Electrochemical impedance detection of DNA hybridization based on the formation of M-DNA on polypyrrole/carbon nanotube modified electrode

Molecular architecture for DNA wiring

Detection of the hybridisation events is of great importance in many different biotechnology applications such as diagnosis, computing, molecular bioelectronics, and among others. However, one important drawback is the low current of some redox reporters that limits their application. This paper demonstrates the powerful features of molecular wires, in particular the case of S-[4-[2-[4-(2-Phenylethynyl)phenyl]ethynyl]phenyl] thiol molecule and the key role that play the nanometric design of the capture probe linkers to achieve an efficient couple of the DNA complementary ferrocene label with the molecular wire for an effective electron transfer in co-immobilised self-assembled monolayers (SAMs) for DNA hybridisation detection. In this article, the length of the linker capture probe was studied for electron transfer enhancement from the ferrocene-motifs of immobilised molecules towards the electrode surface to obtain higher kinetics in the presence of thiolated molecular wires. The use of the right couple of capture probe linker and molecular wire has found to be beneficial as it helps to amplify eightfold the signal obtained.

A nanostructure label-free DNA biosensor for ciprofloxacin analysis as a chemotherapeutic agent: an experimental and theoretical investigation

A nanostructure DNA biosensor based on pencil graphite electrode modified with polypyrrole, single wall carbon nanotubes and ds-DNA (PGE/PP/SWCNTs/DNA) was suggested for the determination of ciprofloxacin.

Carbon nanotube/polymer composite electrodes for flexible, attachable electrochemical DNA sensors

All-solution-processed, easily-made, flexible multi-walled carbon nanotube (MWCNT)/polydimethylsiloxane (PDMS)-based electrodes were fabricated and used for electrochemical DNA sensors. These electrodes could serve as a recognition layer for DNA, without any surface modification, through π-π interactions between the MWCNTs and DNA, greatly simplifying the fabrication process for DNA sensors. The electrodes were directly connected to an electrochemical analyzer in the differential pulse voltammetry (DPV) and cyclic voltammetry (CV) measurements, where methylene blue was used as a redox indicator. Since neither functional groups nor probe DNA were immobilized on the surfaces of the electrodes, the sensor can be easily regenerated by washing these electrodes with water. The limit of detection was found to be 1.3 × 10(2)pM (S/N=3), with good DNA sequence differentiation ability. Fast fabrication of a DNA sensor was also achieved by cutting and attaching the MWCNT-PDMS composite electrodes at an analyte solution-containable region. Our results pave the way for developing user-fabricated easily attached DNA sensors at low costs.

Electrochemical DNA hybridization sensors based on conducting polymers

Conducting polymers (CPs) are a group of polymeric materials that have attracted considerable attention because of their unique electronic, chemical, and biochemical properties. This is reflected in their use in a wide range of potential applications, including light-emitting diodes, anti-static coating, electrochromic materials, solar cells, chemical sensors, biosensors, and drug-release systems. Electrochemical DNA sensors based on CPs can be used in numerous areas related to human health. This review summarizes the recent progress made in the development and use of CP-based electrochemical DNA hybridization sensors. We discuss the distinct properties of CPs with respect to their use in the immobilization of probe DNA on electrode surfaces, and we describe the immobilization techniques used for developing DNA hybridization sensors together with the various transduction methods employed. In the concluding part of this review, we present some of the challenges faced in the use of CP-based DNA hybridization sensors, as well as a future perspective.

