Photoelectrochemical determination of phloroglucinol based on a combination of a ceramic perovskite and bismuth vanadate.

Phloroglucinol (PL) or 1,3,5-trihydroxybenzene is a phenolic compound used therapeutically for its antispasmodic properties. However, an overdose or prolonged exposure to PL can have harmful effects on human health. This work describes for the first time the development of a photoelectrochemical (PEC) sensor to determine PL. The proposed sensor is based on a fluorine-doped tin oxide (FTO) substrate modified with bismuth calcium tantalate (CaBi2Ta2O9), a ceramic perovskite powder, and bismuth vanadate (BiVO4). Both materials were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The morphology of the BiVO4/CaBi2Ta2O9/FTO platform was evaluated using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The photoelectrochemical response of the platform was evaluated by exploiting with light from a 36 W LED lamp confined in a low-cost homemade box. The BiVO4/CaBi2Ta2O9/FTO sensor showed superior photocurrent response compared to the FTO modified by the individual components (BiVO4/FTO and CaBi2Ta2O9/FTO). Under optimized experimental conditions, the photoelectrochemical sensor showed two linear ranges for PL concentrations ranging from 1 up to 900 µmol L-1 and from 900 up to 2000 µmol L-1, respectively.  The BiVO4/CaBi2Ta2O9/FTO sensor exhibited excellent results regarding precision, accuracy, and selectivity for PL detection. PL determination was successfully performed in water and artificial urine samples, with recovery values between 100.1 and 102.2%.

CRISPR-based electrochemical biosensors: an alternative for point-of-care diagnostics?

The combination of CRISPR technology and electrochemical sensors has sparked a paradigm shift in the landscape of point-of-care (POC) diagnostics. This review explores the dynamic convergence between CRISPR and electrochemical sensing, elucidating their roles in rapid and precise biosensing platforms. CRISPR, renowned for its remarkable precision in genome editing and programmability capability, has found a novel application in conjunction with electrochemical sensors, promising highly sensitive and specific detection of nucleic acids and biomarkers associated with diverse diseases. This article navigates through fundamental principles, research developments, and applications of CRISPR-based electrochemical sensors, highlighting their potential to revolutionize healthcare accessibility and patient outcomes. In addition, some key points and challenges regarding applying CRISPR-powered electrochemical sensors in real POC settings are presented. By discussing recent advancements and challenges in this interdisciplinary field, this review evaluates the potential of these innovative sensors as an alternative for decentralized, rapid, and accurate POC testing, offering some insights into their applications across clinical scenarios and their impact on the future of diagnostics.

The Electronic Origin of the Zeta Potential is Supported by the Redox Mechanism on an Aqueous Dispersion of Exfoliated Graphite.

Herein we have proposed that a redox mechanism can produce surface charges and negative zeta potential on an aqueous graphite dispersion. Graphite was kept in contact with a concentrated ammonia aqueous solution, washed, and exfoliated in water, resulting in a dispersion with lyophobic nature. Ammonia treatment did not provide functional groups or nitrogen doping to graphite. Moreover, this material was washed twice before sonication to remove most hydroxide. Therefore, neither functional groups, nitrogen atoms, nor hydroxide excess is responsible for the zeta potential. Kelvin probe force microscopy has shown that the ammonia-treated and exfoliated graphite has higher Fermi level than the water-treated material, indicating that the contact between ammonia and graphite promotes redox reactions that provide electrons to graphite. These electrons raise the Fermi level of graphite and generate the negative zeta potential, consequently, they account for the colloidal stability.

A copper-based metal-organic framework/reduced graphene oxide-modified electrode for electrochemical detection of paraquat.

An electrochemical device using copper-based metalorganic franmeworks (MOF) associated with reduced graphene oxide to improve the charge transfer, stability, and adherence of the structures on the surface of the electrodes was developed. The syntheses of these materials were confirmed using scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared and Raman spectroscopy. For the first time, this type of sensor was applied to a systematic study to understand the action mechanism of MOFs and reduced graphene oxide in the electrochemical detection of paraquat pesticide. Under optimized conditions, paraquat was detected in standard solutions by differential pulse voltammetry (- 0.8 to - 0.3 V vs Ag/AgCl), achieving a linear response range between 0.30 and 5.00 µmol L-1. The limits of detection and quantification were 50.0 nmol L-1 and 150.0 nmol L-1, respectively. We assessed the accuracy of the proposed device to determine paraquat in water and human blood serum samples by recovery study, obtaining recovery values ranging from 98 to 104%. Furthermore, the selectivity of the proposed electrode for paraquat detection was evaluated against various interferences, demonstrating their promising application in environmental analysis.

