Differential Pulse Voltammetry Current Research Articles

An electrochemical aptasensor for the detection of chloramphenicol based on ultra-small Au-inserted hollow PCN-222 MOF.

The excessive utilization of antibiotics has led to significant water contamination and posed severe threats to human well-being. Consequently, the pressing imperative to identify antibiotics in the environment arises. In this study, we have successfully synthesized a hollow PCN-222 MOF distinguished by its substantial surface area and abundant functional groups, particularly the porphyrin cores. To augment the electrical conductivity of the hollow PCN-222 (HPCN-222), gold (Au) particles were incorporated within the porphyrin core using a fundamental hydrothermal method. This modification facilitated the effective immobilization of aptamer strands through π-π stacking and electrostatic interactions. As a result, the Au@HPCN-222 composite demonstrated exceptional efficacy as a substrate for immobilizing the aptamer (Apt) onto the GCE surface. By employing differential pulse voltammetry (DPV) we successfully achieved the detection of chloramphenicol (CAP) with a remarkably low limit of detection of 0.0138ngmL-1 and the peak DPV currents at 0.18V (vs. Ag/AgCl) were used for calibration. Furthermore, this aptasensor exhibited high selectivity and reproducibility.

Liposome functionalized reduced graphene oxide for rapid electrochemical sensing of bacteria.

Pathogenic bacteria represent a severe threat to global public health, particularly with the growing rate of antibiotic resistance, and, therefore, indicate a critical need for developing efficient sensing platforms. Liposome-based sensors are collocating interest due to their intrinsic fusogenic ability to fuse with the outer membrane of bacteria. However, the lack of a conducting property limits their applicability for developing biosensing platforms. In this study, we report conjugation of liposomes with reduced graphene oxide (rGO) for fabricating a rapid and sensitive biosensor for electrochemical detection of Escherichia coli (E. coli). The large surface area of rGO facilitated binding of liposomes with their surface, and the intrinsic electrical and biocompatible properties assisted electrochemical sensing of bacteria. The electrochemical response of the liposome and the rGO-liposome coated electrode shows nonconducting and conducting characteristics, respectively. A significant change in the peak current of differential pulse voltammetry with the gradual variation of bacterial density in the electrolyte was observed for the glassy carbon electrode rGO-liposome (GCE-L-rGO) surface only. The detection sensitivity of GCE-L-rGO sensors was ∼26 μA/106 cells per ml of electrolyte for varying cell densities from 3 × 103 to 3 × 104 cells/ml. The proposed sensing technique can serve as an alternative to conventional methodologies for rapid and in situ detection of bacterial load in different samples, laying the foundation for new applications in clinical diagnostics.

Detection of Staphylococcal Enterotoxin A (SEA) using a sensitive nanomaterial-based electrochemical aptasensor

An electrochemical aptasensor was developed for SEA detection based on the application of chemically reduced graphene oxide and gold nano-urchins for enhancing sensitivity. The complex of the Staphylococcal Enterotoxin A (SEA) molecule and its specific aptamer on the nanomaterial-modified electrode is triggering the aptamer to be detached from the electrode surface and make a difference in the peak current of Differential pulse voltammetry. The fabrication process was confirmed using Cyclic Voltammetry, electrochemical impedance spectroscopy, and Scanning Electron Microscope imaging. As result, the limit of detection was 7.6 fM and the linear range was 25.0–950.0 fM of SEA. The selectivity assessment revealed the high specificity of the aptasensor towards SEA molecules compared to other similar toxin molecules and proteins. Moreover, the functionality of the developed system was tested successfully in spiked real samples of milk and meat as food samples and human serum as a clinical sample. These samples were also tested by a commercial ELISA kit of SEA to compare the results with the aptasensor. The test revealed that the recovery percentages and standard deviation of the aptasensor are superior to the ELISA kit. Therefore, the electrochemical aptasensor can be suggested for being used in food technologies and clinics to detect SEA toxin.

Aptamer-Target Recognition-Promoted Ratiometric Electrochemical Strategy for Evaluating the Microcystin-LR Residue in Fish without Interferences.