Interactions of DNA with graphene and sensing applications of graphene field-effect transistor devices: a review

Graphene field-effect transistors (GFET) have emerged as powerful detection platforms enabled by the advent of chemical vapor deposition (CVD) production of the unique atomically thin 2D material on a large scale. DNA aptamers, short target-specific oligonucleotides, are excellent sensor moieties for GFETs due to their strong affinity to graphene, relatively short chain-length, selectivity, and a high degree of analyte variability. However, the interaction between DNA and graphene is not fully understood, leading to questions about the structure of surface-bound DNA, including the morphology of DNA nanostructures and the nature of the electronic response seen from analyte binding. This review critically evaluates recent insights into the nature of the DNA graphene interaction and its affect on sensor viability for DNA, small molecules, and proteins with respect to previously established sensing methods. We first discuss the sorption of DNA to graphene to introduce the interactions and forces acting in DNA based GFET devices and how these forces can potentially affect the performance of increasingly popular DNA aptamers and even future DNA nanostructures as sensor substrates. Next, we discuss the novel use of GFETs to detect DNA and the underlying electronic phenomena that are typically used as benchmarks for characterizing the analyte response of these devices. Finally, we address the use of DNA aptamers to increase the selectivity of GFET sensors for small molecules and proteins and compare them with other, state of the art, detection methods.

DNA interaction with zinc(II) ions

We focused on interactions of Zn(II) with DNA in this study. These interactions were monitored using UV/vis spectrophotometry and gel electrophoresis. Firstly, we isolated and amplified 498 bp fragment of DNA. Samples were obtained by incubation of DNA fragment with Zn(II) for 60 min at 25 °C. After incubation, the samples were dialyzed and analyzed immediately. In this way, DNA was converted into a metal bound DNA (Zn-DNA). Interaction of Zn(II) with DNA caused change in the absorption spectrum (190-350 nm) and decrease in the melting temperature (Tm) of Zn-DNA. Spectrophotometric (UV/vis) analysis showed that increasing concentrations of zinc(II) ions led to the increase in the absorbance at 200 nm and decrease in absorbance at 251 nm. Application of zinc(II) ions at 5.5 μM concentration caused decrease in Tm for app. 7.5 °C in average in comparison with control (75.5 ± 3 °C). The lowest melting temperature (60.5 ± 2.5 °C) was observed after application of zinc(II) ions at 33 μM concentration. Gel electrophoresis proved significance of Zn(II) in the renaturation of DNA. Samples of Zn-DNA (15 μM DNA+5.5-55 μM Zn(II)) caused significant changes in the renaturation of DNA in comparison with the control, untreated DNA (15 μM DNA).

Simple Label-Free Femtomolar DNA Detection Based on a Nanostructure Composite Material: MWNT-Doped Poly(indole-6-carboxylic acid)

A nanostructure composite material consisting of poly(indole-6-carboxylic acid) (PICA) and carboxylic groups ended multiwall carbon nanotubes (MWNTs) was directly electrosynthesized from indole-6-carboxylic acid (ICA) monomer and MWNTs in one step, in which MWNTs was also used as supporting electrolytes. And a simple electrochemical sensor for recognition of target DNA related to hepatitis B virus (HBV) was directly fabricated by means of this composite material. The corresponding detection limit is 2.0 fmol L^-1. This interesting conducting polymer with a very large surface area will provide new insights into how a biosensor is designed.

Investigation on the interaction between luteolin and calf thymus DNA by spectroscopic techniques

The interaction of luteolin with calf thymus deoxyribonucleic acid (ctDNA) under physiological conditions (Tris-HCl buffer solutions, pH 7.4) was studied by UV-Vis spectroscopy, fluorescence spectroscopy and viscosity measurement method, respectively. The results indicated that a complex of luteolin with ctDNA can be formed. Spectroscopic techniques together with viscosity determination provided evidences of intercalation mode of binding for the interaction between luteolin and ctDNA. The binding constant of luteolin to DNA calculated based on UV-Vis spectroscopy data was found to be 4.52×10(4)L mol(-1) at 310 K. The thermodynamic parameters of the complex were calculated by a double reciprocal method: Δ(r)H(m)(s)=-8.9×10(3)J mol(-1),Δ(r)S(m)(s)=60.5 JK(-1)mol(-1) and Δ(r)G(m)(s)=-2.76×10(4)J mol(-1) (310 K). The interacting forces between luteolin and DNA mainly included hydrophobic interactions and hydrogen bonds. The acridine orange displacement studies revealed that luteolin had significant effect for acridine orange bounded on DNA, which was indicative of intercalation binding.

