Depends on your budget, but the JouleScope [1] can measure down to half a nanoamp. Absolutely amazing piece of kit for the price ($1,000).

They also have a python library [2] so you can do lots of stuff inside Jupyter.

[1] - https://www.joulescope.com/

[2] - https://joulescope.readthedocs.io/en/latest/