Given the significance of food safety, it is highly urgent to develop a sensitive yet reliable sensor for the practical analysis of algal toxins. As most of the developed sensors are disturbed by interfering substances and the target toxin is detected in a single-signal manner based on the immunoassay technology. Herein, we developed an aptamer-based dual-signal ratiometric electrochemical sensor for the sensitive and accurate analysis of microcystin-LR (MC-LR), using it as a proof-of-concept analyte. Methylene blue-tagged ssDNA (MB-ssDNA) was immobilized at the gold electrode surface accompanied with the absence of ferrocene-tagged ssDNA (Fc-ssDNA), resulting in a high differential pulse voltammetry (DPV) current of MB and a low DPV current of Fc. The recognition of MB-ssDNA by MC-LR stimulated the formation of MC-LR@MB-ssDNA, which induced the removal of MB-ssDNA from the electrode and the exposure of SH-ssDNA, enabling Fc-ssDNA to be captured at the electrode surface via nucleic acid hybridization. In comparison with MC-LR deficiency, the DPV signal of MB dropped along with an improved DPV signal of Fc, contributing to the ratiometric detection of MC-LR, with the limit of detection down to 0.0015 nM. Furthermore, this ratiometric electrochemical sensor was successfully explored to assess the bioaccumulated amount of MC-LR in the liver and meat of fish. The aptamer-based ratiometric strategy to develop an electrochemical MC-LR assay will offer a promising avenue to develop high-performance sensors, and the sensor will find more useful application in MC-LR-related aquatic product safety studies.

Hybrid PANI@dialdehyde carboxymethyl cellulose/ZnO nanocomposite modified glassy carbon electrode as a highly sensitive electrochemical sensor

In this research, a highly sensitive voltammetric sensor for hydrogen peroxide (H2O2) detection has been examined using a new hybrid material based polyaniline, dialdyhayed carboxmethyl cellouse and in the presence of ZnO nanoparticles abbreviated as (PANI/D-CMC/ZnO). Various approaches such as cyclic voltammetry (CV), and differential pulse voltammetry were used to investigate the electrocatalytic reduction of H2O2 (DPV). After preparation, (SEM) scanning electron microscopy, (XRD) X-ray diffraction, and (FTIR) Fourier transform infrared techniques were used to characterize and analyze the obtained PANI/D-CMC/ZnO material. Furthermore, as a suitable for determining hydrogen peroxide (H2O2), a high conductivity platform based on PANI/D-CMC/ZnO electrode modified nanocomposite was created. The modified PANI/D-CMC/ZnO, electrode indicated a good linear range and a low detection limit (LOD) of 0.45 M for hydrogen peroxide determination under optimal conditions (pH 5.7). The peak current of differential pulse voltammetry (DPV) method of hydrogen peroxide increased linearly with its concentration. The concentration has been linear from in the ranges of 0.50 to 5 μM and 10 to 50 μM. The sensor was successfully used to test for hydrogen peroxide in real samples like milk.

CRISPR/Cas12a-Derived electrochemical aptasensor for ultrasensitive detection of COVID-19 nucleocapsid protein

Fast, affordable, portable, and sensitive technology to detect COVID-19 is critical to address the current outbreak. Here, we present a CRISPR/Cas12a-derived electrochemical aptasensor for cost-effective, fast, and ultrasensitive COVID-19 nucleocapsid protein (Np) detection. First, an electrochemical sensing interface was fabricated by immobilizing methylene blue labeled poly adenines DNA sequence (polyA-MB electrochemical reporter) on a gold electrode surface. Second, an arched probe was prepared via hybridization of Np aptamer and an activator strand. In the presence of COVID-19 Np, the activator strand could be released from the arched probe due to the specific interaction between the target and the aptamer, which then activated the trans-cleavage activity of the CRISPR/Cas12a system. Subsequently, the polyA-MB reporters were cleaved from the electrode surface, decreasing the current of differential pulse voltammetry (DPV) at a potential of −0.27 V(vs. Ag/AgCl). The CRISPR/Cas12a-derived electrochemical aptasensor shows a highly efficient performance for COVID-19 Np detection in 50 pg mL-1 to 100 ng mL-1 with a limit of detection (LOD) low to 16.5 pg mL-1. Notably, the whole process of one test can be completed within 30 min. Simultaneously, the aptasensor displays a high selectivity to other proteins. The further measurements demonstrate that the aptasensor is robust in a natural system for point-of-care testing, such as in tap water, milk, or serum. The aptasensor is universal and expandable and holds great potential in the COVID-19 early diagnosis, environmental surveillance, food security, and other aspects.

