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This study describes the application of a polypyrrole-based sensor for the determination of SARS-CoV-2-S spike glycoprotein. The SARS-CoV-2-S spike glycoprotein is a spike protein of the coronavirus SARS-CoV-2 that recently caused the worldwide spread of COVID-19 disease. This study is dedicated to the development of an electrochemical determination method based on the application of molecularly imprinted polymer technology. The electrochemical sensor was designed by molecular imprinting of polypyrrole (Ppy) with SARS-CoV-2-S spike glycoprotein (MIP-Ppy). The electrochemical sensors with MIP-Ppy and with polypyrrole without imprints (NIP-Ppy) layers were electrochemically deposited on a platinum electrode surface by a sequence of potential pulses. The performance of polymer layers was evaluated by pulsed amperometric detection. According to the obtained results, a sensor based on MIP-Ppy is more sensitive to the SARS-CoV-2-S spike glycoprotein than a sensor based on NIP-Ppy. Also, the results demonstrate that the MIP-Ppy layer is more selectively interacting with SARS-CoV-2-S glycoprotein than with bovine serum albumin. This proves that molecularly imprinted MIP-Ppy-based sensors can be applied for the detection of SARS-CoV-2 virus proteins., Graphical abstract Image, graphical abstract

Present investigation deals with electrochemical determination of copper(II), lead(II) and mercury(II) ions, using ethylenediaminetetraacetic acid (EDTA) chelating ligand modified polyaniline (PANI) and singe walled carbon nanotubes (SWCNTs) based nanocomposite (PANI/SWNCTs). Stainless steel (SS) electrode was modified with PANI and SWCNTs based nanocomposite. PANI/SWCNTs nanocomposite was electrochemically synthesized using potential cycling technique. Further it was modified with EDTA in the presence of 1-ethyl-3(3-(dimethylamin propyl)carbodiimide (EDC) as activating agent, using dip coating technique at room temperature. The EDTA_PANI/SWCNTs/SS electrode was characterized by cyclic voltammetry in 0.5 M H2SO4, which was complemented with electrochemical impedance spectroscopy (EIS). AFM and SEM analysis was applied for the morphological studies of EDTA_PANI/SWCNTs nanocomposite structure. FTIR analysis was applied for the structural and compositional analysis of EDTA_PANI/SWCNTs nanocomposite. All the characterizations were performed before and after the modification of PANI/SWCNTs nanocomposite structure with chelating ligand. Differential pulse voltammetry (DPV) was used for the determination of Cu(II), Pb(II) and Hg(II) ion concentrations. Analytical characteristic such as selectivity and sensitivity of here above-mentioned metal ions was studied. The limit of detection the EDTA_PANI/SWCNTs/SS toward Cu(II), Pb(II) and Hg(II) was determined as 0.08 μM, 1.65 μM and 0.68 μM respectively.

Scanning electrochemical microscopy (SECM) is an advanced electrochemical method, which is based on electrochemical scanning of electrochemical system surface by an ultramicroelectrode. Due to very high complexity of such systems the evaluation of data collected by this electrochemical method is a challenging task, which could be partly solved by mathematical modeling of processes that are influencing the signal of SECM. Several attempts to describe these processes mathematically have been performed for both feedback and generation-collection SECM modes. However, mathematical models for the redox competition SECM mode still were not elaborated due to high complexity of this problem. Therefore in this research work we have developed a mathematical model for the evaluation of enzyme − glucose oxidase (GOx) − modified surface by SECM, which was acting at redox competition mode. The rates of (i) GOx catalyzed processes, (ii) electrode reactions and (iii) diffusion were taken into account by proposed mathematical model. Using this model, it is possible to calculate oxygen consumption rate, to evaluate enzymatic reaction kinetics, and to determine diffusion coefficients of oxygen diffusion in the SECM-based systems.

