Electrochemical Reduction Signal Research Articles

CTAB-Co-MOFs@AuPt NPs as signal probes for the electrochemical detection of carcinoembryonic antigen 15-3.

A sensitive electrochemical strategy for carcinoembryonic antigen 15-3 (CA15-3) detection isreported using CTAB-Co-MOFs@AuPt NPs as signal probes. The electrochemical strategy was designed as follows: First, the graphene aerogel@gold nanoparticles (GA@Au NPs) nanocomposites were employed to modify the sensing surface for promoting electron transfer rate and primary antibody (Ab1) immobilization due to GA possesses a large specific surface area, eminent conductivity, and a 3D network structure. Cobalt metal-organic frameworks (CTAB-Co-MOFs) synthesized were then used as a carrier for AuPt NPs and secondary antibody (Ab2) immobilization (notes: labelled-Ab2). With sandwich immunoreaction, the labelled-Ab2 was captured on the surface of the GA@Au NPs nanocomposites. Finally, differential pulse voltammetry (DPV) was employed to register the electrochemical signal of the immunosensor at the potential of - 0.85V (vs SCE) in phosphate buffer saline (PBS) containing 2.5mM H2O2. It was verified that the electrochemical reduction signal from Co3+ to Co2+ was recorded. The AuPt NPs could catalyze the reaction of H2O2 oxidizing Co2+ to Co3+, resulting in the amplification of the electrochemical signal. Under the selected conditions, the immunosensor can detect CA15-3 in the range10 µU/mL to 250 U/mL with a low detection limit of 1.1 µU/mL. In the designed strategy, the CTAB-Co-MOFs were not only employed as carriers for AuPt NPs, but also acted as signal probes. The CTAB-Co-MOFs were investigated including SEM, TEM, XPS, and XRD. The applicationability of theimmunosensor was evaluated using serum sample, demonstrating the immunosensor can be applied to clinic serum analysis.

An electrochemical aptasensor based on Ce-MOF@COF to detect carcinoembryonic antigen

In the presence of H2O2, Au@Ce-MOF@COF-HRP can effectively promote the oxidation of hydroquinone (HQ) to benzoquinone (BQ), and the electrochemical reduction signal of BQ was significantly amplified.

Electrochemical aptasensor for aflatoxin B1 detection using cerium dioxide nanoparticle supported on iron-porphyrinic metal–organic framework as signal probes

A novel electrochemical aptasensor was fabricated by using cerium oxide (CeO2) nanoparticle loaded spindle iron-porphyrinic metal–organic framework (PorMOF) as signal probe to detect aflatoxin B1 (AFB1). PorMOF with zirconium ion as the center ion and iron-porphyrin as linker was synthesized. CeO2 nanoparticle was supported on PorMOF to obtain CeO2/PorMOF. PorMOF and CeO2/PorMOF were characterized by scanning electron microscopy, and energy dispersive and X-ray diffraction spectroscopies. CeO2/PorMOF modified electrode showed enhanced electrocatalytic activity for oxygen reduction, and CeO2/PorMOF was functionalized with streptavidin by glutaraldehyde cross-linking to prepare traces of AFB1 aptasensor. A competitive aptasensing assay was applied for AFB1 detection. Firstly, AFB1 capture DNA (cDNA) was fixed on electrode by Au-S bond. Sequentially, AFB1 with biotin was hybridized with cDNA aptamer. Thirdly, after recognizing of biotin and streptavidin, CeO2/PorMOF traces was introduced into electrode to produce a strong electrochemical reduction signal of oxygen. In the presence of AFB1, AFB1 aptamer preferentially bound to AFB1, and the electrochemical signal decreased. The designed method had a wide detection range of 0.1 pM-10 nM, a detection limit as low as 30 fM (S/N = 3), and good selectivity, reproducibility and stability. The aptasensor had been successfully applied to detect AFB1 in peanut and milk samples.

Exploring graphene oxide intrinsic electroactivity to elucidate the non-covalent interactions with DNA oligonucleotides.

We show here how the electrochemical reduction signal of graphene oxide nanocolloids is inhibited upon the formation of non-covalent interactions with single stranded DNA oligonucleotides. The drop in the reduction current intensity is strongly influenced by the nucleobase sequence, and can therefore be directly correlated to the specific DNA homo-oligonucleotide.

Graphene-Assisted Sensor for Rapid Detection of Antibiotic Resistance in Escherichia coli.

