Nanoscope Can Probe Chemistry on the Molecular Scale

A new imaging technique using broadband IR synchrotron light has enabled the in-depth study of complex molecular systems, from batteries and electronic materials to living cells and even stardust.

The technique, developed at Lawrence Berkeley National Laboratory can identify and study molecules at the mesoscale — 10-1000 nm — with extreme sensitivity.

The researchers, collaborating with a team from the University of Colorado, combined the IR synchrotron light with atomic force microscopy, prompting improvement in the spatial resolution of IR spectroscopy. This simultaneously covered the full spectroscopic range, which allowed the team to better study nanoscale, mesoscale and surface phenomena.

Synchrotron infrared nano-spectroscopy makes it possible to image objects like this peptoid nanosheet, which is less than 8 nm thick. Courtesy of Lawrence Berkeley National Laboratory.

This has proven difficult in the past, as IR spectroscopy is typically unable to resolve molecular composition below about 2000 nm, and traditional laser light does not have the flexibility to explore a spectrum of mixed molecules.

“The big thing is that we’re getting full broadband infrared spectroscopy at 100 to 1000 times smaller scale,” said Dr. Hans Bechtel, principal scientific engineering associate at Berkeley Lab. “This is not an incremental achievement. It’s really revolutionary.”

The study demonstrates the nanoscope’s ability to capture broadband spectroscopic data over a variety of samples, including a semiconductor-insulator system, a mollusk shell, proteins and a peptoid nanosheet.

The new technique, called synchrotron infrared nano-spectroscopy (SINS), holds great potential, according to Dr. Michael Martin, a scientist at Berkeley Lab and a member of the team. It brings together two pre-existing infrared technologies: IR scattering-scanning near-field optical microscopy (IR s-SNOM) and Fourier transform infrared spectroscopy. These, combined with the IR light of the synchrotron, provide the ability to identify clusters of molecules as small as 20-40 nm.

“This is actually one of very few examples where synchrotron light has been coupled to scanning probe microscopy,” said Dr. Markus Raschke, a physics professor at Boulder and one of the researchers. “Moreover, the implementation of the technique at the synchrotron brings chemical nanospectroscopy and [nano]-imaging out of the lab of a few laser science experts and makes it available for a broader scientific community at a user facility.”

In the future, the researchers anticipate that SINS could be useful in biochemistry. They could look at the surface of a cell, “inside the bi-layer membrane, the channels and receptors,” Martin said.

“If we could put a SINS tip on a living cell, we could watch biochemistry happen in real time,” he added.

The researchers also hope to use SINS beyond Earth to study lunar rocks and meteorites, which have a molecular diversity that has been difficult to resolve on the nanoscale, Bechtel said, particularly in a nondestructive manner. A better understanding of these materials could lead to a better understanding of planets and the solar system.

More in-depth study of organic solar cells could be in the pipeline, too. Raschke said scientists could use the technique to look at the limitations of such cells, and potentially use it to perform single-molecule chemical spectroscopy.

The study was supported by the US Department of Energy’s Office of Science. The research is published in Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1400502111).

For more information, visit: www.lbl.gov.