| As one of the most popular fruit,kiwi fruit is vulnerable to the pollution of pesticides residue and other hazardous substances during the process of the production,storage and processing.Although conventional instrumental detection methods could detect pesticide residues with high sensitivity and accuracy,they are always time-consuming and costly,and require sophisticated equipment,which are unsuitable for on-site detection of pesticide residues.Therefore,sensitive,accurate and rapid analytical method is essential.Hence,taking the advantages of obvious color change of Au NPs,quantitative evaluation of digital colorimetry and portability of smartphone,several simple and smart colorimetric methods were proposed in this dissertation for the rapid detection of main pesticide residues(including cartap,nereistoxin-related insecticides,acetamiprid and chlorpyrifos)in kiwi fruit.The main contributions of this dissertation are summarized as follows:1.With citrate-coated gold nanoparticles(Au NPs)as colorimetric probe,a visual and spectrophotometric method for rapid assay of cartap is developed.Optimized by the addition of 0.9 m M sodium bisulfate,the results could be read out within 5 min.With the help of UV-vis spectra,cartap could be detected in the concentration range of 0.05 mg/kg ?0.6 mg/kg with a low detection limit of 0.04 mg/kg.The visually detectable color change occurs in the 0.1 mg/kg,which enables a fast visual test on whether or not the concentration of cartap exceeds the tolerated level of 0.1 mg/kg.The result of real sample detection demonstrated the recovery of this method is 76%?103% with the variation coefficient of 4.5%?10.7%,demonstrating the present method provides an easy and effective way with the high accuracy and reliability to analyze pesticide residue in common products.2.By utilizing the color change of Au NPs resulted by addition of nereistoxins hydrolyzed by nereistoxin-related insecticides,as well as combining with advantages of digital camera and photoshop technique,a novel method is developed for the rapid digital determination of total nereistoxin-related insecticide residues.The optimum condition was 3 min reaction time,p H 4 and 0.9 m M addition of sodium bisulfate.The spectrophotometric method has a detection range from 0.05 to 0.25 mg/kg and a detection limit of 0.04 mg/kg for the total quantity of nereistoxin-related insecticides.The color change of image was digitized by phtoshop software,and the relationship between the RGB color values and nereistoxins concentration was analyzed.The results indicate the R value is proportional to the concentration of nereistoxins over the range of 0.05 to 0.25 mg/kg,with a low detection limit of 0.03 mg/kg.The real samples analysis demonstrates that the developed digital colorimetric method possesses satisfactory linear range,low detection limit,and good accuracy for the rapid detection of total nereistoxin-related insecticide residues,which provides an effective way for the control of total nereistoxin-related insecticide in kiwi fruit.3.By combining the advantages of Au NPs with digital colorimetric quantitative model,optical collector and software for smart phones,in this chapter,a smart colorimetric method is developed for rapid determination of acetamiprid by using a home-made sampling setup and self-programming smartphone software.The optimum condition was 6 min reaction time,p H 6 and 30 m M addition of Na Cl.Acetamiprid could be detected in the concentration range from 0.04 to 0.6 mg/kg,0.06 mg/kg ?0.1 mg/kg,and 0.04-0.5 mg/kg,for spectrophotometric method,visual inspection and the developed smart colorimetric method,respectively.The detection limits of the developed smart colorimetric method for acetamiprid could be as low as 0.03 mg/kg.The R value obtained by smartphone decreased with the increase of acetamiprid concentration,and the reduction formula is C=10 ^((45.02-R)/80.84).Furthermore,smartphone-based colorimetric detection system was successfully applied for the determination of acetamiprid in kiwi fruit with well recovery,and the detection results are well coincidence with that of spectrophotometric method and GC method,indicating the developed smart colorimetric method has the great potential for the rapid detection of acetamiprid in real samples.4.On the basis of smartphone software developed in previous chapter,as well as combining the inhibiting effect of chlorpyrifos on the activity of acetylcholinesterase with acetylthiocholine halide induced color change of Au NPs,we designed a novel smart colorimetric method for the on-site detection of chlorpyrifos.The optimum condition was 30 ?M addition of acetylthiocholine iodide,p H 8,2 m U/m L addition of acetylcholinesterase and 8 min reaction time.This method allows detecting chlorpyrifos in the concentration range from 0.01 to 1.0 mg/kg with a detection limit of 0.002 mg/kg,which is sensitive than those of most of existed methods while the use amount of enzyme is less.The real samples analysis demonstrate that the proposed assay presented satisfactory linear range,low detection limit,and good accuracy for the rapid detection of chlorpyrifos,which provides a novel and effective approach for on-site screening of chlorpyrifos in common products,thus benefiting for monitoring and reducing the risk of chlorpyrifos in kiwi fruit. |
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