Document

Hardware

Hardware design

After many discussions within the group(see the discussion and design process below), we finally selected the most suitable method from the competitive method test paper, sandwich method test paper, colourimetric aptamer sensor, visible light aptamer sensor, electrochemical aptamer sensor, and other methods and principles. We chose the competitive test paper.(Fig 1).

Fig 1

Competitive test papers are made based on the principle of "competition". This method allows us to adapt various practical conditions: cost-effectiveness, portability, production cost, the difficulty of operation, and accuracy of results. Now that we have confirmed the principle of the test paper, we move on to the detail of each process.

1. First, the extraction buffer composed mainly of water will thoroughly mix the fish meat, and the mixed sample will be dropped onto the sample pad.
2. Then, the sample flows through the NC membrane to the colloidal conjugate pad and binds with the aptamer with several base A and colloidal gold at the tail.
3. After that, if excess C4-HSL is present, it will fully bound with Aptamer on the conjugate pad, to which the biotin complement to the Aptamer does not react; therefore, no red will present.
4. There is no C4-HSL, Aptamer will be carried to the test line and react with the biotin, and red colour will appear.
5. Furthermore, whether there is C4-HSL or not, the AAA bases on the tail of the Aptamer will always be bound with the TTT complementary bases on the control line. The red colour will turn up, and it shows that the operating conditions, test paper quality, and operator's technique are correct, and the inspection results are valid.
6. Lastly, the excess sample solution is then absorbed on the absorbent pad.

In short, the result is negative if the test line is red and positive when no colour is present. Anyway, the flow chart below shows the processes of corruption detection.(Fig 2)

Fig 2.flow chart of the working scheme of hardware

These are 3D models of our product.

Fig 3. Detail of 3D model

And the description of the 3D model are as follows:

The part at the exit of the cone: the mixture of the sample mixed with the buffer drips from this place（a）.
Sampling spoon: The source of our design inspiration here is the ear pick. Our initial design did not have the curvature of the current version, so it is better to dig out the sample.(b)
Filter layer: This place can prevent large pieces of fish meat from slipping to the outlet to block the mixture when the mixture drips into the test plate.(c)
The connection between the bottle cap and the bottle body: Our design is a spiral structure, so that the two parts can be connected more firmly. The buffer is added to the bottle.(d)
Test version: The ellipse is the place where the mixture drips(e), the square part is the test observation version(f), and the three ellipses(g) are the evaporated part, which can reduce the probability of the sample spreading to other places.

The three pictures in Fig 4 are the testing process(a), positive results(b) and negative results(c) of the strip.

Fig 4. The test results demonstrated by the strip

The desigen preocess and demand analysis

Background research

Currently, there are no scientific household fish corruption detection methods. At present, people judge whether the food is edible or not by checking its appearance, smell, or how long it has been stored. Millions of people worldwide suffer from diarrhea, emesis, fever, stomachaches, or other deadly diseases due to the intake of rotten fish mistakenly.

To find out which functions and characteristics of our product are exactly what the public needs, we had first researched the actual needs for instantaneous detective facilities for fish corruption.

The results(Fig 5）have shown that more than 60 percent of the public are willing to use the test paper, for which the demand for the product is quite considerable.

Fig 5

Design stage 1

After identifying the increasing demand for the product, we stepped into the product designing state. Our group intended to create a portable and efficient tool that can be easily and widely used in family kitchens. Therefore, to suit the practical scenario, we conducted the second questionnaire to find out the opinions for detective tools of the target consumers. (Fig 6)

Also, from the gap-filling questions, people who did the questionnaire are concerned about how convenient, cheap, practical, and necessary (money and time cost).

With the design of the demand of people set, we came to the topic of product requirements. Do you have any specific requirements for the product? We listed the options that we could think of. From the results above, consumers pay the most attention to the test results and the test process. The test results should be accurate (85.71%) and visualized (77.38%). The detection process should be quick and convenient (77.38%) and easy to use. The second is the appearance of the product; the appearance design should be simple and compact. Finally, there is the question of price. As a daily product used in the catering industry and household kitchen, the price should not be too high. These factors are easy to solve in pieces, but how do you fit all these requirements into a small test paper? That's what we need to think about next. What biological components should we combine or modify? What reagent materials are used? What principle is used to make our products? In general, our product design direction to this problem has a rough prototype. We need to make a portable product that fits the needs of the scene and the consumer's needs; it needs to have a good detection function and a simple method of use.

Fig 6

The expected importance of the priority qualities from our 85 questionnaires takers is (ranked from high to low) accuracy - result visualization and convenience - portability - price- appearance. Therefore, our group members tried to make sure the results of the test papers were accurate and work hard on making the hardware easy to read out the results when we were designing the product. The results of the questionnaire are shown in figure 1.2. (The higher the percentage, the more people consider it a priority）

Design stage 2

At the end of the stage, it's time to start preparing the product design, but there's one last thing we need to know: what's the most effective way to communicate how the product is being used. Before we can start designing the structure and use of the product, we need to figure out how to convey the latter message. According to the results of this question, 61.9 percent of respondents said that it is best to write the product description inconspicuous color (Fig 7). The second is to write on the packaging surface (59.52%). The font should be large (35.71%). Finally, instructions and related pictures are provided to help users understand how to use them more intuitively. Here we go on to ask what color is most appropriate. According to the survey results, red was the most appropriate color (53.85%) among 84 respondents(fig 8). Followed by blue, yellow and so on. Generally speaking, our product design direction has been generally clear(as shown above at the hardware desgin). The service groups, usage scenarios, and packaging design of the product are also targeted.

Fig 7

Fig 8

Product package

Here is our package for the final product(Fig 9): the picture above is the packaging on the front of the product. The picture of fish in the upper left corner represents our test paper used for fish, and the blank part in the middle is a layer of transparent plastic, allowing consumers to see the test paper's appearance directly. The four letters GCGS at the bottom right represent our team. We also wrote what the product is and what it is used for at the bottom. These elements make it easy for consumers to understand what it is and highlight the passionate characteristics of our team with bright colours and artistic words. When we look down, the second one is the packaging on the back of our product. On the upper left, there is a large "caution" sign, which uses a large red font to warn people that the followings are pieces of must-know information; the following lines are the warning content, especially the use of capital words and add The bold font gave people a second warning. On the right is the appearance of the test paper when it is positive or negative. People can directly look at the package for comparison when using it. At the bottom left, the team and product use are once again written.

Fig 9.Product package

After finishing the packaging, we started writing the user's manual(Fig 10). This manual is bilingual, English and Chinese, which fits the most widely spoken language in the world and the language spoken by the most people, and does our best to cater to as many people as possible. However, the fish in the upper right corner is our team logo, and the content is mainly divided into three parts, explaining in detail what it is, how to use it, and what to pay attention to.

Fig 10.User's manual

More importantly, The strip was similar with many strip products in the market, we deigned a sampler, in order to promote the comprehension of the bottle size and function, we made a bottle device(Fig 11) similar to our designed bottle.

Fig 11