Unmodified Electrode Research Articles

Synthesis of two-dimensional nanosheet like samarium molybdate with abundant active sites: real-time carbendazimin analysis in environmental samples

The design and construction of efficient nanostructure-based electrocatalyst are the keys to advance in the field of electrochemical sensors. Herein, we synthesize the samarium molybdate (SmM) on a large scale via a straightforward approach. The structure of the as-prepared SmM was investigated using the in-depth electron microscopic and spectroscopic techniques. The SmM modified electrode was electrochemically studied by different voltammetry methods towards the quantitative detection of carbendazim (CDM). This SmM-based electrochemical sensor provides the high activity towards the CDM sensing with a significant decrease in oxidation potential owing to its good conductivity, high carrier mobility and large surface area. The CV results show that the electrode modified with SmM possesses a 1.97-fold increase in the current response compared to the unmodified electrode. Noteworthy, the designed sensor exhibits a dynamic working range of 0.01–22 µM, a trace level detection of 1.0 nM and good selectivity for the practical CDM sensing. The CDM modified electrode has been practically applied in the determination of CDM in environmental samples with satisfactory results.

Graphite Layer Coated on Aluminium Foil as Anti-corrosion Current Collector for Neutral Aqueous Supercapacitors

Neutral aqueous supercapacitors are of interest due to their many advantages such as low-cost, non-flammable, and high ionic conductivity. Interestingly, the current collector is a critical part of these devices since it can be corroded in aqueous electrolytes. The Al foil is a widely used current collector for commercial organic supercapacitors due to its low-cost. However, it is corroded in aqueous electrolytes. To address this issue, we develop the graphite coating layer on the Al current collector to suppress the corrosion of Al and the formation of an oxide-resistive film on Al in an aqueous electrolyte. The corrosion testing was confirmed by the electrochemical impedance spectroscopy (EIS). Furthermore, the electrochemical performance of the as-prepared electrodes with and without the graphite coated layer was studied by using cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The as-prepared electrode with a graphite protective layer exhibits a higher specific capacitance as well as a higher rate capability. The capacitance fading upon increasing scan rate from 10 mV s-1 to 100 mV s-1 of graphite coated aluminium electrode was only 15%, while the capacitance of the unmodified electrode extremely faded up to 75%. The as-prepared electrode with a graphite protective layer can explicitly improve the cycling stability (retain 90 %) after 5,000 cycles at an applied current density of 1 A g-1, which is different from an unmodified electrode with rapid fading up to 55%. This finding may lead to practical neutral aqueous supercapacitors.

Highly-Stable Miniaturized Pt-Nanostructures/Pt Coated Wire Ion Selective Electrode for Fluoxetine HCl

Miniaturized potentiometric ion selective electrodes (ISEs) with improved inner solid contact are demanded for accurate on-line monitoring and quality control analysis. Herein, a new miniaturized all-solid-state ion selective electrode (ISE) with Pt-nanostructures (Pt-NRs) film as a solid contact is developed. Hexachloroplatinic acid and chronoamperometry were used for the nonmanual deposition of Pt-nanostructures onto a miniaturized Pt electrode. The surface morphology of the film was characterized by the Scanning Electron Microscopy (SEM). The double layer capacitance of the Pt-NRs film was characterized by the cyclic voltammetry (CV) and the current reversal chronopotentiometry (CRC). Fluoxetine HCl (FLX), a serotonin reuptake inhibitor, was selected as a model for investigating the potential stability of the Pt-NRs/Pt as an inner solid contact (SC) for coated wires ISEs. The electrode exhibited a near Nernstian response of 56.5±0.5 mV/decade with a wide linear concentration range (1×10 -5 -1×10 -2 M). The Pt-NRs/Pt based ISE showed exceptional potential stability (0.05 μV/s) and reproducibility compared to the unmodified Pt electrode. Moreover, the solid contact (Pt-NRs/Pt) can be reused by dissolving the ion selective membrane (ISM) using an organic solvent and formation of a new ISM by dip coating process. The Pt-NRs film represents a robust SC platform for the construction of portable and reliable all-solid state ISEs for drug analysis.

