Preparation Of Surface Enhanced Infrared Absorption Spectroscopy Substrate And Its Application In Rapid Detection Of Dmds Pesticides

As dimethyl dithiocarbamate pesticides?DMDs?are widely used in agriculture,it is harmful to human health and environmental safety.However,the detection methods nowadays,for the DMDs pesticides,are difficult to achieve rapid on-site emergenc y detection due to the cumbersome steps and harsh conditions.Therefore,it is very important to develop a rapid on-site detection method for DMDs pesticides.Surface enhanced infrared absorption?SEIRA?is a phenomenon,in which noble metal nanostructures are stimulated by energy to produce surface plasmon resonance,and finally enhance the infrared signal of probe molecules by 10-1000 times.Surface enhanced infrared spectroscopy?SEIRAS?is highly sensitive,portable and has attracted more and more attention and application in recent years due to its chemical fingerprint properties.However,the cost,process steps and consuming time of some SEIRA substrate preparation methods reported in the current researches still need to be optimized.Therefore,the aim of this paper is to develop a fast,simple and low-cost method for preparing SEIRA substrate and apply it to the detection of DMDs pesticides.Firstly,the preparation method and material selection of SEIRA transmissio n substrate based on foam metal substrate were researched in this paper.?1?Selection of preparation methods:A method of preparing infrared transmission substrate,based o n improved displacement reaction principle,proposed in this paper was compared with traditional adhesive method.In the improved displacement reaction method,silver nitrate and PVP were used as the precursor solution for the loading of silver nanoparticles.The SEIRA transmission substrate was prepared by the displacement reaction with clean Cu foam.The C=O peak of MUA on this substrate was located at 1693 cm^-1,and the absorption peak intensity was 0.0060.The peak type,the peak position was stable,and the infrared absorption signal was strong;In the adhesive method,trisodium citrate hydrothermally reduced silver nitrate to prepare silver nanoparticles.Using APTMS and MPTMS mixed solution as binder,Cu foam as support material,SEIRA transmission substrate was prepared by adsorption.The C=O peak of MUA detected on this substrate was located at 1559cm^-1.The absorption peak intensity was 0.0038.The peak type and peak position changed greatly,and the infrared absorption signal was weak.Based on this,improved substitution reaction method was selected as the preparation method.?2?Foam metals as supporting materials were selected:Based on the improved displacement reaction method,the SEIRA transmission substrate was prepared by using Cu foam,Ni foam and Ag foam as supporting materials.Silver nitrate and PVP mixed solution was used as precursor solution of silver nanoparticles.The experimental results show that only Cu foam can generate infrared absorption signal for probe molecule MUA.?3?The surfactants as the improve ment factors of displacement reaction were selected:Based on the principle of displacement reaction,using PVP,CTAB and PVA surfactants as the improvement factors of replacement reaction,and using foam copper as supporting material,SEIRA transmission substrate was prepared,and the substrate prepared by PVP was the best.Secondly,3 types of SEIRA transmission substrates?AgNPs-Cu foam,AuNPs-Cu foam,PtNPs-Cu foam?were prepared and characterized.?1?Substrates preparatio n conditions optimization:The preparation conditions of AgNPs-Cu foam,AuNPs-Cu foam,PtNPs-Cu foam were systematically optimized.The main optimization factors were concentration of noble metal ions solution,dosage of surfactant and reaction time.The results showed that for AgNPs-Cu foam SEIRA transmission substrates,the optimum preparation conditions were as follows:AgNO₃ solution?0.2 mM,10 mL?,PVP?0.05 g/mL,2 mL?and reaction time 30s;for AuNPs-Cu foam SEIRA transmission substrates,the optimum preparation conditions were HAuCl₄ solution?0.2 mM,10 mL?,PVP?0.05 g/mL,3mL?and reaction time 10 s;for The optimum preparation conditions of PtNPs-Cu foa m SEIRA transmission substrates are as followed:H₂PtCl₆ solution?0.5 mM,10 mL?,PVP?0.05 g/mL,0.1 mL?,reaction time 30s.?2?characterization of the substrate characteristics:the infrared spectrum showed that,for MUA,the enhancement ratio of the AgNPs-Cu foam SEIRA substrate was 32.7 times;the AuNPs-Cu foam SEIRA substrate was33.6 times;the PtNPs-Cu foam SEIRA substrate was 24.6 times.SEM and XPS?or EDS?characterizations showed that all 3 kinds of SEIRA transmissive substrates had successfully loaded precious metal nanoparticles.Dense,homogeneous and non-aggregated precious metal nanoparticles are the key to generate hot spots and form SEIRA.Thirdly,all 3 kinds of SEIRA transmission substrates were applied to different DMDs pesticides detection:thiram,ziram and febram.?1?AgNPs-Cu foam SEIRA transmission substrates for the detection of thiram:The enhancement ratio of the AgNPs-Cu foam SEIRA substrate to the 1371 cm^-1 of thiram was 2.9 times.The optimum linearity was at 1236 cm^-1,and the correlation coefficient there was 0.9226.The detection limit was as low as 0.024 mg/mL.?2?AuNPs-Cu foam SEIRA transmission substrates for the detection of ziram:The enhancement ratio of the AuNPs-Cu foam SEIRA substrate could reach 188.2 times for the ziram at 1241 cm^-1.It had an excellent linear relationship at1241 cm^-1,and the correlation coefficient was 0.9989.The detection limit was as low as0.018 mg/mL.?3?PtNPs-Cu foam SEIRA transmission substrates for the detection of Febram:The PtNPs-Cu foam SEIRA substrate could enhance the infrared absorption of ferbam at 1241 cm^-1 for 19 times.The linear fitting result at 1241 cm^-1 was optimum.There were two linear intervals.The one was from 0.06 mM to 0.4 mM concentration,the correlation coefficient R² reached 0.9860,the other was from 0.4 mM to 0.8 mM concentration,the correlation coefficient R² value could reach 0.9962,and the detection limit is 0.025 mg/mL.After analyzing the infrared absorption peaks and spectrograms of DMDs pesticides,it could be inferred that the SEIRA effect of the substrates prepared in this stud y was due to their chemical adsorption and enrichment of DMDs pesticides,with the effect of chemical mechanism and electromagnetic field mechanism.In conclusion,the experimental results of this study provided a new method for rapid and simple preparation of SEIRA transmission substrates,and a new idea for on-site rapid detection of DMDs pesticide pollutants.