Electrochemical Impedance Spectroscopy Based Evaluation of 1,10-Phenanthroline-5,6-dione and Glucose Oxidase Modified Graphite Electrode

Electrochemically assisted DNA and thioaromatic assembly as sensing and antifouling interface for food allergens

Food allergies have become a global issue and are estimated to affect approximately 220 million people worldwide. Allergy to peanuts can easily become life-threatening and induce anaphylactic reactions. Mislabeling and cross-contamination during food processing can occur in the frame of world population growth and pose a serious health issue. As the mandatory allergen list is not uniform worldwide, the development of routine analytical strategies with high specificity and sensitivity is a demanding task to aid in the rapid identification of allergenic foods. In this work, an electrochemical aptasensor for Ara h1 peanut allergen was developed by immobilizing the specific aptamer by the inserting method. First, a layer of p-aminothiophenol (p-ATP) was immobilized on the gold surface of screen-printed electrodes (GSPE) to improve the aptamer insertion and reduce the fouling effects at the electrode surface. The grafting of the p-ATP and Ara h1 aptamer on the GSPE surface was monitored by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The resulting disposable aptasensor allowed for indirect electrochemical detection of Ara h1 protein in the presence of 5 mM ferro/ferricyanide as a redox probe. The electrochemical response upon aptamer-target interaction was monitored in the concentration range 1-250 nM, and two limits of detection in the nanomolar range were estimated based on DPV (2.78 nM Ara h1) and EIS (0.82 nM Ara h1) measurements. The aptasensor was successfully applied to real sample analysis.

Electro-oxidation sensing of sumatriptan in aqueous solutions and human blood serum by Zn(II)-MOF modified electrochemical delaminated pencil graphite electrode

An electrochemical sensory platform is presented for determination of sumatriptan (SUM) in aqueous solutions and human blood serum. A pencil graphite electrode (PGE) was electrochemically delaminated by cyclic voltammetry technique, and then further modified using nanoparticles of a zinc-based metal-organic framework (Zn(II)-MOF). The fabricated Zn(II)-MOF/EDPGE electrode was utilized for sensitive electrochemical detection of SUM via an electro-oxidation reaction. The Zn(II)-MOF was hydrothermally synthesized and characterized by various techniques. The electrochemical delamination of PGE results in a porous substrate, facilitating the effective immobilization of the modifier. The designed sensor benefits from both enhanced surface area and an accelerated electron transfer rate, as evidenced by the chronocoulogram and Nyquist plots. Under optimized conditions, the developed sensor exhibited a linear response for 0.99-9.52 µM SUM solutions. A short response time of 5 s was observed for the fabricated sensor and the detection limit was found to be 0.29 μM. Selectivity of Zn(II)-MOF/EDPGE towards SUM was evaluated by examining the interference effect of codeine, epinephrine, acetaminophen, ascorbic acid, and uric acid, which are commonly found in biological samples. The developed sensor shows excellent performance with recovery values falling within the range of 96.6 to 111% for the analysis of SUM in human blood serum samples.

Electric Field-Assisted Uptake of Hexavalent Chromium Ions with In Situ Regeneration of Carbon Monolith Adsorbents

The uptake of hexavalent chromium (Cr(VI)) ions from wastewater is of great significance for environmental remediation and resource utilization. In this study, a self-designed instrument equipped with an oxidized mesoporous carbon monolith (o-MCM) as an electro-adsorbent is developed. o-MCM with a super hydrophilic surface displayed a high specific surface area (up to 686.5 m²  g^-1 ). With the assistance of an electric field (0.5 V), the removal capacity of Cr(VI) ions is as high as 126.6 mg g^-1 , much higher than that without an electric field (49.5 mg g^-1 ). During this process, no reduction reaction of Cr(VI) to Cr(III) ions is observed. After adsorption, the reverse electrode with 10 V is used to efficiently desorb the ions on the carbon surface. Meanwhile, the in situ regeneration of carbon adsorbents can be obtained even after ten recycles. On this basis, the enrichment of Cr(VI) ions in a special solution is achieved with the assistance of an electric field. This work lays a foundation for the uptake of heavy metal ions from wastewater with the assistance of the electric field.