IL-6 and IL-10 are associated with disease severity and higher comorbidity in adults with COVID-19.

AIM: COVID-19 pandemic has caused extensive burden on public life and health care worldwide. This study aimed to assess circulating levels of inflammatory cytokines in adult patients who were hospitalized with COVID-19 and stratified according to age (older or younger than 65 years) aiming to explore associations between these markers of inflammation and comorbidities. METHODS: This was a cross-sectional study of 142 COVID-19 patients consecutively admitted to the University Hospital of the Federal University of São Carlos, from July to October 2020. Sociodemographic data, chronic comorbidities, and baseline NEWS2 and SOFA for clinical deterioration were obtained at hospital admission. Serum levels of inflammatory cytokines were determined by flow cytometry. RESULTS: Older adults with COVID-19 had higher serum levels of IL-6 and IL-10 as compared to those under 65 years of age (p < 0.001 and p = 0.003, respectively). IL-10 was independently associated with age (p = 0.04) and severity of the disease (p = 0.05), whereas serum levels of IL-6 were not directly associated with age (p = 0.5). The comorbidity index seems to be the main responsible for this, being significantly associated with IL-6 levels among those aged 65 and over (p = 0.007), in addition to the severity of the disease. CONCLUSIONS: Higher serum levels of IL-6 and IL-10 are associated with the severity of the disease and a higher comorbidity index among adults aged 65 and over with COVID-19. This should raise awareness of the importance of comorbidity index, rather than age, during risk stratification.

Gravity-assisted distillation on a chip: Fabrication, characterization, and applications.

Distillation is widely used in industrial processes and laboratories for sample pre-treatment. The conventional apparatus of flash distillation is composed of heating source, distilling flask, condenser, and receiving flask. As disadvantages, this method shows manual and laborious analyses with high consumption of chemicals. In this paper, all these limitations were addressed by developing a fully integrated microscale distiller in agreement with the apparatus of conventional flash distillation. The main challenge facing the distillation miniaturization is the phase separation since surface forces take over from the gravity in microscale channels. Otherwise, our chip had ability to perform gravity-assisted distillations because of the somewhat large dimensions of the distillation chamber (roughly 900 µL) that was obtained by 3D-printing. The functional distillation units were integrated into a single device composed of polydimethylsiloxane (PDMS). Its fabrication was cost-effective and simple by avoiding the use of cleanroom and bonding step. In addition to user-friendly analysis and low consumption of chemicals, the method requires cost-effective instrumentation, namely, voltage supply and analytical balance. Furthermore, the so called distillation-on-a-chip (DOC) eliminates the use of membranes and electrodes (usually employed in microfluidic desalinations reported in the literature), thus avoiding drawbacks such as liquid leakage, membrane fouling, and electrode passivation. The DOC promoted desalinations at harsh salinity (NaCl 600.0 mmol L-1) with high throughput and salt removal efficiency (roughly 99%). Besides, the method was used for determination of ethanol in alcoholic beverages to show the potential of the approach toward quantitative purposes.

Multifunctional catalytic platform for peroxidase mimicking, enzyme immobilization and biosensing.

A hybrid platform based on ionic liquid-based alkoxysilane functionalized mesoporous silica was applied for the synthesis of supported Pt nanoparticles with peroxidase-like catalytic activity. The positively charged groups (imidazolium) chemically bonded to the surface provide dual-functionality as ion-exchangers to the hybrid material, firstly used for the in situ synthesis of the highly dispersed Pt nanostructures and, secondly, for the immobilization of biological species aiming biosensing purposes. The peroxidase-like catalytic activity of the SiO2/Imi/Pt material was evaluated towards the H2O2-mediated oxidation of a chromogenic peroxidase substrate (TMB), allowing the colorimetric detection of H2O2. Finally, to further explore the practical application of this nanomaterial-based artificial system, glucose oxidase (GOx) was immobilized on the catalytic porous platform and a bioassay for the colorimetric determination of glucose was successfully conducted as a model system. The enzyme-like catalytic properties of the SiO2/Imi/Pt as well as its ability to immobilize and keep active biological entities on the porous structure indicate that this hybrid porous platform is potentially useful for the development of biosensing devices.

