Researchers at the University of California, San Diego, have made self-propelled microtube rockets that can find and capture cancer cells from blood samples.

The researchers say that these ’microrockets’ could make an effective diagnostic tool. And blood samples would not need significant pre-treating, unlike samples for other micro-diagnostic methods. ’We showed for the first time that this microtube rocket can propel in biological fluid,’ says nano-engineer Joseph Wang, whose team joined forces with that of cancer researcher Liangfang Zhang.

The microrockets run on hydrogen peroxide fuel added to a biological sample. Platinum on the inside of the tube catalyses the splitting of hydrogen peroxide into water and oxygen, and the tapered tube is driven forward as the oxygen gas leaves through the wider back end. Iron layered between the inner platinum and outer gold coatings allows researchers to steer the microrockets with magnetic fields.

The team made the rocket specific for cancer by adding antibodies for a protein commonly found on colorectal, gastric and pancreatic cancer cells to the gold surface of the tube, making the receptor highly selective - it won’t bind to other cells.

Samuel Sanchez and his colleagues at the Leibniz Institute for Solid State and Materials Research in Dresden, Germany, developed this ’microbot’ design, and he says he is pleased to see another group making use them. 

The Californian team tested the microtubes in saline solution and human blood serum. In human serum, the rockets captured their pancreatic cancer cell targets 70 per cent of the time and could still move about while carrying their cellular cargo, with only a small drop in speed.

Sanchez says this work could ’help our community to believe that these tiny machines have real biomedical applications’.

Wang suggests that future nano-machine enabled cancer diagnostics could be as simple as adding hydrogen peroxide to a blood sample, using the magnetic field to guide the tiny rockets on several passes through the fluid and then examining the rockets for captured cancer cells with an optical microscope. 

’This technology has the potential to not only isolate circulating tumour cells (CTCs) from suspension but to manipulate the subsequently captured CTCs in a precise manner,’ says Shashi Murthy of Northeastern University in Boston, US. This would allow the cells to be collected and concentrated for further analysis, he adds.

Kate McAlpine