Papers by Keyword: Lab-on-a-Chip

Abstract: This paper investigates the ability of biomachined lab-on-a-chip (LoC) to perform drug testing of Amphotericin B to the Candida albicans. The chip is made of polydimethyl siloxane (PDMS). Molds are patterned using CNC milling followed by biomachining. CNC milling process creates channel features on the bottom mold, while biomachining forms rough surface on the channels. After the molds are created, LoC can be manufactured using those molds. Hence, contour surface on LoC’s channels is also realized following the mold surface. Later, Candida albicans is seeded on the LoC’s channels for 24 and 48 hours with the continuous flow of Yeast Nitrogen Base (YNB) Sterile. Then, cell viability is tested using 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium (MTT). The result shows that C. albicans could adhere and grow in the LoC channels. Based on this result, drug testing is conducted in the presence and absence of Amphotericin B (Amp B) under two schemes: without (static) and with (dynamic) the continuous flow of YNB Sterile and Amp B. After 48 hour incubation period, C. albicans biofilm of 28.72 % is shown during dynamic scheme, whereas static scheme had C. albicans biofilm of 99.32 % indicating that the dynamic scheme provides a better efficacy compared to the static scheme.

Abstract: The characterization of novel portable microfluidic devices, with capillary phenomena as filling process, was presented. Created for monitoring multiplexed chemiluminescence (CL) reactions, the devices are amenable for integration with organic photodiodes (OPDs) for future incorporation in microelectromechanical systems (MEMS). Using finite element method (FEM), four designs of microfluidic chips were simulated. The parallel design, despite its quick total filling time (TFT), presented a non-uniform filling process and a non-compact structure. The series design was the most compact structure studied. However, it cannot be used in CL reactions with multiple analytes in common, which is a major drawback. Regarding the parallel-series, it solved some of the problems presented in previous designs but its high TFT and non-compactness make it a less attractive solution for a portable microfluidic device. Finally, the optimized parallel design proved to be the best design, presenting a quick TFT, high compactness and the capability to have CL reactions sharing analytes.

Abstract: The use of microfluidic devices brings some benefits such as low reagent consumption, shorter analysis time, portability and cost reduction. The potential of this technology has constantly grown over time and lead to the development of competitive manufacture processes. The production of such microfluidic devices is usually done by molding processes which allow mass production of polymer disposables with a low cost per unit. In a prototype phase these methods are, however, expensive. To overcome the multi-step fabrication the direct milling in polymer is an alternative. In this paper micro structures are directly milled in polymethyl methacrylate (PMMA) with self-developed micro end mills and the proper CAD/CAM integration offering a fast response in manufacturing of complex structures even in the micrometer range The direct milling of structures in PMMA with micro tools-diameter 120 μm is a feasible method to produce a physical prototype. The chosen micro end mills and strategies represent a competitive process in a prototyping level by reducing time to market.

Abstract: Cysteine and homocysteine are the biological thiols which have an important function in various biochemical processes in our body. Alterations in their level lead to various abnormalities. Therefore, we fabricated a miniaturized platform for capillary electrophoresis that could separate and detect these amino thiols electrochemically. The device was fabricated using conventional photolithography technique on the glass substrate. The microchannel was molded in polydimethylsiloxane with gold electrodes deposited on glass for separation and detection. Based on the amperometric detection, we could detect cysteine in 93 sec while homocysteine was detected in 111 sec.

Abstract: Cell-cell fusion is an important natural and engineered process for in-depth studies into hybridomas, developmental biology, immunology and various cellular therapies. It is also a powerful tool for analysis of gene expression, chromosomal mapping, antibody production, cloning mammals, and cancer immunotherapy. However, research so far has primarily focused on cell models such as C.elegans, drosophila, myoblasts, spleen-myeloma cell hybrids and various plant protoplasts. Rhabdomyosarcoma cells are a rare form of musculoskeletal cancer cells found in the head, neck, and other less skeletal areas of the human cancer patient’s body. As these cells do not normally undergo fusion naturally, they are an interesting model for studying cell fusion. Among all the techniques for fusion, electrofusion (or electroporation) can be applied to a wide range of cell types with high efficiency and high post-fusion viability. By coupling these cells with this technique, the effectson cell proliferation, growth pattern, and hybridoma count wereinvestigated. Overall, the experimental results showed that an adequate electrical stimulation helped to facilitate the fusion and proliferation of the RD cells. Furthermore,a DC current produced the highest number of hybridomas, while maintaining the highest proliferation rate.After subtracting for the control samples, an average fusion yield of 24% was obtained under this DC setting, which is comparable to the fusion yield of 20% obtained using the same technique by other researchers. This is a promising result for its application in the production of monoclonal antibodies for cancer research and treatment.

