Search Results (134)

Major vibrational spectroscopy studies have focused on the preparation of chromium coatings via chemical processes (conversion coatings), and few studies have focused on electrochemical processes (electrodeposition). Initially, the chemical precursors were hexavalent chromium salts, but these compounds are now replaced by less toxic trivalent ions. There is a profound understanding of the process when vibrational spectroscopy is used in combination with other techniques. This is the case for chromium(VI) conversion coatings, and the results of several techniques, such as synchrotron infrared microspectroscopy, have made it possible to understand the structure of the two-layer coating and the chemical composition of each layer. Vibrational spectroscopy confirmed the mechanism for coating formation, in which ferricyanide was a redox mediator. In addition, vibrational spectroscopy was effective in determining the mechanism of corrosion resistance of the coatings. Conversely, there are very few studies on the electrodeposition of trivalent chromium ions, and the mechanics of electrodeposition are unknown. To simplify the use of spectroscopy, spectra of potassium dichromate and chromium(III) sulfate are presented as references for coating studies, and a compilation of $\mathrm{C}\mathrm{r}\left(\mathrm{I}\mathrm{I}\mathrm{I}\right)-\mathrm{O}$ and $\mathrm{C}\mathrm{r}\left(\mathrm{V}\mathrm{I}\right)-\mathrm{O}$ vibrational modes is provided to facilitate band assignment. Our review highlights that spectroscopic techniques have been insufficiently applied in this field; however, the results of vibrational spectroscopy accelerate the transition to safer Cr(III) technology. Full article

Poly(3-thienylboronic acid) (PThBA) has recently been suggested as a conducting polymer with affinity for saccharides. In this study, thin films of this compound were deposited onto gold electrodes. The system obtained was studied as a possible chemical sensor. The measurements were performed by impedance spectroscopy using potassium ferro/ferricyanide as a redox mediator. The thickness of the polymer and the deposition of the adhesive sublayer were optimized to achieve a compromise between the blocking of defects in the polymer layer and the unnecessary increase in the internal resistance of this conductometric sensor. A comparative study of the influence of fructose, glucose, and sorbitol on transversal polymer resistance was conducted. The binding constants for these saccharides were extracted from the concentration dependencies of sensor conductance. Among them, sorbitol showed the highest affinity with a binding constant up to ~15,000 L·mol⁻¹, followed by fructose (~8700 L·mol⁻¹) and glucose (~4500 L·mol⁻¹). In order to exclude the contribution of the analyte tautomers on the obtained binding constants, measurements of ethylene glycol were also performed. The effects of pH and the redox state of PThBA on its affinity properties were studied, revealing higher affinities at alkaline pH and in oxidized state of the chemosensitive polymer. The developed system has the capacity to be applied in chemical sensors and virtual sensor arrays with electrical affinity control. Full article

A new automated method for the determination of cholesterol in serum was developed by combining sequential injection analysis (SIA) with potentiometric detection using a gold oxidation–reduction potential (ORP) electrode because serum cholesterol is an important indicator of abnormal lipid metabolism, arteriosclerosis, and hypertension in clinical diagnosis. The method is based on enzymatic hydrolysis of cholesterol esters by cholesterol esterase (CE) to yield free cholesterol, followed by oxidation with cholesterol oxidase (COD) to produce hydrogen peroxide. In the presence of horseradish peroxidase (HRP) and potassium ferrocyanide (K₄[Fe(CN)₆]), hydrogen peroxide oxidizes ferrocyanide to ferricyanide (K₃[Fe(CN)₆]), and the concentration ratio of ferri-/ferrocyanide is determined potentiometrically. Experimental conditions were optimized as follows: 5.0 mM K₄[Fe(CN)₆], 2 min reaction time, 0.5 units/mL HRP, 0.75 units/mL COD for free cholesterol, 1.5 units/mL COD and 10.0 units/mL CE for total cholesterol, and 5.0% (w/v) Triton X-100 with 5.0% (v/v) isopropanol as solubilizing agents. Under these conditions, the calibration curve for total cholesterol exhibited a Nernstian slope of 47.6 mV/decade over the range of 1.0 × 10⁻⁵–1.0 × 10⁻³ M, with no significant interference from common serum constituents. This method offers low reagent consumption, high automation, and simple operation, making it promising for clinical cholesterol analysis. Full article

