Nanobubbles Destroy Some Cells, Treat Others

A single laser blast can activate plasmonic nanobubbles that selectively kill diseased cells while at the same time treating others, and leaving neighboring healthy cells untouched.

The unique tunable plasmonic nanobubble technique developed at Rice University shows promise for replacing several difficult processes now used to treat cancer patients, among others, with a fast, simple, multifunctional procedure.

Nanobubbles form around plasmonic gold nanoparticles that heat up when excited by an outside energy source — in this case, a short laser pulse — and vaporize a thin layer of liquid near the particle's surface. The vapor bubble quickly expands and collapses.

In previous studies, biochemist Dmitri Lapotko and colleagues found that these nanobubbles kill cancer cells by literally exploding them without damaging healthy neighboring cells, a process that showed much higher precision and selectivity compared with processes mediated by gold nanoparticles alone.

Identical cells stained red and blue were the target of research at Rice University to show the effect of plasmonic nanobubbles. The bubbles form around heated gold nanoparticles that target particular cells, like cancer cells. When the particles are hollow, bubbles form that are large enough to kill the cell when they burst. When the particles are solid, the bubbles are smaller and can punch a temporary hole in a cell wall, allowing drugs or other material to flow in. Both effects can be achieved simultaneously with a single laser pulse. Images courtesy of Plasmonic Nanobubble Lab/Rice University.

Now, a series of experiments have proved that a single laser pulse creates large plasmonic nanobubbles around hollow gold nanoshells, which selectively destroy unwanted cells. The same laser pulse creates smaller nanobubbles around solid gold nanospheres that punch a tiny, temporary pore in the wall of a cell and create an inbound nanojet that rapidly "injects" drugs or genes into the other cells.

In the experiments, 60-nm-wide hollow nanoshells were placed in model cancer cells, stained red, while into a separate batch of the same type of cells, stained blue, the team put 60-nm-wide nanospheres.

After suspending the cells together in a green fluorescent dye, they fired a single wide laser pulse at the combined sample, washed the green stain out and checked the cells under a microscope. The red cells with the hollow shells were blasted apart by large plasmonic nanobubbles. The blue cells were intact, but green-stained liquid from outside had been pulled into the cells where smaller plasmonic nanobubbles around the solid spheres temporarily pried open the walls.

As many as 10 billion cells per minute could be selectively processed in a flow-through system like this, Lapotko said, adding that the technique potentially could advance cell and gene therapy and bone marrow transplantation.

Most disease-fighting and gene therapies require “ex vivo” — outside the body — processing of human cell grafts to eliminate unwanted cells and to genetically modify other cells to increase their therapeutic efficiency, Lapotko said.

After the laser pulse, red-stained cells show evidence of massive damage from exploding nanobubbles, while blue-stained cells remained intact, but with green fluorescent dye pulled in from the outside.

“Current cell processing is often slow, expensive and labor-intensive and suffers from high cell losses and poor selectivity,” he said. “Ideally, both elimination and transfection (the introduction of materials into cells) should be highly efficient, selective, fast and safe.”

The nanobubble technology promises “a method of doing multiple things to a cell population at the same time,” said collaborator Malcolm Brenner, a professor of medicine and of pediatrics at Baylor College of Medicine and director of its Center for Cell and Gene Therapy. "For example, if I want to put something into a stem cell to make it turn into another type of cell, and at the same time kill surrounding cells that have the potential to do harm when they go back into a patient — or into another patient — these very tunable plasmonic nanobubbles have the potential to do that."

The team’s long-term objective is to improve the outcome for patients with diseases whose treatment requires ex vivo cell processing, Lapotko said. He plans to build a prototype for human cell testing in the near future.

"We'd like for this to be a universal platform for cell and gene therapy and for stem cell transplantation," he said.

Texas Children's Hospital and the University of Texas MD Anderson Cancer Center also contributed to the research, which appeared in ACS Nano (doi: 10.1021/nn3045243).

For more information, visit: www.rice.edu