The first cell stain, as we far as we know today was saffron, which was used in the late 17th century by Dutchman Anton van Leeuwenhoek (known as the father of microscopy)to dye muscle fibers, which allowed him to obtain more information about the structure of those cells by seeing the detailed structure of the fibers more easily. From van Leeuwenhoek’s time until the late 19th century scientists attempted to find natural products which could be used to dye cells. They were only partially successful until William Perkin’s discovery of the first synthetic dye in 1856. Perkin’s new technology unleashed a deluge of colored compounds to be used as potential stains by the scientific community.
German anatomist Walther Flemming was one of the first scientists to test out these new dyes. He used a number of them to stain cells and observed structures that appeared to strongly absorb these dyes. During the late 19th century, cell staining technology rapidly became more sophisticated. German biologist Carl Weigert discovered that different bacteria were stained different colors by dyes, which spurred the research of his famous cousin, bacteriologist Paul Ehrlich, who wrote a thesis on cell staining. While he was a resident at the Charite Hospital in Berlin Ehrlich discovered ways to identify blood disorders based on how cells absorb dyes, on top of methods for staining mast cells and white blood cells.
Ehrlich became convinced that staining was not a process where cells simply absorb dye. Instead he thought there might be a chemical or physical interaction between the dye and cell that could result in cell death. This led him to search for a dye that would kill harmful bacteria during the process of staining. Over more than a decade, Paul Ehrlich worked to find this dye, resulting him discovering a dye called trypan red that kills trypanosomes, the protozoa that causes sleeping sickness. More importantly, in 1907 he found an even more important bactericide called Salvarsan, an arsenic containing compound which soon became a powerful agent in the treatment of the sexually transmitted disease syphilis.
The most famous stain discovery however, was the Gram stain. The Gram stain was first devised in 1882 by a Danish bacteriologist Hans Christian Joachim Gram, and has gone on to become one of the most important facets of microbiology. The Gram stain was the first to be able to determine the different types of cell walls in bacteria. Gram began his career as a botany student in Denmark, going on to work in the field of botany and zoology which first exposed him to the use of the microscope. While working in a German morgue, Gram developed his staining technique to help to differentiate between the two major types of bacteria (Gram positive and Gram negative).
As he examined the lung tissue of patients who died of pneumonia, Gram discovered that certain bacteria retained their color after undergoing his staining technique (gram positive) while other species of bacteria had their colour bleached (gram negative). They key step to his technique is decolorization, which differentiates between Gram positive and Gram negative bacteria. Over-decolourization can result in Gram positive bacteria appearing negative and under-decolourization can result in Gram negative bacteria appearing Gram positive. Gram published his technique in 1884, and it quickly became widely adopted around the world and expanded upon by other microbiologists. Today, the gram stain is the standard method for classifying bacteria
Another staining technique was created by Italian histologist Camilo Golgi in the 1870’s. Golgi experimented with silver salts as stains instead of organic dyes, discovering that cell structures not visible with organic dyes were now easily seen.
Today, dozens of stains both organic and inorganic have been developed, each for specific uses and often named after their inventors. Such as Borrel’s methlyene blue, Ehrlich’s triacid stain, Renault’s eoisin, Lugol’s iodine and Van Gieson’s stain continue to memorialize their inventors. Despite the relative age of cell staining, it is still routinely used by biologists today, and has helped find cures for a number of diseases including tuberculosis, pneumonia, syphilis and many other less notable bacterial infections. Cell staining is still taught to young scientists today in schools and universities, highlighting it’s continued importance in the 21st century.