3D Nanocomposite with High Aspect Ratio Based on Polyaniline Decorated with Silver NPs: Synthesis and Application as Electrochemical Glucose Sensor

In this paper, we present a new methodology for creating 3D ordered porous nanocomposites based on anodic aluminum oxide template with polyaniline (PANI) and silver NPs. The approach includes in situ synthesis of polyaniline on templates of anodic aluminum oxide nanomembranes and laser-induced deposition (LID) of Ag NPs directly on the pore walls. The proposed method allows for the formation of structures with a high aspect ratio of the pores, topological ordering and uniformity of properties throughout the sample, and a high specific surface area. For the developed structures, we demonstrated their effectiveness as non-enzymatic electrochemical sensors on glucose in a concentration range crucial for medical applications. The obtained systems possess high potential for miniaturization and were applied to glucose detection in real objects-laboratory rat blood plasma.

Electrochemical and Electroconductive Behavior of Silk Fibroin Electrospun Membrane Coated with Gold or Silver Nanoparticles

The surface modification of materials obtained from natural polymers, such as silk fibroin with metal nanoparticles that exhibit intrinsic electrical characteristics, allows the obtaining of biocomposite materials capable of favoring the propagation and conduction of electrical impulses, acting as communicating structures in electrically isolated areas. On that basis, this investigation determined the electrochemical and electroconductive behavior through electrochemical impedance spectroscopy of a silk fibroin electrospun membrane from silk fibrous waste functionalized with gold or silver nanoparticles synthetized by green chemical reduction methodologies. Based on the results obtained, we found that silk fibroin from silk fibrous waste (SF_w) favored the formation of gold (AuNPs-SF_w) and silver (AgNPs-SF_w) nanoparticles, acting as a reducing agent and surfactant, forming a micellar structure around the individual nanoparticle. Moreover, different electrospinning conditions influenced the morphological properties of the fibers, in the presence or absence of beads and the amount of sample collected. Furthermore, treated SF_w electrospun membranes, functionalized with AuNPs-SF_w or AgNPS-SF_w, allowed the conduction of electrical stimuli, acting as stimulators and modulators of electric current.

Towards electrochemical surface plasmon resonance sensor based on the molecularly imprinted polypyrrole for glyphosate sensing

In this research the molecular imprinting technology was applied for the formation of glyphosate-sensitive layer. The glyphosate imprinted conducting polymer polypyrrole (MIPpy) was deposited on a gold chip/electrode and used as an electrochemical surface plasmon resonance (ESPR) sensor. The results described in this study disclose some restrictions and challenges, which arise during the development of glyphosate ESPR sensor based on the molecularly imprinted polymer development stage. It was demonstrated, that glyphosate could significantly affect the electrochemical deposition process of molecularly imprinted polymer on the electrode. The results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and surface plasmon resonance (SPR) have demonstrated that glyphosate molecules tend to interact with bare gold electrode and thus hinder the polypyrrole deposition. As a possible solution, the formation of a self-assembled monolayer (SAM) of 11-(1H-Pyrrol-1-yl)undecane-1-thiol (PUT) before electrochemical deposition of MIPpy and NIPpy was applied. Dissociation constant (KD) and free energy of Gibbs (ΔG0) values of glyphosate on MIPpy and Ppy without glyphosate imprints (NIPpy) were calculated. For the interaction of glyphosate with MIPpy the KD was determined as 38.18 ± 2.33⋅10-5 and ΔG0 as -19.51 ± 0.15 kJ/mol.

Towards application of CRISPR-Cas12a in the design of modern viral DNA detection tools (Review)

