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Using an external redox-active molecule as a DNA hybridization indicator is still a popular strategy in electrochemical DNA biosensors because it is label-free and the multi-site binding can enhance the response signal. A planar and uncharged transition metal complex, Cu(PA) 2 (PA = picolinic acid) with excellent electrochemical activity has been synthesized and its interaction with double-stranded DNA (dsDNA) is studied by experimental electrochemical methods and theoretical molecular docking technology. The experimental results reveal that the copper complex interacts with dsDNA via specific intercalation, which is verified by the molecular docking result. The surface-based voltammetric analysis demonstrates that the planar Cu(PA) 2 can effectively accumulate within the electrode-confined hybridized duplex DNA rather than the single-stranded probe DNA. Based on this phenomenon, the Cu(PA) 2 is utilized as an electrochemical hybridization indicator for the detection of oligonucleotides. The sensing assays show that upon incubation in Cu(PA) 2 solution, the probe electrode does not display any Faraday signal, but the hybridized one has a pair of strong redox peaks corresponding to the electrochemistry of Cu(PA) 2 , showing excellent hybridization indicating function of Cu(PA) 2 without background interference. The signal intensity of Cu(PA) 2 is dependent on the concentrations of the target oligonucleotide ranging from 1 fM to 100 nM with an experimental detection limit of 1.0 fM. Due to the specific intercalation of Cu(PA) 2 with dsDNA, the biosensor also exhibits good ability to recognize oligonucleotide with different base mismatching degree. Image 1 • Cu(PA) 2 (PA = picolinic acid) bearing planarity and electroneutrality was used as a redox hybridization indicator. • Specific intercalation between the Cu(PA) 2 and dsDNA was studied by electrochemistry and molecular docking. • Binding constant and binding site size of Cu(PA) 2 to dsDNA were calculated. • The copper complex shows high recognition to ssDNA and dsDNA. • The Cu(PA) 2 -based biosensor has not background response, good selectivity and high sensitivity. [ABSTRACT FROM AUTHOR]

Foodborne pathogens such as Clostridium perfringens can cause diverse illnesses and seriously threaten to human health, yet far less attention has been given to detecting these pathogenic bacteria. Herein, two morphologies of nanoceria were synthesized via adjusting the concentration of NaOH, and CeO2 nanorod has been utilized as sensing material to achieve sensitive and selective detection of C. perfringens DNA sequence due to its strong adsorption ability towards DNA compared to nanoparticle. The DNA probe was tightly immobilized on CeO2/chitosan modified electrode surface via metal coordination, and the DNA surface density was 2.51 × 10−10 mol/cm2. Under optimal experimental conditions, the electrochemical impedance biosensor displays favorable selectivity toward target DNA in comparison with base-mismatched and non-complementary DNA. The dynamic linear range of the proposed biosensor for detecting oligonucleotide sequence of Clostridium perfringens was from 1.0 × 10−14 to 1.0 × 10−7 mol/L. The detection limit was 7.06 × 10−15 mol/L. In comparison, differential pulse voltammetry (DPV) method quantified the target DNA with a detection limit of 1.95 × 10−15 mol/L. Moreover, the DNA biosensor could detect C. perfringens extracted DNA in dairy products and provided a potential application in food quality control. [ABSTRACT FROM AUTHOR]

