DNA immobilization on a polypyrrole nanofiber modified electrode and its interaction with salicylic acid/aspirin

A double-stranded calf thymus DNA (dsDNA) was physisorbed onto a polypyrrole (PPy) nanofiber film that had been electrochemically deposited onto a Pt electrode. The surface morphology of the polymeric film was characterized using scanning electron microscopy (SEM). The electrochemical characteristics of the PPy film and the DNA deposited onto the PPy modified electrode were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Then the interaction of DNA with salicylic acid (SA) and acetylsalicylic acid (ASA), or aspirin, was studied on the electrode surface with DPV. An increase in the DPV current was observed due to the oxidation of guanine, which decreased with the increasing concentrations of the ligands. The interactions of SA and ASA with the DNA follow the saturation isotherm behavior. The binding constants of these interactions were 1.15 × 10⁴ M for SA and 7.46 × 10⁵ M for ASA. The numbers of binding sites of SA and ASA on DNA were approximately 0.8 and 0.6, respectively. The linear dynamic ranges of the sensors were 0.1–2 μM (r² = 0.996) and 0.05–1 mM (r² = 0.996) with limits of detection of 8.62 × 10⁻¹ and 5.24 × 10⁻⁶ μM for SA and ASA, respectively.     

Study of interactions between DNA and aflatoxin B1 using electrochemical and fluorescence methods

In this study, a carbon paste electrode modified with N-butylpyridinium hexafluorophosphate (BPPF₆) ionic liquid and DNA was introduced as an electrochemical biosensor to study the interaction between DNA and aflatoxin B1 molecules. For this purpose, variations in oxidation peak current of guanine in various concentrations of aflatoxin B1 were measured by using the differential pulse voltammetry (DPV) method. According to this study, the binding constant of DNA–aflatoxin B1 was found to be 3.5 × 10⁶ M⁻¹. This modified electrode was also used for determination of low concentrations of aflatoxin B1 by using differential pulse voltammetry. A linear dynamic range from 8.00 × 10⁻⁸ to 5.91 × 10⁻⁷ M and a limit of detection of 2.00 × 10⁻⁸ M resulted from DPV measurements. To confirm our results, a fluorescence study was also performed. It resulted in a binding constant of 2.8 × 10⁶ M⁻¹, which is in good agreement with that obtained from electrochemical study.     

Voltammetric behavior of complexation of salbutamol with calf thymus DNA and its analytical application

The interaction of salbutamol (Sal), an animal growth promoter, with DNA was investigated by differential pulse voltammetry (DPV), cyclic voltammetry (CV), and fluorescence spectroscopy. An irreversible reduction was observed from the cyclic voltammograms, and the reaction mechanism involved a one-electron change irreversible oxidation. In the presence of DNA, the DPV peak current decreased and the Sal peak shifted to higher potentials, indicating that Sal interacted with DNA to form an intercalation Sal–DNA complex. In addition, reaction binding parameters were extracted from the DPV data with the use of the multivariate curve resolution–alternating least squares (MCR–ALS) method; the binding constant and ratio were found to be (2.0 ± 0.5) × 10⁵ M⁻¹ and 1:1, respectively. Quantitative voltammetric analysis of Sal was performed in the concentration range of 3.02 × 10⁻⁶ to 1.23 × 10⁻⁴ mol L⁻¹, and it was found that the detection limit was 5.11 × 10⁻⁷ mol L⁻¹ in the presence of 1.00 × 10⁻⁶ mol L⁻¹ DNA. The method was applied for the determination of Sal in spiked urine and human serum samples, and the calibration was successfully verified.     

Ultrasensitive DNA sensor based on gold nanoparticles/reduced graphene oxide/glassy carbon electrode

We have designed a simple and novel electrochemical biosensor based on glassy carbon electrode (GCE) for DNA detection. GCE was modified with reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) by the electrochemical method, which is helpful for immobilization of thiolated bioreceptors. The electrode modification processes were characterized by scanning electron microscopy (SEM) and electrochemical methods. Then a single-stranded DNA (ssDNA) probe for BRCA1 5382 insC mutation detection was immobilized on the modified electrode for a specific time. The experimental conditions, such as probe immobilization time and target DNA (complementary DNA) hybridization time and temperature with probe DNA, were optimized using electrochemical methods. The electrochemical response for DNA hybridization and synthesis was measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) methods. The calibration graph contains two linear ranges; the first part is in the range of 3.0 × 10⁻²⁰ to 1.0 × 10⁻¹² M, and the second segment part is in the range of 1.0 × 10⁻¹² to 1.0 × 10⁻⁷ M. The biosensor showed excellent selectivity for the detection of the complementary sequences from noncomplementary sequences, so it can be used for detection of breast cancer.     