Self-Reporting Molecularly Imprinted Polymer with Covalently Immobilized Ferrocene Redox Probe for Selective Electrochemical Sensing of P-Synephrine

Molecularly imprinted polymers (MIPs) belong to the illustrious examples of bio-mimicking recognizing materials.1 They have found numerous applications in the fabrication of selective chemosensors.2 Their analytical parameters, such as sensitivity, selectivity, and detectability, are almost as high as those of biosensors. Additionally, MIP based chemosensors are superior to biosensors concerning their ease of fabrication, durability, and tolerance to harsh conditions, including elevated or decreased temperature, high ionic strength, extreme pH values, the presence of heavy metal ions and organic solvents in the samples. Conductive MIPs have recently become more frequently applied. That is mainly due to the easy control of MIPs deposition as thin films by electropolymerization.3 For the electrochemical determination of non-electroactive analytes, some external redox probe is usually added to the test solution. It is assumed that target analyte molecules' binding into molecular cavities causes MIP film swelling or shrinking. According to the so-called "gate effect" mechanism, this polymer "breathing" causes changes in the redox probe permeability through an MIP film, thus changing faradaic current corresponding to the redox probe's reduction or oxidation in cyclic voltammetry (CV) and differential pulse voltammetry (DPV) determinations.4-5 This mechanism is operative for nonconductive MIP films. Another mechanism may be considered for surface imprinted macromolecular compounds, e.g., proteins. A drop in the faradaic current of the redox probe accompanying protein adsorption originates from physical blocking of the electrode surface by their bulky nonconductive molecules.6 But both of these mechanisms seem to be invalid in case of electrochemical sensors based on conductive MIP films. In our previous studies, we demonstrated that a drop in the DPV current, caused by the appearance in a solution of an analyte, at conductive MIP film-coated electrodes might originate not from hindering the diffusion of the redox probe through the film but from changes in electrochemical properties of the film itself 7. Suppose the redox probe diffusion through the MIP film is not a decisive parameter for the faradaic current involving. Then, in the, e.g., DPV, determinations of electroinactive analytes at conductive MIP film-coated electrodes, this diffusion may be eliminated. For that the redox probe could be immobilized inside the MIP film matrix. Herein, we propose to deposit a self-reporting MIP film and apply it for fabrication of the selective electrochemical sensor determining the target analyte in the redox probe free test solutions. For that purpose, a ferrocene redox probe was covalently immobilized in a bis-bithiophene polymer molecularly imprinted with the p-synephrine template. Simultaneously, this polymer was deposited on the Pt electrode as a thin film. After the template extraction from the film, the analyte was determined with differential pulse voltammetry (DPV) in a redox probe free solution. That was possible because the internal ferrocene redox probe generated the DPV analytical signal. The thickness and morphology of the film were crucial for the sensor's performance. The mechanism of this redox self-reporting MIP film-based chemosensor was examined with electrochemical methods, simultaneous piezomicrogravimetry and electrochemistry at an electrochemical quartz crystal microbalance, and surface plasmon resonance spectroscopy. The devised chemosensor was applied for selective p-synephrine determination in a concentration range of 2.0 to 75 nM. References Cieplak, M.; Kutner, W., Artificial biosensors: How can molecular imprinting mimic biorecognition? Trends Biotechnol. 2016, 34 (11), 922-941. Uzun, L.; Turner, A. P. F., Molecularly-imprinted polymer sensors: realising their potential. Biosens. Bioelectron. 2016, 76, 131-144. Huynh, T.-P.; Sharma, P. S.; Sosnowska, M.; D'Souza, F.; Kutner, W., Functionalized polythiophenes: Recognition materials for chemosensors and biosensors of superior sensitivity, selectivity, and detectability. Prog. Polym. Sci. 2015, 47, 1-25. Yoshimi, Y.; Narimatsu, A.; Nakayama, K.; Sekine, S.; Hattori, K.; Sakai, K., Development of an enzyme-free glucose sensor using the gate effect of a molecularly imprinted polymer. J. Artif. Organs 2009, 12 (4), 264-270. Sharma, P. S.; Garcia-Cruz, A.; Cieplak, M.; Noworyta, K. R.; Kutner, W., 'Gate effect' in molecularly imprinted polymers: the current state of understanding. Curr. Opin. Electroche. 2019, 16, 50-56. Moreira, F. T. C.; Dutra, R. A. F.; Noronha, J. P. C.; Fernandes, J. C. S.; Sales, M. G. F., Novel biosensing device for point-of-care applications with plastic antibodies grown on Au-screen printed electrodes. Sens. Actuators, B 2013, 182, 733-740. Lach, P.; Cieplak, M.; Majewska, M.; Noworyta, K. R.; Sharma, P. S.; Kutner, W., "Gate Effect" in p-Synephrine Electrochemical Sensing with a Molecularly Imprinted Polymer and Redox Probes. Anal. Chem. 2019, 91 (12), 7546-7553. Figure 1

