Kipom Kim

Mechanical unzipping and rezipping of a single SNARE complex reveals hysteresis as a force-generating mechanism.

Formation of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex provides mechanical thrust for membrane fusion, but its molecular mechanism is still unclear. Here using magnetic tweezers, we observe mechanical responses of a single neuronal SNARE complex under constant pulling force. Single SNARE complexes may be unzipped with 34u2009pN force. When rezipping is induced by lowering the force to 11u2009pN, only a partially assembled state results, with the C-terminal half of the SNARE complex remaining disassembled. Reassembly of the C-terminal half occurs only when the force is further lowered below 11u2009pN. Thus, mechanical hysteresis, characterized by the unzipping and rezipping cycle of a single SNARE complex, produces the partially assembled state. In this metastable state, unzipping toward the N-terminus is suppressed while zippering toward the C-terminus is initiated as a steep function of force. This ensures the directionality of SNARE-complex formation, making the SNARE complex a robust force-generating machine.

Low-power nano-optical vortex trapping via plasmonic diabolo nanoantennas

Optical vortex trapping can allow the capture and manipulation of micro- and nanometre-sized objects such as damageable biological particles or particles with a refractive index lower than the surrounding material. However, the quest for nanometric optical vortex trapping that overcomes the diffraction limit remains. Here we demonstrate the first experimental implementation of low-power nano-optical vortex trapping using plasmonic resonance in gold diabolo nanoantennas. The vortex trapping potential was formed with a minimum at 170 nm from the central local maximum, and allowed polystyrene nanoparticles in water to be trapped strongly at the boundary of the nanoantenna. Furthermore, a large radial trapping stiffness, ~0.69 pN nm(-1) W(-1), was measured at the position of the minimum potential, showing good agreement with numerical simulations. This subwavelength-scale nanoantenna system capable of low-power trapping represents a significant step toward versatile, efficient nano-optical manipulations in lab-on-a-chip devices.

Programmed folding of DNA origami structures through single-molecule force control

Despite the recent development in the design of DNA origami, its folding yet relies on thermal or chemical annealing methods. We here demonstrate mechanical folding of the DNA origami structure via a pathway that has not been accessible to thermal annealing. Using magnetic tweezers, we stretch a single scaffold DNA with mechanical tension to remove its secondary structures, followed by base pairing of the stretched DNA with staple strands. When the force is subsequently quenched, folding of the DNA nanostructure is completed through displacement between the bound staple strands. Each process in the mechanical folding is well defined and free from kinetic traps, enabling us to complete folding within 10 min. We also demonstrate parallel folding of DNA nanostructures through multiplexed manipulation of the scaffold DNAs. Our results suggest a path towards programmability of the folding pathway of DNA nanostructures.

Breathing, crawling, budding, and splitting of a liquid droplet under laser heating

The manipulation of droplets with sizes on the millimetre scale and below has attracted considerable attention over the past few decades for applications in microfluidics, biology, and chemistry. In this paper, we report the response of an oil droplet floating in an aqueous solution to local laser heating. Depending on the laser power, distinct dynamic transitions of the shape and motion of the droplet are observed, namely, breathing, crawling, budding, and splitting. We found that the selection of the dynamic modes is determined by dynamic instabilities due to the interplay between the convection flows and capillary effects. Our findings can be useful for constructing microfluidic devices to control the motion and shape of a small droplet by simply altering the laser power, and for understanding thermal convective systems with fully soft boundaries.

Diffusing-wave spectroscopy study of microscopic dynamics of three-dimensional granular systems

Probing micron-scale dynamics is important in understanding the dynamic property of granular systems. Diffusing-wave spectroscopy, which makes use of multiply scattered light in a highly dense solution of small particles, has been used successfully to study various fluidized-granular systems, such as; channel flow, gas-fluidized beds, avalanche flow, and vibro-fluidized beds. This paper summarizes this method and the existing findings, which include the dynamic behaviour on a short time scale and jamming transition on a long time scale. In addition, the analogy between the jamming transition of granular systems and the glass transition of traditional liquid/solid systems is discussed.

Simultaneous detection of biomolecular interactions and surface topography using photonic forcemicroscopy

We developed a photonic force microscope that can map multiple parameters simultaneously, including the surface topography and biomolecular interactions. To track the position of the probe bead and to determine contact position with the sample surface, we adopted a video analysis method using the diffraction pattern of monochromatic light passing through the probe bead. To demonstrate the capability of the microscope, we report the simultaneous measurement of the molecule distribution of DNA oligonucleotides on the surface, the binding strength of DNA hybridization between the bead and surface, and the topography of the smooth molded surface.

Mechanical Unzipping and Rezipping of a Single SNARE Complex Reveals Large Hysteresis as the Force Generating Mechanism

Formation of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex provides mechanical thrust for membrane fusion, but its molecular mechanism is still unclear. Here using magnetic tweezers, we observe mechanical responses of a single neuronal SNARE complex under constant pulling force. Single SNARE complexes may be unzipped with 34 pN force. When rezipping is induced by lowering the force to 11 pN, only a partially assembled state results, with the C-terminal half of the SNARE complex remaining disassembled. Reassembly of the C-terminal half occurs only when the force is further lowered below 11 pN. Thus, mechanical hysteresis, characterized by the unzipping and rezipping cycle of a single SNARE complex, produces the partially assembled state. In this metastable state, unzipping toward the N-terminus is suppressed while zippering toward the C-terminus is initiated as a steep function of force. This ensures the directionality of SNARE-complex formation, making the SNARE complex a robust force-generating machine.

Label-free biosensing over a wide concentration range with photonic force microscopy.

We present a label-free biosensor that measures molecular interactions between biomolecules on the surface of a probe bead and substrate over a wide concentration range. This system is capable of detecting target biomolecules with concentrations varying from 10 nM to 0.1 pM, with high selectivity and sensitivity.

Simultaneous Detection of Bio-Molecular Interactions and Surface Topography using Photonic Force Microscopy

Photonic force microscopy (PFM) is an optical tweezers-based scanning probe microscopy, which measures the forces in the range of fN to pN. The low stiffness leads proper to measure single molecular interaction.We introduce a novel photonic force microscopy to stably map various chemical properties as well as topographic information, utilizing weak molecular bond between probe and objects surface.First, we constructed stable optical tweezers instrument minimized instrumental noise, where an IR laser with 1064 nm wavelength was used as trapping source to reduce damage to biological sample. To manipulate trapped bead two-axis Galvano mirror were used for x, y directional probe scanning and a piezo stage was used for z directional probe scanning. For resolution test probe scans with vertical direction repeatedly at the same lateral position, where the vertical resolution is ∼25 nm. To obtain the topology of surface of etched glass, trapped bead scans with hopping mode and measures the contact position in every cycle.To obtain the chemical mapping, wedesign the DNA oligonucleotide pairs combining as a zipping structure, where one is attached at the surface of bead and other is fixed on surface. We measured the rupture force of molecular bond to investigate chemical property on the surface with various loading rate.We expect this system can realize a high-resolution multi-functional imaging technique able to acquire topographic map of objects and to distinguish chemical difference between these objects simultaneously.