Wonder cups to detect molecule traces
doi:10.1038/nindia.2009.9 Published online 22 January 2009
A specially designed pulsed laser has been used to make tiny silver cups that could be used to detect traces of molecules1. The cups with internal volume of thousandth of trillionth of a litre (femtolitre) have been successfully used to detect thiophenol adsorbed onto their inner surface.
The molecules of thiophenol from the cups' surface exhibited surface enhanced Raman scattering (SERS), which provides the unique chemical identity of a molecule. SERS has emerged as an important tool for trace analysis of molecules. Previous researches have explored molecules adsorbed to metallic colloids of silver and gold in solution phase. But, this has drawbacks like instability in terms of reproducibility.
So, the researchers produced tiny silver cups on a silicon substrate using pulsed laser ablation technique. They filled these cups with thiophenol molecules using two methods – first, by dipping a silicon substrate carrying the silver cups in the thiophenol solution for 30 minutes and second, by gently moving a tungsten microtip immersed in thiophenol around the inner walls of the cups. SERS measurement was carried out by moving the substrate such that individual cups were brought under the photon beam.
The tiny cups with thiophenol had enhanced SERS activity by a factor of one million. This could be attributed to their surface roughness, which is apt for SERS. Some of the cups even had internal volume of an attolitre (millionth of trillionth of a litre). Such cups could be useful as SERS is emerging as an important tool in biochemistry and medicine for trace analysis of molecules.