Synthetic 1,2,3-triazole-linked glycoconjugates bind with high affinity to human galectin-3.

This work describes the synthesis of the 1,2,3-triazole amino acid-derived-3-O-galactosides 1-6 and the 1,2,3-triazole di-lactose-derived glycoconjugate 7 as potential galectin-3 inhibitors. The target compounds were synthesized by Cu(I)-catalyzed azide-alkyne cycloaddition reaction ('click chemistry') between the azido-derived amino acids N3-ThrOBn, N3-PheOBn, N3-N-Boc-TrpOBn, N3-N-Boc-LysOBn, N3-O-tBu-AspOBn and N3-l-TyrOH, and the corresponding alkyne-based sugar 3-O-propynyl-GalOMe, as well as by click chemistry reaction between the azido-lactose and 2-propynyl lactose. Surface plasmon resonance (SPR) assays showed that all synthetic glycoconjugates 1-7 bound to galectin-3 with high affinity, but the highest binders were the amino acids-derived glycoconjugates 2 (KD 7.96µM) and 4 (KD 4.56µM), and the divalent lactoside 7 (KD1 0.15µM/KD2 19µM). Molecular modeling results were in agreement with SPR assays, since more stable interactions with galectin-3 were identified for glycoconjugates 2, 4 and 7. Regarding compounds 2 and 4, they established specific cation-π (Arg144) and ionic (Asp148) interactions, whereas glycoconjugate 7 was capable to bridge two independent galectin-3 CRDs, creating a non-covalent cross-link between two monomers and, thus, reaching a submicromolar affinity towards galectin-3.

A very low potential electrochemical detection of L-cysteine based on a glassy carbon electrode modified with multi-walled carbon nanotubes/gold nanorods.

A nanohybrid platform built with multi-walled carbon nanotubes and gold nanorods, prepared via a cationic surfactant-containing seed-mediated sequential growth process, in aqueous solution, on a glassy carbon substrate has been successfully developed to be used in the electrocatalytic oxidation of L-cysteine (Cys). The nanohybrid was characterized by transmission electron microscopy, Raman spectroscopy and electrochemical measurements. Cyclic voltammetry results had shown that the modified electrode allows the oxidation of Cys at a very low anodic potential (0.00 V vs. Ag/AgCl). The kinetic constant kcat for the catalytic oxidation of Cys was evaluated by chronoamperometry and provided a value of 5.6×10(4) L mol(-1) s(-1). The sensor presents a linear response range from 5.0 up to 200.0 µmol L(-1), detection limit of 8.25 nmol L(-1) and a sensitivity of 120 nA L µmol(-1).

Electrochemical approaches employed for sensing the antioxidant capacity exhibited by vegetal extracts: a review.

Vegetal extracts are among the most important source of polyphenols in the diet, highlighting the importance of their characterization and determination. For this reason, analytical methods have gained increasing interest, with many publications devoted to this subject. Among the wide possibilities of analytical methods, electroanalytical techniques can provide valuable information, since the antioxidant activity of polyphenols is related to their electrochemical properties. This review analyzes and highlights the role of electroanalytical approaches for sensing the antioxidant capacity exhibited by vegetal extracts, as well as focuses on their importance for human health. The analytical capacity of the electrochemistry is comprehensively stated with the selected results found in the literature, mainly from 2000 up to the present date.

Biosensors for antioxidant evaluation in biological systems.

