Real-time snapshot of single molecules
doi:10.1038/nindia.2016.57 Published online 26 April 2016
By using a new technique called photonic nanojet-mediated surface-enhanced Raman scattering, researchers have captured signals from a few specific dye molecules1. This technique is potentially useful for real-time detection of protein molecules that act as markers for various diseases including cancer.
Real-time monitoring of single molecules is essential for understanding chemical and biological processes. Existing sensors estimate the molecular weight and size of single molecules, but assessing the chemical structures of single molecules remains a challenge.
To devise a technique for detecting single molecules in real time, the researchers attached a few molecules of methylene blue to a glass plate coated with gold nanoparticles that had been dipped in a methylene blue dye solution for 3 seconds and then dried. They then focused a laser beam through an optical microscope and observed a photonic nanojet-mediated surface-enhanced Raman scattering signal from the dye molecules.
The fact that the photonic nanojet is much more intense than the incident laser light indicates that a giant electric field was created in the nanogaps between the nanoparticles on the glass plate. This large field improved the signals from molecules residing in the nanogaps. These signals were much larger than those obtained using conventional techniques that do not employ a photonic nanojet.
“This technique could be used to study extremely tiny pathogens and molecules such as a few viruses, protein molecules, and single- and double-stranded DNAs,” says Venkata Ramanaiah Dantham, one of the researchers from Indian Institute of Technology, Patna.
1. Das, G. M. et al. Photonic nanojet-mediated SERS technique for enhancing the Raman scattering of a few molecules. J. Raman Spectros. (2016) doi: 10.1002/jrs.4928