Electrochemical simultaneous determination of hydroquinone, catechol, bisphenol A, and bisphenol S using a novel mesoporous nickel-modified carbon sensor.

The widespread occurrence of endocrine disruptor compounds in wastewater has garnered significant attention owing to their toxicity, even at low concentrations, and their persistence in the water body. Among various analytical techniques, electrochemical sensors become popular for the environmental monitoring of water pollutants due to their low cost, rapid detection, high sensitivity, and selectivity. In this study, the mesoporous Ni (MNi) material was synthesized with an innovative method using Pluronic™ F-127 as a soft template and applied as a modifier for the simultaneous electrochemical sensing of hydroquinone (HQ), catechol (CC), bisphenol A (BPA), and bisphenol S (BPS). MNi with high porosity efficiently enhanced the redox-active surface area and conductivity of the glassy carbon electrode contributing to a significantly improved sensitivity in the detection of target chemicals. The pore size and surface area of MNi were estimated based on atomic force microscopy and Brunauer Emmett and Teller techniques to be ∼14.2 nm and 31.1 m2 g-1, respectively. The limit of detection for HQ, CC, BPA, and BPS was determined to be 5.3, 5.7, 5.6, and 61.5 nM, respectively. The electrochemical sensor presented in this study holds promise as a platform for developing portable and miniaturized tools offering the rapid and sensitive detection of these hazardous phenolic compounds in environmental water samples.

Ultralight 3D Graphene Oxide Aerogel Decorated with Pd-Fe Nanoparticles for the Simultaneous Detection of Eight Biomolecules.

In this proof-of-concept study, an ultralight graphene oxide aerogel (GOx-Aero) decorated with bimetallic palladium-iron nanoparticles (Pd-Fe) was synthesized and immobilized on a glassy carbon electrode (GCE) for electrochemical sensor applications. The main objective of this work was to develop a sensitive electrochemical sensor capable of simultaneously detecting eight biomolecules, including ascorbic acid (AA), dopamine (DA), uric acid (UA), 8-hydroxyguanine (8HG), guanine (G), adenine (A), thymine (T), and cytosine (C). To the best of our knowledge, this is the first time that an electrochemical sensor has been able to detect eight biomolecules simultaneously. The bimetallic GOx aerogel significantly enhanced the performance of the sensor by increasing the electroactive area, conductivity, and anodic peak current response. The sensor demonstrated sharp, well-defined, and continuous oxidation peaks for all eight analytes of interest and wide linear ranges of 5.0-1750, 0.25-100.0, 0.5-500.0, 0.5-375.0, 0.5-500.0, 0.5-500.0, 5.0-1500.0, and 5.0-1500.0 µM for AA, DA, UA, 8HG, G, A, T, and C, respectively. The prepared sensor also exhibited excellent stability, reproducibility, and sensitivity with a very low limit of detection (LOD) of 553.7, 1.8, 69.6, 43.2, 42.9, 72.3, 57.2, and 318.4 nM for AA, DA, UA, 8HG, G, A, T, and C, respectively. The Pd-Fe-GOx-Aero-GCE was also tested in various real samples such as artificial saliva, artificial cerebrospinal fluid (CSF), salmon sperm DNA, and genomic DNA from calf thymus, where it demonstrated good recovery values. Additionally, the novel developed sensor was used to monitor the interaction between the anticancer drug, cisplatin, which has well-described binding affinity with the G and A bases in DNA. Overall, Pd-Fe-GOx-Aero-GCE displayed an extremely promising platform not only for the simultaneous detection of eight biomolecules in complex biological matrices but also for DNA-drug interaction studies toward the development of electrochemical high-throughput drug screening assays, which is of great importance in the field.

Hybrid Nanomaterial of Graphene Oxide Quantum Dots with Multi-Walled Carbon Nanotubes for Simultaneous Voltammetric Determination of Four DNA Bases.

