Qianhe Li

Freely switchable impedimetric detection of target gene sequence based on synergistic effect of ERGNO/PANInanocomposites

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]³⁻/⁴⁻ increased. The negative ssDNA and the steric hindrance blocked the effective electron transfer channel of the [Fe(CN)₆]³⁻/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.

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.

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.

Electrochemically reduced graphene oxide-enhanced electropolymerization of poly-xanthurenic acid for direct, “signal-on” and high sensitive impedimetric sensing of DNA

In this paper, the poly-xanthurenic acid (PXa) was electropolymerized by cyclic voltammetry (CV) on a pre-obtained electrochemically reduced graphene oxide (ERGNO) film to construct a novel direct electrochemical DNA biosensor. Due to the unique properties of graphene, conjugated xanthurenic acid (Xa) monomers tended to be adsorbed on the graphene plane by π–π stacking and the electropolymerization efficiency was greatly improved, resulting in an enhanced electrochemical response of PXa. The PXa not only served as a substrate for DNA immobilization but also reflected the electrochemical transduction originating from DNA immobilization and hybridization without any outer indicators or complicated labeling. The capture probe was immobilized onto a modified electrode by covalent bonds between the amino groups of the capture probe and the carboxyl groups of the PXa/ERGNO film. The sensing platform could selectively recognize its target DNA. It is well-known that ssDNA is a flexible molecule while dsDNA acts as a rigid rod, which resulted in the change of the self-signals of the PXa after hybridization. The dynamic range of this DNA biosensor for detecting the sequence-specific DNA from promyelocytic leukemia was from 1.0 × 10−15 mol L−1 to 1.0 × 10−9 mol L−1 using electrochemical impedance spectroscopy, and the detection limit was 2.5 × 10−16 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.

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).

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.

A simple preparation method for large-area, wavy graphene oxide nanowalls and their application to freely switchable impedimetric DNA detection

In this paper, we report a simple and low-cost method to prepare large-area, wavy graphene oxide (GNO) nanowalls intercalated by sulfonated polyaniline (SPAN). Through ultrasonication of a mixed dispersion of graphite oxide (GO) and SPAN, the negatively charged SPAN continuously diffused and was adsorbed and intercalated into the simultaneously resulting GNO layers to form a homogenous and three-dimensional interconnected nanowall structure. This unique morphology has a large specific surface area and improves the electrochemical response of [Fe(CN)6]3−/4−, which has been widely adopted to monitor the immobilization and hybridization of DNA. The accessible space, large specific surface area and richly conjugated structures were beneficial to efficiently immobilize a probe DNA via π–π* interactions between the conjugated interface and the DNA bases, which also ensured a highly sensitive and freely switchable impedimetric DNA detection due to a hybridization that induces the dsDNA to be released from the conjugated surface.

One-step electropolymerization of xanthurenic acid–graphene film prepared by a pulse potentiostatic method for simultaneous detection of guanine and adenine

A novel one-step electrochemical synthesis via a pulse potentiostatic method (PPM) was adopted to prepare a nanocomposite of poly(xanthurenic acid, Xa)–electrochemically reduced graphene oxide (PXa–ERGNO), which was applied for simultaneous detection of guanine and adenine. In the synthesis process, the graphene oxide (GNO) could be electrochemically reduced to reduced graphene oxide in the cathodic potential section; meanwhile, Xa (an unconventional and low toxicity biomonomer) could be electropolymerized in the anodic potential section. The optimization of fabrication was based on the electrooxidation signals of DNA bases. Since the negative charge and specific structure of the nanocomposite can prompt the adsorption of the electropositive guanine and adenine via strong π–π* interactions or electrostatic adsorption, the resulting nanocomposite shows high electrocatalytic ability for the detection of guanine and adenine.