An electrochemical sensor based on polymeric electrospun nanofibers of polyamide 6 (PA6)/polypyrrole (PPy) surface-modified with two forms of graphene was developed for the detection of malathion, an organophosphorus pesticide. The materials were chosen considering the electrospun nanofibers possess large surface area and porosity, while reduced graphene oxide has remarkable electrical conductivity, which is a good strategy to increase sensor sensitivity and improve the limit of detection towards the pesticide. The surface modification of nanofibers with graphene was carried out using chemically (CRGO) and electrochemically reduced graphene oxide (ERGO), in order to demonstrate how the degree of reduction of graphene oxide can influence its electrical conductivity. The influence of the reduction on the conductivity properties of graphene-based films was studied through electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The platform modified with CRGO, which presented higher electrical conductivity compared to ERGO, was used in the electrochemical detection of the pesticide malathion and exhibited a low detection limit of 0.8 ng ml⁻¹ (S/N = 3). The results indicate that chemically reduced graphene oxide is a potential alternative for modifying electrodes surfaces designed for sensing distinct pollutants of environmental or agricultural interest.

We report a paper-based electrochemical immunosensor made with sustainable materials to detect aflatoxin B1 (AFB1), a highly toxic, carcinogenic mycotoxin found in food. The immunosensor was prepared with a waterproof paper substrate and low-cost graphite-based conductive ink through a simple cut-printing method. The working electrode was functionalized with a drop-cast film of multiwalled carbon nanotubes (MWCNT)/chitosan on which a layer of anti-AFB1 monoclonal antibodies was immobilized covalently. The architecture of the immunosensor was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and electrochemical impedance spectroscopy (EIS), including the effective immobilization of the active layer of anti-AFB1. With EIS as the principle of detection, the immunosensor could detect AFB1 in the range from 1 to 30 ng·mL⁻¹, and detection limit of 0.62 ng·mL⁻¹. This sensitivity is sufficient to detect AFB1 in food according to regulatory agencies. The immunosensor exhibited good repeatability, reproducibility, stability, and selectivity in experiments with a possible interferent. Furthermore, detection of AFB1 in maize flour samples yielded recovery of 97–99%, in a demonstration of the possible use of the paper-based immunosensor to detect AFB1 using extraction solutions from food samples.

The presence of contaminants in water is a subject of paramount importance nowadays, which can make water improper to human consumption even when these contaminants are present at very low concentrations, causing health issues and economic losses. In this work, we evaluated the performance of nanocomposites based on nylon 6,6/chitosan electrospun nanofibers modified by cellulose nanowhiskers combined with functional materials like silver nanoparticles, gold nanoparticles, and reduced graphene oxide to be used as sensing layers of an electronic tongue (e-tongue) to detect Isoborneol. This compound, found in some plants and essential oils, is used as a natural repellent and also to produce many other chemicals. Additionally, its chemical structure is related to that of 2-methylisoborneol, a critical pollutant in aqueous media. The synergism between the nanomaterials combined with electrospun nanofibers could be verified by the enhancement of the charge transference ability. Additionally, electrical capacitance data measured with the impedimetric e-tongue were treated by Principal Component Analysis (PCA), and revealed the sensing system was able to discriminate samples contaminated with Isoborneol at nanomolar concentrations. Moreover, the electronic tongue system could detect Isoborneol in real water samples under different concentrations.