Hello. I am new to cell culture work. May I know whether these small black dots are contaminants or just cell debris? It's quite confusing because they are not moving. This is different from the contamination issue that I used to encounter because I can surely confirm that my cells are contaminated when these small dots move which means bacteria. FYI, this is HEK293T cells.
The presence of small black dots in cell cultures can indeed be confusing, especially for those new to cell culture work. These dots could potentially be cell debris, but they could also indicate contamination⁴.
**Cell Debris:** If the black dots are of varying sizes and shapes, they could be cell debris⁴. Cell debris can occur naturally as cells die and break apart, or it can be a result of mechanical stress during handling.
**Contamination:** If the black dots are of the same size and there is an increase in their number over time, this could indicate bacterial contamination⁴. However, you mentioned that these dots are not moving, which is not typical for bacterial contamination³.
There's also a phenomenon known as "black swimming dots" (BSDs) that has been observed in cell cultures¹. BSDs are extremely tiny dots found in dishes of cultured cells and are very hard to remove¹. They are nonliving inorganic nanoparticles but should derive from an unidentified airborne infectious organism¹. BSDs can bring adverse impact to cell experiments¹.
To determine the nature of these black dots, you might want to consider the following steps:
1. **Observation:** Keep monitoring your culture. If the number of black dots increases over time, it's more likely to be a contamination issue⁴.
2. **Microscopy:** Use a microscope to get a closer look at the black dots. Their shape, size, and behavior can provide clues about their nature⁴.
3. **Testing:** There are various tests available to detect specific types of contamination. For example, PCR-based methods can detect mycoplasma contamination².
(1) What are the little black dots in the cells? – Sage-Answer. https://sage-answer.com/what-are-the-little-black-dots-in-the-cells/.
(2) 3 Culture contaminants you hate and how to save your cells - Quartzy. https://blog.quartzy.com/3-culture-contaminants-you-hate-and-how-to-save-your-cells.
(3) Black swimming dots in cell culture: the identity, detection ... - bioRxiv. https://www.biorxiv.org/content/biorxiv/early/2018/07/15/366906.full.pdf.
(4) Common contamination and solutions in cell cultures_Cell Culture .... https://www.leadingbiology.com/article-131.html.
(5) Observed tiny black dots on cell culture - Cell Biology. http://www.protocol-online.org/biology-forums/posts/35069.html.
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