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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.

The manioc starch (MS) product extracted of many Manihot species, presents low cost and film formation capability. In this work, we report the decoration of MS thin film with reduced graphene oxide to form a novel composite, which we used to modify a glassy carbon electrode for phenolic compounds detection. The characterization of the nanostructured biopolymeric film was performed by scanning electron and atomic force microscopy, electrochemical impedance, ultraviolet-visible and Fourier transform infrared spectroscopies, dynamic light scattering and cyclic voltammetry techniques. Under optimal experimental conditions, the peak currents were independently studied in the concentration range of 0.5 to 200 μmol L−1 and 0.5 to 74 μmol L−1 with a limit of detection of 0.07 μmol L−1 and 0.04 μmol L−1, for dopamine and catechol, respectively, as proof of concept. MS proved to be a great asset for supporting thin film for electroanalytical devices, which were tested in water and synthetic urine samples, with satisfactory results.

In this work, we report the development of a new disposable electroanalytical device based on direct transfer of graphite from a common pencil, by drawing and painting a three electrodes system, on a corrugated fiberboard substrate (PD-CFB). Surface morphology and electrochemical features were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry (CV) techniques. Wide useful potential windows in different electrolyte solutions were verified. As proof of concept, the proposed sensor was applied for catechol (CA) detection in environmental samples. Following the optimal experimental conditions, a linear dynamic response (LDR) was in the range of 0.05–1.1 mmol L−1 with a limit of detection (LOD) of 0.01 mmol L−1. The proposed architecture allowed the construction of electroanalytical device by easy and feasible procedure using non-toxic and renewable materials (ecofriend) with low cost. In addition, the electrodes can be used without any pretreatment of the electrode surface.

The growth in the demand for mass analysis, in a fast and safe way, with good reliability and low cost has aroused great scientific interest in the search for new devices that prioritize precision and time. In this sense, this work presents a simple, disposable, and easy-to-use electrochemical sensor, developed on a waterproof paper substrate with a conductive ink based on shellac, a resin of natural origin, and graphite. The conductive ink was obtained through a simple mixture of its components and deposited on the paper substrate, being ready to use after a drying period. The new sensor was employed for the electrochemical detection of sulfamethoxazole (SMX), an antibiotic belonging to the class of sulfonamides, which presents great importance due to its direct impact on the flow of the food chain and is, therefore, commonly found as a metabolic residue in environmental and food samples. Using the differential pulse voltammetry technique, a linear range of 5.0 μmol L−1–100 μmol L−1 and a limit of detection of 0.4 μmol L−1 were obtained. The electrochemical sensor was also employed for the analysis of SMX in water and milk samples, and recovery values between 91 and 110% were obtained, proving that the development and application of the new conductive ink proposed for the fabrication of disposable devices provided an efficient electrochemical detection of SMX in the applied samples.

In last few years, titanium dioxide (TiO2)-based various dimensional (0D, 1D, 2D, and 3D) nanostructures (NSs) have been extensively investigated because of their outstanding physio-chemical properties and multifunctional applications in the variety of fields, including energy, environment, biomedicine, and so on. Particularly, one dimensional (1D) TiO2 NSs have gained much attention among the researchers as these nanomaterials can be explored in various morphologies, such as nanorods, nanotubes, nanofibers, nanowires, and so on. In addition to their unique 1D shape and large specific surface area, these 1D NSs show confinement in the radial direction making them more valuable than other dimensional NSs. However, owing to their large band gap, these NSs show inability of exploiting visible light and lower charge recombination rate becoming less efficient materials for the practical applications in the society. In order to achieve high efficiency of these materials and to improve their visible light activity, considerable efforts have been made by narrowing the band gap through doping or nanocomposite formation with other functional nanomaterials. This review article is mainly focused on the rare earth metal–doped 1D TiO2 NSs with the detailed mechanism of action, improved optoelectronic properties, and their multifunctional applications in the energy and environmental fields. It includes photocatalytic (photodegradation/surface-enhanced Raman scattering detection of organic pollutants, photocatalytic CO2 reduction, photocatalytic water splitting, and upconversion-based photocatalytic activities) sensing, solar cells, supercapacitors, lithium-ion batteries applications with an emphasis on their fundamental working principles. In addition, synthesis methods of rare earth metal–doped 1D TiO2 NSs, the doping effect on the microstructural and optical properties, and recent advances in these directions followed by challenges and future opportunities have been discussed.