Determination of sunset yellow and tartrazine in drinks using screen-printed carbon electrodes modified with reduced graphene oxide and NiBTC frameworks

A novel electrochemical method was developed for simultaneous determination of SY and Tz using metal–organic frameworks (MOFs) of NiBTC and reduced graphene oxide (rGO) to modify screen printed carbon electrodes (rGO/NiBTC/SPCEs). This sensor offers an inexpensive, rapid and sensitive method of determination for soft drinks.Under optimal conditions, the results of the rGO/NiBTC/SPCEs have good electron transfer characteristics and low electron transfer resistance, and they increase the oxidation current, as determined by differential pulse voltammetry (DPV) and electrochemical impedance analysis (EIS). In addition, the rGO/NiBTC modifiers were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), powder X-ray diffraction (PXRD) and Fourier-transform infrared spectroscopy (FTIR), which confirmed that the modifiers were successfully prepared.Surprisingly, the electrochemical response of the modified electrode was increased by approximately 35.6- and 33.4-fold for SY and Tz, respectively, relative to the unmodified electrode. The detection limits are 0.025 μM and 0.05 μM at S/N = 3, respectively.

Electrochemical modification of electrodes with polymers derived from of hydroxybenzoic acid isomers: Optimized platforms for an alkaline phosphatase biosensor for pesticide detection

This work reports the electropolymerization of the three hydroxybenzoic acid isomers over pencil carbon graphite electrodes, and their characterization followed by further application in biosensors. Scanning electron microscopy images were obtained proving the electrodes modifications with homogeneous material and infrared spectra showed that the polymers present the unchanged carboxyl group suggesting that the polymerization begins through the phenol oxygen atom. pH and scan rate studies revealed that one electron and one proton are involved at the beginning of the polymerization in all of the isomers. A mechanism was proposed for all three structures based on these data. Alkaline phosphatase (ALP) enzyme was immobilized over the platforms through physical adsorption and covalent binding. Differential pulse voltammograms of 4-nitrophenol (4NP), the enzymatic product from the reaction between the ALP and 4-nitrophenylphosphate were recorded. The response with poly(2HB) and poly(4HB) was greater using the covalent binding than using physical adsorption technique, while poly(3HB) responses were lower than unmodified electrodes. Further studies using poly(2HB) and poly(4HB) platforms provided a low limit of detection of 20.0 μM, and 18.0 μM, respectively. The use of ALP allied with polymer platforms is an excellent choice for the determination of 4NP-generating organophosphorus pesticides, with low-cost and sensitive systems.

Pt-Pd-doped NiO nanoparticle decorated at single-wall carbon nanotubes: An excellent, powerful electrocatalyst for the fabrication of An electrochemical sensor to determine nalbuphine in the presence of tramadol as two opioid analgesic drugs

In this study, a Pt-Pd-doped NiO nanoparticle decorated at the surface of single-wall carbon nanotubes (Pt-Pd/NiO-NPs/SWCNTs) was synthesized using a simple chemical precipitation method and characterized by XRD, TEM, and EDS methods. The results confirmed that Pt-Pd/NiO-NPs/SWCNTs were synthesized with good purity and at the nanoscale size. Moreover, a highly sensitive electroanalytical sensor was fabricated by incorporating synthesized Pt-Pd/NiO-NPs/SWCNT nanocomposites into a carbon paste electrode (CPE) in the presence of 1-ethyl-3-methylimidazolium methanesulfonate (EMICH3SO3−) as binder. The Pt-Pd/NiO-NPs/SWCNTs/EMICH3SO3−/CPE showed a powerful electro-catalytic activity for electro-oxidation of nalbuphine, and the results confirmed that the oxidation of nalbuphine was improved 6.34 times and relative oxidation potential was decreased about 110 mV compared to unmodified electrodes. The Pt-Pd/NiO-NPs/SWCNTs/EMICH3SO3−/CPE also showed good catalytic activity for the determination of nalbuphine in the presence of tramadol and the oxidation potential of these opioid analgesic drugs separated with ΔE =460 mV. In the final step, the Pt-Pd/NiO-NPs/SWCNTs/EMICH3SO3−/CPE was used to determine nalbuphine with a detection limit of 0.9 nM and tramadol with a detection limit of 50.0 nM in drug samples. The results confirmed the powerful and interesting ability of the sensor in the analysis of a real sample.

