Visual Detection Of Four Ions Based On Microfluidic Paper-based Analytical Devices

The primitive requirement for human livelihood is water.Water pollution is one of the primary risk factors for disease and death worldwide.It also leads to a steady decrease in drinking water resources.Water pollution is seriously threatening human life.Heavy metal ions and nitrite are important causes of water pollution.In order to improve the ability to prevent and control water pollution,it is urgent to accurately and rapidly detect ions in water.The standard test methods for drinking water mainly include:titration,atomic fluorescence,ion chromatography,ultraviolet spectrophotometry,atomic absorption spectrophotometry,gas chromatography-mass spectrometry,etc.These detection methods are usual complicated to operate,expensive,and require specialized personnel to operate,and the detection time is generally longer,which is limited in versatility and convenience.Paper-based analytical device is a new analytical technology platform,which has the advantages of low cost,simple operation,easy to use,rapid detection and other advantages.It has been widely used in clinical medicine,food safety analysis and environmental monitoring and other fields.In this experiment,a microfluidic paper chip device was constructed to detect Pb²⁺,Cr⁶⁺,Fe³⁺and NO₂^-in water.The quantitative or visual analysis of four ions in water is realized.The results obtained in this experiment are as follows:1. We have prepared a hydrophobic ink using two silylating agents,methyl silica and fluoroalkyl silica.The filter paper was hydrophobized（water contact angle is 143.8±0.5°）.The stability of the super-hydrophobic filter paper was tested.Stability testing shows that hydrophobic reagent can still maintain hydrophobicity in acids,bases（p H 1～11）and common organic（methanol,petroleum ether,ethyl acetate,methylene chloride）solvents.2. We design origami paper chips by inkjet printing,3D printing hydrophobic molds,and mechanical arm drawing.Through the experimental test comparison,we finally chose the mechanical arm drawing method to draw the chip structure,and made the target paper chip with excellent performance.In order to further illustrate that the paper chips prepared by this method can be used in subsequent experiments,we conducted a liquid flow test on the paper chips produced.Experimental results show that the liquid may flow from the injector region by the injection zone directed to the analysis zone,enabling simultaneous detection of multi-channel.3. We use paper-based chips modified with a commercial indicatort to detect Pb²⁺,Cr⁶⁺,Fe³⁺and NO₂^-ions in water.As a result,different types of contaminating ions cause a significant color change in the corresponding area of the paper chip.Chromogenic area captured by the camera and color analyzed,a standard curve was constructed between the RGB value and the nitrite ion concentration（LOD=0.4074 mg/L）.The paper-based device also realizes qualitative analysis of Pb²⁺,Cr⁶⁺,Fe³⁺.Finally,the marked water samples were analyzed and tested,and the visualization detection of four ions in water was realized.