We demonstrate an innovative method of PCR product identification that is based on thermal denatu... more We demonstrate an innovative method of PCR product identification that is based on thermal denaturation of PCR product-captured bead using integrated BioFET. Laborious purification and concentration of PCR product were easily carried by capturing the samples on the solid surface like microbeads. When temperature raised upto the denaturation point of PCR product, potential of BioFET is changed by mobile DNA in solution from PCR product-captured beads. By differentiating potential change with respect to temperature change, melting temperature can be determined. In this way, we successfully discriminated three kinds of PCR product using their different melting temperature and improved sensitivity of detection. We expect that proposed method can potentially be used for the identification of multiplex PCR products.
Small (Weinheim an der Bergstrasse, Germany), 2018
Cancer heterogeneity is a notorious hallmark of this disease, and it is desirable to tailor effec... more Cancer heterogeneity is a notorious hallmark of this disease, and it is desirable to tailor effective treatments for each individual patient. Drug combinations have been widely accepted in cancer treatment for better therapeutic efficacy as compared to a single compound. However, experimental complexity and cost grow exponentially with more target compounds under investigation. The primary challenge remains to efficiently perform a large-scale drug combination screening using a small number of patient primary samples for testing. Here, a scalable, easy-to-use, high-throughput drug combination screening scheme is reported, which has the potential of screening all possible pairwise drug combinations for arbitrary number of drugs with multiple logarithmic mixing ratios. A "Christmas tree mixer" structure is introduced to generate a logarithmic concentration mixing ratio between drug pairs, providing a large drug concentration range for screening. A three-layer structure desig...
Cell migratory direction and speed are predicted based on morphological features using computer v... more Cell migratory direction and speed are predicted based on morphological features using computer vision and machine learning algorithms.
Inflammatory breast cancer (IBC) is the most lethal form of breast cancer. All IBC patients have ... more Inflammatory breast cancer (IBC) is the most lethal form of breast cancer. All IBC patients have lymph node involvement and one-third of patients already have distant metastasis at diagnosis. This propensity for metastasis is a hallmark of IBC distinguishing it from less lethal non-inflammatory breast cancers (nIBC). Genetic profiling studies have been conducted to differentiate IBC from nIBC, but no IBC cancer-cell-specific gene signature has been identified. We hypothesized that a tumor-extrinsic factor, notably tumor-associated macrophages, promotes and contributes to IBC's extreme metastatic phenotype. To this end, we studied the effect of macrophage-conditioned media (MCM) on IBC. We show that two IBC cell lines are hyper-responsive to MCM as compared to normal-like breast and aggressive nIBC cell lines. We further interrogated IBC's hyper-responsiveness to MCM using a microfluidic migration device, which permits individual cell migration path tracing. We found the MCM ...
3D cell culture in the extracellular matrix (ECM), which not only provides structural support to ... more 3D cell culture in the extracellular matrix (ECM), which not only provides structural support to cellular constituents, but also initiates regulatory biochemical cues for a variety of important cell functions in tissue, has become more and more important in understanding cancer pathology and drug testing. Although the ECM-gel has been used in cell culture both in bulk and on-chip, previous studies focused on collective cell behavior rather than single-cell heterogeneity. To track the behavior of each individual cell, we have developed a gel-island chip, which can form thousands of islands containing single cells encapsulated by the desired ECM. Optimized by Poisson's distribution, the device can attain 34% single cell capture efficiency of the exact number of single cells per island. A good culture media exchange rate and high cell viability can be achieved in the gel-islands. The cells in the islands can be automatically counted for high-throughput analysis. As a proof of conce...
Proteolytic degradation of the extracellular matrix (ECM) is critical in cancer invasion, and rec... more Proteolytic degradation of the extracellular matrix (ECM) is critical in cancer invasion, and recent work suggests that heterogeneous cancer populations cooperate in this process. Despite the importance of cell heterogeneity, conventional proteolytic assays measure average activity, requiring thousands of cells and providing limited information about heterogeneity and dynamics. Here, we developed a microfluidic platform that provides high-efficiency cell loading and simple valveless isolation, so the proteolytic activity of a small sample (10-100 cells) can be easily characterized. Combined with a single cell derived (clonal) sphere formation platform, we have successfully demonstrated the importance of microenvironmental cues for proteolytic activity and also investigated the difference between clones. Furthermore, the platform allows monitoring single cells at multiple time points, unveiling different cancer cell line dynamics in proteolytic activity. The presented tool facilitate...
