Ahh yes, I am well acquainted with the piezoelectric effect, having been a victim in the past.
In a previous life, I worked in industrial controls. Some of our radiation sensors had a very low output current, in the nA and pA range. And by that I mean the maximum current. In one application, we were measuring current by accumulating charge over a 100 millisecond period, read by a special 20 bit A/D converter. I recall doing the math and determined each bit on the A/D was about a thousand electrons. We had to take great care with component selection, and circuit fabrication. Teflon insulated posts were your friend, with lots of dead bug construction.