Study of the Oxygen Evolution Reaction at Strontium Palladium Perovskite Electrocatalyst in Acidic Medium.

The catalytic activity of Sr2PdO3, prepared through the sol-gel citrate-combustion method for the oxygen evolution reaction (OER) in a 0.1 M HClO4 solution, was investigated. The electrocatalytic activity of Sr2PdO3 toward OER was assessed via the anodic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The glassy carbon modified Sr2PdO3 (GC/Sr2PdO3) electrode exhibited a higher electrocatalytic activity, by about 50 times, in comparison to the unmodified electrode. The order of the reaction was close to unity, which indicates that the adsorption of the hydroxyl groups is a fast step. The calculated activation energy was 21.6 kJ.mol−1, which can be considered a low value in evaluation with those of the reported OER electrocatalysts. The Sr2PdO3 perovskite portrayed a high catalyst stability without any probability of catalyst poisoning. These results encourage the use of Sr2PdO3 as a candidate electrocatalyst for water splitting reactions.

Electrochemistry of redox probes at thin films of carbon nano-onions produced by thermal annealing of nanodiamonds

Electrochemical data for pristine carbon nano-onions (CNO), radio frequency Ar/O2 plasma oxidized CNO (CNO-RF) and chemically oxidized CNO (CNO-OXI) cast on glassy carbon electrodes (GCE) are presented. The electrochemical response was evaluated by cyclic voltammetry using [Fe(CN)6]3-, [Ru(NH3)6]3+, [Fe(H2O)6]2+ and ferrocenemethanol (FcCH2OH) as redox probes. The electron transfer kinetics for these probes was influenced by the nature of functional groups on the electrode material, adsorption processes and the electrostatic interactions between the redox probes and the surface of the different carbon nano-onions. The electrocatalytic properties for the reduction of O2 to H2O2 at CNO, CNO-RF and CNO-OXI modified electrodes were also evaluated using linear sweep voltammetry. The electroreduction of O2 shifted to more positive potential (up to −0.16 V vs Ag/AgCl) as the oxidation degree of CNO increased. In the same way, the sensitivity for the electrochemical detection of H2O2 was enhanced up to 50-fold respect to unmodified GC electrode. Furthermore, the electrocatalytic oxidation of ascorbic acid (AA), dopamine (DA) and uric acid (UA) was studied by cyclic voltammetry and differential pulse voltammetry at CNO, CNO-RF and CNO-OXI modified electrodes. The electrodes displayed excellent electrocatalytic activity for the oxidation of AA, DA and UA. These results demonstrate that CNO enhance the electroactive properties of redox probes and are thus promising materials for electrochemical detection and metal-free electrocatalysts of different reactions. Additionally, the electrochemical data obtained here can serve to understand the performance of carbon nano-onion thin films as electrode materials.

Electrochemically activated MnO cathodes for high performance aqueous zinc-ion battery

Aqueous Zn-ion batteries (ZIBs) attract ever-growing attention due to low cost, high safety, and environmental friendliness. Among the limited cathode candidates, manganese-based oxides stand out owing to large ion channels and multiple valence of Mn. Notably, MnO, thought to be inactive before, actually exhibits high energy densities in AZIBs, thus arousing wide interests. Herein, the electrochemical behavior of MnO electrode is extensively investigated in ZnSO4 electrolytes with different concentration of MnSO4. It is confirmed that the inactive MnO is electrochemically activated during the initial charge process. Greatly, the initial capacity and the following cycling stability of MnO electrode strongly depends on the concentration of MnSO4, indicating that the activation of MnO could be attributed to Mn dissolution, leading to the higher valence of Mn as evidenced by ex-situ XPS analysis. Greatly, a H+/Zn2+ co-insertion mechanism is suggested for the as-activated Mn1-xO electrode according to the ex-situ XRD results. In addition, by constructing a core-sheath MnO@N-doped graphene scrolls (MnO@NGS) configuration through a modified hydrothermal process, the reversible capacity of MnO has been successfully improved to 288 mAh g−1 (0.1 A g−1), leading to high energy density of 367 mWh g−1. More importantly, benefiting from the graphene wrapping and sufficient internal voids, 98% of the initial capacity can be retained after 300 cycles (0.5 A g−1), much better than the unmodified MnO and MnO2 electrodes. This work is expected to deepen the understanding of the charge-storage mechanism of MnO and help to design durable manganese-based cathodes for ZIBs.

