Question about fluorescence_can you post it on the forum?

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Question about fluorescence_can you post it on the forum?

d'Episcopo, Lorenzo
Dear scientific community,

I am a PhD student form Imperial College London, I need help with a fluorescence-related issue.

I am spotting a solution of quinine on aldehyde-coated glass slides. The quinine is solubilised in 0.1M sulfuric acid.

I am scanning the slide with a fluorescence scanner. The laser is set at 532nm and the (emission) filter is set at 575nm. Based on the absorption/emission spectrum of quinine, there should be no absorption at all above 500nm, and therefore I assumed that no fluorescence should be emitted/visualised. For the propose of our experiment, we have to prove that NO SIGNAL is detected at these settings.

However, when I scan the slide with these parameters, I record a very strong signal from the quinine spots. Why is that? Can anyone help?

The options are: 1) sulfuric acid reacts with the aldehydes on the slides and then somehow modifies the  fluorescence properties of the quinine molecules; 2) I (and my colleagues here) don't understand fluorescence of quinine properly; 3) our scanner has problems, which I am tempted to exclude because it's just undergone maintenance.

Thanks very much

Lorenzo d'Episcopo +44(0)7896931761
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