2014 IEEE 27th International Conference on Micro Electro Mechanical Systems (MEMS), 2014
We present a novel design of single cell-cell interaction platform for studying tumor-stromal int... more We present a novel design of single cell-cell interaction platform for studying tumor-stromal interaction. In cell-cell interaction assays, monitoring single cell behavior is critical to study highly heterogeneous population (e.g., cancer). For example, metastatic cancer cells are typically transported as a single circulating tumor cell; therefore, tumorigenesis should be induced from a single cell because it might be quite different from co-culturing many cells. In this work, we report a microfluidic chip that allows for isolating a pair of cells by using immiscible liquid isolation. We present the method of using a semi-permeable membrane to retain secreted proteins for interaction, while maintaining the exchange of nutrition for long-term cell-cell interaction studies. We verified proliferation enhancement of tumor cells when co-cultured with stromal cells, demonstrating the feasibility of our device as a generic platform of cell-cell interaction studies.
Photodynamic therapy (PDT), wherein light sensitive non-toxic agents are locally and selectively ... more Photodynamic therapy (PDT), wherein light sensitive non-toxic agents are locally and selectively activated using light, has emerged as an appealing alternative to traditional cancer chemotherapy. Yet to date, PDT efficacy has been mostly characterized using 2D cultures. Compared to 2D cultures, 3D sphere culture generates unique spatial distributions of nutrients and oxygen for the cells that better mimics the in-vivo conditions. Using a novel polyHEMA (non-adherent polymer) fabrication process, we developed a microfluidic sphere formation platform that can (1) generate 1,024 uniform (size variation <10%) cancer spheres within a 2 cm by 2 cm core area, (2) culture spheres for more than 2 weeks, and (3) allow the retrieval of spheres. Using the presented platform, we have successfully characterized the different responses in 2D and 3D cell culture to PDT. Furthermore, we investigated the treatment resistance effect in cancer cells induced by tumor associated fibroblasts (CAF). Alt...
We present a new way of multi-spectral fluorescence microscopy using the embedded liquid filters ... more We present a new way of multi-spectral fluorescence microscopy using the embedded liquid filters in a microfluidic chip, providing flexibility of filter changes for target fluorescence wavelengths and low-cost assays for point-of-care (POC) appli-cations. Widely available food color solutions are adopted for emission filter to absorb residual excitation light. Absorbance of the microfluidic liquid filter was measured for various dye concentrations and filter layer thicknesses. Also, absorbance spectrum of two different color mixtures was investigated for tuning the filter wavelength. Both results match with theoretical Beer-Lambert Law. On-chip liquid-filter fluorescence imaging was demonstrated with multiple LED light sources and fluoro-phores. Live (green)/dead (red) fluorescence images of C6 cells viability assays were successfully demonstrated using the fa-bricated microchip with the embedded liquid filters. The images taken with the liquid filter were comparable to those from t...
Tumor cell migration toward and intravasation into capillaries is an early and key event in cance... more Tumor cell migration toward and intravasation into capillaries is an early and key event in cancer metastasis, yet not all cancer cells are imbued with the same capability to do so. This heterogeneity within a tumor is a fundamental property of cancer. Tools to help us understand what molecular characteristics allow a certain subpopulation of cells to spread from the primary tumor are thus critical for overcoming metastasis. Conventional in vitro migration platforms treat populations in aggregate, which leads to a masking of intrinsic differences among cells. Some migration assays reported recently have single-cell resolution, but these platforms do not provide for selective retrieval of the distinct migrating and non-migrating cell populations for further analysis. Thus, to study the intrinsic differences in cells responsible for chemotactic heterogeneity, we developed a single-cell migration platform so that individual cells' migration behavior can be studied and the heterogen...
Cancer heterogeneity has received considerable attention for its role in tumor initiation and pro... more Cancer heterogeneity has received considerable attention for its role in tumor initiation and progression, and its implication for diagnostics and therapeutics in the clinic. To facilitate a cellular heterogeneity study in a low cost and highly efficient manner, we present a microfluidic platform that allows traceable clonal culture and characterization. The platform captures single cells into a microwell array and cultures them for clonal expansion, subsequently allowing on-chip characterization of clonal phenotype and response against drug treatments. Using a heterogeneous prostate cancer model, the PC3 cell line, we verified our prototype, identifying three different sub-phenotypes and correlating their clonal drug responsiveness to cell phenotype.