Electrochemical detection of bisphenol a on a MWCNTs/CuFe2O4 nanocomposite modified glassy carbon electrode

In the present study, a novel electrochemical sensor based on glassy carbon electrode (GCE) modified by multi-walled carbon nanotubes/copper ferrite (MWCNTs/CuFe2O4) nanocomposite was introduced for detection of bisphenol A (BPA). The nanocomposite was prepared by citrate sol-gel method and then characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) systems. Electrochemical characterizations of the bare and modified electrodes were explored with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Also, the peak current of differential pulse voltammetry (DPV) of BPA was increased linearly with its concentration in the ranges of 0.01–120 μM with a low detection limit of 3.2 nM (S/N = 3). Good selectivity and acceptable reproducibility were also attained on the proposed sensor. Finally, this sensor was successfully employed for the BPA determination in different real samples.

Fabrication of an electrochemical mesalazine sensor based on ZIF-67

Abstract This paper describes the application of ZIF-67 nanoparticles for carbon paste electrode (CPE) modification for sensitive voltammetric detection of mesalazine (MSA). The characterization of as-synthesized ZIF-67 nanoparticles was investigated by different techniques. Furthermore, the electrochemical behavior of the modified CPE (MCPE) was investigated using EIS (electrochemical impedance spectroscopy) and CV (cyclic voltammetry) methods. The results showed an irreversible oxidation peak for MSA around 0.540 V vs. the Ag/AgCl reference electrode. The curve of the peak current of differential pulse voltammetry (DPV) vs MSA concentration was linear in the range of 0.03–50 μM with a detection limit of 0.01 µM. The prepared sensor presents good repeatability with acceptable relative standard deviation (RSD) values. Finally, the prepared electrode was successfully used in human serum and urine as real samples.

One-Step Synthesis of Methylene Blue-Encapsulated Zeolitic Imidazolate Framework for Dual-Signal Fluorescent and Homogeneous Electrochemical Biosensing

In vitro diagnosis requires target biomarkers to be reliably detected at an ultralow level. A dual-signal strategy permits self-calibration to overcome the interferences of experimental and environmental factors, and thus is regarded as a promising approach. However, currently reported works mainly concentrated on the same forms of energy of output signals. Herein, we propose a one-step strategy for synthesis of methylene blue-encapsulated zeolitic imidazolate framework-90 (MB@ZIF-90) with high loading, unique dual-signal property, exceptional recognition capability, and good stability, and we further pioneer MB@ZIF-90 as a dual-signal biosensor for label-free, enzyme-free, and ultrasensitive detection of adenosine triphosphate (ATP) by integration of fluorescence and homogeneous electrochemical techniques. The recognition of MB@ZIF-90 by target ATP spurs the decomposition of ZIF-90, subsequently permitting MB to be released into a supernatant. As compared to the case where ATP does not exist, obviously increased intensities in fluorescence and differential pulse voltammetry current are observed and both signals are directly proportional to ATP concentrations. Thus, the MB@ZIF-90-based biosensor achieved dual-signal detection of ATP in an ultrasensitive manner and displayed a more reliable diagnosis result than previously reported ATP biosensors. This dual-signal strategy provides a new opportunity to develop high-performance biosensors for in vitro diagnosis and demonstrates great potential for future applications in bioinformatics and clinical medicine.

Ultrasensitive voltammetric and impedimetric aptasensor for diazinon pesticide detection by VS2 quantum dots-graphene nanoplatelets/carboxylated multiwalled carbon nanotubes as a new group nanocomposite for signal enrichment

