Glassy Carbon Surface Research Articles

The Heterogeneity of Turn-over Number in Electrocatalysis

Chemical catalysts dominate the multi-billion global revenue of the chemical industry because they accelerate the time it takes a particular reaction to reach equilibrium without altering the equilibrium constant. Electrocatalysis can provide significant benefits compared to other methods, as it has minimal purification and separation costs, is operational at low temperatures and pressures, replaces hazardous and toxic chemical sources with electric current, and can be integrated with renewable energy sources. From a techno-economical point of view, some considerations are critical during a catalyst design: cost, activity, and durability. One useful metric to quantify catalyst durability is turn-over number (TON), which represents the maximum yield of products attainable from a catalytic center. Mathematically speaking, the TON is defined as: TON = ∫0 ∞ TOF(t) dt, where TOF is the turn-over frequency, which is the rate of turn-overs (N) per active site. Currently, without any exception, the TON is given as a fixed number describing the total amount of substrate converted until the catalysts fully degrade. Our approach studies electrocatalytic deactivation processes at the single catalyst level using a technique entitled single-entity electrochemistry for freely diffusing catalysts. The hydrogen evolution reaction (HER) is investigated with platinum nanoparticles as the model catalyst because it deactivates at the nanoscale when the catalytic activity decreases over time. At specific applied potentials, the current measured when a single platinum nanoparticle impacts the electrode creates a transient spike and decay back to the baseline current. TON is quantified by fitting the current decay response and integrating above the fit to find the charge transferred to catalyze the reaction. Our results show that electrocatalyst degradation and TON have a distribution, where some catalysts are more stable than others, and depends on the applied potential and size of the nanoparticles. In order to study how the surface facets of platinum affect the TON, SECCM was coupled with scanning electron microscopy (SEM) to compare the deactivation of a polycrystalline platinum surface in the macro scale with immobilized platinum nanoparticles on a glassy carbon surface. Combining local structural, electrochemical activity, and durability will bridge our fundamental understanding of macro and nanoscale catalyst deactivation processes to assist in the bottom-up approach of material development and design of large-scale industrial electrocatalysts.

Layer‐by‐Layer Construction of Hybrid Film Based on PEI Polymer and Preyssler‐Type Polyoxometalates: Its Electrochemical and Quartz Crystal Microbalance Measurement

AbstractIn this work, Preyssler‐type POM (NH4)14[NaP5W30O110].44H2O (NH4P5W30), has been synthesised and its electrochemical behaviour in solution was examined at the surface of glassy carbon (GC) and gold electrodes. Furthermore, multilayer assemblies of NH4P5W30 POM were constructed onto the surfaces of GCE, gold electrode, and gold quartz electrode via the electrostatic Layer‐by‐Layer (LBL) technique employing polyethyleneimine as the cationic layer and POM as an anionic layer. Cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and electrochemical quartz crystal microbalance measurements (EQCM) were used to monitor the LBL assembly as the NH4P5W30 POM layer was being built. These techniques revealed significant differences in film growth. The multilayer film exhibited well‐defined redox couples associated with POM's tungsten‐oxo framework and showed surface‐confined behaviour up to 100 mVs−1 on both the GC and gold electrodes. The pH dependency and stability of the film were investigated. EIS demonstrated that when the POM layer was the outer layer, the layers were less conductive, and resistance increased as the number of layers increased. In addition, the charge transfer resistance values (Rct) for the layers were calculated. The solvation of ions into the film associated with POM redox activity was studied employing an in‐situ EQCM.

Electrosynthesis of a triazole derivative on the glassy carbon surface for the electrochemical determination of catechol

ABSTRACT In this experiment, an electrosynthesis of a triazole-thiol derivative (3-amino-1,2,4-triazole-5-thiol (3ATT)) was carried out on the glassy carbon electrode (GCE) to fabricate an electrochemical sensor to determine catechol (CC) by voltammetry. The characterisation of the modified electrode (3ATT-GCE) was examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Electrochemical oxidation of CC by the differential pulse voltammetry (DPV) with 3ATT-GCE exhibited a perfectly wide linear response in the CC concentration range of 0.088 to 10.5 µM and 10.5 to 629 µM with a detection limit (LOD) of 0.024 µM (3 s/m). Furthermore, it indicated excellent reproducibility and repeatability. The fabricated sensor with a large surface area and high electrical conductivity was successfully employed to determine CC in tap water without being affected by interfering substances.

