Thermal-responsive Textile/paper-based Microfluidic Device And Its Application In Human Sweat Analysis

As an emerging technology that combines life science,electronics,and materials chemistry,wearable electronics has been fueled up in the past decade due to its great potentials in daily health monitoring,motion tracking and disease diagnostics.As one of the most important components in a wearable device,flexible sensor has attracted considerable interest of both academics and industry.However,most of them mainly focus on the measurement of physiological signs such as heartbeat rate,pulse and respiration rate,which cannot meet the requirements of health monitoring on real time and accuracy.Thus,it is highly desirable to develop a new generation of wearable devices for the detection of human biomarkers at molecular level.Sweat,a biofluid secreted from human sweat glands,contains plenty of biomarkers and can be collected non-invasively.If wearable devices can be used for sweat component analysis,it will strongly promote their application in daily health monitoring and disease diagnosis.Polyurethane(PU),a thermal-sensitive shape memory polymer,can deform under thermal stimulation and has been widely used in the construction of thermal-responsive devices.In this thesis,a thermal-responsive textile/paper-based microfluidic analysis system was constructed by combining temperature-sensitive polyurethane,traditional cotton fabrics and paper-based colorimetric sensors.The system was applied to quantitative analysis of glucose in human sweat at relative high temperature.Detailed works are summarized as follows: 1.Construction and Characterization of Thermal-responsive Textile-based Microfluidic DeviceThermal-sensitive PU was coated on commercially purchased cotton fabrics via a layer-by-layer painting method to prepare the thermal-responsive textile-based devices.Fourier transform infrared spectroscopy,scanning electron microscopy and contact angle measurement were employed to characterize the surface chemical groups and morphology of the fabrics with/without polymer modification.The results show that the shape memory polymer was successfully immobilized on the fabrics.The opening angle of the folded device is highly correlated with the number of PU layers and the exposure temperature.With the increase of temperature,the device’s deformation response becomes more obvious.At the same temperature,the devices with 4 and 5 coating layers exhibit the best thermal response.Subsequently,the width of the microfluidic channel was optimized and the channel with the width of 4 mm has the highest liquid transfer rate.Based on the above results,the devices with four layers of PU and a microfluidic channel width of 4 mm were selected for the construction of sweat analysis system in the following experiments.2.Preparation and performance analysis of paper-based glucose colorimetric sensorIn this part,the paper-based glucose colorimetric sensor was prepared by successive dropping chitosan,glucose oxidase(GOD),3,3’,5,5’-tetramethylbenzidine(TMB),peroxidase(HRP)on a filter paper.A smartphone-based color analysis system was coupled with the paper-based sensor for quantitative analysis of glucose concentration.In order to obtain the high sensing performance,in this study,the functionalized paper base was refrigerated in a 4°C refrigerator for obtaining a paper-based glucose colorimetric sensor with uniform color.The dropping amounts of GOD,HRP and TMB were optimized to be 1.6mg,0.12 mg and 3.6mg,respectively.The paper-based colorimetric sensor was applied to detect artificial sweat containing different concentrations of glucose.The linear range of sensor and the detection limit were 50-600 μM and 10.41 μM,respectively,which could meet the needs of human sweat glucose analysis.3.Thermal-responsive Textile/Paper-Based Microfluidic Device and Its Application in Human Sweat AnalysisOn the basis of the above works,the thermal-responsive textile-based microfluidic device was integrated with the paper-based glucose colorimetric sensor to construct a thermal-responsive textile/paper-based microfluidic analysis device.Firstly,the response of the integrated device to artificial sweat samples containing different concentrations of glucose under the flow condition is studied.The system shows the linear range of 50-600 μM and the detection limit of 13.49 μM.Then,the thermal-responsive textile-based device and paper-based glucose sensor were fixed at the upper and lower sides of the inner collar,respectively,for in situ analysis of human sweat in high-temperature environment(60 oC).It is found that when the temperature reaches 60 oC,the folded textile-based part opens up at the collar.After 6 minutes,the recovery angle is stable at 45±3°and the textile channel directly contacts with the paper-based sensor to effectively transfer sweat.The system was further applied to real-time monitor sweat glucose levels of three healthy volunteers at 60 oC.Their sweat glucose concentrations were 34.71±2.93,74.22±1.95 and 224.24±1.77 μM,respectively,falling in the normal range of human sweat.In summary,by combining shape memory polymer with traditional fabrics,a flexible microfluidic device with thermal-responsive property was prepared and further integrated with the paper-based colorimetric sensor to realize human sweat glucose analysis in a high-temperature environment.The construction of the thermal-responsive wearable sweat sensor is expected to provide a low-cost and easy-to-wear sweat monitoring tool for the workers exposed to high temperature.It may also further expand the applications of shape memory polymers and textile-based flexible devices.