Innovative voltammetric techniques for bumadizone analysis in pharmaceutical and biological samples: emphasizing green, white, and blue analytical approaches

There are no documented electroanalytical methods for quantifying the anti-inflammatory drug bumadizone (BUM) in pharmaceutical or biological matrices. So, a new voltammetric method was developed to determine BUM at nano concentrations in pharmaceutical forms, in the presence of its alkaline degradant, and in biological fluids. Five electrodes were tested, including three nano-reduced graphene oxide (nRGO) electrodes (5%, 15%, and 20%), a carbon paste electrode (CPE), and a 10% nRGO-modified CPE. The 10% nRGO-modified electrode showed the best performance, offering high selectivity and low detection limits, with good linearity in the concentration range of 0.9 × 102 to 15 × 102 ng mL-1. Differential pulse voltammetry successfully applied this electrode for BUM determination in various samples, achieving excellent recovery without preliminary separation. The method was validated according to ICH guidelines and compared favorably to the reference method. Its environmental impact was assessed using AGREE and Eco-scale metrics in addition to the RGB algorithm, showing superior greenness and whiteness profiles due to safer solvents and lower energy consumption, along with high practical effectiveness using the BAGI metric.

Application of a PLA/PBAT/Graphite sensor obtained by electrospinning on determination of 2,4,6-trichlorophenol

The widespread use of pesticides requires effective detection and quantification tools to improve monitoring of environmental quality. Electrochemical sensors offer a fast and sensitive response, and can also be optimized by combining several constituents and techniques, including biodegradable materials, being useful in the determination of chemical agents from environmental samples. Here, we produced a polymer-based sensor for 2,4,6-trichlorophenol determination, through electrospinning of poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blend with graphite. The graphite-containing fibres were thermally treated and wetted in mineral oil, thus forming a paste, used as an electrode in the electrochemical sensor. The thermal analysis indicated a disorganization of the polymeric chains between the aromatic carbon chain of the PBAT polymer, resulting in a material with low enthalpy, lower crystallinity and greater thermal degradability after insertion of graphite in polymeric fibres. NIR spectra revealed changes related to the carbonyls of the polymeric ester groups. Cyclic voltammetry and square wave voltammetry techniques were applied to study the electrochemical behaviour of developed sensor. The thermal treatment of graphite-containing fibres increased the adhesion surface in which occurs the adsorption of the analyte on the electrode, which improved the peak current in the electrochemical tests. The PLA/PBAT/Graphite sensor applied to determination of 2,4,6-TCP presented the detection and quantification limits of 7.84 × 10-8 mol L-1 (0.0155 mg L-1) and 2.36 × 10-7 mol L-1 (0.0466 mg L-1) with a linearity response of 1.00 × 10-7 mol L-1 and 2.00 × 10-6 mol L-1 with correlation coefficient of 0.993 (r2).

First electrochemical investigation and determination of non-steroidal anti-inflammatory drug etofenamate using disposable pencil graphite electrode with voltammetric techniques

In this study, the electrochemical properties of etofenamate, an active ingredient belonging to the non-steroidal anti-inflammatory drug group, were investigated using cyclic voltammetry (CV) and square wave voltammetry (SW) techniques on a disposable pencil graphite electrode (PGE). With the CV technique, reversible voltammetric waves of around +0.470 V and irreversible voltammetric waves of around +1.02 V were produced on the PGE. An environmentally friendly, selective and highly sensitive SW voltammetric method was developed using disposable PGE. This voltammetric method gave very good analytical working range on PGE in PBS (pH = 3.0) medium at concentrations ranging from 0.017 μM to 0.306 μM. The LOD value of this analytical method in PBS (pH = 3.0) medium was calculated as 0.0011 μM (0.406 μg L-1). The developed voltammetric method was successfully applied to urine and drug samples. The results of the voltammetric method were compared with the results of the spectrophotometric method. The results were found to be compatible with each other.

