Soyeon Yi

Acrylated hyperbranched polymer photoresist for ultra-thick and low-stress high aspect ratio micropatterns

Different photocurable acrylates, including two hyperbranched monomers, are compared with an epoxy negative-tone photoresist (SU-8) with respect to their suitability for the fabrication of ultra-thick polymer microstructures in a photolithographic process. To this end, a resolution pattern was used and key parameters, such as the maximum attainable thickness and aspect ratio, the minimum resolution and the processing time were determined. Compared to SU-8, all acrylate materials allowed the fabrication of thicker layers with a fast single layer fabrication procedure. Microstructures with thicknesses of up to 850 µm, an aspect ratio of up to 7.7, a 5.5-fold reduction in internal stress and a 6-fold reduction in processing time compared to SU-8 were demonstrated using an acrylated hyperbranched polyether. The specific development process of the hyperbranched polymer combined with channel design moreover enabled us to produce a high-performance valve for micro-battery devices.

A Flow Rate Independent Cell Concentration Measurement Chip Using Electrical Cell Counters Across a Fixed Control Volume

We present a novel method of measuring cell concentration using two electrical cell counters across a fixed control volume. Our device counts cells at the inlet and outlet of a fixed control volume and then measures the cell concentration by calculating the number of cells in the fixed control volume. Previous methods of measuring cell concentration (such as a Coulter counter and a flow cytometer) have attempted to count cells in a given fluid volume or at a known flow rate. Thus, in spite of the miniature nature of previous devices, the accuracy of their results depends on the performance of external mechanisms such as delicate pumps and flow sensors. Our prototype, however, does not depend on accurate fluid measurement or precise control of the flow rate because it measures the number of cells in a fixed control volume. In the experimental study, we measured cell concentrations ranging from 5.8 times 105 to 11.5 times 105 cells/mL without measuring or controlling the flow rate. For measuring the cell concentration, our prototype shows a maximum cell concentration measurement error of 10.3%, which is within the error range of a hemacytometer.

A flow-rate independent cell counter using a fixed control volume between double electrical sensing zones

We present a novel cell counter using a fixed control volume and double electrical sensing zones at the inlet and outlet of the control volume. The present cell counter measures cell concentration based on the difference of the counted cell numbers from the double electrical sensing zones at inlet and outlet of the fixed control volume. In the experimental study, we use the RBC samples of three different concentrations and compare the results from the fabricated device with those from hemacytometer. Using the fabricated devices, we make two different measurements: 1) Cell concentration measurement using single electrical sensing at a fixed flow-rate of 10 /spl mu/l/min.; 2) Cell concentration measurement using double electrical sensing with the fixed control volume of 22.9/spl plusmn/0.98 /spl mu/l. Compared to hemacytometer, the single and double electrical sensing methods show the maximum errors of 20.3% and 16.1%, respectively, which are in the measurement error range of hemacytometer. We also observe that the present cell counter has an immunity for flow-rate change.

Trapping and extraction of target DNA molecules using periodically crossed electrophoresis in the micropillar array

This paper presents a DNA (Deoxyribose Nucleic Acid) extractor based on an electrophoresis using periodically crossed electric fields in a micropillar array. The DNA extractor, having nanometer entropic barriers and micropillar array, was fabricated by micromachining processes. Under the crossed electric field, the DNA molecules, whose reorientation time is longer than the period of the crossed field, are trapped in the micropillar array. We applied the electric fields, crossed at 120/spl deg/, to the DNA molecules in the micropillar array distributed in 120/spl deg/ direction. Three different DNA, including /spl lambda/, micrococcus and T4 show reorientation times of 4.80 /spl plusmn/ 0.44sec, 7.12 /spl plusmn/ 0.75sec, and 9.71 /spl plusmn/ 0.30sec for /spl lambda/ DNA(48.5 kbp), micrococcus DNA (115 kbp), and T4 DNA (169.8 kbp), respectively at E=5V/0.8cm. In the fabricated DNA extractor, T4 DNA cannot come out of the micropillar array for the crossed electric field of 5V/0.8cm at a 10 second interval. We have demonstrated that the present DNA extractor separates DNA molecules longer than a critical value, which can be adjusted by the magnitude and the period of the electric field across the micropillar array.

