Long-term stable poly(ionic liquid)/MWCNTs inks enable enhanced surface modification for electrooxidative detection and quantification of dsDNA

Electrochemical approach for the analysis of DNA degradation in native DNA and apoptotic cells

The aim of this work was to develop an electrochemical approach for the analysis of DNA degradation and fragmentation in apoptotic cells. DNA damage is considered one of the major causes of human diseases. We analyzed the cleavage processes of the circular plasmid pTagGFP2-N and calf thymus DNA, which were exposed to restriction endonucleases (the restriction endonucleases BstMC I and AluB I and the nonspecific endonuclease I). Genomic DNA from the leukemia K562 cell line was used as a marker of the early and late (mature) stages of apoptosis. Registration of direct electrochemical oxidation of nucleobases of DNA molecules subjected to restriction endonuclease or apoptosis processes was proposed for the detection of these biochemical events. Label-free differential pulse voltammetry (DPV) has been used to measure endonuclease activities and DNA damage using carbon nanotube-modified electrodes. The present DPV technique provides a promising platform for high-throughput screening of DNA hydrolases and for registering the efficiency of apoptotic processes. DPV comparative analysis of the circular plasmid pTagGFP2-N in its native supercoiled state and plasmids restricted to 4 and 23 parts revealed significant differences in their electrochemical behavior. Electrochemical analysis was fully confirmed by means of traditional methods of DNA analysis and registration of apoptotic process, such as gel electrophoresis and flow cytometry.

Interaction of Doxorubicin Embedded into Phospholipid Nanoparticles and Targeted Peptide-Modified Phospholipid Nanoparticles with DNA

The interactions of dsDNA with new targeted drug delivery derivatives of doxorubicin (DOX), such as DOX embedded into phospholipid nanoparticles (NPhs) and DOX with the NGR targeted peptide-modified NPhs were studied electrochemically by differential pulse voltammetry technique. Screen-printed electrodes (SPEs), modified with stable fine dispersions of carbon nanotubes (CNTs), were used for quantitative electrochemical investigations of direct electrochemical oxidation of guanine, adenine, and thymine heterocyclic bases of dsDNA, and their changes in the presence of DOX nanoderivatives. Analysing the shifts of peak potentials of nucleobases in the presence of drug, we have shown that the doxorubicin with NGR targeted peptide changed the mode of interaction in DNA-drug complexes from intercalative to electrostatic. Binding constants (K_b) of DNA-drug complexes were calculated in accordance with adenine, guanine, and thymine oxidation signals. Based on our experiments, we have proven that the surface modification of a drug delivery system with NGR targeted peptide dramatically changed the mechanism of interaction of drug with genetic material. DNA-mediated drug toxicity was calculated based on the concentration-dependent "response" of heterocyclic nucleobases on drug influence. DOX, DOX-loaded phospholipid nanoparticles (NPhs), and DOX with NGR addressed peptide-modified NPhs were moderately toxic in the concentration range of 0.5-290 µM.

Improving the Efficiency of Electrocatalysis of Cytochrome P450 3A4 by Modifying the Electrode with Membrane Protein Streptolysin O for Studying the Metabolic Transformations of Drugs

In the present work, screen-printed electrodes (SPE) modified with a synthetic surfactant, didodecyldimethylammonium bromide (DDAB) and streptolysin O (SLO) were prepared for cytochrome P450 3A4 (CYP3A4) immobilization, direct non-catalytic and catalytic electrochemistry. The immobilized CYP3A4 demonstrated a pair of redox peaks with a formal potential of -0.325 ± 0.024 V (vs. the Ag/AgCl reference electrode). The electron transfer process showed a surface-controlled mechanism ("protein film voltammetry") with an electron transfer rate constant (ks) of 0.203 ± 0.038 s-1. Electrochemical CYP3A4-mediated reaction of N-demethylation of erythromycin was explored with the following parameters: an applied potential of -0.5 V and a duration time of 20 min. The system with DDAB/SLO as the electrode modifier showed conversion of erythromycin with an efficiency higher than the electrode modified with DDAB only. Confining CYP3A4 inside the protein frame of SLO accelerated the enzymatic reaction. The increases in product formation in the reaction of the electrochemical N-demethylation of erythromycin for SPE/DDAB/CYP3A4 and SPE/DDAB/SLO/CYP3A4 were equal to 100 ± 22% and 297 ± 7%, respectively. As revealed by AFM images, the SPE/DDAB/SLO possessed a more developed surface with protein cavities in comparison with SPE/DDAB for the effective immobilization of the CYP3A4 enzyme.

