Surgeons lack the tools to detect microtumours during cancer surgery, increasing the risk that cancer will come back. To address this, Dmitri Lapotko, now at the medical-technology firm Masimo in Irvine, California, and his colleagues injected gold nanoparticles into tumour-bearing mice before surgery. The particles, which have cancer-specific antibodies on their surfaces, were taken up by cancer cells. After removing the main tumour, the researchers heated up the nanoparticles using a short laser pulse, causing nanobubbles to form and explode only in the cancer cells, destroying them without harming normal tissue. The explosions generated a detectable acoustic signal.