OP
This resistivity change you are trying to measure, does the reaction affect the whole body of the electrode or only it's surface ?
nikhiljacob123:
Is there any other more effective and reliable methods of measuring differences with nanovolt resolution?
If it is only a surface effect then using an electrode made by thin film deposition may make things a bit easier.
There is also something called the skin effect which may or may not be applicable to your setup.
EDIT
Please ignore i just noticed the goalposts have changed.