Study of the effect of implantation temperature on the migration behaviour of Xe implanted into glassy carbon.

The effect of implantation temperature on the migration behaviour of xenon (Xe) implanted into glassy carbon and the effect of annealing on radiation damage retained by ion implantation were investigated. Glassy carbon substrates were implanted with 320keV Xe+ to a fluence of 2×1016cm-2. The implantation process was performed at room temperature (RT) and 100°C Some of the as-implanted samples were isochronally annealed in vacuum at temperatures ranging from 300°C to 700°C in steps of 100°C for 10h. The as-implanted and annealed samples were characterized using Rutherford backscattering spectrometry (RBS) and Raman spectroscopy. The RT implanted depth profiles indicated that the migration of Xe towards the surface of glassy carbon was accompanied by a loss of Xe ions. The samples implanted at 100°C indicated no diffusion or loss of Xe after annealing at 300°C. However, annealing at temperatures ranging from 400°C to 700°C resulted in a slight shift in the Xe profile tail-end towards the bulk of glassy carbon. The diffusion coefficients (D) in the temperature range of 300°C-700°C for the RT and 100°C implanted samples, activation energies (Ea), and pre-exponential factors (Do), were extracted. The values of D ranged from (9.72±0.48)×10-21 to (1.87±0.09)×10-20m2/s with an activation energy of (6.25±0.31)×10-5eV for RT implanted samples, and the samples implanted at 100°C, D ranged from (3.85±0.19)×10-21 to (6.96±0.34)×10-20m2/s with activation energy of (4.10±0.02)×10-5eV. The Raman analysis revealed that implantation at the RT amorphised the glassy carbon structure while the samples implanted at 100°C showed mild damage compared to RT implantation. Annealing of the RT-implanted sample resulted in some recovery of the damaged region as a function of increasing annealing temperature.

Harnessing Graphene-Modified Electrode Sensitivity for Enhanced Ciprofloxacin Detection.

Increased evidence has documented a direct association between Ciprofloxacin (CFX) intake and significant disruption to the normal functions of connective tissues, leading to severe health conditions (such as tendonitis, tendon rupture and retinal detachment). Additionally, CFX is recognized as a potential emerging pollutant, as it seems to impact both animal and human food chains, resulting in severe health implications. Consequently, there is a compelling need for the precise, swift and selective detection of this fluoroquinolone-class antibiotic. Herein, we present a novel graphene-based electrochemical sensor designed for Ciprofloxacin (CFX) detection and discuss its practical utility. The graphene material was synthesized using a relatively straightforward and cost-effective approach involving the electrochemical exfoliation of graphite, through a pulsing current, in 0.05 M sodium sulphate (Na2SO4), 0.05 M boric acid (H3BO3) and 0.05 M sodium chloride (NaCl) solution. The resulting material underwent systematic characterization using scanning electron microscopy/energy dispersive X-ray analysis, X-ray powder diffraction and Raman spectroscopy. Subsequently, it was employed in the fabrication of modified glassy carbon surfaces (EGr/GC). Linear Sweep Voltammetry studies revealed that CFX experiences an irreversible oxidation process on the sensor surface at approximately 1.05 V. Under optimal conditions, the limit of quantification was found to be 0.33 × 10-8 M, with a corresponding limit of detection of 0.1 × 10-8 M. Additionally, the developed sensor's practical suitability was assessed using commercially available pharmaceutical products.

Carbon Dots Hybrid Nanostructure-based Electrochemical Sensors: Applications in Determining Different Species in a Real Sample

Abstract: This overview describes the synthesis, characterization, and application of different carbon dots hybrid nanostructures obtained by chemical interaction between nanomaterials or nanomaterials bonded to another material, i.e. silicon (SiO2/Carbon dots-N), reduced graphene oxide (rGO/Carbon dots), multiwalled carbon nanotubes (MWCNTs/Carbon dots), nano magnetite (Carbon dots/Fe3O4), reduced graphene oxide and gold nanoparticles (rGO/Carbon dots/AuNPs), copper oxide (CuO/Carbon dots), and Carbon dots/Metallic NPs that were employed in the development of electrochemical (bio)sensors. The formation of different carbon dots hybrid nanostructures has been characterized by X-ray diffraction (XRD), Raman and ultraviolet- visible spectroscopy, atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM), and electrochemical techniques. These carbon dots hybrid nanostructures have been used to modify the surface of glassy carbon and screen-printed electrodes and to determine various analytes, i.e., dopamine, uric acid, paracetamol, ephynefrin, dihydroxybenzenes, pesticides, endocrine disruptors, NADH, and other substances in real samples.