In recent years, antibiotic-resistant bacteria caused by antibiotic abuse in the medical industry have become a new environmental pollutant that endangers public health. Therefore, it is necessary to establish a detection method for evaluating drug-resistant bacteria. In this work, we used Escherichia coli as a target model and proposed a method to evaluate its drug resistance for three antibiotics. Graphene dispersion was used to co-mix with E. coli cells for the purpose of increasing the current signal. This electrochemical-based sensor allows the evaluation of the activity of E. coli on the electrode surface. When antibiotics were present, the electrocatalytic reduction signal was diminished because of the reduced activity of E. coli. Based on the difference in the electrochemical reduction signal, we can evaluate the antibiotic resistance of different E. coli strains.

A label-free electrochemical platform based on a thionine functionalized magnetic Fe-N-C electrocatalyst for the detection of microRNA-21.

Taking a composite of a nanomaterial and a signal molecule as a substrate material can provide a label-free electrochemical platform. Besides, the nanomaterial with a high catalytic activity towards the signal molecule can improve the sensitivity of the platform. Herein, a thionine functionalized Fe-N-C nanocomposite was employed as the substrate. Firstly, the electrocatalytic activity of Fe-N-C towards the electroreduction of thionine was explored. Then, an immobilization-free and label-free electrochemical platform for the determination of microRNA-21 based on Fe-N-C-thionine/Fe3O4@AuNPs was constructed. A magnetic glassy carbon electrode (MGCE) was used to keep the magnetic Fe-N-C-thionine/Fe3O4@AuNPs modified onto the surface of the MGCE. Fe-N-C and Fe3O4 nanoparticles can co-catalyze the electroreduction of thionine and a strong electrochemical reduction signal of thionine could be realized in the differential pulse voltammetry (DPV) test. Also, a catalytic hairpin assembly (CHA) reaction was utilized to enhance the sensitivity of the developed electrochemical biosensor. Besides, the developed biosensor shows excellent specificity and reproducibility in the test of human serum samples, indicating its wide application prospects in the early-stage diagnosis of tumors.

A dual amplification electrochemical immunosensor based on HRP-Au@Ag NPs for carcinoembryonic antigen detection

A sensitive sandwich-type electrochemical immunosensor based on dual amplification strategy was constructed. The dual amplification strategy has been used secondary antibody(Ab2)-horseradish peroxidase(HRP)-Au@Ag nanoparticles (Au@Ag NPs) for carcinoembryonic antigen(CEA) detection. Ab2-HRP-Au@Ag NPs as dual amplification markers triggered the disproportionation of H2O2, which could facilitate the catalytic oxidation of hydroquinone to quinone(BQ). In addition, due to their large surface area and excellent conductivity, nitrogen-doped graphene were used as a platform to firmly assemble primary antibody (Ab1). Above mentioned generated amout of BQ are corresponding to trace CEA, resulting in the highly electrochemical reduction signal. Under the optimal conditions, the linear range of CEA concentration was 0.0001–100 ng mL−1, and the limit of detection (LOD) could be as low as 0.05 pg mL−1. Importantly, the immunosensor also showed acceptable stability, reproducibility and selectivity.

The Hydrogen Peroxide Electrochemical Reduction Mechanism on Silver Nanoparticles

The hydrogen peroxide reduction on a silver nanoparticle modified electrode shows a CE mechanism. A diffusion oxygen layer is formed via the disproportionation of hydrogen peroxide on silver nanoparticles, and then reduced to hydrogen peroxide during electrochemistry process. Cyclic voltammetry and simulation are combined to confirm this mechanism, demonstrating the electrochemical reduction signal depends on the interacting time between silver and hydrogen peroxide via the disproportionation step before the voltammetric analysis.

Electrochemical immunosensor based on hairpin DNA probe for specific detection of N6-methyladenosine RNA

N6-methyladenosine (m6A) has been identified as the most frequent messenger RNA (mRNA) modification which is the reversible process of RNA methylation modification and related to biological rhythm regulation. In this work, an electrochemical immunosensor was developed for RNA methylation detection via using gold nanoparticles modified Au electrode (AuNPs/Au) as substrate electrode. Firstly, the hairpin DNA probe was assembled on the surface of AuNPs/Au via AuS bond. In the presence of the hairpin DNA, which is the template of assistant DNA and target RNA, the ligase can selectively ligate them as the template of the hairpin DNA to form a long DNA: RNA heteroduplex strand. Successively, anti-N6-methyladenosine antibody (anti-m6A antibody) could be specifically conjugated onto the RNA methylation site, and the horseradish peroxidase labeled goat anti mouse IgG (HRP-IgG) was further conjugated onto the anti-m6A antibody. In the detection buffer solution with H2O2 and hydroquinone, HRP-IgG can catalyze hydroquinone oxidation to generate benzoquinone, resulting in a highly electrochemical reduction signal. This developed immunosensor shows a wide linear range for methylated RNA from 10fM to 10nM, low detection limit of 3.35fM (S/N=3), high specificity and satisfactory reproducibility. And this immunosensing method owns great potentials for providing the assay of the expression level of methylated RNA in micro-biological system.

