Design And Experiment Of A Detector For Pesticide Residues On Leaves Surface Based On Excitation Fluorescence

Accurate detection of pesticide residues is of great significance to ensure food safety and protect human health.At present,the conventional pesticide residue detection methods mainly include chromatographic detection methods,chemometric methods and spectral detection methods,the chromatographic detection method and chemometric method have expensive equipment and complicated data processing,so they are not suitable for daily agricultural production.Fluorescence spectroscopy has high detection accuracy,simple instrument structure and low cost,and has made considerable progress in the field of pesticide residue detection.However,the direct detection of pesticide residues on the leaf surface by fluorescence spectroscopy is easily affected by internal and external factors such as light source irradiation angle,leaf surface smoothness,leaf placement position and other internal and external factors,resulting in uncertainty in the detection results,and it is difficult to meet the requirements of precision agriculture for pesticide residue Testing requirements,and there is little research on the design of portable testing instruments.In response to the above problems,this paper takes acetamiprid pesticide residues on lettuce,cabbage and spinach leaves as the research object,and takes the characteristic response wavelength of the pesticide residues on the leaf surface and optimizing the optical path parameters of the detection instrument as the starting point.The condition parameters(such as:the best excitation wavelength and the best emission wavelength,the illumination angle of the light source,the illumination distance of the light source,etc.)are studied in depth,and a portable instrument for pesticide residues on the leaf surface was designed.The main research content and research conclusions are as follows:(1)Analyzed the basic principles of fluorescence spectroscopy to detect pe sticide residues on leaves.It was found that the fluorescence intensity of aceta miprid pesticide residues at characteristic wavelengths had a good linear relatio nship with the pesticide concentration.It was determined that fluorescence spec troscopy was used to detect pesticide residues on leaves.Feasibility,and then analyzed the relevant interference factors that affect the accuracy of the detecti on of pesticide residues on the leaf surface and proposed corresponding solutio ns.(2)Taking lettuce,cabbage and spinach leaves acetamiprid pesticide residues as the research object,obtain and analyze the fluorescence spectrum data of acetamiprid pesticide residues on the leaf surface,and determined the best excitation wavelength and best acetamiprid pesticide residues on the leaf surface Emission wavelength.(3)Determining the optimal parameters of the optical path of the detection instrument.The detection of pesticide residues on the surface of leaves was easily affected by factors such as the illumination angle of the light source and the illumination distance of the light source,so it was necessary to determine the optimal parameters of the optical path of the entire detection instrument.When the light angle was 45~o,the fluorescence intensity excited by the acetamiprid pesticide on the leaf surface was the largest.At the same time,the size of the light path was optimized.When the direct distance between the LED light source and the blade was 4.89 cm,and the vertical distance was 3.46 cm,the illuminance of the blade by the light source was the largest,and the pesticide excitation efficiency was the best.(4)Software and hardware design.To meet the requirement of weak fluorescence signal detection,corresponding control circuit,detection circuit and driving circuit are designed.In terms of the driving circuit,it outputs PWM waves to modulate the LED light source,so that the detected light frequency is different from the ambient light frequency,thereby suppressing the interference of the ambient light on the light source.In terms of control circuit and detection circuit,the STM32 chip was used as the main control chip to design a signal detection system,collect the voltage signal of the detection circuit,and calculate the residual value of the pesticide to be detected according to the built working curve,thereby realizing the real-time detection of pesticide residue.(5)Test and experiment on the developed testing equipment.Construct a linear equation between the pesticide residue content of acetamiprid on the surface of lettuce,cabbage,and spinach and the voltage detected by the instrument.The coefficients of determination of the equation were 0.875?0.895 and 0.888,and the root mean square error(RMSE)were 0.405mg/L,0.454mg/L and 0.414mg/L.It showed that the portable detection instrument designed in this paper had a good detection effect on the pesticide residue on the leaf surface.