Study on Rapid Detection Methods for Organophosphorous Pesticide Residues in Peach Fruit Using Surface Enhanced Raman Spectroscopy

Author:Tehseen Yaseen

Supervisor:sun da wen


Degree Year:2019





In recent years,food safety problems caused by the presence of chemical residues have raised a big deal of apprehension around the world.Pesticides are a vital part of agriculture while growing application leads to trace residues on or in agricultural products.However,the monitoring action is reliant on the technical skill to detect trace residues of pesticides.Earlier used methods are time-consuming,elaborate and require tedious sample preparation.Therefore,this project chiefly emphases on applications of surface enhance Raman spectroscopy(SERS)for detection of different organophosphorus pesticides in peach fruit,one of the most popular and widely consumed fruit.In the first part of this work,a simple and rapid surface-enhanced Raman spectroscopy(SERS)method was used with the silver colloid substrate for detection of omethoate in standard solution and peach extract.The findings demonstrated that the characteristic wavenumber of the pesticide could be precisely identified using the SERS method.The calculated limits of detection for omethoate in standard solution and peach extracts were 0.001 mg/L and 0.01mg/kg,respectively.In the second part,the bimetallic NPs with different core sizes were optimised to obtain the highest SERS effect for rapid detection of organophosphorus pesticides(triazophos and methyl-parathion)in peach fruit.The Raman enhancement effects of the selected Au@Ag NPs was compared with single Ag NPs and Au NPs.It was revealed that the core size of Au NPs was critical variant affecting the enhancement of Raman signals.However,the Au@Ag NPs with(26 nm Au core size and 6 nm Ag shell thickness)showed significant Raman enhancement,and the detection limits of triazophos and methyl-parathion in peach extract were 0.001 mg/kg.Good recovery percentage(93.36 to 123.60%)and high selectivity showed the high SERS activity for the detection of the triazophos and methyl-parathion in peach.In the third part,SERS method based on silver-coated gold nanoparticles(Au@Ag NPs)was used to simultaneously detect multi-class pesticide residues such as thiacloprid(carbamate),profenofos(organophosphate)and oxamyl(neonicotinoid)in standard solution and peach fruit.The findings demonstrated that the characteristic wavenumber of the pesticides(thiacloprid,profenofos,and oxamyl)could be precisely identified using the SERS method and the limit of detection(LOD)was 0.1 mg/kg for thiacloprid and both profenofos and oxamyl was 0.01 mg/kg obtained in the peach extract.Good recovery percentage(78.60 to 162.0%)demonstrated the high SERS potential with better accuracy for the detection of the thiacloprid,profenofos,and oxamyl in peach extract.In last,the effect of cationic(Ca2+,K+,Na+)and anionic(Cl-,Br-)aggregating agents was investigated on the SERS detection of phosalone,using Au@Ag NPs as the substrate.Both anions and cations greatly affect the SERS enhancement.Among these aggregating agent combinations analyzed,the maximum SERS enhancement is achieved employing 1×10-11 mol/L CaBr2 at pH 3.0.The detection limits of phosalone in standard solution and peach extract were0.02 mg/L and 0.2 mg/kg,respectively.This project revealed that the proposed methods could offer a promising SERS platform for rapid identification and simultaneous detection of pesticides residues such as omethoate,triazophos,methyl-parathion,phosalone,profenofos(an organophosphate),thiacloprid(carbamate),and oxamyl(neonicotinoid)in multifaceted food matrices.Moreover,this study explored the sensitivity of surface-enhanced Raman spectroscopy(SERS)which extremely relies on experimental parameters including pH and aggregating agents.