Hui-Fang Cui

Pt–Pb alloy nanoparticle/carbon nanotube nanocomposite: a strong electrocatalyst for glucose oxidation

A Pt–Pb alloy nanoparticle/multi-walled carbon nanotube (Pt–Pb/MWCNT) nanocomposite was prepared by electrodepositing Pt–Pb alloy onto MWCNTs that were vertically aligned on Ta plates. The 10–40 nm diameter Pt–Pb alloy nanoparticles were mainly deposited at the tips, and sparsely dispersed on the sidewalls of the bamboo-like MWCNTs, as demonstrated by scanning electron microscopy, transmission electron microscopy (TEM), and x-ray diffraction. The high resolution TEM (HRTEM) image showed a snowflake-like morphology for the Pt–Pb nanoparticles. This Pt–Pb/MWCNT nanocomposite exhibited much stronger electrocatalytic activity toward glucose oxidation than pristine MWCNTs, Pt–Pb on glassy carbon, and Pt/MWCNT and Au/MWCNT nanocomposites, in both neutral and alkaline solutions. This Pt–Pb/MWCNT nanocomposite electrode is hence promising for development as a nonenzymatic glucose sensor.

Interfacing Carbon Nanotubes with Living Mammalian Cells and Cytotoxicity Issues

The unique structures and properties of carbon nanotubes (CNTs) have attracted extensive investigations for many applications, such as those in the field of biomedical materials and devices, biosensors, drug delivery, and tissue engineering. Anticipated large-scale productions for numerous diversified applications of CNTs might adversely affect the environment and human health. For successful applications in the biomedical field, the issue of interfacing between CNTs and mammalian cells in vitro needs to be addressed before in vivo studies can be carried out systematically. We review the important studies pertaining to the internalization of CNTs into the cells and the culturing of cells on the CNT-based scaffold or support materials. The review will focus on the description of a variety of factors affecting CNT cytotoxicity: type of CNTs, impurities, lengths of CNTs, aspect ratios, dispersion, chemical modification, and assaying methods of cytotoxicity.

Direct Electron Transfer of Glucose Oxidase-Boron Doped Diamond Interface: A New Solution for a Classical Problem

A planar boron-doped diamond (BDD) electrode was treated with KOH and functionalized with 3-aminopropyltriethoxysilane (APTES) to serve as a biosensing platform for biomolecule immobilization with glucose oxidase (GOx) as a test model. The free amino groups of GOx and APTES were cross-linked by glutaraldehyde (X), a bifunctional chemical to form a stable enzyme layer (GOx-X-APTES) on BDD. Micrographs obtained by scanning electron microscopy revealed that a mesoporous structure uniformly covered the BDD surface. Cyclic voltammetry of GOx immobilized showed a pair of well-defined redox peaks in neutral phosphate buffer solution, corresponding to the direct electron transfer of GOx. The apparent heterogeneous electron transfer rate constant of the immobilized GOx was estimated to be 8.85 ± 0.47 s(-1), considerably higher than the literature reported values. The determination of glucose was carried out by amperometry at -0.40 V, and the developed biosensor showed good reproducibility and stability with a detection limit of 20 μM. Both ascorbic and uric acids at normal physiological conditions did not provoke any signals. The dynamic range of glucose detection was further extended by covering the enzyme electrode with a thin Nafion layer. The Nafion/GOx-X-APTES/BDD biosensor showed excellent stability, a detection limit of 30 μM, a linear range between 35 μM and 8 mM, and a dynamic range up to 14 mM. Such analytical performances were compared favorably with other complicated sensing schemes using nanomaterials, redox polymers, and nanowires. The APTES-functionalized BDD could be easily extended to immobilize other redox enzymes or proteins of interests.

Hairpin DNA as a Biobarcode Modified on Gold Nanoparticles for Electrochemical DNA Detection

Hairpin DNA (hpDNA) as a novel biobarcode was conjugated with gold nanoparticles (AuNPs) and a reporter DNA (rpDNA) to form hpDNA/AuNP/rpDNA nanoparticles for the detection of an oligonucleotide sequence associated with Helicobacter pylori as a model target. The rpDNA is complementary to about a half-portion of the target DNA sequence (tDNA). A capture DNA probe (cpDNA), complementary to the other half of the tDNA, was immobilized on the surface of a gold electrode. In the presence of tDNA, a sandwich structure of (hpDNA/AuNP/rpDNA)/tDNA/cpDNA was formed on the electrode surface. The differential pulse voltammetry (DPV) detection was based on [Ru(NH3)5(3-(2-phenanthren-9-yl-vinyl)-pyridine)](2+), an electroactive complex that binds to the sandwich structure by its intercalation with the hpDNA and the double-stranded DNA (dsDNA) of the sandwich structure. The several factors--high density of biobarcode hpDNA on the surface of AuNPs, multiple electroactive complex molecules intercalated with each hpDNA and dsDNA molecule, and the intercalation binding mode of the electroactive complex with the DNA sandwich structure--contribute to the DNA sensor with highly selective and sensitive sensing properties. The DNA sensor exhibited a detection limit of 1 × 10(-15) M (i.e., 1 fM), the DNA levels in physiological samples, with linearity down to 2 × 10(-15) M. It can differentiate even one single mismatched DNA from the complementary tDNA. This novel biobarcode-based DNA sensing approach should provide a general platform for development of direct, simple, repetitive, sensitive, and selective DNA sensors for various important applications in analytical, environmental, and clinical chemistry.