π-Self-Assembly of a Coronene on Carbon Nanomaterial-Modified Electrode and Its Symmetrical Redox and H2O2 Electrocatalytic Reduction Functionalities.

The structure–electroactivity relationship of graphene has been studied using coronene (Cor), polyaromatic hydrocarbon (PAH), and a subunit of graphene as a model system by chemically modified electrode approach. In general, graphene and PAH do not show any redox activity in their native form. Herein, we report a simple electrochemical approach for the conversion of electro-inactive coronene to a highly redox-active molecule (Cor-Redox; E°′ = 0.235 ± 0.005 V vs Ag/AgCl) after being adsorbed on graphitic carbon nanomaterial and preconditioned at an applied potential, 1.2 V vs Ag/AgCl, wherein, the water molecule oxidizes to dioxygen via hydroxyl radical (•OH) intermediate, in acidic solution (pH 2 KCl–HCl). When the same coronene electrochemical experiment was carried out on an unmodified glassy carbon electrode, there was no sign of faradic signal, revealing the unique electrochemical behavior of the coronene molecule on graphitic nanomaterial. The Cor-Redox peak is found to be highly symmetrical (peak-to-peak potential separation of ∼0 V tested by cyclic voltammetry (CV)) and surface-confined (ΓCor-Redox = 10.1 × 10–9 mol cm–2) and has proton-coupled electron-transfer (∂E°′/∂pH = −56 mV pH–1) character. Initially, it was speculated that Cor is converted to a hydroxy group-functionalized Cor molecule (dihydroxy benzene derivative) on the graphitic surface and showed the electrochemical redox activity. However, physicochemical characterization studies including Raman, IR, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), redox-site selective oxidation probe, cysteine (for dihydroxy benzene), radical scavenger ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl, TEMPO), and scanning electrochemical microscopy (SECM) using ferricyanide redox couple have revealed that coronene cationic radical species like electroactive molecule is formed on graphitic material upon the electrochemical oxidation reaction at a high anodic potential. It has been proposed that •OH generated as an intermediate species from the water oxidation reaction is involved in the coronene cationic radical species. Studies on coronene electrochemical reaction at various carbon nanomaterials like multiwalled carbon, single-walled carbon, graphite, graphene oxide, and carbon nanofiber revealed that graphitic structure (without any oxygen functional groups) and its π–π bonding are key factors for the success of the electrochemical reaction. The coronene molecular redox peak showed an unusual electrocatalytic reduction of hydrogen peroxide similar to the peroxidase enzyme-biocatalyzed reduction reaction in physiological solution.

Low-cost voltammetric sensor based on an anionic surfactant modified carbon nanocomposite material for the rapid determination of curcumin in natural food supplement

A highly sensitive and selective voltammetric method was developed for the determination of curcumin using sodium dodecyl sulfate modified carbon nanocomposite paste electrode. The electrochemical performance for curcumin was characterized by the use of linear sweep voltammetry, cyclic voltammetry, and differential pulse voltammetry. These measurements showed that the sodium dodecyl sulfate modified carbon nanocomposite paste electrode provided excellent electrocatalytic enhancement for the oxidation of curcumin compared to an unmodified carbon nanocomposite paste electrode. Using the optimized conditions, the oxidation peak current showed a linear response from 2 × 10−7 to 1 × 10−6 M and 1.5 × 10−6 to 4.5 × 10−6 M with a detection limit equal to 2.7 × 10−8 M and limit of quantification equal to 9.2 × 10−8 M. The simultaneous determination of curcumin and vitamin B2 included a well resolved peaks, that provides rapid and selective analysis in the presence of vitamin B2. Moreover, the practical application of the developed electrode was performed for the analysis of a natural food supplement for curcumin.