Microbial fuel cells can be efficiently used for simultaneous cleaning of wastewater and generation of electricity. This research demonstrates the applicability of Baker yeast cells in the design of microbial biofuel cells. The applicability the 9,10-phenantrenequinone (PQ) as a redox mediator in the design of yeast-based microbial cell (MFC) for the improvement of charge transfer through the yeast cell membrane and cell wall towards the electrode was evaluated. The viability of bakers' yeast and pure Saccharomyces cerevisiae cell strains was investigated by evaluating the growth velocity of cells in the presence of a different concentration of PQ in solution. The growth curves of bakers' yeast showed that they were more resistant to PQ. Electrochemical measurements were performed with PQ as a redox mediator, which was (i) dissolved in solution and (ii) adsorbed on a graphite electrode. Differently modified graphite electrodes (namely: (i) non-modified, (ii) yeast-modified, (iii) modified by PQ and yeast) were evaluated. The modified electrodes were evaluated as anodes of MFC. The dependence of potential on external resistance and generated power of MFC was evaluated. Maximal open circuit potential was 178 mV at 7.8 mM of glucose and 23 mM of potassium ferricyanide. Maximal power of BFC calculated at the same conditions was registered at 56 mV, and it reached 22.2 mW/m2 (at 30 mM of glucose). The application of PQ as a redox mediator for yeast-based MFC improves electron transfer through the yeast cell membrane and cell wall towards electrode without any noticeable decrease of yeast cell viability.

Three-dimensional (3D) cell cultivation systems in vitro are promising biomodels to study the metabolic processes of healthy and diseased human heart cells. Cardiac 3D-spheroids are mimicking cell living conditions and, therefore, they can be employed to investigate processes that occur in both extra-cellular and intra-cellular environments. In this study, human healthy and dilated left ventricle myocardium-derived mesenchymal stem cells (hmMSCs) were grown for 5 days in two different cell cultivation systems in vitro: (i) attached to the cell culture flask (2D-cultivation) and (ii) in spheres (3D-cultivation). Then 2D- and 3D-cultivated healthy and pathological hmMSCs have been investigated by generation-collection mode of scanning electrochemical microscopy (GC-SECM) using 2-methylnaphthalene-1,4-dione (menadione or MD) as a redox mediator. Healthy 2D-cultivated hmMSCs were more redox active, therefore, faster responded to MD and were more sensitive to the high MD concentrations compared to the pathological hmMSCs. 3D-cultivation of pathological cells improved their redox activity and made healthy hmMSCs more resistant to the MD. Data of this study show that SECM measurements, using redox mediator MD, can be applied to investigate changes of intra-cellular redox status of human healthy and dilated hmMSCs grown under different conditions. Moreover, the intra-cellular redox status of dilated hmMSCs can be purposefully improved by 3D-cultivation with further their application for therapeutic purposes.

The amperometric glucose biosensors based on adsorbed electron transfer mediator (ETM) tetrathiafulvalene (TTF) or 1,10-phenanthroline-5,6-dione (PD) and glucose oxidase (GOx) from Aspergillus niger (GOx A.niger ), Penicillium adametzii (GOx P.adametzii ) or Penicillium funiculosum (GOx P.funiculosum ) cross-linked with glutaraldehyde were investigated. ETM and enzyme were immobilized layer by layer on bare graphite rod electrode (GR) premodified with gold nanoparticles (AuNP) of (i) 3.5 nm (GOx/ETM/AuNP 3.5 /GR), (ii) 6.0 nm (GOx/ETM/AuNP 6.0 /GR) and (iii) 13.0 nm (GOx/ETM/AuNP 13.0 /GR) size. The amperometric signals for all the developed biosensors were higher using PD in comparison with TTF. The biosensor based on GOx P.funiculosum showed higher analytical signal to glucose in a comparison to biosensors based on GOx A.niger and GOx P.adametzii . The registered current to glucose using GOx P.funiculosum /PD/AuNP 3.5 /GR electrode was linear in the glucose range from 0.1 to 10.0 mmol L −1 and the limit of detection was 0.024 mmol L −1 . Enzymatical synthesis of polypyrrole (Ppy) layer on the electrode was applied in order to expand the linear glucose detection range. After 22 h of polymerization the amperometric signal was linear in the glucose concentration range from 0.1 to 25.0 mmol L −1 , while after 69 h this rage was increased up to 50.0 mmol L −1 . Additionally Ppy layer on the electrode surface reduced the influence of interfering species on the amperometric signal. The performance of developed biosensor was investigated in human serum samples.

