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The goal of our detection module is high efficiency and low cost, but we encountered a tricky problem in the process of using our detection module -- a centrifuge costs $400- $500, which is slightly expensive in terms of price. At the same time, for non-professionals, its improper operation may lead to danger. In addition, experts in the laboratory know that centrifuges are not particularly convenient to move, which is an important consideration for people working outdoors.
Therefore, we thought of a childhood toy called "Hand-pulled wind turbine", which can achieve the ideal centrifugal speed by releasing the winding rope and the inertial motion of the middle hub itself. Using this principle, we designed the "Hand Centrifuge".
Based on the design of the toy, we designed the 1.0 version of the Hand Centrifuge, whose exterior is secured to the centrifuge tube by recycling discarded cardboard by gluing it in place. The centrifuge tube is clamped in the center. However, through tests conducted by the experimentalists in the laboratory, it was not possible to reach the required centrifugal speed because the weight of the waste paper shells was too light to allow continuous rotation. Also, because the centrifuged reagent would be in an inverted state in the centrifuge tube during rotation, the experimenter told us that we would not end up with the desired centrifugation results this way.
In order to improve the problem of inverted tubes, we redesigned the slot where the centrifuge tubes are placed. In order to increase its weight, we chose to re-dissolve the scrap metal and introduce it into the grinding tool to make our centrifugal tray. In addition, considering that centrifugation requires a relatively smooth rotating tray, we reshaped our Hand Centrifuge after the design of the spindle of a vinyl record player, which also requires a high degree of smoothness.
This design achieved effective centrifugation in the lab, but due to its excessive weight, the wool in its center, which is the same as the one driving the rotation of the turntable, could only support one centrifugation and needed to be replaced each time. Adding a replacement plastic wire for centrifugation, which tends to deform, did not allow the tray to rotate smoothly during centrifugation.
Ultimately, we retooled our selection and design by referencing similar ideas from the 2017 iGEM team TUDelft (Read More)The final result was an effective level of centrifugation.
Our test kit contains all apparatus needed to conduct the experiment, with no requirements for additional accessories or personnel costs. First of all, our hand-powered centrifuge is included for the extraction of supernatant fluid. Ten 15 mL test tubes, paired with adapters and liquid medium, are packed along with 150 mL x-gal solution.
A greyscale chart is provided for comparison of color change and hence the measurement of pollutant levels.
For researchers to culture E. Coli at our system’s optimal temperature, 37 degrees Celsius, we also designed a test tube-shaped thermostat to unfreeze the lyophilized powder of bacteria and culture it under a stable temperature.
Hardware
1. Mix lyophilized E. Coli powder with liquid EB.
2. Place the test tube inside the thermostat
3. Heat the mixture at 22℃ for 2 hours around OD600=0.5.
4. Add 10 ml of water sample and 10ml of x-gal into the comparison tube
5. Add the bacteria mixture to the comparison tube.
6. Plug the tube into the hand-powered centrifuge and start spinning.
7. Wait for 5 minutes, compare the final product color with the greyscale chart and read the scale.
Note: If the sample is too muddy and unable to see through, filter the sample first and then do the test. If the final color is out of the indicator’s range, dilute the sample and then do the test. A more detailed version of testing instructions will be on the instruction manual, printed on A4 paper and folded inside the kit.
Hardware
Unlike other remote-control models, or models that require complex assembly of parts, our test kits do not require the user to attach or detach. Our product solved the problems of time-consuming and complexity, as the experts from the testing institute suggested, instead, we provided a cheap and handy kit, compiled of materials such as biodegradable plastic, and glass for test tubes and droppers. We used 3D printing for our hand-powered centrifuge. All of these materials were safe to use and does not have harmful effects on the human body. Our reagents are non-radioactive, with controlled microbiological activities.
Some test kits only provide essential reagents, and most of the time researchers still need to use laboratory centrifuge or ultrasonic oscillator, which increases their budget. However, our product solved this problem: with all apparatus included, our kits do not require extra personnel costs of complex machines. Lastly, our kits are in a relatively small size, similar to a laptop or an average iPad box, which makes it portable and convenient to carry around and take to different places for investigation.
Hardware
We encountered some problems while developing the kit. After some group discussion and suggestions from our advisors, we learned from the feedback and improved our model.
One of the problems is whether to separate the liquid medium into a different bottle. Initially, we designed the liquid medium as an individual bottle, paired with a dropper, so that volumes of the medium could be customized while conducting the experiment. Some teammates suggested that this may be unnecessary, since we could simply pair the exact amount of liquid medium in each test tube. In this way, not only the experiment was easier for the researchers (one step already done), but we saved the costs of producing an additional bottle and dropper.
Another problem is the fixation of the heating wire. At the very beginning, our team wanted to design a simple device that could heat the lyophilized powder and culture bacteria, so we used a heating wire. However, after wrapping the wire around the tubes ourselves, we soon realized that holding the wire in a fixed shape is very difficult. Moreover, direct contact with the wire is a potential danger, and its efficiency isn’t high, since most of the heat escapes. Therefore, we changed the concept of a heating wire to the design of a thermostat. Details about the development of our thermostat are elaborated below.
Since our product is highly commercialized and standardized, it can be duplicated in mass quantities, and its design is simple enough for other teams to understand and reproduce.
After our first established test kit, the water analysis kit, we are developing more low-cost test kits, such as blood calcium level test kit, uric acid level test kit, blood glucose level test kit, and soil pH test kit. The main structure of each kit is standardized, such as the instruction manual and datasheet. (Click to preview water analysis data sheet With cheap and replicable materials and amateur-friendly experiment procedures, our hardware design is referable to the iGEM community. In the future, we aim to create a series of handy models for environmental, agricultural and industrial usages.
