Disposable molecularly imprinted electrochemical sensors containing reduced graphene oxide and metallic nanoparticles for the determination of phenolic acids in wastes from Brazilian fruticulture.

Author(s)

Edervaldo Buffon

• Document type: Doctoral Thesis
• Press: Araraquara. 2023-04-03.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2023-03-24
• Advisor: Nelson Ramos Stradiotto

Abstract

The fruticulture is an important activity for the Brazilian economy. However, the processing of fruits generates a large amount of waste that, when discarded in inappropriate places, causes a major environmental problem. Banana and orange are the most produced and consumed fruits in Brazil, and the waste generated by processing these fruits is mostly composed of peels, which, in turn, are rich in phenolic compounds. Among the phenolic compounds found in banana and orange peels, ferulic (FA), vanillic (VA) and p-coumaric (p-CA) acids can be highlighted because they are used by the food, pharmaceutical and cosmetic industries in the composition of a wide variety of products. Considering the reuse of banana and orange peels, the phenolic acids found in this waste can be extracted and used to obtain high value- added products. To this end, the development of analytical methods to characterize banana and orange peels for their subsequent reuse is essentially important. Among the analytical methods available for chemical analyses, electroanalytical methods gain prominence because they allow the analysis of complex samples safely and reliably, even when the concentrations of the species of interest are relatively low. The biggest challenge faced by researchers in the development of electrochemical sensors is the regeneration of the electrode surface and the maintenance of the analytical signal for a long period of time. An alternative to circumvent these inconveniences is the use of disposable electrodes. In this regard, screen-printed electrodes have emerged as a viable platform for the development of electrochemical sensors. With this in mind, the aim of this work was to develop disposable electrochemical sensors containing reduced graphene oxide (rGO), metallic nanoparticles and molecularly imprinted polymers for the determination of FA, VA and p-CA in banana and orange peels. The use of rGO and metallic nanoparticles contributed to increase the sensitivity of the electrodes, while the use of the molecularly imprinted polymers ensured the selectivity of the proposed electrochemical sensors. More specifically, a sensor containing rGO, gold nanoparticles and molecularly imprinted poly(phenol) was developed for the determination of FA, a sensor containing rGO, iron nanoparticles and molecularly imprinted polypyrrole was constructed for the determination of VA, and a sensor containing rGO, nickel nanoparticles and molecularly imprinted poly(3-indoleacetic acid) was made for the determination of p-CA. These sensors were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, RAMAN spectroscopy and X-ray photoelectron spectroscopy. The analytical performance of these sensors was evaluated through an indirect approach using potassium ferricyanide as a redox probe. Under optimized conditions, the proposed sensors presented wide linear ranges, with limits of detection and quantification on the order of 10−9 to 10−11 and 10−8 to 10−10 mol L−1, respectively. These devices also presented excellent selectivity for recognition of the target molecules, as well as voltammetric responses with good repeatability and stability over time. The electroanalytical methodologies developed in this work were successfully applied in banana and orange peel samples using a simple, environmentally friendly and low- cost analysis procedure. The results obtained from the recovery tests showed that the proposed sensors have good accuracy for the determination of FA, VA and p-CA in banana and orange peels. (AU)

• FAPESP's process: 19/13818-8 - Development of disposable sensors based on 3D graphene oxide, metal nanoparticles and molecularly imprinted polymers for the determination of phenolic acids in fruticulture waste
• Grantee: Edervaldo Buffon
• Support Opportunities: Scholarships in Brazil - Doctorate