[Cu(phen)2] acts as electrochemical indicator and anchor to immobilize probe DNA in electrochemical DNA biosensor

We demonstrate a novel protocol for sensitive in situ label-free electrochemical detection of DNA hybridization based on copper complex ([Cu(phen)₂]²⁺, where phen = 1,10-phenanthroline) and graphene (GR) modified glassy carbon electrode. Here, [Cu(phen)₂]²⁺ acted advantageously as both the electrochemical indicator and the anchor for probe DNA immobilization via intercalative interactions between the partial double helix structure of probe DNA and the vertical aromatic groups of phen. GR provided large density of docking site for probe DNA immobilization and increased the electrical conductivity ability of the electrode. The modification procedure was monitored by electrochemical impedance spectroscopy (EIS). Square-wave voltammetry (SWV) was used to explore the hybridization events. Under the optimal conditions, the designed electrochemical DNA biosensor could effectively distinguish different mismatch degrees of complementary DNA from one-base mismatch to noncomplementary, indicating that the biosensor had high selectivity. It also exhibited a reasonable linear relationship. The oxidation peak currents of [Cu(phen)₂]²⁺ were linear with the logarithm of the concentrations of complementary target DNA ranging from 1 × 10⁻¹² to 1 × 10⁻⁶ M with a detection limit of 1.99 × 10⁻¹³ M (signal/noise = 3). Moreover, the stability of the electrochemical DNA biosensor was also studied.     

Electrochemical DNA biosensor based on silver nanoparticles/poly(3-(3-pyridyl) acrylic acid)/carbon nanotubes modified electrode

In this work, we present an electrochemical DNA sensor based on silver nanoparticles/poly(trans-3-(3-pyridyl) acrylic acid) (PPAA)/multiwalled carbon nanotubes with carboxyl groups (MWCNTs-COOH) modified glassy carbon electrode (GCE). The polymer film was electropolymerized onto MWCNTs-COOH modified electrode by cyclic voltammetry (CV), and then silver nanoparticles were electrodeposited on the surface of PPAA/MWCNTs-COOH composite film. Thiol group end single-stranded DNA (HS-ssDNA) probe was easily covalently linked onto the surface of silver nanoparticles through a 5′ thiol linker. The DNA hybridization events were monitored based on the signal of the intercalated adriamycin by differential pulse voltammetry (DPV). Based on the response of adriamycin, only the complementary oligonucleotides gave an obvious current signal compared with the three-base mismatched and noncomplementary oligonucleotides. Under the optimal conditions, the increase of reduction peak current of adriamycin was linear with the logarithm of the concentration of the complementary oligonucleotides from 9.0 × 10⁻¹² to 9.0 × 10⁻⁹ M with a detection limit of 3.2 × 10⁻¹² M. In addition, this DNA sensor exhibited an excellent reproducibility and stability during DNA hybridization assay.     

Application of multivariate curve resolution alternating least squares method for determination of caffeic acid in the presence of catechin interference

In the current article, preparation and application of a graphene oxide nanosheets-based sensor for electrochemical determination of caffeic acid (CA) in the presence of catechin is described. This measurement was performed using the differential pulse voltammetry (DPV) technique and chemometric methods such as multivariate curve resolution–alternating least squares (MCR–ALS). The modified sensor was characterized by various techniques such as Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet–visible, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Operating conditions and influencing variables (involving several chemical and instrumental variables) were optimized with central composite rotatable design and response surface methodology. The second-order electrochemical data were generated by changing the pulse height in DPV, and after potential shift correction MCR–ALS was applied. Under the optimized conditions, the dynamic range for CA was from 0.5 to 100.0 μM and the detection limit was found to be 1.1 × 10^–9 M. The results revealed that the modified electrode shows an improvement in anodic oxidation activity of CA due to a marked enhancement in the current response compared with the bare carbon paste electrode. The modified electrode demonstrated good sensitivity, selectivity, and stability. The proposed method was successfully applied in determination of caffeic acid in the presence of unexpected electroactive interferences with a very high degree of overlapping such as catechin in real samples.     

