3. Conclusion

of in vivo in the biosensor has its special significance both in the clinical monitoring of the

The internal environment is very complex, not as easy to control as in vitro environment. After implantation of biosensor, it is important not only to ensure normal performance parameters of biosensors but also to ensure that implanted sensor systems cannot pose any danger to patients or subjects. Therefore, we should not only face some special technical problems but also follow strict regulations on medical instrument management and obtain experimental licenses. Biosensor for in vivo monitoring needs to be implanted into the body (such as blood vessels, cerebral cortex, subcutaneous tissue) and faces many complex environments, including the tissue response, biocompatibility, disinfection problems, oxygen interference, and other tech-

Many companies and research institutes carry out the research on in vivo sensor system in recent years. Several glucose sensor systems that continuously monitor the blood glucose level under the subcutaneous have been commercially developed and applied. Nowadays, these blood glucose sensors belong to this kind of "percutaneous," which directly pierce the fineneedle sensor into the skin, and the base and data part are fixed on the skin. The CGMS probe sensor from Medtronic company has three layers containing the semipermeable membrane, glucose oxidase, and platinum electrode [59]. Among them, the platinum electrode of the Medtronic probe is the tri-electrode probe system, which can reduce the interference of the impurity to the current signal. The CGMS probe was implanted subcutaneously for 3 days in the patient's abdomen (Figure 9). The probe generates electrical signals by chemical reaction with glucose in the subcutaneous intercellular fluid of the patient. The electrical signal is proportional to the concentration of blood sugar, but it is delayed for about 20 minutes. The Abbott freestyle continuous glucose monitoring system contains implantable needle biosensor and wireless reading device. The implantable needle biosensor adopted the same principal with the size of length 5 and 0.4 mm diameter on a coin-sized sticker (Figure 10), long term for 14 days sticking on the upper arm [60]. When we want to check blood sugar, the blood glucose meter is close to the circle sticker, which is accurate and convenient. The Eversense Continuous Glucose Monitoring (CGM) developed by Senseonics medical company has been approved by

patients and in the basic physiological research [56–58].

Figure 9. The Medtronic needle sensor and reader.

nical issues.

64 MEMS Sensors - Design and Application

Biosensor has the characteristics of cross disciplinary integration. The development trends of biosensors are miniaturization, multifunction, integration, and intelligence. The introduction of some new frontier technology such as microelectronics, nanotechnology, and microelectromechanical technology (Microelectronic Mechanism) is applied to the biomedical sensor to develop a new generation of biosensor with low cost, high sensitivity, high reliability, high life and bionic function, achieving rapid and accurate test of trace components in the sample. At the same time, the biomedical sensor has developed from planar two-dimensional to three-dimensional microelectronic mechanical system sensors. With the development of computer software and hardware technology, sensor technology will also develop, and the biological system of closed-loop control will be possible. In the future, biosensors will be widely used in many fields, such as food detection, medical care, disease diagnosis, environmental monitoring, fermentation industry, and so on.
