Viewing Baker’s Yeast-#Indiafoldscopephase 1

Dear Sir,

We are viewing “Baker’s yeast” sample, using Foldscope, stained with Gram stain. We are able to get a clear vision of the yeast cells after gram staining.

Fig. 1: Stained Baker’s yeast slide under foldscope

Kindly let us know, how to estimate the microbial load using foldscope? Can we use slide A1 and A2 for this purpose?

Fig. 2: Foldscope PVC reusable slide A1 and A2

We are working with Foldscope for rapid estimation of microbial quality in food samples and would like to get technical guidance and support from your end. We look forward to hearing from you soon.


Soumitra Banerjee

Meghashree H. M.

4 Comments Add yours

  1. laksiyer says:

    Hi @Soumitra. There are many ways to estimate density in the foldscope setup that we can think about. It just depends on what you have in your setup.
    1. Calibrate your phone at maximum and minimum zoom (maximum zoom is what you will need for yeast cells). using the grid or a slide scale if you have one. That way you will know the area of the field that you are looking at under the phone. See this post.
    You can then decide to measure 4-5 areas per slide to get multiple readings of cells.

    2. However, you might immediately notice that you dont get the third dimension for volume, which is needed for cell density calculation. I have two solutions for that.
    A) In the simpler one. Mark a 5mmx5mm area on your slide (you can use the grid too), and put a fixed volume that you can evenly spread over that area. Perhaps 50 microliters? Let it dry– stain and count cells. Count either within the whole 5mmx5mm area or a part of the whole. Now you know the fraction of the area that your counted, you multiply that by the volume (50 microliters for example) and that will give you the number of cells in 50 microliters which you can scale up to what ever scale.

    — In the slightly more involved version use the Foldscope kit reusable PVCs which is either 0.15/0.25 mm thick. You would need to compute the volume of that ditch in the slide and you fill it up with that much volume of sample, put a coverslip and count small areas wet (this I would think is a bit tough with sample coming out) , or just let it dry, perhaps stain and then count 4-5 areas.
    Did you all come up with some other way? We could ponder on this a bit more depending on your setup.

    1. Soumitra Banerjee says:

      @laksiyer: Thank you for your kind reply. I am taking a known volume of sample, in a known slide area and staining it. After completion of the process, the dried slide is placed below the foldscope and microbial cells are counted using PVC grid (0.5×0.5 sq. mm). The method produced results are near to haemocytometer cell count using DMC method, but difference do exist. Thank you for showing me a path towards the solution. I would look forward to get your valuable guidance to standardise this method of microbial load determination using foldscope.

      Yeast cells are well visible but bacterial cells are quite difficult to view at 140 X foldscope.

  2. Manu Prakash says:

    Dear @Soumitra; one way if imaging bacteria is either in dark field or pseudo phase. This will take time and care – but these two techniques are very powerful. All you need is a decent table lamp

    See the following posts:


    1. Soumitra Banerjee says:

      Dear Sir,
      Woww.. !! I still can’t believe I received reply directly from you Sir. Thank you so much for your reply. I would definitely try your advised methods and would update in the website. I am working on food microbiology aspect and I was feeling negative about viewing live bacteria. I feel motivated and extremely happy after receiving your text. Thank you so much, Sir.

      Soumitra (a big fan)

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