• 한국가시화정보학회지
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• 제14권1호
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• pp.57-61
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• 2016

We report a finding of fast(exceeding 2,000 K/s) heating of polydimethylsiloxane(PDMS), one of the most commonly-used microchannel materials, under cyclic loadings at high(~MHz) frequencies. A microheater was created based on the finding. The heating mechanism utilized vibration damping of sound waves, which were generated and precisely manipulated using a conventional surface acoustic wave(SAW) microfluidic system, in PDMS. The penetration depths were measured to range from $210{\mu}m$ to $1290{\mu}m$, enough to cover most microchannel heights in microfluidic systems. The energy conversion efficiency was SAW frequency-dependent and measured to be the highest at around 30 MHz. Independent actuation of each interdigital transducer(IDT) enabled independent manipulation of SAWs, permitting spatiotemporal control of temperature on the microchip. All the advantages of this microheater facilitated a two-step continuous flow polymerase chain reaction(CFPCR) to achieve the billion-fold amplification of a 134 bp DNA amplicon in less than 3 min. In addition, a technique was developed for establishing dynamic free-form temperature gradients(TGs) in PDMS as well as in gases in contact with the PDMS.

• 전기학회논문지
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• 제65권4호
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• pp.628-634
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• 2016

This paper demonstrates a microfluidic electrochemical sensor for detecting endocrine disruptor such as estradiol at a very low concentration by using preconcentration technique. In addition, self-assembled monolayer(SAM) was also employed on the working electrode of the electrochemical sensor in order to increase the estradiol capture efficiency of the sensor. SAM treatment on the working electrode enhanced the specific binding between the surface of the working electrode and the estradiol antibody. The estradiol antibody was applied on the working electrode at different concentrations(10, 20, 50, 100, 200 pg/ml) for observing the concentration dependency. The measured electrochemical redox current changed with the amount of the bound estradiol on the Au working electrode surface and the sensor can detect all the target material when the immobilized antibody amount is more than the estradiol amount in the water. The elecrochemical estradiol sensor without SAM treatment showed a low current of 7.79 nA, while the sensor treated with SAM resulted in 339 nA at 200 pg/ml, which is more than 40 fold higher output current. When combining the preconcentration technique and the SAM-treated electrode, the measured current became more than 100 fold higher than that of the sensor without neither SAM treatment nor preconcentration technique. The combination of these two techniques can would enable the proposed microfluidic electrochemical sensor to detect a very low concentration endocrine disruptor.

• 대한전자공학회논문지SD
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• 제46권4호
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• pp.15-20
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• 2009

레이저 광 산란을 이용한 검출 시스템 및 레이저를 이용한 광학적 검출에 있어서 높은 발광 강도를 통해 궁극적으로 높은 효율의 광 산란 신호를 광검출기에서 얻기 위해서는 발광 레이저빔을 미세유체 칩의 채널 중앙에 집광하는 것이 매우 중요하다. 본 논문을 통해 레이저 광 산란을 이용한 세포 검출을 위해 PDMS 마이크로렌즈가 집적화된 PDMS 미세유체 칩을 소개하고자 한다. 기존에 제작된 PDMS 미세유체 칩 위에 간편히 정렬하여 올려놓아 사용함으로써 검출 효율을 증가시킬 수 있는 PDMS 마이크로렌즈를 제작하였다. PDMS 마이크로렌즈는 포토레지스트 리플로우와 PDMS 복제 몰딩에 의해 제작되었다. 이 제작 방법은 간단하며 높은 치수 정확성 및 좋은 마이크로렌즈의 성능을 제공한다. PDMS 미세유체 칩 위에 집적화된 PDMS 마이크로렌즈가 적혈구를 이용한 레이저 광 산란을 통한 세포 검출 실험에서 레이저 강도를 증가시켜 신호대잡음비 및 감도를 증가시킴을 검증하였다.