Determination of dopamine in the presence of ascorbic acid using poly(3,5-dihydroxy benzoic acid) film modified electrode

A polymerized film of 3,5-dihydroxy benzoic acid (DBA) was prepared on the surface of a glassy carbon electrode (GCE) in neutral solution by cyclic voltammetry (CV). The poly(DBA) film-coated GCE exhibited excellent electrocatalytic activity toward the oxidation of dopamine (DA). A linear range of 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M and a detection limit of 6.0 × 10⁻⁸ M were observed in pH 7.4 phosphate buffer solutions. Moreover, the interference of ascorbic acid (AA) was effectively eliminated. This work provides a simple and easy approach to selective detection of DA in the presence of AA.     

Highly sensitive and selective uric acid biosensor based on a three-dimensional graphene foam/indium tin oxide glass electrode

A three-dimensional (3D) continuous and interconnected network graphene foam (GF) was synthesized by chemical vapor deposition using nickel foam as a template. The morphologies of the GF were observed by scanning electron microscopy. X-ray diffraction and Raman spectroscopy were used to investigate the structure of GF. The graphene with few layers and defect free was closely coated on the backbone of the 3D nickel foam. After etching nickel, the GF was transferred onto indium tin oxide (ITO) glass, which acted as an electrode to detect uric acid using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The GF/ITO electrode showed a high sensitivity for the detection of uric acid: approximately 9.44 mA mM⁻¹ in the range of 25 nM–0.1 μM and 1.85 mA mM⁻¹ in the range of 0.1–60 μM. The limit of detection of GF/ITO electrode for uric acid is 3 nM. The GF/ITO electrode also showed a high selectivity for the detection of uric acid in the presence of ascorbic acid. This electrode will have a wide range of potential application prospects in electrochemical detection.     

A new interference-free lysine biosensor using a non-conducting polymer film

An electrochemical biosensor for the determination of lysine to be used for rapid evaluation of food quality has been developed. Platinum electrodes have been coated by electropolymerisation with 1,2-diaminobenzene (1.2-DAB) using cyclic voltammetry. The reduction in the oxidation of interferents compared with the bare platinum electrode was 100% for ascorbic acid, 99% for acetaminophen and 99% for cysteine. The enzyme L-lysine-α-oxidase was then immobilised onto the polymer layer by passive adsorption and a calibration curve for lysine constructed. This gave a linear range of 1×10⁻⁵ mol/l to 1×10⁻³ mol/l and a limit of detection of 2×10⁻⁷ mol/l.     

Formation of electrochemically reduced graphene oxide on melamine electrografted layers and its application toward the determination of methylxanthines

The current study describes the electrografting of 2,4-diamino-1,3,5-triazine (AT) groups at the surfaces of glassy carbon electrode (GCE) and indium tin oxide (ITO) through in situ diazotization of melamine. The presence of AT groups at the surface of the electrode was confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Furthermore, graphene oxide (GO) was self-assembled on AT grafted GCE. The oxygen functional groups present on the surface of GO were electrochemically reduced to form an electrochemically reduced graphene oxide (ERGO) on AT grafted electrode surface. Raman spectra show the characteristic D and G bands at 1340 and 1605 cm⁻¹, respectively, which confirms the successful attachment of GO on AT grafted surface, and the ratio of D and G bands was increased after the electrochemical reduction of GO. EIS shows that the electron transfer reaction of [Fe(CN)₆]^3−/4− was higher at the ERGO modified electrode than at bare, AT grafted, and GO modified GCEs. The electrocatalytic activity of ERGO was investigated toward the oxidation of methylxanthines. It shows excellent electrocatalytic activity toward these methylxanthines by not only shifting their oxidation potentials toward less positive potentials but also enhancing their oxidation currents.     

Biosensor based on the biocatalysis of microperoxidase-11 in nanocomposite material of multiwalled carbon nanotubes/room temperature ionic liquid for amperometric determination of hydrogen peroxide

A novel nanocomposite material of multiwalled carbon nanotubes (MWCNTs) and room temperature ionic liquid (RTIL) N-butylpyridinium hexafluorophosphate (BPPF₆) was explored and used to construct a novel microperoxidase-11 (MP-11) biosensor for the determination of hydrogen peroxide (H₂O₂). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to characterize the performance of the biosensor. Under the optimized experimental conditions, H₂O₂ could be detected in a linear calibration range of 0.5 to 7.0 × 10⁻⁷ mol L⁻¹ with a correlation coefficient of 0.9949 (n = 9) and a detection limit of 3.8 × 10⁻⁹ mol L⁻¹ at 3σ. The modified electrodes displayed excellent electrochemical response, high sensitivity, long-term stability, and good bioactivity and selectivity.     

