Controllable Cellular Micromotors Based on Optical Tweezers

Xiaobin Zou, Qing Zheng, Dong Wu, Hongxiang Lei

Micromotors hold exciting prospects in biomedical applications but still face a great challenge. To date, there have been few reports of micromotors with high safety, flexible controllability, and full biocompatibility. Here, a multifunctional method based on an optical tweezer system is presented to realize controllable cellular micromotors. The method not only satisfies all of the above criteria but is also independent of the cell types and materials. Optical tweezers are used to generate a dynamic scanning optical trap along a given circular trajectory, which can trap and drive a microparticle or a single cell to move along the trajectory and thus generate a microvortex. Cells within the microvortex will be controllably rotated under an action of shear stress or torque and their rotation rate and direction can be controlled by changing the scanning frequency and direction of the dynamic optical trap. The proposed method is effective for both immotile target cells and swimming target cells. Additionally, it is further applied to realize synchronous translation and rotation of cellular micromotors and to assemble controllable and fully biocompatible cellular micromotor assays. The proposed method is believed to have potential applications in targeted drug delivery, biological microenvironment monitoring and sensing, and biomedical treatment.

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Red‐Blood‐Cell Waveguide as a Living Biosensor and Micromotor

Yuchao Li, Xiaoshuai Liu, Xiaohao Xu, Hongbao Xin, Yao Zhang, Baojun Li

With great potential in intelligent sensing and actuating systems, biosensors and micromotors are expected to be powerful instruments for early diagnosis and drug delivery in precision medicine. However, it is difficult to ensure the synthetic biosensors and micromotors are compatible with biosystems because of their exogenous building blocks. Biocompatible biosensors and micromotors assembled are reported from living red blood cells (RBCs) optically bound into a waveguide using fiber probes. By monitoring light propagation of the RBC waveguide, the pH of blood solution is detected in real time with an accuracy of 0.05. This can be used for the diagnosis of pH‐related disorders of the blood. After diagnosis, optical torque is exerted on the RBC waveguide, allowing it to rotate as a micromotor and transport microparticles to a target region. The RBC waveguide is then constructed inside zebrafish blood vessels to validate in vivo application. The living biosensors and micromotors are expected to provide a “smart” platform for precise biosensing, medical analysis, and drug delivery.

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Silver‐Nanowire‐Based Interferometric Optical Tweezers for Enhanced Optical Trapping and Binding of Nanoparticles

Fan Nan, Zijie Yan

Light‐induced self‐assembly offers a new route to build mesoscale optical matter arrays from nanoparticles (NPs), yet the low stability of optical matter systems limits the assembly of large‐scale NP arrays. Here it is shown that the interferometric optical fields created by illuminating a single Ag nanowire deposited on a coverslip can enhance the electrodynamic interactions among NPs. The Ag nanowire serves as a plasmonic antenna to shape the incident laser beam and guide the optical assembly of colloidal metal (Ag and Au) and dielectric (polystyrene) NPs in solution. By controlling the laser polarization direction, both the mesoscale interactions among multiple NPs and the near‐field coupling between the NPs and nanowire can be tuned, leading to large‐scale and stable optical matter arrays consisting of up to 60 NPs. These results demonstrate that single Ag nanowires can serve as multifunctional antennas to guide the optical trapping and binding of multiple NPs and provide a new strategy to control electrodynamic interactions using hybrid nanostructures.

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Light‐Driven Rotation of Plasmonic Nanomotors

Lei Shao, Mikael Käll

Colloidal metal nanocrystals exhibit distinct plasmonic resonances that can greatly enhance optical forces and torques. This article highlights the recent application of such particles as light‐driven rotary motors at the nanoscale. By using laser tweezers, it is possible to achieve unprecedented rotation performance in solution, providing a variety of exciting possibilities for applications ranging from nanomechanics to biochemical sensing. Recent developments in this emerging field are discussed, and the physics behind the rotation mechanism, the Brownian dynamics, and the photothermal heating effects influencing the performance of the plasmonic nanomotors are introduced. Possible applications, open questions, and interesting future developments are also discussed.

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Combinatorial Particle Patterning

Clemens von Bojnicic-Kninski, Roman Popov, Edgar Dörsam, Felix F. Loeffler, Frank Breitling, Alexander Nesterov-Muelle

The unique properties of solid particles make them a promising element of micro- and nanostructure technologies. Solid particles can be used as building blocks for micro and nanostructures, carriers of monomers, or catalysts. The possibility of patterning different kinds of particles on the same substrate opens the pathway for novel combinatorial designs and novel technologies. One of the examples of such technologies is the synthesis of peptide arrays with amino acid particles. This review examines the known methods of combinatorial particle patterning via static electrical and magnetic fields, laser radiation, patterning by synthesis, and particle patterning via chemically modified or microstructured surfaces.

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Light-Driven Delivery and Release of Materials Using Liquid Marbles

Maxime Paven, Hiroyuki Mayama, Takafumi Sekido, Hans-Jürgen Butt, Yoshinobu Nakamura, Syuji Fujii

Remote control of the locomotion of small objects is a challenge in itself and may also allow for the stimuli control of entire systems. Here, it is described how encapsulated liquids, referred to as liquid marbles, can be moved on a water surface with a simple near-infrared laser or sunlight. Using light rather than pH or temperature as an external stimulus allows for the control of the position, area, timing, direction, and velocity of delivery. This approach makes it possible to not only transport the materials encapsulated within the liquid marble but also to release them at a specific place and time, as controlled by external stimuli. Furthermore, it is shown that liquid marbles can work as light-driven towing engines to push or pull objects. Being able to remotely transport and push/pull the small objects by light and control the release of active substances on demand should open up a wide field of conceivable applications.

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Controllable Patterning of Different Cells Via Optical Assembly of 1D Periodic Cell Structures

Hongbao Xin, Yuchao Li andBaojun Li

Flexible patterning of different cells into designated locations with direct cell–cell contact at single-cell patterning precision and control is of great importance, however challenging, for cell patterning. Here, an optical assembly method for patterning of different types of cells via direct cell–cell contact at single-cell patterning precision and control is demonstrated. Using Escherichia coli and Chlorella cells as examples, different cells are flexibly patterned into 1D periodic cell structures (PCSs) with controllable configurations and lengths, by periodically connecting one type of cells with another by optical force. The patterned PCSs can be flexibly moved and show good light propagation ability. The propagating light signals can be detected in real-time, providing new opportunities for the detection of transduction signals among patterned cells. This patterning method is also applicable for cells of other kinds, including mammalian/human cells.

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