Melatonin is a hormone that affects sleep-wake cycles and plays a role in the understanding of neuronal disorders and has excellent potential for therapeutical applications in infectious diseases, becoming an important target of chemical analysis. In this context, we report the development of an electrochemical device comprising a self-adhesive electrode based on a graphite-automotive varnish (Gr-AV) mixture as a conductive material to produce a printable ink applied over a paper adhesive easily transferred to a polyethylene terephthalate substrate. The Gr-AV electrode presented a high electrochemically active surface area which showed to be suitable for melatonin oxidation. The association of the device alongside a square-wave voltammetry method offered a linear behavior in the concentration range from 10.0 to 100.0 µmol L−1, a limit of detection of 0.49 µmol L−1, as well as presenting exciting recovery and relative standard deviation over samples analysis. The results showed the valid application of the device for the determination of melatonin in biological samples, pharmaceutical formulations, and its potential for point-of-care analysis.

Quality and authenticity monitoring are activities of growing necessity worldwide. However, methods of rapid evaluation and low cost need to be further explored to intensify and optimize the monitoring process. Hence, the present study proposes a procedure for discrimination of lager beers (premium and standard American lager beers) using commercially available screen-printed electrodes (SPEs) (carbon (SPCE), gold (SPGE), and carbon nanotube (SPEs-CNT)) and chemometric classification methods (soft independent modeling of class analogy (SIMCA) and partial least squares regression discriminant analysis (PLS-DA)). Overall, PLS-DA models obtained, on average, 88% for sensitivity, specificity, and precision in the validation dataset. The SIMCA models, on the other hand, showed, on average, 72% of sensitivity, 82% specificity and 80% of precision. The electronic tongue's final configuration of an SPCE coupled with PLS-DA showed a predictive power of 94%, using only one SPCE with the capacity of analyze up to 35 beers per SPEs.

Made available in DSpace on 2022-04-29T08:30:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-09-10 The present paper describes a new way to construct composite electrodes by using beeswax as an alternative binder and graphite powder as the conductive phase. Beeswax can be an attractive binder since it is a biodegradable and renewable material. Also, it attributes to the composite material a good rigidity after dry at room temperature. The monitoring of hydrogen peroxide (H2O2) in honey is extremely important due to its antibacterial properties, which are vital for the maintenance of the hive. The determination of H2O2 by electrochemical techniques is widely noted in the literature, mainly using redox mediators or catalysts, such as Prussian blue (PB). Therefore, the proposed composite electrode was prepared with beeswax and graphite in n-hexane, and the PB was electrochemically synthesized by cyclic voltammetry. The constructed electrode showed a low resistance of electronic transfer (60 Ω), high electroactive surface area, and high electronic transference constant (1.73×10−3 cm s−1) when compared with other composite electrodes. The presence of PB on composite electrode allowed the amperometric determination of H2O2 with good linearity (R2 = 0.997) at a concentration range of 1.0−180 µmol L−1 H2O2, showing a sensitivity of 0.184 µAL µmol−1. Consequently, it was possible to determine H2O2 accurately at three concentration levels in wild honey samples (RSD = 98.5−102%), suggesting the use of this alternative method for the quality control analysis of honey. Department of Nature Sciences Mathematics and Education Federal University of São Carlos Institute of Chemistry University of Campinas Department of Chemistry Federal University of Paraná Center of Social Insects Studies São Paulo State University Institute of Biosciences Center of Social Insects Studies São Paulo State University Institute of Biosciences

Detection of mutations related to cancer predisposition has been an important action in the prevention of cancer and in the cancer genetic profiling. Breast cancer (BRCA) genes mutations are widely known for their relation to genetic predisposition to breast and ovarian cancer. However, the access to genetic tests is still limited. Here, a label-free DNA sensor to detect the mutation 185delAG in the breast cancer 1, early onset (BRCA 1) gene, a founder mutation in the Ashkenazi population, is described. Based on the DNA hybridization and electrochemical impedance spectroscopy (EIS), the sensor was able to distinguish between the mutated and non-mutated sequences, a two-base mismatch. Using a single-strand thiol-modified 25-mer DNA sequence (HS-ssDNA) as probe immobilized in a gold electrode, hybridization studies were performed with [Fe(CN) 6 ] 4 − as redox probe and resulted in DNA sensor with a low limit of detection of 0.15 nmol L − 1 in a linear range from 1 to 200 nmol L − 1 . This DNA sensor shows prominent electrochemical performance and might be an interesting alternative to distinguish between mutated and non-mutated BRCA1 genes.

