I am measuring PET-FCS of a peptide and after measuring for 90 min. I am noticing that there is no PET in the FCS figure. However, if I run the experiment for only 5 min, there is some PET. Also, the diffusion time decreases over time during the measurement. I am assuming that some kind of fragmentation is happening due to the excitation laser.
I will be glad if anyone can explain this fact or any possible theories are also welcomed.
Kırmızı lazer ışınları peptit bağlarının kimyasal olarak parçalanmasına ve bir süre sonra yok olmasına neden olmuştur.
It seems your suggestion is right. Laser exposure even at red wavelength (620-670 nm) could induce permanent damage to peptides or other biomolecules, and rate of possible signal degradation should depend on laser power in focal volume and total volume of the sample.
There are 3 of possible effects: 1) peptide fragmentation, 2) permanent peptide conformation switching 3) peptide precipitation/condensation out from solution and seeing FCS signal from impurities in the solution.
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