Highly selective detection of adenine and guanine by NH2-MIL-53(Fe)/CS/MXene nanocomposites with excellent electrochemical performance

Adenine (A) and guanine (G) are mainly found in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) and play a crucial role in genetic information transfer and protein synthesis. In this study, NH₂-MIL-53(Fe)/CS/MXene nanocomposites were prepared for detecting guanine and adenine. With high specific surface area, excellent water dispersion, and numerous active sites, MXene (transition metal carbides, nitrides, and carbonitrides) provides a good platform for loading primitive metal-organic frameworks (MOFs). At the same time, the problem of poor conductivity and dispersion of MOFs is solved. The electrochemical catalytic oxidation of adenine and guanine of NH₂-MIL-53 (Fe)/CS/MXene nanocomposites was carried out by differential pulse voltammetry (DPV). Operating voltage of DPV: 0.7-0.9 V (vs. Ag/AgCl) for G, 1.0-1.2 V (vs. Ag/AgCl) for A, 0.8 V (vs. Ag/AgCl), and 1.1 V (vs. Ag/AgCl) for G and A. The concentration ranges for detecting A and G were 3-118 μM and 2-120 μM with detection limits of 0.57 μM and 0.17 μM (S/N = 3), respectively. The nanocomposite was used for detecting G and A in herring sperm DNA, and the content of G and A was found to be about 9 and 11 μM; the RSD values were 3.4 and 1.3%, respectively.

Electroenzymatic Model System for the Determination of Catalytic Activity of Erwinia carotovora L-Asparaginase

An electrochemical method for the determination of the catalytic activity of L-asparaginase (ASNase) from Erwinia carotovora was proposed. Our approach is based on the electrooxidation of amino acids from L-asparaginase polypeptide backbones. The electrochemical behavior of ASNase on electrodes obtained by screen-printing modified with single-wall carbon nanotubes (SPE/SWCNTs) as sensing elements demonstrated a broad oxidation peak at 0.5–0.6 V centered at 0.531 ± 0.010 V. We have shown that in the presence of the substrate L-asparagine, the oxidation current of the enzyme was reduced in a concentration-dependent manner. The specificity of electrochemical analysis was confirmed in experiments with glycine, an amino acid with no substrate activity on ASNase and does not reduce the oxidation peak of L-asparaginase. The addition of glycine did not significantly influence the amplitude of the oxidation current. The innovative aspects of the proposed electrochemical sensor are the direct monitoring of ASNase catalytic activity and a reagentless approach, which does not require additional reagents or labels.

Conductive graphene coated carboxymethyl cellulose hybrid fibers with polymeric ionic liquids as intermediate

In this study, a kind of polymeric ionic liquid (PIL) called PIL-Cl was synthesized and modified to obtain conductive graphene coated carboxymethyl cellulose hybrid fibers. Carboxymethyl cellulose (CMC) was formed into fibers by wet spinning assisted with PILCl. Co-precipitation test of CMC and PIL-Cl demonstrated that PIL-Cl could precipitate with CMC through strong electrostatic interaction and molar ratio of CMC and PIL-Cl (calculated in repeating units) would affect the formation of precipitation. Secondly, modified PIL-Cl named PIL-Ac was used as an intermediate connecting CMC fiber and graphene to fabricate conductive CMC/PIL/graphene fibers. A series of tests were performed on CMC/PIL/graphene fibers, including Raman spectroscopy, scanning electron microscopy and conductivity test. The results showed that PIL-Cl could help form CMC fiber, and PIL-Ac could functionalize it and make it conductive.

