But if DNA from healthy cells is added, the DNA binds to the particles differently, and turns the water blue.
Abu Sina, Research Fellow, The University of Queensland; Laura G. Carrascosa, Postdoctoral Research Fellow, The University of Queensland, and Matt Trau, Professor, The University of Queensland.
"Virtually every piece of cancerous DNA we examined had this highly predictable pattern", he explained.
Joyce Ohm, an associate professor of oncology at Roswell Park Comprehensive Cancer Center in Buffalo, New York, agreed that the work is "an exciting potential advance" in looking for a general epigenetic biomarker for cancer.
Currently, the test detects only the presence of cancer, not the type of cancer.
The DNA in cancer cells can have mutations that affect the growth of a specific tumour, but these differences depend on the type of cancer. Instead, they are now just one step in the process. This allowed them to develop a test that distinguishes between healthy cells and cancerous ones, even from the tiny traces of DNA that find their way into the bloodstream.
It is based on a process known as epigenetics - the attachment of a chemical tag known as a methyl group to DNA. In cancer cells, this patterning is hijacked so that only genes that help the cancer grow are switched on.
Co-author Dr. Abu Sina said: "Because cancer is an extremely complicated and variable disease, it has been hard to find a simple signature common to all cancers, yet distinct from healthy cells".
"Our technique could be a screening tool to inform clinicians that a patient may have a cancer, but they would require subsequent tests with other techniques to identify the cancer type and stage", Carrascosa said.
The discovery was made by a medical research team in Queensland.
The team found that in the healthy cells these methyl groups are spread across the genome.
For this test, he said, they looked at patterns of methyl groups over the DNA. The researchers called this methylation pattern the "methylation landscape", or "methylscape".
Taking advantage of this finding, the researchers designed a new test that uses gold nanoparticles to detect cancer. Professor Trau said that the next step would be to start clinical trials to hone the test. "You can detect it by eye, it's as simple as that".
That's because the test is only accurate 90 per cent of the time - while it does not reveal where the cancer cells are located and how serious it is. "It's not flawless yet, but it's a promising start".
It will be some years before it can be used in clinics.
"If it's very sensitive, we could use it for early diagnosis of cancer ... especially for cancers where there is no screening paradigm, like ovarian and pancreatic", she said. "We certainly don't know yet whether it's the holy grail for all cancer diagnostics, but it looks really interesting as an incredibly simple universal marker for cancer, and as an accessible and cheap technology that doesn't require complicated lab-based equipment like DNA sequencing", Trau said.