Enhancing Photoredox Catalysis in Aqueous Environments: Ruthenium Aqua Complex Derivatization of Graphene Oxide and Graphite Rods for Efficient Visible-Light-Driven Hybrid Catalysts

A ruthenium aqua photoredox catalyst has been successfully heterogeneneized on graphene oxide (GO@trans-fac-3) and graphite rods (GR@trans-fac-3) for the first time and have proven to be sustainable and easily reusable systems for the photooxidation of alcohols in water, in mild and green conditions. We report here the synthesis and total characterization of two Ru(II)-polypyridyl complexes, the chlorido trans-fac-[RuCl(bpea-pyrene)(bpy)](PF6) (trans-fac-2) and the aqua trans-fac-[Ru(bpea-pyrene)(bpy)OH2](PF6)2 (trans-fac-3), both containing the N-tridentate, 1-[bis(pyridine-2-ylmethyl)amino]methylpyrene (bpea-pyrene), and 2,2'-bipyridine (bpy) ligands. In both complexes, only a single isomer, the trans-fac, has been detected in solution and in the solid state. The aqua complex trans-fac-3 displays bielectronic redox processes in water, assigned to the Ru(IV/II) couple. The trans-fac-3 complex has been heterogenized on different types of supports, (i) on graphene oxide (GO) through π-stacking interactions between the pyrene group of the bpea-pyrene ligand and the GO and (ii) both on glassy carbon electrodes (GC) and on graphite rods (GR) through oxidative electropolymerization of the pyrene group, which yield stable heterogeneous photoredox catalysts. GO@trans-fac-3- and GR/poly trans-fac-3-modified electrodes were fully characterized by spectroscopic and electrochemical methods. Trans-fac-3 and GO@trans-fac-3 photocatalysts (without a photosensitizer) showed good catalytic efficiency in the photooxidation of alcohols in water under mild conditions and using visible light. Both photocatalysts display high selectivity values (>99%) even for primary alcohols in accordance with the presence of two-electron transfer processes (2e-/2H+). GO@trans-fac-3 keeps intact its homogeneous catalytic properties but shows an enhancement in yields. GO@trans-fac-3 can be easily recycled by filtration and reused for up to five runs without any significant loss of catalytic activity. Graphite rods (GR@trans-fac-3) were also evaluated as heterogeneous photoredox catalysts showing high turnover numbers (TON) and selectivity values.

Dip-coated carbon nanotube surface deposits as stable, effective response enhancers in pencil lead electrode voltammetry

Graphitic pencil leads (PLs) are inexpensive writing accessories, readily available in stationery shops. Because the round filaments have high conductivity, they are excellent candidates for sustainable electroanalytical sensor fabrication. Here, we show that dip-coated carbon nanotube (CNT) surface deposits can stably enhance the faradaic redox response of cylindrical pencil lead electrodes (PLEs), with just ten simple sequential immersions of assembled PLEs in an aqueous suspension of CNTs producing significant improvement in their analytical performance. Cyclic (CV) and differential pulse (DPV) voltammetry of ferricyanide with unmodified and CNT-modified PLEs confirmed the reproducibility of the modification procedure and the reliability of the extent of signal amplification, as well as the stability of the response. A series of DPV tests with drugs, an environmental pollutant, an enzyme-substrate redox label and an industrial chemical proved the practical applicability of the proposed CNT-PLEs. Based on their observed properties, PLEs with dip-coated CNT deposits are suggested as cost-effective tools for advanced electroanalysis and as green platforms for enzyme biosensor construction.

An acetylcholinesterase-based biosensor for isoprocarb using a gold nanoparticles-polyaniline modified graphite pencil electrode

An analysis tool for isoprocarb has been successfully developed as a biosensor system based on enzymatic inhibition of acetylcholinesterase (AChE) by isoprocarb. A gold nanoparticles-polyaniline modified graphite pencil electrode (AuNPs-PANI-GPE) was utilized to detect the change of thiocholine in the presence of isoprocarb. This electrode was prepared by two cyclic voltammetry steps, including the electro-polymerization of aniline on a graphite pencil and the electro-deposition of gold nanoparticles on the polyaniline surface. Characterization performed by SEM-EDX indicates that 8-80 nm size of gold nanoparticles could be deposited on the surface of polyaniline-modified graphite pencil (PANI-GPE). Electrochemical characterization using cyclic voltammetry suggested that the active surface area of the prepared electrode was 0.17019 cm², which was about 4 times higher than (PANI-GPE) and 13 times higher than the unmodified GPE. Furthermore, an oxidation peak of thiocholine could be observed at the modified GPE at a potential of + 0.675 V (vs. Ag/AgCl), formed by an enzymatic reaction of AChE in the presence of acetylthiocholine. This peak current was found to linearly increase with acetylthiocholine concentrations, while in the presence of isoprocarb in a constant concentration of AChE and acetylthiocholine the peak linearly decreases. At the optimum condition of 0.1 M phosphate buffer solution pH 7.4 containing 0.1 M KCl; 100 mU/ml AChE; and 1 mM acetylthiocholine chloride in an inhibition and contact time of 25 and 15 min, respectively, a linear calibration curve of isoprocarb in the concentration range of 0.05-1.0 μM could be provided. Estimated limits of detection and quantifications of 0.1615 nM and 0.5382 nM, respectively, with a sensitivity of 1.7771 μA/μM.mm² could be achieved. Furthermore, an excellent stability for 8 times measurements was observed with an RSD of 4.87%, suggesting that the developed tool is promising for the real detection of isoprocarb.