The potential of king grass biomass as a precursor for carbon-based materials was evaluated through comprehensive physicochemical characterization. The biomass showed high fixed carbon content, reactive oxygenated groups, and favorable atomic ratios, supporting its suitability for conversion into porous carbon structures. This study focused on the synthesis of graphene-like materials via high-temperature pyrolysis (~1000 °C), employing FeCl₃ and potassium ferricyanide (K₃[Fe(CN)₆]) as catalytic agents. Although FeCl₃ is widely studied, it showed limited capacity to promote graphitic ordering. In contrast, K₃[Fe(CN)₆] exhibited a synergistic effect, combining iron-based catalytic species (Fe, Fe₃C) and potassium-derived activating compounds (K₂CO₃), which significantly enhanced graphitization and porosity. Characterization by Raman spectroscopy, XRD, and SEM confirmed that materials synthesized with K₃[Fe(CN)₆] presented improved crystallinity, lower defect densities (I_D/I_G = 0.37–1.11), and distinct 2D bands (I_2D/I_G = 0.32–0.80), indicating the formation of few-layer graphene domains. The most promising structure was obtained from cellulose treated with alkaline peroxide and deoxygenated prior to pyrolysis with K₃[Fe(CN)₆], showing properties comparable to commercial graphene. BET analysis revealed surface areas up to 714.50 m²/g. While non-catalyzed samples yielded higher mass, the catalytic approach with K₃[Fe(CN)₆] demonstrates a sustainable and efficient pathway for producing graphene-like carbon materials from lignocellulosic biomass. Full article

Assays of total antioxidant capacity (TAC) of complex materials bring no information on the composition of antioxidants present in a sample. As the thermodynamic condition for a redox reaction is that redox potential of the oxidant must be higher than that of a reductant (antioxidants), it seemed to be of interest whether it is possible to estimate the content of antioxidants of various ranges of redox potentials using a set of assays employing oxidants/indicators of different values of redox potentials. Antioxidant activities of nine antioxidants and TAC of an aqueous garlic extract were estimated using nine assays of E_o′ of oxidants/indicators ranging from 0.11 to 1.15 V. The antioxidant activities were expressed in mol Trolox equivalents/mol compound. The thermodynamic conditions made some antioxidants unreactive with indicators of sufficiently low E_o′, but otherwise, no dependence between the antioxidant activities and redox potentials of oxidants/indicators and reactivities of antioxidants was observed. TAC of the garlic extract did not show any regular dependence on the redox potential of the oxidant/indicator, being the highest in the test of 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) radical (ABTS^•) decolorization. These results indicate that kinetic factors play a primary role in determining the antioxidant activities of antioxidants and TAC in various assays. Full article

Cyanide species pose an environmental concern as they inhibit important biological processes in humans and aquatic systems. There is more focus on free-CN and weak acid dissociables cyanide as hazardous species compared to strong acid dissociables due to their higher reactivity and toxicity. However, the strong acid dissociables cyanide also poses health concerns as it liberates free-CN under ultraviolet irradiation or when present in acidic solutions. Detection of strongly acid dissociables cyanide typically requires its digestion in acidic solutions and measurement of the gaseous HCN produced. A simple infrared spectroscopic method is described here to speciate and quantify three strong acid dissociables cyanide: [Fe(CN)₆]³⁻, [Co(CN)₆]³⁻, and [Au(CN)₂]⁻. The strategy involves precipitating the strongly acid dissociables cyanide using cetyltrimethylethylammonium bromide, capturing the precipitate on a polyethylene membrane, and quantifying the individual strongly acid dissociables cyanide from the IR spectrum recorded in transmission mode through the membrane. Controlling the particle diameter to be in the range of 0.2–2 µm is important. Particles less than 0.2 µm pass through the membrane, whereas particles larger than about 2 µm lead to nonlinearity in quantification. The average %recoveries for [Fe(CN)₆]³⁻, [Co(CN)₆]³⁻, and [Au(CN)₂]⁻ were 100% (%RSD = 7), 91% (%RSD = 7), and 101% (%RSD = 8), respectively. The detection limit for [Fe(CN)₆]³⁻ and [Co(CN)₆]³⁻ were both 20 ppb CN⁻, whereas [Au(CN)₂]⁻ was 100 ppb CN⁻. The detection range was 20–750 ppb CN⁻ for [Fe(CN)₆]³⁻ and [Co(CN)₆]³⁻ and 100–750 ppb CN⁻ for [Au(CN)₂]⁻ with a linear regression of R² = 0.999–1.000. Full article