Charge transfer through modified peptide nucleic acids

We studied the charge transfer properties of bipyridine-modified peptide nucleic acid (PNA) in the absence and presence of Zn(II). Characterization of the PNA in solution showed that Zn(II) interacts with the bipyridine ligands, but the stability of the duplexes was not affected significantly by the binding of Zn(II). The charge transfer properties of these molecules were examined by electrochemistry for self-assembled monolayers of ferrocene-terminated PNAs and by conductive probe atomic force microscopy for cysteine-terminated PNAs. Both electrochemical and single molecular studies showed that the bipyridine modification and Zn(II) binding do not affect significantly the charge transfer of the PNA duplexes.

Ultrasensitive in situ label-free DNA detection using a GaN nanowire-based extended-gate field-effect-transistor sensor

In this study, we have successfully demonstrated that a GaN nanowire (GaNNW) based extended-gate field-effect-transistor (EGFET) biosensor is capable of specific DNA sequence identification under label-free in situ conditions. Our approach shows excellent integration of the wide bandgap semiconducting nature of GaN, surface-sensitivity of the NW-structure, and high transducing performance of the EGFET-design. The simple sensor-architecture, by direct assembly of as-synthesized GaNNWs with a commercial FET device, can achieve an ultrahigh detection limit below attomolar level concentrations: about 3 orders of magnitude higher in resolution than that of other FET-based DNA-sensors. Comparative in situ studies on mismatches ("hotspot" mutations related to human p53 tumor-suppressor gene) and complementary targets reveal excellent selectivity and specificity of the sensor, even in the presence of noncomplementary DNA strands, suggesting the potential pragmatic application in complex clinical samples. In comparison with GaN thin film, NW-based EGFET exhibits excellent performance with about 2 orders higher sensitivity, over a wide detection range, 10(-19)-10(-6) M, reaching about a 6-orders lower detection limit. Investigations illustrate the unique and distinguished feature of nanomaterials. Detailed studies indicate a positive effect of energy band alignment at the biomaterials-semiconductor hybrid interface influencing the effective capacitance and carrier-mobility of the system.

Advancement in carbon nanotubes: basics, biomedical applications and toxicity

Objectives

Carbon nanotubes (CNTs) have attracted much attention by researchers worldwide in recent years for their small dimensions and unique architecture, and for having immense potential in nanomedicine as biocompatible and supportive substrates, as a novel tool for the delivery of therapeutic molecules including peptides, RNA and DNA, and also as sensors, actuators and composites.

Key findings

CNTs have been employed in the development of molecular electronic, composite materials and others due to their unique atomic structure, high surface area-to-volume ratio and excellent electronic, mechanical and thermal properties. Recently they have been exploited as novel nanocarriers in drug delivery systems and biomedical applications. Their larger inner volume as compared with the dimensions of the tube and easy immobilization of their outer surface with biocompatible materials make CNTs a superior nanomaterial for drug delivery. Literature reveals that CNTs are versatile carriers for controlled and targeted drug delivery, especially for cancer cells, because of their cell membrane penetrability.

Summary

This review enlightens the biomedical application of CNTs with special emphasis on utilization in controlled and targeted drug delivery, as a diagnostics tool and other possible uses in therapeutic systems. The review also focuses on the toxicity aspects of CNTs, and revealed that genotoxic potential, mutagenic and carcinogenic effects of different types of CNTs must be explored and overcome by formulating safe biomaterial for drug delivery. The review also describes the regulatory aspects and clinical and market status of CNTs.

