Jonghee Yoon

Label-free characterization of white blood cells by measuring 3D refractive index maps.

The characterization of white blood cells (WBCs) is crucial for blood analyses and disease diagnoses. However, current standard techniques rely on cell labeling, a process which imposes significant limitations. Here we present three-dimensional (3D) optical measurements and the label-free characterization of mouse WBCs using optical diffraction tomography. 3D refractive index (RI) tomograms of individual WBCs are constructed from multiple two-dimensional quantitative phase images of samples illuminated at various angles of incidence. Measurements of the 3D RI tomogram of WBCs enable the separation of heterogeneous populations of WBCs using quantitative morphological and biochemical information. Time-lapse tomographic measurements also provide the 3D trajectory of micrometer-sized beads ingested by WBCs. These results demonstrate that optical diffraction tomography can be a useful and versatile tool for the study of WBCs.

Measuring optical transmission matrices by wavefront shaping

We introduce a simple but practical method to measure the optical transmission matrix (TM) of complex media. The optical TM of a complex medium is obtained by modulating the wavefront of a beam impinging on the complex medium and imaging the transmitted full-field speckle intensity patterns. Using the retrieved TM, we demonstrate the generation and linear combination of multiple foci on demand through the complex medium. This method will be used as a versatile tool for coherence control of waves through turbid media.

Common-path diffraction optical tomography for investigation of three-dimensional structures and dynamics of biological cells: erratum.

An erratum is presented to correct a typographical error on Fig. 1 in [Opt. Express 22(9), 10398 (2014)].

Simultaneous 3D visualization and position tracking of optically trapped particles using optical diffraction tomography

Precise tracking of three-dimensional (3D) positions of objects, often associated with optical tweezers, is important for the study of biophysics and cell biology. Although various approaches for 3D particle tracking have been proposed, most are limited in resolution and axial localization for objects of complex geometry. Holographic tomography systems circumvent these problems and offer improved capability in localization of objects over current methods. Here, we present a combined system employing optical diffraction tomography and holographic optical tweezers capable of simultaneous 3D visualization of the shapes and tracking positions of trapped microscopic samples. We demonstrated the capability of the present combined system using optically trapped silica beads and biological cells.

Minimally invasive molecular delivery into the brain using optical modulation of vascular permeability

Systemic delivery of bioactive molecules in the CNS is hampered by the blood–brain barrier, which has bottlenecked noninvasive physiological study of the brain and the development of CNS drugs. Here we report that irradiation with an ultrashort pulsed laser to the blood vessel wall induces transient leakage of blood plasma without compromising vascular integrity. By combining this method with a systemic injection, we delivered target molecules in various tissues, including the brain cortex. This tool allows minimally invasive local delivery of chemical probes, nanoparticles, and viral vectors into the brain cortex. Furthermore, we demonstrated astrocyte-mediated vasodilation in vivo without opening the skull, using this method to load a calcium indicator in conjunction with label-free photoactivation of astrocytes.

Antibacterial Activities of Graphene Oxide–Molybdenum Disulfide Nanocomposite Films

Two-dimensional (2D) nanomaterials, such as graphene-based materials and transition metal dichalcogenide (TMD) nanosheets, are promising materials for biomedical applications owing to their remarkable cytocompatibility and physicochemical properties. On the basis of their potent antibacterial properties, 2D materials have potential as antibacterial films, wherein the 2D nanosheets are immobilized on the surface and the bacteria may contact with the basal planes of 2D nanosheets dominantly rather than contact with the sharp edges of nanosheets. To address these points, in this study, we prepared an effective antibacterial surface consisting of representative 2D materials, i.e., graphene oxide (GO) and molybdenum disulfide (MoS2), formed into nanosheets on a transparent substrate for real device applications. The antimicrobial properties of the GO-MoS2 nanocomposite surface toward the Gram-negative bacteria Escherichia coli were investigated, and the GO-MoS2 nanocomposite exhibited enhanced antimicrobial effects with increased glutathione oxidation capacity and partial conductivity. Furthermore, direct imaging of continuous morphological destruction in the individual bacterial cells having contacts with the GO-MoS2 nanocomposite surface was characterized by holotomographic (HT) microscopy, which could be used to detect the refractive index (RI) distribution of each voxel in bacterial cell and reconstruct the three-dimensional (3D) mapping images of bacteria. In this regard, the decreases in both the volume (67.2%) and the dry mass (78.8%) of bacterial cells that came in contact with the surface for 80 min were quantitatively measured, and releasing of intracellular components mediated by membrane and oxidative stress was observed. Our findings provided new insights into the antibacterial properties of 2D nanocomposite film with label-free tracing of bacterial cell which improve our understanding of antimicrobial activities and opened a window for the 2D nanocomposite as a practical antibacterial film in biomedical applications.

