Haibo Pan

Electrochemical sensor for detection of hydrazine based on Au@Pd core–shell nanoparticles supported on amino-functionalized TiO2 nanotubes

In this paper, we reported a simple strategy for synthesizing well-defined TiO2NTs-Au@Pd hybrid nanostructures with prior TiO2 nanotube functionalization (F-TiO2NTs). TiO2NTs with larger surface area (BET surface area is 184.9m(2)g(-1)) were synthesized by hydrothermal method, and the NTs are anatase phase with a range of 2-3μm in length and 30-50nm in diameter after calcined at 400°C for 3h. 3-Aminopropyl-trimethoxysilane (APTMS) as a coupling agent was reacted with the surface hydroxyl groups as anchoring sites for flower-shaped bimetallic Au@Pd nanostructures, self-assembling amine functionality on the surface of TiO2NTs. Note that two faces at the interface between F-TiO2NTs with (004) plane and Au@Pd nanostructures with (111) one of cubic Au and Pd nanoparticles are compatible, benefiting to the charge transfer between two components due to their crystalline coordination. The results showed that as-prepared F-TiO2NTs-Au@Pd hybrid nanostructures modified glassy carbon electrode (GCE) exhibits high electrocatalytic activity toward hydrazine (N2H4) at low potential and a linear response from 0.06 to 700μM with the detection limit for N2H4 was found to be 1.2×10(-8)M (S/N=3). Based on scan rate effect during the hydrazine oxidation, it indicates that the number of electrons transferred in the rate-limiting step is 1, and a transfer coefficient (α) is estimated as 0.73. The self-assembled F-TiO2NTs-Au@Pd hybrid nanostructures as enhanced materials present excellent electrocatalytic activity, fast response, highly sensitive and have a promising application potential in nonenzymatic sensing.

Preparation of novel silver nanoplates/graphene composite and their application in vanillin electrochemical detection.

Hexagonal Ag nanoplates (NPs) were synthesized by polyvinylpyrrolidone (PVP) and trisodium citrate (TSC) which selectively absorbed to Ag (100) and Ag (111) surfaces, then were anchored to graphene (GN) to form novel Ag NPs/GN composite. The thickness of Ag NPs is ~4 nm and the length is 18-66 nm. Transmission electron microscopy (TEM) image shows that the plates are f-c-c crystals containing {111} facets on their two planar surfaces. Zeta potential indicated that the surface of Ag NPs/GN is negatively charged while vanillin is positively charged. Thus Ag NPs/GN modified on glass carbon electrodes (GCE) allowed abundant adsorption for vanillin and electron transfer between vanillin and Ag NPs/GN/GCE. Square wave voltammetry (SWV) results indicated that the over potential on Ag NPs/GN/GCE negatively shifts 52 mV than that on Ag NPs/GCE. Ag NPs/GN with enhanced surface area and good conductivity exhibited an excellent electrocatalytic activity toward the oxidation of vanillin. The corresponding linear range was estimated to be from 2 to 100 μM (R(2)=0.998), and the detection limit is 3.32×10(-7) M (S/N=3). The as-prepared vanillin sensor exhibits good selectivity and potential application in practical vanillin determination.

A low detection limit penicillin biosensor based on single graphene nanosheets preadsorbed with hematein/ionic liquids/penicillinase.

In this study, we reported on a low detection limit penicillin biosensor with layer-by-layer (LbL) film containing single-graphene nanosheets (SGNs) preadsorbed with hematein, ionic liquids (ILs) and penicillinase. The penicillinase catalyzes the hydrolysis of penicillin to penicilloic acid, where H(+) is liberated and monitored amperometrically with hematein as a pH indicator. The SGN-hematein/ILs/penicillinase biosensor exhibited excellent performance for penicillin in PBS with a wide range from 1.25×10(-13) to 7.5×10(-3)M, and a low detection limit of 10(-13)M (0.04ppt, S/N≥3). Furthermore, the detection of penicillin concentration in real sample (milk) had acceptable accuracy with the assay system.

