‘Gold’ fish thrive as cancers die

RICE (US) — Gold nanoparticles and a laser pulse can detect and destroy diseased cells in living tissue by creating tiny, shiny vapor bubbles that reveal and then explode them.

The discovery holds potential for the combined diagnostic and therapeutic–or theranostic–treatment of cancer and other diseases at the cellular level.

A paper in the October print edition of the journal Biomaterials details the effect of plasmonic nanobubble theranostics on zebra fish implanted with live human prostate cancer cells, demonstrating the guided ablation of cancer cells in a living organism without damaging the host.

Rice University physicist Dmitri Lapotko and colleagues developed the concept of cell theranostics to unite three important treatment stages—diagnosis, therapy, and confirmation of the therapeutic action—into one connected procedure.

The unique tunability of plasmonic nanobubbles makes the procedure possible. Their animal model, the zebra fish, is nearly transparent, which makes it ideal for such in vivo research.

In earlier research in Lapotko’s home lab in the National Academy of Sciences of Belarus, plasmonic nanobubbles demonstrated their theranostic potential.

In another study on cardiovascular applications, nanobubbles were filmed blasting their way through arterial plaque.

The stronger the laser pulse, the more damaging the explosion when the bubbles burst, making the technique highly tunable. The bubbles range in size from 50 nanometers to more than 10 micrometers.

In the zebra-fish study, Lapotko directed antibody-tagged gold nanoparticles into the implanted cancer cells.

A short laser pulse overheated the surface of the nanoparticles and evaporated a very thin volume of the surrounding medium to create small vapor bubbles that expanded and collapsed within nanoseconds; leaving cells undamaged while generating a strong optical scattering signal that was bright enough to detect a single cancer cell.

A second, stronger pulse generated larger nanobubbles that exploded (or, as the researchers called it, “mechanically ablated”) the target cell without damaging surrounding tissue in the zebra fish. Scattering of the laser light by the second bubble confirmed the cellular destruction.

That the process is mechanical in nature is key, Lapotko says. The nanobubbles avoid the pitfalls of chemo- or radiative therapy that can damage healthy tissue as well as tumors.

“It’s not a particle that kills the cancer cell, but a transient and short event,” he says. “We’re converting light energy into mechanical energy.”

Lapotko will study the biological effects of plasmonic nanobubbles and combine their functions into a single sequence that would take a mere microsecond to detect and destroy a cancer cell and confirm the results.

“By tuning their size dynamically, we will tune their biological action from noninvasive sensing to localized intracellular drug delivery to selective elimination of specific cells,” he says.

“Being a stealth, on-demand probe with tunable function, the plasmonic nanobubble can be applied to all areas of medicine, since the nanobubble mechanism is universal and can be employed for detecting and manipulating specific molecules, or for precise microsurgery.”

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