We demonstrate a new optical approach to generate high-frequency (.15 MHz) and high-amplitude foc... more We demonstrate a new optical approach to generate high-frequency (.15 MHz) and high-amplitude focused ultrasound, which can be used for non-invasive ultrasound therapy. A nano-composite film of carbon nanotubes (CNTs) and elastomeric polymer is formed on concave lenses, and used as an efficient optoacoustic source due to the high optical absorption of the CNTs and rapid heat transfer to the polymer upon excitation by pulsed laser irradiation. The CNT-coated lenses can generate unprecedented optoacoustic pressures of .50 MPa in peak positive on a tight focal spot of 75 mm in lateral and 400 mm in axial widths. This pressure amplitude is remarkably high in this frequency regime, producing pronounced shock effects and non-thermal pulsed cavitation at the focal zone. We demonstrate that the optoacoustic lens can be used for micro-scale ultrasonic fragmentation of solid materials and a single-cell surgery in terms of removing the cells from substrates and neighboring cells. H igh-amplitude focused ultrasound can provide localized perturbation in liquids and tissues by inducing shock, acoustic cavitation, and heat deposition within focal volumes 1-4. Such mechanical and thermal disturbances have been widely used to deliver targeted impacts to cells and tissues for biomedical therapy: for example, trans-membrane drug delivery (e.g. trans-dermal and blood-brain barrier opening) 5-7 , neural activity modulation in brain 8,9 , and thrombolysis 10 , often relying on acoustic cavitation or externally injected micro-bubbles. Remarkable progress have been made in clinical kidney-stone fragmentation 11,12 as well as ablation-based tumor therapy under high-intensity focused ultrasound (HIFU) 13-15. Moreover, cavitation-based ultrasound therapy such as histotripsy has shown some success as a new invasive mechanical ablation tool 16. Although the above beneficial effects have been confirmed over a broad range of biomedical applications, their focal dimensions are insufficiently large: typically .2 mm in a lateral plane and often .10 mm in an axial plane. This is because the focused ultrasound has been generated using low-frequency piezoelectric transducers (a few MHz) 14. Moreover, the low-frequency pressure waves necessitate large lens sizes on the order of several centimeters which are not proper for intra-operative applications. High-frequency ultrasound (tens of MHz) would provide obvious advantages on spatial and temporal confinement, opening numerous opportunities for highaccuracy cell therapy as well as ablation-treatment over single tissue layers and micro-vasculatures. It should be also noted that tumors are very often grown adjacent to a vital blood vessel that should be kept intact, and can be hardly addressed by the bulky focal spots in a selective manner. Therefore, high-precision ablation is essential for use in surgery. However, it is challenging to achieve therapeutic pressure amplitudes in the high-frequency regime (.10 MHz): for example, stronger tensile pressure (P) is required at higher frequency (f) to induce the acoustic cavitation (i.e. P / f 1/2 approximately 17) which can create significant impacts upon adjacent media through liquid micro-jets and shock waves due to bubble collapse. Furthermore, such high pressure must be achieved at the focal spot in spite of severe acoustic attenuation for the high-frequency components (2.2 3 10 23 dB/(cm 3 MHz 2) in water). The acoustic cavitation can be facilitated by heat deposition through repetitive pulses, but thermal heating should be avoided in many cases of cell therapy applications (e.g. gene therapy) because cellular metabolism is easily transformed by a slight temperature change. A single pulsed cavitation without heat deposition would be useful in these applications.
2013 IEEE 26th International Conference on Micro Electro Mechanical Systems (MEMS), 2013
This paper reports on solid UV cross-linked Poly(ethylene)-glycol-diacrylate (PEGDA) as a materia... more This paper reports on solid UV cross-linked Poly(ethylene)-glycol-diacrylate (PEGDA) as a material for microfluidic devices for biological applications. We have evaluated biocompatibility of PEGDA through two separate means: 1) by examining cell viability and attachment on cross-linked PEGDA surfaces for cell culture applications, and 2) by determining if cross-linked PEGDA inhibits the polymerase chain reaction (PCR) processes for on-chip PCR. Through these studies a correlation has been found between degree of curing and cell viability, attachment, as well as on PCR outcome.
The oscillating behaviour of TGS813 and TGS203S sensors in hazardous gases such as LPG and CO was... more The oscillating behaviour of TGS813 and TGS203S sensors in hazardous gases such as LPG and CO was studied under the oscillating conditions of rectangular wave, applied voltage 5 V, and duty ratio as 30 s/(30 s + 20 s). It was shown that the oscillating behaviour was obviously different with the two type sensors. The data features were extracted by using Fourier and wavelet transform (WT). There were some very obscure differences among the amplitudes in fast Fourier transform (FFT) under different concentrations of LPG or CO. Further FFT analysis showed that it was difficult to discriminate between 800 ppm LPG and 800 ppm CO because of very little difference in the frequency content. By comparison, the corresponding coefficient plots in continuous wavelet transform (CWT) were investigated, and the original signal was also decomposed into coarse approximation A1 and five detailed information D5-D1. The results showed that the WT was more appropriate than FFT for the frequency-time problem.
This paper demonstrates a new method of implementing complex microchannels in PDMS, which is simp... more This paper demonstrates a new method of implementing complex microchannels in PDMS, which is simply constructed using three-dimensional photoresist structures as a master mold for the PDMS replica process. The process utilizes UV-insensitive LOR resist as a sacrificial layer to levitate the structural photoresist. In addition, the thickness of photoresist structures can be controlled by multi-step UV exposure. By using these techniques, various three-dimensional photoresist structures were successfully implemented, including the recessed cantilevers, suspended bridges, and the complex plates with micro-pits or micro-villi. We demonstrate that the three-dimensional photoresist structures are applicable to implementing complex multiple microchannels in PDMS by using the PDMS replica method.
