Sensitive Paper-based Analytical Device For Colorimetric Analysis Of Nitrite And Chemiluminescence Detection Of Hemin

As a new on-site analytical platform,paper-based analytical device(PAD)has been widely used in environmental monitoring,food quality control and clinical diagnostic and drug control since it was introduced by Whitesides in 2007.The major advantages of PAD include simplicity,portability,easy to operate,low cost and so on.This is important for developing countries and remote areas where industrialization degree is low and requires professional and laboratory analytical techniques for portable and real-time detection.However,compared with laboratory based analytical instruments,the sensitivity of PAD is often limited for low abundant analytes,which hinders their extensive applications.Improving the sensitivity of PAD is necessary to achieve on-site detection of target analytes.In the first chapter of this work,we mainly introduced the development of PAD,major detection methods and the application in environmental monitoring,food quality control and clinical diagnostic.In addition,the research status of colorimetric and chemiluminescence in PAD was emphasized.In the second chapter,we attempted to combine the Griess reaction with electrokinetic stacking(ES)to achieve the colorimetric analysis of the colorless nitrite on simple PAD using a smartphone.Firstly,the experimental conditions such as the position of the side channel,the electrokinetic stacking time and the colorimetric time were optimized,respectively.Under the optimal conditions,we tried to explore the analytical sensitivity and enrichment effect of the method,which the limit of detection(LOD)was 0.073 μg/mL.The sensitivity of nitrite was 160-fold increased.The limit of detection was 10 times lower than the reported,and closed to that achieved by a desktop spectrophotometer.In order to verify the feasibility of the method,we applied the method to the detection of nitrite in human saliva samples,drinking water and environmental water samples with recovery in the range of 91.0%～108.7%.This method has various advantages of the conventional paper-based analysis method compared with other instrumental analysis methods(spectrophotometry and so on).In addition,the sensitivity of traditional paper-based analysis methods has been improved.This method provides a method for highly sensitive on-site determination of colorless target analytes.In the third chapter,a sensitive PAD system with chemiluminscence(CL)detection and electrokinetic preconcentration was introduced,and the performance was demonstrated by the detection of hemin.A commercial available low cost and miniaturized optical detection module was used for the CL detection.Firstly,we investigated the effects of the applied voltage,the concentration of background electrolyte solution,luminol,hydrogen peroxide and sodium hydroxide in the luminescent reagent on the chemiluminescence signal.Under the optimal conditions,the detection sensitivity and selectivity of the method using hemin was explored,and the sensitivity was 13-fold increased.The limit of detection(LOD)was 0.58 nmol/L.On this basis,we successfully achieved the detection of hemin in common iron supplements and human serum with recovery in the range of 84.0%～116.0%.The sensitivity of the paper-based analysis device was improved with this method while characteristics of the portable and on-site detection of the PAD system was maintained.