Precision nutrition is an emerging approach that tailors dietary recommendations based on an individual’s unique genetic, metabolic, microbiome, and lifestyle factors. β-hydroxybutyrate (β-HB) is a key ketone body produced during fat metabolism, especially in states of fasting, low-carbohydrate intake, or prolonged exercise. Therefore, monitoring β-HB levels provides valuable insights into an individual’s metabolic state, making it an essential biomarker for precision and personalized nutrition. A smartphone-connected electrochemical biosensor for single-use, rapid, low-cost, accurate, and selective detection of β-HB in whole blood and saliva at the Point-of-Care (POC) is reported. A graphite screen-printed carbon electrode modified with potassium ferricyanide (Fe(III)GSPE) was used as an electrode platform for the deposition of β-hydroxybutyrate dehydrogenase (HBDH), nicotinamide adenine dinucleotide oxidized form (NAD⁺), and chitosan nanoparticles (ChitNPs). An outer poly(vinyl) chloride (PVC) diffusion-limiting membrane was used to protect the modified electrode. The biosensor showed a linear range in the clinically relevant range, between 0.4 and 8 mM, with a detection limit (LOD) of 0.1 mM. The biosensor was tested on human blood and saliva samples, and the results were compared to those obtained with a commercial ketone meter, showing excellent agreement. Full article

This study presents a microbial sensing device that employs a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) matrix to immobilize viable and metabolically Escherichia coli cells. This device enables the monitoring of microorganism metabolic activity in response to external stimuli such as variations in carbon sources or exposure to inhibitory or toxic compounds. PEDOT:PSS, a conductive and chemically stable polymer, was electrodeposited onto screen-printed electrodes, successfully entrapping approximately 1.26 × 10⁷ cells per electrode. The confocal microscopy of Live/Dead-stained samples confirmed a uniform cell distribution and an average viability of ~78%. Ferricyanide respirometry validated the metabolic activity of the immobilized cells. The biosensor’s performance was evaluated using 3,5-dichlorophenol (3,5-DCP) as a reference toxicant. The observed inhibition of microbial activity correlated with 3,5-DCP concentration, yielding a half-maximal effective concentration (EC₅₀) of 9 ppm, consistent with the literature values. Full article

Due to its unique molecular fingerprinting capability and multiplex detection advantages, surface-enhanced Raman scattering (SERS) has shown great application potential in the field of biological analysis. However, the weak signal intensity and large background interference significantly limited the application of SERS in biosensing and bioimaging. Loading a large amount of Raman molecules with signal in the silent region on the hotspots of the electromagnetic field of the SERS substrate can effectively avoid severe background noise signals and significantly improve the signal intensity, making the sensitivity and specificity of SERS detection remarkably improved. To achieve this goal, a new SERS signal-amplification strategy is herein reported for background-free detection of Cu²⁺ by using Raman-silent probes loaded on cabbage-like gold microparticles (AuMPs) with high enhancement capabilities and single-particle detection feasibility. In this work, carboxyl-modified AuMPs were used to enable Cu²⁺ adsorption via electrostatic interactions, followed by ferricyanide coordination with Cu²⁺ to introduce cyano groups, therefore generating a stable SERS signal with nearly zero background signals owing to the Raman-silent fingerprint of cyano at 2137 cm⁻¹. Based on the signal intensity of cyano groups correlated with Cu²⁺ concentration resulting from the specific coordination between Cu²⁺ and cyanide, a novel SERS method for Cu²⁺ detection with high sensitivity and selectivity is proposed. It is noted that benefiting from per ferricyanide possessing six cyano groups, the established method with the advantage of signal amplification can significantly enhance the sensing sensitivity beyond conventional approaches. Experimental results demonstrated this SERS sensor possesses significant merits towards the determination of Cu²⁺ in terms of high selectivity, broad linear range from 1 nM to 1 mM, and low limit of detection (0.1 nM) superior to other reported colorimetric, fluorescence, and electrochemical methods. Moreover, algorithm data processing for optimization of SERS original data was further used to improve the SERS signal reliability. As the proof-of-concept demonstrations, this work paves the way for improving SERS sensing capability through the silent-range fingerprint and signal amplification strategy, and reveals SERS as an effective tool for trace detection in complex biological and environmental matrices. Full article

