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25 july 2008
What was done
After being briefed about the status of our project the previous week, we proceed with our trial and error in making the micro channel chip usingthe SU-8.
This week focuses on finding the proper way to develop the SU-8 photoresist without affecting the chemical.
We started off by putting the glass pieces under UV light in which a stencil is placed over it to get the desired design that we wanted. This procedure is called UV masking.
Following that, the glass pieces were then heated up again. A point to note is that the heating up of the glass pieces in the oven SHOULD take place immediately after the UV masking. This step is called the post exposure bake.
Following that, the glass pieces were then left fully submerged in a beaker of the SU-8 developer. The glass pieces were then rinsed with tap water for about 10 seconds before being soaked into a beaker of Isopropyl Alcohol (APA) for another 10 seconds.
The end product
Recommended program:
UV masking
We used a stronger UV light machine. Thus, the energy emitted was 150-160MJ in which the glass pieces were exposed for a time of 13 seconds.
Post Exposure Bake
The glass pieces were heated in the oven for 1o minutes.
Developing
This took some time for perfection as the SU-8 always comes of for the first few runs. But we managed to get it right after several tries. The glass pieces should be soaked in the developer for 10 minutes. Not longer than 11 minutes.
Conclusion
For an experiment that was full of trial and error, we did quite well as we managed to find the proper timings in making a good mico channel chip. Though this week was quite a success since we exceed expectations in finding the right blend of timings, we should not be too complacent. This is due to the fact that we have yet to find a way to stick the glass pieces together without melting the micro channels form on the glass pieces. Till then, we have to be constantly be on our toes.
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What have we done?
· Learning from Mr Ting more details about making our own micro-chips using SU-8.
· Obtaining references for further reading regarding fluid flow in different micro-channels.
· Propose a plan for activities to be done in July, August and September.
What have we learnt?
We have learnt theoretically from Mr Ting on how to make our own micro-chip from SU-8. He told us that common manufacture of micro-chips from SU-8 requires a mould to be made. However, to save time and materials, he suggested that we try to directly produce the cast without having to create the mould. This procedure has not been tried before but that does not mean we cannot try out. Hence, we have decided to make use of the expired SU-8 as a trial to find the best methods to create a reliable micro-chip.
Some Problems encountered
· Since our project is research-based, at some point of time we found ourselves not knowing what to do next.
· Having doubt as to whether we are able to make our own chips.
· Our schedule seems to be changing as our next step is unknown.
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What was done
We did a continuation of what we did last week which is to make our own micro channel chips.
Before doing anything to the glass pieces which had been left in the lab for a week, we had to heat up the glass at a temperature of 280 degrees Celsius for 10 minutes. This is to prevent any contamination that might have been on the glass pieces and also to ensure the ‘stickiness’ of the glass for the spin coating later on. We also heat up a small beaker at the same conditions for the same reasons.
The SU-8 was then poured into the beaker ,after it had cooled down, to about ¾ full. Following that, the SU-8 was then put in small quantities onto the glass pieces for the spin coating. After spin coating, the glass pieces were then for soft baking.
The recommended program for chemical SU-8 2025
Spin coating
Based on the dimension of our glass piece, 4-5mL of SU-8 was poured with slight excess onto the glass piece as the recommended volume to be poured on to the glass is 1ml per 25mm. Spin coat the glass piece twice with the first one at 500rpm for 5 to 10 seconds with an acceleration of 100rpm/second and the second one at 3000rpm for 30 seconds with an acceleration of 300rpm/second.
Soft baking
It is best to bake on a lead hotplate with good thermal control and uniformity.
For the size of our glass piece, it was bake at a temperature of 65 degrees Celsius for 0 to 3minutes then at 95degrees Celsius for 5 to 6 minutes.
NOTE: After removing the glass piece from the hotplate, be careful of the hot glass pieces. Allow the glass piece to cool. If wrinkles appear, soft bake the piece again at the same temperature at 5 minutes interval. Repeat until there are no more wrinkles on the glass piece.
Problems
There is only 1 problem, which are the air bubbles in the SU-8. We will try to solve the problem but we have not encountered any big problems till date as our SU-8 coating is very thin. Our problem may or will arise in the latter part of this phase when dealing with a much thicker coating
Conclusion
Though this week’s experiment might have been a short session, it was worth noting that we familiarized ourselves with the same equipments we used at the start of our FYP research. Also, we cannot proceed on with the making of the micro channel chips as the chemicals needed for developing the glass pieces are still not ready. Hopefully, the chemicals will be ready next week. If not, we can always start again with the PIV equipment.
This is still early of part of our development of using SU-8. By having this experience from these 2 weeks, it will be a stepping stone for to learn more about this chemical and how to handle it properly. This is because this is our first time handling with this chemical. By having this experience we can also predict what problems it may occur.
