Development Of Oxygen Sensors With Low Cost And Long Life

In recent years,mobile health devices,such as portable metabolism trackers for breath analysis,have gradually entered people's lives as people begin to pay more attention to health.The concentration of oxygen in breath gas varies not only from person to person but also from time to time.Oxygen concentration can be used to measure maximal oxygen uptake,metabolic rate,and so on.While the measurement of maximal oxygen uptake is useful for the assessment of cardiopulmonary fitness and aerobic capacity,and the detection of metabolic rate is important for weight management.Therefore,the detection of oxygen concentration in breath gas can help people manage their health.At present,the detection principle of oxygen sensor in metabolism trackers on the market is mainly based on electrochemical method,colorimetric method and fluorescence quenching.Electrochemical methods are most commonly used with reliable detection and small size,but they are expensive and require regular correction and sensor replacement.Colorimetric oxygen sensors are cheap and calibration-free,and its sensing array is easily to be built for multi-sensors fabrication with small size.But the operating life of colorimetric sensing chip is short with one-time use only,therefore it costs too much for long-term use.Based on these backgrounds,this dissertation aims to develop low-cost oxygen sensors for mobile health devices,with a focus on improving the life of sensors.The main contents are as follows:1.Thin Layer Electrochemical Oxygen Sensor with ReservoirIn order to achieve the longer sensor life,we chose the amperometric method for oxygen detection,with the use of non-consuming screen-printed carbon electrode and the design of the reservoir.Water evaporation is an inevitable problem for aqueous electrolyte,while the reservoir is designed for water replenishment.The carbon electrode has the advantages of wide electrochemical window,low background current,good stability,mature preparation process,low price and small size.The use of screen-printed carbon electrode not only avoids the short-life problem caused by anode consumption but also reduces the sensor price.In order to get fast response time,we designed a thin electrolyte layer for shortening the diffusion time that oxygen diffuse to the electrode surface.The sensor is easily fabricated,cheap,and the life of the sensor is long.The sensor can be used for real-time measurement of oxygen concentration in breath gas(deep breathing)with the sensing range of 13-24%O2,resolution of 0.5%O2,and the response time of 14 s when the oxygen concentration difference is 5%O2.2.Oxygen Sensing Based on the Yellowing of NewspaperThe air contains 20.9%O2,so normally the oxygen colorimetric sensors need to be sealed in oxygen-free atmosphere.Once opened,oxygen in the air greatly shortens its life.With light-induced discoloration material as the oxygen-sensitive material,this storage problem can be avoided.Newspapers contain lignin which is a kind of light-induced discoloration material.Newspaper is stable even after a long time exposure in an indoor oxygen-containing environment but becomes yellow quickly under ultraviolet light of which the yellowing rate can be used for oxygen detection.We offer here this new approach for solving the storage issue of oxygen colorimetric sensors.Based on newspaper yellowing,we present a colorimetric sensor and a fluorescence sensor for oxygen detection.The experimental result that the sensitivity of the newspaper did not change significantly after being stored in air and dark after 8 months,showed good stability of the newspaper.We also studied other properties of the two sensors,including calibration curves,cross-sensitivity and uniformity,which showed that the sensors have good anti-interference performance and uniformity.We also observed the relationship between the colorimetric sensor and the fluorescence sensor,finding that the sensitivities of the two sensors are related to the lignin content in the newspaper.3.Long-Life Oxygen Sensor with Light Controlled Configurable Colorimetric Sensing ArrayThe colorimetric sensor is designed for disposable generally,which limits their use in the application of continuous detection.We present a method here to increase the sensor lifetime which is similar to the principle of data storage devices.The sensor combines the mobile phone screen as a configurable light array and cyanine dye as oxygen-sensitive material which can easily lose its color triggered by visible light in oxygen gas.By sequential turning on and off of the light irradiated on individual regions of the sensing material,where each region can be used for oxygen sensing,the colorimetric sensor can be used multiple times.Its life depends on the size of the light array element area,the smaller the area,the longer the lifetime.We verified the feasibility of the method through the fabrication of light controlled configurable colorimetric sensing array.The oxygen sensing of each array unit does not affect other array units,and the sensitivity of each array unit showed good uniformity.Therefore,the operating life of the sensor can be improved by this method.We also measured other sensor performances,including calibration curve,cross-sensitivity,humidity effect,and stability.The results showed that the sensor is highly resistant to interference and can be stored stably in the dark with oxygen-containing atmosphere.Limited by the maximal brightness of the phone screen and the noise level of the camera,the area of the light array unit affects the sensitivity and noise of the sensor,thus affects the signal-to-noise ratio.The larger the area,the higher the signal to noise ratio.The increase of detection time increases the degree of color change,so for a given signal-to-noise ratio,the minimum array element area required for sensing is inversely proportional to the detection time.By lengthening the detection time,the area of the array unit required to achieve the proper signal-to-noise ratio can be reduced,thus maximizing the life of the sensor.