I need to design a couple of differential input pre- amplifiers for a high impedance electrochemistry potential type of measurement. The target impedances of my circuitry are 10 megOhm and 100 megOhm or greater (both).. the differential signal range is about 1 volt.. The frequency of the signals is DC to 4 Khz. This is a battery operated system with 20v battery. The output is going to a National instruments DAQ with 24 bit sampling at 10Khz (1 meg Ohm input impedance). Other features I would like are over-voltage protection, and ESD input protection,, obviously I will need to filter RFI .
Which IA should I choose and any recommendations on the circuitry would be nice. This is a new realm for me and I am not experienced with the tricks of dealing with high impedance signals.