General Overview

      Our Test Kit package is priced at around USD 4, which falls into the acceptable price range found in our survey. Users are provided the sample-taking tools, reagents for biosensor activation, and a capsule containing the biosensor hydrogel (capsule design inspired by Prof. Marshal Liu).

Proposed user flow:

      Before applying the sample, the food suppliers would need to add LB medium to the gel to germinate the cells and leave it for 1 hour. Then, after adding the sample, wait for 2 hours for the result. For the result reading, we would provide a box-sized UV transilluminator and image analysis software. After testing, they could drop the gel along with the capsule, into killing agents such as bleach to kill the cells, ensuring biosafety. After research and consultation with local food service companies, we propose users could conduct several tests at certain time points.

Target Users and Background Information

      We are targeting food handlers who treat a great batch of food, including catering companies specializing in event-based food services, lunch box service companies, and canteens, as our users. To gain a better understanding of their food processing procedures, we conducted a meeting with SeaMart 鮮物, a local food service company. In the meeting, we got to know how food service Companies handle leftover rice for fried rice cooking and how they process lunchboxes.

Figure 1 Meeting with SeaMart and their lunch box manufacturing process

SeaMart's Rice Treatment Procedures for Fried Rice's leftover rice preparation:

  1. Cooked rice cools down to 0-4 °C (not speed-cooling, bacteria start to produce Cereulide)
  2. Store at 0-4°C in cool room
  3. Reheating/Fried Rice Cooking: 70/80 °C
  4. Disinfection: Around 100°C(heat more than 30 minutes)
  5. Delivery to consumers

According to Food Safety Guidelines[1]:

  • The bacteria can multiply rapidly and produce toxins in starchy food if they are stored in the "temperature danger zone" for a prolonged period of time.
  • When the conditions turn favorable (e.g. between the temperature range of 5°C - 60°C), the spores can turn into bacteria and multiply in numbers.
    • Figure 2 B. Cereus cells, B. Cereus spores and Cereulide production in different temperatures[2]

    Test Kit Prototype and User Manual

    Test Kit Package Prototype

          We consulted Professor Marshal Liu who specializes in food technology and bioproducts, and he suggested we could make a capsule design for safety and try to use household keeping that users already owned such as ethanol for extraction and bleach for disinfection.

    Figure 3 Meeting with Professor Marshal Liu
    Figure 4 Proposed Test Kit Package

    Proposed User Manual

    Figure 5 Proposed prototype user flow
    1. Biosensor Activation
      1. Open the cap of the capsule
      2. Add 1ml LB medium to rehydrate and nurture the cells trapped in the gel disc
      3. Close the cap before putting it at 37 °C for incubation and germination
      4. Wait for one hour for activation
    2. Sample Extraction
      1. Dissolve susceptible rice sample from fridge in 50% ethanol (gram to ml = 1:5)
      2. Spread the rice to make sure surface contact for 1 minute and stand for 4 mins
      3. Add a few drops of the filtered sample in ethanol onto the activated biosensors gel disc
      4. Put it at room temperature for better processing performance
    3. Result Analysis based on Fluorescent Protein Expression Extent
      1. Turn on the blue light beam
      2. Cover the transparent capsule with Orange filters
      3. Put the mobile phone on top of the box with a hole
      4. Take a photo of the gel
      5. Upload the photo to the app for image intensity analysis
    4. Disposal
      1. Open the cap
      2. Turn over the capsule
      3. Fully immerse the gel into 5ml bleach solution for 30 mins to kill the cells

    Price Estimation

    Components Price per Test Kit(HKD)
    3g Spoon 0.18
    Transparent Plastic Mini Container (Holding gels) 0.1
    Transparent Plastic Mini Container (Containing bleach to hold cells) 0.1
    50% Ethanol (15 ml) 0.5
    Bleach (5ml) 0.14
    LB (5ml) 0.08
    5ml Dropper Bottle (2 units) 0.27
    PVA Gel embedded Engineered Cells (18mm diameter * 2mm thickness) 0.046
    LED Blue Light Plane 3
    Orange Color Filter 1.2
    Plastic Black Lunchbox * 2 24
    Total Price 29.616

          The estimated cost of our test kit is HKD 29.616 ~= USD 4, which is within an acceptable budget range from our questionnaire result ($15-45, 62.1% of our respondents).

    Figure 6 Questionnaire Result regarding acceptable price range

    References

      [1] Singapore Goverment Singapore Food. (2021, July 15). Risk at a glance. RIsk At A Glance: B.cereus in Rice-based Food. https://www.sfa.gov.sg/food-information/risk-at-a-glance/b.cereus-in-rice-based-food.
      [2] CHONG, Ken. Bacillus Cereus in Processed Food, Center for Food Safety, the government of the HKSAR, 9 June 2017. www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_97_01.html.