The prevention of oxidative reactions in a biological medium as well as the role of reactive oxygen species (ROS) in chronic degenerative diseases are questions that continue to be investigated. Electrochemical biosensors have shown attractive features to evaluate the oxidative stress condition at a level comparable to chromatographic and spectroscopic techniques. The biosensors developed so far are based on direct analysis of specific indicators such as biomarkers of oxidative stress on the monitoring of reactive oxygen species the free radicals in cells or tissues, aiming to obtain a correlation between the index obtained from these indicators with the oxidative stress levels in cells. In this review we will provide an overview of the development of electrochemical biosensors to evaluate the content of antioxidants and reactive oxygen species in physiological systems. Some discussion regarding the analysis of antioxidant capacity at the single cell level is also presented.

Influence of microwave heating on fluoride, chloride, nitrate and sulfate concentrations in water.

This paper describes a study about the influence of microwave radiation using closed vessels on fluoride, chloride, nitrate and sulfate concentrations in aqueous media. The experiments were processed by heating water using PFA vessels and a microwave cavity oven, determining the anions by ion chromatography. The influence of the exposure time, the atmospheric composition, the kind of heating (water bath or microwave radiation) and the possible formation of hydrogen peroxide were investigated. The limits of quantification for fluoride, chloride, nitrate and sulfate were respectively of 0.17, 0.15, 0.55 and 0.57 µg L(-1), and precision, expressed as RSD, was <4% for all considered anions. The hydrogen peroxide was quantified by spectrophotometry, and the limit of quantification and precision were 24 µg L(-1) and <5% (n=10), respectively. The results demonstrate a significant increase in the anion concentration levels (between 63 and 89%) when microwave heating was used in comparison with heating by water bath. In addition, these changes observed can be mainly attributed to the species transfers, either between gaseous (atmospheric gases) and liquid (water) phases for nitrate, or between vessels walls and water for fluoride, chloride and sulfate. Additionally, hydrogen peroxide concentration higher than 45 µg L(-1) was determined when water was exposed to microwave radiation.

Novel electrochemical sensor for the selective recognition of chlorogenic acid.

In this study, a novel sensitive molecularly imprinted electrochemical sensor was constructed for the selective detection of chlorogenic acid (CGA) by deposition of a molecularly imprinted siloxane (MIS) film, prepared by sol-gel process, onto Au bare electrode surface. Initially, a (3-mercaptopropyl)siloxane layer (MSL) was formed on the Au bare surface, followed by a siloxane layer obtained from the acid-catalyzed hydrolysis/condensation of a solution constituted by tetraethoxysilane (TEOS), phenyltriethoxysilane (PTEOS), 3-(aminopropyl)trimethoxysilane (APTMS) and CGA, as a molecular template. After the GCA extraction the MIS imprinted film was electrochemically characterized using differential pulse voltammetry (DPV). The MIS/Au sensor was tested in a solution of the CGA template and other similar molecules. This electrode displayed excellent selectivity towards CGA when compared with structurally similar molecules. Under optimized experimental conditions, the peak current response of the sensor for CGA was linear from 5.0 × 10(-7)mol L(-1) to 1.4 × 10(-5)mol L(-1), and the detection limit was 1.48 × 10(-7)mol L(-1). The MIS/Au sensor was successfully applied for the determination of CGA in coffee and tea samples.

Electrochemical detection in a paper-based separation device.

Prototypes of microfluidic paper-based separation devices with amperometric detection were developed and evaluated. Photolithography was used to make a gold electrochemical microcell on polyester and that microcell was coupled to a strip of paper where a chromatographic separation occurs. The device performance was demonstrated with the separation and quantification of uric and ascorbic acid in mixtures. The method provides an analytical alternative for the determination of compounds where low cost and simplicity are essential.

Speciation of Sb(III) and Sb(V) in meglumine antimoniate pharmaceutical formulations by PSA using carbon nanotube electrode.

