Conjugated self-doped polyaniline-DNA hybrid as trigger for highly sensitive reagentless and electrochemical self-signal amplifying DNA hybridization sensing.

In very recent years, polyaniline or its derivatives have been adopted to efficiently immobilize probe DNA via π-π interaction between conjugated interface and DNA bases. In this work, self-doped polyaniline (SPAN)-DNA hybrid was adopted as the platform to construct a DNA biosensor with label-free, reagentless and electrochemical self-signal amplifying features. This was achieved by the π-π interaction between conjugated SPAN and DNA bases, also the intrinsic differences between single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The tightly cross-linked hybrid was tethered to Au electrode, which had been anchored by p-aminothiophenol (PATP) self-assembled monolayer (SAM) previously, based on the phosphoramidate bond between PATP and ssDNA. SPAN in the recognition surface exhibited well-defined redox signals under neutral conditions. Due to the intrinsic property differences between ssDNA and dsDNA, such as rigidity, π-stacked bases, charge distribution and long-range electron transfer, SPAN-DNA underwent a major conformational change after hybridization. The redox behaviors of SPAN were modulated by DNA, which served as signals to monitor hybridization. As an example, the gene fragment related to one of the screening genes for the genetically modified plants, cauliflower mosaic virus 35S gene was satisfactorily detected with this strategy. Under optimal conditions, the dynamic range for the DNA assay was from 1.0 × 10(-14) mol L(-1) to 1.0 × 10(-8) mol L(-1) with the detection limit of 2.3 × 10(-15) mol L(-1). This work presents the construction of a recognition surface for the highly-sensitive electrochemical DNA hybridization detection via the self-signal amplifying procedure of conjugated SPAN-DNA hybrid. Unlike most signal amplifying processes using outer indicators, complex labels or other reagents, this procedure possesses simplicity and convenience.

Highly sensitive and synergistic detection of guanine and adenine based on poly(xanthurenic acid)-reduced graphene oxide interface.

In order to achieve the large direct electrochemical signals of guanine and adenine, an urgent request to explore novel electrode materials and interfaces has been put forward. In this paper, a poly(xanthurenic acid, Xa)-reduced graphene oxide (PXa-ERGNO) interface, which has rich negatively charged active sites and accelerated electron transfer ability, was fabricated for monitoring the positively charged guanine and adenine. Scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectra, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry were adopted to characterize the morphology and prove the electrochemical properties of the prepared interface. The PXa-ERGNO interface with rich negative charge and large electrode surface area was an excellent sensing platform to prompt the adsorption of the positively charged guanine and adenine via strong π-π* interaction or electrostatic adsorption. The PXa-ERGNO interface exhibited prominent synergistic effect and good electrocatalytic activity for sensitive determination of guanine and adenine compared with sole PXa or ERGNO modified electrode. The sensing platform we built could be further applied in the adsorption and detection of other positively charged biomolecules or aromatic molecules.

Electrochemical impedimetric DNA sensing based on multi-walled carbon nanotubes-SnO2-chitosan nanocomposite.

A sensitive electrochemical impedimetric DNA biosensor based on the integration of tin oxide (SnO2) nanoparticles, chitosan (CHIT) and multi-walled carbon nanotubes (MWNTs) is presented in this paper. The MWNTs-SnO2-CHIT composite modified gold electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared with individual MWNTs-CHIT, SnO2-CHIT and bare gold electrode, this composite showed the most obvious electrochemical signal of the redox probe [Fe(CN)6](3-/4-). According to the change of the electron transfer resistance (R(et)) induced by the hybridization, target DNA was successfully detected via EIS. This DNA electrochemical biosensor was applied to detect phosphinothricin acetyltransferase (PAT) gene in transgenic corn. The synergistic effect of the MWNTs-SnO2-CHIT remarkably enhanced DNA immobilization and hybridization detection. The dynamic detection range was from 1.0×10(-11) mol/L to 1.0×10(-6) mol/L with a detection limit of 2.5×10(-12) mol/L. This sensing platform showed inner advantage, such as simplicity, good stability, and high sensitivity.