Electrochemical cytosensor based on gold nanoparticles for the determination of carbohydrate on cell surface

An electrochemical cytosensor was designed based on the specific recognition of mannosyl on a cell surface to concanavalin A (ConA) and the signal amplification of gold nanoparticles (NPs). By sandwiching a cancer cell between a gold electrode modified with ConA and the gold NPs with ConA and 6-ferrocenylhexanethiol (Fc), the electrochemical cytosensor was established. The cell number and the amount of cell surface mannose moieties were quantified by cyclic voltammetry (CV) analysis of the Fc loaded on the surface of the gold NPs. Since a single gold NP could be loaded with hundreds of Fc, a significant amplification for the detection of target cell was obtained. By using K562 leukemic cells (K562 cells) as a model, the electrochemical response was proportional to the cell concentration in the range from 1.0 × 10² to 1.0 × 10⁷ cells mL⁻¹, showing very high sensitivity. The signal amplification could be further used to evaluate the cell surface mannose moieties, and the amount of mannose moieties on a single living K562 cell was detected to correspond to 4.7 × 10⁹ molecules of free mannose. This strategy presents a promising platform in a highly sensitive cytosensor and convenient estimation of cell surface carbohydrate.     

An electrochemical DNA biosensor based on gold nanorods decorated graphene oxide sheets for sensing platform

A simple electrochemical sensor for sensitive and selective DNA detection was constructed based on gold nanorods (Au NRs) decorated graphene oxide (GO) sheets. The high-quality Au NRs–GO nanocomposite was synthesized via the electrostatic self-assembly technique, which is considered a potential sensing platform. Differential pulse voltammetry was used to monitor the DNA hybridization event using methylene blue as an electrochemical indicator. Under optimal conditions, the peak currents of methylene blue were linear with the logarithm of the concentrations of complementary DNA from 1.0 × 10⁻⁹ to 1.0 × 10⁻¹⁴ M with a detection limit of 3.5 × 10⁻¹⁵ M (signal/noise = 3). Moreover, the prepared electrochemical sensor can effectively distinguish complementary DNA sequences in the presence of a large amount of single-base mismatched DNA (1000:1), indicating that the biosensor has high selectivity.     

Zinc oxide/redox mediator composite films-based sensor for electrochemical detection of important biomolecules

Electrochemical oxidation of serotonin (SN) onto zinc oxide (ZnO)-coated glassy carbon electrode (GCE) results in the generation of redox mediators (RMs) that are strongly adsorbed on electrode surface. The electrochemical properties of zinc oxide-electrogenerated redox mediator (ZnO/RM) (inorganic/organic) hybrid film-coated electrode has been studied using cyclic voltammetry (CV). The scanning electron microscope (SEM), atomic force microscope (AFM), and electrochemical techniques proved the immobilization of ZnO/RM core/shell microparticles on the electrode surface. The GCE modified with ZnO/RM hybrid film showed two reversible redox peaks in acidic solution, and the redox peaks were found to be pH dependent with slopes of −62 and −60 mV/pH, which are very close to the Nernst behavior. The GCE/ZnO/RM-modified electrode exhibited excellent electrocatalytic activity toward the oxidations of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in 0.1 M phosphate buffer solution (PBS, pH 7.0). Indeed, ZnO/RM-coated GCE separated the anodic oxidation waves of DA, AA, and UA with well-defined peak separations in their mixture solution. Consequently, the GCE/ZnO/RMs were used for simultaneous detection of DA, AA, and UA in their mixture solution. Using CV, calibration curves for DA, AA, and UA were obtained over the range of 6.0 × 10⁻⁶ to 9.6 × 10⁻⁴ M, 1.5 × 10⁻⁵ to 2.4 × 10⁻⁴ M, and 5.0 × 10⁻⁵ to 8 × 10⁻⁴ M with correlation coefficients of 0.992, 0.991, and 0.989, respectively. Moreover, ZnO/RM-modified GCE had good stability and antifouling properties.     

Hybridization biosensor using 2-nitroacridone as electrochemical indicator for detection of short DNA species of Chronic Myelogenous Leukemia

A new acridone derivative 2-nitroacridone (NAD) was synthesized in this paper, and it was found that NAD had excellent electrochemical activity on the glassy carbon electrode (GCE) with a couple reversible redox peaks at 0.051 V and 0.103 V, respectively. Voltammetry was used to investigate the electrochemical behavior of NAD and the interaction between NAD and salmon sperm DNA. In pH 4.0 phosphate buffer solution, the binding ratio between NAD and salmon sperm DNA was calculated to be 2:1 and the binding constant was 3.19 × 10⁵ L/mol. A Chronic Myelogenous Leukemia (CML, Type b₃a₂) DNA biosensor was developed by immobilizing covalently single-stranded CML DNA fragments to a modified GCE. The surface hybridization of the immobilized single-stranded CML DNA fragment with its complementary DNA fragment was evidenced by electrochemical methods using NAD as a novel electrochemical indicator, with a detection limit of 6.7 × 10⁻⁹ M and a linear response range of 1.8 × 10⁻⁸ M to 9.1 × 10⁻⁸ M for CML DNA. Selective determination of complementary ssDNA was achieved using differential pulse voltammetry (DPV).     

