Abstract: Systems and methods for detecting ions in samples. In one embodiment, the system includes a field-effect transistor sensor and an electronic controller. The field-effect transistor sensor is in contact with the sample and includes a first electrode and a second electrode. The electronic controller is coupled to the field-effect transistor sensor. The electronic controller is configured to apply a pulse wave excitation signal to the first electrode. The electronic controller is also configured to receive a response signal from the second electrode. The electronic controller is further configured to determine an electrical characteristic of the field-effect transistor sensor based on the response signal. The electronic controller is also configured to determine an amount of the ions in the sample based on the electrical characteristic of the field-effect transistor sensor.