Chitosan/Ionic Liquid Composite Electrode for Electrochemical Monitoring of the Surface‐Confined Interaction Between Mitomycin C and DNA

In the present study a chitosan/ionic liquid modified pencil graphite electrode (CHIT‐IL‐PGEs) was developed for the first time for enhanced electrochemical monitoring of nucleic acid, and the interaction of the anticancer drug Mitomycin C (MC) and calf thymus double stranded DNA (dsDNA) by measuring the oxidation signals of MC and guanine in the same voltammetric scale. Differential pulse voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to evaluate the performance of the CHIT‐IL based biosensor on electrochemical monitoring of DNA, and drug‐DNA interaction. The experimental parameters, IL, dsDNA and MC concentration and the interaction time were then optimized.     

Amperometric Ethanol Biosensors Based on Chitosan‐NAD+‐Alcohol Dehydrogenase Films

The reagentless and oxygen‐independent biosensors for ethanol were developed based on the covalent immobilization of alcohol dehydrogenase (ADH) and its cofactor nicotinamide adenine dinucleotide (NAD⁺) on chitosan (CHIT) chains. The CHIT‐NAD⁺‐ADH structures were adsorbed onto carbon nanotubes (CNT) in order to provide a signal transduction based on the recycling of redox states of NAD cofactor at CNT (detection limit, 8–30 µM ethanol; dynamic range up to 20 mM). The CHIT‐NAD⁺‐dehydrogenase/CNT hybrid material represents a general approach to the development of dehydrogenases‐based electrochemical biosensors. Interestingly, the CHIT‐NAD⁺ solutions preserved their enzymatic activity even after five years of storage at 4 °C.     

Interaction of Mitomycin C with DNA Immobilized onto Single‐walled Carbon Nanotube/Polymer Modified Pencil Graphite Electrode

The electrochemical investigation of the interaction between the anticancer drug mitomycin C (MC) and DNA was described using a single‐walled carbon nanotube (SWCNT)/poly(vinylferrocenium) (PVF⁺) modified pencil graphite electrode (PGE). The electrochemical oxidation signals of guanine were monitored before and after the interaction between MC and DNA by using differential pulse voltammetry. The effects of DNA and MC concentration and MC interaction time were examined based on the electrode response. Cyclic voltammetry and electrochemical impedance spectroscopy were used for the characterization of SWCNT/PVF⁺ modified and PVF⁺ modified PGEs. The detection limit corresponded to 625 ng/mL for MC using calf thymus double‐stranded DNA immobilized SWCNT/PVF⁺ modified PGE.     

Carbon Nanotubes Modified Graphite Electrodes for Monitoring of Biointeraction Between 6‐Thioguanine and DNA

In this present study, single‐walled carbon nanotubes (SWCNT) modified disposable pencil graphite electrodes (SWCNT‐PGEs) were developed for the electrochemical monitoring of anticancer drug, and its interaction with double stranded DNA (dsDNA). Under this aim, SWCNT‐PGEs were applied for the first time in the literature to analyse of 6‐Thioguanine (6‐TG), and also to investigate its interaction with DNA by voltammetric and impedimetric methods. The surface morphologies of PGE and SWCNT‐PGE were explored using scanning electron microscopy (SEM) and electrochemical characterization of unmodified/modified electrodes was performed by cyclic voltammetry (CV). Experimental parameters; such as, the concentration of 6‐TG and its interaction time with dsDNA were optimized by using differential pulse voltammetry (DPV). Additionally, the interaction of 6‐TG with dsDNA was studied in case of different interaction times by electrochemical impedance spectroscopy (EIS) in contrast to voltammetric results. The detection limit of 6‐TG was found to be 0.25 μM by SWCNT‐PGE.     