Selective Detection of Cysteine at a Mesoporous Silica Film Electrode Functionalized with Ferrocene in the Presence of Glutathione

AbstractUnmodified and ferrocene‐functionalized mesoporous silica layers exhibiting vertical nanochannels have been grown through electrochemically assisted self‐assembly onto indium‐tin oxide (ITO), and the resulting film electrodes have been applied for the electrochemical detection of cysteine. When using the unmodified film electrode and ferrocenedimethanol (Fc(MeOH)2) as a mediator in solution, both cysteine and glutathione can be oxidized by the Fc(MeOH)2+ generated at the electrode surface, but the electron transfer rates were three times faster with cysteine than with glutathione. This can be exploited for the reagent‐free selective detection of cysteine over glutathione by using a ferrocene‐functionalized mesoporous silica film on an ITO electrode, based on a combination of charge transfer kinetic and mass transport limitations through the oriented nanochannels. This has been demonstrated here by using cyclic voltammetry and amperometry in flow‐injection analysis mode. A sensitivity of 1.28 mA M−1 was measured for the cysteine concentration range of 3–20 μM with a repeatability of the signal between 3 and 12 %. The lowest concentration of cysteine experimentally detected was 3 μM.

Determination of levofloxacin in pharmaceutical formulations and urine at reduced graphene oxide and carbon nanotube-modified electrodes

In this paper, we compare reduced graphene oxide (RGO) electrode with multi-walled carbon nanotubes (MWCNT) as modifiers for the sensitive detection of levofloxacin. The RGO-based sensor showed higher currents for levofloxacin compared with the MWCNT-modified (4-fold) and unmodified electrodes (20-fold). A thin-layer adsorptive process was verified for the oxidation of levofloxacin on the RGO-modified electrode which explains the higher currents. Differential pulse voltammetry (DPV), square wave voltammetry (SWV), and amperometric detection using flow-injection analysis (FIA-AMP) were evaluated for levofloxacin determination in urine and pharmaceutical samples. Detection limits of 1.45, 6.70, and 1.90 μmol L−1 and recovery levels of 91, 106, and 103%, respectively were obtained. A relative standard deviation lower than 7.7% indicated proper precision. The FIA-AMP using the RGO-modified electrode presented high analytical frequency (around 100 injections per hour) and thus was selected for the analysis of the samples. Statistically, similar results (95% confidence level) compared with ultra-fast liquid chromatography (UFLC) analysis and recovery level of 96% for the analysis of urine were obtained.

A nano-sensor based on screen printed electrode (SPE) for electro-chemical detection of vitamin B9

The present study designed an electro-chemical instrument with high sensitivity and selectivity on the basis of a SPE modified with La+3/Co3O4 nano-cubes in order to analyze vitamin B9. It was confirmed that this sensor possesses very good electron-moderating behaviors to oxidize vitamin B9 in a 0.1 M phosphate buffer solution (PBS) (pH=7.0). In addition, according to optimal conditions (pH=7.0), a potential around 110 mV less positive than the one in the un-modified electrodes is required for vitamin B9 oxidation at this electrode surface. This technique limit of determination for vitamin B9 has been estimated to be 0.3 μM (S/N = 3). Responses have been linear in concentrations range between 1.0 and 600.0 μM. The modified electrode has been applied to detect vitamin B9 in real specimens, which was accompanied by acceptable outputs. Experiments showed that La+3/Co3O4 nano-cubes will be valuable electrode materials providing a high ratio of surface to volume that enhances sensitivity. The study introduces a novel sensor with simpleness, quickness, sensitivity, and affordability features to quantify vitamin B9.

Electrochemical Properties of pH-Dependent Flavocytochrome C 3 from Shewanella Putrefaciens Adsorbed Onto Catechol-Modified Carbon Electrode

