Electrokinetic Stacking And Detection Of Charged Or Electrically Neutral Analytes On Paper-based Microfluidic Analytical Device

Paper-based analytical device(PAD)has a wide application for environmental monitoring,diagnostic detection and food testing due to its low cost,simplicity of fabrication,compatibility with other detection methods,capacity for on-site detection and so on.However,low sensitivity is a limit for the widespread application of PAD.Therefore,the introduction of on-line sample enrichment method into the PAD is of significance for the high sensitive detection of low content analytes.In the first chapter,the development process,the fabrication method and the detection means of PAD were introduced.This chapter reviewed the methods and applications of sample enrichment in PAD system,and mainly focused on the electrokinetic stacking(ES)modes including isotachophoresis(ITP),ion concentration polarization(ICP)and field-amplified sample stacking(FASS).In the second chapter,we investigated the quantitative potential of anion detection in the PAD system with ES.Taking a widely used fluorescence whitening agent(FWA)component VBL in daily commodities as the typical anion target composition,the effects of electroosmotic flow inhibitor concentration,stacking time and electrode position were discussed.Experimental results showed that in the optimized experiment conditions,up to 85%of the probe was effectively stacked on the paper channel,and the sensitivity of the PAD system was 160-fold enhanced,and a limit of detection compared to that of a desktop fluorescent spectrophotometer was achieved.FWAs of four brands of napkins and toilet paper were measured by the established method,which was verified by the measured result with the benchtop fluorescence spectrophotometer.The recovery rates of three different napkin sample solutions spiked with various VBL concentrations were in 90%～95%,and inter-day and intra-day RSDs were less than 15%.High sensitivity,high recovery and reasonable reproducibility all indicated that the proposed method had the potential of practical application in field rapid test.In the third chapter,we demonstrated ES of electrically neutral analytes on PAD.Firstly,anionic surfactant stacked and formed a micelle band on an open paper fluidic channel by ES,during which the target analyte preloaded on the paper strip was swept by the micelles.Meanwhile,the probes at the anode side were carried into the micelle stacking zone by electroosmotic flow Eventually,an integrated sample stacking band formed on the paper channel.Based on the above principle,the effects of EOF inhibitor concentration,background electrolyte concentration,anionic surfactant concentration and cationic surfactant on the stacking of target components were investigated.Under optimized experiment conditions,based on characterization results by smartphone fluorescence colorimetric and direct colorimetric,the signal levels of rhodamine B and Sudan Ⅲ were increased by 30-fold and 6-fold,respectively.Fluorescence detection limit of rhodamine B and the colorimetric detection limit for Sudan Ⅲwere 0.05 μmol/L and 5.2 μmol/L,demonstrating the quantitative potential of the PAD system.