Freely switchable impedimetric detection of target gene sequence based on synergistic effect of ERGNO/PANI nanocomposites.

An impedimetric and freely switchable DNA sensor based on electrochemically reduced graphene oxide (ERGNO) and polyaniline (PANI) film was presented, where ERGNO was prepared on PANI modified glassy carbon electrode (GCE). When the probe DNA was noncovalently assembled on the surface of electrode through π-π* stacking between the ring of nucleobases and the rich-conjugated structure of the nanocomposite, the electron transfer resistance value of [Fe(CN)6]³â»/4⁻ increased. The negative ssDNA and the steric hindrance blocked the effective electron transfer channel of the [Fe(CN)6]³â»/4⁻. After hybridization with the complementary DNA, the formation of helix induced dsDNA to release from the surface of conjugated nanocomposite, accompanied with the curtailment of the impedimetric value. The selectivity and sensitivity of this DNA sensing platform were characterized using electrochemical impedance spectroscopy in detail. The fabricated biosensor exhibited excellent performance for the detection of specific DNA sequence with a wide linear range (1.0×10⁻¹5 to 1.0×10⁻8 mol/L) and a low detection limit of 2.5×10⁻¹6 mol/L due to the synergistic effect of ERGNO/PANI nanocomposites. The hosphinothricin acetyltransferase gene (PAT) was also detected to show the switchable ability of ERGNO/PANI.

Synchronous electrosynthesis of poly(xanthurenic acid)-reduced graphene oxide nanocomposite for highly sensitive impedimetric detection of DNA.

A novel and simple synchronous electrochemical synthesis of poly(xanthurenic acid, Xa), electrochemically reduced graphene oxide nanocomposite (PXa-ERGNO), via cyclic voltammetry (CV) was reported, where graphene oxide (GNO) and Xa monomer were adopted as precursors. The resulting PXa-ERGNO nanocomposite was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, CV and electrochemical impedance spectroscopy (EIS). The π-π interactions between the conjugated GNO layers and aromatic ring of Xa-enhanced the electropolymerization efficiency accompanied with an increased electrochemical response of PXa. The rich carboxyl groups of PXa-ERGNO film were applied to stably immobilize the probe DNA with amino groups at 5' end via covalent bonding. The captured probe could sensitively and selectively recognize its target DNA via EIS. The dynamic detection range was from 1.0 × 10(-14) mol/L to 1.0 × 10(-8) mol/L with a detection limit of 4.2 × 10(-15) mol/L due to the synergistic effect of integrated PXa-ERGNO nanocomposite. This graphene-based electrochemical platform showed intrinsic advantage, such as simplicity, good stability, and high sensitivity, which could serve as an ideal platform for the biosensing field.

Large-area, three-dimensional interconnected graphene oxide intercalated with self-doped polyaniline nanofibers as a free-standing electrocatalytic platform for adenine and guanine.

In this work, we prepared large-area, three-dimensional interconnected graphene oxide (GNO) intercalated by self-doped polyaniline nanofibers (SPAN, a copolymer of aniline and m-aminobenzenesulfonic acid) through a simple adsorption and intercalation route via sonication of the mixed dispersions of both components. The strong π-π* stacking between the backbones of SPAN and the GNO basal planes, and the electrostatic repulsion between the negatively charged SPAN and graphene oxide sheets yield a unique free-standing, three-dimensional interconnected nanostructure. The nanocomposite possesses a large specific surface area and maintains a homogenous and stable dispersion with SPAN, which endows it with a high conductivity and good electrocatalytic activity. Because the negative charge and specific structure of the nanocomposite can prompt the adsorption of positively charged guanine and adenine via strong π-π* interactions or electrostatic adsorption, the hybrid was adopted as an excellent sensing platform for highly sensitive determination of guanine and adenine. The electrocatalytic platform exhibited some advantages, such as high sensitivity, good reproducibility and long-term stability.