Abstract: The present work presents the availability of using porous matrix in microfluidic devices as a solid phase matrix for immunoassays. Porous matrixes on the surface of the microchannels were microfabricated by MEMS technology and electrochemical etching technology, which were coated on the wall of the rectangular microchannel in the microdevices to provide a surface-enlarging matrix. The microfabrication process of porous matrixes was investigated and optimized. Then the surface morphology of the porous matrixes was characterized by SEM. Both direct method and dual-antibody sandwich method were used for fluorescence immunoassays. Using sandwich immunoassay, 6.25μg/mL - 25μg/mL human IgG in real samples have been detected with a correlation coefficient of 0.9773. These porous microdevices have shown some advantages over its large-scale counterparts, including lower sample and reagent consumption, lower cost, less analytical time and so on, which enables detection for clinical testing.

Abstract: This paper reviews the ways in which micro and nano sensors have evolved within biology and medicine. The target measurands include an ever-increasing number of simple and complex molecules, physical quantities, and electrical and magnetic phenomena. Micro sensors based on electrochemical, acoustic, piezoelectric and optical principles are contributing to clinical care of patients who may benefit from the continuous monitoring of critical variables in intensive care or from the ability to perform convenient self-monitoring during normal daily life. Sensors constructed on the nano-scale are now emerging, especially for complex bio-molecules such as DNA. These are strengthening basic research, for example in the study of genetic factors in disease and for discovery of new drugs. Scanning probe technology and nano optics, including surface enhanced Raman spectroscopy, play important roles in these developments. Sensor science and technology has gained significant benefits through inspiration arising from biological sensory systems. This includes the sense of olfaction, which has led to the artificial nose, and the sense of vision that has been emulated in several versions of the artificial retina. The impact of micro and nano sensors on fundamental understanding in biomedicine and on clinical diagnosis and care are highlighted.

Abstract: In this work, we present a device for cell manipulation and separation by using travelling wave dielectophoretic force. The device consists of a 16 parallel electrode array and microchamber. The dielectrophoretic PDMS chamber was fabricated by using standard microfabrication techniques. The Cr/Au parallel electrode array of 100 µm wide and 300 nm thick was patterned on a glass slide by sputtering through microshadow mask. The polystyrene microspheres suspension in de-ionized water and red blood cells in D-mannitol solution were used as tested cells. Cells respond to the electric field in various mechanisms depending on the applied voltage and frequency of the AC signals. For 4.5 µm polystyrene, the traveling wave dielectrophoresis happened when the applied voltage was 10 V, and the frequency of the applied signals was in the range of 50 kHz-700 kHz. For 10 µm polystyrene the twDEP occurred when the applied voltage was 7 V, and frequency was in the range 30 kHz-1MHz. While the red blood cells experienced the twDEP when the applied voltage was 3 V and frequency was in the range 50 kHz-2MHz. The mixed solution containing equal amount of 4.5 and 10 µm microspheres were used for separation test. The big microspheres were moved under twDEP force when the applied voltage was 7 V, and the frequency was in the range of 25 kHz-1MHz while the small microspheres were attached to the electrodes. Therefore, the twDEP device can manipulate and separate the microspheres with different sizes, and it can be further applied for cells selection.

Abstract: The sealing of microchannels is a key step in the fabrication of microfluidic devices and thermal bonding is a common technique used. Here, major manufacturing issues and considerations in thermal bonding are investigated, including bonding quality and microchannel deformations. Flatness of substrate is extremely crucial to the uniformity in bonding. While increased bonding pressure helps to overcome problems related to surface topography and to enhance bond strength, its significant impact on geometrical changes of microchannel due to viscoelastic effect should also be taken into consideration.

Abstract: This paper describes a fully-integrated lab-on-a-chip device for testing and monitoring biochemical parameters in biological fluids. The major innovation of this microdevice is the application of an acoustic microagitation technique with automatic electronic control based on a β-PVDF piezoelectric polymer placed underneath the microfluidic structures. Experimental results regarding the influence of the thickness of the polymer on the reaction rate of biological fluids are presented. Moreover, the study of the transmittance curve of β-PVDF with transparent conductive electrodes is also presented. Transparent electrodes are a constraint once the polymer is incorporate underneath the reaction chamber due to the analytical measurement by spectrophotometry.