Development Of Flexible Strain Sensor Chip Based On Molybdenum Disulfide And Its Biomedical Application

With the development of society and the improvement of living standards,people are paying more and more attention to health and hoping to early find underlying diseases in the body before they happen.Flexible wearable devices have drawn more and more attention since they possess the advantages of small size,light weight and convenience to wear and comfortable.Thus,they can be used to collect and monitor physiological signals of human body in real time,achieving early prevention and detection of diseases.The key component of a flexible wearable device is the high-performance flexible sensor.Among various kinds of flexible sensors,the flexible stress sensor,due to its advantages of simple preparation process,flexible stretch,good adhesion and rich detection signals,is widely used in real-time acquisition of human physiological signals.However,the developed flexible stress sensors at present still have some disadvantages such as low sensitivity and small range of stress detection,limiting their application and development.In this thesis,we proposed a thermoplastic elastic insulator as the substrate material of the flexible stress sensor.Then,high-conductivity AgNFs and low-conductivity layered MoS2nano chips are chosen to be blended into the elastic insulator for the first time.Finally,a flexible stress sensor with an ultrahigh sensitivity was successfully developed,achieving real-time and dynamic detections of various physiological signals of human body.The main work is included of the following aspects:We proposed SEBS as the substrate material of the flexible stress sensor and employed a low-cost,solution-processable method to fabricate a flexible film substrate with thickness of only 25?m.We blended two kinds of nanomaterials--AgNFs and MoS2 into the substrate to obtain a flexible stress sensor with high sensitivity and wide stress detection range.We investigated the effects of AgNFs and MoS2 on the performance of the device.It was found that when pure AgNFs was blended into the film,high-conductivity AgNFs network with the characteristic of metal state was formed,and under a certain stress,the high-conductivity AgNFs network was closely connected and hard to be separated,resulting a small sensitivity of 2.5.However,when AgNFs and MoS₂ are blended,the highly-conductivity AgNFs network were embedded with low-conductivity MoS2nanosheets.Under a certain stress,obvious fracture phenomenon happened in the conductive path of AgNFs network,resulting in great reduction of conductivity.When the mass ratio of AgNFs to MoS2 was optimized to about 1:2000,the sensitivity of the flexible strain sensor was up to 3300 in a stress range of 0-10%,which is more than 1000 times higher than that of the device without MoS₂.Furthermore,we found that when the stress increased gradually,the device experienced sudden change from metallic state to insulation state.When the external force was removed,the device recovered from insulation state to metallic state.Furthermore,the device remained stable during a two-hours cycling of continuous stretching and releasing operations.It is greatly important to achieve real-time detection and information fusion of multi parameter human body signals for disease diagnosis,prevention and treatment.For this reason,we applied the MoS2 flexible stress sensor on the skin surface of the subject,and successfully achieved real-time detections of various physiological signals in human body such as pulse,voice,breath and limb movement.Furthermore,with the help of the flexible stress sensor,we attempted to extract blood pressure signal by synchronous detections of pulse and ECG signals.We successfully developed a wearable ECG acquisition system,which is involved of an analog signal acquisition circuit based on AD8232 chip and a digital signal processing circuit based on STM32 microprocessor chip.Using this system,we successfully achieved real-time detections of ECG signals,laying a solid foundation for the research and development of wearable acquisition system of blood pressure signals.