bettinelli, Daniel Jaque and Patricia Haro-González

3D remote control of multifunctional fluorescent up-converting nanoparticles (UCNPs) using optical forces is being required for a great variety of applications including single-particle spectroscopy, single-particle intracellular sensing, controlled and selective light-activated drug delivery and light control at the nanoscale. Most of these potential applications find a serious limitation in the reduced value of optical forces (tens of fN) acting on these nanoparticles, due to their reduced dimensions (typically around 10 nm). In this work, this limitation is faced and it is demonstrated that the magnitude of optical forces acting on UCNPs can be enhanced by more than one order of magnitude by a controlled modification of the particle/medium interface. In particular, substitution of cationic species at the surface by other species with higher mobility could lead to UCNPs trapping with constants comparable to those of spherical metallic nanoparticles.

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Laser Heating Tunability by Off-Resonant Irradiation of Gold Nanoparticles

Silvia Hormeño, Paula Gregorio-Godoy, Jorge Pérez-Juste, Luis M. Liz-Marzán, Beatriz H. Juárez, J. Ricardo Arias-Gonzalez
Temperature changes in the vicinity of a single absorptive nanostructure caused by local heating have strong implications in technologies such as integrated electronics or biomedicine. Herein, the temperature changes in the vicinity of a single optically trapped spherical Au nanoparticle encapsulated in a thermo-responsive poly(N-isopropylacrylamide) shell (Au@pNIPAM) are studied in detail. Individual beads are trapped in a counter-propagating optical tweezers setup at various laser powers, which allows the overall particle size to be tuned through the phase transition of the thermo-responsive shell. The experimentally obtained sizes measured at different irradiation powers are compared with average size values obtained by dynamic light scattering (DLS) from an ensemble of beads at different temperatures. The size range and the tendency to shrink upon increasing the laser power in the optical trap or by increasing the temperature for DLS agree with reasonable accuracy for both approaches. Discrepancies are evaluated by means of simple models accounting for variations in the thermal conductivity of the polymer, the viscosity of the aqueous solution and the absorption cross section of the coated Au nanoparticle. These results show that these parameters must be taken into account when considering local laser heating experiments in aqueous solution at the nanoscale. Analysis of the stability of the Au@pNIPAM particles in the trap is also theoretically carried out for different particle sizes.
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Quantum Dot-Based Thermal Spectroscopy and Imaging of Optically Trapped Microspheres and Single Cells

Patricia Haro-González, William T. Ramsay, Laura Martinez Maestro, Blanca del Rosal, Karla Santacruz-Gomez, Maria del Carmen Iglesias-de la Cruz, Francisco Sanz-Rodríguez, Jing Yuang Choo, Paloma Rodriguez Sevilla, Marco Bettinelli, Debaditya Choudhury, Ajoy K. Kar, José García Solé, Daniel Jaque, Lynn Paterson

Laser-induced thermal effects in optically trapped microspheres and single cells are investigated by quantum dot luminescence thermometry. Thermal spectroscopy has revealed a non-localized temperature distribution around the trap that extends over tens of micrometers, in agreement with previous theoretical models besides identifying water absorption as the most important heating source. The experimental results of thermal loading at a variety of wavelengths reveal that an optimum trapping wavelength exists for biological applications close to 820 nm. This is corroborated by a simultaneous analysis of the spectral dependence of cellular heating and damage in human lymphocytes during optical trapping. This quantum dot luminescence thermometry demonstrates that optical trapping with 820 nm laser radiation produces minimum intracellular heating, well below the cytotoxic level (43 °C), thus, avoiding cell damage.

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