A century after the demonstration that electrons from microbial metabolism can be harvested with electrodes, electron transfer processes in biofilms of microorganisms performing respiration on extracellular solids are now being studied in order to increase the performance of microbial electrochemical technologies such as microbial fuel cells. Extracellular electron transfer occurring at the microorganism/electrode interface stimulated a wide range of fundamental and applied studies because of important implications in biotechnology, bioenergetics and bioremediation. Most studies focus on two Gram-negative mesophilic bacteria able to transfer electrons from their respiratory metabolism to extracellular solids, namely Shewanella oneidensis MR-1 and Geobacter sulfurreducens. In these model electroactive microorganisms, multiheme c-type cytochromes transfer electrons from cytoplasmic and inner-membrane oxidizing enzymes towards cell surface redox proteins that are responsible for the reduction of solid phase electron acceptors. It is also known that electron transfer is usually coupled to proton transfer which causes acidification in the anodic biofilms and in the anolyte with deleterious consequences for the biofilm metabolism and stability. The fundamental understanding of these processes that involve large proteins (>70 kDa) often with complex redox properties (with ≥10 heme centers in some multihemes cytochromes) is still in its infancy and precludes the optimization of microbial electrochemical technologies. In Gram-negative electroactive bacteria such as Shewanella, several redox proteins have pH-dependent potentials, such as flavocytochrome c 3 (M r = 63.8 kDa) which is one of the most abundant proteins in the periplasm and the only functional fumarate reductase in this microorganism.This work focuses on the design and the development of an efficient and versatile electrochemical platform able to probe charge (electron/proton) transfer properties of proteins from Gram-negative electroactive bacteria on modified carbon electrodes.[1] The electrodes are first modified with pH-responsive electrophores such as quinone units and then proteins are immobilized for electrochemical studies. If relevant, the protein electroactivity can be probed directly at the modified electrode while proton transport, if any, performed by the protein can be detected thanks to the grafted pH sensor.The electrochemical detection of a pH-dependent redox protein from electroactive bacteria at an electrode modified to act additionally as an efficient pH sensor based on a redox readout is demonstrated. The pH sensing electrode was previously designed and showed to allow the immobilization and study of pH-independent and redox active cytochrome c.[1] Here we extend this work to flavocytochrome c 3, a tetraheme FAD-containing periplasmic flavoenzyme isolated from the bacterium Shewanella putrefaciens, taken as a model pH-dependent redox protein from electroactive bacteria [2]. The modification of the electrode surface with the pH sensing modifier (catechol) stems from our previous experience in the tailoring of bio-interfaces of carbon electrodes with covalent electrografting. Flavocytochrome c 3 adsorption onto the modified electrode surface is successfully achieved by cyclic voltammetry in a flavocytochrome c 3 solution containing polymyxin as co-adsorbate. The electrochemical activity of the immobilized flavocytochrome c 3 is detected without alteration of its native structure and by keeping intact its electrochemical properties and its catalytic fumarate reductase activity.[2] The redox activity of the protein arises from its FAD and four hemes cofactors. The experiments evidence that the hemes’ redox potentials of flavocytochrome c 3 from Shewanella putrefaciens, for which no crystal structure is yet available, depend on pH which is at variance with data from the other strains Shewanella frigidimarina or Shewanella oneidensis.[1] Lebègue, E.; Louro, R. O.; Barrière, F. Electrochemical Detection of pH-Responsive Grafted Catechol and Immobilized Cytochrome c onto Lipid Deposit-Modified Glassy Carbon Surface. ACS Omega 2018, 3 (8), 9035–9042. https://doi.org/10.1021/acsomega.8b01425.[2] Lebègue, E.; Costa, N. L.; Fonseca, B. M.; Louro, R. O.; Barrière, F. Electrochemical Properties of pH-Dependent Flavocytochrome C3 from Shewanella Putrefaciens Adsorbed onto Unmodified and Catechol-Modified Edge Plane Pyrolytic Graphite Electrode. Journal of Electroanalytical Chemistry 2019, 847, 113232. https://doi.org/10.1016/j.jelechem.2019.113232. Figure 1

Impedimetric Detection of Haemophilus Influenzae on Antibodies-Modified Boron-Doped Carbon Nanowall Electrodes