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What was done
Basically, we started to make micro-channel chips again. This time with the SU-8 photo resist which is to familiarize ourselves in making the chips when the real materials come in a few weeks time.
Like the previous experiment that we did in the first 3 weeks, the same procedures can be applied to this week’s experiment.
We started by cutting the glass into smaller desired pieces before the edges were blunted. This is to prevent the glass pieces from having sharp edges which may cut our fingers when handling it. The glass pieces were then rinsed several times so as to ensure that the glass pieces are sterilized.
We ended the experiment by heating up the glass pieces to dry and disinfect in at the same time at a temperature of 200 degrees Celsius for 30 minutes. The glass pieces were then left to cool before being stored at a safe place.
Conclusion
We did not manage to complete the experiment as there was not enough time. Though there was a lot of waiting time, we managed to use the time efficiently by reading up on the chemical SU-8 which will be useful for next week’s experiment. We hope that we can have enough time to play around with the chemical which will require different set of instructions as opposed to the common photo resist in the lab.
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We decided to take a break from doing our fyp. This is to allow ample time to study for the upcoming mid semester tests and rest during the holidays.
Week 10
MID SEMESTER TESTS
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Objectives
We have written an experimental procedure of the PIV system earlier in the week. As Hariz missed the first part of the training, we decided to run the experiment again with our own experimental procedures and Hariz doing it from the start. Also, we wanted to see how the differential pressure between the two inlets will affect the liquid flow in the liquid.
What was done
As we were the pilot research group for this experiment, we were asked to write down a list on procedures by our supervisor Mr. Ting. This is to act as a reference for the future FYP groups that will be doing this experiment and also enable us to do the experiment without any doubts. So as to ensure that the experimental procedures are user-friendly, Hariz was tasked to run the whole experiment by just referring to the experimental procedures.
Our experimental procedures are still subjected to changes. After more feedback from our project supervisor, we will amend it.
For the differential pressure, we decided to try out how the difference in height of the 2 inlet syringes affects the way the fluid flow. By having a difference in the height between the syringes, it creates a differential pressure. Initially we thought that the speed of the higher placed syringe would travel much faster then the lower placed syringe. But after seeing the results from the software, we found out that the liquid flow in the channel within the chip was turbulent as the vectors calculated by the software were all over the place. It also shows some mixing.
We also noticed a particular pattern from the few runs that we conducted is that there is a vacuum effect at the junction where the 2 streams meets, this vacuum effect causes some of the liquid to flow to the lower positioned inlet syringe.
Another pattern we found out is, there is some circular patterns from the vectors after the junction. We conclude that there is mixing occurring at these circular patterns and it continues mixing due to the incoming stream of fluid.
Problems
We are unable to testify fully that the circular patterns plotted out by the software pattern are mixing as we made a mistake by starting with a high differential height between the 2 syringes.
For the vacuum created, we are only able to conduct a firm conclusion when we have tested with various differential heights.
Solution
To solve the above problems, we are going to start of with a minimal differential height to the differential height we did this week. By doing this, we are able to see the pattern on each stage conducted, thus, concluding into a firm statement.
Conclusion
This week’s experiment on the differential height will give us a firm foundation on the topic mixing for micro fluidics. Though the lesson we learnt today is based on gravity creating a differential pressure, we are able to learn the basic foundation of how fluid flows in such condition. By having this foundation knowledge, we are able to proceed into a more challenging task for pressure driven by using 2 syringe pumps, both at different speeds.
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the glass cutter machine
the glass after being cut into pieces
the machine that blunts all the sharp edges
rinsing each piece of glass 
heating up the glass to disinfect
leaving the glass pieces to dry
the spin coat resistor machine
coating the glass piece with photo resist
soft baking the glass pieces 
the UV ray machine
imprinting the design desired for the glass piece
soaking into for the first bath
checking for any abnormalities after the imprinting
followed by the second bath
the last bath before being dried
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30 May 2008 & 6 June 2008
What have we learnt?
- Some basics on micro fluidics
- How we set the equipment up
- How to operate the equipment and find out the relevant data collected using the software Dynamic Studio
Some Basics on micro fluidics
Micro fluidics is the study of liquid movement in a micro channel using small particles. By using these small particles mixed with the liquid, we are able to monitor the liquid movement with the help of a light source and a camera. When the camera captures a set of images within a period of time, a software will then tabulate the movement of the particles, showing the speed and direction at which is going by using a highly profound statistics.
Equipment set-up
Before everything, we have to open the database that we want then we go to the acquisition mode in which all these options can be done. This can be done by clicking the green icon at the top. Then, we can choose whether to carry out free run, preview, acquire or stop. Basically, the free run allows the software to run continuously with the camera capturing images at selected time interval.