Voltammetry in Microemulsion Formed by Electron Donor Solution in Organic Solvent|Ionic Liquid Microdroplets in Aqueous Electrolyte

Oxygen reduction reaction (ORR)1 or hydrogen evolution reaction (HER)2 at liquid|liquid interface provide the possibility of separation of their products: hydrogen peroxide or hydrogen.3,4 Typically, these reactions are studied at single interface formed between immiscible electrolyte solutions in quiescent conditions. In such geometry the frequency of successful reaction events when highly hydrophobic electron donor (i.e. decamethylferrocene (DMFc) or excited form of decamethylruthenocene (DMRc)) dissolved in organic phase meet proton from aqueous phase is rather limited. Importantly, electrochemical recycling of electron donor at electrode positioned close to the liquid|liquid interface increases efficiency of this reaction.5,6 The use of microemulsion is promising higher efficiency alternative, because of extended interfacial area of numerous organic droplets. As efficient electron exchange between oxidized form of electron donor and the electrode is crucial for biphasic ORR and HER one has to focus on electrochemical studies of DMFc or DMRc in emulsions.are important. Voltammetric signal of various redox probes as ferrocene or ferrocene surfactants in quiescent emulsions is similar to that in single phase with some variation of peak density currents or redox potential.7-11 Other studies focused on chronoamperometric experiments to detect collisions of redox probe (e.g. ferrocene12) containing droplets with the electrode surface. It was found that the addition of an hydrophobic ionic liquid, typically trihexyltetradecyl-phosphonium bis(trifluoro-methylsulfonyl) amide to the organic phase as stabiliser and electrolyte, does not influence the magnitude of the electrochemical signal.13 Here we will report results of electrochemical studies of emulsion prepared from aqueous HClO4 and DMFc or DMRc and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide (IL-PI) solution in toluene. As aqueous phase acid solution was selected, because in biphasic ORR or HER it serves as a source of protons. During the measurements the microemulsion was stirred to achieve faster droplets transport towards the electrode surface. Results will be compared with these obtained in a single organic phase.Voltammograms obtained with glassy carbon disc electrode indicate reversible oxidation/reduction of the redox probe similar to the seen with an electrode immersed in single organic phase. During continuous scanning redox only small change of peak currents is seen. Importantly, when after experiment in emulsion working electrode was transferred to aqueous HClO4, the voltammetric signal is still seen, but the peak currents are significantly smaller. This may indicate the redox reaction in liquid film formed on the electrode surface. Formation of liquid organic film is confirmed by the results of chronoamperometric experiments. When the electrode is set at potential corresponding to the oxidation of the redox probe, of the current is seen after c.a. 100 s drop, what may indicate the gradient of redox probe concentration. As DMFc is insoluble in water this points out on gradient of organic phase close to the glassy carbon surface.14 In turn voltammetric current related to electroreduction of highly hydrophilic hexacyanoferrate(III) is significantly diminished in emulsion as compared to pure aqueous electrolyte indicating partial coverage of the GC surface by hydrophobic film.Other effects related with electrochemical behavior of studied emulsions will be also presented and discussed.