Dengue is a neglected disease mainly affecting tropical and subtropical countries. The diagnosis of dengue fever is still a problem since most of it is made from whole or recombinant DENV proteins, which present cross-reactions with other members of the Flavivirus family. Therefore, there is still a huge demand for new diagnostic methods that provide rapid, low-cost, easy-to-use confirmation. Thus, in this study, we developed an affordable electrochemical biosensor for rapidly detecting immunoglobulin G (IgG) serological antibodies in the sera of DENV-infected patients. An identified linear B-cell epitope (DENV/18) specific for DENV 1–4 serotypes recognized by IgG in patient sera was selected as a target molecule after a microarray of peptides using the SPOT-synthesis methodology. After chemical synthesis, the DENV/18-peptide was immobilized on the surface of the working electrode of a commercially available screen-printed gold electrode (SPGE). The capture of DENV-specific IgG allowed for the formation of an immunocomplex that was measured by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using a potassium ferrocyanide/ferricyanide ([Fe(CN)₆]^3−/4−) electrochemical probe. An evaluation of the biosensor’s performance showed a detection limit of 100 µg mL⁻¹ for the synthetic peptides (DENV/18) and 1.21 ng mL⁻¹ in CV and 0.43 ng mL⁻¹ in DPV for human serum, with a sensitivity of 7.21 µA in CV and 8.79 µA in DPV. The differentiation of infected and uninfected individuals was possible even at a high dilution factor that reduced the required sample volumes to a few microliters. The final device proved suitable for diagnosing DENV by analyzing real serum samples, and the results showed good agreement with molecular biology diagnostics. The flexibility to conjugate other antigenic peptides to SPEs suggests that this technology could be rapidly adapted to diagnose other pathogens. Full article

Salt lake brine contains abundant rubidium resources; however, the separation of rubidium from brine with a high K content remains a significant challenge in metallurgical processes and materials science. In this study, PAN-KCuFC-PEG particles were synthesized by phase transformation, using hydrophilic polyacrylonitrile (PAN) as the skeleton structure, potassium cupric ferricyanide (KCuFC) as the active component and water-soluble polymer polyethylene glycol (PEG) as the pore regulator. Characterization revealed that the addition of PEG increased the pore volume of PAN-KCuFC-PEG by 63% and the BET surface area by 172%. KCuFC powder was uniformly dispersed in PAN-KCuFC-PEG, and its crystal structure remained stable after loading. In static adsorption experiments, the maximum adsorption capacity of PAN-KCuFC-PEG for Rb⁺ reached 190 mg/g. The adsorption behavior followed a pseudo-second-order kinetic model, with the rate jointly controlled by external diffusion, intraparticle diffusion, and chemical reaction. In the column experiment, PAN-KCuFC-PEG was used to adsorb Qarhan Salt Lake brine (K: 26,000 mg/L, Rb: 65 mg/L). NH₄Cl was employed for elution and desorption of PAN-KCuFC-PEG. During the adsorption–desorption process, the separation factor between Rb and K reached 160, the desorption rate reached 96.6%, and the overall yield was 68.3%. The enrichment and separation of Rb were successfully achieved. Full article

Polysulfide-ferricyanide redox flow batteries (PFRFBs) are gaining significant attention in long-duration energy storage for their abundant availability and environmental benignity. However, the sluggish kinetics of the polysulfide redox reactions have tremendously constrained their performances. To address this issue, we developed a NiMoS catalyst-modified carbon felt (NiMoS-CF) electrode, which significantly accelerates the electrochemical reaction rates and enhances the cycling stability of PFRFB. Our PFRFB system, integrated with the NiMoS-CF electrode, exhibited an energy efficiency of 70% and a voltage efficiency of 87%, with a remarkable doubling of its cycle life as opposed to the pristine carbon felt (CF) electrode at a current density of 40 mA cm⁻². Notably, during 2500 cycles of charge–discharge testing, we achieved an average coulombic efficiency exceeding 99%. These improvements in PFRFB performance can be attributed to the NiMoS-CF electrode’s large surface area, low resistance, and robust redox activity. This study offerings a novel approach for enhancing the electrochemical reaction kinetics and cycling stability in PFRFBs, laying a scientific foundation in the applications of practical PFRFBs for next-generation energy storage. Full article

