Old, new mix in sensor development

InTech, Jul 2005

BIOSENSORS AND OTHER NANOTECH devices may soon go old school, researchers said.

Amines, a large and important class of organic molecules, when mixed with carbon disulfide, can bond to gold more robustly than thiols, which are commonly used materials for giving new functions to metal surfaces, said Alexander Wei, an associate professor of chemistry in Purdue University's College of Science. Gold surfaces often see use as baseplates for sensors and in nanomaterials. Scientists have been searching for stable organic coatings they can attach to gold to form an interface between the organic and inorganic worlds. The group's findings suggest amines may be the best candidate group of such materials.

"Amines could allow us to expand the range of molecules, which can be incorporated into sensors for the biotech field," said Wei." Amines react with carbon disulfide to form dithiocarbamates (DTCs) and appear to be better suited for coating surfaces than thiols, which have been the standard thus far. The DTC chemistry itself has been around for over 100 years, but we think it can offer many opportunities for current applications in biosensors and nanotechnology."

Nanotechnologists and other materials scientists use gold as an interface between electronic components and organic or biomolecular substances. Gold's conductivity and resistance to corrosion makes it an ideal surface for attaching molecules that can detect the presence of proteins in the blood that indicate disease.

"Up to this point, the standard practice has been to modify gold surfaces with thiols, because they are relatively easy to work with and form coatings quickly," Wei said. "Thiols are well known to adsorb, or stick, onto gold surfaces to form highly uniform films with adjustable surface properties. But a drawback to thiols is their intermittent hold on the surface, and the relatively weak chemical bond makes them less attractive for applications that require environmentally durable coatings."

Wei's team found that converting amines into DTCs empowers them with an ability to grasp gold surfaces with a strength that thiols do not possess.

"As DTCs, the amines are armed with a 'pincer' made of two sulfur atoms," Wei said. "Thiols are typically bonded to gold by one sulfur atom, like pins stuck in a gold pincushion. DTCs are more like a vice grip, so we hope they will last longer on the gold."

Although DTCs have been around for a long time, Wei said, researchers have overlooked their application to surface chemistry.

Wei said further studies need to establish the full scope and limitations of DTCs for various applications.