Development of an inexpensive and rapidly preparable enzymatic pencil graphite biosensor for monitoring of glyphosate in waters

Glyphosate (GLY) is the most widely used non-selective broad-spectrum herbicide worldwide under well-reported side effects on the environment and human health. That's why it's necessary to control its presence in the environment. This work describes the development of an affordable, simple, and accurate electrochemical biosensor using a pencil graphite electrode as support, a horseradish peroxidase enzyme immobilized on a polysulfone membrane doped with multi-walled carbon nanotubes. The developed electrochemical sensor was used in the determination of GLY in river and drinking water samples. Cyclic voltammetry and amperometry were used as electrochemical detection techniques for the characterization and analytical application of the developed biosensor. The working mechanism of the biosensor is based on the inhibition of the peroxidase enzyme by GLY. Under optimal experimental conditions, the biosensor showed a linear response in the concentration range of 0.1 to 10 mg L^-1. The limits of detection and quantification are 0.025 ± 0.002 and 0.084 ± 0.007 mg L^-1, respectively, which covers the maximum residual limit established by the EPA for drinking water (0.7 mg L^-1). The proposed biosensor demonstrated high reproducibility, excellent analytical performance, repeatability, and accuracy. The sensor proved to be selective against other pesticides, organic acids, and inorganic salts. Application on real samples showed recovery rates ranging between 98.18 ± 0.11 % and 97.32 ± 0.23 %. The analytical features of the proposed biosensor make it an effective and useful tool for the detection of GLY for environmental analysis.

A pencil graphite-based disposable device for electrochemical monitoring of sulfanilamide in honey and water samples

The present paper reports a simple, fast, and inexpensive process of manufacturing a disposable pencil graphite electrode (PGE) from widely available materials, which showed a reproducibility of at least 7.5%. The electrode was compared to the commercial glassy carbon electrode (GCE) and showed superior electroanalytical performance for sulfanilamide (SFA) with approximately 3.9-fold higher current density. Additionally, a displacement of the oxidation peak from approximately 80 mV to more cathodic regions was observed. Therefore, a method based on square wave voltammetry (SWV) was developed for the determination of the antimicrobial SFA in honey and tap water samples using the proposed sensor. The optimized method presented good detectability (LOD = 2.37 μmol L^-1), with excellent precision and accuracy (relative standard deviation < 4.2%) and percent recovery from spiked samples ranging from 92 to 97%. In addition, the sensor did not suffer significant interference from sample matrix components and other commonly evaluated antimicrobials, which demonstrates the potential of these electrodes for implementation in routine analysis and quality control.

Graphene nanosheet-sandwiched platinum nanoparticles deposited on a graphite pencil electrode as an ultrasensitive sensor for dopamine

An ultra-sensitive sensor of dopamine is introduced. The sensor is constructed by encapsulating platinum nanoparticles (PtNPs) between reduced graphene oxide (GR) nanosheets. The sandwiched PtNPs between GR layers acted as a spacer to prevent aggregation and provided a fine connection between the GR nanosheets to provide fast charge transfer. This specific orientation of the GR nanosheets and PtNPs on the graphite pencil electrode (GPE) substantially improved the electrocatalytic activity of the sensor. The synthesized graphene oxide and the fabricated sensor were comprehensively characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission-scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and square wave voltammetry (SWV). The value of the charge transfer coefficient (α), apparent heterogeneous electron transfer rate constant (k s), and electroactive surface area for dopamine were found to be about 0.57, 8.99 s-1, and 0.81 cm2, respectively. The developed sensor is highly sensitive towards dopamine, and the detection limit is 9.0 nM. The sensor response is linear for dopamine concentration from 0.06 to 20 μM (R 2 = 0.9991). The behavior of the sensor for dopamine in the presence of a high concentration of l(+) Ascorbic acid and other potential interferents was satisfactory. High recovery percentage between 90% and 105% in the human urine sample, good reproducibility, and facile fabrication of the electrode make it a good candidate for dopamine sensing.