Haemophilus influenzae (Hi) is a gram-negative pathogenic bacterium. Type b bacteria (Hib) and non-enveloped strains are of greatest clinical importance. Hib causes systemic infections by hematopoietic dissemination from the respiratory system to distant sites such as meninges.Nowadays the most reliable method for Hib infections diagnosis is isolation in microbiological culture. A cerebrospinal fluid sample from a patient suspected of having meningitis is stained and microbiologically cultured. Isolation efficiency and quality depend on many factors also in addition, carrying out the complete test procedure is time consuming and expensive. Thus it is crucial to develop techniques that allow detecting pathogenic bacteria in fast and qualitative way before the first symptoms appear.In the following work the electrochemical impedance methods were used to detect Hi bacteria and specific protein (protein D) appearing on its surface. Hi immunosensor was developed on boron-doped carbon nanowall (B:CNW) electrodes modified with anti-protein D antibodies.The B:CNW modification steps included electrochemical reduction of the aminobenzoic acid diazonium salt and antibody binding via EDC/NHS chemistry. Many scientists deal with the topic of use bovine serum albumin (BSA) for the blockage of unmodified electrode. Here this step was abandoned due to high resistance occurring on the sample after the electrografting stage, which indicates a very effective modification of the electrode surface. An additional argument confirming the correctness of skipping the BSA stage are the results of the sensor's cross-reactivity with other pathogens. For the determination of the sensor selectivity, three non-target pathogens were selected: S. pyogenes, S. pneumoniae, B. parapertussis. For each pathogen used for the selectivity study, the impedimetric responses were significantly lower than for Hi at similar concentrations.Electrochemical impedance spectroscopy measurements were performed on anti-protein D antibodies (ap. D) for protein D (Fig. 1a) and Hi. Then calibration curve was constructed as a relative change in the electron transfer resistance (Rct) (Fig. 1b). Since the calibration curve shows the logarithmic relationship of the antigen concentration to the impedimetric sensor response, linear regression cannot be used to calculate the LOD. It is therefore necessary to modify the calculation procedure so that it can be applied in the present case. This requires changing the equation's layout and then deriving the formula for the deviation of the logarithm of the concentration. The LOD value calculated in this way for Hi bacteria was 19.45 CFU/ml which is a reliable value.For the sensor’s selectivity studies, the electrodes were prepared identically to the electrodes intended for Hi detection. The response of sensor for S. pyogenes (64750 CFU/ml) and B. parapertussis (17200 CFU/ml) were less than 5%, which are almost unnoticeable in comparison to the response for Hi at level of 50% (47910 CFU/ml).This work was supported by the National Centre for Research and Development TECHMATSTRATEG 1/347324/12/NCBR/ 2017 Figure 1

Studies on the Mechanism of Electrochemical Detection of Haemophilus Influenzae at Diamond-Based Electrodes

Haemophilus influenzae (HI) is a Gram-negative pathogenic bacterium whose infections occur worldwide and mainly affect unvaccinated children and those who have not completed the basic vaccination course. Type B of this bacterium (Hib) can cause sepsis, and other invasive diseases as dermatitis or arthritis but the most dangerous is pneumonia meningitis. The most reliable method for recognizing Hib infections is isolation in microbiological culture. Serological tests are also performed to diagnose Hib infections. They rely on the detection of the presence of bacterial antigens or antibodies which have the ability to bind to specific antigens. Detection of antibodies doesn’t mean disease but only indicate contact with a given bacterium in the past. Recognition of bacteria using presently known methods takes a long time and requires expensive equipment although fast and sensitive detection of Haemophilus influenzae is crucial l to start treatment early enough.In this work, we present electrochemical detection of HI on diamond-based pastes electrodes using binding specific antibodies (ap. D) with proteins occurring on the surface of bacteria (protein D). The measuring system consisted of a specially prepared printed circuit board (PCB) and diamond-based electrode, which was prepared by screen printing in special conditions. Places printed on it, served as a working electrode, counter electrode and reference. Ceramics was first used as a substrate, but it was quickly changed to Teflon, which showed better adhesion to diamond pastes. Better sample strength was also obtained, so it could be washed in an ultrasonic cleaner without fear of damage. Before detection, the electrode had to be modified by electrochemical reduction of the aminobenzoic acid diazonium salt, antibodies deposition via EDC / NHS and blocking the unmodified electrode sites by incubating in solution of Bovine Serum Albumin (BSA). The last step of modification prevents unspecific adsorption on electrode surface which would lead to false detection results.Electrochemical Impedance Spectroscopy Fig. 1) were used to bacteria detection. The electron transfer resistance rises with each step of electrode modification and increased bacterial concentration in solution. Then a calibration curve was constructed.Three pathogens were selected to check the biosensor selectivity: S. pyogenes, S. pneumoniae, B. parapertussis. For each pathogen responses were significantly lower than for HI at similar concentrations. For example, the response of sensor for S. pyogenes (67474,28 CFU/ml) and B. parapertussis (17819,27 CFU/ml) were less than 5%, which are much smaller in comparison to response at level of 30% for HI (47003,48 CFU/ml). Acknowledgments The authors gratefully acknowledge financial support from the National Centre for Science and Development Grant Techmatstrateg No. 347324 2015/16/T/ST7/00469. Figure 1

