> Then I decided I'd screwed up my design sketch by requiring one of the opamps to sink significant current very close to the negative rail, which is something

> Then I decided I'd screwed up my design sketch by requiring one of the opamps to sink significant current very close to the negative rail, which is something even "rail-to-rail" opamps can't do; I was planning to use millivolts from ground to represent measured nanoamps. Get an OpAmp specifically designed for current sense applications. OpAmps for current sense applications have high accuracy near 0 Volts and Vos measured in single digit microvolts. Oh, you WILL lose bandwidth with these designs. So make sure you are allowed to be much much slower.