In this proof-of-concept study, a novel hybrid nanomaterial-based electrochemical sensor was developed for the simultaneous detection of four DNA bases. For the modification of the working electrode surface, graphene oxide quantum dots (GOQDs) were synthesized using a solvothermal method. GOQDs were then used for the preparation of a hybrid nanomaterial with multi-walled carbon nanotubes (GOQD-MWCNT) using a solvothermal technique for the first time. Transmission electron microscopy (TEM) was used to characterize the GOQDs-MWCNTs. A glassy carbon electrode (GCE) was modified with the GOQDs-MWCNTs using Nafion™ to prepare a GOQD-MWCNT/GCE for the simultaneous determination of four DNA bases in phosphate buffer solution (PBS, pH 7.0) using differential pulse voltammetry (DPV). The calibration plots were linear up to 50, 50, 500, and 500 µM with a limit of detection at 0.44, 0.2, 1.6, and 5.6 µM for guanine (G), adenine (A), thymine (T) and cytosine (C), respectively. The hybrid-modified sensor was used for the determination of G, A, T, and C spiked in the artificial saliva samples with the recovery values ranging from 95.9 to 106.8%. This novel hybrid-modified electrochemical sensor provides a promising platform for the future development of a device for cost-effective and efficient simultaneous detection of DNA bases in real biological and environmental samples.

Durum wheat semolina-modified ceramic membranes as novel porous separators for enhanced power generation and wastewater remediation using microbial fuel cell.

This proof-of-concept study describes the enhanced performance efficiency of the dual-chambered microbial fuel cell equipped with the fabricated unmodified ceramic membranes and ceramic membranes modified with 5 % and 10 % (w/w) durum wheat semolina in comparison with the commercially available NafionTM 117 membranes. The chemical oxygen demand removal efficiencies were determined to be 85.6 ± 0.1, 72.1 ± 0.2 and 68.6 ± 0.1 % for microbial fuel cell equipped with 10 % (w/w) semolina-modified, 5 % (w/w) semolina-modified and unmodified ceramic membrane, respectively, which indicated the improved wastewater treatment efficiency with increasing content of semolina. Preliminary studies showed that the 10 % (w/w) semolina-modified ceramic was cost-effective (64 USD/m2) with improved water uptake, good proton mobility, low oxygen diffusion in addition to the enhanced power and current density output. The semolina-modified ceramic membranes have the potential to become a cost-effective alternative for the high-efficiency production of bioelectricity using microbial fuel cells.

Electrografting a Hybrid Bilayer Membrane via Diazonium Chemistry for Electrochemical Impedance Spectroscopy of Amyloid-ß Aggregation.

Herein, a novel hybrid bilayer membrane is introduced as a platform to study the aggregation of amyloid-ß1-42 (Aß1-42) peptide on surfaces. The first layer was covalently attached to a glassy carbon electrode (GCE) via diazonium electrodeposition, which provided a highly stable template for the hybrid bilayer formation. To prepare the long-chain hybrid bilayer membrane (lcHBLM)-modified electrodes, GCE surfaces were modified with 4-dodecylbenzenediazonium (DDAN) followed by the modification with dihexadecyl phosphate (DHP) as the second layer. For the preparation of short-chain hybrid bilayer membrane (scHBLM)-modified electrodes, GCE surfaces were modified with 4-ethyldiazonium (EDAN) as the first layer and bis(2-ethylhexyl) phosphate (BEHP) was utilized as the second layer. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to characterize the bilayer formation. Both positively charged [Ru(NH3)6]3+ and negatively charged ([Fe(CN)6]3-/4-) redox probes were used for electrochemical characterization of the modified surfaces using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS results showed a decrease in charge transfer resistance (Rct) upon incubation of Aß1-42 on the hybrid bilayer-modified surfaces. This framework provides a promising electrochemical platform for designing hybrid bilayers with various physicochemical properties to study the interaction of membrane-bound receptors and biomolecules on surfaces.

Understanding the Inhibitory and Antioxidant Effects of Pyrroloquinoline Quinone (PQQ) on Copper(II)-Induced α-Synuclein-119 Aggregation.