We present a novel high-throughput microfluidic platform that enables the evaluation of the antic... more We present a novel high-throughput microfluidic platform that enables the evaluation of the anticancer efficacy of photodynamic therapy (PDT) drugs over multiple microenvironmental factors. PDT is uniquely complex, originating from its dependence on three separate but essential elements: drug (or also called photosensitizer), oxygen, and light. Thus, obtaining a reliable evaluation of PDT efficacy is highly challenging, requiring considerable effort and time to evaluate all three interdependent parameters. In this paper, we report a high-throughput efficacy screening platform that we implemented by developing microfluidic components that individually control basic PDT elements (photosensitizer concentrations, oxygen levels, and light fluence), and then integrating them into a single triple-layer device. The integrated microfluidic chip consists of an array of small compartment, each corresponding to a specific combination of these three variables. This allows for more than 1,000 different conditions being tested in parallel. Cancer cells are cultured within the device, exposed to different PDT conditions, and then monitored for their viability using live/dead fluorescence staining. The entire screening assay takes only 1 hour, and the collected PDT outcomes (cell viability) for combinatorial screening are analysed and reported as traditional dose-response curves or 3D bubble charts using a custom software. As a proof of concept, methylene blue is adopted as a photosensitizer and its drug efficacy on C6 glioma cells has been successfully evaluated for total 324 PDT conditions using the fabricated chip. This platform can facilitate not only the development of new photosensitizers but also the optimization of current PDT protocols.
Journal of Micromechanics and Microengineering, 2001
We propose the concept of a microelectromechanical system (MEMS) scale reciprocating device power... more We propose the concept of a microelectromechanical system (MEMS) scale reciprocating device powered by burnt gas and we have fabricated its prototype to investigate the applicability of the concept in a microscale power generator. In this investigation, combustion in a microscale chamber was studied using thermodynamic principles to estimate theoretical power output. We have carried out an evaluation of relevant subsystems and fabrication processes to realize the heat engine in such a small scale for further development of similar devices. A variable depth microcombustion chamber was built in-house to test the combustion characteristics in a small volume. Measurements include pressure transition after ignition and high-speed flame visualization. Test conditions include combustion chamber depth around the flame quenching distance, below which combustion theory predicts no burning. By analyzing the measured data, the combustion efficiency and available work were obtained and used for the design of a reciprocating MEMS device. The results of the combustion measurements required that the chamber height be 1 mm or more for stable ignition and flame propagation. Based on these findings of the microcombustion experiment, we formulated a MEMS fabrication process and made a reciprocating device. The device has a combustion chamber with a volume of 1 mm 3 , and the cross section of the cylinder has a rectangular shape with a height of 1 mm and a width of 2 mm. Photosensitive glass was chosen as a structural material. A thick photoresist mold and electroplating were used for constructing the overall structure. A single stroke experiment with hydrogen as a fuel was recorded by a high-speed digital video camera showing piston displacement at reasonable speeds.
In this letter, we report on thermally driven thin film bulk acoustic resonator (TFBAR) voltage-c... more In this letter, we report on thermally driven thin film bulk acoustic resonator (TFBAR) voltage-controlled oscillators (VCOs) integrated with a microheater element. The oscillation frequency of TFBAR VCOs is controlled by applying different power (or bias voltage) to the microheaters implemented on the TFBAR membrane. The TFBARs with the microheater elements are fabricated by Si bulk micromachining technology. The series feedback schematic TFBAR VCO has an oscillation frequency of 3.566 GHz, an output power of À21 dBm, and a phase noise of À110 dBc/Hz at an offset frequency of 100 kHz. The measured frequency controllability and the measured temperature coefficient of resistance (TCR) of the heater element are 3.19 MHz/V and 0.24%/ C, respectively, with a resistance of 88.1 at room temperature.
A high fill-factor uncooled infrared (IR) bolometer has been fabricated by using thin-film titani... more A high fill-factor uncooled infrared (IR) bolometer has been fabricated by using thin-film titanium resistors sandwiched in a surfacemicromachined silicon oxinitride membrane (50 m 2 50 m). This bolometer is realized in multilevel electrothermal structures with a fillfactor over 92%. From the multilevel structure, thermal isolation can be independently optimized without sacrificing IR absorbing area. Initial measurements show a thermal time constant of 12 ms, a responsivity of 1600 V/W, and a detectivity (D 3) of 5 2 10 8 cm p Hz/W.
