Fabrication Of Graphene-Based Electrochemical Sensing Platform And Their Application In Pesticide Residue Determination

Public concern over pesticide residues has been increasing dramatically owing to the high toxicity and bioaccumulation effects of pesticides and the serious risks that they pose to the environment and human health. The development of biosensors for pesticides has been an active research area for some years in response to the demand for rapid, simple, selective, and low-cost techniques for pesticide detection, which offer great advantages over conventional analytical techniques, including high specificity for real-time analysis in complex mixtures, high sensitivity, simple operation without the need for extensive sample pretreatment, and low cost. Driven by these needs, great efforts have been made in the design, fabrication, and applicatio n of nanomaterials for electrochemical sensing devices. By incorporation of graphene-based functionalized nanomaterials in the fabrication of electrochemical sensor for pesticide residue and based on the electrochemical techniques such as photoelectrochemical (PEC), electrochemiluminescent (ECL), amperometric methods, herein, several electrochemical sensors have been successfully constructed for pesticide residue determination, as described as follows:(1) A visible light PEC platform coupled with enzyme-inhibition for rapid and sensitive determination of dursban was constructed based on dual-functional Cd0.5Zn0.5S/graphene (Cd0.5Zn0.5S/G) nanocomposite. Due to the inherent biocompatibility and remarkable PEC property of Cdo.5Z110.5S/G nanocomposite, the acetylcholinesterase (AChE) immobilized on the modified electrode can hydrolyze acetylthiocholine chloride into thiocholine, which could increase the photocurrent of the modified enzyme electrode, and the further inhibition of dursban on the enzyme electrode could decrease the photocurrent response. Based on the notable change of dursban in PEC response of the AChE-Cd0.5Zn0.5S/G modified electrode, a simple and effective way for PEC monitoring of dursban is proposed, which showed wide liner range of1ng mL-1～1μg mL-1with a low detection limit of0.3ng mL(2) Based on the amplifying ECL behavior of graphene quantum dots/CdS nanocrystals (CdS NCs/GQDs), an ultrasensitive ECL sensor was constructed for the detection of pentachlorophenol (PCP). Due to the presence of the doped GQDs, the resulting CdS NCs/GQDs exhibited4-fold enhanced ECL intensity than pure CdS NCs with the ECL onset potential80mV positively shifted. Furthermore, based on the effective inhibition of PCP on the ECL response of CdS NCs/GQDs film, a simple method for ultrasensitive determination of PCP was constructed, which showed wide linear range of0.01～500ng mL-1and low detection limit of3pg mL-1with good stability and reproducibility.(3) A novel PEC sensor for detection of the organophosphorus (OPs) pesticide parathion-methyl using CdS NCs/GQDs coupled with a screen-printed efectrode is presented. The CdS NCs/GQDs inherited the excellent electron transport of GQDs and facilitated the spatial separation of photo-generated charge carrier, resulting in the enhanced photocurrent4-fold higher than CdS NCs under visible irradiation. Based on the inhibition of parathion-methyl on the PEC response of CdS NCs/GQDs modified electrode, a simple way for PEC detection of parathion-methyl was proposed, which show good performances with a wide linear range (0.01-100ng mL-1), low detection limit (3pg mL-1), instrument simple and portable, rapid response and good stability.(4) Based on the signal amplification of core-shell structure MWCNTs@GONRs on the ECL signal of luminol, a novel ECL sensor for PCP determination was constructed. The MWCNTs@GONRs modified on the electrode can catalyze the luminol oxidation process, compared with bare electrode, the ECL of luminol was enhanced for4.4-fold on the MWCNTs@GONRs modified electrode. And PCP is found to be able to enhance the ECL intensity, based on this, a method for PCP detection was fabricated. An acceptable linear range was obtained between the log[PCP] and ECL intensity with a limit of detection of0.7pg mL-1. Moreover, the method exhibits good stability and reproducibility, which provide new way for application of MWCNTs@GONRs in pesticide determination.(5) Based on AChE immobilized on MWCNTs@GONRs nanostructure, a rapid and sensitive organophosphates amperometric biosensor was fabricated. The MWCNTs@GONRs can provide a unique microenvironment for AChE, and the immobilized AChE on the MWCNTs@GONRs modified electrode can possess its native structure and electrocatalytic activities effectively. The as-prepared biosensor shows high affinity to acetylthiocholine with a Michaelis-Menten constant value of0.25mmol L-1. Based on the inhibition of carbaryl on the enzymatic activity of the immobilized AChE, the resulting biosensor exhibits excellent performance for carbaryl detection including good reproducibility, acceptable stability, and a reliable linear relationship between the inhibition and log[carbaryl] from1ng mL-1up to1μg mL-1with a detection limit of0.3ng mL-1.(6) Fe3O4/functionalized graphene nanoribbons (Fe3O4/GNRs) were prepared in situ by a facile one-step solvothermal process, and further, an amperometric electrochemical sensor for the determination of dopamine was fabricated based on the resulting Fe3O4/GNRs. The result indicated that the electrochemical activity of Fe3O4/GNRs was better than Fe3O4-functionalized graphene nanosheets (Fe2O4/G) for the redox of dopamine. The resulting electrochemical sensor showed a linaer range of1～30μmol L-1with a detection limit of0.3μmol L-...