Thermally responsive reduced graphene oxide with electroactive functionality for controllable electroanalysis

A thermally responsive hybrid poly(NIPAm-b-BVIm[FcCOO])-rGO composed of block co-polymer poly(NIPAm-b-BVImBr), reduced graphene oxide (rGO) and electroactive anions was designed and synthesized to achieve electroactive functionality. It is the polymeric ionic liquids (PILs) segment in the block co-polymer that integrated the three different components into a whole hybrid. Such segment of PILs could not only promote the modification of polar PNIPAm onto the non-polar rGO by cation-π interaction, but also realize the immobilization of ferrocenecarboxylate anion (FcCOO^-) via anion-exchange reaction. The PNIPAm moiety endowed the poly(NIPAm-b-BVIm[FcCOO])-rGO with thermal responsiveness, while the anion moiety provided additional electroactive function. It is noteworthy that the conformational change of PNIPAm segment upon different temperature could reveal or seal the redox probe of FcCOO^-, thereby leading to a controllable expression of electroactivity switching by thermal stimuli. Owing to such regulation on surface property and conformation of PNIPAm segment, the modified electrode exhibited excellent thermally responsive electrocatalysis with reversible 'ON-OFF' effect toward the detection of ascorbic acid (AA), which led to two different catalytic states at the same electrode. The reversible electrocatalytic performance with switching capability of the poly(NIPAm-b-BVIm[FcCOO])-rGO/GCE is expected to have a broad application in the field of intelligent electrochemical sensors and devices.

A novel tool for the adsorption of dsDNA: Electrochemical reduction of Pd nanoparticles onto reduced-keratin particles extracted from wool wastes

This work outlines the fabrication of a novel electrochemical platform for the dsDNA adsorption, using one of the most sustainable materials, wool fabric waste, and Pd²⁺ ions. To develop a functional material with a significant adsorption capability, the waste wool was subjected to the chemical reduction process, and the keratin-SH (KerSH) particles were extracted in powder form. These particles were used in the adsorption of Pd²⁺ ions by monitoring with the UV-vis spectra. The dispersion of the KerSH-Pd²⁺ particles was subsequently drop-casted onto a glassy carbon electrode (GCE) and electrochemically reduced to the GCE/KerSH-PdNPs composite by chronoamperometry at -0.4 V for 500 s. It was found that the KerSH particles were self-assembled by revealing chemically attractive NH₂ groups after the electrochemical PdNPs deposition. A GCE/KerSH-PdNPs composite was then employed in the electrochemical dsDNA detection by Differential Pulse Voltammetry (DPV), using the oxidation signals of guanine and adenine bases at 0.8 V and 1.2 V, respectively. Accordingly, relatively stable, repeatable, and reproducible dsDNA adsorption was ensured through the positively charged-NH₂ groups of KerSH-PdNPs. This finding reveals the potential of textile waste for various electrochemical applications, such as DNA biosensors for environmental, pharmaceutical, and medicinal fields.

Cytotoxicity assessment of antibiotics on Ctenopharyngodon idellus kidney cells by a sensitive electrochemical method

As emerging pollutants, antibiotics are ubiquitous in the environment and pose a threat to human health, giving rise to an urgent need to assess their biological toxicity. In the present study, a cell electrochemical method based on the bromocresol violet/carbon nanotubes/glassy carbon electrode (BCP/MWCNTs/GCE) was established to evaluate the cytotoxicities of sulfamethoxazole (SMZ), ciprofloxacin (CIP), and tetracycline (TC). BCP/MWCNTs/GCE has advantages due to its excellent electrocatalytic activity for the oxidation of electroactive species of the Ctenopharyngodon idellus kidney (CIK) cells. The half-maximal inhibitory concentration (IC₅₀) values of SMZ, CIP, and TC obtained by the electrochemical method were 831.51 μM, 354.98 μM, and 184.51 μM, which were lower than those of the traditional methyl-thiazolyl-tetrazolium (MTT) assay (907.47 μM, 414.87 μM, and 208.11 μM). These results indicate the higher sensitivity of the electrochemical method. This study provided a sensitive tool for the cytotoxicity evaluation of antibiotics in the environmental toxicology field.

Electroanalysis of Biomolecules: Rational Selection of Sensor Construction

Methods of electrochemical analysis of biological objects based on the reaction of electro-oxidation/electro-reduction of molecules are presented. Polymer nanocomposite materials that modify electrodes to increase sensitivity of electrochemical events on the surface of electrodes are described. Examples of applications electrochemical biosensors constructed with nanocomposite material for detection of biological molecules are presented, advantages and drawbacks of different applications are discussed.