Comparative studies on zirconia and graphene composites obtained by one-step and stepwise electrodeposition for deoxyribonucleic acid sensing.

In this paper, the comparison of two kinds of electrochemically reduced graphene oxide (ERGNO) and zirconia composites, obtained by one-step (ZrO2-ERGNO) and stepwise (ZrO2/ERGNO) electrodeposition for DNA sensing, is systematically studied. The resulting composites were characterized by scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The results indicated that the ZrO2-ERGNO presented fine globular nanostructure. However, ZrO2/ERGNO presented agglomerate massive microstructure due to the absence of the oxygen-containing groups of graphene oxide, confirming the oxygen-containing groups provided a better affinity for the deposition of ZrO2. Due to the strong binding of the phosphate groups of DNA with the zirconia film, DNA probes were attached on the ZrO2-based composites. ZrO2-ERGNO/Au owning fine nanostructure presented larger surface area than microstructured ZrO2/ERGNO/Au. Moreover, compared with microstructured ZrO2/ERGNO, the nanostructured ZrO2-ERGNO provided more accessible space for immobilized DNA probe hybridization with target sequence, which consequently resulted in higher hybridization efficiency. Therefore, the ZrO2-ERGNO was chosen for fabricating DNA sensor with a limit of detection 1.21×10(-14) mol L(-1).

Highly sensitive electrochemical impedance sensing of PEP gene based on integrated Au-Pt alloy nanoparticles and polytyramine.

Fabrication of an electrochemical impedimetric DNA biosensor based on the integration of Au-Pt alloy nanoparticles (Au-Pt(NPs)) and electropolymerized polytyramine (Pty) film for the detection of phosphoenolpyruvate carboxylase (PEP) gene is described in this article, where Pty films acted as an ideal combination platform for Au-Pt(NPs) via electrostatic adsorption. The electrochemical properties of the Au-Pt(NPs)/Pty, the characteristics of the immobilization and hybridization of DNA were investigated by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy (EIS), respectively. Primary study indicated that Au-Pt(NPs)/Pty had a synergistic effect on the electrochemical signal of [Fe(CN)(6)](3-/4-), which served as the classic redox probe in the most electrochemical impedimetric sensors. DNA sequence-specific of PEP transgene existed in some transgenic crops was detected by this EIS protocol. The dynamic detection range of this DNA electrochemical biosensor to the DNA target sequence was from 1.0×10(-12)M to 1.0×10(-7)M. The detection limit was measured to be 3.6×10(-13)M. The DNA biosensor also had good selectivity, stability and reproducibility.

Ultrasonic chemical oxidative degradations of 1,3-dialkylimidazolium ionic liquids and their mechanistic elucidations.

A highly efficient process for oxidative degradation of 1,3-dialkylimidazolium ionic liquids in hydrogen peroxide/acetic acid aqueous medium assisted by ultrasonic chemical irradiation is, for the first time, described. It is shown that more than 93% of the 1,3-dialkylimidazolium cation with the corresponding Cl-, Br-, BF4- and PF6- counter-anions at a concentration of 2.5 mM can be degraded at 50 degrees C within 12 h while at 72 h the conversions approach 99%. A tentative mechanism for the degradation of these ILs is for the first time proposed through a detailed kinetic analysis of several characteristic transients and/or immediate products, which are identified during the ILs degradation using GC-MS. The results clearly indicate that three hydrogen atoms in the imidazolium ring are the first sites preferably oxidized, followed by cleavage of the alkyl groups attached to the N atoms from the ring. The nature of the alkyl chain length on the imidazolium ring and the type of counter anion do not seem to affect the degradation process. Further, selective fragmentations of C-N bonds of the imidazolium or derived ring lead to ring opening, forming degraded intermediates. It is also shown that acetoxyacetic acid and biurea are the final kinetically stable degraded products from the ILs under the degradation conditions.