You don't even need DACs or ADCs, you just need an SRAM cell leaking current through an electrode. The process is entirely separate from that. By analog, I don't mean the signal, I mean the chip is interacting with the world physically. I need the electrodes physically touching chemicals. Those chemicals are incompatible with the aluminum or other normal metals on those connections - you pretty much need platinum or the metal from the chip will screw up the chemical reaction.

You also need large amount of input/output - a good start on a chip would be about 1,000 to 10,000 electrodes. I think it is going to be difficult to put that many on an FPGA.