Electrochemical studies of the interaction of rifampicin and nanosome/rifampicin with dsDNA

The interactions of dsDNA with rifampicin (RF) or with rifampicin after encapsulation in phospholipid micelles (nanosome/rifampicin) (NRF) were studied electrochemically. Screen-printed electrodes (SPEs) modified by stable dispersions of multi-wolled carbon nanotubes (MWCNTs) in aqueous solution of poly(1,2-butadiene)-block-poly(2-(dimethylamino)ethyl methacrylate) (PB₂₉₀-b-PDMAEMA₂₄₀) diblock copolymer were used for quantitative electrochemical investigation of direct electrochemical oxidation of guanine at E = 0.591 V (vs. Ag/AgCl) and adenine at E = 0.874 V (vs. Ag/AgCl) of dsDNA and its change in the presence of RF or NRF. Due to RF or NRF interaction with dsDNA, the differential pulse voltammetry (DPV) peak currents of guanine and adenine decreased and the peak potentials shifted to more positive values with increasing drug concentration (RF or NRF). Binding constants (K_b) of complexes RF-dsDNA and NRF-dsDNA were calculated based on adenine and guanine oxidation signals. The K_b values for RF-dsDNA were 1.48 × 10⁴ M^-1/8.56 × 10⁴ M^-1, while for NRF-dsDNA were 2.51 × 10⁴ M^-1/1.78 × 10³ M^-1 (based on adenine or guanine oxidation signals, respectively). The values of K_b revealed intercalation mode of interaction with dsDNA for RF and mixed type of interaction (intercalation and electrostatic mode) for NRF. The estimated values of ΔG (Gibbs free energy) of the complex formation confirmed that drug-dsDNA interactions are spontaneous and favourable reactions.

Nanoconfined Crosslinked Poly(ionic liquid)s with Unprecedented Selective Swelling Properties Obtained by Alkylation in Nanophase-Separated Poly(1-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks

Despite the great interest in nanoconfined materials nowadays, nanocompartmentalized poly(ionic liquid)s (PILs) have been rarely investigated so far. Herein, we report on the successful alkylation of poly(1-vinylimidazole) with methyl iodide in bicontinuous nanophasic poly(1-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) to obtain nanoconfined methylated PVImMe-l-PTHF poly(ionic liquid) conetworks (PIL-CNs). A high extent of alkylation (~95%) was achieved via a simple alkylation process with MeI at room temperature. This does not destroy the bicontinuous nanophasic morphology as proved by SAXS and AFM, and PIL-CNs with 15-20 nm d-spacing and poly(3-methyl-1-vinylimidazolium iodide) PIL nanophases with average domain sizes of 8.2-8.4 nm are formed. Unexpectedly, while the swelling capacity of the PIL-CN dramatically increases in aprotic polar solvents, such as DMF, NMP, and DMSO, reaching higher than 1000% superabsorbent swelling degrees, the equilibrium swelling degrees decrease in even highly polar protic (hydrophilic) solvents, like water and methanol. An unprecedented Gaussian-type relationship was found between the ratios of the swelling degrees versus the polarity index, indicating increased swelling for the nanoconfined PVImMe-l-PTHF PIL-CNs in solvents with a polarity index between ~6 and 9.5. In addition to the nanoconfined structural features, the unique selective superabsorbent swelling behavior of the PIL-CNs can also be utilized in various application fields.

Rational Design of Amphiphilic Diblock Copolymer/MWCNT Surface Modifiers and Their Application for Direct Electrochemical Sensing of DNA