• 대한기계학회논문집B
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• 제34권7호
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• pp.671-677
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• 2010

본 연구에서는 직경이 수백 nm로부터 수 ${\mu}m$에 이르는 균일한 크기의 액적을 생성하는 마이크로 플루이딕 플랫폼이 설계되었다. 미세한 액적을 생성하기 위하여 T-정션과 유동집속 장치가 마이크로�a푸이딕 채널로 통합되었다. 상대적으로 큰 수성 액적들이 상류의 T-정션에서 생성되어 유동집속 장치로 이송되는데, 여기에서 각각의 액적은 압력과 점성응력의 작용에 의하여 목표로 하는 크기로 잘게 쪼개진다. 이러한 구성은 내부 유체의 매우 느린 유량과 유동집속 영역에서 내부 및 외부 유체 사이의 높은 유량비를 가능하게 한다. 본 마이크로플루이딕 장치는 약 $1\;{\mu}m$ 크기의 직경을 가지는 액적들을 3%보다 작은 표준 편차로 생성할 수 있음이 제시되었다.

• 센서학회지
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• 제27권4호
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• pp.237-241
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• 2018

The real-time enrichment and detection of pathogens are serious issues and rapidly evolving field of research because of the ability of these pathogens to cause infectious diseases. In general, bacterial detection is accomplished by conventional colony counting or by polymerase chain reaction (PCR) after DNA extraction. As colony counting requires considerable time to cultivate, PCR is an attractive method for rapid detection. A small number of pathogens can cause diseases. Hence, a pretreatment process, such as enrichment is essential for detecting bacteria in an actual environment. Thus, in this study, we developed a microfluidic chip capable of performing rapid enrichment of bacteria and the extraction of their genes. A lectin, i.e., Concanavalin A (ConA), which shows binding affinity to the surface of most bacteria, was coated on the surface of magnetic particles to nonspecifically capture bacteria. It was subsequently concentrated through magnetic forces in a microfluidic channel. To lyse the captured bacteria, magnetic particles were irradiated by a wavelength of 532nm. The photo-thermal effect on the particles was sufficient for extracting DNA, which was consequently utilized for the identification of bacteria. Our device will help monitor the existence of bacteria in various environmental situations such as water, air, and soil.

• Biotechnology and Bioprocess Engineering:BBE
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• 제11권5호
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• pp.455-461
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• 2006

In this study, we have described a method for the fabrication of a protein chip on silicon substrate using hydrophobic thin film and microfluidic channels, for the simultaneous detection of multiple targets in samples. The use of hydrophobic thin film provides for a physical, chemical, and biological barrier for protein patterning. The microfluidic channels create four protein patterned strips on the silicon surfaces with a high signal-to-noise ratio. The feasibility of the protein chips was determined in order to discriminate between each protein interaction in a mixture sample that included biotin, ovalbumin, hepatitis B antigen, and hepatitis C antigen. In the fabrication of the multiplexed assay system, the utilization of the hydrophobic thin film and the microfluidic networks constitutes a more convenient method for the development of biosensors or biochips. This technique may be applicable to the simultaneous evaluation of multiple protein-protein interactions.

• Korean Chemical Engineering Research
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• 제51권6호
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• pp.760-765
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• 2013

액적기반 미세유체 시스템을 이용해 난백단백질인 라이소자임의 결정화실험을 하였다. Flow-focusing 칩을 이용해 water-in-oil 형태의 액적을 만들고 페트리 디쉬와 십자몰드에 넣은 후, 액적 내부에서 라이소자임 수용액과 침전제 (NaCl) 사이의 액-액 반응을 관찰하였다. 그리고 수용액의 pH가 4.8일 때와 7.2일 때의 결정형태를 비교하였다. 그 결과, pH 4.8에서는 다면체 또는 판상형의 결정이 형성되었고, pH 7.2에서는 침상형 결정이 생성되었다. pH 4.8, 7.2 두 경우 액적이 홀로 있을 때에는 액적부피가 유지되거나 감소하면서 결정이 형성되었다. 하지만 액적이 서로 인접해 있을 때는 액적사이의 상호작용이 관찰되었고, 두 pH에서 다른 경향성을 보였다. pH 4.8에서는 인접한 액적의 부피에 영향을 주어 한 액적의 부피가 커졌고, 부피가 커진 액적에서 결정이 형성되었다. pH 7.2에서는 부피에 영향을 서로 주지 않고 각각의 액적에서 결정이 형성되었다.

