Single-Molecule Imaging for Soft- and Bio-Materials

In various solution systems of soft materials such as proteins or synthetic polymers, macromolecules exist in a wide range of conformations, which shift via dynamic transitions. Understanding such structures of soft materials in native environments is crucial for applications in synthetic chemistry or pharmaceutical design.

Our research focuses on developing analytical methods to directly visualize dynamics of soft materials using liquid-phase TEM or obtain high-throughput 3D structures of proteins with cryo-EM to understand soft-material conformations at the single-molecule scale.

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Diffusion and Conformational Dynamics of Soft Matter in Liquid Phase

Soft matters in solution exist in a wide range of conformations and undergo dynamic structural fluctuations. Our research focuses on analyzing the diffusion and conformational dynamics of soft materials or biological molecules with liquid-phase TEM. By utilizing graphene liquid cells, we have found that single-molecule polymers in theta solvents exhibit dynamic structural transitions that are governed by their intrinsic intramolecular forces. We have also observed non-equilibrium processes of polymers such as interaction with graphene or bubble-induced scission, bringing insight into the solution-phase dynamics of other chain-like polymers or proteins that exist in various natural or synthetic processes. 

Self-Assembly Pathways of Soft Materials

Assembly of soft or organic materials into ordered superstructures have been known to occur both by classical and non-classical pathways. We aim to further elucidate the assembly pathways of protein macromolecule crystals, biological or organic filaments, and helical structures at the nanoscale level, focusing on the roles of the intermediate stages preceding superstructure formation. Through cryo-EM, electron tomography, and liquid-phase EM, we perform aliquot studies of the assembly of various monomers and observe the formation of superstructures, gaining insight into the step-by-step process of non-classical nucleation at the monomeric level. 

High-Throughput Cryo-EM Single Particle Analysis

Recent advances in cryo-EM enable high resolution analysis of various protein structures and air- or radiation-sensitive materials. To obtain high-resolution cryo-TEM images, specimen must be fixed in a homogeneous, tens-of-nanometers-thick vitreous ice layer. Our research aims to develop high-throughput Si-based cryo-EM grids with MEMS technology to enhance sample loading stability and overcome challenges associated with producing thin ice. We develop micro-fabicated cryo-EM grids that are customizable, are robust, and increase image yield. We also demonstrate that these grids can be used with 3D single-particle analysis of proteins and other types of biomolecules. Along with cryo-EM grids, we are also currently developing grids for liquid-phase TEM, and for correlative analysis with optical spectroscopy or SERS.