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The detection and identification of molecular traces in the environment as well as in the human breath are very significant for the development of a healthy society.

The electrochemical method is the most effective, facile, and economical approach for the detection of small molecules. The present article deals with the design and engineering of polymer–graphene-based thin films through an in situ facile synthesis technique for the development of high performance electrochemical sensors. We report a facile technique for preparing polyaniline (PANI) and polyaniline/graphene (PANI/G) nanocomposite thin films and their application as enzyme-free electrochemical sensors for hydrogen peroxide (H2O2). PANI and PANI/G films were deposited on a dopamine modified ITO substrate via spin coating and in situ deposition techniques. The in situ fabricated films, which exhibited better electrical properties and stability as compared to the spin coated films, were studied in detail. These thin films were characterized using UV-visible spectroscopy, FT-IR spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) to study their optical, chemical, and surface textural properties. Results show a homogeneous distribution of the constituting materials. From the AFM results, it was found out that the PANI/G film showed increased surface roughness (∼20 nm) as compared to the PANI film (∼15 nm). The electrochemical properties of the films were determined using the van der Pauw method and cyclic voltammetry technique. The conductivity of the PANI and PANI/G films was estimated to be 5.38 × 103 and 6.84 × 103 S cm−1, respectively. Finally, the electrochemical sensing performances of the PANI and PANI/G films were investigated towards H2O2 reduction in a wide potential range of −0.6 to 0.6 V in 0.1 M PBS solution of pH 7.0. This work demonstrates the application of thin-film technology for the development of nanodevice sensors.

The use of nanostructured materials is already well-known as a powerful tool in the development of electrochemical sensors. Among several immobilization strategies of nanomaterials in the development of electrochemical sensors, the use of low-cost and environmentally friendly polymeric materials is highlighted. In this context, a new nanostructured biocomposite electrode is proposed as an electrochemical sensor for the analysis and determination of tetracycline. The composite electrode consists of a modified glassy carbon electrode (GCE) with a nanodiamond-based (ND) and manioc starch biofilm (MS), called ND-MS/GCE. The proposed sensor showed better electrochemical performance in the presence of tetracycline in comparison to the unmodified electrode, which was attributed to the increase in the electroactive surface area due to the presence of nanodiamonds. A linear dynamic range from 5.0 × 10 − 6 to 1.8 × 10 − 4 mol L−1 and a limit of detection of 2.0 × 10 − 6 mol L−1 were obtained for the proposed sensor. ND-MS/GCE exhibited high repeatability and reproducibility for successive measurements with a relative standard deviation (RSD) of 6.3% and 1.5%, respectively. The proposed electrode was successfully applied for the detection of tetracycline in different kinds of water samples, presenting recoveries ranging from 86 to 112%.

Analytical assurance of coffees' geographical indication (GI) authenticity is essential for producers and consumers. In this way, chemometric methods, electrochemical techniques, and 3D printed sensors become attractive to assure the coffee's quality. These sensors are low-cost, fast, and simple, with the possibility of miniaturization and portability. Therefore, 3D printed electrodes with chemometrics were used to classify-three Brazilian coffees from regions with GI. Further, Au/Gpt-PLA electrodes with partial least squares regression were used to detect the blending of GI coffee with traditional coffee. Soft independent modelling of class analogies coupled with cyclic voltammetry had the best performance, with 91-95% accuracy, specificity of 94-100%, and 80-83% sensitivity. Furthermore, the calibration models detected and quantified traditional coffee in all three coffees from regions with GI. The detection limits ranged from 1.4 to 10% (w/w), and quantification 4.6-32%, depending on the specific coffee.

Leaf-cutting ants (genera Atta and Acromyrmex) are defoliation pests of great agronomic importance. Currently, the most effective control method is chemical using granulated baits containing sulfluramid as a standard active ingredient. In this work, a new protocol was proposed for the synthesis of the encapsulates with chitosan, tapioca, citrus pulp and sulfluramid. A sulfluramid is a pesticide which is used extensively in Brazil for management of leaf cutting ants. The main focus of this work is to use a polymeric combination aligned with the active ingredient that allows the formation of an encapsulated which the ants can transport and incorporate to their nests, being an effective methodology for the death of colonies. The encapsulated makes the active ingredient less available to the environment, but maintains the mortality level similar to the used granulated baits. For this reason, it was proposed to develop a chitosan and tapioca encapsulated for the control of leaf-cutting ants.The presence of sulfluramid in the encapsulated was confirmed by Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The behavioral acts related to the transport and the incorporation of leaf disks and encapsulates were observed utilizing A. sexdens colonies. The encapsulates containing sulfluramid have presented a similar intoxication of A. sexdens workers causing mortality in the same proportion as the commercial baits. The protocol for the synthesis of the encapsulates can be utilized with other substances, as entomopathogenic and parasite microorganisms.