Synergistically Enhanced Electrochemical Sensing of Bisphenol A in Real Water Samples at Carbon Nanotubes/β‐Cyclodextrin/Gold Nanoparticles Composite

AbstractMonitoring of bisphenol A (BPHA) is required as its release with byproducts into the aquatic environment every year, causes pollution and toxicity which affects the human health. An efficient electrochemical sensor is therefore needed to determine BPHA in water from natural resources. To construct the sensor, a thin layer of carbon nanotubes (CNTs) is applied to the surface of glassy carbon (GC) then β‐CD and Aunano are sequentially electrodeposited. The performance of the sensor is optimized and shows excellent catalytic effect in wide concentration range 7 nM to 700 μM with low detection limit of 5.02 nM compared to other cited modified electrodes. Each of the sensor constituents share in the enhancement of its performance; Aunano has intrinsic surface electroactivity, β‐CD “host” allows for BPHA “guest” surface accumulation, and CNTs with large conductive surface area realize homogeneous distribution of the other two components. The advantages of the BPHA electrochemical sensor are simple to prepare, timesaving, and shows good sensitivity, stability, selectivity in presence of interfering ions and compounds, it is suitable for use with portable simple equipment for in situ measurements. Furthermore, the application of the sensor in wastewater samples shows good recovery of BPHA.

Growth of surfactant-free Au-Co bimetallic atom-bomb cracker-like microstructures: A highly active morphological dependent hybrid electrocatalyst for dioxygen reduction

This paper reports the formation of atom-bomb fire cracker (ABC) like Au-Co heterostructures by attaching folic acid-capped AuNPs (FA-AuNPs) on a glassy carbon (GC) electrode followed by cobalt electrodeposition. The characteristic absorption band at 516 nm from the UV–visible spectrum confirms the AuNPs formation and their average size was ∼6 nm as evidenced from HR-TEM. The AuNPs were then assembled on a GC electrode via 1,6-hexadiamine linker followed by the electrodeposition of Co at various applied potentials and time. XPS spectra of Au-Co clearly revealed the zero valent nature of Au and Co and Co2+ in the bimetallic assembly. The SEM results exhibited the variations in the morphology of Au-Co with respect to the applied potential and time. It was found that the deposition of Co at -0.50 V for 600 s leads to the formation of ABC-like structure only at FA-AuNPs surface. The specific atom-bomb morphology of Au-Co was not obtained at bare GC and citrate-capped AuNPs surfaces, indicating the influence of FA-AuNPs. The Au-Co showed higher electrocatalytic activity towards dioxygen reduction by shifting the onset potential by 230 and 280 mV towards zero respectively than Co and AuNPs alone. The Koutecky-Levich plot confirms the four-electron transfer mechanism of oxygen reduction at Au-Co fabricated electrode.

Electropolymerised thin films of (ANIH)5[PCu(H2O)W11O39](ANI).8H2O for the detection of iodate

Keggin-type polyoxometalate (POM) containing anilinium cation, (ANIH)5[PCu(H2O)W11O39](ANI).8H2O, has been synthesised and analysed using FT-IR and UV–vis spectroscopy. A thin film of (ANIH)5[PCu(H2O)W11O39](ANI).8H2O, abbreviated as PANI/[PCu(H2O)W11O39], has been formed onto glassy carbon surfaces by the electro polymerisation technique. The electrochemical behaviour of the modified electrode was investigated using various electrochemical methods, such as cyclic voltammetry and electrochemical impedance spectroscopy. Amperometric detection of iodate studies revealed that the PANI/[PCu(H2O)W11O39] modified electrode has two linear ranges of 2–20 μM and 40–2500 μM, as well as a limit of detection (LOD) and sensitivity of 0.8 μM (S/N = 3) and 0.347 μAcm−2/μM for the lower range and 1.7 μM (S/N = 3) and 0.014 μAcm−2/μM for the higher range respectively. In the presence of typical interfering analytes such as KH2PO4, KCl, NaClO3, NaNO3, Na2SO4, and NaClO4, the suggested electrochemical sensor exhibits significant catalytic activity. The modified electrode showed excellent stability, rapid amperometric response (within 3 s), and the possibility of rapid electrode preparation. Chemico-physical characterisation of the target systems was performed scanning electron microscopy, Fourier transform infrared spectroscopy and UV–visible spectroscopy.