Parkinson's disease (PD) is associated with the aggregation and misfolding of a-synuclein (a-syn) protein in dopaminergic neurons. The misfolding process is heavily linked to copper dysregulation in PD. Experimental evidence supports the hypothesis that the co-presence of Cu(II) and α-syn facilitates the aggregation of α-syn, affecting the pathological development of PD. Recent literature has shown that pyrroloquinoline quinone (PQQ) contains strong neuroprotective activity by reducing the reactive oxygen species (ROS) production by α-syn. Despite these known facts, minimal studies have been done on the antioxidant effect of PQQ against ROS formation in the presence of Cu(II) and α-syn-119. Thus, it is of great significance to study the interaction between all three components, PQQ, Cu(II), and α-syn-119. In this proof-of-concept study, a variety of chemical techniques were employed to examine the antioxidant effect of PQQ on ROS that α-syn-119 produced in the presence of Cu(II). Our results showed that PQQ effectively prevented ROS formation in SH-SY5Y human differentiated neuronal cells. Thioflavin T (ThT) fluorescence assay, circular dichroism (CD) spectroscopy, and transmission electron microscopy (TEM) were applied, where PQQ was able to actively prevent fibrillation of α-syn-119 in the presence of Cu(II). This finding was further confirmed using electrochemical impedance spectroscopy (EIS), where the binding of PQQ to the α-syn-119 suppressed the aggregation process on the electrode surface. With these encouraging results, we envisage that PQQ and its derivatives can be a promising candidate for further studies as a multitarget therapeutic agent toward PD therapy.

Do glutathione and copper interact to modify Alzheimer's disease pathogenesis?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder first described in 1906 that is currently estimated to impact ∼40 million people worldwide. Extensive research activities have led to a wealth of information on the pathogenesis, hallmarks, and risk factors of AD; however, therapeutic options remain extremely limited. The large number of pathogenic factors that have been reported to potentially contribute to AD include copper dyshomeostasis as well as increased oxidative stress, which is related to alterations to molecular antioxidants like glutathione (GSH). While the individual roles of GSH and copper in AD have been studied by many research groups, their interactions have received relatively little attention, although they appear to interact and affect each other's regulation. Existing knowledge on how GSH-copper interactions may affect AD is sparse and lacks focus. This review first highlights the most relevant individual roles that GSH and copper play in physiology and AD, and then collects and assesses research concerning their interactions, in an effort to provide a more accessible and understandable picture of the role of GSH, copper, and their interactions in AD.

Electrochemical flow injection analysis of the interaction between pyrroloquinoline quinone (PQQ) and α-synuclein peptides related to Parkinson's disease.

α-Synuclein (α-syn) is a hallmark protein of Parkinson's disease (PD). The aggregation process of α-syn has been heavily associated with the pathogenesis of PD. With the exponentially growing number of potential therapeutic compounds that can inhibit the aggregation of α-syn, there is now a significant demand for a high-throughput analysis system. Herein, a novel flow injection analysis system with an electrochemical biosensor as the detector was developed to study the interaction of a well-described antioxidant and amyloid inhibitor, pyrroloquinoline quinone (PQQ) with α-synuclein peptides. Screen-printed gold electrodes (SPEs) were modified using heptapeptides from α-syn wild-type (WT) and mutants such as lysine knock-out (ETEE) and E46K. Affinity binding events between these peptides and PQQ were analyzed by electrochemical impedance spectroscopy (EIS) and further confirmed by high-performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS), and nuclear magnetic resonance (NMR) spectroscopy. HPLC and LC/MS results revealed that PQQ formed a stable complex with α-syn. NMR results confirmed that the α-syn-PQQ complex was formed via a Schiff base formation-like process. In addition, results showed that lysine residues influenced the binding event, in which the presence of an extra lysine stabilized the α-syn-PQQ complex, and the absence of a lysine significantly decreased the interaction of α-syn with PQQ. Therefore, we concluded that EIS is a promising technique for the evaluation of the interaction between PQQ-based amyloid inhibitors and α-syn. The electrochemical flow injection analysis assembly provided a rapid and low-cost drug discovery platform for the evaluation of small molecule-protein interactions.

Electrochemical biosensors for biometal-protein interactions in neurodegenerative diseases.