A novel method for sensitive microRNA detection: Electropolymerization based doping

In the proposed study, for the first time, sensitive electrochemical detection of a breast cancer biomarker microRNA (miRNA), mir-21 was achieved via electropolymerized polypyrrole (PPy) modified pencil graphite electrodes (PPy/PGE). The detection of hybridization of electrochemically doped probe miRNA, antimir-21, with its complementary target, mir-21 was monitored by either electrochemical impedance spectroscopy (EIS) via comparison of charge transfer resistance (Rct) values before and after hybridization or by electrochemical reduction signal of an hybridization indicator, Meldola's blue (MDB). The study covers all the optimization steps for hybridization procedure and electropolymerization of pyrrole as well as detection from real samples of breast cancer cell line, MCF-7. The designed sensor shows a high selectivity and a low detection limit of 0.17nM thanks to electrical conductivity and porous structure of PPy.

Application of mercury–mediated thymine–base pairs for successful voltammetric detection of HPV 18

Formation of mercury(II)–mediated thymine base pairs (T − Hg(II) − T) can be successfully used for efficiently bonding partially complementary, thymine rich DNA sequences. For the first time this highly selective T − Hg(II) − T connection was used for effective voltammetric detection of specific DNA sequences characteristic for Human Papillomavirus type 18 (HPV 18) without additional labeling step. The detection of target DNA sequence was based on the electrochemical reduction signal of Hg(II) ions bonded with opposite thymine bases (mispairs) in DNA helix. The obtained detection and quantification limits were equaled (1.2±0.2)·10−14 and (7.5±0.1)·10−14M respectively. Furthermore the laser ablation coupled with inductively coupled plasma mass spectrometry (LA–ICP–MS) and circular dichroism (CD) were used as an auxiliary technique to get additional information and confirm the formation of DNA duplex via specific interaction between Hg(II) ions and thymine bases.

Electrochemical immunosensor for N6-methyladenosine RNA modification detection

N6-methyladenosine (m6A) is a ubiquitous modification in mRNA and other RNAs across most eukaryotes, which is likely dynamically regulated throughout developmental processes. In this work, an electrochemical immunosensor was fabricated for RNA methylation detection using gold nanoparticles modified glassy carbon electrode (AuNPs/GCE) as substrate electrode. The assembly of 4-aminophenylboronic acid on AuNPs/GCE triggered the further immobilization of anti-m6A antibody on the substrate electrode through the specific interaction between boric acid and glycosyl of antibody, which led to the following capture of methylated RNA through the immunoreaction. A decreased electrochemical reduction signal of the redox probe of [Fe(CN)6]3− was obtained based on the synergistic effect of electrostatic repulsion and steric hindrance. The developed method showed a wide linear range for methylated RNA from 0.01 to 10nM and the detection limit was 2.57pM (S/N=3). Moreover, the down-regulated expression of methylation level of mRNA in the leaves of rice seedlings after incubation with 6-benzylaminopurine was confirmed by the fabricated biosensor, indicating the great potential for assaying the expression level of methylated RNA in real sample.

Electroanalytical Characterization of Montelukast Sodium and Its Voltammetric Determination in Pharmaceutical Dosage Form and Biological Fluids

The electrochemical properties of montelukast sodium (MKST) at zinc oxide nanoparticles modified carbon paste electrode were investigated by cyclic voltammetry and square wave voltammetry. All studies were based on the irreversible and adsorption-controlled electrochemical reduction signal of montelukast sodium at about -0.7 vs. Ag/AgCl at pH 2.3 in methanol-Britton-Robinson buffer mixture. This adsorptive character of the molecule was used to develop a novel, validated, rapid, selective and simple square wave cathodic adsorptive stripping voltammeric method for the direct determination of montelukast sodium in pharmaceutical and biological fluids without time-consuming steps prior to drug assay. Peak current of electrochemical reduction of montelukast sodium was found to vary linearly with the concentration in the range from 1.0 × 10-8 to 1.28 × 10-6 mol L-1. In this method, limit of detection was found to be 7.7 × 10-9 mol L-1. The method was applied to determine the content of MKST tablet and spiked human serum.

