Combining diagnosis, treatment and guidance represents a challenge, especially when the disease is at an early stage and is expressed only through a few specific cells. Detecting these cells, being able to kill them immediately and selectively without harming healthy cells, and then identifying that the diseased cells have been destroyed will be a basis for future medicine. Such three-in-one medicine (recently referred to as theranostics) requires an agent or probe that can find, signal, kill and report on the target cells.

Scientists are busy searching for such a tunable probe that can switch from diagnosis to treatment and then to treatment guidance in a fast and reliable way, and without toxicity to the host organism.

Universal platform

A team from Belarus and the US has proposed a system involving light and heat (but no chemicals) – the two most natural factors of life – together with gold nanoparticles that can find target cells with the help of diagnosis-specific molecules (antibodies).

When excited by a short laser pulse, the gold nanoparticles convert light into heat thanks to the mechanism of plasmon resonance. Fast and local heating evaporates the nano-environment around the tiny particles to create a vapour nanobubble referred to as a plasmonic nanobubble (PNB). The size and lifetime of these bubbles can be controlled at the nanoscale by varying the energy of the laser (see plots in top image). Unlike the nanoparticles themselves, PNBs do not exist until activated by a laser and can be thought of as a stealth probe.

Researchers have discovered several features of PNBs that can be applied to theranostics. The bubbles scatter light more strongly than gold nanoparticles, which means that a PNB is a very bright optical probe that may help to discover a single cell. Next, a PNB can provide treatment through mechanical disruption of the target cells without thermal impact to surrounding tissues. At the same time, the cell-killing PNB can be easily distinguished optically from the non-invasive diagnostic PNB to give guidance of the treatment.

All three stages of PNB theranostics take less than a microsecond and can be performed in individual diseased cells. By tuning the diameter of the PNB with a laser pulse, the concept can be adapted to support several biomedical applications including drug delivery, gene transfection, imaging, micro-surgery and, ultimately, theranostics.

Full results can be found in the journal Nanotechnology.