A new architecture for a sensor and a voltammetric procedure were proposed, using a glassy carbon electrode modified with nanodiamonds and dihexadecyl phosphate for determination of codeine (COD) in pharmaceutical and biological fluid samples. Square-wave voltammetry (SWV) was used and the relevant experimental parameters were optimized. Under optimal experimental conditions, the analytical curve presented a linear concentration range from 0.299 to 10.8 μmol L −1 , and a limit of detection of 54.5 nmol L − 1 . The proposed voltammetric method was used for COD determination in commercial pharmaceutical and biological fluid samples such as urine and human serum with satisfactory results.

The development of a bismuth film on a disposable minisensor for electroanalytical determination of Diquat (DQ) and Paraquat (PQ) using voltammetric techniques as square-wave (SWV) and differential-pulse (DPV) is reported. The disposable minisensor consisted of a bismuth film-working electrode, a silver-pseudo-reference and copper-counter electrodes. Copper boards of a printed circuit were used as substrate and nail varnish was used as an electrical insulator to limit the electrode area. The disposable proposed minisensor was applied for the determination of DQ using SWV and PQ using DPV. Under optimal experimental conditions, the cathodic peak current was linear in the DQ concentration range of 0.19 × 10 −6 –9.3 × 10 −6 mol L −1 with a detection limit of 8.9 × 10 −8 mol L −1 , and, for PQ the peak current was linear in the concentration range of 0.12 × 10 −6 –4.2 × 10 −6 mol L −1 with a detection limit of 1.2 × 10 −8 mol L −1 . The proposed method was applied for the determination of both pesticides in natural water samples and the obtained results are in good agreement with those results obtained using a high-performance liquid chromatography at a 95% confidence level.

The monitoring of species of medical, environmental, and industrial interests has been urgently demanded. Several times, the necessity of point of care and/or point of use is important to obtain precise and rapid quantification, in which wearable and flexible disposable electrochemical sensors and biosensors have been great alternatives. In this context, a short review describing the main advances in the fabrication and development of conductive inks for the construction of miniaturized and disposable electrochemical devices is presented. Electrochemical devices developed from conductive inks have been an innovative system that promotes flexibility for the design of the electrodes. The growing increase in the number of researches regarding the development of inks is driven by the search for simplicity, low-cost, less waste generation, mass production, and environmentally friendly manufacturing methods. The present review focuses on alternative conductive inks and their compounds, binders, and conductive materials for electrochemistry. The binder such as varnishes, natural resins, and natural polymeric compounds will be presented, once they promote the dispersion of conductive material, as well as the adhesion on the substrate. Special attention is given to conductive materials. We highlight some nanostructured materials such as platinum, silver, and gold nanoparticles, due to their great conductivity and extensive use to develop electrochemical sensors. Inks and electrodes from carbon-based materials are also discussed, such as graphite, carbon nanotubes, carbon black, and graphene. The biocompatibility of these materials, especially important for wearable sensors, will also be approached. Finally, we present new perspectives on the development of sensors and biosensors using conductive inks.

In this work, a biosensor using a glassy carbon electrode modified with gold nanoparticles (AuNPs) and tyrosinase (Tyr) within a dihexadecylphosphate film is proposed. Cystamine and glutaraldehyde crosslinking agents were used as a support for Tyr immobilization. The proposed biosensor was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cyclic voltammetry in the presence of catechol. The determination of catechol was carried out by amperometry and presented a linear concentration range from 2.5×10(-6) to 9.5×10(-5)molL(-1) with a detection limit of 1.7×10(-7)molL(-1). The developed biosensor showed good repeatability and stability. Moreover, this novel amperometric method was successfully applied in the determination of catechol in natural water samples. The results were in agreement with a 95% confidence level for those obtained using the official spectrophotometric method.

