A Non-enzymatic Organophosphorus Pesticides Sensor Based On Copper Nanomaterials

In modern agriculture, extensive use of pesticides to preserve crops from pests hasraised serious environmental and food safety problems because of the harm for ourhealthiness[1,2]. As a group of commonly used pesticides, organophosphates pesticides(OPs) can exert irreversibly inhibitory effect toward acetylcholinesterase (AChE) onceinto human body. When the function of AChE is inhibited, accumulation ofacetylcholine occurs and results in overstimulation of corresponding muscarinic andnicotinic receptors, which can cause long-term damage to livers even to death[3,4].As one of important branches of the instrumental analysis in modern days,electrochemical analysis technology shows great potential and advantages in analysisfields and more applications in pesticide residues. The reported pesticide residuedetection electrochemical sensors are two types, one we call it enzymaticelectrochemical sensor, and the other is non-enzymatic electrochemical sensor. Thedevelopment of the enzymatic type is earlier than the non-enzymatic one but limited inpromotion which due to the poor stability, harsh and no easy controlling of reactionconditions and high price of enzymes. Based on the above factors, more attention hasraised in non-enzymatic electrochemical sensors. In order to develop non-enzymaticpesticide residue sensors, a variety of metals and metal oxides, metals/metaloxides-CNTs composites and bimetallic nanomaterials have been explored. However,most studies focused on noble metal such like Ag, Au or metal oxide which needstedious synthesis pathways such like ZrO2and ignored the metals/metal oxides whichpossess the same performance and the lower price.In this study, the copper-based nanomaterials were used to fabricate non-enzymaticpesticide residue sensors, which successfully detected OPs. In this dissertation, wefocused on following researches:（1）According to the synthesis methods in the reference[5], we prepared Cu NWs.The results of SEM have shown a uniform distribution of Cu NWs and which with ahigh surface area. The electrochemical behavior and mechanism of methyl parathion(MP) detection in Cu NWs modified GCE (Nafion/Cu NWs/GCE) was studied byultraviolet spectroscopy (UA-vis spectra), cyclic voltammograms (CV) and square wavevoltammetry (SWV). One irreversible reduction peak (Epc,-0.56V) and one pairreversible oxide-reduction peak (Epa,-0.433V, Epc,-0.332V) were observed in MP electrochemical reaction which provides an theoretical basis for the development ofelectrochemical sensor for OPs which contains a similar nitrobenzene ring. Thepresented sensor successfully detected MP with a wide dynamic detection range from0.1ppm to2ppm, a high sensitivity (471.1μA·cm-2·ppm-1) and the detection limit was49.4ppb which was much lower than some other reported sensors. In the interferencetest, the Nafion/Cu NWs/GCE showed a strong anti-interference capability towards tosome conventional compounds containing nitrobenzene which further indicated CuNWs had specific detection in OPs.（2）Based on the above study, we prepared Cu NWs/GNs-Chit composite whichpossess a overhead net structure through simple mixture treatment and we found itselectro-catalytic ability to MP was much more prominent than Nafion/Cu NWs/GCE.Because of the good film-forming property of chitosan, the steps of fabrication inmodified electrode were simplified and with no use of Nafion membrane, the cost alsogreatly reduced. The prepared sensor realized the detection of MP and compared withNafion/Cu NWs/GCE, a much wider dynamic range from0.2ppm to5ppm wasobtained with no more expense of linear ranges.（3）CuO NWs was obtained by simple calcinations and combined with SWCNTsto form a hybrid complex in use of malathion detection. The results of SEM and XRDcharacterization showed that CuO NWs-SWCNTs hybrid complex formed a highlydense and porous network in which CuO NWs were entangled with a large number offilamentous SWCNTs bundles. A linear range reached200ppb (R2=0.976) with asensitivity as high as628.71μA·cm-2·ppb-1and detection limit as low as0.1ng/mL (ppb)by CV, electrochemical impedance spectroscopy (EIS) and differential pulsevoltammetry (DPV) study. Besides, the results showed a different electrochemicalbehavior and mechanism in malathion detection compared with those of MP. With theaddition of higher concentration of malathion, the response currents were decreased andthese results were speculated that because of the adsorption between the CuONWs-SWCNTs hybrid complex and malathion, a barrier layer was formed and it mighthinder the electron transfer. The hypothesis indicates there has a potential responsemechanism that through the binding ability rather than electro-catalytic reaction todetection some OPs which not contain electrochemical activity groups such likenitrobenzene.