1,10-Phenanthroline-5,6-dione and glucose oxidase modified and unmodified graphite electrodes were analysed in buffer/glucose media by the electrochemical impedance spectroscopy (EIS) method. The EIS analysis was carried out under potentiostatic conditions. The gathered impedimetric data was evaluated applying estimated equivalent circuits. It was determined that equivalent circuit RΩ(RF2C2)(C[RFW]) most optimally describes this electrochemical system. The study revealed redox mediating properties of 1,10-phenanthroline-5,6-dione deposited on graphite electrodes.

In this study development of impedimetric sensor based on oxygen terminated boron-doped nanocrystalline diamond (B:NCD:O) modified with theophylline imprinted polypyrrole is described. Hydrogen peroxide induced chemical formation of polypyrrole molecularly imprinted by theophylline was applied for the modification of conducting silicon substrate covered by B:NCD:O film. Non-imprinted polypyrrole layer was formed on similar substrate in order to prove efficiency of imprinted polypyrrole. Electrochemical impedance spectroscopy was applied for the evaluation of analyte-induced changes in electrochemical capacitance/resistance. The impact of polymerization duration on the capacitance of impedimetric sensor was estimated. A different impedance behavior was observed at different ratio of polymerized monomer and template molecule in the polymerization media. The influence of ethanol as additive to polymerization media on registered changes in capacitance/resistance was evaluated. Degradation of sensor stored in buffer solution was evaluated.

Electrochemical modification of glassy carbon (GC) electrode by poly-4-nitroaniline (P4NA), electrochemical reduction of P4NA and applicability of electrode modified in this way for determination of copper(II) (Cu(II)) is reported in this study. Electrochemical surface modification was performed by cyclic voltammetry in the potential range between +0.9 V and +1.4 V vs. Ag/Ag + (in 10 mM AgNO 3 ) at the scan rate of 100 mV/s by 100 cycles in non-aqueous media. In order to provide electrochemical reduction of nitro groups on the P4NA-modified GC electrode surface (P4NA/GC), the cyclic voltammograms inducing/evidencing the reduction of nitro groups were performed in the potential range between −0.1 V and −0.8 V vs. Ag/AgCl/(sat.KCl) at the scan rate of 100 mV/s. The reduced P4NA/GC surfaces (Reduced-P4NA/GC) were treated with aqueous solution of nitrilotriacetic acid. The sensitivity of GC electrode modified in described way towards Cu(II) was investigated in Britton-Robinson buffer solution, pH 5.0. The potentiometric generic pulse technique was applied as innovative electrochemical method for detection of analytical signal. It was shown that GC electrodes modified in here described way will be suitable for the determination of Cu(II) in technological waste water and/or some other solutions containing Cu(II) ions.

Conducting polymers can be exploited as an excellent tool for the preparation of nanocomposites with nano-scaled biomolecules. Polypyrrole (Ppy) is one of the most extensively used conducting polymers in design of bioanalytical sensors. In this review article significant attention is paid to immobilization of biologically active molecules within Ppy during electrochemical deposition of this polymer. Such unique properties of this polymer as prevention of some undesirable electrochemical interactions and facilitation of electron transfer from some redox enzymes are discussed. Recent advances in application of polypyrrole in immunosensors and DNA sensors are presented. Some new electrochemical target DNA and target protein detection methods based on changes of semiconducting properties of electrochemically generated Ppy doped by affinity agents are introduced. Recent progress and problems in development of molecularly imprinted polypyrrole are considered.