Electrochemical biosensors have been adopted into a wide range of applications in the study of biometal-protein interactions in neurodegenerative diseases. Transition metals such as zinc, copper, and iron that are significant to biological functions have been shown to have strong implications in the progressive neural degeneration in Alzheimer's disease (AD), Parkinson's disease (PD), and prion protein diseases. This review presents a summative examination of the progress made in the design, fabrication, and applications of electrochemical biosensors in recent literature at understanding the metal-protein interactions in neurodegenerative diseases. The focus will be drawn on disease-causing biomarkers such as amyloid-ß (Aß) and tau proteins for AD, α-synuclein (α-syn) for PD, and prion proteins (PrP). Topics such as the use of electrochemical biosensing in monitoring biometal-induced conformational changes, elucidation of complexation motifs, production of reactive oxygen species (ROS) as well as the influence on downstream biomolecular interactions will be discussed. Major results and important concepts presented in these studies will be summarized in the hope to spark inspiration for the next generation of electrochemical sensors.

Electrochemical Biosensors for the Detection of SARS-CoV-2 and Other Viruses.

The last few decades have been plagued by viral outbreaks that present some of the biggest challenges to public safety. The current coronavirus (COVID-19) disease pandemic has exponentiated these concerns. Increased research on diagnostic tools is currently being implemented in order to assist with rapid identification of the virus, as mass diagnosis and containment is the best way to prevent the outbreak of the virus. Accordingly, there is a growing urgency to establish a point-of-care device for the rapid detection of coronavirus to prevent subsequent spread. This device needs to be sensitive, selective, and exhibit rapid diagnostic capabilities. Electrochemical biosensors have demonstrated these traits and, hence, serve as promising candidates for the detection of viruses. This review summarizes the designs and features of electrochemical biosensors developed for some past and current pandemic or epidemic viruses, including influenza, HIV, Ebola, and Zika. Alongside the design, this review also discusses the detection principles, fabrication techniques, and applications of the biosensors. Finally, research and perspective of biosensors as potential detection tools for the rapid identification of SARS-CoV-2 is discussed.

Synergistic influence of mesoporous spinel nickel ferrite on the electrocatalytic activity of nano-structured palladium.

Structure and surface area are critical factors for catalysts in fuel cells. Hence, a spinel nickel ferrite mesoporous (SNFM) is prepared via the solution combustion technique, an efficient and one-step synthesis. Dynamic X-ray analysis has clarified the structural properties of SNFM. The grain size of SNFM is determined to be ∼11.6 nm. The specific surface area (87.69 m2. g-1) of SNFM is obtained via the Brunauer-Emmett-Teller method. The Barrett-Joyner-Halenda pore size distributions revealed that the size of the mesopores in as-synthesized SNFM mainly falls in the size range of 2-16 nm. Scanning electron microscopy studies showed the regularities involved during porous-structure formation. SNFM is employed as the support for nano-structured palladium (PdNS). Field emission scanning electron microscope studies of PdNS-SNFM showed the deposition of PdNS in cavities and on/in the pores of SNFM. The electrochemical surface area obtained for PdNS-SNFM is about 27 times larger than that of PdNS via cyclic voltammetry. The electrochemical studies are utilized to study the features and catalytic performance of PdNS-SNFM in the electro-oxidation of diverse small organic fuels, whereas the electrooxidation of diethylene glycol is reported for first-time.

Experimental and computational interaction studies of terbium (III) and lanthanide (III) complexes containing 2,2'-bipyridine with bovine serum albumin and their in vitro anticancer and antimicrobial activities.

To investigate the chemotherapeutic and pharmacokinetic aspects of two lanthanide complexes (Tb(III) and La(III) containing 2,2'-bipyridine ligand), in vitro binding studies were carried out with BSA by employing multiple biophysical methods and molecular modeling study. There are different techniques containing fluorescence, absorption spectroscopy and competitive experiments to determine the interaction mode between BSA and these complexes. These complexes efficiently quenched the BSA emission through a static procedure. The results showed that the terbium and lanthanum complexes exhibited a high propensity for BSA interaction via van der Waals force. Further, competitive examination and docking study showed that the interaction site of these complexes on BSA is site III. The results of docking calculations were in good agreement with experimental examinations. Also, the energy transfer from BSA to these complexes has happened with high possibility. Moreover, antimicrobial studies of different bacterial and fungi indicated its promising antibacterial activity. In vitro cytotoxicity of the Tb complex and La complex was carried out in MCF-7 and A-549 cell lines, which revealed significantly good activity.Communicated by Ramaswamy H. Sarma.

