H. B. Halsall

An integrated microfluidic biochemical detection system with magnetic bead-based sampling and analysis capabilities

This paper presents the development and characterization of an integrated microfluidic biochemical detection system for fast and low volume immunoassays using magnetic beads, which are used as both immobilization surfaces and bio-molecule carriers. Magnetic bead-based immunoassay, as a typical example of biochemical detection and analysis, has been successfully performed on the integrated microfluidic biochemical analysis system that includes a surface-mounted biofilter and immunosensor on a glass microfluidic motherboard. Total time required for full immunoassay was less than 20 minutes including sample incubation time and sample volume wasted was less than 50 /spl mu/l during five repeated assays. Fast and low volume biochemical analysis has been successfully achieved with the developed biofilter and immunosensor, which is integrated to microfluidic system.

A microchip electrochemical immunosensor fabricated using micromachining techniques

Using micromachining techniques, an electrochemical immunosensor has been designed, fabricated and tested on a Pyrex glass wafer. The sensor has an electrochemical cell that is composed of a reference, an auxiliary and two working electrodes on a spin-coated polyimide film, where the reference electrode is silver and the others are platinum. The polyimide film is used for antibody immobilization instead of a polystyrene sheet which is usually used in conventional immunosensors. A reaction chamber is fabricated separately on a silicon wafer using anisotropic etching techniques. The electrochemical cell on a glass wafer and the reaction chamber on a silicon wafer are then bonded together to construct the immunosensor using polymer bonding techniques. Fabricated immunosensors are tested by the method of cyclic voltammetry (CV) before analyzing the antigen-antibody reaction. Test antibodies are well attached to the polyimide substrate, and the results of the CV test shows that this immunosensor can be successfully applied for electrochemical immunoassay.

A nanotube composite microelectrode for monitoring dopamine levels using cyclic voltammetry and differential pulse voltammetry

Needle-type nanotube composite microelectrodes were fabricated by injecting a carbon nanotube epoxy solution into pulled-glass tubes. Electrochemical impedance spectroscopy was used to study the complex impedance of the electrode and showed that the electron transfer resistance of the electrode decreases with an increase in the percentage of nanotubes in the epoxy. Cyclic voltammetry was performed under reducing conditions in 6.0mM K3Fe(CN)6 to examine the surface properties of the microelectrodes. The results showed a steady-state response up to 0.5 V/s attributable to radial diffusion with a high steady-state current density. Cyclic voltammetry and differential pulse voltammetry were then used to detect dopamine. The results showed a linear response with a sensitivity of 100nA/mM. Based on the cyclic voltammetry and differential pulse voltammetry results, needle-type nanotube composite microelectrodes are promising sensors for detecting neurotransmitters.

Carbon Nanotube Array Immunosensor Development

This paper describes the development of a label-free immunosensor using carbon nanotube array electrodes. Highly aligned multi-walled carbon nanotubes were grown by chemical vapor deposition using a metallic catalyst, Fe/Al2O3/SiO2, On Si wafers. Harvested towers were cast in epoxy and polished on both ends; one end being for electrical connection and the other being the electrode array surface. The nanotubes were functionalized electrochemically to form carboxyl groups and then coupled to antibodies. EIS was used to directly monitor the antibody-antigen binding.

Fabrication and Characterization of a Multiwall Carbon Nanotube Needle Biosensor

A nanotube electronic needle biosensor was developed to provide fast, low cost, accurate detection of biomolecules. The sensor was formed by synthesizing highly aligned multi-wall carbon nanotube arrays. Nanotube bundles from the array were welded onto the tips of tungsten needles using a microscope. The needles were then encased in glass and a polymer coating. Cyclic voltammetry (CV) for the respective reduction of 6 mM K3Fe(CN)6in a 1.0 M KNO3was performed to examine the redox behavior of the nanotube needle. The CV results showed a steady-state response attributable to radial diffusion with a high steady-state current density. An amperometric sensor was then developed for glucose detection by physical attachment of glucose oxidase on the nanotube needle. A label-free immunosensor based on electrochemical impedance spectroscopy was also formed. The nanotube needle amperometric have good sensitivity with a low detection limit, and the possibility exists to keep decreasing the size of the needle to increase the sensitivity.

The Columbi Eggs of Nanotechnology

The use of nanoscale materials to form larger size materials and devices is limited by many processing problems. These problems must be overcome to achieve many of the possible benefits of nanotechnology. In the context of finding seemingly simple solutions to complex problems, this paper looks at several of the barrier problems in nanoscale materials processing for different applications and proposes possible solutions to the problems. It is also noted that interdisciplinary and inter-institutional collaboration has made possible the progress reported in this paper.