This study demonstrates, for the first time, the formation of a hemiester of carbonic acid on self-assembled monolayers using voltammetric techniques and redox probes. A gold electrode (GE) was modified with 2-mercaptoethanol (ME) through self-assembly. With this modified electrode (GE-ME), a well-defined peak was observed by differential pulse voltammetry (DPV) for the negatively charged redox probe, ferricyanide/ferrocyanide, [Fe(CN)₆]³⁻/⁴⁻, in sodium acetate as an electrolyte adjusted to pH 8.2. In the presence of dissolved CO₂ in equilibrium with bicarbonate, there is a decrease in the ferrocyanide peak current with time (~30% in 60 min), attributed to the formation of hemiester 2-mercapto ethyl carbonate at the GE-ME/solution interface. Similarly, dissolved CO₂ and bicarbonate also affect the electrochemical impedance measurements by increasing resistance to the charge transfer process with time (elevation of Rct values), compatible with the formation of the hemiester. The addition of barium salt led to the displacement of the equilibrium towards BaCO₃ precipitation and consequent dissociation of the hemiester, attested by the recovery of the initial ferricyanide DPV signal. With the positively charged redox probe [Ru(NH₃)₆]²⁺, no decrease in the DPV peak was observed during the formation of the hemiester by reaction with bicarbonate. The repulsion of [Fe(CN)₆]³⁻, but not of [Ru(NH3)₆]²⁺, suggests that the formed species is the negatively charged 2-mercapto-ethyl carbonate, i.e., the hemiester with a dissociated proton. Due to the lack of a voltammetric signal from the hemiester itself, the formation of a self-assembled layer of thio-alcohol followed by the gradual formation of the corresponding carbonic acid hemiester allowed us to reach an elegant way of electrochemically demonstrating the formation of these species. Full article

This study investigated the effect of surface treatments on the electrochemical performance of 3D-printed electrodes for versatile applications. The conductive filament was obtained from a mixture of polylactic acid (PLA) and carbon black (CB) at a 7:3 ratio (PLA/CB) dispersed in acetic acid and dichloroethane (3:1) medium. The treatments used were HNO₃, NaOH, DMF (immersion for 30, 30, and 15 min, respectively), and electrochemical activation (amperometry 150 s, 1.8 V). In general, the treatments allow greater exposure of the conductive material and active sites present on the sensor surface. This was confirmed using cyclic voltammetry and electrochemical impedance spectroscopy. The analyses were conducted with a 0.10 M KCl solution containing the redox pair ferricyanide/ferrocyanide 5.00 mmol L⁻¹. Based on the results obtained, the electroactive area, kinetic constant and resistance to electron transfer were determined for each treatment. The treatment in basic medium stood out as the treatment that was most appropriate for the device used in this work. The device was also tested for its potential in the analysis of acetaminophen, demonstrating satisfactory results permitting the application of 3D-S_Basic in the analysis of acetaminophen. Full article

In recent years, interest in screen-printed electrodes (SPEs) has grown due to their wide range of applications. Diclofenac (DCF), a widely used non-steroidal anti-inflammatory drug, is a subject of interest in pharmaceutical research as well as environmental research, primarily due to its environmental contamination and therapeutic applications. This study describes the development and characterization of an innovative screen-printed sensor based on graphene oxide (GO) and phenanthroline (PHEN) for the rapid and highly sensitive determination of diclofenac. The modified sensor was characterized by Fourier Transform Infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The electrochemical behavior of the screen-printed electrodes was assessed through cyclic voltammetry (CV) in phosphate buffer solution (PBS) and potassium ferrocyanide/potassium ferricyanide solution. The cyclic voltammograms of the electrodes modified with GO and PHEN revealed peaks in PBS related to redox processes of PHEN immobilized in the carbonaceous matrix. Additionally, the active surface area of the electrodes was found to be larger for the modified carbon screen-printed electrode with GO and PHEN, which also showed improved sensitivity to the detection of DCF. The limit of detection (1.53 nM) and the sensitivity of the novel sensor were promising, and these performance characteristics enabled the sensitive detection of DCF in different pharmaceutical products. The selectivity was confirmed to be appropriate based on recovery studies conducted with the pharmaceutical products, which produced values close to 100%. Full article