Differential pulse voltammetric simultaneous determination of acetaminophen and ascorbic acid using single-walled carbon nanotube-modified carbon-ceramic electrode

Single-walled carbon nanotube-modified carbon–ceramic electrode (SWCNT/CCE) was employed for the simultaneous determination of acetaminophen (APAP) and ascorbic acid (AA). The SWCNT/CCE displayed excellent electrochemical catalytic activities toward APAP and AA oxidation compared with bare CCE. In the differential pulse voltammetry technique, both AA and APAP gave sensitive oxidation peaks at −62 and 302 mV versus saturated calomel electrode, respectively. Under the optimized experimental conditions, APAP and AA gave linear responses over ranges of 0.2 to 150.0 μM (R² = 0.998) and 5.0 to 700.0 μM (R² = 0.992), respectively. The lower detection limits were found to be 0.12 μM for APAP and 3.0 μM for AA. The investigated method showed good stability, reproducibility, and repeatability as well as high recovery in pharmaceutical and biological samples.     

An ultrasensitive electrochemical genosensor for Brucella based on palladium nanoparticles

Palladium nanoparticles were potentiostatically electrodeposited on a gold surface at a highly negative potential. The nanostructure, as a transducer, was utilized to immobilize a Brucella-specific probe and the process of immobilization and hybridization was detected by electrochemical methods. The proposed method for detection of the complementary sequence and a non-complementary sequence was applied. The fabricated genosensor was evaluated for the assay of the bacteria in the cultured and human samples with and without PCR. The genosensor could detect the complementary sequence with a sensitivity of 0.02 μA dm³ mol⁻¹, a linear concentration range of 1.0 × 10⁻¹² to 1.0 × 10⁻¹⁹ mol dm⁻³, and a detection limit of 2.7 × 10⁻²⁰ mol dm⁻³.     

Preparation of cadmium sulfide nanoparticles and their application for improving the properties of the electrochemical sensor for the determination of enrofloxacin in real samples

An advanced electrochemical sensor for the detection of enrofloxacin (ENR) based on the use of a modified electrode containing cadmium sulfide (CdS) nanoparticles (NPs) is reported. The CdS NPs were synthesized and characterized and then coated onto the electrode to fabricate a modified electrode that exhibited a lower limit of detection of 9.5 × 10^?8 mol·L^?1. This detection limit compares with a traditional electrode that exhibited a concentration detection range of 1.0 × 10^?2 to 1.0 × 10^?7 mol·L^?1. This modified electrode demonstrated good selectivity, reproducibility, response time (<40 s), lifetime (up to 12 wk), and pH range (3.3‐7.2) for the determination of ENR in real samples (eg, pig urine).     

Electrocatalysis and simultaneous determination of catechol and quinol by poly(malachite green) coated multiwalled carbon nanotube film

Electrochemically active composite film that contains multiwalled carbon nanotubes (MWCNTs), Nafion (NF), and poly(malachite green) (PMG) has been synthesized on glassy carbon electrode (GCE), gold, and indium tin oxide (ITO) electrodes by potentiodynamic method. The presence of MWCNTs in the composite film (MWCNT–NF–PMG) enhances the surface coverage concentration (Γ) of PMG by fivefold. Similarly, an electrochemical quartz crystal microbalance study revealed enhancement in the deposition of PMG at MWCNT–NF film when compared with bare and only NF modified electrodes. The surface morphology of the composite film was studied using atomic force microscopy, which revealed that the PMG incorporated on MWCNT–NF film. The composite film exhibited enhanced electrocatalytic activity toward the mixture of biochemical compounds catechol and quinol. The electrocatalytic responses of analytes at MWCNT–NF–PMG composite film were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electrocatalysis studies, well-separated voltammetric peaks were obtained at the composite film for catechol and quinol with a peak separation of 147 mV. The sensitivity values of the composite film toward catechol and quinol by the DPV technique were 0.4 and 3.2 mA mM⁻¹ cm⁻², respectively, which are higher than the values obtained by the CV technique. Similarly, the above-mentioned values are better than the previously reported electroanalytical values for the same analytes.