Early detection of viral pathogens by DNA-sensors in clinical samples, contaminated foods, soil or water can dramatically improve clinical outcomes and reduce the socioeconomic impact of diseases such as COVID-19. Clustered regularly interspaced short palindromic repeat (CRISPR) and its associated protein Cas12a (previously known as CRISPR-Cpf1) technology is an innovative new-generation genomic engineering tool, also known as 'genetic scissors', that has demonstrated the accuracy and has recently been effectively applied as appropriate (E-CRISPR) DNA-sensor to detect the nucleic acid of interest. The CRISPR-Cas12a from Prevotella and Francisella 1 are guided by a short CRISPR RNA (gRNA). The unique simultaneous cis- and trans- DNA cleavage after target sequence recognition at the PAM site, sticky-end (5-7 bp) employment, and ssDNA/dsDNA hybrid cleavage strategies to manipulate the attractive nature of CRISPR-Cas12a are reviewed. DNA-sensors based on the CRISPR-Cas12a technology for rapid, robust, sensitive, inexpensive, and selective detection of virus DNA without additional sample purification, amplification, fluorescent-agent- and/or quencher-labeling are relevant and becoming increasingly important in industrial and medical applications. In addition, CRISPR-Cas12a system shows great potential in the field of E-CRISPR-based bioassay research technologies. Therefore, we are highlighting insights in this research direction.

Polymer-dispersed reduced graphene oxide nanosheets and Prussian blue modified biosensor for amperometric detection of sarcosine

A new disposable amperometric biosensor for sarcosine (Sar, a biomarker for prostate cancer) was designed based on screen-printed carbon electrodes, Prussian blue, polymer dispersed reduced graphene oxide (P-rGO) nanosheets, and sarcosine oxidase (SOx). Poly(sodium 4-styrenesulfonate-r-LAHEMA) denoted as PSSL was newly synthesized as dispersant for rGO. The P-rGO was utilized for SOx immobilization, the sulfonate and disulfide functionalities in PSSL enable physical adsorption of SOx and its bioactivity and stability properties were improved. The biosensor was optimized by various enzyme concentration, applied potential, and operating pH. Under the optimized conditions, the biosensor exhibited maximum current responses within 5 s at an applied potential of -0.1 V vs. integrated Ag/AgCl reference electrode. The biosensor had a dynamic linear range of 10-400 μM, with a sensitivity of 9.04 μA mM^-1 cm^-2 and a low detection limit of 0.66 μM (S/N = 3). Additionally, the biosensor possesses strong anti-interference capability, high reproducibility, and storage stability over 3 weeks. Furthermore, its clinical applicability was tested in urine samples from both prostate cancer patients and healthy control, and the analytical recoveries were satisfactory. Therefore, this biosensor has significant potential in the rapid and non-invasive point-of-care testing for prostate cancer diagnosis.

Solvothermal synthesis of Fe3O4 nanospheres for high-performance electrochemical non-enzymatic glucose sensor

Ferroferric oxide (Fe3O4) nanospheres have been synthesized via a facile solvothermal procedure to serve as an electrode material for high performance non-enzymatic glucose sensor. The as-synthesized Fe3O4 nanospheres with a uniform size from 16 to 18 nm, which can increase the reaction contact area and the active sites in the process of glucose detection. Benefiting from the particular nanoscale structure, the Fe3O4 nanospheres obviously enhanced the activity of electrocatalytic oxidation towards glucose. When the Fe3O4 nanospheres material was used for non-enzymatic glucose sensor, several electrochemical properties including the high sensitivity 6560 μA mM-1 cm-2 (0.1-1.1 mM), limit of detection 33 μM (S/N = 3) and good long-term stability were well demonstrated. Furthermore, Fe3O4 nanospheres electrode confirmed the excellent performance of selectivity in glucose detection with the interfering substances existed such as urea, citric acid, ascorbic acid, and NaCl. Due to the excellent electrocatalytic activity in alkaline solution, the Fe3O4 nanospheres material can be considered as a promising candidate in blood glucose monitoring.

Combining Electrospinning and Vapor-Phase Polymerization for the Production of Polyacrylonitrile/ Polypyrrole Core-Shell Nanofibers and Glucose Biosensor Application