We demonstrate an innovative method of PCR product identification that is based on thermal denatu... more We demonstrate an innovative method of PCR product identification that is based on thermal denaturation of PCR product-captured bead using integrated BioFET. Laborious purification and concentration of PCR product were easily carried by capturing the samples on the solid surface like microbeads. When temperature raised upto the denaturation point of PCR product, potential of BioFET is changed by mobile DNA in solution from PCR product-captured beads. By differentiating potential change with respect to temperature change, melting temperature can be determined. In this way, we successfully discriminated three kinds of PCR product using their different melting temperature and improved sensitivity of detection. We expect that proposed method can potentially be used for the identification of multiplex PCR products.
Small (Weinheim an der Bergstrasse, Germany), 2018
Cancer heterogeneity is a notorious hallmark of this disease, and it is desirable to tailor effec... more Cancer heterogeneity is a notorious hallmark of this disease, and it is desirable to tailor effective treatments for each individual patient. Drug combinations have been widely accepted in cancer treatment for better therapeutic efficacy as compared to a single compound. However, experimental complexity and cost grow exponentially with more target compounds under investigation. The primary challenge remains to efficiently perform a large-scale drug combination screening using a small number of patient primary samples for testing. Here, a scalable, easy-to-use, high-throughput drug combination screening scheme is reported, which has the potential of screening all possible pairwise drug combinations for arbitrary number of drugs with multiple logarithmic mixing ratios. A "Christmas tree mixer" structure is introduced to generate a logarithmic concentration mixing ratio between drug pairs, providing a large drug concentration range for screening. A three-layer structure desig...
Cell migratory direction and speed are predicted based on morphological features using computer v... more Cell migratory direction and speed are predicted based on morphological features using computer vision and machine learning algorithms.
Inflammatory breast cancer (IBC) is the most lethal form of breast cancer. All IBC patients have ... more Inflammatory breast cancer (IBC) is the most lethal form of breast cancer. All IBC patients have lymph node involvement and one-third of patients already have distant metastasis at diagnosis. This propensity for metastasis is a hallmark of IBC distinguishing it from less lethal non-inflammatory breast cancers (nIBC). Genetic profiling studies have been conducted to differentiate IBC from nIBC, but no IBC cancer-cell-specific gene signature has been identified. We hypothesized that a tumor-extrinsic factor, notably tumor-associated macrophages, promotes and contributes to IBC's extreme metastatic phenotype. To this end, we studied the effect of macrophage-conditioned media (MCM) on IBC. We show that two IBC cell lines are hyper-responsive to MCM as compared to normal-like breast and aggressive nIBC cell lines. We further interrogated IBC's hyper-responsiveness to MCM using a microfluidic migration device, which permits individual cell migration path tracing. We found the MCM ...
3D cell culture in the extracellular matrix (ECM), which not only provides structural support to ... more 3D cell culture in the extracellular matrix (ECM), which not only provides structural support to cellular constituents, but also initiates regulatory biochemical cues for a variety of important cell functions in tissue, has become more and more important in understanding cancer pathology and drug testing. Although the ECM-gel has been used in cell culture both in bulk and on-chip, previous studies focused on collective cell behavior rather than single-cell heterogeneity. To track the behavior of each individual cell, we have developed a gel-island chip, which can form thousands of islands containing single cells encapsulated by the desired ECM. Optimized by Poisson's distribution, the device can attain 34% single cell capture efficiency of the exact number of single cells per island. A good culture media exchange rate and high cell viability can be achieved in the gel-islands. The cells in the islands can be automatically counted for high-throughput analysis. As a proof of conce...
Proteolytic degradation of the extracellular matrix (ECM) is critical in cancer invasion, and rec... more Proteolytic degradation of the extracellular matrix (ECM) is critical in cancer invasion, and recent work suggests that heterogeneous cancer populations cooperate in this process. Despite the importance of cell heterogeneity, conventional proteolytic assays measure average activity, requiring thousands of cells and providing limited information about heterogeneity and dynamics. Here, we developed a microfluidic platform that provides high-efficiency cell loading and simple valveless isolation, so the proteolytic activity of a small sample (10-100 cells) can be easily characterized. Combined with a single cell derived (clonal) sphere formation platform, we have successfully demonstrated the importance of microenvironmental cues for proteolytic activity and also investigated the difference between clones. Furthermore, the platform allows monitoring single cells at multiple time points, unveiling different cancer cell line dynamics in proteolytic activity. The presented tool facilitate...
