Kwanoh Kim

Ultrahigh-speed rotating nanoelectromechanical system devices assembled from nanoscale building blocks

The development of rotary nanomotors is crucial for advancing nanoelectromechanical system technology. In this work, we report design, assembly and rotation of ordered arrays of nanomotors. The nanomotors are bottom-up assembled from nanoscale building blocks with nanowires as rotors, patterned nanomagnets as bearings and quadrupole microelectrodes as stators. Arrays of nanomotors rotate with controlled angle, speed (over 18,000 r.p.m.), and chirality by electric fields. Using analytical modelling, we reveal the fundamental nanoscale electrical, mechanical and magnetic interactions in the nanomotor system, which excellently agrees with experimental results and provides critical understanding for designing metallic nanoelectromechanical systems. The nanomotors can be continuously rotated for 15 h over 240,000 cycles. They are applied for controlled biochemical release and demonstrate releasing rate of biochemicals on nanoparticles that can be precisely tuned by mechanical rotations. The innovations reported in this research, from concept, design and actuation to application, are relevant to nanoelectromechanical system, nanomedicine, microfluidics and lab-on-a-chip architectures.

Recent Progress on Man‐Made Inorganic Nanomachines

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.

Ordered Arrays of Raman Nanosensors for Ultrasensitive and Location Predictable Biochemical Detection

Surface enhanced Raman scattering (SERS) is sensitive enough for single-molecule biochemical detection, but it is extremely difficult to obtain a large number of SERS hotspots for sensitive and reproducible detection. It is even more challenging to assemble the hotspots at designated positions for location predictable sensing. Here, we report an original strategy for the synthesis, manipulation, and assembling of plasmonic nanocapsule SERS sensors for high-sensitivity biochemical detection at predictable locations.

Tunable Release of Multiplex Biochemicals by Plasmonically Active Rotary Nanomotors

It is highly desirable to precisely tune the molecule release rate from the surfaces of nanoparticles (NPs) that are relevant to cancer therapy and single-cell biology. An innovative mechanism is reported to actively tune the biochemical release rate by rotation of NPs. Plasmonic nanomotors were assembled from NPs and applied in multiplex biochemical release and detection. Both single and multiplex biosignals can be released in a tunable fashion by controlling the rotation speed of the nanomotors. The chemistry and release rate of individual chemicals can be revealed by Raman spectroscopy. The fundamental mechanism was modeled quantitatively and attributed to the fluidic boundary-layer reduction owing to the liquid convection. This work, which explored the synergistic attributes of surface enhanced Raman scattering and nanoelectromechanical systems, could inspire new sensors that are potentially interesting for various bio-applications.

Micromotors with step-motor characteristics by controlled magnetic interactions among assembled components.

In this study, we investigated the control of the rotation dynamics of an innovative type of rotary micromotors with desired performances by tuning the magnetic interactions among the assembled micro/nanoscale components. The micromotors are made of metallic nanowires as rotors, patterned magnetic nanodisks as bearings and actuated by external electric fields. The magnetic forces for anchoring the rotors on the bearings play an essential role in the rotation dynamics of the micromotors. By varying the moment, orientation, and dimension of the magnetic components, distinct rotation behaviors can be observed, including repeatable wobbling and rolling in addition to rotation. We understood the rotation behaviors by analytical modeling, designed and realized micromotors with step-motor characteristics. The outcome of this research could inspire the development of high-performance nanomachines assembled from synthetic nanoentities, relevant to nanorobotics, microfluidics, and biomedical research.

Innovative mechanisms for precision assembly and actuation of arrays of nanowire oscillators.

Bottom-up assembling of Micro/Nano Electromechanical System (MEMS/NEMS) devices from nanoscale building blocks is highly desirable but extremely difficult to achieve. In this work, we report innovative mechanisms for precision assembly and actuation of arrays of nanowire NEMS devices that can synchronously oscillate between two designated positions for over 4000 cycles. The assembly and actuation mechanisms are based on unique magnetic interactions between nanoentities with perpendicular magnetic anisotropy (PMA) and electric-tweezer manipulation, our recent invention. Quantitative analysis of the dynamics of torques involved in the nano-oscillators reveals that the induced electrostatic torques due to the external electric fields between metallic NEMS components play a significant role in the mechanical actuation. These new findings are expected to inspire new in situ assembly and actuation strategies in the general field of NEMS devices such as nanomechanical switches for toggling on/off circuits and nanoresonators for biochemical sensors and radio frequency communication.