In this work, polyacrylonitrile (PAN) nanofiber mats coated with conductive polypyrrole layers were produced at the surface of gold electrodes by a two-step approach combining electrospinning and vapor phase polymerization. In the first step, smooth and uniform PAN fibers exhibiting an average diameter of 650 ± 10 nm were generated through electrospinning of 12 wt% PAN solutions. The electrospun PAN fibers were impregnated with iron(III)tosylate (FeTos), annealed at 70°C and used as a robust and stable template for the growth of a thin layer of conductive polymer by co-polymerizing pyrrole (Py) and pyrrole-3-carboyxylic acid (Py3COOH) vapors under nitrogen atmosphere. The carboxyl groups introduced in polypyrrole coatings enabled further covalent binding of a model enzyme, glucose oxidase. The effect of different parameters (concentration of FeTos into the immersion solution, time of polymerization, Py/Py3COOH molar ratio) on the PAN/PPy/PPy3COOH/GOx impedimetric biosensor response was investigated. In the best conditions tested (immersion of the PAN fibers into 20 wt% FeTos solution, polymerization time: 30 min, 1:2 Py/Py3COOH ratio), the biosensor response was linear in a wide range of glucose concentration (20 nM−2μM) and selective toward ascorbic and uric acids. A very low limit of detection (2 nM) compared to those already reported in the literature was achieved. This value enables the determination of glucose in human serum after a large dilution of the sample (normal concentrations: 3.6 mM−6.1 mM range).

TiO2-x/TiO2-Structure Based 'Self-Heated' Sensor for the Determination of Some Reducing Gases

In this research we report the gas-sensing properties of TiO2-x/TiO2-based hetero-structure, which was 'self-heated' by current that at constant potential passed through the structure. Amperometric measurements were applied for the evaluation of sensor response towards ethanol, methanol, n-propanol and acetone gases/vapours. The sensitivity towards these gases was based on electrical resistance changes, which were determined by amperometric measurements of current at fixed voltage applied between Pt-based contacts/electrodes deposited on the TiO2-x/TiO2-based layer. X-ray diffraction (XRD) analysis revealed the formation of TiO2-x/TiO2-based hetero-structure, which is mainly based on Ti3O5/TiO2 formed during the hydro-thermal oxidation-based sensing-layer preparation process. Additionally, photoluminescence and time-resolved photoluminescence decay kinetics-based signals of this sensing structure revealed the presence of TiO2 mainly in the anatase phase in the TiO2-x/TiO2-based hetero-structure, which was formed at 400 °C annealing temperature. The evaluation of TiO2-x/TiO2-based gas-sensing layer was performed at several different temperatures (25 °C, 72 °C, 150 °C, 180 °C) and at these temperatures different sensitivity to the aforementioned gaseous materials was determined.

Electrochemical Deposition and Investigation of Poly-9,10-Phenanthrenequinone Layer

In this research, a 9,10-phenanthrenequinone (PQ) was electrochemically polymerized on a graphite rod electrode using potential cycling. The electrode modified by poly-9,10-phenanthrenequinone (poly-PQ) was studied by means of cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and scanning electron microscopy. The poly-PQ shows variations in growth pattern depending on the number of potential cycles for the initiation of polymerization. Formed poly-PQ layer demonstrates good electric conductivity, great degree of electrochemical capacitance and unique oxidation/reduction properties, which are suitable for broad technological applications, including applicability in biosensors, supercapacitors and in some other electrochemical systems.

Electrochemical polypyrrole formation from pyrrole 'adlayer'

In this research study, we investigated the morphology of polypyrrole nanostructures, which were formed during the electrochemical deposition of conducting polymer. An electrochemical quartz crystal microbalance (EQCM) cell equipped with a flow-through system was employed to exchange solutions of different compositions within the EQCM cell. When bare PBS buffer in the EQCM cell was exchanged with PBS buffer with pyrrole we observed a distinct increase in the resonance frequency Δf. This change in the resonance frequency and electrical capacitance, which was calculated from electrochemical impedance spectroscopy (EIS) data, illustrate that pyrrole on the surface of the gold electrode formed an adsorbed layer (adlayer). The formation of a pyrrole adlayer before the potential pulse that induced polymerization was investigated by QCM-based measurements. The electrochemical polymerization of this adlayer was induced by a single potential pulse and a nanostructured layer, which consisted of adsorbed polypyrrole (Ppy) nanoparticles with a diameter of 50 nm, was formed. QCM and EIS data revealed that by the next cycle of the electrochemical formation of Ppy, which was investigated after flow-through-based exchange of solutions, the initially formed Ppy surface was covered by the adlayer of pyrrole. This adlayer was desorbed when pyrrole was removed from the solution. When electrochemical polymerization was performed using 50 potential pulses, a Ppy layer, which had more complex morphology, was formed on the EQCM crystal. Scanning electron microscopy showed that the conductivity of this layer was unequally distributed. We observed that the polypyrrole layer formed by electrochemical deposition, which was performed using potential pulses, was formed out of aggregated spherical Ppy particles with a diameter of 50 nm.

