Hardware
1.Background
As one of the most successful model animals, C. elegans has a highly sensitive "nose" to sense environmental stimulation. Worms can use the smell to track the food source or avoid harmful chemical stimulation. Microcystis aeruginosa, which take the main responsibility of the water blooming, will secret molecules when the water blooming happens. Unfortunately, it's usually too late for us to clear out the algal when people can see it through naked eyes or smell it. Worms can hardly sense the Microcystis aeruginosa at 1*10^6 cell/L which merely attracts C. elegans to move toward it. But luckily, when the concentration increases to 2*10^6, which is exactly the key concentration to evaluate whether the water blooming will happen, the attraction index will suddenly increase to a high level. Therefore, we wish to design a small, portable device that can make use of nematodes to estimate the concentration of the algal in environment. We call this device "Algal Chip".
2.Introduction
When C. elegans is about to starve, it will try to move around, roaming the area to seek for the food source. For the wild-type worms, they often roam for a large range, which may be impeditive for them to detect something. Therefore, we want to design a chip for worms to choose instead of seek algal. In our products, we create some barriers to limit their moving area to get more precise results. Our device consists of 2 parts: a small dish and a T-shaped frame (Figure 1).
Figure 1. Schematic describing the algalchip device and the corresponding actual parts.
The whole device is based on the chemotaxis of the C. elegans. We prepare the cultural medium especially for the chemotaxis experiment (Difco-agar, MgSo4, CaCl2 and potassium phosphate, please see the whole protocol at this pages), which would be sterilized by high temperature. When the temperature cools down to 60℃, we will pour the medium into dishes and insert the frame (its height is 1cm) into the medium to make a barrier to limit the moving space of worms (Figure 2).
Figure 2. Algalchips with agarose for chemotaxis assay.
The T-shaped area is divided into 3 parts: sampling area(left), control area(right) and the middle to place the worms as the initial start point. Before the beginning of the experiment, we need to add the sample (different concentration of the algal suspension) and the control (special cultural medium for the algal) to corresponding positions (Figure 3). When the liquid sink into the medium, the device is ready to use. After collection and wash of worms, we will pipette worms to the device and observe their behavior after 45min.
Figure 3. Algalchip with Microcystis aeruginosa suspension on the left side and control buffer on the right side.
3.How it works
We will perform a series of experiment to get the respond tendency of worms to fixed gradients of algal concentrations. For the sample outside the laboratory, worms may be attracted by the algal and try to move toward the sampling area if the concentration is high. Although the single worm may have some random behavior, we can observe the whole group worms’ behavior and calculate chemotaxis index. Compare this chemotaxis index with the index under different concentration of laboratory algal, we can evaluate the concentration of Microcystis aeruginosa in the sampling water. The biggest advantage for this device is that we can observe the tendency directly by naked eyes (Figure 4), by which we can estimate the concentration of our sample out of the lab. After some cycles of design, we have narrowed the device area and we are focusing on the real-time examine now.
Figure 4. The trend of chemotaxis experiments can be judged by the naked eye observation.