Are fluorescent probes biological stains?   On 29th April 2021 Richard W. Horobin wrote:

There are various communities of clinical lab workers who use “traditional” microscopic staining methods, such as hematoxylin and eosin, and the Gram or Papanicolaou stains. However even these three stains are most commonly used by three quite distinct groups of people, typically working in departments of histopathology, microbiology and cytology respectively. How distinct? Don’t they talk to each other? Maybe not so much – perhaps in the coffee shop, but they may be in different buildings, or at least on different corridors.

And away from the clinical setting — and especially over the past 20 or 30 years — scattered across the biomedical research world are large numbers of other lab workers who use “fluorescent probes”. These are commonly used to image living cells, or indeed living organisms. Yes, some grad student might be expected to check out the calcium level in her cultured cells with the fluorescent probe fura-2 on Monday. Then on Tuesday she might fix a cell monolayer with formalin, carry out an immunostaining procedure, and finally counterstain the nuclei with, say, Harris’ hematoxylin. Two worlds at least in that case, but not much cross talk.

So where does all this leave the Biological Stain Commission? Historically the Commission was concerned with the purity and quality control of “traditional” dyes, all of them, from hematoxlin and eosin, to the gentian violet and basic fuchsine of the Gram stain not to mention the light green and orange G of Papanicolaou. No fluorescent probes there.

BUT another way the Commission has sought to achieve its quality control goals was, starting in 1925, to produce repeated editions of a remarkable handbook of dyes and … yes … fluorochromes used in biology and medicine. AND in the 10th edition, by now termed Conn’s biological stains: a handbook of dyes, stains and fluorochromes for use in biology and medicine, there were a lot of fluorescent probes. In fact, of the more than  200 monographs on different imaging compounds in this reference text, over a third concerned fluorescent probes.

So, in practice the Biological Stain Commission thinks fluorescent probes are biological stains! Even though most bench workers using these reagents probably do not. And so, in future “News from the BSC” items, we will be addressing a variety of practical issues arising when using these fluorochromes. Stay tuned …

Footnote: if any of the terms in this item puzzle or intrigue you — for instance, who was Conn? And why is his name on the handbook? — then move over to the Stains Glossary and check it out.