Low-cost and simple FDM-based 3D-printed microfluidic device for the synthesis of metallic core–shell nanoparticles

A fused deposition modeling-based 3D-printed microfluidic device is designed and built to synthesize core–shell metallic Au@Ag nanoparticles based on the reduction of a silver salt on gold nanoparticles seeds by sodium borohydride in a continuous flow manner. A microfluidic device consisting of three inlets for the reactants and one outlet to collect the synthesized nanoparticles is printed in less than two hours using poly(lactic acid) as the polymer, presenting channels width and height of approximately 260 µm. After synthesis, the nanoparticles samples were analyzed by UV–Vis spectroscopy and transmission electron microscopy to confirm the formation of the core–shell structure. The concentration of the silver salt was varied, while the flow rate was kept constant, and the results indicated that too high silver concentration in relation to amount of gold seeds could lead to coalescence of the synthesized nanoparticles. We obtained core–shell nanoparticles of approximately 23 nm in diameter. Finally, we employed the synthesized Au@Ag nanoparticles in the surface modification of a carbon paste electrode, which showed improved charge transfer behavior compared to the unmodified electrode against a ferri-ferrocyanide probe, while working as a functionalized electrode in the sensing of thiocyanate ions.

A new electroanalytical methodology for the determination of formaldehyde in wood-based products

A new electroanalytical methodology was developed for the sensitive and selective determination of formaldehyde in wood-based products (WBPs), featuring an extraction process using a Headspace Liquid Acceptor System (HLAS), and detection by square-wave voltammetry (SWV) on unmodified screen-printed carbon electrodes (SPCEs). HLAS, here presented for the first time, captures and derivatizes formaldehyde released from the sample by using the acetylacetone reagent as acceptor solution. The product of formaldehyde with acetylacetone, in the presence of ammonium salt, is 3,5-diacetyl-1,4-dihydrolutidine (DDL) which we have found to be electrochemically active at unmodified SPCEs, generating a selective oxidation peak at +0.4 V. Detection and quantification limits of 0.57 and 1.89 mg kg−1 were obtained, together with intra- and inter-day precisions below 10% (as relative standard deviation, RSD). The methodology was used to determine formaldehyde content in seven WBPs, with similar results being obtained by the developed HLAS-SPCE method and the European standard method EN 717–3, with a profound reduction of total analysis time.The developed HLAS-SPCE combines the use of a new sample preparation procedure for volatiles with, as far as we know, the first determination of formaldehyde (as the derivative product, DDL) on unmodified SPCEs, offering a promising alternative for the determination of formaldehyde in WBPs and other samples.

Electrochemical Determination of Hydrogen Peroxide by a Nonenzymatic Catalytically Enhanced Silver-Iron (III) Oxide/Polyoxometalate/Reduced Graphene Oxide Modified Glassy Carbon Electrode

The synergism of phosphomolybdic acid hydrate (POM) decorated with silver-iron (III) oxide (Ag-Fe2O3) nanoparticles and anchored on reduced graphene oxide (RGO) have been demonstrated to be effective as a nonenzymatic H2O2 sensor platform. The assembly of the sensor components and their interactions were probed morphologically, spectroscopically and electrochemically. The Ag-Fe2O3/POM/RGO nanocomposite sensor provided an enhanced electroactive surface area, electrical conductivity and sensitivity for hydrogen peroxide compared to an unmodified glassy carbon electrode (GCE) at –0.55 V versus a saturated calomel electrode. The developed sensor amperometric response was linear across the concentration range from 0.3 mM to 3.3 mM (R2 = 0.992) with a detection limit and sensitivity of 0.2 μM and 271 μA·mM‒1·cm−2 respectively. Concomitantly, a short response time of T90 < 5 sec at a signal-to-noise ratio of 4 was achieved. The sensor was shown to determine hydrogen in the presence of interfering species, and exhibited high selectivity with relative standard deviation values less than 4.2%. The results indicate that the use of RGO to anchor and photochemically reduce POM also improved the reduction properties due to the irregular size distribution and catalytic activity of Ag-Fe2O3 stimulated by its adhesion to the distinctive POM/RGO matrix.