In addition to the microfluidics device, we have designed a mechanical device for the project. The whole system consists of four parts: the main body, lighting board, shading baffle and microfluidics chip. The details for each part are described in the Hardware
When assembling, four LED lights are inserted into the corresponding holes. Four single-pole double-throw switches on the external circuit board can switch the light color (red or green). The power switch is on the battery box. Microfluidics chip is inserted into the upper slot. The shading baffle, which has the same size as the microfluidics chip, is inserted into the lower slot, to avoid the interference from stray light.
Fig.1 The whole view
Fig.2 Operation Demonstration
While using, the overall device will be placed in incubator of 37 ° . Pressing the four switches can adjust the LED light into the appropriate color, waiting for bacteria to respond to light signals. Later, take out the baffle and observe the color of each chamber, and that is the "cipher text" we get.
There are five kinds of bacteria in our cipher machine: the core bacteria with the oscillation circuit and four affiliated bacteria. As for these four bacteria, they are controlled by the oscillation system and contain the signal transformation circuit (which is composed of the light control circuit and the logic gate circuit). Before using the cipher machine, we should first mix these five bacteria together according to a certain proportion and insert them into the microfluidics chip. Then, insert the chip in our device and put the whole device in the thermos-stated container.
While encrypting, we should select a specific time (for example, to begin counting when the bacteria solution is added into the microfluidics chip) to press the LED switch on the top of the device according to the input information (for example, if the input is 0101, then the LED light should be red, green, red, green). Using corresponding light to irradiate different areas on the chip (we regard each area as an encryption unit. In our initial device, we select 4 areas as encryption units). After a period of time, we can observe fluorescence which is the cipher text (for example, if we observe gfp, rfp, rfp, gfp, then the output is 1001).
While decrypting, input the cipher text by pressing the LED switch at the same time, or at the same phase in the oscillation period (for example, if the cipher text is 1001, then the LED light should be green, red, red, green). After a period of time, we can observe the original text (for example, if we observe rfp, gfp, rfp, gfp, then the output is 0101).
However, if we input the cipher text at a wrong time (which means the user does not know the encryption time), even if the cipher text is true (1001), the output is not convincing, sometimes even opposite from the real information (for example, 0110) because at this phase, the codebook is not the same as encrypting. So, compared with the first generation, this second generation of cipher machine is more reliable.
We have got the double-period oscillation circuit already. But when doing an experiment, we could not realize a stable oscillation because of the continuous split of bacteria and the accumulation of autoinducers. In order to solve this problem, we use micro-fluid technology. Microfluidics is science and technology using micro-channel to operate micro fluid. By this methods, we can keep the quantity of bacteria at a certain level and take the accumulated autoinducers away, making the system a better coupling and could operate steadily.