Direct Electrochemical Nano‐immunosensor for Microcystin‐LR in Seawater

Microcystins are potent hepatotoxins produced by cyanobacteria, which proliferate in wastewaters with high nutrient content. Due to their high toxicity and potential risk to human health, even at low concentrations, the development of a sensitive and rapid method for the monitoring of microcystin‐LR (MC‐LR) in water samples is of great importance. In this context, a new direct electrochemical nano‐immunosensor for MC‐LR detection using the liquid crystal (E)‐1‐decyl‐4‐[(4‐decyloxyphenyl)diazenyl]pyridinium bromide (Br‐Py) as a redox probe and gold nanoparticles stabilized in bovine serum albumin (AuNP‐BSA) is described herein. The microcystin‐LR antibody (anti‐MC‐LR) was covalently immobilized using N‐(3‐dimethylaminopropyl)‐N‐ethylcarbodiimide hydrochloride (EDC) and N‐hydroxysuccinimide (NHS) on an AuNP‐BSA/BrPy film. The proposed sensor response is based on the inhibition of the Br‐Py electrochemical signal after the specific interaction of MC‐LR with immobilized anti‐MC‐LR on the electrode surface. The electrochemical behavior of the immunosensor was studied by square‐wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions, using SWV and an incubation time of 15 min, the immunosensor exhibits a linear response to MC‐LR concentrations of 0.05 to 500.0 ng mL⁻¹ with a detection limit of 0.05 ng mL⁻¹. The anti‐MC‐LR/AuNP‐BSA/Br‐Py/GCE was successfully applied in the determination of MC‐LR in spiked seawater samples.     

Electrochemical Study of Chitosan‐SiO2‐MWNT Composite Electrodes for the Fabrication of Cholesterol Biosensors

We report a novel composite electrode made of chitosan‐SiO₂‐multiwall carbon nanotube (CHIT‐SiO₂‐MWNT) composite coated on the indium‐tin oxide (ITO) glass substrate. Cholesterol oxidase (ChOx) was covalently immobilized on the CHIT‐SiO₂‐MWNT/ITO electrode that resulted in a ChOx/CHIT‐SiO₂‐MWNT/ITO cholesterolactive bioelectrode. The CHIT‐SiO₂‐MWNT/ITO and ChOx/CHIT‐SiO₂‐MWNT/ITO electrodes were characterized with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The influence of various parameters was investigated, including the applied potential, pH of the medium, and the concentration of the enzyme on the performance of the biosensor. The cholesterol bioelectrode exhibited a sensitivity of 3.4 nA/ mgdL^?1 with a response time of five seconds. The biosensor using ChOx/CHIT‐SiO₂‐MWNT/ITO as the working electrode retained its original response after being stored for six months. The biosensor using ChOx/CHIT‐SiO₂‐MWNT/ITO as the working electrode showed a linear current response to the cholesterol concentration in the range of 50–650 mg/dL.     

Ionic Liquid Modified Single‐use Electrode Developed for Voltammetric Detection of miRNA‐34a and its Application to Real Samples

The ionic liquid (IL) modified chemically activated (CA) pencil graphite electrodes (PGEs) were developed for label‐free voltammetric detection of miRNA‐34a, and implemented to the real samples. Firstly, the electrochemical characterization of unmodified PGE, CA‐PGE, IL‐PGE and IL‐CA‐PGE was performed by cyclic voltammetry (CV) as well as their DNA binding capacity was studied by electrochemical impedance spectroscopy (EIS) technique. The microscopic characterization of the surface of each electrodes was investigated by scanning electron microscopy (SEM). Differential pulse voltammetry (DPV) technique was used for measuring the oxidation signal of guanine in order to perform a label‐free voltammetric monitoring of a full‐match hybridization specific to miRNA‐34a. The selectivity of biosensor was tested against to miRNA‐155, miRNA‐660 as well as to the mismatch sequence of miRNA‐34a. The further selectivity of this proposed biosensor was studied in the mixture of samples containing miRNA‐34a with other miRNAs (1 : 1). The voltammetric detection of miRNA‐34a was also explored in the artificial serum medium as fetal bovine serum (FBS) and also in total RNA samples isolated from HUH‐7 human hepatocellular carcinoma cell line.     

Differential Pulse Voltammetry Determination of Ofloxacin in Human Serum and Urine Based on a Novel Tryptophan‐graphene Oxide‐carbon Nanotube Electrochemical Sensor

The highly sensitive determination of ofloxacin (OFL) in human serum and urine was achieved on a novel tryptophan‐graphene oxide‐carbon nanotube (Trp‐GO‐CNT) composite modified glassy carbon electrode (Trp‐GO‐CNT/GCE). The Trp‐GO‐CNT composite was fabricated, and its morphologies and surface functional groups were characterized by field emission scanning electron microscopy (FE‐SEM) and Fourier transform infrared (FT‐IR) spectroscopy. The electrochemical properties of Trp‐GO‐CNT/GCE were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The superior electrochemical behaviors of Trp‐GO‐CNT/GCE toward OFL can be mainly assigned to the excellent electrocatalytic activity of Trp, the great conductivity and high surface area of GO and CNT, and the synergistic effect between Trp, GO and CNT. Under optimum conditions, a wide and valuable linear range (0.01–100 μM), a low detection limit (0.001 μM, S/N=3), a good linear relationship (R2>0.999), good stability and repeatability were obtained for the quantitative determination of OFL. Furthermore, the Trp‐GO‐CNT electrochemical sensor was successfully applied to the determination of OFL in human serum and urine samples, and satisfactory accuracy and recovery could be obtained.     