Polyacrylamide hydrogels doped with different shapes of silver nanoparticles: Antibacterial and mechanical properties.

The incorporation of nanoparticles into a hydrogel matrix enables the development of innovative smart materials with enhanced biophysical properties. In this proof-of-concept study, we encapsulated different shapes (spherical, triangular and rod) of silver nanoparticles (AgNPs) within a hydrogel matrix of polyacrylamide (PAA) and N-methylenebisacrylamide (MBA) (PAA-MBA) to investigate whether these hydrogels exhibited shape-dependent antimicrobial and mechanical properties. We examined the mechanism of adsorption of different shapes of AgNPs using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Results showed that the adsorption of AgNPs was primarily occurring on the surface/outer pores of the PAA-MBA hydrogel and that rod AgNPs demonstrated a relatively slower adsorption within the hydrogel matrix. The mechanical properties of AgNP-doped hydrogels were evaluated using rheology and atomic force microscopy (AFM) quantitative imaging. We observed a higher storage and Young's modulus which proved that the incorporation of the various shapes of AgNPs increased the mechanical properties of the hydrogels with no significant differences between the different shapes. While both spherical and triangular AgNP-doped hydrogels showed strong antimicrobial activity, the hydrogel with the rod AgNPs had a relatively lower antimicrobial activity. Overall, our preliminary results demonstrated that nanocomposite hydrogels were promising materials for applications in the future development of wound dressings.

Attenuation of Oxidative Stress by Cannabinoids and Cannabis Extracts in Differentiated Neuronal Cells.

In this proof-of-concept study, the antioxidant activity of phytocannabinoids, namely cannabidiol (CBD) and Δ9- tetrahydrocannabinol (THC), were investigated using an in vitro system of differentiated human neuronal SY-SH5Y cells. The oxidative stress was induced by hydrogen peroxide, as reactive oxygen species (ROS). Alzheimer's disease (AD)-like pathological conditions were mimicked in vitro by treating the differentiated neuronal cells with amyloid-ß1-42 (Aß1-42) in the presence of Cu(II). We showed that THC had a high potency to combat oxidative stress in both in vitro models, while CBD did not show a remarkable antioxidant activity. The cannabis extracts also exhibited a significant antioxidant activity, which depended on the ratio of the THC and CBD. However, our results did not suggest any antagonist effect of the CBD on the antioxidant activity of THC. The effect of cannabis extracts on the cell viability of differentiated human neuronal SY-SH5Y cells was also investigated, which emphasized the differences between the bioactivity of cannabis extracts due to their composition. Our preliminary results demonstrated that cannabis extracts and phytocannabinoids have a promising potential as antioxidants, which can be further investigated to develop novel pharmaceuticals targeting oxidative stress therapy.

Recent Advances in Monitoring Cell Behavior Using Cell-Based Impedance Spectroscopy.

Cell-based impedance spectroscopy (CBI) is a powerful tool that uses the principles of electrochemical impedance spectroscopy (EIS) by measuring changes in electrical impedance relative to a voltage applied to a cell layer. CBI provides a promising platform for the detection of several properties of cells including the adhesion, motility, proliferation, viability and metabolism of a cell culture. This review gives a brief overview of the theory, instrumentation, and detection principles of CBI. The recent applications of the technique are given in detail for research into cancer, neurodegenerative diseases, toxicology as well as its application to 2D and 3D in vitro cell cultures. CBI has been established as a biophysical marker to provide quantitative cellular information, which can readily be adapted for single-cell analysis to complement the existing biomarkers for clinical research on disease progression.

Evaluation of parent and nano-encapsulated terbium(III) complex toward its photoluminescence properties, FS-DNA, BSA binding affinity, and biological applications.

