The use of aptamers, small chains of nucleotides that bind to specific target molecules, has proliferated in recent years. A key to understanding how these tailored nanostructures work, however, is determining how they contort when binding with their substrates. Until now, researchers have had difficulty imaging molecules with such weak optical signals.

In Biointerphases, a research team presents a new application of a technique that uses cutting-edge tip-enhanced Raman scattering (TERS), chemically imaging DNA aptamers on the nanoscale for the first time. With the help of new, highly sensitive commercial instruments, the group mapped the aptamers specific to the foodborne pathogen Listeria monocytogenes. Using the tip-enhanced fields in measurements of aptamer vibrational signal data, they ultra precisely mapped all without potentially molecule-deforming stains and labels that are widely used in research today.

TERS combines techniques associated with scanning probe microscopy with surface-enhanced Raman scattering, which draws on plasmonic resonances of metallic nanostructure surfaces to enhance the laser scattering signals of biomolecules.

Mapping in 3-nanometer steps and using a gold-coated nanoscale tip, the TERS demonstration has begun to achieve an image resolution high enough for biologists to study the tiny aptamers. Aptamers in their study ranged from 5 to 20 nanometers. Spatial resolution under 10 nanometers has been a challenge in previous Raman imaging studies. TERS was also able to characterize the aptamers’ composition.

The study’s authors report that the long-term goal is to fill the need in the scientific community for a device that utilizes TERS images to determine molecular conformations. They said they hope their work with Listeria leads to a point-of-care device that can optically detect the bacteria in food.

Source: “Tip-enhanced Raman scattering of DNA aptamers for Listeria monocytogenes,” by Siyu He, Hongyuan Li, Carmen L. Gomes, and Dimitri V. Voronine, Biointerphases (2018). The article can be accessed at https://doi.org/10.1116/1.5022303.