Electrochemical Synthesis of Chitosan‐co‐polyaniline/WO3⋅nH2O Composite Electrode for Amperometric Detection of NO2 Gas

An electrode of hydrated tungsten oxide (WO₃?nH₂O) embedded chitosan‐co‐polyaniline (CHIT‐co‐PANI) composite was electrochemically prepared on an indium tin oxide (ITO) coated glass surface using mineral acid as a supporting electrolyte. The resulting CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode was characterized using ultraviolet‐visible spectroscopy (UV‐vis), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and scanning electron microscopy (SEM). The composite electrode exhibited a three‐dimensional nanofibrous structure with the diameter of the nanofibers ranging from 20 to 100 nm. The CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode allowed for the low potential detection of NO₂ gas in acidic medium. The NO₂ gas sensing characteristics were studied by measuring change in the current with respect to concentration and time. Using the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode, NO₂ gas was detected electrochemically without interference at pH 2.0 and 0.25 V vs. Ag/AgCl. The current of the electrochemical cell with the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode decreased linearly with an increase in NO₂ gas concentration in a range from 100 to 500 ppb with a response time of eight seconds.     

Chitosan‐Functionalized Carbon Nanotubes as Support for the High Dispersion of PtRu Nanoparticles and their Electrocatalytic Oxidation of Methanol

Carbon nanotubes (CNTs) were non‐covalently functionalized with chitosan (Chit) and then employed as the support for PtRu nanoparticles. The functionalization was carried out at room temperature without the use of corrosive acids, thereby preserving the integrity and the electronic conductivity of the CNTs. Transmission electron microscopy reveals that PtRu nanoparticles were highly dispersed on the surface of Chit‐functionalized CNTs (CNT‐Chit) with small particle‐size. Cyclic voltammetry studies indicated that the PtRu nanoparticle/CNT‐Chit nanohybrids have a higher electrochemical surface area, electrocatalytic performance, and stability towards methanol oxidation compared to PtRu nanoparticles supported on the pristine CNTs.     

Sensitively Electrochemical Sensing for Sequence‐Specific Detection of Phosphinothricin Acetyltransferase Gene: Layer‐by‐Layer Films of Poly‐L‐Lysine and Au‐Carbon Nanotube Hybrid

An electrochemical DNA sensing film was constructed based on the multilayers comprising of poly‐L ‐lysine (pLys) and Au‐carbon nanotube (Au‐CNT) hybrid. A precursor film of mercaptopropionic acid (MPA) was firstly self‐assembled on the Au electrode surface. pLys and Au‐CNT hybrid layer‐by‐layer assembly films were fabricated by alternately immersing the MPA‐modified electrode into the pLys solution and Au‐CNT hybrid solution. Cyclic voltammetry was used to monitor the consecutive growth of the multilayer films by utilizing [Fe(CN)₆]^3?/4? and [Co(phen)₃]^3+/2+ as the redox indicators. The outer layer of the multilayer film was the positively charged pLys, on which the DNA probe was easily linked due to the strong electrostatic affinity. The hybridization detection of DNA was accomplished by using methylene blue (MB) as the indicator, which possesses different affinities to dsDNA and ssDNA. Differential pulse voltammetry was employed to record the signal response of MB and determine the amount of the target DNA sequence. The established biosensor has high sensitivity, a relatively wide linear range from 1.0×10^?10 mol/L to 1.0×10^?6 mol/L and the ability to discriminate the fully complementary target DNA from single or double base‐mismatched DNA. The sequence‐specific DNA related to phosphinothricin acetyltransferase gene from the transgenically modified plants was successfully detected.     

Direct DNA Hybridization on the Single‐Walled Carbon Nanotubes Modified Sensors Detected by Voltammetry and Electrochemical Impedance Spectroscopy

Carboxylic acid functionalized single‐walled carbon nanotubes modified graphite sensors (SWCNT‐PGEs) were developed for electrochemical monitoring of direct DNA hybridization related to specific sequence of Hepatitis B virus, which substantially enhance the electrochemical transduction resulting from guanine oxidation signal comparison to bare PGEs. The performance characteristics of DNA hybridization on disposable CNT‐PGE were explored measuring the guanine signal in terms of optimum analytical conditions; probe and target concentration, hybridization time, and selectivity. The voltammetric results were also complemented with electrochemical impedance spectroscopy (EIS), that was used to characterize the successful construction of carbon nanotubes modification onto the surface of PGEs.     