2014 IEEE 27th International Conference on Micro Electro Mechanical Systems (MEMS), 2014
We present a novel design of single cell-cell interaction platform for studying tumor-stromal int... more We present a novel design of single cell-cell interaction platform for studying tumor-stromal interaction. In cell-cell interaction assays, monitoring single cell behavior is critical to study highly heterogeneous population (e.g., cancer). For example, metastatic cancer cells are typically transported as a single circulating tumor cell; therefore, tumorigenesis should be induced from a single cell because it might be quite different from co-culturing many cells. In this work, we report a microfluidic chip that allows for isolating a pair of cells by using immiscible liquid isolation. We present the method of using a semi-permeable membrane to retain secreted proteins for interaction, while maintaining the exchange of nutrition for long-term cell-cell interaction studies. We verified proliferation enhancement of tumor cells when co-cultured with stromal cells, demonstrating the feasibility of our device as a generic platform of cell-cell interaction studies.
Photodynamic therapy (PDT), wherein light sensitive non-toxic agents are locally and selectively ... more Photodynamic therapy (PDT), wherein light sensitive non-toxic agents are locally and selectively activated using light, has emerged as an appealing alternative to traditional cancer chemotherapy. Yet to date, PDT efficacy has been mostly characterized using 2D cultures. Compared to 2D cultures, 3D sphere culture generates unique spatial distributions of nutrients and oxygen for the cells that better mimics the in-vivo conditions. Using a novel polyHEMA (non-adherent polymer) fabrication process, we developed a microfluidic sphere formation platform that can (1) generate 1,024 uniform (size variation <10%) cancer spheres within a 2 cm by 2 cm core area, (2) culture spheres for more than 2 weeks, and (3) allow the retrieval of spheres. Using the presented platform, we have successfully characterized the different responses in 2D and 3D cell culture to PDT. Furthermore, we investigated the treatment resistance effect in cancer cells induced by tumor associated fibroblasts (CAF). Alt...
We present a new way of multi-spectral fluorescence microscopy using the embedded liquid filters ... more We present a new way of multi-spectral fluorescence microscopy using the embedded liquid filters in a microfluidic chip, providing flexibility of filter changes for target fluorescence wavelengths and low-cost assays for point-of-care (POC) appli-cations. Widely available food color solutions are adopted for emission filter to absorb residual excitation light. Absorbance of the microfluidic liquid filter was measured for various dye concentrations and filter layer thicknesses. Also, absorbance spectrum of two different color mixtures was investigated for tuning the filter wavelength. Both results match with theoretical Beer-Lambert Law. On-chip liquid-filter fluorescence imaging was demonstrated with multiple LED light sources and fluoro-phores. Live (green)/dead (red) fluorescence images of C6 cells viability assays were successfully demonstrated using the fa-bricated microchip with the embedded liquid filters. The images taken with the liquid filter were comparable to those from t...
Tumor cell migration toward and intravasation into capillaries is an early and key event in cance... more Tumor cell migration toward and intravasation into capillaries is an early and key event in cancer metastasis, yet not all cancer cells are imbued with the same capability to do so. This heterogeneity within a tumor is a fundamental property of cancer. Tools to help us understand what molecular characteristics allow a certain subpopulation of cells to spread from the primary tumor are thus critical for overcoming metastasis. Conventional in vitro migration platforms treat populations in aggregate, which leads to a masking of intrinsic differences among cells. Some migration assays reported recently have single-cell resolution, but these platforms do not provide for selective retrieval of the distinct migrating and non-migrating cell populations for further analysis. Thus, to study the intrinsic differences in cells responsible for chemotactic heterogeneity, we developed a single-cell migration platform so that individual cells' migration behavior can be studied and the heterogen...
Cancer heterogeneity has received considerable attention for its role in tumor initiation and pro... more Cancer heterogeneity has received considerable attention for its role in tumor initiation and progression, and its implication for diagnostics and therapeutics in the clinic. To facilitate a cellular heterogeneity study in a low cost and highly efficient manner, we present a microfluidic platform that allows traceable clonal culture and characterization. The platform captures single cells into a microwell array and cultures them for clonal expansion, subsequently allowing on-chip characterization of clonal phenotype and response against drug treatments. Using a heterogeneous prostate cancer model, the PC3 cell line, we verified our prototype, identifying three different sub-phenotypes and correlating their clonal drug responsiveness to cell phenotype.