Fabrication and Robotization of Ultrasensitive Plasmonic Nanosensors for Molecule Detection with Raman Scattering

In this work, we introduce the history and mechanisms of surface enhanced Raman scattering (SERS), discuss various techniques for fabrication of state-of-the-art SERS substrates, and review recent work on robotizing plasmonic nanoparticles, especially, the efforts we made on fabrication, characterization, and robotization of Raman nanosensors by design. Our nanosensors, consisting of tri-layer nanocapsule structures, are ultrasensitive, well reproducible, and can be robotized by either electric or magnetic tweezers. Three applications using such SERS nanosensors were demonstrated, including location predictable detection, single-cell bioanalysis, and tunable molecule release and monitoring. The integration of SERS and nanoelectromechanical system (NEMS) devices is innovative in both device concept and fabrication, and could potentially inspire a new device scheme for various bio-relevant applications.

Biobased High-Performance Rotary Micromotors for Individually Reconfigurable Micromachine Arrays and Microfluidic Applications

In this work, we report an innovative type of rotary biomicromachines by using diatom frustules as integrated active components, including the assembling, operation, and performance characterization. We further investigate and demonstrate unique applications of the biomicromachines in achieving individually reconfigurable micromachine arrays and microfluidic mixing. Diatom frustules are porous cell walls of diatoms made of silica. We assembled rotary micromachines consisting of diatom frustules serving as rotors and patterned magnets serving as bearings in electric fields. Ordered arrays of micromotors can be integrated and rotated with controlled orientation and a speed up to ∼3000 rpm, one of the highest rotational speeds in biomaterial-based rotary micromachines. Moreover, by exploiting the distinct electromechanical properties of diatom frustules and metallic nanowires, we realized the first reconfigurable rotary micro/nanomachine arrays with controllability in individual motors. Finally, the diatom micromachines are successfully integrated in microfluidic channels and operated as mixers. This work demonstrated the high-performance rotary micromachines by using bioinspired diatom frustules and their applications, which are essential for low-cost bio-microelectromechanical system/nanoelectromechanical system (bio-MEMS/NEMS) devices and relevant to microfluidics.

Location deterministic biosensing from quantum-dot-nanowire assemblies

Semiconductor quantum dots (QDs) with high fluorescent brightness, stability, and tunable sizes, have received considerable interest for imaging, sensing, and delivery of biomolecules. In this research, we demonstrate location deterministic biochemical detection from arrays of QD-nanowire hybrid assemblies. QDs with diameters less than 10 nm are manipulated and precisely positioned on the tips of the assembled Gold (Au) nanowires. The manipulation mechanisms are quantitatively understood as the synergetic effects of dielectrophoretic (DEP) and alternating current electroosmosis (ACEO) due to AC electric fields. The QD-nanowire hybrid sensors operate uniquely by concentrating bioanalytes to QDs on the tips of nanowires before detection, offering much enhanced efficiency and sensitivity, in addition to the position-predictable rationality. This research could result in advances in QD-based biomedical detection and inspires an innovative approach for fabricating various QD-based nanodevices.

A study on arrangement characteristics of microparticles in sedimentation on flat and round substrates

Recent advances of microfabrication techniques have enabled diverse structures and devices on the microscale. This fabrication method using microparticles is one of the most promising technologies because it can provide a cost effective process for large areas. So, many researchers are studying modulation and manipulation of the microparticles in solution to obtain a proper arrangement. However, the microparticles are in sedimentation status during the process in many cases, which makes it difficult to control their arrangement. In this study, droplets containing microparticles were placed on a substrate with minimal force and we investigated the arrangement of these microparticles after evaporation of the liquid. Experiments have been performed with upward and downward substrates to change the direction of gravity. The geometry of substrates was also changed, which were flat or round. The results show that the arrangement depends on the size of particles and gravity and geometry of the substrate. The arr...