New technique developed to look at cells, tissues under the skin

A team of researchers have developed a new technique, the first of the kind, to look at cells and tissues under the skin in a living animal.

The technique, known as MOZART, for MOlecular imaging and characteriZation of tissue noninvasively At cellular ResoluTion, has so far provided intricate real-time details in three dimensions of the lymph and blood vessels.

The research team, at Stanford Bio-X, an interdisciplinary biosciences institute within Stanford University on the U.S. west coast, has expected the new technique to help detect tumors in the skin, colon or esophagus, or see the abnormal blood vessels that appear in the earliest stages of macular degeneration.

As senior author on a paper published on Friday by the online journal Scientific Reports, Adam de la Zerda, an assistant professor of structural biology at Stanford and a member of Stanford Bio-X, said "we've been trying to look into the living body and see information at the level of the single cell. Until now there has been no way do that."

A technique exists for peeking into a live tissue several millimeters under the skin. But that technique, called optical coherence tomography, or OCT, isn't sensitive or specific enough to see the individual cells or the molecules that the cells are producing.

A major issue has been finding a way of differentiating between cells or tissues; for example, picking out the cancerous cells beginning to multiply within an overall healthy tissue.

In other forms of microscopy, tags are latched onto molecules or structures of interest to illuminate those structures and provide a detailed view of where they are in the cell or body.

No such beacons existed for OCT, though de la Zerda knew that tiny particles called gold nanorods had some of the properties he was looking for. The problem was that the commercially available nanorods didn't produce nearly enough signal to be detected in a tissue.

Nanorods are analogous to organ pipes, said graduate student Elliott SoRelle, because longer pipes vibrate at lower frequencies, creating a deep, low sound.

Longer nanorods also vibrate at lower frequencies, or wavelengths, of light. Those vibrations scatter the light, which the microscope detects. If all the other tissues are vibrating in a white noise of higher frequencies, longer nanorods would stand out like low organ notes amidst a room of babble.

"My background was biochemistry, and this turned out to be a problem of materials science and surface chemistry," said SoRelle, who was co-first author of the paper. He can now make nontoxic nanorods in various sizes that all vibrate at unique and identifiable frequencies.

Next, to filter out the nanorods' frequency from the surrounding tissue, electrical engineering graduate student Orly Liba developed computer algorithms that could separate out the frequencies of light scattered by nanorods of various lengths and differentiate those from surrounding tissue.

With large nanorods and sensitive algorithms, de la Zerda and his team had solved the initial problem of detecting specific structures in three-dimensional images of living tissues.

The team tested their technology in the ear of a living mouse, where they were able to watch as the nanorods were taken up into the lymph system and transported through a network of valves.

They were able to distinguish between two different size nanorods that resonated at different wavelengths in separate lymph vessels, and they could distinguish between those two nanorods in the lymph system and the blood vessels.

"Nobody has shown that level of detail before," said Liba, who was co-first author of the paper.

De la Zerda said the technique could allow doctors to monitor how an otherwise invisible tumor under the skin is responding to treatment, or to understand how individual cells break free from a tumor and travel to distant sites. Endit