Taking selfies with conference speakers

Yes, it is acceptable. I heard a rumor that scientists are human beings. I have not been able to confirm it, but it seems like a plausible assumption, and if you are willing to accept this as a working hypothesis, it follows that it is acceptable to behave around them as you would with other human beings.

In particular, most human beings are flattered if you approach them with excitement and admiration and ask to have your photo/selfie taken with them because you want to brag to your friends (or whoever) about meeting them, and would either happily agree or (less likely, but possible) politely refuse. Scientists - even protein chemists! - are no exception to this rule.

Here is a better idea.

Ask if you can have your picture taken with them. Ask someone else to hold the camera/phone.

And don't ask at the dinner, ask before or after if the opportunity presents itself. Don't be that guy that pushes through people to ask someone for a photo op.

Tell them how much you liked their lecture, etc.

Also, just to cover all bases a Forbes article on business dining etiquette The list at the end is the biggest thing to pay attention to.