Rapid Assessment Of Agrochemical Residues In Fruits Using Surface Enhanced Raman Spectroscopy

In order to meet the increasing food demand globally,various strategies are employed including application of agrochemicals.These chemicals protect crops from insects,pests,and various fungal diseases during pre and postharvest conditions.But the improper application can also lead to many serious health issues in public.Therefore,efforts have been exerted globally for their proper monitoring of agricultural commodities worldwide.Previously developed conventional methodologies for monitoring such unsafe toxic residues in agricultural production are tedious,requires a lengthy and complicated sample preparation step.Thus,this current project focused on the applications of surface enhanced Raman spectroscopy（SERS）as a rapid,sensitive reliable,and nondestructive tool for assessing of various agrochemical residues in apple and pear fruit extracts.In the 1^st part of this study,bimetallic core-shell nanoparticles based on octanethiol（OCT）functionalized combine with SERS was developed for the assessment of ziram residues in apple and pear fruit extracts.By acquiring high-magnification TEM images,HAADF-STEM-EDS element maps and their superimposed images,the morphology of the newly proposed substrate was studied,and it was confirmed that the Au@Ag NPs with an average core size of 28 nm（gold）and 5.5 nm shell thickness（silver）showed high enhancement which later was successfully grafted with OCT.The obtained results have shown that the developed OCT/Au@Ag NPs could detect residues of ziram in apple and pear extracts up to 0.015 and 0.016 ppm,with high coefficient of determination（R²）of 0.998 and0.999,and satisfactory percent recoveries of 80-106%,respectively.In the 2^nd part of this study,silver-coated gold nanoparticles were optimized with various gold core sizes to achieve the highest SERS enhancement effect,and then the surface gold core optimized Au@Ag NP was modified with mercaptooctane（MCO）for rapid evaluation of tricyclazole（TCZ）and thiram residues in pear fruit samples.The proposed substrate（MCO/Au@Ag NPs）,having an average Au core size of 28 nm and Ag shell thickness of 6 nm,showed greater sensitivity in evaluating fungicide residues in the tested samples with a significant enhancement in Raman scattering.Results showed low limit of detections for TCZ and thiram down to 0.005 and 0.003 ppm with high R² values of 0.0998,0.997,recoveries ranged from 80–107,and 80–109.5%,and the relative standard deviations（RSDs）of 1.5-7.9,and 3.7–9.5%,respectively,in pear fruit samples.In addition,the developed MCO/Au@Ag NP was also exploited to investigate the residue of analytes in the as collected real samples without pretreatment,and the principal component analysis was employed to ensure the suitability of the developed technique for quantitative assessment of residual of TCZ and thiram in tested samples.Results proved that the constructed MCO/Au@Ag NPs revealed higher sensitivity in evaluating agrochemicals detected sample with and without pretreatments.In the 3^rd part of the current study,we attempted to synthesis a simple,stable and more sensitive SERS sensing platform by functionalizing the surface of Au@Ag NPs with thiol（sulfur）containing ligand 2-mercaptoethanole（MCE）to construct MCE/Au@Ag NPs as SERS active substrate for the rapid evaluation of ferbam and thiabendazole（TBZ）in apple fruit samples.The morphology of proposed MCE/Au@Ag NPs were studied by acquiring high magnification TEM images,HAADF-STEM-EDS elemental maps and their superimposed images,which verified the successful creation of the uniform silver shell thickness on the surface of gold core and successful distribution and scatter of the thiol sulfur（S）elements on the surface of Au@Ag NPs from MCE.Findings demonstrated that the MCE/Au@Ag NPs could achieve a low detection limit for ferbam and TBZ residues in apple puree up to 0.003 and 0.005 ppm with a high R² values of 0.992 and 0.995.recoveries ranged from 80 to 107%and 82 to 103%,and RSDs of 3–7.5%and 3.8–8.5%respectively.In the 4^th part of the current study,Mercaptoacetic acid（MAA）surface functionalized silver coated gold nanorods were first time developed for direct and quick evaluation of pesticide residues in pear and apple fruit juices by employing a simplified pretreatment procedure using SERS technique.The morphology of the constructed substrate was confirmed by obtaining high resolution TEM images,HAADF-STEM-EDS,elemental mapping and their superimposed images,which proved the creation of uniform size and shape silver shell on the surface of Au NRs and successful distribution and grafting of S elements from MAA on the surface of Au@Ag NRs,demonstrating successful construction of MAA/Au@Ag NRs.Results revealed that the proposed MAA/Au@Ag NRs had potential to detect residues of paraquat residues and up to 0.012 ppm and 0.024 ppm in pear and apple samples with a high R² values of 0.9954 and 0.9914,good percent recoveries ranged from 80to 110.5%and 80 to 104%and RSD of 3.4–7.5%and 2.2–9%respectively integrating with SERS technique.This current project revealed that the established methods could deliver a promising SERS sensing platform for the rapid and direct assessment of pesticide residues such as ziram,tricyclazole,thiram,ferbam,thiabendazole,and paraquat in fruits samples with and without sample pretreatments.Moreover,the modification of SERS substrates with thiol containing compounds could significantly enhance the substrates stability,spectral reproducibility and sensitivity on which the success of the SERS application depends entirely.