Nanoelectrodes
Nanoelectrodes are electrodes with a critical dimension in the range of one to hundreds of nanometers and include individual electrodes, nanoelectrode ensembles, and arrays. Metallic nanowires, carbon nanotubes, magnetic nanoparticles and metal oxide nanowires have been employed to fabricate nanoelectrodes and platforms. The development of a nanobiosensor based on individual nanoelectrodes and nanoelectrode arrays or nanoelectrode ensembles offers unprecedented avenues for screening and detection at ultrahigh sensitivities.
Applications
Nanoelectrodes offer great advantages in many biological investigations, particularly in single cells studies, fabrication of microchips, design of coordinated biosensors, addressable patterned electrodes, ultra sensitive nanobiosensors, in the development of specific and intelligent sensors for use as direct, point of care clinical devices and to monitor biorecognition events and interactions.
Single-molecule transport
Nanoelectrode devices for single-molecule transport measurements have been fabricated using different techniques. They notably differ in the way the nanogap or the molecular junction is created. Different types of nanoelectrodes for single-molecule transport measurements are: electro migration, angle evaporation, breaks junction and nanoparticle dimmers.
Gold electrodes for biological sensors
While creating a new generation of biological sensors and nanomachines, usually nanodevices are typically built by connecting tiny components. To fix components in place biological molecules, notably DNA are used as the binding material. Researchers of University of Wisconsin-Madison use microbes for this purpose. The cells have surface proteins that attach to certain biological molecules. Once the cells are placed at specific sites on a silicon wafer, nanoparticles tagged with these molecules can bind to the cells in those locations. This is easier than dragging the nanoparticles themselves to the right spot, because their high density makes them harder to move through fluid media than the less dense living cells. The technique gives one a way to fix components such as quantum dots or carbon nanowires at very precise locations. The researchers pass a solution containing the cells over a silicon wafer with gold electrodes on its surface. The charge on the electrodes captures the Bacillus mycoides, a rod-shaped bacteria, which flow along the electrodes' edges having tiny gaps. The bacterium is trapped there by the electric field from where it can be released by reducing the voltage, or permanently immobilized by increasing the voltage to a level high enough to break its cell wall.
Carbon nanotube array to sense DNA
Multiwalled nanotubes with well-defined nanoscale geometry are attractive nanoelectrode materials. They present a wide electrochemical window, flexible surface chemistry and biocompatibility. Scientists at the NASA Ames Research Center, US, have developed an array of multiwalled carbon nanotubes that can detect low levels of DNA. To make the devices, the scientists grew vertical arrays of multiwalled carbon nanotubes on prepatterned microelectrodes by plasma-enhanced chemical vapour deposition (CVD). Then they encapsulated the nanotubes in silica grown by tetraethoxysilane CVD and used chemical mechanical polishing to flatten the surface and expose the tips of the tubes. It can be employed in enzyme-based biosensors such as glucose sensors, for antibody-antigen-based immunosensors by functionalizing appropriate biomolecules and for measuring small redox species in bulk solution.
According to researchers DNA detection can be employed into handheld devices for molecular diagnostics such as early cancer detection, point-of-care and field uses, the enzyme-based biosensors can be used for household healthcare, while pathogen sensors can be used for homeland protection.