A bisphenol A sensor based on novel self-assembly of zinc phthalocyanine tetrasulfonic acid-functionalized graphene nanocomposites.

In this work, a novel zinc phthalocyanine tetrasulfonic acid (ZnTsPc)-functionalized graphene nanocomposites (f-GN) was synthesized by a simple and efficient electrostatic self-assembly method, where the positive charged GN decorated by (3-aminopropyl) triethoxysilane (APTES) was self-assemblied with ZnTsPc, a two dimensional (2-D) molecules. It not only enhanced its stability for the hybrid structure, but also avoided the reaggregation of ZnTsPc or f-GN themselves. Based on layered ZnTsPc/f-GN nanocomposites modified glassy carbon electrode, a rapid and sensitive sensor was developed for the determination of bisphenol A (BPA). Under the optimal conditions, the oxidation peak current increased linearly with the concentration of BPA in the range of 5.0×10(-8) to 4.0×10(-6)M with correlation coefficient 0.998 and limits of detection 2.0×10(-8)M. Due to high absorption nature for BPA and electron deficiency on ZnTsPc/f-GN, it presented the unique electron pathway arising from π-π stackable interaction during redox process for detecting BPA. The sensor exhibited remarkable long-term stability, good anti-interference and excellent electrocatalytic activity towards BPA detection.

Self-assembly of palladium nanoparticles on functional TiO2 nanotubes for a nonenzymatic glucose sensor.

Polydiallyldimethylammonium chloride, PDDA, was used as a stabilizer and linker for functionalized TiO2 nanotubes (TiO2 NTs). Self-assembled process with palladium nanoparticles (NPs) was successfully synthesized and used for the oxidation of glucose on glassy carbon electrodes. Based on the voltammetric and amperometric results, Pd NPs efficiently catalyzed the oxidation of glucose at -0.05 V in the presence of 0.1 M NaCl and showed excellent resistance toward interference poisoning from such interfering species as ascorbic acid, uric acid and urea. To further increase sensitivity, the Pd NPs-PDDA-TiO2 NTs/GCE was electrochemically treated with H2SO4 and NaOH, the glucose oxidation current was magnified 2.5 times than that before pretreatments due to greatly enhancing the electron transport property of the sensor based on the increased defect sites and surface oxide species. In view of the physiological level of glucose, the wide linear concentration range of glucose (4×10(-7)-8×10(-4)M) with a detection limit of 8×10(-8)M (S/N=3) was obviously good enough for clinical application.

Ag–SnO2 nano-heterojunction–reduced graphene oxide by a stepwise photocatalyzed approach and its application in ractopamine determination

Photocatalyzed synthesis by using SnO2 as a photocatalyst is a green and alternative approach. Here, a nanocomposite of SnO2–Ag nanoparticles (AgNPs) and reduced graphene oxide (RGO) was prepared by a stepwise photocatalyzed approach. HRTEM shows that SnO2 and AgNPs were attached along the lattice matching each other and both of them were anchored upon RGO. Under UV irradiation, photo-excited holes from SnO2 were scavenged by ethanol while electrons were accumulated at the side of SnO2, leading to the reduction of both graphene oxide (GO) and Ag+. Here, SnO2 and metal Ag formed a heterostructure, and RGO played the dual role of conductor and support. During UV irradiation, the (101) facet of SnO2 offered a preferential growth direction for the (111) facet of AgNPs with an interfacial angle of 118°, which can be attributed to their similar D-spacings. A unique morphology of a combination of two semi-spheres was established. The energy-band structure of the composite was characterized to understand its mechanism of electrocatalysis. Owing to the difference between their binding energy in the heterostructure, electrons in AgNPs are transferred into SnO2, inducing AgNPs with positive charge and facilitating the redox of ractopamine (RAC). Under the optimal experimental conditions, a linear relationship between the relative amperometric response to RAC ranges from 5.0 × 10−8 to 5.5 × 10−6 M while the lower limit of detection reaches 2 × 10−8 M (S/N = 3.0).