Interaction of an anthracycline disaccharide with ctDNA: Investigation by spectroscopic technique and modeling studies

This study was designed to examine the interaction of an anthracycline disaccharide, 4'-O-(beta-L-oleandrosyl) daunorubicin (DNR-D2), with calf thymus deoxyribonucleic acid (ctDNA) by UV-vis in combination with fluorescence spectroscopy and molecular modeling techniques under physiological conditions (Britton-Robinson buffer solutions, pH 7.4). By the analysis of UV-vis and fluorescence spectrum, it was observed that the binding mode between DNR-D2 and ctDNA might be intercalation, and fluorescence quenching mechanism of DNR-D2 by ctDNA was a static quenching type. Upon binding to ctDNA, the anthraquinone chromophore of DNR-D2 could slide into the C-G rich region of ctDNA. Hydrogen bonding forces may play an essential role in the binding of DNR-D2 to ctDNA. Furthermore, the results obtained from computational modeling corroborated the experimental results obtained from spectroscopic investigations. These studies are valuable for a better understanding the datailed mode of DNR-D2-DNA interaction, which should be important in deeper insight into the therapeutic efficiency of DNR-D2.

Shear and AC Field Enhanced Carbon Nanotube Impedance Assay for Rapid, Sensitive, and Mismatch-Discriminating DNA Hybridization

Other than concentrating the target molecules at the sensor location, we demonstrate two distinct new advantages of an open-flow impedance-sensing platform for DNA hybridization on carbon nanotube (CNT) surface in the presence of a high-frequency AC electric field. The shear-enhanced DNA and ion transport rate to the CNT surface decouples the parasitic double-layer AC impedance signal from the charge-transfer signal due to DNA hybridization. The flow field at high AC frequency also amplifies the charge-transfer rate across the hybridized CNT and provides shear-enhanced discrimination between DNA from targeted species and a closely related congeneric species with three nucleotide mismatches out of 26 bases in a targeted attachment region. This allows sensitive detection of hybridization events in less than 20 min with picomolar target DNA concentrations in a label-free CNT-based microfluidic detection platform.

Recent development of nano-materials used in DNA biosensors

As knowledge of the structure and function of nucleic acid molecules has increased, sequence-specific DNA detection has gained increased importance. DNA biosensors based on nucleic acid hybridization have been actively developed because of their specificity, speed, portability, and low cost. Recently, there has been considerable interest in using nano-materials for DNA biosensors. Because of their high surface-to-volume ratios and excellent biological compatibilities, nano-materials could be used to increase the amount of DNA immobilization; moreover, DNA bound to nano-materials can maintain its biological activity. Alternatively, signal amplification by labeling a targeted analyte with nano-materials has also been reported for DNA biosensors in many papers. This review summarizes the applications of various nano-materials for DNA biosensors during past five years. We found that nano-materials of small sizes were advantageous as substrates for DNA attachment or as labels for signal amplification; and use of two or more types of nano-materials in the biosensors could improve their overall quality and to overcome the deficiencies of the individual nano-components. Most current DNA biosensors require the use of polymerase chain reaction (PCR) in their protocols. However, further development of nano-materials with smaller size and/or with improved biological and chemical properties would substantially enhance the accuracy, selectivity and sensitivity of DNA biosensors. Thus, DNA biosensors without PCR amplification may become a reality in the foreseeable future.

Impedimetric genosensors employing COOH-modified carbon nanotube screen-printed electrodes

Screen-printed electrodes modified with carboxyl functionalised multi-walled carbon nanotubes were used as platforms for impedimetric genosensing of oligonucleotide sequences specific for transgenic insect resistant Bt maize. After covalent immobilization of aminated DNA probe using carbodiimide chemistry, the impedance measurement was performed in a solution containing the redox marker ferrocyanide/ferricyanide. A complementary oligomer (target) was then added, its hybridization was promoted and the measurement performed as before. The change of interfacial charge transfer resistance between the solution and the electrode surface, experimented by the redox marker at the applied potential, was recorded to confirm the hybrid formation. Non-complementary DNA sequences containing a different number of base mismatches were also employed in the experiments in order to test specificity. A signal amplification protocol was then performed, using a biotinylated complementary target to capture streptavidin modified gold nanoparticles, thus increasing the final impedimetric signal (LOD improved from 72 to 22 fmol, maintaining a good reproducibility, in fact RSD<12.8% in all examined cases). In order to visualize the presence and distribution of gold nanoparticles, a silver enhancement treatment was applied to electrodes already modified with DNA-nanoparticles conjugate, allowing direct observation by scanning electron microscopy.