Dear Sir. Concerning your issue about the protocol/techniques to detect the concentration of dyes (Toxic chemicals) in tissues. I think the following below links may help you in your analysis:

https://www.spexsampleprep.com/knowledge-base/resources/application_notes/0714-165645-Malachite%20Green%20in%20Seafood%20-%20LC-MS.pdf

https://www.tandfonline.com/doi/full/10.1080/10942912.2017.1303708

https://eurl-ecvam.jrc.ec.europa.eu/validation-regulatory-acceptance/eurl-ecvam/validation-regulatory-acceptance/skin-corrosion-docs/SkinEthic_INVITTOX_protocol_corrosivity_test_OECD_Jan2012.pdf

Thanks

There are several ways to do it depending on the type of pesticide and the type of sample. Normally you would use gas's chromatography coupled with mass spectrometry. See for example the following papers:

https://www.sciencedirect.com/science/article/pii/S0269749105003805

https://link.springer.com/article/10.1007/s00128-008-9382-0

https://onlinelibrary.wiley.com/doi/abs/10.1002/jssc.200700380

https://www.sciencedirect.com/science/article/pii/S0308814608010236

The simple approach is to look at the emission spectra of the dyes and hope that they are different than background autofluorescence.

If the project is to look for a variety of pesticides in fish tissues then you may need a more complex method. You might have to adapt methods from similar studies in different systems. There is no one method that will detect all insecticides, herbicides, fungicides, and so forth. The issue becomes more complex if you include metabolites some of which can be more toxic than the parent compound.

Soil

https://pubs.usgs.gov/tm/tm5c3/pdf/tm5-C3.pdf

Fish

http://cehea.org/wp-content/uploads/2017/01/33-.pdf

Article Rapid determination of chlorinated pesticides in fish by fre...

General (some parts useful:

https://nctc.fws.gov/resources/course-resources/pesticides/index.html

Methodologies

https://www.epa.gov/pesticide-analytical-methods