This study describes the fabrication of carbon screen-printed electrodes (SPEs) from alternative and low-cost materials. The carbon conductive ink was prepared from a mixture of graphite powder and colorless nail polish. To produce the SPEs, the ink was spread on polyester overhead projector sheets, which acted as a flexible and water-impermeable substrate. To improve the analytical performance, the SPEs were chemically modified with multiwalled carbon nanotubes (MWCNTs) by a simple drop-casting procedure. The effects of the acidic functionalization and size of the MWCNTs on the electrochemical behavior of the SPEs were evaluated. As a proof of concept, the MWCNT/SPEs were applied to determine caffeic acid (CA) in tea samples. CA is a biologically important molecule with antioxidant activity and several beneficial effects on human health, therefore its determination in food and beverages is relevant. The SPEs modified with the acidic-functionalized longer diameter MWCNTs presented the broadest linear range for CA, from 2.0 µmol L−1 to 50 µmol L−1. These MWCNTs also provided low limits of detection and quantification, 0.20 and 0.66 µmol L−1, respectively. Tea samples were analyzed by using these electrodes and recovery percentages from 99 to 109% were obtained with low relative standard deviation values, demonstrating the accuracy of the proposed sensor. Moreover, the developed SPE allowed performing the voltammetric measurements using only 100 µL of solution which is extremely attractive from an economical and environmental point of view. Therefore, this study brings exciting advances in the electroanalysis field regarding the importance of the development of disposable electrochemical sensors with improved performance and capability to perform electrochemical measurements in microvolumes.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive and irreversible cognitive decline. Currently, it affects 36 million people and due to population ageing it is estimated that in 2030 disease incidence will reach 60 million individuals. The precise diagnosis of AD is still a complex task, being mainly performed by cerebrospinal fluid (CSF) analysis or neuroimaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI). Despite being effective these techniques are expensive, time-consuming and not accessible for most part of the population. In this scenario biosensors are presented as promising alternatives for simple, rapid and low cost diagnosis of AD. In this revision we summarize the recent advances on biosensors that brings more accessibility to AD diagnosis. We introduce the most used biorecognition elements in miniaturized biosensing systems as well as AD biomarkers present in CSF, in plasma and in genetic material which can be used for disease identification even in early stages. The recent developed biosensors for AD diagnosis using optical, electrochemical and colorimetric techniques as well as their strategies and analytical performances are discussed. Advancements in signal amplification methodologies with nanomaterials to increase biosensors sensitivity are also presented. This review highlights the potential of biosensors to be used as an accurate and portable tool to improve the early AD diagnosis.

In this study, platinum electrodes were fabricated on the bio-based poly(ethylene terephthalate) (Bio-PET) substrates for the development of flexible electrochemical sensors for the detection of Parkinson's disease biomarkers. Dopamine was detected by voltammetric measurements, displaying a 3.5 × 10−5 mol L−1 to 8.0 × 10−4 mol L−1 linear range with a limit of detection of 5.1 × 10−6 mol L−1. Parkinson's disease protein 7 (PARK7/DJ-1) was successfully detected by electrochemical impedance spectroscopy after electrode functionalization with specific anti-PARK7/DJ-1 antibodies. In this case, analytical curves presented a linear behavior from 40 ng mL−1 to 150 ng mL−1 of PARK7/DJ-1 with a limit of detection of 7.5 ng mL−1. Besides, the electrodes did not suffer any change in the electrochemical response after manual tests of mechanical tension. The proposed sensor and immunosensor were applied for the determination of Parkinson's disease biomarkers concentrations found in the human body, being adequate as an alternative method to diagnose this disease.