Optical diffraction tomography techniques for the study of cell pathophysiology

Three-dimensional imaging of biological cells is crucial for the investigation of cell biology, provide valuable information to reveal the mechanisms behind pathophysiology of cells and tissues. Recent advances in optical diffraction tomography (ODT) have demonstrated the potential for the study of various cells with its unique advantages of quantitative and label-free imaging capability. To provide insight on this rapidly growing field of research and to discuss its applications in biology and medicine, we present the summary of the ODT principle and highlight recent studies utilizing ODT with the emphasis on the applications to the pathophysiology of cells.

Three-dimensional label-free imaging and quantification of lipid droplets in live hepatocytes.

Lipid droplets (LDs) are subcellular organelles with important roles in lipid storage and metabolism and involved in various diseases including cancer, obesity, and diabetes. Conventional methods, however, have limited ability to provide quantitative information on individual LDs and have limited capability for three-dimensional (3-D) imaging of LDs in live cells especially for fast acquisition of 3-D dynamics. Here, we present an optical method based on 3-D quantitative phase imaging to measure the 3-D structural distribution and biochemical parameters (concentration and dry mass) of individual LDs in live cells without using exogenous labelling agents. The biochemical change of LDs under oleic acid treatment was quantitatively investigated, and 4-D tracking of the fast dynamics of LDs revealed the intracellular transport of LDs in live cells.

Phenotypic Modulation of Primary Vascular Smooth Muscle Cells by Short-Term Culture on Micropatterned Substrate

Loss of contractility and acquisition of an epithelial phenotype of vascular smooth muscle cells (VSMCs) are key events in proliferative vascular pathologies such as atherosclerosis and post-angioplastic restenosis. There is no proper cell culture system allowing differentiation of VSMCs so that it is difficult to delineate the molecular mechanism responsible for proliferative vasculopathy. We investigated whether a micropatterned substrate could restore the contractile phenotype of VSMCs in vitro. To induce and maintain the differentiated VSMC phenotype in vitro, we introduced a micropatterned groove substrate to modulate the morphology and function of VSMCs. Later than 7th passage of VSMCs showed typical synthetic phenotype characterized by epithelial morphology, increased proliferation rates and corresponding gene expression profiles; while short-term culture of these cells on a micropatterned groove induced a change to an intermediate phenotype characterized by low proliferation rates, increased migration, a spindle-like morphology associated with cytoskeletal rearrangement and expression of muscle-specific genes. Microarray analysis showed preferential expression of contractile and smooth muscle cell-specific genes in cells cultured on the micropatterned groove. Culture on a patterned groove may provide a valuable model for the study the role of VSMCs in normal vascular physiology and a variety of proliferative vascular diseases.

Endoplasmic reticulum-specific BH3-only protein BNIP1 induces mitochondrial fragmentation in a Bcl-2- and Drp1-dependent manner

Bcl‐2/adenovirus E1B 19‐kDa interacting protein 1 (BNIP1), which is predominantly localized to the endoplasmic reticulum (ER), is a pro‐apoptotic Bcl‐2 homology domain 3 (BH3)‐only protein. Here, we show that the expression of BNIP1 induced not only a highly interconnected ER network but also mitochondrial fragmentation in a BH3 domain‐dependent manner. Functional analysis demonstrated that BNIP1 expression increased dynamin‐related protein 1 (Drp1) expression followed by the mitochondrial translocation of Drp1 and subsequent mitochondrial fission. Both BNIP1‐induced mitochondrial fission and the translocation of Drp1 were abrogated by Bcl‐2 overexpression. These results collectively indicate that ER‐specific BNIP1 plays an important role in mitochondrial dynamics by modulating the mitochondrial fission protein Drp1 in a BH3 domain‐dependent fashion. J. Cell. Physiol. 227: 3027–3035, 2012.