Activation of Glassy Carbon Surfaces by Alkaline Anodization Enhances Dopamine Adsorption and Electron‐Transfer Kinetics

AbstractSurface activation can increase the sensitivity of carbon electrodes for electrochemical detection of neurotransmitters, such as dopamine (DA). However, fully understanding the changes in DA behavior after electrode activation remains elusive. Herein, we use scanning electrochemical cell microscopy (SECCM) to investigate DA adsorption and electrochemistry on glassy carbon (GC) after anodization in alkaline media. Through localized microscale anodization to different extents (two distinct times and same potential), followed by spatially‐resolved SECCM, we achieve direct visualization of DA electrochemistry across unmodified and anodized GC regions, with complementary microscopy and spectroscopy unraveling the effects of co‐located carbon surface chemistry and structure. Our findings reveal that short anodization times (60 s) enhance DA adsorption, rapidly reaching nearly complete monolayer coverage. Longer anodization (300 s) induces further changes in electrochemical surface area so that although the DA surface concentration increased based on geometric area, it was smaller based on specific surface area. This work highlights that even small differences in surface properties after activation can significantly impact electrode performance for neurotransmitter sensing, and separating the individual contribution of chemical and topographical factors remains challenging. SECCM provides an excellent platform to assess activation methods in a high throughput format to help accelerate the discovery of optimal modified electrodes.

C-MEMS-derived glassy carbon electrochemical biosensors for rapid detection of SARS-CoV-2 spike protein

According to a World Health Organization (WHO) report, the world has experienced more than 766 million cases of positive SARS-CoV-2 infection and more than 6.9 million deaths due to COVID through May 2023. The WHO declared a pandemic due to the rapid spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, and the fight against this pandemic is not over yet. Important reasons for virus spread include the lack of detection kits, appropriate detection techniques, delay in detection, asymptomatic cases and failure in mass screening. In the last 3 years, several researchers and medical companies have introduced successful test kits to detect the infection of symptomatic patients in real time, which was necessary to monitor the spread. However, it is also important to have information on asymptomatic cases, which can be obtained by antibody testing for the SARS-CoV-2 virus. In this work, we developed a simple, advantageous immobilization procedure for rapidly detecting the SARS-CoV-2 spike protein. Carbon-MEMS-derived glassy carbon (GC) is used as the sensor electrode, and the detection is based on covalently linking the SARS-CoV-2 antibody to the GC surface. Glutaraldehyde was used as a cross-linker between the antibody and glassy carbon electrode (GCE). The binding was investigated using Fourier transform infrared spectroscopy (FTIR) characterization and cyclic voltammetric (CV) analysis. Electrochemical impedance spectroscopy (EIS) was utilized to measure the change in total impedance before and after incubation of the SARS-CoV-2 antibody with various concentrations of SARS-CoV-2 spike protein. The developed sensor can sense 1 fg/ml to 1 µg/ml SARS-CoV-2 spike protein. This detection is label-free, and the chances of false positives are minimal. The calculated LOD was ~31 copies of viral RNA/mL. The coefficient of variation (CV) number is calculated from EIS data at 100 Hz, which is found to be 0.398%. The developed sensor may be used for mass screening because it is cost-effective.A schematic representation of the SARS-CoV-2 spike protein sensing using surface functionalized glassy carbon electrode

Kinetics of Electrocatalytic Oxidation of Gallic Acid by Activated Glassy Carbon Electrode in Acidic Medium

AbstractAn electrochemically functionalized glassy carbon (GC) electrode was prepared to study Gallic acid (GA) oxidation reaction in an acidic medium. The functionalized GC electrode was found to enhanced GA oxidation reaction in acidic medium by lowering oxidation potential and increasing corresponding current in comparison to a pristine GC. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and x‐ray photoelectron spectroscopy (XPS) methods were used to analyze functionalized GC surface. The development of electropositive C=O functional groups were assumed to enhance the catalytic process. The specific capacitance of the electrode was calculated to be 92.91 μF by analysing EIS. Kinetics of GA oxidation over activated GC was calculated from CVs data. By analysing concentration dependent CVs it was found that the electrode process followed mass transfer limited first order kinetics. The GA oxidation mechanism is potential‐dependent. For potentials above 0.42 V, the oxidation reaction involves the transfer of 2e− and 2H+ via a concerted mechanism, while at potentials below 0.42 V, the mechanism is stepwise. The reaction‘s standard rate constant (k°) was evaluated as 2.08×10−4 cm s−1.

