I haven't modified the cheapstat to have a +/- 1uA range - however I'm pretty sure this should be doable.
Also, we have a new potentiostat design coming out soon which is basically a shield for the teensy 3.2 development boards (https://www.pjrc.com/teensy/teensy31.html). It has current ranges of +/- 1, 10, 100, 1000 uA and output voltage ranges of +/- 1, 2, 5, and 10V. We just got a batch of the new of the PCBs in - I've attached an image below. We should have them up on our website within the next 2-3 weeks.