Study On Flexible Sensors Towards Healthcare Realted Monitoring

Health is the most common and fundamental requirements for human being.The report of the 19th National Congress of the Communist Party of China,pointed out the strategy of 'Healthy China',focusing on implementing the food safety strategy,and dealing with the population aging actively,to provide full-range and full-cycle health services for Chinese People.The development of 'Internet of Things' pushes the development of remote and personalized healthcare network,which demands wide ranges of sensors.Flexible sensors have many advantages,such as facile fabrication,low cost,excellent performance and wide applicability,etc.,which are of great value in monitoring human health-related information comprehensively.Therefore,we study on two kinds of flexible sensors in this thesis.One kind is the flexible strain sensor based on electrical response,towards monitoring individual vital signs and physiological signals,another kind is the flexible SERS(Surface-enhanced Raman Scattering)substrate based on optical response,towards in-situ detection of molecular fingerprint.The flexible strain sensors based on nanomaterials,with high sensitivity and comfort,are suitable for wearable monitoring.Graphene based flexible strain sensor has many advantages such as low-cost,facile fabrication,and outstanding performance.Therefore,we focused on the graphene-based flexible sensor,and fabricated two kinds of flexible sensors towards healthcare monitoring.The main research results are as follow:1.Based on dip-coating and chemical reduction,the double covered elastic fiber is coated by reduced graphene oxide(RGO),thus the RGO/elastic fiber sensor is successfully achieved.The micro-scale PE winding layers of elastic fiber is selected as the flexible supporter,providing a three-dimensional RGO conductive network.In the small tensile strain range(under 3%),the graphene coated fiber sensor presents GF?2.7 and fast responsibility(down to 60 ms),and the best linearity in flexible sensors up to now,(R2?0.9914).2.Based on graphene coated elastic fiber,we fabricate a radial artery pulse sensor and sensor patch for the first time.The pulse sensor achieves the precise detection of pulse waveform for several volunteers,from which the radial augmentation index(AIr)can be calculated,which is consistent the medical report.In addition,with the sensor patch adhered to different body regions,we realized not only the vital signs monitoring,but also comprehensive healthcare monitoring for the first time,including chewing,swallowing,muscle movement,and knee-jerk reflex.Flexible SERS substrates,using the flexible carrier to support plasmonic noble metallic nanostructures,polymer-based flexible SERS substrates with distinctive advantages on transparency,bendability,and bio-compatibility,shows valuable appliacaton for in-situ contamination detection in life application.Therefore,we fabricated two kinds of polymer-based flexible SERS substrates,based on plasma etching.The main research results are as follow:1.Based on Ar plasma etching on PET,and followed by Au evaporation,flexible SERS substrates based on Au nanostructures are achieved in a facile,high-throughput,and reproducible method.A systematic study on the SERS intensity versus Ar plasma etching time and Au thickness is conducted,combining morphology observation to achieve the best performance.The optimal Au nanoworm SERS substrates present high enhancement effects in the advanced level,with EF calculated to be?1.2×108.2.Based on reactive ion etching(RIE)and nanoimprinting lithography(NIL),the large-area polymer-based SERS substrates with nanoseeds structures are successfully achieved for the first time.This part of work was completed during the joint education in Techincal Univerity of Denmark(DTU).(1)Starting from a 4-inch Si wafer,a maskless RIE was employed to etch dense and uniform Si nanopillars;followed by evaporation of Au/Ag,the metallic nanocaps on Si nanopillars are formed;finally,through nanoimprinting,the nanocaps on Si wafer stamp are partially planted into PMMA film like nanoseeds,Au or Ag nanoseed flexible SERS substrates are obtained.The fabrication throughput is as high as 4 inch,and the process is highly stable and reproducible.(2)Both Au and Ag nanoseed SERS substrate present excellent uniformity through mapping imaging within 2mm×2mm area,it's worth to mention that the RSD of optimal SERS substrate is only 3.4%,obtained from Au nanoseeds excited by 633 nm laser,which is lowest up to now.The highest averaged SERS enhancement factor is caculated to be as high as 106,obtained from Ag nanoseeds excited by 532 nm laser,presenting great enhancement effect.(3)Both Au and Ag nanoseed SERS substrate are capable for the Raman signals collection form the back side,and the measured Raman signal are almost identical to that from the front side.In addition,the nanoseed SERS substrates are operative during a wide bending range.With a small piece of Au nanoseed SERS substrate directly adhered onto grape,an in-situ detection of fungicide,Tebuconazole on grape,was achieved with portable Raman spectrometer for the first time.The in-situ detection limitation of Tebuconazole is as low as 20 ng/mm2,which is lower than EU safe standard,250 g/ha.