The depletion of natural resources and consequently increase in the importance of environmental conservation are reflected in the scientific community. The search for scientific methodologies or eco-friendly and low-cost materials is becoming more evident and current, for example, through the use of renewable materials. In this review, we have addressed the use of biochar, a low-cost material obtained from renewable resources for the development of electrochemical devices. Biochar is a carbon-rich material obtained from the pyrolysis of biomass under a low-concentration oxygen atmosphere. Normally, biochar has a highly functionalized surface, promoting high sorptive or interaction capacity. This characteristic makes its use attractive, especially for spontaneous preconcentration or the incorporation of species. Here, we have presented some of the main biochar-based devices applied for different strategies, such as sensors and biosensors, supercapacitors, fuel cells, and batteries. The main parameters that directly influence biochar's final characteristics, namely, the influence of pyrolysis temperature, activation treatments, and anchoring of species, have also been detailed. Finally, we have presented some new perspectives in biochar-based electrochemical devices or strategies for the sensing of species, or energy storage and production.

Simple, low-cost, and sensitive new platforms for electrochemical immunosensors for virus detection have been attracted attention due to the recent pandemic caused by a new type of coronavirus (SARS-CoV-2). In the present work, we report for the first time the construction of an immunosensor using a commercial 3D conductive filament of carbon black and polylactic acid (PLA) to detect Hantavirus Araucaria nucleoprotein (Np) as a proof-of-concept. The recognition biomolecule was anchored directly at the filament surface by using N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride and N-Hydroxysuccinimide (EDC/NHS). Conductive and non-conductive composites of PLA were characterized using thermal gravimetric analysis (TGA), revealing around 30% w/w of carbon in the filament. Morphological features of composites were obtained from SEM and TEM measurements. FTIR measurement revealed that crosslinking agents were covalently bonded at the filament surface. Electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for the evaluation of each step involved in the construction of the proposed immunosensor. The results showed the potentiality of the device for the quantitative detection of Hantavirus Araucaria nucleoprotein (Np) from 30 μg mL−1 to 240 μg mL−1 with a limit of detection of 22 μg mL−1. Also, the proposed immunosensor was applied with success for virus detection in 100x diluted human serum samples. Therefore, the PLA conductive filament with carbon black is a simple and excellent platform for immunosensing, which offers naturally carboxylic groups able to anchor covalently biomolecules., Graphical abstract Image 1

Made available in DSpace on 2021-06-25T10:37:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) The development of new materials for electrochemical sensors has been received attention due to the search for sustainability. However, the use of in natura materials from vegetable and animal origin is still little explored for this purpose. Therefore, this work aims to use beeswax as biofilm, as an environmentally friendly and sustainable platform for incorporating carbon black nanoparticles. The electrode was prepared by a simple dispersion of beeswax and carbon black on the surface of the glassy carbon electrode. The proposed modified electrode was used to determine the herbicide paraquat (PQ) in 3 different samples of Apis mellifera honey. The presence of carbon black decreases the electrical resistance when compared with the bare electrode. The beeswax-carbon black film considerably increased the sensitivity of the PQ determination measures at a concentration range between 5.0 × 10−7 and 7.5 × 10−6 mol L−1. Samples with PQ contents between 7.5 × 10−7 and 7.5 × 10−6 mol L−1 presented recovery values from 97.2 to 114%. Also, the proposed sensor showed good repeatability and reproducibility for successive measurements. This suggests the use of the proposed electrode is feasible as an alternative strategy in the monitoring of herbicides in honey samples. Department of Nature Sciences Mathematics and Education Federal University of São Carlos Institute of Chemistry University of Campinas Center of Social Insects Studies Institute of Biosciences São Paulo State University (Unesp) Center of Social Insects Studies Institute of Biosciences São Paulo State University (Unesp) FAPESP: 2013/22127-2 FAPESP: 2017/21097-3 FAPESP: 2019/00473-2 FAPESP: 2019/01844-4 CNPq: 303338/2019-9 CAPES: Finance Code 001

In this work, the use of medical adhesive tape—as a substrate to develop novel sensor architecture for the detection of hemoglobin (HB) has been investigated. The electrodes were fabricated based on the screen-printing method. The proposed electrode was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and cyclic voltammetry. The medical adhesive electrode showed excellent electrochemical behavior for dopamine, which was used for characterization and proof of concept. Also, the electrode was applied for HB electrochemical detection in the range of 1.0 to 10 mg mL−1, with a detection limit of 0.7 mg mL−1 by using differential pulse voltammetry. This sensor has shown resistance to mechanical stress, even when deformed based on its wearable functions, which is an exciting alternative for the development of low-cost electrochemical devices.

