Kyoohyun Kim

Quantitative Phase Imaging Techniques for the Study of Cell Pathophysiology: From Principles to Applications

A cellular-level study of the pathophysiology is crucial for understanding the mechanisms behind human diseases. Recent advances in quantitative phase imaging (QPI) techniques show promises for the cellular-level understanding of the pathophysiology of diseases. To provide important insight on how the QPI techniques potentially improve the study of cell pathophysiology, here we present the principles of QPI and highlight some of the recent applications of QPI ranging from cell homeostasis to infectious diseases and cancer.

High-resolution three-dimensional imaging of red blood cells parasitized by Plasmodium falciparum and in situ hemozoin crystals using optical diffraction tomography

Abstract. We present high-resolution optical tomographic images of human red blood cells (RBC) parasitized by malaria-inducing Plasmodium falciparum (Pf)-RBCs. Three-dimensional (3-D) refractive index (RI) tomograms are reconstructed by recourse to a diffraction algorithm from multiple two-dimensional holograms with various angles of illumination. These 3-D RI tomograms of Pf-RBCs show cellular and subcellular structures of host RBCs and invaded parasites in fine detail. Full asexual intraerythrocytic stages of parasite maturation (ring to trophozoite to schizont stages) are then systematically investigated using optical diffraction tomography algorithms. These analyses provide quantitative information on the structural and chemical characteristics of individual host Pf-RBCs, parasitophorous vacuole, and cytoplasm. The in situ structural evolution and chemical characteristics of subcellular hemozoin crystals are also elucidated.

Profiling individual human red blood cells using common-path diffraction optical tomography

Due to its strong correlation with the pathophysiology of many diseases, information about human red blood cells (RBCs) has a crucial function in hematology. Therefore, measuring and understanding the morphological, chemical, and mechanical properties of individual RBCs is a key to understanding the pathophysiology of a number of diseases in hematology, as well as to opening up new possibilities for diagnosing diseases in their early stages. In this study, we present the simultaneous and quantitative measurement of the morphological, chemical, and mechanical parameters of individual RBCs employing optical holographic microtomography. In addition, it is demonstrated that the correlation analyses of these RBC parameters provide unique information for distinguishing and understanding diseases.

Real-time visualization of 3-D dynamic microscopic objects using optical diffraction tomography.

3-D refractive index (RI) distribution is an intrinsic bio-marker for the chemical and structural information about biological cells. Here we develop an optical diffraction tomography technique for the real-time reconstruction of 3-D RI distribution, employing sparse angle illumination and a graphic processing unit (GPU) implementation. The execution time for the tomographic reconstruction is 0.21 s for 96(3) voxels, which is 17 times faster than that of a conventional approach. We demonstrated the real-time visualization capability with imaging the dynamics of Brownian motion of an anisotropic colloidal dimer and the dynamic shape change in a red blood cell upon shear flow.

Diffraction optical tomography using a quantitative phase imaging unit

A simple and practical method to measure three-dimensional (3-D) refractive index (RI) distributions of biological cells is presented. A common-path self-reference interferometry consisting of a compact set of polarizers is attached to a conventional inverted microscope equipped with a beam scanning unit, which can precisely measure multiple 2-D holograms of a sample with high phase stability for various illumination angles, from which accurate 3-D optical diffraction tomograms of the sample can be reconstructed. 3-D RI tomograms of nonbiological samples such as polystyrene microspheres, as well as biological samples including human red blood cells and breast cancer cells, are presented.

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.

A Facile Route to Efficient, Low‐Cost Flexible Organic Light‐Emitting Diodes: Utilizing the High Refractive Index and Built‐In Scattering Properties of Industrial‐Grade PEN Substrates

An industrial-grade polyethylene naphthalate (PEN) substrate is explored as a simple, cost-effective platform for high-efficiency organic light-emitting diodes (OLEDs). Its high refractive index, combined with the built-in scattering properties inherent to the industrial-grade version, allows for a significant enhancement in outcoupling without any extra structuring or special optical elements. Flexible, color-stable OLEDs with efficiency close to 100 lm W(-1) are demonstrated.

Characterizations of individual mouse red blood cells parasitized by Babesia microti using 3-D holographic microscopy

Babesia microti causes “emergency” human babesiosis. However, little is known about the alterations in B. microti invaded red blood cells (Bm-RBCs) at the individual cell level. Through quantitative phase imaging techniques based on laser interferometry, we present the simultaneous measurements of structural, chemical, and mechanical modifications in individual mouse Bm-RBCs. 3-D refractive index maps of individual RBCs and in situ parasite vacuoles are imaged, from which total contents and concentration of dry mass are also precisely quantified. In addition, we examine the dynamic membrane fluctuation of Bm-RBCs, which provide information on cell membrane deformability.

Measurement Techniques for Red Blood Cell Deformability: Recent Advances

Human red blood cells (RBCs) or erythrocytes have remarkable deformability. Upon external forces, RBCs undergo large mechanical deformation without rupture, and they restore to original shapes when released. The deformability of RBCs plays crucially important roles in the main function of RBCs oxygen transport through blood circulation. RBCs must withstand large deformations during repeated passages through the microvasculature and the fenestrated walls of the splenic sinusoids (Waugh and Evans, 1979). RBC deformability can be significantly altered by various pathophysiological conditions, and the alterations in RBC deformability in turn influence pathophysiology, since RBC deformability is an important determinant of blood viscosity and thus blood circulation. Hence, measuring the deformability of RBCs holds the key to understanding RBC related diseases. For the past years, various experimental techniques have been developed to measure RBC deformability and recent technical advances revolutionize the way we study RBCs and their roles in hematology. This chapter reviews a variety of tools for measuring RBC deformability. For each technique, we seek to provide insights how these deformability measurement techniques can improve the study of RBC pathophysiology.

Synthetic Fourier transform light scattering.

We present synthetic Fourier transform light scattering, a method for measuring extended angle-resolved light scattering (ARLS) from individual microscopic samples. By measuring the light fields scattered from the sample plane and numerically synthesizing them in Fourier space, the angle range of the ARLS patterns is extended up to twice the numerical aperture of the imaging system with unprecedented sensitivity and precision. Extended ARLS patterns of individual microscopic polystyrene beads, healthy human red blood cells (RBCs), and Plasmodium falciparum-parasitized RBCs are presented.