A DNA tetrahedral nanostructure-based electrochemical biosensor was developed to detect avian influenza A (H7N9) virus through recognizing a fragment of the hemagglutinin gene sequence. The DNA tetrahedral probe was immobilized onto a gold electrode surface based on self-assembly between three thiolated nucleotide sequences and a longer nucleotide sequence containing complementary DNA to hybridize with the target single-stranded (ss)DNA. The captured target sequence was hybridized with a biotinylated-ssDNA oligonucleotide as a detection probe, and then avidin-horseradish peroxidase was introduced to produce an amperometric signal through the interaction with 3,3',5,5'-tetramethylbenzidine substrate. The target ssDNA was obtained by asymmetric polymerase chain reaction (PCR) of the cDNA template, reversely transcribed from the viral lysate of influenza A (H7N9) virus in throat swabs. The results showed that this electrochemical biosensor could specifically recognize the target DNA fragment of influenza A (H7N9) virus from other types of influenza viruses, such as influenza A (H1N1) and (H3N2) viruses, and even from single-base mismatches of oligonucleotides. Its detection limit could reach a magnitude of 100 fM for target nucleotide sequences. Moreover, the cycle number of the asymmetric PCR could be reduced below three with the electrochemical biosensor still distinguishing the target sequence from the negative control. To the best of our knowledge, this is the first report of the detection of target DNA from clinical samples using a tetrahedral DNA probe functionalized electrochemical biosensor. It displays that the DNA tetrahedra has a great potential application as a probe of the electrochemical biosensor to detect avian influenza A (H7N9) virus and other pathogens at the gene level, which will potentially aid the prevention and control of the disease caused by such pathogens.

In this study, an electrochemical biosensor system for the detection of DNA hybridization by using gelatin methacrylate (GelMA) modified electrodes was developed. Electrochemical behavior of GelMA modified Pencil Graphite Electrode (PGE) that serve as a functional platform was investigated by using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) and compared with those of the bare PGE. Hybridization was achieved in solution phase and guanine oxidation signal changes were evaluated. The decrease in the guanine oxidation peak currents at around +1.0 V was used as an indicator for the DNA hybridization. Also, more interestingly GelMA intrinsic oxidation peaks at around +0.7 V changed substantially by immobilization of different oligonucleotides such as probe, hybrid and control sequences to the electrode surface. It is the first study of using GelMA as a part of an electrochemical biosensor system. The results are very promising in terms of using GelMA as a new DNA hybridization indicator. Additionally, GelMA modified electrodes could be useful for detecting ultra low quantity of oligonucleotides by providing mechanical support to the bio-recognition layer. The detection limit of this method is at present 10(-12)mol. Signal suppressions were increased from 50% to 93% for hybrid with using GelMA when it was compared to bare electrode which facilitates the hybridization detection., (Copyright © 2014 Elsevier B.V. All rights reserved.)

An electrochemical DNA biosensor for human papillomavirus (HPV) 16 detection has been developed. For this proposed biosensor, L-cysteine was first electrodeposited on the gold electrode surface to form L-cysteine film (CYSFILM). Subsequently, HPV16-specific probe was immobilized on the electrode surface with CYSFILM. Electrochemistry measurement was studied by differential pulse voltammetry method (DPV). The measurement was based on the reduction signals of methylene blue (MB) before and after hybridization either between probe and synthetic target or extracted DNA from clinical samples. The effect of probe concentration was analyzed and the best results were seen at 1000 nM. The hybridization detection presented high sensitivity and broad linear response to the synthetic-target concentration comprised between 18.75 nM and 250 nM as well as to a detection limit of 18.13 nM. The performance of this biosensor was also investigated by checking probe-modified electrode hybridization with extracted DNA from samples. The results showed that the biosensor was successfully developed and exhibited high sensitivity and satisfactory selectivity to HPV16. These results allow for the possibility of developing a new portable detection system for HPVs and for providing help in making an effective diagnosis in the early stages of infection., (Copyright © 2013 Elsevier B.V. All rights reserved.)

An efficient DNA electrochemical biosensor, based on the gold nanoparticles (GNPs) in situ synthesized at the surface of multiwalled carbon nanotubes (MWCNTs), cerium dioxide (CeO2) and chitosan (Chits) composite membrane, was developed for the detection of BCR/ABL fusion gene in chronic myelogenous leukemia (CML). The capture probe was attached onto the nanocomposite membrane modified glassy carbon electrode (GCE) through the conjugated structure. Owing to the synergistic effects of CeO2 nanoparticles with a strong adsorption ability and MWCNTs with a large surface area and excellent electron transfer ability, the prepared composite membrane was demonstrated an efficient electron transfer ability. The biosensor was electrochemically characterized by cyclic voltammogram (CV) and differential pulse voltammetry (DPV), and the decrease of the peak currents upon hybridization was observed using methylene blue (MB) as the electroactive indicator. Under the optimized conditions, peak currents were linear over the range from 1 × 10(-9) M to 1 × 10(-)(12) M, with a detection limit of 5 × 10(-)(13) M (based on the 3σ). And the proposed method was successfully applied for the detection of PCR real samples with satisfactory results. Furthermore, the developed DNA biosensor was demonstrated a good selectivity, a reasonable stability and a favorable reproducibility, which could be regenerated easily., (© 2013 Elsevier B.V. All rights reserved.)