BACKGROUND: There is a crucial need for finding and developing new compounds as the anticancer and antimicrobial agents with better activity, specific target, and less toxic side effects. OBJECTIVES: Base on the potential anticancer properties of lanthanide complexes, in the paper, the biological applications of terbium (Tb) complex, containing 2,9-dimethyl- 1,10-phenanthroline (Me2Phen) such as anticancer, antimicrobial, DNA cleavage ability, the interaction with FS-DNA (Fish-Salmon DNA) and BSA (Bovine Serum Albumin) was examined. METHODS: The interaction of Tb-complex with BSA and DNA was studied by emission spectroscopy, absorption titration, viscosity measurement, CD spectroscopy, competitive experiments, and docking calculation. Also, the ability of this complex to cleave DNA was reported by gel electrophoresis. Tb-complex was concurrently screened for its antibacterial activities by different methods. Besides, the nanocarriers of Tb-complex (lipid nanoencapsulation (LNEP) and the starch nanoencapsulation (SNEP)), as active anticancer candidates, were prepared. MTT technique was applied to measure the antitumor properties of these compounds on human cancer cell lines. RESULTS: The experimental and docking results suggest significant binding between DNA as well as BSA with terbium-complex. Besides, groove binding plays the main role in the binding of this compound with DNA and BSA. The competitive experiment with hemin demonstrated that the terbium complex was bound at site III of BSA, which was confirmed by the docking study. Also, Tb-complex was concurrently screened for its DNA cleavage, antimicrobial, and anticancer activities. The anticancer properties of LNEP and SNEP are more than the terbium compound. CONCLUSIONS: Tb-complex can bond to DNA/BSA with high binding affinity. Base on biological applications of Tb-complex, it can be concluded that this complex and its nanocarriers can suggest as novel anticancer, antimicrobial candidates.

Graphene Oxide Nanoribbons in Chitosan for Simultaneous Electrochemical Detection of Guanine, Adenine, Thymine and Cytosine.

Herein, graphene oxide nanoribbons (GONRs) were obtained from the oxidative unzipping of multi-walled carbon nanotubes. Covalent coupling reaction of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxy succinimide (NHS) with amine functional groups (-NH2) of the chitosan natural polymer (CH) was used for entrapping GONRs on the activated glassy carbon electrode (GCE/GONRs-CH). The nanocomposite was characterized by high-resolution transmission electron microscopy (HRTEM), and field-emission scanning electron microscopy (FESEM). In addition, the modification steps were monitored using FTIR. The nanocomposite-modified electrode was used for the simultaneous electrochemical determination of four DNA bases; guanine (G), adenine (A), thymine (T) and cytosine (C). The nanocomposite-modified GCE displayed a strong, stable and continuous four oxidation peaks during electrochemistry detection at potentials 0.63, 0.89, 1.13 and 1.27 V for G, A, T and C, respectively. The calibration curves were linear up to 256, 172, 855 and 342 µM with detection limits of 0.002, 0.023, 1.330 and 0.641 µM for G, A, T and C, respectively. The analytical performance of the GCE/GONRs-CH has been used for the determination of G, A, T and C in real samples and obtained a recovery percentage from 91.1%-104.7%. Our preliminary results demonstrated that GCE/GONRs-CH provided a promising platform to detect all four DNA bases for future studies on DNA damage and mutations.

Simultaneous Determination of Four DNA bases at Graphene Oxide/Multi-Walled Carbon Nanotube Nanocomposite-Modified Electrode.

In this study, we developed a modified glassy carbon electrode (GCE) with graphene oxide, multi-walled carbon nanotube hybrid nanocomposite in chitosan (GCE/GO-MWCNT-CHT) to achieve simultaneous detection of four nucleobases (i.e., guanine (G), adenine (A), thymine (T) and cytosine (C)) along with uric acid (UA) as an internal standard. The nanocomposite was characterized using TEM and FT-IR. The linearity ranges were up to 151.0, 78.0, 79.5, 227.5, and 162.5 µM with a detection limit of 0.15, 0.12, 0.44, 4.02, 4.0, and 3.30 µM for UA, G, A, T, and C, respectively. Compared to a bare GCE, the nanocomposite-modified GCE demonstrated a large enhancement (~36.6%) of the electrochemical active surface area. Through chronoamperometric studies, the diffusion coefficients (D), standard catalytic rate constant (Ks), and heterogenous rate constant (Kh) were calculated for the analytes. Moreover, the nanocomposite-modified electrode was used for simultaneous detection in human serum, human saliva, and artificial saliva samples with recovery values ranging from 95% to 105%.