A new architecture for a biosensor is proposed using a glassy carbon electrode (GCE) modified with hemoglobin (Hb) and silver nanoparticles (AgNPs) encapsulated in poly(amidoamine) dendrimer (PAMAM). The biosensors were characterized using ultraviolet-visible spectroscopy, ζ-potential and cyclic voltammetry to investigate the interactions between Hb, AgNPs and the PAMAM film. The biosensor exhibited a well-defined cathodic peak attributed to reduction of the Fe(3+) present in the heme group in Hb, as revealed by cyclic voltammetry in the presence of O2. An apparent heterogeneous electron transfer rate of 4.1s(-1) was obtained. The Hb-AgNPs-PAMAM/GCE third generation biosensor was applied in the amperometric determination of hydrogen peroxide over the linear range from 6.0 × 10(-6) to 9.1 × 10(-5)mol L(-1) with a detection limit of 4.9 × 1 0(-6)mol L(-1). The proposed method can be extended to immobilize and evaluate the direct electron transfer of other redox enzymes.

Surfactants have been extensively used in electrode modification for electroanalysis in recent years. In this review we highlight dihexadecylphosphate (also known as dicetylphosphate, dihexadecyl hydrogen phosphate, DHP), which is a hydrophobic surfactant molecule with a negatively charged polar head located at a phosphate group on one side of the molecule, linked to two long hydrocarbon chains (two long hydrophobic tails) on the other side. DHP has been used in association with other electroactive nanomaterials such as carbon nanotubes, gold nanoparticles, and/or graphene in sensing and biosensing. In this paper, we present an overview of the use of DHP in the modification of electrode surfaces. In the course of the paper, we first introduce DHP, followed by an overview of its applications in electrochemical sensors and biosensors. The prospects and future applications of DHP in the field of electrochemistry are also evaluated.

Nowadays, there is growing interest in portable and disposable electrochemical sensors due to the low-cost, simplicity, and excellent analytical performance associated with these devices. Despite recent advances, however, there remains a need to create cheap, high-performance electrode materials. Thus, this study evaluated the suitability of carbon conductive inks prepared by the mixture of glass varnish and graphite powder to produce disposable electrochemical sensors. Two different ink manufacturing processes and compositions were studied to produce different disposable electrodes, each providing high electrical conductivity and adhesion on paper and polyethylene terephthalate (PET) substrates. Electrochemical impedance spectroscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used for the characterization of inks. The electrodes were applied for the electrochemical determination of some compounds. For the paper electrode, the electrochemical detection of dopamine was performed, ranging from 15 μmol to 100 μmol L−1, with a detection limit of 4.1 μmol L−1; the individual electrochemical detection of catechol was performed ranging from 10 μmol L−1 to 1000 μmol L−1, with a detection limit of 9.0 μmol L−1. The detection of hydroquinone was performed, ranging from 10 μmol L−1 to 1000 μmol L−1, with a detection limit of 5.3 μmol L−1. Also, the screen-printed electrode was applied for estriol electrochemical determination in the linear range from 0.1 μmol L−1 to 8.0 μmol L−1 with a detection limit of 0.08 μmol L−1. The glass varnish is an alternative to creating carbon composite electrodes, and the new devices are inexpensive and simple to prepare, with attractive analytical performance.

Disposable electrochemical sensors using sustainable and cheap materials are an exciting alternative to produce new kinds of sensing platforms. Waterproof paper (WP) is a biodegradable and biocompatible material that allows dropped of the sample on its surface without absorption by fibers. Also, WP can be used for miniaturized sensors construction. In this work, a conductive ink was produced with nail polish and graphite powder, using the WP as the sensor substrate for paracetamol (PAR) and melatonin (MEL) voltammetric determination. PAR is a pharmaceutical commonly used in high doses for the relief of pain and fever, and MEL is a hormone related to several diseases besides a direct relation to sleep quality. Using differential pulse voltammetry for PAR determination, the WP sensor showed a linear response in the concentration ranging from 0.50 μmol L−1 to 100 μmol L−1 with a limit of detection (LOD) of 53.6 nmol L−1. Square wave voltammetry was applied for MEL determination, and the proposed electrode presented linear response ranging from 0.80 μmol L−1 to 100 μmol L−1 and LOD of 32.5 nmol L−1. The sensor showed excellent repeatability and reproducibility for consecutive measurements. Then, the disposable WP sensor was successfully applied in the determination of PAR and MEL in pharmaceutical and biological samples, with recovery values, above 91.1%. The described architecture allowed the manufacture of a disposable, simple, and low-cost electroanalytical device that can be used for electrochemical sensing.

