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.

An integrated platform for gas-diffusion separation and electrochemical determination of ethanol on fermentation broths.

An integrated platform was developed for point-of-use determination of ethanol in sugar cane fermentation broths. Such analysis is important because ethanol reduces its fuel production efficiency by altering the alcoholic fermentation step when in excess. The custom-designed platform integrates gas diffusion separation with voltammetric detection in a single analysis module. The detector relied on a Ni(OH)2-modified electrode. It was stabilized by uniformly depositing cobalt and cadmium hydroxides as shown by XPS measurements. Such tests were in accordance with the hypothesis related to stabilization of the Ni(OH)2 structure by insertion of Co(2+) and Cd(2+) ions in this structure. The separation step, in turn, was based on a hydrophobic PTFE membrane, which separates the sample from receptor solution (electrolyte) where the electrodes were placed. Parameters of limit of detection and analytical sensitivity were estimated to be 0.2% v/v and 2.90 µA % (v/v)(-1), respectively. Samples of fermentation broth were analyzed by both standard addition method and direct interpolation in saline medium based-analytical curve. In this case, the saline solution exhibited ionic strength similar to those of the samples intended to surpass the tonometry colligative effect of the samples over analyte concentration data by attributing the reduction in quantity of diffused ethanol vapor majorly to the electrolyte. The approach of analytical curve provided rapid, simple and accurate analysis, thus contributing for deployment of point-of-use technologies. All of the results were accurate with respect to those obtained by FTIR method at 95% confidence level.

Ultrasensitive biosensor for detection of organophosphorus pesticides based on a macrocycle complex/carbon nanotubes composite and 1-methyl-3-octylimidazolium tetrafluoroborate as binder compound.

This work describes the highly sensitive detection of organophosphorus pesticides employing the cobalt(II) 4,4,4,4-tetrasulfo-phthalocyanine (CoTSPc) macrocycle complex, carbon nanotubes (CNT), and 1-methyl-3-octylimidazolium tetrafluoroborate (OMIM[BF4]). The technique is based on enzyme acetylcholinesterase (AChE) inhibition. The composite was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and amperometry. The AChE was immobilized on the composite electrode surface by cross-linking with glutaraldehyde and chitosan. The synergistic action of the CoTSPc/CNT/OMIM[BF4] composite showed excellent electrocatalytic activity, with a low applied potential for the amperometric detection of thiocholine (TCh) at 0.0 V vs. Ag/AgCl. The calculated catalytic rate constant, k(cat), was 3.67 × 10(3) mol(-1) L s(-1). Under the optimum conditions, the inhibition rates of these pesticides were proportional to their concentrations in the ranges of 1.0 pmol L(-1) to 1.0 nmol L(-1) (fenitrothion), 2.0 pmol L(-1) to 8.0 nmol L(-1) (dichlorvos), and 16 pmol L(-1) to 5.0 nmol L(-1) (malathion).

Simple on-plastic/paper inkjet-printed solid-state Ag/AgCl pseudoreference electrode.

A miniaturized, disposable, and low cost Ag/AgCl pseudoreference electrode based on inkjet printing has been developed. Silver ink was printed and chlorinated with bleach solution. The reference electrodes obtained in this work showed good reproducibility and stability during at least 30 min continuous measurement and even after 30 days storage without special care. Moreover, the strategy used in this work can be useful for large scale production of a solid-state Ag/AgCl pseudoreference electrode with different designs and sizes, facilitating the coupling with different electrical/electrochemical microsensors and biosensors.

Critical View on graphene oxide production and its transfer to surfaces aiming electrochemical applications.

Graphene and related materials has been studied aiming their use in several applications including electrochemical sensing systems for a large number of different analytes. However, there have been proportionally only a few studies discussing deeply the implications of the different variables that could be tuned in the preparations of these materials for the development of the electrochemical platforms. In this review it is discussed how the size, number of layers, crystallinity and purity of the graphite starting material affects the final graphene oxide (GO) and reduced graphene oxide (rGO) prepared by chemical exfoliation. The exfoliation process and the most frequently applied transfer methods used to prepare thin films of GO and rGO on surfaces/electrodes of sensing platforms are also discussed. The electrochemical behavior of these materials is evaluated as a role of surface organization and adsorption. Considering the parameters previously presented, it is outlined some of the most relevant sensors and biosensor systems, which employ graphene related materials and attempts to explore different possibilities of deposition.

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.

Sensing small neurotransmitter-enzyme interaction with nanoporous gated ion-sensitive field effect transistors.

Ion-sensitive field effect transistors with gates having a high density of nanopores were fabricated and employed to sense the neurotransmitter dopamine with high selectivity and detectability at micromolar range. The nanoporous structure of the gates was produced by applying a relatively simple anodizing process, which yielded a porous alumina layer with pores exhibiting a mean diameter ranging from 20 to 35 nm. Gate-source voltages of the transistors demonstrated a pH-dependence that was linear over a wide range and could be understood as changes in surface charges during protonation and deprotonation. The large surface area provided by the pores allowed the physical immobilization of tyrosinase, which is an enzyme that oxidizes dopamine, on the gates of the transistors, and thus, changes the acid-base behavior on their surfaces. Concentration-dependent dopamine interacting with immobilized tyrosinase showed a linear dependence into a physiological range of interest for dopamine concentration in the changes of gate-source voltages. In comparison with previous approaches, a response time relatively fast for detecting dopamine was obtained. Additionally, selectivity assays for other neurotransmitters that are abundantly found in the brain were examined. These results demonstrate that the nanoporous structure of ion-sensitive field effect transistors can easily be used to immobilize specific enzyme that can readily and selectively detect small neurotransmitter molecule based on its acid-base interaction with the receptor. Therefore, it could serve as a technology platform for molecular studies of neurotransmitter-enzyme binding and drugs screening.

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.