Thiol functionalized carbon ceramic electrode modified with multi-walled carbon nanotubes and gold nanoparticles for simultaneous determination of purine derivatives.

In this proof-of-concept study, a thiol-functionalized sol-gel-based carbon ceramic electrode (CCE) was developed. This CCE was further modified by immobilizing gold nanoparticles (AuNP) in the thiol-functionalized ceramic matrix as well as incorporating multi-walled carbon nanotubes (MWCNT) within the pores of this ceramic sol-gel. The proposed electrode (MWCNT-AuNP-CCE) was used for the simultaneous determination of purine derivatives, uric acid (UA), xanthine (XA) and caffeine (CA). The simultaneous detection of these compounds is essential because these purine derivatives often coexist in real samples. Moreover, since these analytes have the capacity to interchange structures, developing a simultaneous detector is important. This electrode was successfully characterized using environmental scanning electron microscopy (ESEM) with secondary and back scattering electron detectors, energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), and Fourier-transform infrared (FT-IR) spectroscopy. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements were performed in phosphate buffer solution (0.1 M PBS, pH 6) at a potential window of 0.2 to 1.1 V (vs. Ag/AgCl). The proposed modified electrode (MWCNT-AuNP-CCE) displayed three well-defined, stable and continuous oxidation peaks at 0.3, 0.7 and 1.0 V for UA, XA, and CA, respectively. The resulting catalytic current at the surfaces showed a linear dependence to the concentrations of UA, XA and CA for up to 225, 225 and 1500 µM, respectively. The limit of detection was determined to be 50, 63 and 354 nM for UA, XA and CA, respectively. The analytical performance of MWCNT-AuNP-CCE was challenged with real samples such as human serum and urine with recoveries ranging between 98.1 and 102.6%. Moreover, the selectivity of sensor was further challenged with very similar purine molecules, theobromine and theophylline, which contain one less methyl group than CA. Overall, MWCNT-AuNP-CCE exhibited a promising platform for the future development of sensitive electrochemical sensors for the detection of purine derivatives in real samples.

Prussian blue-doped nanosized polyaniline for electrochemical detection of benzenediol isomers.

Simultaneous speciation of benzenediol isomers (BDIs), 1,2-benzenediol (catechol, CC), 1,3-benzenediol (resorcinol, RS), and 1,4-benzenediol (hydroquinone, HQ), was investigated by differential pulse voltammetry (DPV) using a graphite paste electrode (GPE) modified with Prussian blue-polyaniline nanocomposite. The modified GPE showed good stability, sensitivity, and selectivity properties for all the three BDIs. Prussian blue-doped nanosized polyaniline (PBNS-PANI) was synthesized first by using mechanochemical reactions between aniline and ferric chloride hexahydrate as the oxidants and then followed by the addition of potassium hexacyanoferrate(II) in a solid-state and template-free technique. The material was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The DPV measurements are performed in phosphate electrolyte solution with pH 4.0 at a potential range of - 0.1 to 1.0 V. The proposed modified electrode displayed a strong, stable, and continuous three well-separated oxidation peaks towards electrooxidation at potentials 0.20, 0.31, and 0.76 V for HQ, CC, and RS, respectively. The calibration curves were linear from 1 to 350.5 µM for both HQ and CC, while for RS, it was from 2 to 350.5 µM. The limit of detection was determined to be 0.18, 0.01, and 0.02 µM for HQ, CC, and RS, respectively. The analytical performance of the PBNS-PANI/GPE has been evaluated for simultaneous determination of HQ, CC, and RS in creek water, commercial hair dye, and skin whitening cream samples with satisfactory recoveries between 90 and 106%. Overall, we demonstrated that the presence of NS-PANI and PB resulted in a large redox-active surface area that enabled a promising analytical platform for simultaneous detection of BDIs. Graphical abstract.