The determination of serotonin has become relevant in biological fluid analysis since some neurological disorders may be related to abnormal amounts of this neurotransmitter in human beings. In this work, it is proposed the construction of a low-cost electrode sensitive to the quantification of serotonin by a biofilm of graphite, nanodiamonds and gold nanoparticles anchored in casein. The casein biofilm was used to anchor the conductive nanomaterials on the GCE. Measurements were performed by differential pulse voltammetry in which showed a linear response with LDR of 0.3 to 3.0 μmol L−1, LOD of 0.1 μmol L−1 and a sensitivity of 0.18 µA L mol−1. The sensor was applied for the serotonin quantification in synthetic urine samples enriched with good recovery (91.4 to 103%). Therefore, the proposed electrode improved the conductivity and the electronic transfer capacity of the pristine electrode by low-cost biofilm, which could be applied in electrochemical biosensing.

In this work, an alternative voltammetric procedure for the determination of Pb(II) was developed using a carbon nanotube paste electrode modified with crosslinked chitosan with glutaraldehyde (GA-CTS-CNTPE). Square-wave adsorptive stripping voltammetry (SWAdSV) was used and the relevant experimental parameters were optimized. Under optimal experimental conditions, the voltammetric response was linear in the range of 9.90 × 10 − 8 to 2.00 × 10 − 6 mol L − 1 with a detection limit of 5.70 × 10 − 8 mol L − 1 . The proposed voltammetric method showed good repeatability and low interference from other metallic species. It was successfully applied in the determination of Pb(II) in natural water samples and the results were in very close agreement with those obtained using a comparative method (inductively coupled plasma optical emission spectrometry (ICP-OES)).

Graphene is a material that has attracted attention with regard to sensing and biosensing applications in recent years. Here, we report a novel treatment (using ultrasonic bath and ultrasonic tip) to obtain graphene oxide (GO) and a new stable conducting film using reduced graphene oxide (RGO) and dihexadecylphosphate film (DHP). The GO was obtained by chemical exfoliation and it was reduced using NaBH4. Subsequently, RGO–DHP dispersion was prepared and it was dropped onto a glassy carbon electrode by casting technique. The electrode was characterized by cyclic voltammetry and electrochemical spectroscopy impedance. The voltammetric behavior of the RGO–DHP/GC electrode in the presence of estradiol was studied, and the results reported an irreversible oxidation peak current at 0.6 V. Under the optimal experimental conditions, using linear sweep adsorptive stripping voltammetry, the detection limit obtained for this hormone was 7.7 × 10−8 mol L−1 . The proposed electrode can be attractive for applications as electrochemical sensors and biosensors.

Carbon nanomaterials thin films have been attracted considerable attention in the last years due to relative low cost and excellent electrical conductivity features. We report here on novel sensor architecture consisted of a glassy carbon surface modified with manioc starch and nanodiamonds nanoparticles. Structural and morphological properties of this thin film were investigated by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopies. By using square-wave voltammetry as electroanalytical tool, the widely used herbicide diquat (DQ) was determined in environmental samples. The modified electrode presented a linear response to DQ in the concentration range of 5.0 × 10−7 to 4.6 × 10−5 mol L−1 with a limit of detection of 1.1 × 10−7 mol L−1. This novel sensor proved to be efficient to determine if DQ is present in rivers and drinking water samples.

In this work, we detail the progress of a novel electrochemical disposable device, which has a relatively low cost and easy production, with a novel conductive ink, that consists of graphite and automotive varnish mixture, deposited over a self-adhesive paper, granting an easy production with relatively low cost. The electrode surface was characterized by scanning electron microscopy, X-ray powder diffraction and Fourier transforms infrared and Raman, cyclic voltammetry and electrochemical impedance spectroscopies. In addition, the proposed electrode was applied for individual electrochemical determination of dopamine and serotonin. The device achieved a linear response between 30 and 800 μmol L−1 and a limit of detection (LOD) of 0.13 μmol L−1, by square wave voltammetry for dopamine and a linear range from 6.0 to 100 μmol L−1, with a LOD of 0.39 μmol L−1, by differential pulse voltammetry for serotonin. Later, the working electrode was modified with glucose oxidase and dihexadecyl phosphate film in order to obtain a biosensor. At this stage, CV was applied to detect glucose in the range of 1.0–10 μmol L−1 and LOD of 0.21 μmol L−1. By three different techniques and analytes, the sensoring and biosensoring processes presented high reproducibility. The proposed adhesive electrode is easy to prepare, disposable, within non-restrictive nature, which allows an approach of a new device for electrochemical sensing and biosensing.