A Sensitive Simultaneous Determination of Adrenalin and Paracetamol on a Glassy Carbon Electrode Coated with a Film of Chitosan/Room Temperature Ionic Liquid/Single‐Walled Carbon Nanotubes Nanocomposite

The present work demonstrates that simultaneous determination of adrenalin (AD) and paracetamol (PAR) can be performed on single‐walled carbon nanotube/chitosan/ionic liquid modified glassy carbon electrode (SWCNT‐CHIT‐IL/GCE). The electro‐oxidations of AD and PAR were investigated with cyclic voltammetry (CV), differential pulse voltammetry (DPV) and also chronoamperometry (CA) methods. DPV experiments showed that the oxidation peak currents of AD and PAR are proportional to the corresponding concentrations over the 1–580 μmol/L and 0.5–400 μmol/L ranges, respectively. The RSD at a concentration level of 15 μmol/L AD and 15 μmol/L PAR were 1.69% and 1.82%, respectively. Finally the modified electrode was used for simultaneous determination of AD and PAR in real samples with satisfactory results.     

Direct Electrochemistry of Multi‐Copper Oxidases at Carbon Nanotubes Noncovalently Functionalized with Cellulose Derivatives

This study describes the direct electron transfer of multi‐copper oxidases, i.e., laccase (from Trametes versicolor) and bilirubin oxidase (BOD, from Myrothecium verrucaria) at multiwalled carbon nanotubes (MWNTs) noncovalently functionalized with biopolymers of cellulose derivatives, i.e., hydroxyethyl cellulose (HEC), methyl cellulose (MC), and carboxymethyl cellulose (CMC). The functionalization of the MWNTs with the cellulose derivatives is found to substantially solubilize the MWNTs into aqueous media and to avoid their aggregation on electrode surface. Under anaerobic conditions, the redox properties of laccase and BOD are difficult to be defined with cyclic voltammetry at either laccase/MWNT‐modified or BOD/MWNT‐modified electrodes. The direct electron transfer properties of laccase and BOD are thus studied in terms of the bioelectrocatalytic activities of the laccase/MWNT‐modified and BOD/MWNT‐modified electrodes toward the reduction of oxygen and found to be facilitated at the functionalized MWNTs. The possible application of the laccase‐catalyzed O₂ reduction at the laccase/MWNT‐modified electrode is illustrated by constructing a CNT‐based ascorbate/O₂ biofuel cell with the MWNT‐modified electrode as the anode for the oxidation of ascorbate biofuel.     

A Laccase/Chitosan‐Lambda‐Carrageenan Based Voltammetric Biosensor for Phenolic Compound Detection

In this contribution, a new concept of voltammetric catechol biosensor, based on the encapsulation of laccase (LAC) in a chitosan+lambda‐carrageenan (CHIT+CAR) polyelectrolyte complex (PEC) employing a simple coacervation process is presented. Chitosan (CHIT) was prepared from α‐chitin extracted from shrimp shells and lambda‐carrageenan (CAR) was extracted from red algae, both polysaccharides and PEC being characterized using FTIR spectrometry and electrochemistry. Cyclic voltammetry was utilized to determine the analytical features of the laccase (LAC) biosensor for catechol detection. The linear range was from 10^?20 M to 10^?14 M with a sensitivity of 1.55 mA/p[catechol] and a limit of detection of 3×10^?21 M.The laccase biosensor exhibits good repeatability (RSD 2.38 %) and stability (four weeks). The developed biosensor was tested by applying it to the evaluation of the total polyphenolic content in natural oil samples.     

The Electrocatalytic Oxidation of Thymine at α‐Cyclodextrin Incorporated Carbon Nanotube‐Coated Electrode

Electrocatalytic oxidation of thymine at α‐cyclodextrin (α‐CD) incorporated carbon nanotube‐coated electrode (CNT/CE) was thoroughly studied in alkaline media. CNT showed an electrocatalytic effect on the oxidation of thymine, formation of a supramolecular inclusion complex between α‐CD and thymine at CNT/CE further enhanced the sensitivity to thymine. The electrocatalytic behavior was further developed as a sensitive detection scheme for thymine by differential pulse voltammetry. A linear calibration over the concentration range from 2.5×10^?5 to 1.8×10^?3 mol/L in pH 10.8 NaHCO₃‐Na₂CO₃ buffer solution was obtained with a detection limit of 5×10^?6 mol/L.     