Prior to acquiring the images, we used the microscope to focus on the micro slide. However, the focus on the microscope from the eyepiece and from the camera is different. Hence, we have to adjust the focus based on the camera focus which is shown on the computer. This can be done by turning the focus knob (both fine and coarse) at the microscope. Before we are able to adjust the focus according to the image taken by the camera, we must run the program at preview mode to get the precise image when the LED light and camera is running at the specific timing we adjusted to just that it is not saving any images to the buffer space* or the hard disk of the PC. From what Mr Edward told us, the higher the modifications we made using the microscope focus by choosing a larger objective lens, the smaller will be the depth of field. The depth of field refers to the distance of focus on the object from the objective lens.
*the buffer space is an amount of memory being set aside making use of the RAM of the PC to save images during the run temporarily.
1) After focusing, we must change to single frame mode and acquire. The reason this is being done is to do calibration of the width of the channel so as to obtain the vector, the speed at which the solid particles are moving. After we acquire, we switch the window to acquire data to save the image under calibration. Exit acquisition mode. Under the database that the image is saved in, select the image under calibration.
2) Open the image and right click on the image. Select measure scale factor.
3) In the new window that is opened, click on absolute distance and type 1mm (since the distance between opposite walls in the straight channel is 1mm).
4) Then, select X-Y markers below. Using the instructions given, mark points A and B on the image which represents the respective points on opposite walls.
5) Once done, the scale factor will be shown on the right hand side. Calibration is complete.
In order to start acquiring images, we selected “acquire” button on the right. Once the run is over, the images can be browsed on the acquired data windows. Then, we must save the images unless the images from the 2 frames do not show any difference or dissatisfaction of images captured. If we do not save the images, the software is unable to analyze the pictures as it is not saved into the hard disk of the computer. After we save the images, it is better to clear the buffer images as it will take up unnecessary space on the RAM which may not be enough for subsequent runs.
Furthermore, we can analyse the saved images using various calibration methods such as “Cross-calibration”, “Moving Average calibration” or etc. For our project, Mr Edward informs us that “Cross calibration” is to be used. Hence, by selecting cross calibration, all the saved images are analysed and a new analyzed windows of all the images are opened. These windows show the vectors profile indicated by arrows.
Problems encountered
During our training, we faced a problem with the software. At one point, while Mr Edward was demonstrating the acquisition on the software, the time between pulses kept on changing when we tried to set a certain value. However, after a while, Mr Edward figured the problem and he found out that the camera settings are affecting the time between pulses. This was because the time between pulses has to be set within the camera exposure time.
During our actual day when Mr Edward was not there, we also encountered two problems. While we were setting up the micro slide and introducing the fluid into the syringes, there were many air bubbles formed and trapped inside the tubes and micro channel. To solve this problem, we consulted Mr Edward and he told us to fill the fluid from the big syringe connected to one end of the channel and allow the fluid to flow to the two smaller syringes connected to the other two ends of the channel. By doing this, the air bubbles are removed and we were glad we can continue with our experiment.
Another problem we encountered was that after we acquired the images in the software, we noticed that frame 2 was in complete darkness while frame 1 was well-lit. After a while of finding the cause of the problem, we finally realised that the second pulse width did not coincide with the camera exposure time. As a result, frame two was not exposed to any light resulting in darkness.
Conclusion
In conclusion, we have learnt a few important lessons. These include a basic understanding of fluid flow in micro channel, how to use the Dynamic Studio software and also how to set up the equipment and apparatus for our experiment. Firstly, a basic understanding of micro-fluidic flow gave us a rough idea of how the flow in micro-channel differs from flow in macro-channel such as flow pattern etc. Also, it relates to how the software can be used to determine particle velocity in micro-channel.
Moreover, although learning how to use the software is almost as similar as learning another photo-editing program, the important steps are to be able to precisely select the timing between pulses, camera exposure time as well as analyzing the captured images using the correct correlations and analysis.
Lastly, we learnt how to set up our equipment and apparatus for the experiment. It was a minor attribute but after a few runs on the software, we found out that even the slightest change in set up could result in vast differences in results. Hence, setting up the equipment which includes the syringes and microscope focus correctly definitely affects the results and if not done properly, could end up in long delays.
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23 May 2008
What have we done?
We plan out what are we going to do in the following weeks of our project, how is suppose to go according to our plan with extra time for unforeseen circumstances.
We also went to research out on what equipments are needed for doing our experiment especially for electric driven micro fluidics as the equipments needed is different than the one being used by pressure driven.
We also went to research on various fields that will affect our results and data like viscosity, two inlets both at different speeds.
In conclusion, this week allows ample time to regroup our initial plans that we had and had more concrete ideas on our project research.
