Kak Namkoong

Surface acoustic wave immunosensor for real-time detection of hepatitis B surface antibodies in whole blood samples

We demonstrate an application of Love wave mode surface acoustic wave (SAW) immunosensor to detect hepatitis B surface antibody (HBsAb) in aqueous conditions. SiO(2) guiding layer was deposited on 36 degrees YX-LiTaO(3) piezoelectric single crystal substrate to protect the electrodes and to trap the acoustic energy near the surface, and hepatitis B surface antigen (HBsAg) was immobilized on the sensing area. The resonance frequency shift was monitored to detect specific binding of HBsAb to immobilized HBsAg. To eliminate the effects of other physical factors except for the mass change, the resonance frequency was compared to that of a reference SAW device coated with bovine serum albumin (BSA) to block binding of HBsAb. The guiding layer thickness with maximum mass sensitivity was found to be 5 microm, which was in agreement with the theoretical calculation, and the center resonance frequency was around 199 MHz. The sensor showed binding specificity to HBsAb and a linear relationship between the frequency shift and the antibody concentration with sensitivity of 0.74 Hz/(pg/microl) and detection limit below 10 pg/microl. In addition, our SAW immunosensor successfully detected HBsAb in whole blood samples without any pretreatment, opening up its applicability in fast label-free protein detection methods.

Simultaneous capture and in situ analysis of circulating tumor cells using multiple hybrid nanoparticles

Using hybrid nanoparticles (HNPs), we demonstrate simultaneous capture, in situ protein expression analysis, and cellular phenotype identification of circulating tumor cells (CTCs). Each HNP consists of three parts: (i) antibodies that bind specifically to a known biomarker for CTCs, (ii) a quantum dot that emits fluorescence signals, and (iii) biotinylated DNA that allows capture and release of CTC-HNP complex to an in-house developed capture & recovery chip (CRC). To evaluate our approach, cells representative of different breast cancer subtypes (MCF-7: luminal; SK-BR-3: HER2; and MDA-MB-231: basal-like) were captured onto CRC and expressions of EpCAM, HER2, and EGFR were detected concurrently. The average capture efficiency of CTCs was 87.5% with identification accuracy of 92.4%. Subsequently, by cleaving the DNA portion with restriction enzymes, captured cells were released at efficiencies of 86.1%. Further studies showed that these recovered cells are viable and can proliferate in vitro. Using HNPs, it is possible to count, analyze in situ protein expression, and culture CTCs, all from the same set of cells, enabling a wide range of molecular- and cellular-based studies using CTCs.

Bacterial DNA Sample Preparation from Whole Blood Using Surface-Modified Si Pillar Arrays

A novel bacterial DNA sample preparation device for molecular diagnostics has been developed. On the basis of optimized conditions for bacterial adhesion, surface-modified silicon pillar arrays for bacterial cell capture were fabricated, and their ability to capture bacterial cells was demonstrated. The capture efficiency for bacterial cells such as Escherichia coli, Staphylococcus epidermidis, and Streptococcus mutans in buffer solution was over 75% with a flow rate of 400 microL/min. Moreover, the proposed method captured E. coli cells present in 50% whole blood effectively. The captured cells from whole blood were then in- situ lyzed on the surface of the microchip, and the eluted DNA was successfully amplified by qPCR. These results demonstrate that the full process of pathogen capture to DNA isolation from whole blood could be automated in a single microchip.

Numerical analysis of two-dimensional motion of a freely falling circular cylinder in an infinite fluid

The two-dimensional motion of a circular cylinder freely falling or rising in an infinite fluid is investigated numerically for the range of Reynolds number Re < 188 (Galileo number G < 163), where the wake behind the cylinder remains two-dimensional, using a combined formulation of the governing equations for the fluid and the dynamic equations for the cylinder. The effect of vortex shedding on the motion of the freely falling or rising cylinder is clearly shown. As the streamwise velocity of the cylinder increases due to gravity, the periodic vortex shedding induces a periodic motion of the cylinder, which is manifested by the generation of the angular velocity vector of the cylinder parallel to the cross-product of the gravitational acceleration vector and the transverse velocity vector of the cylinder. Correlations of the Strouhal-Reynolds-number and Strouhal-Galileo-number relationship are deduced from the results. The Strouhal number is found to be smaller than that for the corresponding fixed circular cylinder when the two Reynolds numbers based on the streamwise terminal velocity of the freely falling or rising circular cylinder and the free-stream velocity of the fixed one are the same. From numerical experiments, it is shown that the transverse motion of the cylinder plays a crucial role in reducing the Strouhal number. The effect of the transverse motion is similar to that of suction flow on the low-pressure side, where a vortex is generated and then separates, so that the pressure on this side recovers with the vortex separation retarded. The effects of the transverse motion on the lift, drag and moment coefficients are also discussed. Finally, the effect of the solid/fluid density ratio on Strouhal-Reynolds-number relationship is investigated and a plausible correlation is proposed.

Solid phase DNA extraction with a flexible bead-packed microfluidic device to detect methicillin-resistant Staphylococcus aureus in nasal swabs.

