Ion Concentration Polarization Effect In Paper-based Analytical Device And Its Application In Urine Protein Detection

Ion concentration polarization(ICP)effect is an effective preconcentration method for charged species in microfluidic systems.It has been drawn special attention due to the interface is easy to introduce and manipulate.The paper-based analytical device(PAD)has great application potential in POCT due to its cheap and portable,easy to process,but its low sensitivity has been a problem to be solved.In recent years,ICP has also been introduced in PAD to improve the detection sensitivity.The first chapter introduced the common electrokinetic stacking methods,including field-amplified sample stacking,isotachophoresis,isoelectric focusing and ICP.Then the principle and the common methods for establishing interfaces of ICP effect were briefly introduced.Finally,the common detection and readout methods in PAD were summarized.In the second chapter,a simple and cheap ICP interface was introduced in a PAD by using commercially available ion exchange membrane(IEM)that is commonly used in industry.Significant ICP effect was observed by placing the IEM directly on a wetted paper fluidic channel,and electrokinetic stacking of both anion and cation probes was demonstrated with cation exchange membrane(CEM)and anion exchange membrane(AEM),respectively.Simply based on LED illumination and smart phone fluorescent imaging,about 10-fold signal improvement was achieved for negatively charged fluorescent probes of fluorescein sodium and FITC-BSA with CEM,and 50-fold signal improvement was achieved for positively charged fluorescent probe of rhodamine 6G with AEM.The quantitative performance based on this electrokinetic stacking method was also investigated.The third chapter proposed an instrument-free detection method based on ICP online stacking by PAD and smartphone imaging system,which showed its performance by detecting the total protein in urine samples.The results showed that proteins from physiological samples without any pretreatment could be directly and repeatedly loaded onto the depletion region of the ICP interface established by the cation exchange membrane(CEM)on paper channel,and the protein could be cumulatively stacked as a narrow band as visually observed by a smartphone camera.Colorimetric detection of model protein(Phyco)showed that at least 60-fold enrichment could be achieved with this method.With post-staining of the stacked albumin from artificial urine,a linear response in the diagnostic meaningful range of 50～350 mg/L(R2=0.994)was achieved.Total protein from clinical urine samples was detected,and the recovery rate was found in the range of 93～108%,and the RSD was less than 11%.Comparative assays showed no significant difference between the results of this and that of the clinical method.The proposed ICP interfaces based on IEM provided a cost-effective route for improving the detection sensitivity of charged species on PAD.Combining electrokinetic stacking with smartphone colorimetric detection,this paper demonstrated the feasibility of directly stacking and quantitative detection for target component in physiological samples using PAD-ICP platform.