A high sensitive detector detects and determines the presence of a very small amount of biological substances. The high sensitive detector comprises a sensor part, a sense amplifier, and microprocessor. A sensor part of the detector comprises two components; one comprises transistors and the other comprises affinity binding molecules for capturing biological substances. The affinity binding molecules can capture biological substances through specific molecular recognition. The electrical properties of a transistor-based circuit are changed when the affinity binding molecules capture biological substances on the gate of the transistors. The electrical signal is amplified by an amplifier and transferred to a microprocessor. The microprocessor modulates the transferred signal to determine the presence of biological substances.