DNA hybridization biosensor using chitosan–carbon nanotubes composite film as an immobilization platform and [Cu(bpy)(MBZ)2(H2O)] (bpy=2,2′-bipyridine, MBZ=p-methylbenzoate) as a novel redox indicator

A planar and uncharged copper(II)-picolinic acid chelate: Its intercalation to duplex DNA by experimental and theoretical studies and electrochemical sensing application

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.

Enzymatic amplification detection of peanut allergen Ara h1 using a stem-loop DNA biosensor modified with a chitosan-mutiwalled carbon nanotube nanocomposite and spongy gold film

In this paper, a highly sensitive biosensor was constructed for peanut allergen Ara h1 detection. The biosensor was constructed by coating a glassy carbon electrode with a chitosan-mutiwalled carbon nanotube nanocomposite and then adding a spongy gold film via electro-deposition to increase the effective area. The probe switched from an "on" to an "off" state in the presence of target DNA, which detached biotin from the electrode surface. This also detached streptavidin-horseradish peroxidase (HRP-SA), which was bound to the electrode via specific interaction with biotin. The HRP-SA catalyzed chemical oxidation of hydroquinone by H2O2 to form benzoquinone, and when it was detached, electrochemical reduction of the signal of benzoquinone could be used to monitor DNA hybridization via chronoamperometry. Under optimum conditions, a wide dynamic detection range (3.91 × 10(-17)-1.25 × 10(-15) mol L(-1)) and a low detection limit (1.3 × 10(-17) mol L(-1)) were achieved for the complementary sequence. Furthermore, the DNA biosensor exhibited an excellent ability to discriminate between a complementary target and a one-base mismatch or non-complementary sequence. The sensor was successfully applied to Ara h1 analysis in peanuts.

Hybrid integrated label-free chemical and biological sensors

Label-free sensors based on electrical, mechanical and optical transduction methods have potential applications in numerous areas of society, ranging from healthcare to environmental monitoring. Initial research in the field focused on the development and optimization of various sensor platforms fabricated from a single material system, such as fiber-based optical sensors and silicon nanowire-based electrical sensors. However, more recent research efforts have explored designing sensors fabricated from multiple materials. For example, synthetic materials and/or biomaterials can also be added to the sensor to improve its response toward analytes of interest. By leveraging the properties of the different material systems, these hybrid sensing devices can have significantly improved performance over their single-material counterparts (better sensitivity, specificity, signal to noise, and/or detection limits). This review will briefly discuss some of the methods for creating these multi-material sensor platforms and the advances enabled by this design approach.

DNA interaction of [Cu(dmp)(phen-dion)] (dmp=4,7 and 2,9 dimethyl phenanthroline, phen-dion=1,10-phenanthroline-5,6-dion) complexes and DNA-based electrochemical biosensor using chitosan-carbon nanotubes composite film

The interaction of two new water-soluble [Cu(4,7-dmp)(phen-dione)Cl]Cl (1) and [Cu(2,9-dmp)(phen-dione)Cl]Cl (2) which dmp is dimethyl-1,10-phenanthroline and phen-dion represents 1,10-phenanthroline-5,6-dion, with DNA in solution and immobilized DNA on a chitosan-carbon nanotubes composite modified glassy carbon electrode were investigated by cyclic voltammetry and UV-Vis spectroscopy techniques. In solution interactions, spectroscopic and electrochemical evidences indicate outside binding of these complexes. To clarify the binding mode of complexes, it was done competition studies with Hoechst and Neutral red as groove binder and intercalative probes, respectively. All these results indicating that, these two complexes (1) and (2) interact with DNA via groove binding and partially intercalative modes, respectively. The electrochemical characterization experiments showed that the nanocomposite film of chitosan-carbon nanotubes could effectively immobilize DNA and greatly improve the electron-transfer reactions of the electroactive molecules that latter finding is the result of strong interactions between captured DNA and Cu complexes. This result indicates that these complexes could be noble candidates as hybridization indicators in further studies. At the end, these new complexes showed excellent antitumor activity against K562 (human chronic myeloid leukemia) cell lines.

Use of a chitosan–cadmium polymer as a redox hybridization indicator for CaMV35S promoter gene detection

A water-soluble chitosan-coordinated cadmium polymer was synthesized, and its recognition of single-stranded and double-stranded DNA was investigated. The electrochemical analysis in the homogeneous solutions revealed that the chitosan-coordinated cadmium polymer association with a single stranded DNA was 48 times greater than with double-stranded DNA due to the different interaction with the two kinds of DNA. The surface-based electrochemically absorbed chitosan-coordinated cadmium polymer molecules were easily removed from the double-stranded DNA-modified electrode via rinsing but could not be removed from a single-stranded DNA-modified electrode. Based on this fact, the polymer was utilized as a redox indicator for DNA hybridization detection, as the polymer was able to recognize complementary, noncomplementary, and base-mismatched sequences with a low background interference. The target DNA sequence was quantified from 5.0 × 10-9 to 5.0 × 10-7 M with a detection limit of 4.2 × 10-9 M. The polymerase chain reaction amplification of DNA from the real sample of a kind of transgenically modified soybeans was also detected satisfactorily.