1. 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 single shared node, and a sensing surface formed directly on a portion of a gate dielectric comprising SiON, the method comprising: placing an electrolyte containing the biomolecules or charged ions on the sensing surface of the sensor, the sensing surface located over the single shared node, and 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 an unshared node of the second FET; leaving the shared node and the gate of the second FET floating; determining a change in a drain current flowing between the unshared node of the first FET and the unshared node of the second FET, wherein the change in the drain current is caused by the biomolecules or charged ions in the electrolyte binding to the sensing surface of the sense FET; and determining an amount of biomolecules or charged ions contained in the electrolyte based on the determined change in the drain current, wherein the sensor further comprises an insulating material located directly over the gate dielectric, the unshared node of the first FET, the unshared node of the second FET, a gate of the first FET, and the single shared node such that only the gate of the second FET is exposed to the electrolyte during the placing of the electrolyte.