• 대한기계학회논문집B
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• 제31권3호
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• pp.209-216
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• 2007

Bacterial chemotaxis is essential to the study of structure and function of bacteria. Although many studies have accumulated the knowledge about chemotaxis in the past, the motion of a single bacterium has not been studied much yet. In this study, we have developed a device microfabricated by soft lithography and consisting of microfluidic channels. The microfluidic assay generates a concentration gradient of chemoattractant linearly in the main channel by only diffusion of the chemicals. Bacteria are injected into the main channel in a single row by hydrodynamic focusing technique. We measured the velocity of bacteria in response to a given concentration gradient of chemoattractant using the microfludic assay, optical systems with CCD camera and simple PTV (Particle Tracking Velocimetry) algorithm. The advantage of this assay and experiment is to measure the velocity of a single bacterium and to quantify the degree of chemotaxis by statistically analyzing the velocity at the same time. Specifically, we measured and analyzed the motility of Escherichia coli strain RP437 in response to various concentration gradients of L-aspartate statistically and quantitatively by using this microfluidic assay. We obtained the probability density of the velocity while RP437 cells are swimming and tumbling in the presence of the linear concentration gradient of L-aspartate, and quantified the degree of chemotaxis by analyzing the probability density.

• 한국분말재료학회지
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• 제23권2호
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• pp.143-148
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• 2016

A microfluidic reactor with computer-controlled programmable isocratic pumps and online detectors is employed as a combinatorial synthesis system to synthesize and analyze materials for fabricating CdSe quantum dots for various applications. Four reaction condition parameters, namely, the reaction temperature, reaction time, Cd/Se compositional ratio, and precursor concentration, are combined in synthesis condition sets, and the size of the synthesized CdSe quantum dots is determined for each condition. The average time corresponding to each reaction condition for obtaining the ultraviolet-visible absorbance and photoluminescence spectra is approximately 10 min. Using the data from the combinatorial synthesis system, the effects of the reaction conditions on the synthesized CdSe quantum dots are determined. Further, the data is used to determine the relationships between the reaction conditions and the CdSe particle size. This method should aid in determining and selecting the optimal conditions for synthesizing nanoparticles for diverse applications.

• 한국전자파학회논문지
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• 제26권1호
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• pp.47-53
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• 2015

본 논문은 미세유체채널에 채워진 유체를 이용하여 위상응답을 제어하는, 잉크젯 프린터로 인쇄된 미세유체채널 복합 좌 우향 전송선로(CRLH TL: Composite Right/Left Handed Transmission Line)를 제안한다. 제안된 CRLH TL은 종이 위에 은 나노입자 잉크를 이용하여 인쇄되었으며, Poly Methyl Methacrylate(PMMA)에 레이저 식각을 이용하여 제작된 미세유체채널은 잉크젯 프린터로 인쇄된 접착물질인 SU-8을 이용하여 CRLH TL 위에 부착되었다. 제안된 CRLH TL은 미세유체채널에 채워진 유체에 따라서 위상응답을 변화시킬 수 있으며, 미세유체채널에 각기 다른 유체가 흐를 때, 900 MHz에서 -10 dB 이하의 반사계수를 유지한 상태로 위상 지연, $0^{\circ}$ 위상, 위상 앞섬 특성을 모두 나타낼 수 있음을 확인하였다. 제안된 CRLH TL의 성능은 시뮬레이션 결과와 측정 결과를 통하여 성공적으로 증명되었다.