Qin Xu

Shanghai Normal University, Shanghai, Shanghai Shi, China

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Publications (4)20.21 Total impact

  • Ningning Zhu · Qin Xu · Sini Li · Huan Gao
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    ABSTRACT: This study describes a simple and reliable method for the electrochemical determination of nitrite based on poly(amidoamine)-modified carbon nanotubes. Amine-terminated poly(amidoamine) (generation 4.0, G4-NH4) were covalently attached onto multi-walled carbon nanotube (MWNT)-modified glass carbon (GC) electrodes (written as G4-NH4/MWNT-modified GC) and which were used for the electrochemical determination of nitrite. The studies show that the G4-NH4/MWNT-modified electrodes demonstrated significantly enhanced electrochemical activity towards nitrite oxidation. Chronoamperometry studies reveal that the amperometric response is rapid, stable, and offers a linear dependence over a wide range of nitrite concentrations from 5μM to 1.5mM. The proposed method can be used for the continuous monitoring of nitrite in real samples. The electrochemical properties of the G4-NH4/MWNT nanocomposites are reasonably envisaged to be promising for providing a nanostructured platform in the development of electrochemical sensors or biosensors.
    No preview · Article · Dec 2009 · Electrochemistry Communications
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    ABSTRACT: This study demonstrates a new impedimetric DNA biosensor with second-generation poly(amidoamine) dendrimer (G2-PAMAM) covalently functionalized onto multi-walled carbon nanotube (MWNT) electronic transducers as the tether for surface confinement of probe DNA. G2-PAMAM dendrimer was covalently functionalized onto purified MWNTs and the as-formed G2-PAMAM-functionalized MWNT composite (i.e., G2-PAMAM/MWNT) was used both as the support to confine the single-stranded DNA (ssDNA) probe and as the electronic transducer to form the DNA biosensors. Upon the occurrence of hybridization events between surface-confined ssDNA probe with target DNA in solution to form a double-stranded DNA (dsDNA) at electrode surface, the negative charge in the electrode/electrolyte interface and, as such, the interfacial charge-transfer resistance of the electrodes towards the Fe(CN)(6)(3-/4-) redox couple were changed. Such a change was used for the impedimetric DNA biosensing. The use of G2-PAMAM dendrimer attached onto MWNT electronic transducer as the tether for probe DNA provides a large number of amino groups to increase the surface binding of probe DNA, results in the increase the sensitivity of the impedimetric biosensor for the target DNA. Under the conditions employed here, the change in the interfacial charge-transfer resistance was linear with the logarithm of the concentration of the target DNA within a concentration range from 0.5 to 500 pM with a detection limit of 0.1 pM (S/N=3). The excellent analytical properties of the impedimetric DNA biosensors developed here substantially makes them potentially useful for practical applications.
    No preview · Article · Nov 2009 · Biosensors & Bioelectronics
  • Ying Shen · Qin Xu · Huan Gao · Ningning Zhu
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    ABSTRACT: This study describes a facile method for preparing amine-terminated poly(amidoamine) (G4-NH2)-encapsulated palladium nanocatalysts with carbon nanotubes as a support. The Pd2+/G4-NH2 complexes are synthesized by a template approach in which PdCl42- ions are extracted into the interior of G4-NH2 dendrimers, and then bonded on multi-walled carbon nanotubes (MWNTs) support through dendrimer covalent linkage. Conversion of Pd2+/G4-NH2 into dendrimer-encapsulated nanoparticles was achieved by the addition of NaBH4. Transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–vis spectroscopy confirmed that the size-monodisperse Pd nanoparticles anchored on MWNTs was about 2nm in diameter. The obtained Pd/G4-NH2/MWNT nanocomposites exhibit high electro-catalytic activity for the hydrazine oxidation by cyclic voltammetry.
    No preview · Article · Jun 2009 · Electrochemistry Communications
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    ABSTRACT: A novel, simple and sensitive DNA biosensor based on DNA-poly(amidoamine) (PAMAM) dendrimer nanoconjugates was developed by using the electrochemical impedance spectroscopy (EIS) technique. In this context, the assay relies on the hybridization of the single-stranded DNA (ssDNA) probe covalently conjugated on a mercaptoacetic acid self-assembled monolayer on gold electrodes, with the generation 4.5 (G-4.5) PAMAM-target DNA complex in solution. Once the double-stranded DNA (dsDNA) formed on the gold electrodes, G-4.5 PAMAM bearing carboxyls on the periphery was anchored on the hybrids; the changes of interfacial electron-transfer resistance (R(et)) of the electrodes were measured using an Fe(CN)(6)(3-/4-) redox probe by electrochemical impedance spectroscopy. The results showed that only a complementary sequence could form a dsDNA-PAMAM with the DNA-PAMAM probe and give an obviously enlarged R(et) value. The non-complementary and three-base mismatched sequence exhibited negligible impedance change compared with the blank measurement (the blank measurement means: ssDNA probe-modified gold electrode was directly measured by EIS). The unique spherical structure combining with more negative charges on the G-4.5 PAMAM periphery anchored on the hybrids could significantly amplify the hybridization signal (R(et) value), and the detection limit for measuring the full complementary sequence is down to pM level.
    No preview · Article · Jun 2009 · The Analyst