SCIENCE CHINA Information Sciences, Volume 60, Issue 8: 082403(2017) https://doi.org/10.1007/s11432-016-0645-2

## A micro-array bio detection system based on a GMR sensor with 50-ppm sensitivity

• ReceivedSep 29, 2016
• AcceptedNov 21, 2016
• PublishedApr 24, 2017
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### Abstract

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 $-116.84$ dBm/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.

### Acknowledgment

This work was supported by National Natural Science Foundation of China (Grant Nos. 61204026, 61101001, 61674087), Guangdong's High-Tech Project (Grant No. 2015B020233001), Dongguan's High-Tech Project (Grant No. 2014215102), and Tsinghua University Initiative Scientific Research Program.

• Figure 1

(Color online) Steps in GMR biosensor detection. MNPs are utilized to tag analytes and change the resistance of the sensor in an applied magnetic field.

• Figure 2

(Color online) (a) Multilayer structure of the proposed GMR sensor; (b) GMR sensor resistance relative to the applied magnetic field; (c) signal versus passivation layer thickness.

• Figure 3

(Color online) The GMR biosensor chip consists of $12$ independent sensors.

• Figure 4

(Color online) The GMR biosensor is fabricated in parallel.

• Figure 5

(Color online) Read-out strategy of the GMR biosensor.

• Figure 6

(Color online) 4-channel signal extraction biochip.

• Figure 7

(Color online) Side tone of the detection sensor and reference sensor.

• Figure 8

(Color online) (a) $\alpha$ prototype detector utilizing discrete circuit; (b) the structure of the $\alpha$ prototype detector; (c) the detecting card of the $\alpha$ prototype detector.

• Figure 9

(Color online) Output noise spectrum of the read-out biochip.

• Figure 10

Magnetic signal of the GMR biosensor. The short dash line indicates the surface reaction.

• Figure 11

(Color online) The picture on the top right is obtained by an optical microscope. The bottom left picture shows the partial enlarged view of the part in the red circle and is obtained by SEM.

• Figure 12

(Color online) Magnetic signal relative to the number of MNPs, each MNP with a diameter of 200 nm produces a signal that approximately corresponds to mbox0.09 ppm

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