Meijia Wang

Fabrication of Magnetic Luminescent Nanocomposites by a Layer-by-Layer Self-assembly Approach

Magnetic luminescent nanocomposites were prepared via a layer-by-layer (LbL) assembly approach. The Fe3O4 magnetic nanoparticles of 8.5 nm were used as a template for the deposition of the CdTe quantum dots (QDs)/polyelectrolyte (PE) multilayers. The number of polyelectrolyte multilayers separating the nanoparticle layers and the number of QDs/polyelectrolyte deposition cycles were varied to obtain two kinds of magnetic luminescent nanocomposites, Fe3O4/PEn/CdTe and Fe3O4/(PE3/CdTe)n, respectively. The assembly processes were monitored through microelectrophoresis and UV−vis spectra. The topography and the size of the nanocomposites were studied by transmission electron microscopy. The LbL technique for fabricating magnetic luminescent nanocomposites has some advantages to tune their properties. It was found that the selection of a certain number of the inserted polyelectrolyte interlayers and the CdTe QDs loading on the nanocomposites could optimize the photoluminescence properties of the nanocomposites....

Application of impedance spectroscopy for monitoring colloid Au-enhanced antibody immobilization and antibody-antigen reactions.

We used colloidal Au to enhance the amount of antibody immobilized on a gold electrode and ultimately monitored the interaction of antigen-antibody by impedance measurement. Self-assembly of 6 nm (diameter) colloidal Au onto the self-assembled monolayers (SAMs) of 4-aminothiophenol modified gold electrode resulted in an easier attachment of antibody. The redox reactions of [Fe(CN)6](4-)/[Fe(CN)6](3-) on the gold surface were blocked due to the procedures of self-assembly of 4-aminothiophenol and antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.4 with various concentrations of antigen at 37 degrees C for 30 min. The antibody recognition layers and their interactions with various concentrations of antigen could be detected by measurements of the impedance change. The results show that this method has good correlation for detection of Hepatitis B virus surface antigen in the range of 0.5-200 microg/l and a detection limit of about 50 ng/l.

A novel room temperature ionic liquid sol–gel matrix for amperometric biosensor application

A novel type of ionic liquid (IL) sol–gel hybrid material was developed for amperometric biosensor application. This material was prepared by the hydrolysis of tetraethyl orthosilicate in a 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4−) solution. The viscous IL prevented the cracking of the sol–gel derived glasses. Horseradish peroxidase (HRP) was immobilized in the hybrid material for the production of an amperometric hydrogen peroxide biosensor. The IL sol–gel enzyme electrodes retained the high activity of HRP and provided long-term stability of HRP in storage. The morphology of the matrix-containing enzyme was characterized by scanning electron microscopy. The characteristics of the biosensor were also investigated by cyclic voltammetry and chronoamperometry. In the presence of ferrocene as a mediator, the biosensor exhibited an excellent stability and sensitivity, and the linear calibration ranged from 0.02 to 0.26 mM with a detection of 1.1 µM. The apparent Michaelis–Menten constant of the immobilized HRP was 2.0 mM.

Highly active horseradish peroxidase immobilized in 1-butyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquid based sol–gel host materials

Dramatically enhanced activity and excellent thermal stability of horseradish peroxidase were obtained by immobilizing it in a 1-butyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquid based sol-gel matrix.

Electrochemical detection of DNA immobilized on gold colloid particles modified self-assembled monolayer electrode with silver nanoparticle label.

The target DNA was immobilized successfully on gold colloid particles associated with a cysteamine monolayer on gold electrode surface. Self-assembly of colloidal Au onto a cysteamine modified gold electrode can enlarge the electrode surface area and enhance greatly the amount of immobilized single stranded DNA (ssDNA). The electron-transfer processes of [Fe(CN)6](4-)/[Fe(CN)6](3-) on the gold surface were blocked due to the procedures of the target DNA immobilization, which was investigated by impedance spectroscopy. Then single stranded target DNA immobilized on the gold electrode hybridized with the silver nanoparticle-oligonucleotide DNA probe, followed by the release of the silver metal atoms anchored on the hybrids by oxidative metal dissolution, and the indirect determination of the released solubilized Ag(I) ions by anodic stripping voltammetry (ASV) at a carbon fiber microelectrode. The results show that this method has good correlation for DNA detection in the range of 10-800 pmol/l and allows the detection level as low as 5 pmol/l of the target oligonucleotides.