Polluted water and groundwater resources contaminated by pesticides are among the most important environmental distresses. Therefore, a simple, ultrasensitive, and selective electrochemical aptasensor is proposed for diazinon (DZN) determination as an organophosphorus compound. The vanadium disulfide quantum dots (VS2QDs) were synthesized by a facile hydrothermal method and doped on the graphene nanoplatelets/carboxylated multiwalled carbon nanotubes (GNP/CMWCNTs) as a new group of nanocomposite. The prepared nanocomposite (VS2QDs-GNP/CMWCNTs) on a glassy carbon electrode (GCE) was incubated with the DZN binding aptamer (DZBA) through electrostatic interaction (GCE/VS2QDs-GNP/CMWCNTs/DZBA). The modified electrode was used for the low detection of DZN by monitoring the oxidation of [Fe(CN)6]3−/4− as the redox probe. The characterizations of the modified electrode were performed by several electrochemical methods include: cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Also, the prepared nanocomposite was characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV–Vis absorption spectroscopy, fourier transform infrared (FT-IR), fluorescence emission spectroscopy, dynamic light scattering (DLS), elemental mapping, and energy dispersive spectroscopy (EDS). The DZBA selectively adsorbs DZN on the modified electrode, leading to a decrease and increase in the current of DPV and charge transfer resistance (RCT) of EIS, respectively, as analytical signals. The developed electrochemical aptasensor at the optimal conditions have low limits of detection (LOD) equal to 1.1 × 10−14 and 2.0 × 10−15 mol L−1 with wide dynamic ranges of 5.0 × 10−14-1.0 × 10−8 mol L−1 and 1.0 × 10−14-1.0 × 10−8 mol L−1 for DPV and EIS calibration curves, respectively. Finally, this aptasensor had good selectivity, stability, reproducibility, and feasibility for the DZN detection in various real samples.

Facile strategy for synthesis of silver-graphene hybrid with controllable size and excellent dispersion for ultrasensitive electrochemical detection of acetamiprid

Electrochemical properties of metal-graphene hybrid depend on size and dispersion of metal nanoparticles on graphene sheets. The study reports a facile synthesis of silver-graphene hybrid with controllable size and excellent dispersion. Histidine-functionalized graphene quantum dots (His-GQDs) are firmly bound on graphene sheets of graphite oxide (GO) and then combined with Ag+ to form stable Ag/His-GQD/GO complex. Followed by heating in N2 to produce Ag/His-GQD/G. The resulting hybrid offers well-defined three-dimensional structure, in which all Ag nanoparticles are uniformly dispersed on the surface of graphene sheets. Interestingly, the size and density of Ag nanoparticles can be effectively adjusted by varying mass ratio of His-GQD/GO or Ag+/GO. To construct on the aptasensor, aptamer of acetamiprid was connected to Ag nanoparticles via Ag-S bond in the hybrid immobilized on surface of glass carbon electrode. The architecture creates an excellent catalytic activity. The aptasensor based on Ag/His-GQD/G exhibits ultrahigh sensitivity, specificity and stability for electrochemical detection of acetamiprid. A linear relationship between the peak current of differential pulse voltammetry and logarithm value of acetamiprid concentration was obtained in the range from 1.0 × 10−16 to 5.0 × 10−12 M with a detection limit of 4.0 × 10−17 M. The method has been successfully applied in detection of acetamiprid in tea.

Polyethyleneimine/Graphene Multilayer Film Supported Ferric Cobalt Modified Electrode for High-Performance Sensing of L-cysteine

One novel chemically modified electrode (CME) was prepared through fabricating polyethyleneimine/oxidized graphene multilayers on indium tin oxide (ITO) slide via layer-by-layer assembly followed by electrochemically depositing cobalt hexacyanoferrate. A large range of methods were used to characterize the morphology and electrochemical properties of the electrode including field-emission scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, cyclic voltammetry, differential pulse voltammetry (DPV), electrochemical impedance spectroscopy and chronoamperometry. Under optimized conditions, the oxidation current of DPV (typically at 0.2 V vs. saturated calomel electrode) increased linearly in the range of 5 × 10−5 to 2 × 10−3 mol L−1. And the limit of detection and the limit of quantity were 4.6 × 10−7 mol L−1 and 1.5 × 10−6 mol L−1 (based on signal-to-noise ratio of 3 and 10), respectively. Average recoveries from (spiked) commercial mask were between 98.1% and 104.5% with relative standard derivations less than 3.14% (n = 3) at three spiked levels. The method was validated by HPLC. Furthermore, the possible mechanism of L-Cys detection was studied based on chronoamperometric experiments.