A new and simple electroanalytical method for speciation of Sb(III) and Sb(V) in pharmaceutical formulation by potentiometric stripping analysis (PSA) using a multiwall carbon nanotube paste electrode was developed. All instrumental and chemical parameters influencing the performance of the method were carefully assessed and optimized. Trivalent antimony was determined in acid medium (pH 3.6) under the optimized condition (deposition potential of -0.7 V, deposition time of 180 s, ionic strength of 0.3M and oxidant mercury concentration of 10 mg l(-1)). Total antimony was determined after quantitative reduction of Sb(V) with l-cysteine (1.5%, w/v) and its concentration was calculated from difference between the total antimony and Sb(III). The developed method provided two distinct linear calibration one ranging from 10 up to 50 microg l(-1) and other from 100 up to 800 microg l(-1) with respective correlation coefficient of 0.9978 and 0.9993, presenting a detection limit of 6.2 microg l(-1). Repeatability for the six independent samples expressed in terms of relative standard deviation was found to be 3.01 and 1.39% for 40.0 and 300.0 microg l(-1) antimony concentration, respectively. Results on the effect of foreign substances [Al(III), Mg(II), Fe(III), Cd(II), Zn(II) and meglumine] on analytical signal of antimony showed no interference even using high content of foreign ions in the analyte:interferent ratio up to 1:100. The proposed method was successfully applied for the speciation of Sb(III) and Sb(V) in pharmaceutical formulation and the accuracy was assessed from addition and recovery tests as well as comparing with graphite furnace atomic absorption spectrometry (GF AAS) technique used as reference analytical method.

Simultaneous determination of zinc, cadmium and lead in environmental water samples by potentiometric stripping analysis (PSA) using multiwalled carbon nanotube electrode.

The present paper has focused on the potential application of multiwalled carbon nanotube for the development of a new, simple and highly selective electrochemical method for simultaneous Zn (II), Cd (II) and Pb (II) monitoring in water samples (lake and effluent waters), by using potentiometric stripping analysis (PSA). The electrochemical method is based on simultaneous preconcentration/reduction of metal ions onto a multiwall carbon nanotube electrode at -1.3V (versus Ag/AgCl(sat)) in 0.3 mol L(-1) acetate solution containing 15 mg L(-1) Hg (II) ions during 180s, followed by subsequent chemical stripping. The analytical curve for all analytes covered the linear range varying from 58.4 up to 646.2 microg L(-1) with correlation coefficients higher than 0.981. The limits of detection for Zn (II), Cd (II) and Pb (II) were found to be 28.0, 8.4 and 6.6 microg L(-1), while the relative standard deviation (RSD) at 352 microg L(-1) was 5.6, 7.1 and 5.6% (n=5), respectively. The behavior of the simultaneous determination in the presence of following ions Co (II), Cr (III) and Cu (II) was affected by using the analyte:interferent ratio 1:10. Therefore, by using standard addition method, Zn (II), Cd (II) and Pb (II) ions in lake and effluent water samples were determined after the spiking procedure and the results were successfully compared with those obtained by atomic absorption spectrometry (AAS). The obtained results suggest that the proposed method can be applied as a simple and efficient alternative for the simultaneous monitoring of heavy metals in water samples, according to those established requirements from environmental organizations. In addition, this method demonstrates the powerful application of carbon nanotubes in the field of potentiometric stripping analysis.

Synthesis and application of a peroxidase-like molecularly imprinted polymer based on hemin for selective determination of serotonin in blood serum.

This work reports the preparation of a molecularly imprinted polymer (MIP) for selective catalytic detection of serotonin (5-hydroxytryptamine, 5-HT). The process is based on the synthesis of polymers with hemin introduced as the catalytic center to mimic the active site of peroxidase. The copolymer MIP, containing artificial recognition sites for 5-HT, has been prepared by bulk polymerization using methacrylic acid (MAA) and hemin as the functional monomers, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. For the determination of 5-HT, a flow injection analysis system coupled to an amperometric detector was optimized using multivariate analysis. The effects of different parameters, such as pH, buffer flow rate, buffer nature, peroxide concentration and sample volume were evaluated. After optimizing the experimental conditions, a linear response range from 1.0 up to 1000.0 micromolL(-1) was obtained with a sensitivity of 0.4nA/ micromolL(-1). The detection limit was found to be 0.30 micromolL(-1), while the precision values (n=6) evaluated by relative standard deviation (R.S.D.) were, respectively, 1.3 and 1.7% for solutions of 50 and 750 micromolL(-1) of 5-HT. No interference was observed by structurally similar compounds (including epinephrine, dopamine and norepinephrine), thus validating the good performance of the imprinted polymer. The method was applied for the determination of 5-HT in spiked blood serum samples.