A robust electrochemical sensor based on AgNWs@MoS2 for highly sensitive detection of thiabendazole residues in food samples

Thiabendazole (TBZ), a highly toxic phosphorothioate insecticide commonly used in postharvest fruit management, has the potential to cause detrimental effects on human health as an endocrine disruptor. In this study, an electrochemical sensor was developed to detect TBZ by modifying MoS2 on silver nanowires (Ag NWs@MoS2) and integrating them onto a glassy carbon surface. Cyclic voltammetry revealed that TBZ underwent an irreversible, diffusion-controlled process on Ag NWs@MoS2, leading to a two-fold increase in peak current compared to unmodified MoS2. Square wave voltammetry facilitated TBZ detection, and the sensor exhibited a linear range of 0.05–10 μM with a high coefficient of determination (R2 = 0.9958) and a limit of detection (LOD) of 1.75 nM (signal-to-noise ratio = 3). The sensor's applicability for food safety monitoring was verified through TBZ analysis in pear and apple samples, achieving recoveries of 95.5–103.6% with RSDs in the range of 1.98–3.25%.

Chiral "doped" MOFs: an electrochemical and theoretical integrated study.

This work reports on the electrochemical behaviour of Fe and Zn based metal-organic framework (MOF) compounds, which are "doped" with chiral molecules, namely: cysteine and camphor sulfonic acid. Their electrochemical behaviour was thoroughly investigated via "solid-state" electrochemical measurements, exploiting an "ad hoc" tailored experimental set-up: a paste obtained by carefully mixing the MOF with graphite powder is deposited on a glassy carbon (GC) surface. The latter serves as the working electrode (WE) in cyclic voltammetry (CV) measurements. Infrared (IR), X-ray diffraction (XRD) and absorbance (UV-Vis) techniques are exploited for a further characterization of the MOFs' structural and electronic properties. The experimental results are then compared with DFT based quantum mechanical calculations. The electronic and structural properties of the MOFs synthesized in this study depend mainly on the type of metal center, and to a minor extent on the chemical nature of the dopant.

Discriminating macromolecular interactions based on an impedimetric fingerprint supported by multivariate data analysis for rapid and label-free Escherichia coli recognition in human urine

This manuscript presents a novel approach to address the challenges of electrode fouling and highly complex electrode nanoarchitecture, which are primary concerns for biosensors operating in real environments. The proposed approach utilizes multiparametric impedance discriminant analysis (MIDA) to obtain a fingerprint of the macromolecular interactions on flat glassy carbon surfaces, achieved through self-organized, drop-cast, receptor-functionalized Au nanocube (AuNC) patterns. Real-time monitoring is combined with singular value decomposition and partial least squares discriminant analysis, which enables selective identification of the analyte from raw impedance data, without the use of electric equivalent circuits. As a proof-of-concept, the authors demonstrate the ability to detect Escherichia coli in real human urine using an aptamer-based biosensor that targets RNA polymerase. This is significant, as uropathogenic E. coli is a difficult-to-treat pathogen that is responsible for the majority of hospital-acquired urinary tract infection cases. The proposed approach offers a limit of detection of 11.3 CFU/mL for the uropathogenic E. coli strain No. 57, an analytical range in all studied concentrations (up to 105 CFU/mL), without the use of antifouling strategies, yet not being specific vs other E.coli strain studied (BL21(DE3)). The MIDA approach allowed to identify negative overpotentials (−0.35 to −0.10 V vs Ag/AgCl) as most suitable for the analysis, offering over 80% sensitivity and accuracy, and the measurement was carried out in just 2 min. Moreover, this approach is scalable and can be applied to other biosensor platforms.

Electrochemically programmed evolution of 3-dimensional Ag-microstructure dictating dramatic Raman amplification for sensitive detection of molecules

Surface-enhanced Raman scattering (SERS), as a commonly utilized non-destructive analytical technique, has been widely applied in chemical and environmental fields to identify the trace amounts of analytes. However, instability and low reusability of substrate remains an unresolved challenge. In accordance with the necessity for effective SERS-substrate, we have directly deposited 3-dimensional Ag microstructures on glassy carbon surface through programmed electrodeposition varying the electrode potential in a particular sequence; and thereby morphology-controlled Ag-deposits such as densely packed microflake structure and sparsely scattered microskein structure are eventually developed. Interestingly, morphological properties of as-prepared Ag-deposits have a big influence on Raman signal enhancement; the SERS activities are highly dependent on the presence of protruded sharp edge on metallic surface that led to enlargement of surface area. When using microflake Ag-deposit as a SERS substrate, enhancement factors of 5.2×107 and 3.0×106 are achieved for 4-ATP and thiram, respectively. The SERS performances are better and comparable to those of previously reported Ag-based substrates. In addition, Ag-deposit exhibited highly reproducible SERS signals, which implies a homogeneous distribution of active sites responsible for signal enhancement. This work thus opens a new strategic dimension preparing an efficient SERS substrate by a programmed electrochemical deposition process.