Well-defined hierarchically aloe-like gold micro/nanostructures (HAG) are one-step electrochemically fabricated without introducing any template or surfactant. The formation kinetics of the HAG can be described as a nucleation and three-dimensional growth process controlled by the reactant diffusion from the solution side. As the applied electro-deposition potential moved in the negative direction, the gold crystal density increased, and the crystal shape changed from a quasi-spherical to dendritic fractal morphology. Under the optimal potential of -0.1 V and the time of 10 min, well-defined HAG possessing a hydrophilic surface with large effective area (ca. 8 times of its geometrical area) were obtained, which was used as the substrate for fabricating an ultrasensitive DNA biosensor. The DNA biosensor displayed a significantly enhanced detection limit of 12 aM, a wide linear response from 50 aM to 1 pM, as well as good selectivity, stability and reusability. This efficient DNA molecule immobilization platform may have implications in the preparation of many other gold micro/nanostructures (GMNs) with interesting properties and application potentials in many fields, such as biosensing, biocatalysis and biofuel cells., (Copyright © 2013 Elsevier B.V. All rights reserved.)

An electrochemical DNA nanobiosensor was prepared by immobilization of a 20mer thiolated probe DNA on electro-deposited generation 4 (G4) poly(propyleneimine) dendrimer (PPI) doped with gold nanoparticles (AuNP) as platform, on a glassy carbon electrode (GCE). Field emission scanning electron microscopy results confirmed the codeposition of PPI (which was linked to the carbon electrode surface by C-N covalent bonds) and AuNP ca 60 nm. Voltammetric interrogations showed that the platform (GCE/PPI-AuNP) was conducting and exhibited reversible electrochemistry (E°' = 235 mV) in pH 7.2 phosphate buffer saline solution (PBS) due to the PPI component. The redox chemistry of PPI was pH dependent and involves a two electron, one proton process, as interpreted from a 28 mV/pH value obtained from pH studies. The charge transfer resistance (R ct ) from the electrochemical impedance spectroscopy (EIS) profiles of GCE/PPI-AuNP monitored with ferro/ferricyanide (Fe(CN)₆ 3-/4- ) redox probe, decreased by 81% compared to bare GCE. The conductivity (in PBS) and reduced Rct (in Fe(CN)₆ 3-/4- ) values confirmed PPI-AuNP as a suitable electron transfer mediator platform for voltammetric and impedimetric DNA biosensor. The DNA probe was effectively wired onto the GCE/PPI-AuNP via Au-S linkage and electrostatic interactions. The nanobiosensor responses to target DNA which gave a dynamic linear range of 0.01 - 5 nM in PBS was based on the changes in Rct values using Fe(CN)₆ 3-/4- redox probe.

An electrochemical DNA biosensor for the detection of NOS gene sequences from genetically modified organisms (GMOs) is presented in this paper. Single-stranded DNA (ssDNA) was covalently attached through the carboxylate ester formed by the 3'- hydroxy end of the DNA with the carboxyl of a mercaptoacetic acid self-assembled monolayer-modified gold electrode using N-hydroxysuccinimide (NHS) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) as linkers. The electrochemical behavior of methylene blue (MB) on the ssDNA and dsDNA modified gold electrode were carefully studied. Compared with ssDNA/Au electrode, an increase of redox peak current of MB on dsDNA/Au electrode was found, which could be further used for monitoring the recognition of DNA hybridization. Based on this result, the polymerase chain reaction (PCR) product of the common inserts NOS terminator from real GMOs samples was detected successfully.