A method of detecting a detection target using a sensor requires a sensor having a transistor selected from the group of field-effect transistors or single electron transistors. The transistor includes a substrate, a source electrode disposed on the substrate and a drain electrode disposed on the substrate, and a channel forming a current path between the source electrode and the drawing electrode; an interaction-sensing gate comprising a specific substance; and a voltage gate. The method includes (a) providing the detection target on the interaction-sensing gate; (b) setting the gate voltage in the voltage gate at a predetermined level; (c) selectively interacting the specific substance with the detection target; (d) when the detection target interacts with the specific substance, changing a gate voltage in the voltage gate to adjust a characteristic of the transistor; and (e) measuring a change in the characteristic of the transistor to determine a presence of the detection target.