We demonstrate a new optical approach to generate high-frequency (.15 MHz) and high-amplitude foc... more We demonstrate a new optical approach to generate high-frequency (.15 MHz) and high-amplitude focused ultrasound, which can be used for non-invasive ultrasound therapy. A nano-composite film of carbon nanotubes (CNTs) and elastomeric polymer is formed on concave lenses, and used as an efficient optoacoustic source due to the high optical absorption of the CNTs and rapid heat transfer to the polymer upon excitation by pulsed laser irradiation. The CNT-coated lenses can generate unprecedented optoacoustic pressures of .50 MPa in peak positive on a tight focal spot of 75 mm in lateral and 400 mm in axial widths. This pressure amplitude is remarkably high in this frequency regime, producing pronounced shock effects and non-thermal pulsed cavitation at the focal zone. We demonstrate that the optoacoustic lens can be used for micro-scale ultrasonic fragmentation of solid materials and a single-cell surgery in terms of removing the cells from substrates and neighboring cells. H igh-amplitude focused ultrasound can provide localized perturbation in liquids and tissues by inducing shock, acoustic cavitation, and heat deposition within focal volumes 1-4. Such mechanical and thermal disturbances have been widely used to deliver targeted impacts to cells and tissues for biomedical therapy: for example, trans-membrane drug delivery (e.g. trans-dermal and blood-brain barrier opening) 5-7 , neural activity modulation in brain 8,9 , and thrombolysis 10 , often relying on acoustic cavitation or externally injected micro-bubbles. Remarkable progress have been made in clinical kidney-stone fragmentation 11,12 as well as ablation-based tumor therapy under high-intensity focused ultrasound (HIFU) 13-15. Moreover, cavitation-based ultrasound therapy such as histotripsy has shown some success as a new invasive mechanical ablation tool 16. Although the above beneficial effects have been confirmed over a broad range of biomedical applications, their focal dimensions are insufficiently large: typically .2 mm in a lateral plane and often .10 mm in an axial plane. This is because the focused ultrasound has been generated using low-frequency piezoelectric transducers (a few MHz) 14. Moreover, the low-frequency pressure waves necessitate large lens sizes on the order of several centimeters which are not proper for intra-operative applications. High-frequency ultrasound (tens of MHz) would provide obvious advantages on spatial and temporal confinement, opening numerous opportunities for highaccuracy cell therapy as well as ablation-treatment over single tissue layers and micro-vasculatures. It should be also noted that tumors are very often grown adjacent to a vital blood vessel that should be kept intact, and can be hardly addressed by the bulky focal spots in a selective manner. Therefore, high-precision ablation is essential for use in surgery. However, it is challenging to achieve therapeutic pressure amplitudes in the high-frequency regime (.10 MHz): for example, stronger tensile pressure (P) is required at higher frequency (f) to induce the acoustic cavitation (i.e. P / f 1/2 approximately 17) which can create significant impacts upon adjacent media through liquid micro-jets and shock waves due to bubble collapse. Furthermore, such high pressure must be achieved at the focal spot in spite of severe acoustic attenuation for the high-frequency components (2.2 3 10 23 dB/(cm 3 MHz 2) in water). The acoustic cavitation can be facilitated by heat deposition through repetitive pulses, but thermal heating should be avoided in many cases of cell therapy applications (e.g. gene therapy) because cellular metabolism is easily transformed by a slight temperature change. A single pulsed cavitation without heat deposition would be useful in these applications.
2013 IEEE 26th International Conference on Micro Electro Mechanical Systems (MEMS), 2013
This paper reports on solid UV cross-linked Poly(ethylene)-glycol-diacrylate (PEGDA) as a materia... more This paper reports on solid UV cross-linked Poly(ethylene)-glycol-diacrylate (PEGDA) as a material for microfluidic devices for biological applications. We have evaluated biocompatibility of PEGDA through two separate means: 1) by examining cell viability and attachment on cross-linked PEGDA surfaces for cell culture applications, and 2) by determining if cross-linked PEGDA inhibits the polymerase chain reaction (PCR) processes for on-chip PCR. Through these studies a correlation has been found between degree of curing and cell viability, attachment, as well as on PCR outcome.
The oscillating behaviour of TGS813 and TGS203S sensors in hazardous gases such as LPG and CO was... more The oscillating behaviour of TGS813 and TGS203S sensors in hazardous gases such as LPG and CO was studied under the oscillating conditions of rectangular wave, applied voltage 5 V, and duty ratio as 30 s/(30 s + 20 s). It was shown that the oscillating behaviour was obviously different with the two type sensors. The data features were extracted by using Fourier and wavelet transform (WT). There were some very obscure differences among the amplitudes in fast Fourier transform (FFT) under different concentrations of LPG or CO. Further FFT analysis showed that it was difficult to discriminate between 800 ppm LPG and 800 ppm CO because of very little difference in the frequency content. By comparison, the corresponding coefficient plots in continuous wavelet transform (CWT) were investigated, and the original signal was also decomposed into coarse approximation A1 and five detailed information D5-D1. The results showed that the WT was more appropriate than FFT for the frequency-time problem.
This paper demonstrates a new method of implementing complex microchannels in PDMS, which is simp... more This paper demonstrates a new method of implementing complex microchannels in PDMS, which is simply constructed using three-dimensional photoresist structures as a master mold for the PDMS replica process. The process utilizes UV-insensitive LOR resist as a sacrificial layer to levitate the structural photoresist. In addition, the thickness of photoresist structures can be controlled by multi-step UV exposure. By using these techniques, various three-dimensional photoresist structures were successfully implemented, including the recessed cantilevers, suspended bridges, and the complex plates with micro-pits or micro-villi. We demonstrate that the three-dimensional photoresist structures are applicable to implementing complex multiple microchannels in PDMS by using the PDMS replica method.
