| Determination of pesticide residues has become an extremely important part in the management of food safety. Now in China and abroad, the determination of pesticide residues based on enzyme inhibition has complicated steps and is less-automated. Therefore, this article designed a paper-based microfluidic system used for detection of pesticides and researched mixing characteristics of paper-based passive micro-mixer. The mainly research contents and results are as follows:(1)Basic theories of microfluidic dynamics and microfluidic mixing were analyzed, including three typical problems of microfluidic dynamics, two mechanisms of microfluidic mixing and four basic equations. Apart from these, a new kind of paper-based microfluidic chip’s production technology was found out. This article researched mixing characteristics of paper-based passive micro-mixer through experiments. The results of experiments show that line-shaped micro-mixer’s optimal parameters are V=0.01ml/min, α=30°, Z-shaped micro-mixer’s optimal parameters are V=0.01ml/min, S=3mm, θ=30°, square-wave micro-mixer’s optimal parameters are V=0.01ml/min, H=2mm, P=5mm and square-wave micro-mixer has the best mixing performance under its optimal parameters; Paper-based passive micro-mixer has some fiber in its channel, it can provide dynamic of flowing and enhance the diffusion of liquid pesticides. On the other hand, it can limit the convection to a certain degree.(2)This article studied the mechanism of paper-based microfluidic system detecting pesticide residues, including AchE’s catalysis on substrate, pesticides’ inhibition on AchE and the order of reaction. This article also analyzed specific detecting process, inhibition rate’s formula. This article chose graphitic carbon and Ag/AgCl as materials of screen-printing three-electrodes and designed ring-shaped three-electrodes, the diameter of working electrode was set to 3mm; MB was modified to three-electrodes firstly, then AchE was immobilized to it; Enzyme electrode was characterized with EIS and CV. This article also designed width and length of channels, injection and detection pools’ size, layout of paper-based microfluidic chip and then manufactured them. Data acquisition device was developed, hardware circuits, which used SCM as the core, were designed and the SCM was programmed.(3)Paper-based microfluidic system’s parameters was optimized and it’s performance was tested. The optimal parameters are pH-7.5, concentration of substrate-1mmol/L, quantity of AchE-3μL, time of inhibition-15 min. The results of performance’s testing show that the enzyme electrode can be prepared for several times and preserved for a long time; Inhibition rate and the negative logarithm of concentration of parathion show a good linear relationship between 1×10-5mol/L and 1×10-7mol/L, linear regression equation is I=159.3+21.21 lgC, R2=0.987, the detection limit is 9.14×10-8g/mL; Inhibition rate and the negative logarithm of concentration of carbaryl show a good linear relationship between 1×10-6mol/L and 1×10-8mol/L, linear regression equation is I=195.2+21.73 lgC, R2=0.986, the detection limit is 3×10-9g/mL. The recovery rate is between 92.3% and 115% when detecting pesticides in river water; The recovery rate is between 95.7% and 111% when detecting pesticides in cucumber juice; The recovery rate is between 94.5% and 110% when detecting pesticides in tomato juice; So this system has high accuracy, it can be used for detecting actual samples. |
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