An electrochemical aptasensor for staphylococcal enterotoxin B detection based on reduced graphene oxide and gold nano-urchins

Detection of staphylococcal enterotoxin B (SEB) as a bacterial toxin causing severe food poisoning is of great importance. Herein, we developed an electrochemical aptasensor for SEB detection using a screen printed electrode modified with reduced graphene oxide (rGO) and gold nano-urchins (AuNUs). Afterward, the single-stranded DNA probe was attached to the surface of AuNUs on the modified electrode and then the specific aptamer was attached to the probe. In the presence of SEB molecules, the aptamer detached from the electrode surface and after applying the electrochemical signal generator, hematoxylin and the peak current of differential pulse voltammetry (DPV) were recorded. Due to the intercalation mechanism of hematoxylin-DNA interaction, the detachment of aptamer from electrode surface decreased the DPV peak current and the calibration graph (peak current vs SEB concentration) can be used for quantification of SEB. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and also field emission scanning electron microscope imaging were used for electrode characterization. Selectivity experiments of the developed aptasensor showed a very distinct difference between SEB and other nonspecific molecules. A wide linear range from 5.0 to 500.0 fM was achieved and the detection limit was calculated as 0.21 fM. The performance of the aptasensor was checked in spiked food samples as simulated real samples and the results showed no significant difference compared to the synthetic samples. Results of selectivity and repeatability of the aptasensor were satisfactory. In addition, better recovery percentages and also lower standard deviation of aptasensor compared to a commercial ELISA kit of SEB detection proved the superior performance of the proposed aptasensor.

Developing an electrochemical sensor based on a carbon paste electrode modified with nano-composite of reduced graphene oxide and CuFe2O4 nanoparticles for determination of hydrogen peroxide

In this paper, a highly sensitive voltammetric sensor based on a carbon paste electrode with CuFe2O4 nanoparticle (RGO/CuFe2O4/CPE) was designed for determination of hydrogen peroxide (H2O2). The electrocatalytic reduction of H2O2 was examined using various techniques such as cyclic voltammetry (CV), chronoamperometry, amperometry and differential pulse voltammetry (DPV). CuFe2O4 nanoparticles were synthesized by co-precipitation method and characterized with scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) techniques. Then, a high conductive platform based on a carbon paste electrode modified with RGO and CuFe2O4 nanoparticles was prepared as a suitable platform for determination of hydrogen peroxide. Under the optimum conditions (pH5), the modified electrode indicated a fast amperometric response of <2s, good linear range of 2 to 200μM, low detection limit of 0.52μM for determination of hydrogen peroxide. Also, the peak current of differential pulse voltammetry (DPV) of hydrogen peroxide is increased linearly with its concentration in the ranges of 2 to 10μM and 10 to 1000μM. The obtained detection limit for hydrogen peroxide was evaluated to be 0.064μM by DPV. The designed sensor was successfully applied for the assay of hydrogen peroxide in biological and pharmaceutical samples such as milk, green tea, and hair dye cream and mouthwash solution.

Conducting Polymer-Layered Carbon Nanotube as Sensor Interface for Electrochemical Detection of Dacarbazine In-Vitro

A reusable electrochemical sensor ensembling carbon nanotubes and a conducting polymer together is fabricated for the detection of an important anti-cancer drug, dacarbazine (DTIC). A thin film of a conducting polymer, poly(2-amino-1,3,4-thiadiazole) (poly-ATD), is formed on the carbon nanotube paste electrode (CNPE) by employing a potentiodynamic polymerization technique. The fabricated sensor surface has been characterized by FTIR spectroscopy and scanning electron microscopy (SEM) for the structural and chemical properties of the electrode system. The electrochemical capability of the fabricated poly-ATD/CNPE composite electrode for the detection of DTIC is examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopic analysis (EIS), and the poly-ATD/CNPE electrode is found to be efficient for electrocatalytic oxidation of DTIC. Optimization and evaluation of the sensor system are examined by differential pulse voltammetry (DPV). A linear relationship of DTIC concentration over the peak current of DPVs is exhibited over a wide concentration range of 0.05–24.0 μM with a low detection limit (3σ/b) of 35 nM. Steady state current–time analysis experiments under hydrodynamic conditions exhibited a low detection limit of 20 nM, and the analysis time is as low as 10 s. Practical utility of the fabricated poly-ATD/CNPE biosensor for the detection of DTIC directly from artificial urine and pharmaceutical formulations has been demonstrated with very good recovery limits.

