Hyundoo Hwang

Lab-on-a-disc for fully integrated multiplex immunoassays.

This paper presents a cost-effective, rapid, and fully automated lab-on-a-disc for simultaneous detection of multiple protein biomarkers in raw samples such as whole blood or whole saliva. For the diagnosis of cardiovascular disease, here, a novel centrifugal microfluidic layout was designed to conduct the simultaneous detection of high sensitivity C-reactive protein, cardiac troponin I, and N-terminal pro-B type natriuretic peptide based on a bead-based sandwich type enzyme-linked immunosorbent assay (ELISA). Three reaction chambers are initially interconnected for the common processes such as sample injection, incubation, and washing and then isolated on-demand for the independent processes such as substrate incubation and final detection. The assay performances such as the limit of detection and the dynamic range were comparable with those of the conventional ELISA despite the significant reduction of the minimum sample volume (200 μL), the amount of washing buffer (700 μL), and the total process time (20 min).

Flexible fabrication and applications of polymer nanochannels and nanoslits.

Fluidic devices that employ nanoscale structures (<100 nm in one or two dimensions, slits or channels, respectively) are generating great interest due to the unique properties afforded by this size domain compared to their micro-scale counterparts. Examples of interesting nanoscale phenomena include the ability to preconcentrate ionic species at extremely high levels due to ion selective migration, unique molecular separation modalities, confined environments to allow biopolymer stretching and elongation and solid-phase bioreactions that are not constrained by mass transport artifacts. Indeed, many examples in the literature have demonstrated these unique opportunities, although predominately using glass, fused silica or silicon as the substrate material. Polymer microfluidics has established itself as an alternative to glass, fused silica, or silicon-based fluidic devices. The primary advantages arising from the use of polymers are the diverse fabrication protocols that can be used to produce the desired structures, the extensive array of physiochemical properties associated with different polymeric materials, and the simple and robust modification strategies that can be employed to alter the substrates surface chemistry. However, while the strengths of polymer microfluidics is currently being realized, the evolution of polymer-based nanofluidics has only recently been reported. In this critical review, the opportunities afforded by polymer-based nanofluidics will be discussed using both elastomeric and thermoplastic materials. In particular, various fabrication modalities will be discussed along with the nanometre size domains that they can achieve for both elastomer and thermoplastic materials. Different polymer substrates that can be used for nanofluidics will be presented along with comparisons to inorganic nanodevices and the consequences of material differences on the fabrication and operation of nanofluidic devices (257 references).

Interactive manipulation of blood cells using a lens-integrated liquid crystal display based optoelectronic tweezers system.

This paper reports a lens‐integrated liquid crystal display (LCD)‐based optoelectronic tweezers (OET) system for interactive manipulation of polystyrene microspheres and blood cells by optically induced dielectrophoretic force. When a dynamic image pattern is projected into a specific area of a photoconductive layer in an OET, virtual electrodes are generated by spatially resolved illumination of the photoconductive layer, resulting in dielectrophoresis of microparticles suspended in the liquid layer under nonuniform electric field. In this study, the simple‐structured OET system has been easily constructed with an OET device, an LCD and a condenser lens integrated in a conventional microscope. By using a condenser lens, both stronger dielectrophoretic forces and higher virtual electrode resolution than previously reported lens‐less LCD‐based OET platform are obtained. The effects of blurred LCD image and liquid chamber height on the performances of optoelectronic particle manipulation are investigated by measuring the bead velocities according to their sizes. An interactive control program for OET‐based microparticle manipulation is also developed by Flash language. The integrated system is successfully applied to the parallel and interactive manipulation of red and white blood cells. Due to its simple structures, cheap manufacturing costs, and high performances, this new LCD‐based OET platform may be a widely usable integrated system for optoelectronic manipulation of microparticles including living cells.

Label-Free Cell Separation Using a Tunable Magnetophoretic Repulsion Force

This paper describes a new label-free cell separation method using a magnetic repulsion force resulting from the magnetic susceptibility difference between cells and a paramagnetic buffer solution in a microchannel. The difference in the magnetic forces acting on different-sized cells is enhanced by adjusting the magnetic susceptibility of the surrounding medium, which depends on the concentration of paramagnetic salts, such as biocompatible gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), dissolved therein. As a proof-of-concept demonstration, Gd-DTPA solutions at concentrations of 0-80 mM were applied to separate U937 cells from red blood cells (RBCs) and to distinguish two different-sized polystyrene (PS) beads (8 and 10 μm in diameter). By increasing the Gd-DTPA concentration from 0 to 40 mM, the separation resolution of PS beads was increased from 0.08 to 0.91. Additionally, we successfully achieved label-free separation of U937 cells from RBCs with >90% purity and 1 × 10(5) cells/h throughput using a 40 mM Gd-DTPA solution.