Electrochemistry combined with economical and sustainable platforms (such as paper) provides portable, affordable, robust, and user-friendly devices. In general, techniques such as photolithography and sputtering are excellent alternatives for producing these platforms. However, due to the requirement of expensive and sophisticated instrumentation as well as cleanroom facilities, these techniques have limited access. Thus, the search for easy to use and produce approaches have been reported, employing consumables, including adhesives, carbon ink, graphite, pencil, office paper, paperboard, among others. In this sense, in this mini-review, we discuss various strategies explored to fabricate low-cost electrochemical sensors, including its main applications. Different manufacturing methods, such as screen and stencil printing, laser-scribing, and pencil drawing, will be discussed here, emphasizing the performance of the obtained devices, in addition to their advantages and disadvantages.

Made available in DSpace on 2022-04-29T08:35:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-01 Greener materials have been used in the construction of electrochemical devices, becoming one of the main strands of this scientific development area. Thin films based on natural and renewable sources, such as propolis, allow the development of biocomposites. Hence, we have proposed the use of a thin film based on propolis for the stable and homogeneous immobilization of carbon nanotubes (CNTs), which increased the electrical conductivity of the base electrode (glassy carbon electrode) by almost 500 thousand times. The CNTs/propolis biofilm proportion was optimized by multivariate analysis, providing a decrease in the number of experiments, the demand for reagents, and analysis time. The biocomposite thin film was used for the spontaneous preconcentration and anchoring of metal ions, and the electrochemical synthesis of redox mediators and catalysts. This qualifies the proposed strategies for the development of eco-friendly electrochemical devices. Department of Nature Sciences Mathematics and Education Federal University of São Carlos Institute of Chemistry University of Campinas Center of Social Insects Studies São Paulo State University Institute of Biosciences Center of Social Insects Studies São Paulo State University Institute of Biosciences

This work presents a feasible process for preparation screen-printed electrode (SPE) using a lab-made conductive ink based on cellulose acetate (CAc) and graphite powder (GP) printed on polyvinyl chloride (PVC) sheet. The CAc present in the composition of this SPE is a binding agent for conductive inks with GP, which are relatively low-cost and easily obtainable materials, compared to other similar commercial sensors. The SPE was evaluated through cyclic voltammetry (CV) using an equimolar [Fe(CN)6]3-/4− solution as a redox probe to find an adequate ink composition. Electrode surface was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). To show the analytical potential of SPE proposed it was used for Levodopa (L-dopa) determination. L-dopa is a drug frequently used to reduce the symptoms of Parkinson's disease. The GP-CAc/PVC electrode was evaluated for the determination of L-dopa under square wave voltammetric (SWV) conditions. The electrode presented a linear dynamic range (LDR) from 8.00 to 100 µmol L−1 and a limit of detection (LOD) of 0.06 µmol L−1. As a proof-of-concept, the proposed electrode was used to quantify L-dopa in drug samples as an alternative tool for quality control tests, being applied to two commercial drugs. The electrode construction strategy proved to be reproducible with an analytical performance comparable to other similar electrodes reported in the literature.

3D printing technology combined with electrochemical techniques have allowed the development of versatile and low-cost devices. However, some aspects need to be considered for the good quality and useful life of the sensors. In this work, we have demonstrated herein that the filament aging, the conductive material, and the activation processes (post-treatments) can influence the surface characteristics and the electrochemical performance of the 3D printed sensors. Commercial filaments and 3D printed sensors were morphologically, thermally, and electrochemically analyzed. The activated graphene-based (Black Magic®) sensor showed the best electrochemical response, compared to the carbon black-filament (Proto-Pasta®). In addition, we have proven that filament aging harms the performance of the sensors since the electrodes produced with three years old filament had a considerably lower intra-days reproducibility. Finally, the activated graphene-based sensor has shown the best performance for the electrochemical detection of bisphenol A, demonstrating the importance of evaluating and control the characteristics and quality of filaments to improve the mechanical, conductive, and electrochemical performance of 3D printed sensors.

This paper reports the comparison of the electrochemical properties of 3D PLA-graphene electrodes (PLA-G) under different activation conditions and through different processes. In this work, the performance of the electrodes was evaluated after polishing, electrochemical and chemical treatments and a combination of them. The best results were obtained with hydroxide activation using 1.0 mol L-1 NaOH for 30 min of immersion, which promoted the saponification of PLA exposing the graphene nanoribbon structures. The improvement was more evident also after electrochemical activation, which led to a great increase in surface area, defects, electron transfer rate and amount of edge sites. The analytical performance of the proposed PLA-GNaOH-30-EC electrode was evaluated in the presence of dopamine (DA) by three electrochemical techniques, presenting a broad linear range, and limits of detection of 3.49, 2.17 and 1.67 μmol L-1 were obtained by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV), respectively. The separation and quantification of DA in the presence of AA and UA was also reported. The sensor showed good repeatability and reproducibility and was successfully applied to DA determination in synthetic urine and human serum, showing good recovery, from 88.8 to 98.4%. Therefore, the activation methods were essential for the improvement in the 3D PLA-G electrode properties, allowing graphene surface alteration and electrochemical enhancement in the sensing of molecular targets.