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9 May 2008 & 16 May 2008
Purpose of Carrying Out Fabrication of Biochip Practical
The purpose of doing this practical is basically to prepare us for our Final Year Project (FYP). This practical gives us the fundamental understanding on how to manufacture a micro-channel in a chip which is going to be used for our FYP. Due to this understanding, we can now be able to create flow channels in the chip to study closely on how the fluid particles flow within these small channels on various patterns which we are interested in.
What have we learnt?
We learnt how to use the various machines which were useful for our project ahead. By doing this we also get to know why is each step important, what does each step does and how it works, from cutting a piece of glass to cleaning the glass with numerous chemicals, coating the glass pieces with photo-resist to using Ultra-violet light to imprint a pattern on the glass microchip and cleanse it to produce the final product.
What difficulties we encountered
When handling the glass pieces for cleaning and other procedures, we encountered some problems of handling the glass pieces using a pincer as it was quite difficult to grip the glass especially when it was wet
Conclusion
In conclusion, we have learnt that patience and accuracy are the two most important points in doing this practical as every procedures is crucial as a small mistake in any process can ruin the whole chip or it may cause some chemical residues to be left on the glass causing the product to be defective. When doing the actual micro channel, the procedures may vary according to the TSO, but by we were still able to grasp hold of the finer details in making a mircro channel.
Credits
Mr Goh, TSO of the nano frabrication lab in T12a, for helping us and guiding us throughout the whole experiment and the start of our project
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We search on various types of process that is actually happening in the process of microfluidics.
The topics we searched on are:
Laser-induced fluorescence (LIF)
Laser Doppler Velocimetry (LDV)
Photolithography
Photoresist
Electrophoresis (capillary electrophoresis)
Electro-osmosis
Particle Image Velocimetry (PIV)
Lab-on-a-chip
What have we learnt?
We have learnt about the various processes by sharing each of our work to get a head start for our project.
Laser-induced fluorescence (LIF)
Spectroscopic method used for studying structure of molecules, detection of selective species and flow visualization and measurements.
The species that is to be examined is excited with help of a laser. The wavelength is often selected to be the one at which the species has its largest cross section.
Excited species will after some time, usually in the order of few nanoseconds to microseconds, de-excite and emit light at a wavelength larger than the excitation wavelength.
This light, fluorescence, is measured.
Laser Doppler Velocimetry (LDV)
Also known as Laser Doppler Anemometry (LDA)
Technique for measuring the direction and speed of fluids like air and water
Used in clinical research as a mechanism to partially quantify blood flow in human tissues such as skin.
Within the clinical environment, LDV is referred to as Laser Doppler flowmetry (LDF.)
Gained popularity because it is simple to use, painless and non-invasive.
LDV crosses two beams of collimated, monochromatic, and coherent laser light in the flow of the fluid being measured. The two beams are usually obtained by splitting a single beam, thus ensuring coherency between the two.
The two beams are made to intersect at their waists (the focal point of a laser beam), where they interfere and generate a set of straight fringes.
The sensor is then aligned to the flow such that the fringes are perpendicular to the flow direction. As particles pass through the fringes, they reflect light (only from the regions of constructive interference) into a photodetector (typically an avalanche photodiode),
Since the fringe spacing d is known (from calibration), the velocity can be calculated to be u = f x d
where f is the frequency of the signal received at the detector
Photolithography
Also known as optical lithography
Is a process used in microfabrication to selectively remove parts of a thin film (or the bulk of a substrate).
Uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical on the substrate.
A series of chemical treatments then engraves the exposure pattern into the material underneath the photoresist. In a complex integrated circuit (for example, modern CMOS), a wafer will go through the photolithographic cycle up to 50 times.
Shares some fundamental principles with photography, in that the pattern in the etching resist is created by exposing it to light, either using a projected image or an optical mask.
This step is like an ultra high precision version of the method used to make printed circuit boards. Subsequent stages in the process have more in common with etching than to lithographic printing.
It is used because it affords exact control over the shape and size of the objects it creates, and because it can create patterns over an entire surface simultaneously.
Its main disadvantages are that it requires a flat substrate to start with, it is not very effective at creating shapes that are not flat, and it can require extremely clean operating conditions.
Photoresist
A light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.
Photoresists are classified into two groups, positive resists and negative resists.
Most commonly used at wavelengths in the ultraviolet spectrum or shorter (<400 efficiency="output/input" eqe="(electrons/sec)/(photons/sec)">
CCD Camera, Progressive Scan
• A charge-coupled device (CCD) is an analog shift register, enabling analog signals (electric charges) to be transported through successive stages (capacitors) controlled by a clock signal.
• Progressive scanning is a method for displaying, storing or transmitting moving images in which all the lines of each frame are drawn in sequence.
• Interlace is a technique of improving the picture quality of a video signal primarily on Cathode Ray Tube (CRT) devices without consuming extra bandwidth.
• Interlacing causes problems on common display devices such as LCDs.
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