Electrochemical Principle-based Wearable Sensor For Sweat Analysis

In recent years,wearable sensors based on human vital signs monitoring were widely studied and have been commercialized.However,it is limited to reflect the health level of human body through vital signs data,because it can not provide the information of human metabolism at molecular level.As a kind of body fluid,sweat contains a lot of substances closely related to human metabolism,such as inorganic salts,organic small molecules,proteins,hormones,etc.Analysis of these components in sweat can obtain a lot of health informations,including diet status,pressure level,electrolyte balance and hydration.Traditional sweat analysis often relies on large-scale biochemical analysis equipment,such as high performance liquid chromatography,mass spectrometer,which is not conducive to timely in-situ analysis of sweat.Electrochemical detection rely on substances in the electrode surface electrochemical reaction,and then convert the perceived signal into electrical signal,which has a wide range of applications in environmental monitoring,clinical diagnosis,food analysis,public safety,drug testing and many other fields.In recent years,the breakthrough of wearable assistant sensor technology has helped the development of electrochemical sensor in the field of rapid detection.Wearable analytical equipment based on electrochemical principle has the advantages of portable device,high sensitivity and continuous monitoring,which has great potential in the detection of biochemical indicators of body fluids.In this paper,based on the principle of electrochemical detection,the enzyme-free glucose sensor is applied to wearable sweat analysis for the first time,and the multi-step potential detection method is developed and systematically studied.Through this method,a series of problems in practical application of traditional enzyme/enzyme-free glucose analysis can be solved.The main research contents are as follows:1.An enzyme-free glucose detection method based on multi-step potential technology was developed,and a wearable bracelet which can be used for the analysis of sweat sugar was developed.We use gold as the working electrode and apply multi potential steps on the gold electrode,including the high negative potential pretreatment step for proton reduction to create local alkaline conditions,the conventional potential step for electrocatalytic oxidation of glucose under alkaline conditions,and a positive potential step for electrode cleaning.The p H change in diffusion layer and the electrochemical behavior of gold electrode in neutral environment were studied.The selective protective film was modified on the gold electrode and its selectivity and stability were investigated.The wearable bracelet was developed to continuously monitor sweat glucose during physical activity,and compared with the results that were measured by large equipment.2.The method of in-situ electroplating of micro three electrodes on the metal substrate of circuit board was developed,which further integrated a sensor detection-signal processing chip for enzyme-free glucose detection.Gold working electrode with good electrochemical performance,platinum counter electrode and Ag / Ag Cl reference electrode were fabricated by in-situ electroplating on the surface of metal substrate.The cathodic current and electroplating time were optimized.The electrochemical behavior of micro three electrode system in buffer solution was discussed,and its long-term stability in air environment was investigated.The wearable bracelet made of Tyvek is expected to be used to monitor the glucose content of sweat and reflect the fluctuation of blood glucose concentration.3.A wearable sweat band based on flexible screen-printed electrode was developed.The imidazole metal organic framework(ZIF-67)coated palladium nanoparticles composite was prepared,and then mixed with conductive ink to print electrodes which can be used for enzyme-free glucose detection under physiological p H.The anti bubble interference ability of the screen-printed electrode in the pretreatment process was investigated and compared with the traditional screen-printed electrode.The performances of screen-printed electrode for sweat glucose analysis were reported,including repeatability,stability and anti-interference ability.The screen-printed electrode and flexible circuit board were integrated into a sweat band to monitor the sweat glucose level of the wearer for several days,and the results were compared with commercial blood glucose meter.4.A new patch for the analysis of glucose based on the electrochemical four-electrode system was developed.Based on traditional three-electrode system,we developed a four-electrode system,including a working electrode,a reference electrode and two counter electrodes.Porous nickel nanomaterials were in situ prepared on the surface of the screen-printed electrode using nickel salt solution as the precursor.The detection of glucose on four-electrode sensor chip with porous nickel nanoparticle as the working electrode at neutral p H was investigated.The results show that the sensor has the advantages of high sensitivity,low background current and no bubble interference.The four-electrode sensor chip was integrated into a patch which can be used for sweat glucose analysis,and the repeatability and long-term stability were also investigated.