Novel Microfluidic Paper-based Devices Based On Polymeric Materials And Their Applications In Environmental Analysis

With the continuous development of global industrialization and urbanization,environmental pollution has seriously threatened the sustainable development of economy and society,and health of human life.Therefore,it is of great significance for scientific and accurate monitoring the environment condition.Currently,the detection of environmental pollutants is commonly implemented in laboratories.Although the traditional laboratory analysis methods have high sensitivity and accuracy,the expensive equipment is required and the assay process is also time-consuming and inefficient.In addition,it is difficult to achieve in-situ detection.Hence,it is urgent to develop inexpensive,real-time and efficient detection technologies and platforms in environmental analysis.The emergence of microfluidic chip technology provides a powerful tool to promote the development of analytical instruments with miniaturization,portability and integration,which has become one of the important development frontiers in analytical science.As the latest development field of microfluidic chip technology,microfluidic paper-based analytical devices are particularly suitable for the fabrication of disposable micro analytical platform because of their low cost,easy to obtain and capillary drive,and have shown great application potential for in-situ environmental monitoring.In this dissertation,a series of novel microfluidic paper-based analytical devices were fabricated by using functional polymer materials such as photopolymer,dendrimers and photonic crystal hydrogels.By further designing fluid channels,moving valves and control mode on paper substrates and combining with sensing technologies such as colorimetry analysis,Surface-enhanced raman scattering(SERS)and Enzyme-linked immunosorbnent assay(ELISA)to achieve the precise control of fluid and multi-channel analysis of environmental pollutants,and resolve the problems of tedious procedure,slow speed,poor immediacy and high cost in environmental analysis.The application potential of the proposed paper-based devices was verified and evaluated by detecting E.coli,phenols and biomarkers as target molecules.Finally,on the basis of the above works and the technical accumulation of our group in the development of marine monitoring instruments for many years,marine total phosphorus and total nitrogen in-situ monitoring system based on microfluidic chip technology were constructed.The main research contents are as follows:1.Fabrication of microfluidic paper-based analytical devices with polyurethane acrylate and their applications for bacterial detection in water.At present,microfluidic paper-based analytical devices prepared with the traditional wax material,which could be penetrated by surfactant solutions and organic solvents commonly used in chemical reaction and bioanalysis,resulting in the destruction of the chip structure and limiting the scope of application.In this research,microfluidic paperbased analytical devices were fabricated by using water-based polyurethane acrylate(PUA)via Ultraviolet(UV)light curing in this work.First,the filter paper was modified by physical adsorption of PUA prepolymer,and then the specific area of the filter paper covered mask was irradiated by UV light.The PUA in the exposed area was crosslinked to form the hydrophobic barriers,and the uncured PUA in the shelter area was rinsed off with water,thus forming the hydrophilic patterns in the filter paper.The filter paper’s barriers created by cured PUA could effectively withstand surfactant solutions(CTAB,SDS and Triton X-100)and organic solvents(methanol,isopropanol,DMF,DMSO).To further verify the applicability of the proposed paper-based devices in complex analysis,E.coli BL21 in tap water and seawater was simply and fast detected through colorimetric assay combining a handheld color analyzer.The results revealed that the detection limit was 3.7 × 103 cfu/m L.This paper-based device has the potential for the in-situ detection at limited resources or remote areas.2.Rotational paper-based analytical devices fabricated in nitrocellulose membrane and their applications for detection of biomarkers.Ntrocellulose(NC)membrane,as a porous paper-like material with high protein binding performance,is very popular in the field of point-of-care immunoassay.However,how to generate robust hydrophobic structures in NC membranes to fabricate microfluidic paper-based analytical devices is still a great challenge.On the basis of the first work,a simple,fast and low-cost method for fabricating paper-based devices in NC membrane was developed.Firstly,the PUA was printed by screen-printing to form flow channels and reaction zones,and then cured under UV light to fabricate the paper-based analytical devices.To validate the feasibility of this paper-based device based on NC membrane for immunoassay in point-of-care testing(POCT),rotational paper-based analytical