Electrochemical and theoretical analysis of the reactivity of shikonin derivatives: dissociative electron transfer in esterified compounds

An electrochemical and theoretical analysis of a series of shikonin derivatives in aprotic media is presented. Results showed that the first electrochemical reduction signal is a reversible monoelectronic transfer, generating a stable semiquinone intermediate; the corresponding E(I)⁰ values were correlated with calculated values of electroaccepting power (ω(+)) and adiabatic electron affinities (A(Ad)), obtained with BH and HLYP/6-311++G(2d,2p) and considering the solvent effect, revealing the influence of intramolecular hydrogen bonding and the substituting group at position C-2 in the experimental reduction potential. For the second reduction step, esterified compounds isobutyryl and isovalerylshikonin presented a coupled chemical reaction following dianion formation. Analysis of the variation of the dimensionless cathodic peak potential values (ξ(p)) as a function of the scan rate (v) functions and complementary experiments in benzonitrile suggested that this process follows a dissociative electron transfer, in which the rate of heterogeneous electron transfer is slow (~0.2 cm s(-1)), and the rate constant of the chemical process is at least 10(5) larger.

Electrochemical Studies of Olmesartan Medoxomil and its Detection in Pharmaceutical Dosage Forms and Biological Fluids by Cathodic Adsorptive Stripping Voltammetric Method

The electrochemical properties of olmesartan (OLME) were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at hanging mercury drop electrode (HMDE). All studies were based on the irreversible and adsorption-controlled electrochemical reduction signal of OLME at about -1.2 and -1.5 V vs. Ag/AgCl at pH 5.0 in Britton-Robinson (BR) buffer. This adsorptive character of the molecule was used to develop a novel, fully validated, rapid, selective and simple differential pulse cathodic adsorptive stripping voltammeric (DPCAdSV) method for the direct determination of OLME in pharmaceutical dosage form and human urine without time-consuming steps prior to drug assay. Peak current of electrochemical reduction of OLME was found to vary linearly with the concentration in the range from 4.7 × 10-8 mol L-1 (0.0262 µg mL-1) to 8.3 × 10-6 mol L-1 (4.636 µg mL-1). In this method, limit of quantification (LOQ) was found to be 5.1 × 10-7 mol L-1 (0.284 µg mL-1). The method was applied to determine the content of OLME in commercial pharmaceutical preparation and spiked human urine. It was found to be highly accurate and precise, having a relative standard deviation of less than 10% for all applications.

Novel electrochemical aptamer biosensor based on an enzyme–gold nanoparticle dual label for the ultrasensitive detection of epithelial tumour marker MUC1

A novel platform based on a hairpin oligonucleotide (HO) switch, gold nanoparticles (AuNPs), and enzyme signal amplification for the ultrasensitive detection of mucin 1 protein (MUC1) was developed in this assay. This HO aptamers and horseradish peroxidase (HRP) were immobilised on the AuNPs to yield HO–AuNP–HRP conjugates. AuNPs were used as labels and bridges between the HO and HRP. HRP was also used as label for catalysing the oxidation of o-phenylenediamine by H2O2. The reaction product was 2,3-diaminophenazine (DAP), which was reduced and could be detected at surface of modified electrode. The reduction signal of DAP was used as a probe for the sensitive detection. After the recognition between oligonucleotide and MUC1, biotin was exposed. Biotin, along with the conjugate, was captured by streptavidin onto the surface of modified electrode. Therefore, the detection of target MUC1 which was a membrane-associated glycoprotein of the mucin family could be sensitively transduced via detection of the electrochemical reduction signal of DAP. Compared to other aptasensors, this biosensor has a good linear correlation ranges from 8.8nM to 353.3nM and a lower detection limit of 2.2nM for MUC1. The proposed method provided a new electrochemical approach for the detection of MUC1.

