Bio detection is widely utilized in hospitals and laboratories. However, conventional bio detection methods suffer from long detection time, complex operation, and low sensitivity, and these issues prevent their use in point of care testing(POCT) applications. Microelectronic bio detection methods are proposed to overcome these issues. Bio detection based on a micro-electronic technique allows easy integration of a system, leading to a fast detection speed and simple operation. In this work, a fully microelectronic bio detection system including a sensor design, a read-out strategy, and data processing is proposed based on a GMR biosensor. A GMR sensor chip is designed and different passivation layer thicknesses are tested to improve sensitivity. A 40 nm thickness passivation is realized to produce the largest response without oxidization and breakdown. In order to integrate the read-out circuit and simplify operations, a 4-channel read-out biochip is designed and fabricated, and this exhibits a super-low output noise corresponding to-116.84 d Bm/Hz at the operation frequency. This means that the noise only approximately corresponds to the signal level of five magnetic nanoparticles with a diameter of 200 nm. A reference sensor is also utilized to cancel the unwanted signal and reduce common-mode noise and error to improve sensitivity. Measurements indicate that 90% suppression is achieved. The measurements also reveal that a sensitivity of 50 ppm is achieved with the proposed GMR bio detection system. However, conventional bio detection methods suffer from long detection time, complex operation, and low sensitivity, and these issues prevent their use in point of care testing (POCT) applications. Microelectronic bio detection methods are proposed to overcome these issues. Bio-based based on a micro-electronic technique allows easy integration of a system, leading to a fast detection speed and simple operation. In this work, a fully microelectronic bio-detection system includes a sensor design, a read- out strategy, and data processing is proposed based on a GMR biosensor. A GMR sensor chip is designed and different passivation layer thicknesses are tested to improve sensitivity. A GMR sensor chip is designed to produce the largest response without oxidization and breakdown. to integrate the read-out circuit and simplify operations, a 4-channel read-out biochip is designed and fabricated, and this exhibits a super-low output noise corresponding to-116.84 d Bm / Hz at the operation frequency. This means that the noise only approximately corresponds to the signal level of five magnetic nanoparticles with a diameter of 200 nm. A reference sensor is also utilized to cancel the unwanted signal and reduce common-mode noise and error to improve sensitivity. Measurements indicate that 90% suppression is achieved. The measurements also reveal that a sensitivity of 50 ppm is achieved with the proposed GMR bio detection system.