Joon-Ho Kim

Effects of residual impurities in electroplated Cu on the Kirkendall void formation during soldering

Additions of bis-(sodium sulfopropyl)-disulfide (SPS) to the Cu electroplating bath strongly affected the characteristics of Kirkendall void formation when the Cu film is soldered with Sn–3.5Ag solder and subsequently aged. Voids were predominantly distributed near the Cu3Sn∕Cu interface with SPS, but randomly distributed in the Cu3Sn layer without SPS. In situ Auger electron spectroscopy of voids at the Cu3Sn∕Cu interface revealed surface segregation of S atoms, which came from SPS put into the bath as an additive. The S segregation to Cu3Sn∕Cu interface lowers the interface energy, thereby accelerating the void nucleation. Assisted by the high surface diffusivity of Cu and the presence of excess vacancies arising from the Kirkendall effect, voids tend to localize at the interface, which would result in serious degradation of the joint reliability.

Inertial blood plasma separation in a contraction–expansion array microchannel

Continuous inertial blood plasma separation is demonstrated in a contraction–expansion array microchannel with a low aspect ratio (AR). The separation cutoff value of the particle size can be controlled by modulation of the force balance between inertial lift and Dean drag forces. The modulation is achieved by changing the channel AR at contraction region, which causes the change in magnitudes of the inertial lift forces on the particles. The presented blood plasma separator provides a level of yield and throughput of 62.2% and 1.2 ml/h(∼1.0×108 cells/min), respectively.

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.

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 new monolithic micro biosensor for blood analysis

A new micro biosensor has been proposed and fabricated for the measurement of glucose concentration in whole blood. The proposed micro biosensor has been monolithically integrated with enzymatic metal microelectrode array in a micromachined chamber attached to a microsyringe. The fabricated micro biosensor has a high sensitivity of 470 nA/cm/sup 2/.mM for detecting glucose levels in a wide linear range of 0/spl sim/50 mM in potassium phosphate buffer solution (pH7.0).

A Disposable Passive Microfluidic System Integrated with Micromixer and DNA Purification Chip for DNA Sample Preparation

In this paper, we have fabricated a prototype microfluidic system for DNA sample preparation of nucleic acid probe assay. The fabricated module is composed of a mixer and a DNA purification chip. We have demonstrated that the fabricated microfluidic system can extract and purify DNAs from the sample solution with comparable results to a conventional commercial kit.