We present a novel high-throughput microfluidic platform that enables the evaluation of the antic... more We present a novel high-throughput microfluidic platform that enables the evaluation of the anticancer efficacy of photodynamic therapy (PDT) drugs over multiple microenvironmental factors. PDT is uniquely complex, originating from its dependence on three separate but essential elements: drug (or also called photosensitizer), oxygen, and light. Thus, obtaining a reliable evaluation of PDT efficacy is highly challenging, requiring considerable effort and time to evaluate all three interdependent parameters. In this paper, we report a high-throughput efficacy screening platform that we implemented by developing microfluidic components that individually control basic PDT elements (photosensitizer concentrations, oxygen levels, and light fluence), and then integrating them into a single triple-layer device. The integrated microfluidic chip consists of an array of small compartment, each corresponding to a specific combination of these three variables. This allows for more than 1,000 different conditions being tested in parallel. Cancer cells are cultured within the device, exposed to different PDT conditions, and then monitored for their viability using live/dead fluorescence staining. The entire screening assay takes only 1 hour, and the collected PDT outcomes (cell viability) for combinatorial screening are analysed and reported as traditional dose-response curves or 3D bubble charts using a custom software. As a proof of concept, methylene blue is adopted as a photosensitizer and its drug efficacy on C6 glioma cells has been successfully evaluated for total 324 PDT conditions using the fabricated chip. This platform can facilitate not only the development of new photosensitizers but also the optimization of current PDT protocols.
Journal of Micromechanics and Microengineering, 2001
We propose the concept of a microelectromechanical system (MEMS) scale reciprocating device power... more We propose the concept of a microelectromechanical system (MEMS) scale reciprocating device powered by burnt gas and we have fabricated its prototype to investigate the applicability of the concept in a microscale power generator. In this investigation, combustion in a microscale chamber was studied using thermodynamic principles to estimate theoretical power output. We have carried out an evaluation of relevant subsystems and fabrication processes to realize the heat engine in such a small scale for further development of similar devices. A variable depth microcombustion chamber was built in-house to test the combustion characteristics in a small volume. Measurements include pressure transition after ignition and high-speed flame visualization. Test conditions include combustion chamber depth around the flame quenching distance, below which combustion theory predicts no burning. By analyzing the measured data, the combustion efficiency and available work were obtained and used for the design of a reciprocating MEMS device. The results of the combustion measurements required that the chamber height be 1 mm or more for stable ignition and flame propagation. Based on these findings of the microcombustion experiment, we formulated a MEMS fabrication process and made a reciprocating device. The device has a combustion chamber with a volume of 1 mm 3 , and the cross section of the cylinder has a rectangular shape with a height of 1 mm and a width of 2 mm. Photosensitive glass was chosen as a structural material. A thick photoresist mold and electroplating were used for constructing the overall structure. A single stroke experiment with hydrogen as a fuel was recorded by a high-speed digital video camera showing piston displacement at reasonable speeds.
In this letter, we report on thermally driven thin film bulk acoustic resonator (TFBAR) voltage-c... more In this letter, we report on thermally driven thin film bulk acoustic resonator (TFBAR) voltage-controlled oscillators (VCOs) integrated with a microheater element. The oscillation frequency of TFBAR VCOs is controlled by applying different power (or bias voltage) to the microheaters implemented on the TFBAR membrane. The TFBARs with the microheater elements are fabricated by Si bulk micromachining technology. The series feedback schematic TFBAR VCO has an oscillation frequency of 3.566 GHz, an output power of À21 dBm, and a phase noise of À110 dBc/Hz at an offset frequency of 100 kHz. The measured frequency controllability and the measured temperature coefficient of resistance (TCR) of the heater element are 3.19 MHz/V and 0.24%/ C, respectively, with a resistance of 88.1 at room temperature.
A high fill-factor uncooled infrared (IR) bolometer has been fabricated by using thin-film titani... more A high fill-factor uncooled infrared (IR) bolometer has been fabricated by using thin-film titanium resistors sandwiched in a surfacemicromachined silicon oxinitride membrane (50 m 2 50 m). This bolometer is realized in multilevel electrothermal structures with a fillfactor over 92%. From the multilevel structure, thermal isolation can be independently optimized without sacrificing IR absorbing area. Initial measurements show a thermal time constant of 12 ms, a responsivity of 1600 V/W, and a detectivity (D 3) of 5 2 10 8 cm p Hz/W.
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Papers by Euisik Yoon