Print Email Facebook Twitter Micro and Nanofluidic devices: For Single cell and DNA analysis Title Micro and Nanofluidic devices: For Single cell and DNA analysis Author Mokkapati, V.R.S.S. Contributor French, P.J. (promotor) Faculty Electrical Engineering, Mathematics and Computer Science Department Microelectronics Date 2011-04-05 Abstract Research in the field of Micro/nanofluidics has been extensively carried out for the last few years. With the available technological advancements today many complex systems can be fabricated in a more efficient and simpler way. Conventional methods in a laboratory consumes a lot of time, chemicals and in turn generates a lot of waste unlike the Lab-on-a-chip (LOC) devices where all the processes are carried out on a small chip with small drops of chemicals, negligible wastes and in minimum time. Most of all this is very efficient and inexpensive. Most of the work in this project was concentrated on developing and optimizing the technologies for the fabrication of micro and nanofluidic devices. Conventional soft-lithography was used initially to fabricate the microfluidic devices using PDMS. Realizing the limitations in working with PDMS the choice was made to replace PDMS with TMMF S2030 dry film photoresist (DFR) which turned out to be fruitful. Working with DFR is inexpensive, more accurate and easier compared to working with PDMS in microfluidics. Dry film photoresist (DFR) is a new type of photoresists, which is gaining importance in semiconductor industry. These are generally negative tone photoresists in the form of a thin foil protected by PET (Polyethylene terephthalate) on both sides. They are differentiated into permanent and non-permanent resists. The minimum known thickness of the available dry films is 15 µm and the maximum reaching to few hundreds of microns. They can potentially replace soft lithographic materials, since they are easier to process. Dry film photoresists have a big role to play in microfluidics, which is yet to be completely explored. Manipulating a single cell has been an interesting topic for the researchers in the field of microfluidics for a long time. Our design fulfils the idea of trapping, cell viability, manipulation, sensing and detection. The devices were equipped with different channels for different applications like, providing nutrients to the cell, to hold the cell with suction and to collect the reaction by-products, sense and detect them. Di-electrophoresis is a well known technique for manipulating neutral particles/cells in fluids and it is widely used in micro fluidic systems for forcing particles to desired trajectories. Since the particle has to be moved in the horizontal plane, the width and the introduction point of the particle are more critical variables. Presorter electrodes were introduced more upstream in the entrance channel which will bring far-off particles to the trapping range and also a minimum distance between presorter and trapping electrodes should be regarded. One more important goal is to keep the cell in the reservoir once it is there. This can be achieved by a simple electrode pair blocking the outlet of the hole. The particle is repelled from the resulting field. The same repelling force will prevent other particles to enter the hole. The geometry of electrodes was designed so that it is only necessary to modify the applied voltage according to the entrance speed. Experiments for trapping polystyrene beads followed by E.coli bacteria were successfully carried out with the help of a dedicated holder and an Olympus inverted microscope. Research stops nowhere. Following the path from microfluidic devices for single cell analysis, we have concentrated on developing nanofluidic devices for DNA analysis. Lot of research has been carried out in nanofluidics for DNA, protein and nucleic acid analysis studies. Existing devices have electrodes placed at the ends of microchannels and a potential is applied to move the particles into the nanochannels. The devices we aimed at have electrodes embedded within the nanochannels along with electrodes at the junctions of micro and nanochannels. The main idea in designing and fabricating these devices with embedded electrodes is to study the behavior of the biomolecules in a localized electrical field. Devices were fabricated by a conventional anodic bonding process and a completely new single silicon wafer process. To our knowledge this is the first time that nanofluidic devices (200 nm deep channels and integrated electrodes) were fabricated on a single silicon wafer. The nanochannels in this case were defined by sacrificial etching. Electrodes were patterned on the top side of the nanochannels. Microchannels were etched from the back side of the silicon wafer connecting to the nanochannels through a membrane of silicon nitride. Initial experiments were carried out with rhodamine + ethanol solution to prove the opening of nanochannels without any leakage followed by trapping carboxylate modified fluorescent polystyrene beads to confirm the working of embedded electrodes. Further experiments were carried out with DNA molecules tagged with a fluorescent dye. DNA molecules were injected into the microchannel and once the channels were filled completely, electrodes in the microchannels were switched on to drag the DNA molecule towards the entrance of the nanochannel. Then the EOF voltage over the nanochannel was switched on to drag the DNA through the nanochannel. A single DNA molecule was successfully tracked over the length of the nanochannel. Time and the distance travelled by the molecule were calculated. Using microfluidic devices further experiments on sensing and detection can be carried out with single cells. Behavior of different lengths of DNA within the electrical double layer in a localized electric field can be studied with the help of the fabricated nanofluidic devices. Experiments were also carried out to define the best etch mask to etch completely through a glass wafer. Amorphous silicon turned out to be the best etch mask material to etch the glass in 40% HF. Even though slight pin holes were observed by using PECVD amorphous silicon, we recommend that thick layers sputtered in batches will resolve this problem and a clear surface can be achieved. It is recommended that LPCVD amorphous silicon would be the best etch mask if it can be sputtered at lower temperatures. Along with amorphous silicon, Molybdenum can also be a good etch mask if more research has been done on improving the adhesion of ‘Mo’ to glass substrates. Subject microfluidicsnanofluidicsdry film photoresist To reference this document use: http://resolver.tudelft.nl/uuid:7cf3908d-62de-402b-9551-c83c5239b003 ISBN 9789090261133 Part of collection Institutional Repository Document type doctoral thesis Rights (c) 2011 Mokkapati. V.R.S.S. Files PDF PhD_Thesis_Mokkapati.pdf 4.45 MB Close viewer /islandora/object/uuid:7cf3908d-62de-402b-9551-c83c5239b003/datastream/OBJ/view