Simple and sensitive electroanalytical method for the determination of ascorbic acid in urine samples using measurements in an aqueous cationic micellar medium.

An electroanalytical study for the amperometric determination of ascorbic acid (AA) in a human urine sample at a bare glassy carbon electrode using the CPC (cetylpyridinium chloride) surfactant is described. Under the optimized conditions of E(pa), I(pa), CPC concentration and pH, the oxidation peak potential of the AA shifts towards a less positive potential, and the peak current increase in a significant way in the presence of the surfactant. Under the best conditions, the method provided a linear calibration curve to AA in a 0.1 mol L(-1) phosphate buffer solution (pH 7.0) in the concentration range from 5.0 x 10(-7) up to 4.3 x 10(-4) mol L(-1), with a detection limit of 2.0 x 10(-7) mol L(-1) and a high correlation coefficient (r = 0.9996). The recovery test presented values of 98 - 105%, suggesting a great potential of the proposed method for AA determination in complex samples, such as urine.

Electrochemical investigations of the reaction mechanism and kinetics between NADH and redox-active (NC)2C6H3-NHOH/(NC)2C6H3-NO from 4-nitrophthalonitrile-(NC)2C6H3-NO2-modified electrode.

A simple and sensitive method for the electrocatalytic detection of NADH on a carbon paste electrode modified with a redox-active (NC)(2)C(6)H(3)-NO/(NC)(2)C(6)H(3)-NHOH (NOPH/NHOHPH) electrogenerated in situ from 4-nitrophthalonitrile (4-NPHN) is presented. The electrode modified with 4-NPHN showed an efficient electrocatalytic activity towards the oxidation of NADH with activation overpotential of 0.12V vs. Ag/AgCl. The formation of an intermediate charge transfer complex is proposed for the charge transfer reaction between NADH and the 4-NPHN-resulting system. The second-order rate constant for electrocatalytic oxidation of NADH, kappa(obs), and the apparent Michaelis-Menten constant K(M), at pH 7.0 were evaluated with rotating disk electrode (RDE) experiments, giving 1.0 x 10(4)mol(-1)Ls(-1) and 2.7 x 10(-5)mol L(-1), respectively. Employing the Koutecky-Levich approach indicated that the NADH oxidation reaction involves two electrons. The sensor provided a linear response range for NADH from 0.8 up to 8.5 micromol L(-1) with sensitivity, detection, quantification limits and time response of 0.50 microA L micromol(-1), 0.25micromol L(-1), 0.82 micromol L(-1) and 0.1s, respectively. The repeatability of the measurements with the same sensor and different sensors, evaluated in terms of relative standard deviation, were 4.1 and 5.0%, respectively, for n=10.

A catalytically active molecularly imprinted polymer that mimics peroxidase based on hemin: application to the determination of p-aminophenol.

Despite the increasing number of applications of molecularly imprinted polymers (MIP) in analytical chemistry, the synthesis of polymers with hemin introduced as the catalytic center to mimic the active site of peroxidase remains as a challenge. In the current work, a new type of molecularly imprinted polymer (MIP) was synthesized with 4-aminophenol (4-APh) as the template and two monomers: hemin, which acts as the catalytic center, and methacrylic acid (MAA), which is used to build the active sites. This work shows that MIP successfully mimics peroxidase. For this purpose, a flow injection analysis system coupled to an amperometric detector was investigated through multivariate analysis. The determination of 4-APh was not affected by the equimolar presence of structurally similar phenol compounds, including catechol, 4-chloro-3-methylphenol, 2-aminophenol, guaiachol, chloroguaiachol and 2-cresol, thus highlighting the good performance of the imprinted polymer. Under the optimized experimental conditions, an analytical curve covering a wide linear response range from 0.8 up to 500 micromol L(-1) (r > 0.999) was obtained, and the method gave satisfactory precisions (n = 8), as evaluated via the relative standard deviation (RSD), of 4.1 and 3.2% for solutions of 4-APh of 50 and 500 micromol L(-1), respectively. Recoveries of 96-111% from water samples (tap water and river water) spiked with 4-APh were achieved, thus illustrating the accuracy of the proposed system.