Chulmin Joo

We describe a novel microscopy technique for quantitative phase-contrast imaging of a transparent specimen. The technique is based on depth-resolved phase information provided by common path spectral-domain optical coherence tomography and can measure minute phase variations caused by changes in refractive index and thickness inside the specimen. We demonstrate subnanometer level path-length sensitivity and present images obtained on reflection from a known phase object and human epithelial chee

We present a simple smartphone-based measurement system consisting of a smartphone, a holder, and a lateral flow immune strip. The smartphone camera and light source were used to read the colorimetric signal from the lateral flow assay. A smartphone application was written and installed onto the smartphone. Various concentrations of cortisol were successfully measured using the images captured by the smartphone. Measurement of human salivary cortisol was then demonstrated using the lateral flow

We present a multi-contrast microscope based on color-coded illumination and computation. A programmable three-color light-emitting diode (LED) array illuminates a specimen, in which each color corresponds to a different illumination angle. A single color image sensor records light transmitted through the specimen, and images at each color channel are then separated and utilized to obtain bright-field, dark-field, and differential phase contrast (DPC) images simultaneously. Quantitative phase im

We present polarization-sensitive Fourier ptychographic microscopy (PS-FPM) capable of generating high-resolution birefringence images of optically anisotropic specimens over a large field of view (FoV). FPM produces high-resolution images of transparent samples over a large FoV based on multiple intensity measurements acquired at various illumination angles and ptychographic phase retrieval. We combine this attractive feature of FPM with a single-input-state illumination and polarization-divers

Copper sulphide materials have received great attention due to their low bandgap semiconducting properties. As compared to other chalcogenides, few synthetic examples have been reported, and a simple and scalable synthetic method for preparing size- and shape-controlled copper sulphide nanoparticles is required for potential wide application of these materials. Herein, a facile one pot scalable synthetic route has been developed for preparing highly monodisperse djurleite Cu1.94S hexagonal nanop

Quantitative measurement of diffusive and directional processes of intracellular structures is not only critical in understanding cell mechanics and functions, but also has many applications, such as investigation of cellular responses to therapeutic agents. We introduce a label-free optical technique that allows non-perturbative characterization of localized intracellular dynamics. The method combines a field-based dynamic light scattering analysis with a confocal interferometric microscope to

We describe simultaneous quantitative phase contrast and multiphoton fluorescence imaging by combined spectral-domain optical coherence phase and multiphoton microscopy. The instrument employs two light sources for efficient optical coherence microscopic and multiphoton imaging and can generate structural and functional images of transparent specimens in the epidirection. Phase contrast imaging exhibits spatial and temporal phase stability in the subnanometer range. We also demonstrate the visua

Conventional methods for analyzing heavy metal contamination in soil and water generally require laboratory equipped instruments, complex procedures, skilled personnel and a significant amount of time. With the advancement in computing and multitasking performances, smartphone-based sensors potentially allow the transition of the laboratory-based analytical processes to field applicable, simple methods. In the present work, we demonstrate the novel miniaturized setup for simultaneous sample prep

Structural arrangement and dimension play vital roles in wave transport and amplification as they can restrict the volume explored by the waves. However, it is challenging to systematically investigate the interplay among structural, optical, and mechanical properties, in part because of limited experimental platforms that modulate the structural arrangement in a continuous manner. We present light amplification action in Rhodamine B doped silk fibroin (SF) nanofibrous scaffolds and its modulati

In this Letter, we describe a single-pixel polarization-sensitive imaging technique, capable of generating the birefringence map of a thin specimen by using single-pixel detectors. Spatially modulated light is circularly polarized to illuminate the specimen. The transmitted light through the specimen is then focused via a lens and measured by position-sensitive detectors in two orthogonal polarization channels. The measurement of the irradiance and centroid position of the optical focus and subs

A dithiophene-bearing benzothiazole derivative (DTBz) was synthesized as a moisture-sensitive fluorescent probe for the detection of water in hygroscopic solvents. In a mixture of water and organic solvents, such as THF, 1,4-dioxane, MeOH, and EtOH, the fluorescence intensity of DTBz showed ratiometric changes in response to the content of water in the organic solvents. Moreover, the emission color of DTBz changed drastically from blue to red, which facilitated the development of the smartphone-