A method may comprise (a) inserting an
insulin delivery device subcutaneously into a body of a subject, which comprises an amperometric glucose sensor comprising an
electrode layer comprising an indicating
electrode and underlying a
redox-catalytic layer comprising a
redox mediator; (b) using said
insulin delivery device to deliver an
insulin formulation (e.g., comprising a
phenol or
cresol excipient) subcutaneously to said subject; and (c) using said amperometric glucose sensor to measure a subcutaneous glucose concentration, which comprises using said
redox-catalytic layer to allow
electron transfer from subcutaneous glucose to said indicating
electrode sufficient to cause a response of said amperometric glucose sensor at an applied bias potential of no more than +250 millivolts, wherein (b) and (c) are performed at the same time for at least one hour, while maintaining a sensor sensitivity of at least 50% of an initial sensor sensitivity for up to one hour.