Sensitivity (or responsitivity?) of an electrochemical sensor - Definition
Responsivity is a measure of the gain of the detector, output/incident ratio. If the output is current, measured in amps, and the input is radiation power, measured in watts, then the responsivity will have units of amps/watt. With a voltage output, it would be volts/watt.

Sensitivity sounds like it ought to be a measure of the smallest signal a detector can reliably sense. However, if it's given in units of amps, for a current output detector, then it's the output at the minimum detectable input level. It obviously needs scaling by the responsivity if it's to represent the minimum detectable input level itself.