Tyrosinase (Tyr)-based biosensors might be interesting devices for fast analytical screening of phenols, especially if gold nanoparticles (AuNPs) are used as mediators of the direct electron transfer (DET) reaction between enzyme and electrode substrate. Therefore, by immobilizing Tyr on AuNPs electrodeposited on a boron-doped diamond (BDD) electrode. The best conditions (applied potential and deposition time) to electrodeposit AuNPs on BDD were selected by factorial design; homogeneously distributed quasi-spherical AuNPs (33 nm average diameter) were obtained by applying − 0.4 V vs. Ag/AgCl (3 M KCl) for 40 s. Then, Tyr was immobilized on AuNPs previously modified using cystamine and glutaraldehyde. The occurrence of DET between the electrode surface and the Tyr active site was verified by cyclic voltammetry, yielding the following parameter values: formal redox potential, 115 mV vs. Ag/AgCl (3 M KCl); transfer coefficient, 0.45; heterogeneous electron transfer rate constant, 0.032 s − 1 . Using square-wave voltammetry (SWV), a sensitive electrochemical reduction of phenol was attained: concentration range, 0.10–11.0 μM; detection limit, 0.07 μM; intra-day and inter-day repeatability RSDs, 3.4% and 4.24%, respectively; reasonably good stability (only 15% response decrease after 30 days). Furthermore, the obtained apparent Michaelis – Menten kinetic constant for phenol (13.0 μM) is quite good when compared to the ones reported in the literature. Hence, the developed Tyr-AuNPs/BDD biosensor exhibits good sensitivity, stability, and reproducibility for the determination of phenol by SWV.

A functionalized carbon nanotubes paste electrode modified with cross-linked chitosan for the determination of trace amounts of cadmium(II) and mercury(II) by linear anodic stripping voltammetry is described. Under optimal experimental conditions, the peak current was linear in the Cd(II) concentration range from 5.9 × 10−8 to 1.5 × 10−6 mol L−1 with a detection limit of 9.8 × 10−9 mol L−1 and, for Hg(II) from 6.7 × 10−9 to 8.3 × 10−8 mol L−1with a detection limit of 2.4 × 10−9 mol L−1. The proposed method was successfully applied for the determination of Hg(II) in natural and industrial wastewater samples, and Cd(II) in sediments, human urine, natural, and industrial wastewater samples.

The development and application of a functionalized carbon nanotubes paste electrode (CNPE) modified with crosslinked chitosan for determination of Cu(II) in industrial wastewater, natural water and human urine samples by linear scan anodic stripping voltammetry (LSASV) are described. Different electrodes were constructed using chitosan and chitosan crosslinked with glutaraldehyde (CTS-GA) and epichlorohydrin (CTS-ECH). The best voltammetric response for Cu(II) was obtained with a paste composition of 65% (m/m) of functionalized carbon nanotubes, 15% (m/m) of CTS-ECH, and 20% (m/m) of mineral oil using a solution of 0.05 mol L−1 KNO3 with pH adjusted to 2.25 with HNO3, an accumulation potential of −0.3 V vs. Ag/AgCl (3.0 mol L−1 KCl) for 300 s and a scan rate of 100 mV s−1. Under these optimal experimental conditions, the voltammetric response was linearly dependent on the Cu(II) concentration in the range from 7.90 × 10−8 to 1.60 × 10−5 mol L−1 with a detection limit of 1.00 × 10−8 mol L−1. The samples analyses were evaluated using the proposed sensor and a good recovery of Cu(II) was obtained with results in the range from 98.0% to 104%. The analysis of industrial wastewater, natural water and human urine samples obtained using the proposed CNPE modified with CTS-ECH electrode and those obtained using a comparative method are in agreement at the 95% confidence level.