Self-focusing chips for size-dependent DNA separation in nonuniformly distributed asymmetric electric fields

This paper presents the first experimental study to realize a DNA separation chip based on the self-focusing effect in a micropillar array. The present self-focusing chip redistributes DNA molecules within a specific area of micropillar arrays based on the size- and field-dependent nonlinearity of DNA drift velocity. Compared to conventional electrophoresis chips, the present self-focusing chip reduces a substantial amount of the separation channel length, the influence of sample starting location, and the necessity of time-consuming continuous monitoring process. We focus on the design of DNA self-focusing chips, with identifying the nonlinearity of DNA drift velocity using three different DNA molecules including /spl lambda/ DNA (48.5 kbp), micrococcus DNA (115 kbp), and T4 DNA (169.8 kbp) in microfabricated test chips. It is demonstrated that the present DNA self-focusing chips have potentials not only for the miniaturization of DNA analysis systems, but also for the tunable capability of the target DNA size to be separated, trapped and extracted.

DNA Separation Chips Using Asymmetrically-Switched Nonuniform Electric Fields

Abstract We present the experimental study to realize a DNA separation chip using asymmetrically-switched nonuniform electric fields. The DNA separation chip redistributes DNA molecules within a specific area based on the size- and field-dependent nonlinearity of DNA drift velocity. The present chip is composed of a width variable channel to distribute nonuniform electric field, a DNA loading slit and a pair of electrodes to apply electric field. We focus on the design of DNA separation chips with identifying the nonlinearity of DNA drift velocity using three different DNA molecules (11.1kbp, 15.6kbp, and 48.5kbp) in the chips. It is demonstrated that different size of DNA shows different net migration in different direction under the asymmetrically-switched n onuniform electric field.기호설명 E 전기장 T 전기장 인가 주기 M DNA 분자의 크기 1. 서론 본 연구은 DNA 분리소자에 관한 것으로, 채널 내에 형성된 불균일한 전기장의 방향이 변함에 따라, DNA는 그 6cm크기에 따라 알짜이동 방향과 속도가 달라지게 된다. 본 논문에서는 이론적으로 제시된 바 있는 (1)이러한 래칫(ratchet) 효과를 실험적으로 검증하였다. 제안한 DNA분리소자(Fig. 1)에서는 비대칭 교차전기장(Fig. 2) 6mm미소유로을 양단에 인가하고 미소유로의 폭을 변화시켜 불균일 전기장을 형성하였다. 기존의 전기영동 소자

DNA Self-Focusing Chips Using Nonuniformly Distributed Asymmetric Electric Fields

This paper presents the experimental study to realize a DNA separation chip based on the self-focusing effect in a microfabricated PDMS chip. The present self-focusing chip redistributes DNA molecules within a specific area based on the size- and field-dependent nonlinearity of DNA drift velocity. Compared to conventional electrophoresis chips, the present self-focusing chip offers the advantages of simple structure, short separation channel length, and starting-point independent DNA separation. We focus on the design of DNA self-focusing chips, with identifying the nonlinearity of DNA drift velocity using three different DNA molecules (11.1kbp, 15.6kbp, and 48.5kbp) in test chips. It is demonstrated that the present DNA self-focusing chips have potentials not only for the miniaturization of DNA analysis systems, but also for the tunable capability of the target DNA size to be separated, trapped and extracted.

Micro Cell Counter Using a Fixed Control Volume Between Double Electrical Sensing Zones

We present a novel flow-rate independent cell counter using a fixed control volume between double electrical sensing zones. The previous device based on the single electrical cell sensing in a given flow-rate requires an accurate fluid volume measurement or precision flow rate control. The present cell counter, however, offers the flow-rate independent method for the cell concentration measurement with counting cells in a fixed control volume of . In the experimental study, using the RBC (Red Blood Cell), we have compared the measured RBC concentrations from the fabricated devices with those from Hemacytometer. The previous and present devices show the maximum errors of , which are in the measurement error range of Hemacytometer (about ). The present device also shows the flow-rate independent performance at the constant flow-rates ( and ) and the varying flow-rate (4, 2, and ). Therefore, we demonstrate that the present cell counter is a simple and automated method for the cell concentration measurement without requiring an accurate fluid measurement and precision flow-rate control.