I would like to stain live bacteria with bio fluorescent dyes.

I got plasmids from Addgene, such as this one:

https://www.addgene.org/54630/

The bacteria grow in ampicillin, and they are positive for the plasmid by PCR, so I reckon the plasmid is in place.

However, I don't get any signal on the fluorescent microscopes.

From PerkinElmer, they told me that one needs a very long exposure to get a signal from the bacteria. In fact, the camera they use is cooled to -70/-90 to reduce the noise during very long exposure times.

I was expecting the cells to glow at least in the dark, but the lack of visible fluorescence in microscopy might simply be that the signal is minimal.

Thus, I don't know if the lack of signal is due to the bacteria or the detector.

Can somebody confirm whether these plasmids need to be induced?

Is it normal to have a very faint staining?

Do I need to add a substrate to the medium? (I bought them because I was told there was no need for it)

Thank you