Team:BIT/HW2
Hardware
We divided the instrument into eight functional module:microfluidic chip, confocal detection of optical path, power board, structure, serial screen, microcontroller, temperature control module, peristaltic pump.Their size and position in the instrument can be seen in Fig 1.2. The power supply provides the rated voltage for each power unit. The structure printed by 3D printer is used for fixing individual components.The microcontroller is responsible for controlling of the work of the various components,passing information to the serial port, processing the data of the detection.The serial screen is responsible for displaying the test results, and providing the human-computer interaction platform.The microfluidic chip is used as a platform for the entire reaction, and the detection is also done directly on it.Temperature control module and peristaltic pump assist microfluidic chip to achieve it’s function.The confocal detection of optical path is used to detect the fluorescence intensity.Here we will introduce their function one by one.
Microfluidic chip
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Temperature control module
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Peristaltic pump
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Confocal detection of optical path
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Ⅰ.Microfluidic chip
We chose the microfluidic chip because it has three significant advantages in the application:
1.The tiny volume of the microfluidic chip allows the liquid reaction system to be miniaturized and integrated. It can use a small amount of liquid and space to achieve complex biochemical reactions;
2.Reactions on the microfluidic chip can be quantitative analysis and detection;
3. Microfluidic chip can be combined with external devices to make biochemical reactions become automated and intelligent.
Based on the characteristics of microfluidic chip, more and more people use microfluidic chip as the platform of biochemical detection and POCT [1]. For example, there has been a microfluidic platform which can detect C-reactive protein in 2008,and the limit of detection is 2.6 ng/ml.Besides,it can be produced in large quantities[2].Similarly, in the case of hepatotoxicity assessment, a POCT method based on microfluidic systems overcomes the shortcomings of long processing times and high levels of personnel in traditional methods[3].It is worth mentioning that there already have mature POCT equipments based on microfluidic platform in the market.It can be seen that the microfluidic platform not only has irreplaceable performance advantages, but also has certain marketization potential.
Design
An important feature of microfluidic chips is that they are capable of artificially designing liquid lines and reaction chambers. Our project involves three reaction processes: the separation of the aptamer and the complementary strand on the magnetic beads, the separation of the complementary strand from the small molecule, and the biochemical reaction of the small molecule and the engineered bacteria. According to the needs of the project, we designed the two reaction chambers as shown in Figure 2.1, and used the peristaltic pump, the magnet plate and the heating plate as supporting auxiliary equipment.
Picture One
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Picture Two
View moreAs can be seen from Figure 2.2, our chip consists of two chambers: Chamber 1 is oval(long axis length:18mm, short axis length:6mm). In our design, the function of the chamber is to hold our magnetic beads (fixed with magnets) with the aptamer and provide a place for the sample to bind to the aptamer so that the the complementary strands with lysine can get detached . Our intention to design the chamber as an oval is that the elongated structure can reduce the bubble generated by the difference in flow rate between the cavity wall and the middle stream. Chamber 2 is round( diameter:12mm) Within this chamber ,there are gel pillars(diameter: 0.5mm). The contents of the chamber are engineering bacteria frozen into dry powdery and trypsin. After the reaction in the chamber is carried out for a certain period of time, the mixed reaction of the culture medium and the reaction liquid flows from the upstream into the chamber under the negative pressure generated by the peristaltic pump (see the equipment section), the following reaction occurs: ①: Freeze-dried engineering bacteria’s recovery with the help of culture medium and constant temperature provided by the heating plate ②: Trypsin catalyzes cracking of DNA chain,lysine on the complementary strand falls into free small molecule ③: Lysine goes into the engineering bacteria, biochemical reaction within the engineering bacteria began. We can use the design of hardware to detect the reaction generated fluorescence generated in reaction③, and we can draw a conclusion through analyzing and processing.
Ⅱ.Temperature control module
nbsp;Temperature control module provide constant temperature environment in the chip for two reasons:1.E.coil need constant temperature environment when they restore activity from freeze-dried state;2.E. coli have the best growth and metabolism state in constant temperature environment. Design Temperature control module consists of four parts(Figure 3.1), namely: alumina ceramic, heating piece, temperature sensor module and it’s supporting control module.The alumina ceramic is the base of the chip, and the chip is connected to it. The rest of the temperature control board is located on the instrument, and the chip is placed on it when used.The alumina ceramic allow the chips to heat evenly.The control module control the work of the heater piece.The temperature sensor provide temperature information of microfluidic chip to the microcontroller at real-time.
Ⅲ.Peristaltic pump
The injection and the flow of liquid in the chip is achieved through the negative pressure produced by the peristaltic pump.Peristaltic pump suck the air inside the chip, so that the air pressure inside the chip will be less than atmospheric pressure.That’s how the negative pressure is produced.Under the negative pressure,the liquid will flows into the chip.What’s more,the flow rate can be determined by controlling the pumping speed of the peristaltic pump, and the liquid inflow volume can be controlled by controlling the pumping time.Through the experiment we found that the best speed of liquid flow is 37uL/min(Experiment can be found in project page).And the pumping time can be set on the serial screen. Our design can be seen in Figure 3.2
Ⅳ,Confocal detection of optical path
In order to detect the intensity of GFP and RFP that produced by E.coli, we designed a dual optical path confocal fluorescence detection device(Figure 3.4).This is our optical path diagram(Figure 3.5), we used two high-power LED, four filters, five convergence lens, three long-shaped two-color lens and two photoelectric sensor OPT101(The detailed information of the parts are listed in the component information table).
Ⅴ.Operation
As shown in Figure 4.1,while detecting,a user mainly need to finish sampling,injecting and connecting process.The specific reacting and optical detecting process is automatic,which can be operated simply on serial screen.Also,we designed concise UI on serial screen for users(Figure 4.2): As can be seen above,our UI offered brief guidance to users,making sure users can easily finish a detection.
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