Team:CCU Taiwan/Hardware








Prototype

The device is designed with 3 characteristics: mobile, automated and cost efficient. Base on these concepts, we have designed a device with 3 major components. They include an experiment kit, a magnetic bead delivery system and a fluorometer.

Figure 1. Prototype of device.

Experiment kit:
The experiment kit is able to inject reagent into the blood serum sample automatically and conduct the test.

Magnetic bead delivery system:
After the reaction is complete, this system will separate the magnetic beads and bonded ssDNA and place them in the buffer which contains fluorescent dyes.

Fluorometer:
At an early stage, we surveyed various of currently available spectrophotometers and fluorometers on the market. Unfortunately, all are very expensive. The reason for the high price is their multifunctionality, featuring unique capabilities not necessary in the ASFAST device. Thus, we decided to design and manufacture our own simple fluorometer. We believe that our fluorometer can reduce the cost of the device by at least 60%.
Experiment kit
Magnetic bead delivery mechanism
Fluorometer





Hardware
Animation 1. Experience kit.

Experiment kit

The experiment kit has a simple and straightforward design, we use three separate reagent injectors and a linear guideway rail. At the beginning of the procedure, reagents like Cas12a protein, fluorescent dyes and self-designed ssDNA will be added to the serum sample step by step by automatic reagent injectors placed on the top of the experiment kit. A linear guideway rail will move the sample between these injectors. After that, the sample will be moved back and forth to ensure that the reagents are mixed evenly with the serum. Finally, the sample will move to the end of the rail and proceed to the next step.

Animation 2. Magnetic bead delivering mechanism.

Magnetic bead delivering mechanism

To minimize the potential interferences from other substances in the blood serum affecting the accuracy of the fluorescence measurement, we discussed with Wet Lab colleagues and came up with the idea of binding our ssDNA to a magnetic bead, and separating it from the serum sample before attempting the measurement. We believe that ssDNA isolation can bring significant enhancement to the accuracy and sensitivity of our test, so we developed a compact magnetic bead delivery system to separate these magnetic beads from the serum sample.

To draw magnetic beads out of the serum sample, we decided to use an electromagnet, which has the ability to attract magnetic beads only when it is energized. The electromagnet is installed on a DC motor, which can also induce a slow spin to create a minor centrifugal force. This ensures that all the magnetic beads are released into the buffer solution using in the fluorescence measurement.

To prevent tangling of the wiring cable when the DC motor spins the electromagnet, we optimized the wiring connection. As shown in the diagram below, we turned both anode and cathode into a ring and added an extra outer ring. The spaces between these three rings will form two circular tracks. We place the live wire and ground wire in these two circular tracks. As a result, the wire connecting the ring to the electromagnet will spin together with electromagnet, so they will not tangle when the electromagnet spins.


Animation 3. Parts of Fluorometer.

Fluorometer

In our experimental design, we utilize PicoGreen as the fluorescent dye, which has the excitation and emission wavelengths of 480 nm and 520 nm respectively. Hence, our home-made fluorometer is specifically designed to work at these two wavelengths.
Optical path
For the design of the optical path, the light will be focused on the sample and excite the fluorescent dyes. Then, the emission of PicoGreen will be detected at a right angle, as indicated, to prevent interference from the incident ray.
Light sensor
To detect the intensity of the emission of PicoGreen, we employed light dependent resistor (LDR) as the light sensor. The LDR is paired with a voltage divider and analog-digital converter (ADC) to enhance its sensitivity to low intensity light.




Manufacture

In our device, there are some parts with complex shapes. Manufacturing these parts with traditional machining will be complicated and time consuming. Hence, we decided to utilize 3D printing technology to manufacture these parts.

Figure 2. 3D printed parts.


The process and operation of 3D printing are relatively simple and straightforward. We first came up with a Computer-Aided-Design (CAD) diagram of these parts using Solidworks, a widely used software for engineering drawings. The dimensions of all the parts used in our device were carefully calculated and analyzed using Solidworks. After that, it will be turned into a mechanical code (.gcode) that is ready to be read and printed by the 3D printer using Ultimaker Cura 4.0. Images below show some of the examples of our tiny parts fabricated using the 3D-printer and their corresponding CAD diagrams.


Figure 3. Device parts.





Electrical components

Electric motors

All the moving parts of the device are driven by industrial motors. In the device, there are a total of 9 electric motors, carefully chosen and precisely tuned to complete certain specific movements. These electric motors are driven by specific drivers and controlled by a Linux application. Among these electric motors, there is 1 DC motor, 5 stepper motors, and 3 servo motors.

Figure 4. Electric circuit.




Safety

Since the device carries a test sample that is potentially contaminated, it is very important to consider the safety of the device. First of all, to prevent the leakage of test samples, all the edges and openings of the device has to be sealed with silicone and rubbers. Besides that, the device cannot be break easily on physical impacts. To solve this problem, we referred to how the authorities transfer hazardous test sample from place to place. It inspired us that a few layers of shock absorption materials can be added to the outer of device to protect it from breaking apart. Despite careful design of the device, operation errors may cause dangers. Thus, an operation protocol must be provided alongside the device to brief through the precautions.




Image gallery

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  1. Wang, T., Sun, Y., & Qiu, H. J. (2018). African swine fever: an unprecedented disaster and challenge to China. Infectious diseases of poverty, 7(1), 111.
  2. Ahn, S. J., Costa, J., & Rettig Emanuel, J. (1996). PicoGreen quantitation of DNA: effective evaluation of samples pre-or psost-PCR. Nucleic acids research, 24(13), 2623-2625.