We demonstrate the application of amphiphilic ionic poly(n-butylmethacrylate)-block- poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers (PnBMA₄₀-b-PDMAEMA₄₀, PnBMA₄₀-b-PDMAEMA₁₂₀, PnBMA₇₀-b-PDMAEMA₁₂₀) for dispersing multiwalled carbon nanotubes (MWCNTs) in aqueous media, a subsequent efficient surface modification of screen-printed electrodes (SPEs), and the application of the modified SPEs for DNA electrochemistry. Stable and fine aqueous dispersions of MWCNTs were obtained with PnBMA_x-b-PDMAEMA_y diblock copolymers, regardless of the structure of the copolymer and the amount of MWCNTs in the dispersions. The effect of the diblock copolymer structure was important when the dispersions of MWCNTs were deposited as modifying layers on surfaces of SPEs, resulting in considerable increases of the electroactive surface areas and great acceleration of the electron transfer rate. The SPE/(PnBMA_x-b-PDMAEMA_y + MWCNT) constructs were further exploited for direct electrochemical oxidation of the guanine (G) and adenine (A) residues in a model salmon sperm double-stranded DNA (dsDNA). Two well-defined irreversible oxidation peaks were observed at about +600 and +900 mV, corresponding to the electrochemical oxidation of G and A residues, respectively. A multi-parametric optimization of dsDNA electrochemistry enables one to get the limits of detection (LOD) as low as 5 μg/mL (0.25 μM) and 1 μg/mL (0.05 μM) for G and A residues, respectively. The achieved sensitivity of DNA assay enables quantification of the A and G residues of dsDNA in the presence of human serum and DNA in isolated human leukocytes.

Silsesquioxane-Polythiophene Hybrid Copolymer as an Efficient Modifier for Single-Walled Carbon Nanotubes

One silsesquioxane-polythiophene hybrid copolymer, with combined star-like structure and intramolecular heterogeneity, was synthesized and sufficiently characterized via various methods, including FTIR, NMR, and SEC measurements. According to the exploration and characterization results, it was much more efficient at modifying SWNTs than its linear analogs in aqueous solution. The hydrophobic silsesquioxane core and PEDOT chains could locally anchor to the surface of the nanotubes, while the soluble flexible copolymer chains extended into the solution and rigid conjugated chains provided some π-π stacking effect to enhance adhesive force with the conjugated structure of the carbon nanotube, imparting steric stabilization to nanotube dispersion. The noncovalent interaction with SWNTs and solubility in aqueous solution improved the electrochemical characteristics of the modified-SWNT composite and availed for the preparation of a flexible and transparent electroactive film. Accordingly, this kind of silsesquioxane-polythiophene hybrid copolymer will be forwarded to apply to the assembling of flexible optoelectronic devices.

[Electroanalytical and electrocatalytical characteristics of cytochrome P450 3A4 using electrodes modified with nanocomposite carbon nanomaterials]

The electroanalytical characteristics of recombinant cytochrome P450 3A4 (P450 3A4) immobilized on the surface of screen-printed graphite electrodes modified with multi-walled carbon nanotubes have been studied. The role and the influence of graphite working electrode modification with carbon nanotubes on electroanalytical characteristics of cytochrome P450 3A4 have been demonstrated. The conditions for the immobilization of cytochrome P450 3A4 on the obtained screen-printed graphite electrodes modified with carbon multi-walled nanotubes have been optimized. The electrochemical parameters of the oxidation and reduction of the heme iron of the enzyme have been estimated. The midpoint potential E0' was -0.35±0.01 V vs Ag/AgCl; the calculated heterogeneous electron transfer rate constant ks, was 0.57±0.04 s-1; the amount of electroactive cytochrome P450 3A4 on the electrode Г0, was determined as (2.6±0.6)⋅10-10 mol/cm2. The functioning mechanism of P450 3A4-based electrochemical sensor followed the "protein film voltammetry". In order to develop electrochemical analysis of drugs being substrates of that hemoprotein and respective medical biosensors the voltammetric study of catalytic activity of immobilized cytochrome P450 3A4 was carried out. Electrocatalytic properties of cytochrome P450 3A4, immobilized on modified screen-printed graphite electrodes, has been investigated using erythromycin (macrolide antibiotics). It has been shown that the modification of electrodes plays a decisive role for the study of the properties of cytochromes P450 in electrochemical investigations. Smart electrodes can serve as sensors for analytical purposes, as well as electrocatalysts for the study of biotransformation processes and metabolic processes. Electrodes modified with carbon nanomaterials are applicable for analytical purposes in the registration of hemoproteins. Electrodes modified with synthetic membrane-like compounds (e.g. didodecyldimethylammonium bromide) are effective in enzyme-dependent electrocatalysis.