Spaser detects and destroys circulating tumor cells to prevent cancer metastases

A team of researchers from Georgia State University (Atlanta, GA), the University of Arkansas for Medical Sciences, the University of Arkansas at Little Rock (both in Little Rock, AR), and the Siberian Branch of the Russian Academy of Science (Novosibirsk, Russia) has shown that a certain nanolaser type can serve as a super-bright, water-soluble, biocompatible probe capable of finding metastasized cancer cells in the blood stream and then killing these cells.

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The team's study found that the nanolaser, called a spaser, can be used as an optical probe. When released into the body (possibly through an injection or drinking a solution), it can find and go after circulating tumor cells (CTCs), stick to them, and destroy these cells by breaking them apart to prevent cancer metastases. It absorbs laser light, heats up, causes shock waves in the cell, and destroys the cell membrane.

A spaser, which stands for surface plasmon amplification by stimulated emission of radiation, is a nanoparticle about 20 nm in size. It has folic acid attached to its surface, which allows selective molecular targeting of cancer cells. The folate receptor is commonly overexpressed on the surface of most human cancer cells and is weakly expressed in normal cells.

"This biocompatible spaser can go after these cells and destroy them without killing or damaging healthy cells," says Dr. Mark Stockman, director of the Center for Nano-Optics and professor of physics at Georgia State. "Any other chemistry would damage and likely kill healthy cells. Our findings could play a pivotal role in providing a better, life-saving treatment option for cancer patients."

The researchers studied the 22 nm spaser's capabilities in vitro in human breast cancer cells with high folate receptor expression and endothelial cells with low folate receptor expression, as well as in mouse cells in vivo.

They found cells with spasers demonstrated high image contrasts with one or many individual "hot spots" at different laser energies above the spasing threshold. The presence of spasers was confirmed with several optical and electron microscopy techniques, which revealed an initial accumulation of individual spasers on the cell membrane followed by their entrance into the cell cytoplasm.

The study also found low toxicity of the spasers for human cells. At the same time, the spasers subjected to laser irradiation selectively killed the tumor cells without damaging the healthy ones.

Based on the study's results, spaser-based therapeutic applications with high-contrast imaging is a promising field. The data suggest spasers have high potential as therapeutic and diagnostic agents that integrate optical diagnosis and photothermal-based cell killing, using just a few laser pulses to kill cancer cells.

Full details of the work appear in the journal Nature Communications.