Interesting document from WW Biomedical User Group:
To Sum Up Bio medial applications have 2 specific needs related to Isolation/Safety and Performance.
You need to avoid your sample or patient recieve a discharge so you need to use a certified isolated amplifier (UL 60601-1 or EN60601-1).
Performance relates to the quality of the signal, an hence the signal conditioning,here are some good sources for signal conditioners:
Comments based on your experience are welcome.