Reduced Graphene Oxide/Carbon Nanotube/Gold Nanoparticles Nanocomposite Functionalized Screen‐Printed Electrode for Sensitive Electrochemical Detection of Endocrine Disruptor Bisphenol A

We fabricated a highly sensitive electrochemical sensor for the determination of bisphenol A (BPA) in aqueous solution by using reduced graphene oxide (RGO), carbon nanotubes (CNT), and gold nanoparticles (AuNPs)‐modified screen‐printed electrode (SPE). GO/CNT nanocomposite was directly reduced to RGO/CNT on SPE at room temperature. AuNPs were then electrochemically deposited in situ on RGO/CNT‐modified SPE. Under optimized conditions, differential pulse voltammetry (DPV) produced linear current responses for BPA concentrations of 1.45 to 20 and 20 to 1,490 nM, with a calculated detection limit of an ultralow 800 pM. The sensor response was unaffected by the presence of interferents such as phenol, p‐nitrophenol, pyrocatechol, 2,4‐dinitrophenol, and hydroquinone.     

Chitosan‐Glutamate Oxidase Gels: Synthesis,Characterization, and Glutamate Determination

The biopolymer chitosan (CHIT) was chemically modified with glutaric dialdehyde (GDI) and used for the covalent immobilization of enzyme glutamate oxidase (GmOx). The relationships between the loaded, retained, and active units of GmOx in the CHIT‐GDI‐GmOx gels were determined by electrochemical assays. The latter indicated that on average ca. 95% of the GmOx was retained in the CHIT‐GDI matrix that was loaded with 0.10–3.0 units of the enzyme. The maximum activity of the GmOx immobilized in the gels corresponded to ca. 5% of the activity of the free enzyme. Platinum electrodes coated with CHIT‐GDI‐GmOx gels (films) were used as amperometric biosensors for glutamate. Such biosensors displayed good operational and long‐term stability (at least 11 h and 100 days, respectively) in conjunction with low detection limit of 0.10 μM glutamate (S/N=3), linear range up to 0.5 mM (R²=0.991), sensitivity of 100 mA M^?1 cm^?2, and short response time (t_90%=2 s). This demonstrated an efficient signal transduction in the Pt/CHIT‐GDI‐GmOx+glutamate system. The CHIT‐GDI‐GmOx gels constitute a new biosensing element for the development of glutamate biosensors.     

Electrochemical sensing platform based on the carbon nanotubes/redox mediators-biopolymer system

A new electrochemical sensing platform was developed that relied on synergy between carbon nanotubes (CNT) and redox mediators that were co-immobilized in the biopolymer chitosan (CHIT). To demonstrate the concept, the redox mediator Toluidine Blue O (TBO) and CNT were integrated in CHIT and used for the determination of a reduced form of nicotinamide adenine dinucleotide (NADH). As compared to CHIT-TBO, the CHIT-TBO/CNT films displayed large amplification of a current due to the TBO-mediated oxidation of NADH at -0.10 V. This was discussed in terms of the TBO/CNT synergy that resulted in the improved charge propagation through the CHIT-TBO/CNT matrix.     

Simultaneous Anodic Adsorptive Stripping Voltammetric Determination of Luteolin and 3‐Hydroxyflavone in Biological Fluids Using Renewable Pencil Graphite Electrodes

Simultaneous anodic adsorptive stripping voltammetry was applied for selective and sensitive electrochemical determination of the flavones luteolin (LU) and the basic flavone core 3‐hydroxyflavone (3HF) using a renewable pencil graphite electrode (PGE). The increased separation of the anodic peak potential of LU and 3HF on a PGE surface together with the increased sensitivity renders their simultaneous determination feasible by square wave anodic adsorptive stripping voltammetry (SWAASV). The electrochemical parameters such as surface concentration (Γ), electron transfer coefficient (α), and the standard rate constant (k_s) of both LU and 3HF at a PGE were calculated. For simultaneous detection of both compounds by synchronous change of the concentration of LU and 3HF, the detection limits were 1.34 nM and 5.15 nM, respectively. The proposed procedure was successfully applied for the simultaneous detection of LU and 3HF in human serum and urine samples with satisfactory results.