Electrochemical co-reduction synthesis of Au/ferrocene–graphene nanocomposites and their application in an electrochemical immunosensor of a breast cancer biomarker

The nanocomposites (Fc–GO) of ferrocene (Fc) hybridized graphene oxide (GO) were prepared by π–π stacking interactions. Fc–GO and Au(III) are electrochemically co-reduced to obtain Au nanoparticles (AuNPs) and Fc hybridized electrochemically reduced graphene oxide (Fc–ERGO) nanocomposites (AuNPs/Fc–ERGO). Scanning electron microscopy reveals that Au particles are about 10 nm and are dispersed uniformly on Fc–ERGO. The electrochemical behavior of AuNPs/Fc–ERGO demonstrates great electrochemical activity and stability. The AuNPs/Fc–ERGO was applied in a highly sensitive immunosensor of the biomarker carbohydrate antigen 15-3 (CA 15-3). This unique immunosensor, with AuNPs/Fc–ERGO as the immobilization platform and signal probe, exhibited significant sensitivity toward CA 15-3. Under optimal conditions, the peak current of differential pulse voltammetry (DPV) of the immunosensor decreased with increasing CA 15-3 concentration, showing two linear ranges of 2.0–25.0 U mL−1 and 0.05–2.0 U mL−1 with a low detection limit of 0.015 U mL−1. The strategy developed for this immunosensor provides a promising approach for clinical research and diagnostic applications.

Microcystin-(Leucine-Arginine) Immunosensor Based on Iron(II, III) Magnetic Nanoparticles

An electrochemical immunosensor for microcystin-(leucine-arginine) based on magnetic bionanoparticles and iron(II, III) oxide was developed. The bionanoparticles were prepared by cross-linking antibodies of microcystin-(leucine-arginine) and amino-functionalized magnetic iron(II, III) oxide nanoparticles with glutaraldehyde, followed by immobilization on the surface of a magnetic electrode. The immunosensor was based on the model of direct competition, as microcystin-(leucine-arginine) and horseradish peroxidase-conjugated microcystin-(leucine-arginine) competitively combined with immobilizing antibodies. The peak current of differential pulse voltammetry (DPV) decreased with an increase of microcystin-(leucine-arginine) concentration after antigen-antibody reaction. When the background current was stabilized, the anodic peak current response and change in peak response were recorded. Under the optimized conditions, the change in response was proportional to the microcystin-(leucine-arginine) concentration between 0.010 and 100 µg/L with a limit of detection equal to 0.009 µg/L. Amperometry was adopted to determine microcystin-(leucine-arginine); the linear dynamic range was 0.10 to 100 µg/L with a detection limit of 0.08 µg/L. The method was successfully applied in the determination of microcystin-(leucine-arginine) in river water and the recoveries were between 90.2% and 110.5%.

Simultaneous determination of guanine and adenine on CuO shuttle-like nanocrystals/poly(neutral red) film on glassy carbon electrode

CuO shuttle-like nanocrystals on a poly(neutral red) glassy carbon electrode (nano-CuO/PNR/GCE) has been fabricated and used to simultaneously detect guanine and adenine. The sample is characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). It has been shown that the oxidation peak current of guanine and adenine could be greatly enhanced with the nano-CuO/PNR/GCE. Under optimal conditions, the anodic peak current of differential pulse voltammetry is proportional to the concentration of the guanine and adenine in the range of 0.05 to 3.0 μM. The corresponding detection limits are 1.6 × 10−2 μM for guanine and 2.3 × 10−2 μM for adenine (S/N = 3). The nano-CuO/PNR/GCE exhibits good storage stability and reproducibility for practical application. It could be applied to simultaneously determination of guanine and adenine for the samples with good anti-interference ability.

Mga Genosensor for Early Detection of Human Rheumatic Heart Disease

The 5' amino-labeled DNA probe complementary to mga gene of Streptococcus pyogenes was immobilized on carboxylated multiwall carbon nanotubes electrode and hybridized with 0.1-100 ng/6 μl single-stranded genomic DNA (ssG-DNA) of S. pyogenes from throat swab of suspected rheumatic heart disease (RHD) patients. Electrochemical response was measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance (EI). The sensitivity of the sensor was 106.03 (μA/cm(2))/ng and limit of detection (LOD) was found 0.014 ng/6 μl with regression coefficient (R(2)) of 0.921 using DPV. The genosensor was characterized by FTIR and SEM, and electrode was found stable for 6 months on storage at 4 °C with 5-6 % loss in initial DPV current. mga genosensor is the first report on RHD sensor which can save life of several suspected patients by early diagnosis in 30 min.