What's the smallest scale at which dark matter has been measured? What is the smallest scale at which we have detected "dark matter" (more kinetic energy than would be predicted)?

If you don't mind indulging a follow-up: Would its detection on smaller scales be beneficial at all to advancing our understanding?

(aside: I base this question purely on the notion that our instruments have surely improved a bit since the 1930s.)
It looks like Segue 2, found by the Keck Observatory, is a candidate for the lightest galaxy, but I don't know if its the smallest one.