I have a circuit that is essentially just a 1kV DC source connected to a very high resistance (basic circuit outline), within which current in the range from 0.1nA to 500uA flows that I am trying to measure using an Arduino (the current varies because the resistance varies due to outside factors). I had the idea of using this (or similar) connected to an Arduino: https://www.adafruit.com/product/904
However this works up to 26V and only has a 0.8mA resolution.
To solve this I first thought of using a potential divider to have a parallel section of the circuit with voltage reduced to ~13V where the INA219 can go (reduced voltage section), with high resistance resistors so essentially all the current flows through this section.
However I now need to amplify the current in this section to a value the INA219 can measure. After looking things up I thought that a good idea for this would be a Darlington pair and implemented it like this: with Darlington pair. However I find there's no amplification for this. Am I implementing the Darlington pair incorrectly or does it not work for such small currents, or is a Darlington pair completely the wrong idea here to amplify the current? If this is the wrong way to go about it, what would be a good way to measure the current of this low current high volt circuit with an Arduino?
Edit: I've included a schematic of the diagram that I think is described by Olin Lathrop's answer