Fluorescence in situ hybridization (FISH) is an old method based on a hybridization reaction between a specific fluorescently labeled probe and complementary target RNA or DNA sequences. This technique is used to study gene expression and to detect and localize nucleotide sequences in various samples (environmental, human, or animal) while preserving cell integrity. FISH involves four steps: sample fixation, permeabilization, hybridization, detection, and analysis of the target by microscopic visualization. FISH can be used to localize the viruses in the tissue samples like brain, heart, muscle, and other tissues. Many laboratories are using PCR methods to detect the presence of pathogens. Once the sample is positive, particularly in tissue, now the question arises: where is this virus located in the tissue samples? Hence, the FISH method is the right method to locate the presence of pathogens, particularly intracellular pathogens like Chlamydia, Borrelia, Plasmodium, Anaplasma, and different viruses. FISH can be used to show the effectiveness of the therapy, as before the therapy there will be the presence of pathogens, and after that the pathogens will be no more available.

Therefore, we have developed a number of FISF probes, which are based on quantum dots. Quantum dots are nanoparticles, which have a very narrow range of emission; therefore, they can be used as multiplexes also. Moreover, the quantum dots are very stable; hence, they do not fade away, which is the case of conventional dyes like FAM, Cy3, Cy5, and so on. The samples can be stored for many years with loss of fluorescence.

Genekam Biotechnology AG is focusing on pathogen-specific FISH probes for various bacteria, parasites, fungi, DNA, and RNA viruses. The user has to standardize the protocol to use the FISH probes. The FISH probes can be used directly on the samples. Once there is a specific target in the sample, it will hydrate to this, and this reaction can be observed under the fluorescent microscope.

Genekam is developing different FISH probes to target the different genes or regions of pathogens so that one can show the different parts of pathogens in the samples. Such detection may be helpful to see which parts of the pathogens are expressed under the particular physiological or pathological conditions. This may provide new research results; hence, this may be an opportunity for conducting research, e.g., loss of memory is being shown that there are a number of viruses involved; hence, tissue sections of brain can be used for the FISH method, where a particular virus is located and which important gene is being expressed.

FISH is a unique technique combining molecular biological and histochemical techniques with the visual information from microscopy. FISH can be combined with flow cytometry for a high-resolution automated analysis of mixed microbial populations. It allows the identification, visualization, and quantification of individual cells in the natural habitat or diseased tissues. Nucleotide sequences can be examined without altering cells‘ morphology.