The amplifier for bioloop required quite a bit of trial and error. I thought I had got it working, and the next day it didn't. After days of testing and many spilled resistors I decided on a final design, based off of a very helpful PDF that I linked. The original 'Cornell' sensor is connected to a differential amplifier with a gain of 1, along with a similar voltage divider/follower circuit as shown below.
The dividers will be connected directly to a microcontroller pin, which will allow then to be shut on and off, saving power. Otherwise, small amounts of power would trickle through the voltage dividers, draining the battery.
The schematic is from my final PCB design for the bioloop, which has a dedicated analog sensing board to avoid noise from other electronics. It also allows the final design to be very small-only about 1inch by 1inch. I will post more pictures of the schematics when I get things squared away and working properly with the attiny84. Otherwise, hit up the github.