Comparison of Two Types of Overoxidized PEDOT Films and Their Application in Sensor Fabrication

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were prepared by electro-oxidation on Au microelectrodes in an aqueous solution. Electrolyte solutions and polymerization parameters were optimized prior to overoxidation. The effect of overoxidation time has been optimized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which results in the film overoxidized for 45 s at 1.35 V presenting a strong adsorption. The other one-step overoxidation film prepared by direct CV ranging from −0.6 V to 1.35 V was polymerized for comparison. Scanning electron microscope (SEM) analysis and Fourier transform infrared (FTIR) spectroscopy were used for monitoring morphological changes and the evolution of functional groups. Both of them indicate increased abundant oxygen functional groups and roughness, yet the products exhibit dendritic morphology and piles of spherical protrusions, respectively. Moreover, double-step overoxidized film showed better electrochemical performance toward lead ion sensing. These characterizations highlight some novel properties that may be beneficial for specific sensing applications.

Immobilisation of cyclodextrin glucanotransferase into polyvinyl alcohol (PVA) nanofibres via electrospinning

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Fabrication of enzyme-carrying polymeric nanofibers by electrospinning.

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PVA nanofibers structure and size were not affected by the addition of enzyme.

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The electrospun CGTase/PVA nanofibers show excellent immobilisation efficiency.

Immobilisation of cyclodextrin glucanotransferase (CGTase) on nanofibres was demonstrated. CGTase solution (1% v/v) and PVA (8 wt%) solution were mixed followed by electrospinning (−9 kV, 3 h). CGTase/PVA nanofibres with an average diameter of 176 ± 46 nm were successfully produced. The nanofibres that consist of immobilised CGTase were crosslinked with glutaraldehyde vapour. A CGTase/PVA film made up from the same mixture and treated the same way was used as a control experiment. The immobilised CGTase on nanofibres showed superior performance with nearly a 2.5 fold higher enzyme loading and 31% higher enzyme activity in comparison with the film.

Vapor grown carbon fiber combined with polyaniline and gold nanoparticles in composite bioelectrodes and their application in glucose fuel cells

In this study, novel VGCF-based composite bioelectrodes PANI/VGCF/GOx and AuNPsNGCF/GOx are fabricated and compared to CNT-based bioelectrodes.

Scanning electrochemical impedance microscopy for investigation of glucose oxidase catalyzed reaction

In this research biointerface based on immobilized glucose oxidase (GOx) was evaluated by scanning electrochemical impedance microscopy (SEIM), which consisted of merged scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). The gluconolactone, which is quickly hydrolyzed to gluconic acid, is produced during the enzyme-catalyzed glucose oxidation reaction. Gluconic acid formed above an enzyme-modified not-conducting plastic surface, was evaluated by EIS technique. A two electrode cell consisting of a scanning probe, which was based on 10 μm diameter ultramicroelectrode and stationary platinum counter/reference electrode was applied for the measurement. Locally measured solution impedance depends on the gluconic acid concentration close to the ultramicroelectrode surface and on the ion diffusion, which is hindered when the electrode is approaching close to the GOx-modified surface. EIS results were evaluated by applying an equivalent circuit consisting of elements representing solution resistance, double-layer capacitance, charge-transfer resistance and Warburg impedance. Solution resistance was calculated and showed to be dependent on the position of ultramicroelectrode. Also it was observed that the thickness of the conducting layer and gluconic acid concentration both are changing in time. The results indicate that here proposed SEIM technique could become a valuable tool for the investigation and characterization of enzyme-modified surfaces of biosensors and biofuel cells.

Comparative investigation of spectroelectrochemical and biosensor application of two isomeric thienylpyrrole derivatives

In the present work, we performed a comparative investigation of spectroelectrochemical and biosensor application of two isomeric thienylpyrrole derivatives.