A sensitive electrochemical method for DNA methyltransferase assay and inhibitor screening based on DNA methylation-sensitive cleavage

A sensitive electrochemical method for detection of DNA methylation and assay of DNA methyltransferase (Dam) was investigated based on methylation-sensitive restriction endonuclease, DNA-Au bio bar code and enzymatic signal amplification. After the DNA probe was hybridized with complementary DNA sequence, and the obtained double-strand DNA (dsDNA) was further methylated by Dam MTase, it could be successively digested by Dpn I at the methylated sites. As a result, the bio bar code and streptavidin-horseradish peroxidase (S-HRP) could not be conjugated on the electrode surface through the specific interaction between biotin and S-HRP, where biotin was labeled at the DNA-Au bio bar code. Thus, only a low electrochemical reduction signal was obtained. However, the hybridized probe could hybrid with DNA-Au bio bar code, and then S-HRP could be conjugated on the electrode surface in the absence of Dam MTase and Dpn I, so a larger reduction current of enzymatic product was obtained. The change of the reduction current of enzymatic product was used to detect DNA methylation and Dam MTase activity. The detection limit of Dam MTase was 0.02unit/mL (S/N=3). Moreover, the inhibitions of mitomycin C, paclitaxel, chlorogenic acid and epicatechin were also investigated. Therefore, this method provided a sensitive platform for monitoring DNA methylation and DNA MTase activity.

Ultrasensitive electrochemical immunoassay for DNA methyltransferase activity and inhibitor screening based on methyl binding domain protein of MeCP2 and enzymatic signal amplification

In this work, we fabricated a novel electrochemical immunosensor for detection of DNA methylation, analysis of DNA MTase activity and screening of MTase inhibitor. The immunosensor was on the basis of methyl binding domain protein of MeCP2 as DNA CpG methylation recognization unit, anti-His tag antibody as “immuno-bridge” and horseradish peroxidase labeled immuneglobulin G functionalized gold nanoparticles (AuNPs–IgG–HRP) as signal amplification unit. In the presence of M. SssI MTase, the symmetrical sequence of 5′-CCGG-3′ was methylated and then recognized by MeCP2 protein. By the immunoreactions, anti-His tag antibody and AuNPs–IgG–HRP was captured on the electrode surface successively. Under the catalysis effect of HRP towards hydroquinone oxidized by H2O2, the electrochemical reduction signal of benzoquinone was used to analyze M. SssI MTase activity. The electrochemical reduction signal demonstrated a wide linear relationship with M. SssI concentration ranging from 0.05unit/mL to 90unit/mL, achieving a detection limit of 0.017unit/mL (S/N=3). The most important advantages of this method were its high sensitivity and good selectivity, which enabled the detection of even one-base mismatched sequence. In addition, we also verified that the developed method could be applied for screening the inhibitors of DNA MTase and for developing new anticancer drugs.

Electrochemical Determination of Phenylethanolamine A Based on Nafion/MWCNTs/AuNPs Modified Carbon Electrode

AbstractPhenylethanolamine A (PEA), a β‐agonist, was found to be illegally used as a growth promoter in pigs last year, causing Chinese government's great attention. Here, a sensitive electrochemical method was developed for detecting PEA by immobilization of gold nanoparticles (AuNPs), multiwalled carbon nanotubes (MWCNTs) and Nafion on the surface of a glassy carbon electrode (GCE). The Nafion/MWCNTs/AuNPs film was characterized by scanning electronic micrographs (SEM) and electrochemical impedance spectroscopy (EIS). The electrochemical behaviors of PEA at the modified GCE were investigated in detail. The synergetic effects of AuNPs, MWCNTs and Nafion amplify the electrochemical reduction signal of PEA, and result in high sensitivity for PEA determination. Under the optimal conditions, the electrochemical sensor shows a wide linear range of 0.01 to 10 (mol/L with a detection limit of 0.005 µmol/L. Moreover, the fabricated sensor presents high selectivity and long‐term stability, which paves a new way for simple, rapid, sensitive detection of PEA.

A novel protocol for ultra-trace detection of pesticides: Combined electrochemical reduction of Ellman's reagent with acetylcholinesterase inhibition

This paper proposed a novel method for ultra-trace detection of pesticides combining electrochemical reduction of Ellman's reagent with acetylcholinesterase (AChE) inhibition. The amperometric biosensor, fabricated by immobilizing AChE on multi-walled carbon nanotubes-chitosan (MWCNTs-Chi) nanocomposites modified glassy carbon electrode, enjoyed high sensitivity owing to the excellent conductivity and favourable biocompatibility of MWCNTs-Chi nanocomposites. Meanwhile, the sensitivity of the biosensor was further enhanced using the electrochemical reduction signal of DTNB for determination. Under optimum conditions, methyl parathion was detected based on its inhibition effect on AChE activity and the subsequent change in electrochemical reduction response of DTNB. Good relationship was obtained between the reduction current and pesticide concentration in the ranges of 5.0×10−7 to 1.0×10−12M with a detection limit of 7.5×10−13M (S/N=3). Moreover, the proposed protocol was successfully employed for the determination of methyl parathion in water and soil samples.