M9 vs ddH2O - effects on fluorescence emission

Hi all,

Has anyone observed whether a fluorescent compound/dye in solution has quenched/diminished fluorescence emission in M9 buffer compared to distilled-water (ddH2O) or DMSO? I am working with a dye (excitation 620nm, emission 680nm, in the TXred range) that seems to have significantly reduced/quenched fluorescence than when I would dissolve it in ddH2O or DMSO.
Just wondering if anyone has observed the phenomenon with any compound or dye. The dye is known to be very soluble in all solvents tested (M9, ddH2O, DMSO).
I carried out a serial dilution of the dye in each of the solvents and at all concs., M9 did worst (lowest FI) and DMSO the best (highest FI). Adding 2% DMSO to ddH2O improved the FI of the dye compared to when dissolved in ddH20 alone.

Any insight would be helpful.

can this incident be Dye specific?
never faced anything like this, specially between water and M9.

Yes, it’s probably dye specific, or at least M9 component specific. You could try omitting the divalent cations in M9 or see if it’s just the salt or phosphate. If it’s pH sensitive that could change things. Most fluorescent molecules are brighter in organic solvents compared to aqueous solution, so I’m surprised that water is better than M9. I assume the small amount of DMSO is keeping the dye happy and in solution.