A method for operating a sensor for biomolecules or charged ions, the sensor comprising a first field effect transistor (FET) and a second FET, wherein the first FET and the second FET comprise a shared node includes placing an electrolyte containing the biomolecules or charged ions on a sensing surface of the sensor, the electrolyte comprising a gate of the second FET; applying an inversion voltage to a gate of the first FET; making a first electrical connection to an unshared node of the first FET; making a second electrical connection to unshared node of the second FET; determining a change in a drain current flowing between the unshared node of the first FET and the unshared node of the second FET; and determining an amount of biomolecules or charged ions contained in the electrolyte based on the determined change in the drain current.