Enhanced discrimination of normal oocytes using optically induced pulling-up dielectrophoretic force

We present a method to discriminate normal oocytes in an optoelectrofluidic platform based on the optically induced positive dielectrophoresis (DEP) for in vitro fertilization. By combining the gravity with a pulling-up DEP force that is induced by dynamic image projected from a liquid crystal display, the discrimination performance could be enhanced due to the reduction in friction force acting on the oocytes that are relatively large and heavy cells being affected by the gravity field. The voltage condition of 10 V bias at 1 MHz was applied for moving normal oocytes. The increased difference of moving velocity between normal and starved abnormal oocytes allows us to discriminate the normal ones spontaneously under the moving image pattern. This approach can be useful to develop an automatic and interactive selection tool of fertilizable oocytes.

Optoelectrofluidic sandwich immunoassays for detection of human tumor marker using surface-enhanced Raman scattering.

A sandwich immunoassay is a powerful tool for identifying a specific substance in a biological sample. However, its heterogeneous strategy always requires repetitive liquid handlings and long processing time. Here an optoelectrofluidic immunoassay platform for simple, fast, and automated detection of human tumor marker based on surface-enhanced Raman scattering (SERS) has been developed. By using a conventional optoelectrofluidic device and a liquid crystal display module, simple and quantitative detection of human tumor marker, alpha-fetoprotein, in a ∼500 nL sample droplet has been automatically conducted with lower detection limit of about 0.1 ng/mL within 5 min. This study depicts the first practical application, for protein detection, of the optoelectrofluidic manipulation technology. This image-driven immunoassay platform opens a new way for simple, fast, automated, and highly sensitive detection of antigens.

Programmable manipulation of motile cells in optoelectronic tweezers using a grayscale image

This paper describes a grayscale optoelectronic tweezers (OET) which allows adjustment of the electric field strength at each position of OET. A grayscale light image was used to pattern vertical electric field strength on an OET. As an electric field depends on the brightness at each point, the brighter light patterns generate the stronger electric field in the OET. Its feasibility for application to cell manipulation was demonstrated by aligning highly motile protozoan cells in vertical direction. Depending on the brightness of each pixel, the behaviors of aligned cells varied due to the different electric field strength to each cell.

Lab-on-a-disc for simultaneous determination of nutrients in water.

In this study, we describe a novel platform based on centrifugal microfluidics for simultaneous determination of nitrite, nitrate and nitrite, ammonium, orthophosphate, and silicate in water samples. All processes from sample metering to detection were integrated and automatically conducted on a rotating disc-shaped device. Fluid transfer was controlled by laser irradiation on the ferrowax-based microvalves. Liquid samples and reagents were pumped by centrifugal force in the rotating disc, and their positions and movements were controlled through a programmable light from a laser diode. This novel water analysis platform required only 500 μL of sample (100 μL for each nutrient) and 10-30 μL of reagents for colorimetric detection. In addition, the fully automated parallel processes and efficient mixing in the rotating disc allowed for a significant reduction in total analysis time (∼7 min 40 s) and increased accuracy. Validation with a seawater certified reference material indicated that the platform accurately measured nutrient concentrations in water samples. In addition, we showed that the nutrients in the seawater collected from Chunsu Bay in Korea measured by the proposed lab-on-a-disc and by a commercialized autoanalyzer are comparable.

Experimental investigation of electrostatic particle-particle interactions in optoelectronic tweezers.

This paper reports experimental and theoretical investigation of electrostatic attraction and repulsion of microparticles in an optoelectronic tweezers (OET). When we manipulate dielectric particles suspended in a fluid using OET, the electrostatic interactions of the polarized particles occur, limiting the effective manipulation of microparticles using a light-induced dielectrophoresis. In this study, we first demonstrate the electrostatic particle-particle interactions in the OET device using a liquid crystal display. At the same time, the experimental investigation of the dipole interactions between two spherical particles has been performed using the OET device. On the basis of the point-dipole model, simulation studies on the dipole forces acting on the particles and their trajectories by the forces are also performed. The experimental results show good agreement with the previously reported numerical studies as well as the results of our simulation studies.

Microfluidic tools for developmental studies of small model organisms –nematodes, fruit flies, and zebrafish

Studying the genetics of development with small model organisms such as the zebrafish (Danio Rerio), the fruit fly (Drosophila melanogaster), and the soil‐dwelling nematode (Caenorhabditis elegans), provide unique opportunities for understanding related processes and diseases in humans. These model organisms also have potential for use in drug discovery and toxicity‐screening applications. There have been sweeping developments in microfabrication and microfluidic technologies for manipulating and imaging small objects, including small model organisms, which allow high‐throughput quantitative biological studies. Here, we review recent progress in microfluidic tools able to manipulate small organisms and project future directions and applications of these techniques and technologies.