devices were further designed and assembled for implementing multiplexed and complicated enzyme-linked immunosorbent assays(ELISAs)in simple and flexible manners.Under the optimized conditions,alpha-fetoprotein(AFP)and carcinoembryonic antigen(CEA)were detected by the proposed device with the LOD of 136 pg/m L and 174 pg/m L,respectively,both of which were lower than the clinical diagnostic thresholds of the two biomarkers.3.Paper-based SERS devices modified with dendritic polycarbosilane and their applications for detection of catechol in water.Paper-based surface-enhanced Raman scattering(SERS)devices,which prepared by coating colloidal solution of metal nanoparticles(NPs)as “ink” on filter paper are an effective strategy for detection of trace analytes.However,due to the inherent high porosity and hygroscopic property of the filter paper,it was difficult for metal NPs retaining on the surface of filter paper,resulting in the reduced sensitivity and the reproducibility of SERS sensors based on paper substrate.In this work,dendritic polycarbosilane was modified on the surface of filter paper via chemical bonding to enhance the hydrophobicity of the surface,so that Ag NPs could be evenly and compactly distributed on the surface of filter paper,and formed nanoclusters which contributed to improve the Raman signal and the detection reproducibility.Using DTTC as the Raman reporter molecule,the performances of paper-based SERS devices were investigated.The results showed that the Raman signal strength of the hydrophobic modified paper-based SERS devices was greatly improved and the Raman peaks of DTTC at 1238cm-1 on 20 pieces of paper-based SERS devices showed relatively consistent data(RSD = 4.14%).Finally,ultrasensitive detection of catechol in water was achieved in the paper-based SERS devices and the LOD could be as low as 9 × 10-8 M.4.Hybrid paper-based microfluidic devices combined with molecularly imprinted photonic hydrogel and their applications for multi-channel detection of phenolic pollutants.In order to achieve highly selective and sensitive detection of different phenolic pollutants in water,in this work,a 3D hybrid paper-based microfluidic device was developed by combining molecular imprinted photonic hydrogel(MIPH),which has the special recognition performance of molecular imprint polymer and the special optical properties of photonic crystal.The hybrid paper-based device was set to two detection channels,which could simultaneously detect different phenolic pollutants.In addition,for solving the problem of single direction and onetime use of the paper substrate valves on the paper-based device,the movable valves were designed on the hybrid paper-based microfluidic devices,which could improve the control flexibility and use times,and realize convenient and efficient fluid operation in different channels.The combined MIPH membrane could selectively recognize target molecules and directly generate readable optical signals.When the concentration of 4-nitrophenol(4-NP)and 2,4,6-trinitrophenol(TNP)was as low as 1 × 10-4 mg/L,they could still be detected.The proposed device provides a potential portable analysis platform for simple and rapid detection of different phenolic pollutants.5.Construction of UV digestion devices for total phosphorus and nitrogen based on microfluidic chip technology.In order to achieve the efficient digestion of total phosphorus and nitrogen in ocean and following accurate and rapid detection of their content,UV digestion devices for total phosphorus and nitrogen based on microfluidic chip technology were developed in this work.By taking the advantages of the integration and miniaturization of the microfluidic chip,the compact UV digestion device with an efficient digestion method was constructed.Compared with GB standard,the digestion efficiency of the proposed device was up to 88.22% for total phosphorus and 90.56% for total nitrogen under lower digestion temperature(50℃)and shorter digestion time(20 min).The detection limits of total phosphorus and total nitrogen were as low as 8 μg/L and 16 μg/L respectively using the developed digestion device combined with spectrophotometry.Because of the small volume,low energy consumption and high digestion efficiency of the digestion device,it can be effectively integrated into the total phosphorus and total nitrogen in-situ monitoring system to realize online monitoring of marine ecological environment.To sum up,this dissertation constructed multifarious cheap,convenient and sensitive paper-based analysis devices,combining advanced functional polymer materials,reliable sensing technology and efficient fluid control mode,from the demand of low-cost,portable and real-time detection technology and platforms in environmental analysis.Rapid and effective detection of several typical environmental pollutants was carried out on the proposed devices.Moreover,compact and efficient instrument technology and method were provided for in-situ monitoring of marine ecological environment.