Amperometric detection of tumor suppressor protein p53 via pencil graphite electrode for fast cancer diagnosis

Cancer occupies the second place in terms of worldwide mortality. Early and fast diagnosis of cancer helps clinicians to expand therapeutic approaches ultimately leading towards early diagnosis of cancer patients. In the present work, we delineated an amperometric immunosensor to diagnose cancer to detect p53, a biomarker for cancer. The immunosensor was fabricated by immobilizing anti-p53 antibodies onto the pencil graphite electrode (PGE). The immobilization of probe was studied by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The immunosensor was optimized for pH, incubation temperature, antibody concentration, incubation time and antigen concentration. The developed immunosensor, showed a linear range between 10 pgmL^-1 to 10 ngmL^-1 with a detection limit (LOD) of 10 pgmL^-1. p53 antigen was analyzed by measuring current under optimal conditions. The occurrence of p53 was determined in sera of prostate, breast, colon and lung cancer patients by the present immunosensor. The lower incubation time i.e., fast response and lower LOD demonstrated an improved p53 immunosensor for early diagnosis of cancer.

Recent Advancement in Disposable Electrode Modified with Nanomaterials for Electrochemical Heavy Metal Sensors

Heavy metal pollution has gained global attention due to its high toxicity and non-biodegradability, even at a low level of exposure. Therefore, the development of a disposable electrode that is sensitive, simple, portable, rapid, and cost-effective as the sensor platform in electrochemical heavy metal detection is vital. Disposable electrodes have been modified with nanomaterials so that excellent electrochemical properties can be obtained. This review highlights the recent progress in the development of numerous types of disposable electrodes modified with nanomaterials for electrochemical heavy metal detection. The disposable electrodes made from carbon-based, glass-based, and paper-based electrodes are reviewed. In particular, the analytical performance, fabrication technique, and integration design of disposable electrodes modified with metal (such as gold, tin and bismuth), carbon (such as carbon nanotube and graphene), and metal oxide (such as iron oxide and zinc oxide) nanomaterials are summarized. In addition, the role of the nanomaterials in improving the electrochemical performance of the modified disposable electrodes is discussed. Finally, the current challenges and future prospect of the disposable electrode modified with nanomaterials are summarized.

Pencil graphite as electrode platform for free chlorine sensors and energy storage devices

Multifunctional and low-cost electrode materials are desirable for the next-generation sensors and energy storage applications. This paper reports the use of pencil graphite as an electrode for dual applications that include the detection of free residual chlorine using electro-oxidation process and as an electrochemical energy storage cathode. The pencil graphite is transferred to cellulose paper by drawing ten times and applied for the detection of free residual chlorine, which shows a sensitivity of 27 μA mM^-1 cm^-2 with a limit of detection of 88.9 μM and linearity up to 7 mM. The sample matrix effect study for the commonly interfering ions such as NO₃^-, SO₄^2-, CO₃^2-, Cl^-, HCO₃^- shows minimal impact on free residual chlorine detection. Pencil graphite then used after cyclic voltammogram treatment as a cathode in the aqueous Zn/Al-ion battery, showing an average discharge potential plateau of ~1.1 V, with a specific cathode capacity of ~54.1 mAh g^-1 at a current of 55 mA g^-1. It maintains ~95.8% of its initial efficiency after 100 cycles. Results obtained from the density functional theory calculation is consistent with the electro-oxidation process involved in the detection of free residual chlorine, as well as intercalation and de-intercalation behavior of Al³⁺ into the graphite layers of Zn/Al-ion battery. Therefore, pencil graphite due to its excellent electro-oxidation and conducting properties, can be successfully implemented as low cost, disposable and green material for both sensor and energy-storage applications.

Low-cost smartphone-controlled potentiostat based on Arduino for teaching electrochemistry fundamentals and applications

Accessibility to potentiostats is crucial for research development in electrochemistry, but their cost is the principal drawback for their massive use. With the aim to provide an affordable alternative for resource-constrained communities, we present a low-cost, portable electrochemical workstation that integrates an open-source potentiostat based on Arduino and a smartphone application. This graphical user interface allows easy control of electrochemical parameters and real-time visualization of the results. This potentiostat can perform the most used electrochemical techniques of cyclic and linear voltammetry and chronoamperometry, with an operating range of ±225 μA and ±1.50 V, and results that are comparable with those obtained with commercial potentiostats. Three applications reported here demonstrate the capacity and the good performance of this low-cost potentiostat as a teaching tool: identification of redox pairs, electrochemical characterization of pencil graphite electrodes, and detection of heavy metals using an electrodeposited film of bismuth on the pencil graphite electrode. Furthermore, detailed schemes of the device and its software are entirely available, expecting to provide an open-source potentiostat easy to replicate to further support education in electrochemical fundamentals and instrumentation.