A glassy carbon electrode (GCE) modified with single-walled carbon nanohorns (SWCNH) and zein (ZE), a prolamin type-protein find in maize, for the differential pulse adsorptive cathodic stripping voltammetric determination of fenitrothion (FT) is proposed. The proposed film was characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Regarding the electrochemical characterization, comparing the results obtained by cyclic voltammetry and electrochemical impedance spectroscopy, the modified electrode (SWCNH-ZE/GCE) showed an electroactive surface area 3 times higher and faster electron transfer kinetic than bare GCE. By using differential pulse adsorptive cathodic stripping voltammetry and SWCNH-ZE/GCE the analytical curve exhibited a linear response ranging of 9.9 × 10−7 to 1.2 × 10−5 mol L−1, with a limit of detection of 1.2 × 10−8 mol L−1. The proposed sensor was successfully applied for the determination of FT pesticide in natural water and orange juice samples. Moreover, the electrochemical sensor showed good repeatability and reproducibility arising from the excellent film stability, suggesting that the proposed architecture has broad potential for applications in sensing and biosensing.

In this study, we report an electrochemical study based on nanocellulose (NC) and single-walled carbon nanohorns (SWCNH). SWCNH and NC ensure large surface area, good conductivity, high porosity and chemical stability, becoming attractive for electrodes. The materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Scanning Electron Micrograph (SEM), Transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential. Using XRD and FTIR it was possible to observe particular characteristics of NC and SWCNH. The presence of dahlia-like assemblies on the NC surface was observed by MEV and TEM. Then, we investigated the electrochemical behavior of NC-SWCNH, which showed the excellent results when it was used guanine and adenine, as proof of concept, by using cyclic and linear sweep voltammetry (LSV). LSV was also employed for simultaneous detection resulting in limits of detection of 1.7 × 10−7 mol L−1 and 1.4 × 10−6 mol L−1, for guanine and adenine, respectively. In addition, the proposed electrode was applied for determination of both bases in synthetic human serum and fish sperm. We demonstrate that it is possible to use NC, a renewable material, in conducting thin films with SWCNH, and due to simplicity in the preparation and high conductivity, this new thin film could be extended for others electrochemical purposes such as sensing and biosensing.

In this study, graphene oxide (GO) has been reduced in two different ways for the production of oppositely charged reduced graphene oxide (rGO) sheets. One reduction route consisted of the covalent modification of GO with (3-aminopropyl) triethoxysilane and subsequent chemical reduction to produce positively charged rGO. In the second route employed, GO was reduced in a domestic microwave oven, in which the presence of urea doped the material with nitrogen, increasing its electrical conductivity considerably. Multilayers of oppositely charged rGO were manufactured using the layer-by-layer (LbL) assembly technique. The kinetics and growth of multilayers were monitored by UV–Vis absorption spectroscopy and quartz crystal microbalance. rGO multilayers on the interdigitated gold electrodes originate high conductive films, in which the number of deposited layers controls the conductivity. As a solution-gated field-effect transistor, the devices presented high transconductance; (90 µS and 55 µS for holes and electrons, respectively). Upon modification of the LbL films with papain, used as a biological recognition element, the devices were capable of detecting Cystatin C protein (a chronic renal disease biomarker) in synthetic urine in concentrations as low as 5 ng.mL−1. Therefore, the proposed transistors proposed here represent interesting alternatives as novel sensors and biosensors platforms.

In this research, a boron-doped diamond (BDD) electrode has been explored to detect the chloroquine drug. The electrochemical performance of BDD electrode towards the irreversible anodic response of chloroquine was investigated by subjecting this electrode to the cathodic (&minus, 0.5 A cm&minus, 2 by 180 s, generating a predominantly hydrogen-terminated surface) and anodic (+0.5 A cm&minus, 2 by 30 s, oxygen-terminated surface) pretreatments. The cathodically pretreated BDD electrode ensured a better-defined anodic peak and higher current intensity. Thus, by applying the cathodically pretreated BDD electrode and square-wave voltammetry (SWV), the analytical curve was linear from 0.01 to 0.25 &micro, mol L&minus, 1 (correlation coefficient of 0.994), with sensitivity and limit of detection of 12.2 &micro, A L &micro, mol&minus, 1 and 2.0 nmol&minus, 1, respectively. This nanomolar limit of detection is the lowest recorded so far with modified and unmodified electrodes.