Graphene and gold nanoparticle-based bionanocomposite for the voltammetric determination of bisphenol A in (micro)plastics

The monitoring of endocrine disruptors in the environment is one of the main strategies in the investigation of potential risks associated with exposure to these chemicals. Bisphenol A is one of the most prevalent endocrine-disrupting compounds and is prone to leaching out from polycarbonate plastic in both freshwater and marine environments. Additionally, microplastics also can leach out bisphenol A during their fragmentation in the water environment. In the quest for a highly sensitive sensor to determine bisphenol A in different matrices, an innovative bionanocomposite material has been achieved. This material is composed of gold nanoparticles and graphene, and was synthesized using a green approach that utilized guava (Psidium guajava) extract for reduction, stabilization, and dispersion purposes. Transmission electron microscopy images revealed well-spread gold nanoparticles with an average diameter of 31 nm on laminated graphene sheets in the composite material. An electrochemical sensor was developed by depositing the bionanocomposite onto a glassy carbon surface, which displayed remarkable responsiveness towards bisphenol A. Experimental conditions such as the amount of graphene, extract: water ratio of bionanocomposite and pH of the supporting electrolyte were optimized to improve the electrochemical performance. The modified electrode displayed a marked improvement in current responses for the oxidation of bisphenol A as compared to the uncovered glassy carbon electrode. A calibration plot was established for bisphenol A in 0.1 mol L−1 Britton-Robinson buffer (pH 4.0), and the detection limit was determined to equal to 15.0 nmol L−1. Recovery data from 92 to 109% were obtained in (micro)plastics samples using the electrochemical sensor and were compared with UV–vis spectrometry, demonstrating its successful application with accurate responses.

Ultra-Fast Impedimetric Immunoassay for Detection of Streptococcus agalactiae Using Carbon Electrode with Nanodiamonds Film.

This publication presents the results of work on the development of a quick and cheap electrochemical immunosensor for the diagnosis of infections with the pathogen Streptococcus agalactiae. The research was carried out on the basis of the modification of the well-known glassy carbon (GC) electrodes. The surface of the GC (glassy carbon) electrode was covered with a film made of nanodiamonds, which increased the number of sites for the attachment of anti-Streptococcus agalactiae antibodies. The GC surface was activated with EDC/NHS (1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-Hydroxysuccinimide). Determination of electrode characteristics after each modification step, performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).

Covalent modification of glassy carbon surface via radical-induced grafting from electrochemical oxidation of imine derivatives

The selective surface modification and functionalization methods through organic or inorganic grafting are a permanent challenge for constructing custom-made molecular interfaces with high performance as part of electroactive surfaces. We report the novel use of imine derivatives as a source of radical species for modifying a glassy carbon (GC) surface using electrochemical grafting. Based on the above work related to imine compounds, we designed and synthesized two structural isomers, ferrocenyl-nitro imine derivatives. These electroactive ferrocenyl and nitro functional groups served as redox signaling. In order to identify which part of the imine derivatives was grafted on the GC surface, they were subjected to electrolysis at a constant potential to monitor changes in its imine fragment response. Electrochemical and spectroelectrochemical results suggested that just one of two synthesized isomers (η5-C5H4-CH=N-C6H4-NO2)Fe(η5-C5H5) produced a radical species by electrochemical oxidation of the imine with bond cleavage. After the electrolysis process, the cyclic voltammetry and spectroscopic studies showed that a covalent modification of GC surfaces took place via forming a new bond from a nitro-aryl species on the GC surface. Due to imine bond cleavage, the ferrocenyl scissioned fragment was lost far from the electrode surface.