Electrochemical prostate-specific antigen biosensors based on electroconductive nanomaterials and polymers

Prostate cancer (PCa), the second most malignant neoplasm in men, is also the fifth leading cause of cancer-related deaths in men globally. Unfortunately, this malignancy remains largely asymptomatic until late-stage emergence when treatment is limited due to the lack of effective metastatic PCa therapeutics. Due to these limitations, early PCa detection through prostate-specific antigen (PSA) screening has become increasingly important, resulting in a more than 50% decrease in mortality. Conventional assays for PSA detection, such as enzyme-linked immunosorbent assay (ELISA), are labor intensive, relatively expensive, operator-dependent and do not provide adequate sensitivity. Electrochemical biosensors overcome these limitations because they are rapid, cost-effective, simple to use and ultrasensitive. This article reviews electrochemical PSA biosensors using electroconductive nanomaterials such as carbon-, metal-, metal oxide- and peptide-based nanostructures, as well as polymers to significantly improve conductivity and enhance sensitivity. Challenges associated with the development of these devices are discussed thus providing additional insight into their analytic strength as well as their potential use in early PCa detection.

Prototyping of a highly sensitive and selective chemisresistive sensor based on pencil graphite for the rapid detection of NO2 and NH3

Commercially available high quality 9B pencil graphite was used for sensing of trace concentrations of nitrogen dioxide (NO₂) and ammonia (NH₃) at sub-ppm levels in air at ambient temperature and pressure.

Paracetamol Sensing with a Pencil Lead Electrode Modified with Carbon Nanotubes and Polyvinylpyrrolidone

The determination of paracetamol is a common need in pharmaceutical and environmental samples for which a low-cost, rapid, and accurate sensor would be highly desirable. We develop a novel pencil graphite lead electrode (PGE) modified with single-wall carbon nanotubes (SWCNTs) and polyvinylpyrrolidone (PVP) polymer (PVP/SWCNT/PGE) for the voltammetric quantification of paracetamol. The sensor shows remarkable analytical performance in the determination of paracetamol at neutral pH, with a limit of detection of 0.38 μM and a linear response from 1 to 500 μM using square-wave voltammetry (SWV), which are well suited to the analysis of pharmaceutical preparations. The introduction of the polymer PVP can cause dramatic changes in the sensing performance of the electrode, depending on its specific architecture. These effects were investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results indicate that the co-localization and dispersion of PVP throughout the carbon nanotubes on the electrode are key to its superior electrochemical performance, facilitating the electrical contact between the nanotubes and with the electrode surface. The application of this sensor to commercial syrup and tablet preparations is demonstrated with excellent results.

Nanostructured pencil graphite electrodes for application as high power biocathodes in miniaturized biofuel cells and bio-batteries

This work describes a simple method for the fabrication of an enzymatic electrode with high sensitivity to oxygen and good performance when applied as biocathode. Pencil graphite electrodes (PGE) were chosen as disposable transducers given their availability and good electrochemical response. After electrochemical characterization regarding hardness and surface pre-treatment suited modification with carbon-based nanostructures, namely with reduced graphene, MWCNT and carbon black for optimal performance was proceeded. The bioelectrode was finally assembled through immobilization of bilirubin oxidase (BOx) lashed on the modified surface of MWCNT via π-π stacking and amide bond functionalization. The high sensitivity towards dissolved oxygen of 648 ± 51 µA mM-1 cm-2, and a LOD of 1.7 µM, was achieved for the PGE with surface previously modified with reduced graphene (rGO), almost the double registered for direct anchorage on the bare PGE surface. Polarization curves resulted in an open circuit potential (OCP) of 1.68 V (vs Zn electrode) and generated a maximum current density of about 650 μA cm-2 in O2 saturated solution.

A novel copper(ıı) phthalocyanine-modified multiwalled carbon nanotube-based electrode for sensitive electrochemical detection of bisphenol A

A novel copper(ii) phthalocyanine (CuPc)-modified multiwalled carbon nanotube-based electrode was prepared for the sensitive electrochemical detection of bisphenol A, by the modification of a pencil graphite electrode via the adsorption method.