We have developed a bead-packed microfluidic device with a built-in flexible wall to automate extraction of nucleic acids from methicillin-resistant Staphylococcus aureus (MRSA) in nasal swabs. The flexible polydimethylsiloxane (PDMS) membrane was designed to manipulate the surface-to-volume ratio (SVR) of bead-packed chambers in the range of 0.05 to 0.15 (μm(-1)) for a typical solid phase extraction protocol composed of binding, washing, and eluting. In particular, the pneumatically assisted close packing of beads led to an invariant SVR (0.15 μm(-1)) even with different bead amounts (10-16 mg), which allowed for consistent operation of the device and improved capture efficiency for bacteria cells. Furthermore, vigorous mixing by asynchronous membrane vibration enabled ca. 90% DNA recovery with ca. 10 μL of liquid solution from the captured cells on the bead surfaces. The full processes to detect MRSA in nasal swabs, i.e., nasal swab collection, prefiltration, on-chip DNA extraction, and real-time polymerase chain reaction (PCR) amplification, were successfully constructed and carried out to validate the capability to detect MRSA in nasal swab samples. This flexible microdevice provided an excellent analytical PCR detection sensitivity of ca. 61 CFU/swab with 95% confidence interval, which turned out to be higher than or similar to that of the commercial DNA-based MRSA detection techniques. This excellent performance would be attributed to the capability of the flexible bead-packed microdevice to enrich the analyte from a large initial sample (e.g., 1 mL) into a microscale volume of eluate (e.g., 10 μL). The proposed microdevice will find many applications as a solid phase extraction method toward various sample-to-answer systems.

A world-to-chip microfluidic interconnection technology with dual functions of sample injection and sealing for a multichamber micro PCR chip

This paper presents a practical world-to-chip microfluidic interconnection technology with dual functions of sample injection and sealing for a multichamber Micro PCR (Polymerase Chain Reaction) chip. After sample injection and sealing, leakage test is conducted by elevating the temperature up to 100 /spl deg/C for 30 min. No leakage flows are found during the test for 10 cartridges. In conclusion, we have introduced a simple and cheap microfluidic interconnection technology for both sample injection and sealing, which provides a zero dead volume, a zero leakage flow, and biochemical compatibility. Also, this world-to-chip interconnection technology enables one or more operators to interface between the micro world and real world easily by using conventional pipettes.

SAW immunosensors for HBsAb detection

This paper presents the implementation of a surface acoustic wave (SAW) immunosensor system for real sample detection of antibody to hepatitis B surface antigen (HBsAg). The SAW sensor device was based on the mass detection using LOVE wave with the central frequency of 200 MHz. The thickness of the SiO2 guiding layer was optimized both theoretically and experimentally to obtain the maximum sensitivity. A detection circuitry using a differential scheme measured the frequency difference by subtracting the resonant frequency of the sample SAW from that of the reference SAW. The sensitivity of the sensor was 0.74 Hz/(pg/mulscr) and the detection limit was 10 pg/mulscr. Our SAW sensor successfully detected natural anti-HBsAg antidbody (HBsAb) of the real whole blood samples, which opens up a possibility of label-free protein detection without any pretreatment procedures.

Wrist-wearable bioelectrical impedance analyzer with contact resistance compensation function

Bioelectrical impedance analysis (BIA) is used to calculate the body fat percentage of a human by applying a small amount of alternating current through a human body and measuring the impedance. As the electrode size of a BIA device becomes small, the measurement error of impedance becomes large due to the contact resistance between the electrode and human skin. Most commercial BIA devices, therefore, utilize electrodes large enough to ignore the effect of contact resistance, e.g. 35×40 mm2 × 4EA. We propose a novel method for compensating the contact resistance by performing a 4-point and a 2-point measurement alternately such that body impedance can be accurately estimated even with a considerably smaller size of electrode (8×8 mm2 × 4EA). Also, we report a wrist-wearable BIA device with single-finger contact measurement and analysis results of user data acquired from 148 volunteers: the correlation coefficient of body fat percentage was 0.903 and the SEE (Standard Error of Estimate) of body fat percentage was 3.07% when compared with InBody 720 (whole-body composition analyzer), which was found to be at the same level of performance as commercial portable upper-body BIA device.

Computation of Dynamic Fluid-Structure Interaction in a 2-Dimensional Laminar Channel Flow Divided by a Plate

In the FSI (Fluid-Structure Interaction) problems, two different governing equations are to be solved together. One is fur the fluid and the other for the structure. Furthermore, a kinematic constraint should be imposed along the boundary between the fluid and the structure. We use the combined formulation, which incorporates both the fluid and structure equations of motion into a single coupled variational equation so that it is not necessary to calculate the fluid force on the surface of structure explicitly when solving the equations of motion of the structure. A two-dimensional channel flow divided by a Bernoulli-Euler beam is considered and the dynamic response of the beam under the influence of channel flow is studied. The Navier-Stokes equations are solved using a P2P1 Galerkin finite element method with ALE (Arbitrary Lagrangian-Eulerian) algorithm. The internal structural damping effect is not considered in this study and numerical results are compared with a previous work fer steady case. In addition to the Reynolds number, two non-dimensional parameters, which govern this fluid-structure system, are proposed. It is found that the larger the dynamic viscosity and density of the fluid are, the larger the damping of the beam is. Also, the added mass is found to be linearly proportional to the density of the fluid.