Spacer Parameters (a) Schematic of spaser as multimodal cellular nanoprobe. (b) Comparison of emission in suspensions of uranine spaser at 528 m (green peak; pump energy fluence 70 mJ cm−2), fluorescein spaser (magenta peak), QD with maximum at 576 nm (inset, red peak) and GNRs (right) with silica shell doped with DCM. TEM images shows 22-nm spaser (left inset) and GNRs (right inset).
A nanolaser known as the spaser 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, according to a new research study. The study found the spaser can be used as an optical probe and 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. The spaser absorbs laser light, heats up, causes shock waves in the cell and destroys the cell membrane.
The spaser, “surface plasmon amplification by stimulated emission of radiation”, is a nanoparticle, about 20 nm in size or hundreds times smaller than human cells. 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.
“There is no other method to reliably detect and destroy CTCs,” said Dr. Mark Stockman, director of the Center for Nano-Optics and professor of physics at Georgia State. “This is the first. This biocompatible spaser can go after these cells and destroy them without killing or damaging healthy cells. 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.”
Most results were obtained with a gold, spherical nanoparticle surrounded by a silica shell and covered with a uranine dye, which is widely used for tracing and biomedical diagnostics. The researchers studied the 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.
https://www.nature.com/articles/ncomms15528
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