Electrochemical functionalization of vertically aligned carbon nanotube arrays with molybdenum oxides for the development of a surface-charge-controlled sensor

The modification of inorganic polymeric oxides at the surface of carbon nanotubes is of paramount importance for developing new sensors. In this study, molybdenum oxide (MoOx) film was electrodeposited on the surface of multi-walled carbon nanotubes (MWNTs) by cycling the potential between +0.20 and ?0.80?V (versus 3?M KCl?Ag|AgCl) in Na2MoO4 solution. The MoOx-modified nanotube (MoOx/MWNT) electrode displays well-defined redox transitions in 5?mM H2SO4 or in phosphate buffer solution (PBS), which can be attributed to the reductive formation and the re-oxidation of hydrogen molybdenum oxides. X-ray photoelectron spectra (XPS) showed that the deposited MoOx films are mainly Mo6+ complexes. Both MWNT and MoOx/MWNT electrodes have ideal reversibility in 5?mM K3[Fe(CN)6] in 1?M KCl as supporting electrolytes at all sweep rates (0.02?1.00?V?s?1) by cyclic voltammetry. The negatively charged surface of MoOx/MWNTs can further attract molecular cations such as Ru(NH3)63+. The MoOx/MWNT electrode exhibited electrocatalytic ability towards the reduction of bromate due to high surface area and the fast electron transfer rate of nanotubes. Thus, electrochemical modification of inorganic polymeric oxides on the carbon nanotube provides a simple method for the preparation of novel sensors.

Electrochemical Biochip for Drug Screening At Cellular Level

Drug screening at cellular level has becomes an attractive field of research. Different researchers have tried to record cellular response to drugs by electrical or optical approach using both invasive and non-invasive methods. Silicon-based microelectrode integrated microchips are useful tools for in situ temporal recording of neurotransmitter releasing from neural cells. A microfabricated electrochemical biochip is presented in this paper. Using dopaminergic cells grown on the chip, the dopamine excytosis can be electrochemical amperomatric detected non-invasively from drug incubated dopaminegic cells by the microelectrode integrated on chip. This silicon-based electrochemical chip has been designed with an electrode array located on the cell culture chamber bottom. Each electrode is individually electrical controlled. MN9D and PC12 dopaminergic cell lines have been demonstrated on this chip for drug effects study. This silicon-based electrochemical microchip provides a non-invasive, in situ , temporal detection of dopamine exocytosis from dopaminegic cells, and holds the potential for applications in studying the mechanisms of dopamine exocytosis and drug screening. It is also extendable for other cell culture and drug effects study.

Microelectrodes integrated cell-chip for drug effects study

Silicon-based microelectrode chips are useful tools for temporal recording of neurotransmitter releasing from neural cells. Both invasive and non-invasive methods are targeted by different group researchers to perform electrical stimulating on neural cells. A microfabricated microelectrodes integrated biochip will be presented in this paper, which describes the dopaminergic cells growing on the chip directly. The dopamine exocytosis can be detected non-invasively from drug incubated dopaminergic cells growing on the chip. The abovementioned silicon-based electrochemical sensor chip has been designed with an electrode array located on the bottom of reaction chamber and each electrode is individually electrical controlled. MN9D, a mouse mesencephalic dopaminergic cell line, has been grown on the surface of the biochip chamber directly. Dopamine exocytosis from the chip-grown MN9D cells was detected using amperometry technology. The amperometric detection limit of dopamine of the biochip microelectrodes was found from 0.06μM to 0.21μM (S/N=3) statistically for the electrode diameters from 10 μm to 90 μm, the level of dopamine exocytosis from MN9D cells was undetectable whithout drug incubation. In contrast, after MN9D cells were incubated with L-dopa, a dopamine precursor, K+ induced dopamine extocytosis was temporally detected. The microelectrodes integrated biochip provides a non-invasive, temporal detection of dopamine exocytosis from dopaminergic cells, and holds the potential for applications in studying the mechanisms of dopamine exocytosis, and drug screening. It also provides a tool for pharmaceutical research and drug screening on dopaminergic cells, extendably to be used for other cell culture and drug effects study.

Chapter 8 Interfaces, Bifaces, and Nanotechnology

Abstract Nanotechnology is the construction and use of functional structures designed from atomic or molecular scale with at least one characteristic dimension measured in nanometers. Nanomaterials, such as carbon nanotubes (CNTs) and nanoparticles, exhibit novel and significantly improved physical, chemical, and biological properties, phenomena, and processes because of their size. Functionalization of nanomaterials is one of the most active fields in nanotechnology. In natural systems, such as cells, nano-scale structures are formed at room temperature using the approach of self-assembly. Alignment of linear molecules in an ordered array on the surface of CNTs or nanoparticles (self-assembled monolayer and/or bilayer) can function as a new generation of nanomaterials for chemical and biological sensors. The developments of self-assembled lipid-CNTs nanocomposites and/or lipid-nanoparticle hybrids have opened research opportunities in studying hitherto unapproachable phenomena at interfaces and bifaces. Particular emphasis is directed to the use of lipid-functionalized CNTs as well as lipid-nanoparticle nanocomposites for sensors and biosensors and for the fabrication of photo switched-functional devices.