Scientists have developed a new DNA-based logic circuit which they say can identify and kill cancer cells without harming the healthy ones.

The researchers, who developed the cell-level diagnostic system, said it could be used for drug screening or perhaps for disease treatment, killing tumors while leaving healthy cells alone. The circuit, they said, works like any other logic circuit: It analyses multiple inputs and makes a decision.

In this case, the circuit really consists of genes that can detect up to five cancer-specific molecules and their concentrations. When all five of those characteristics are present, the circuit makes a positive determination, and then it triggers cell death, they reported in the journal Science.

"The biocomputer combines the factors using logic operations such as AND and NOT, and only generates the required outcome, namely cell death, when the entire calculation with all the factors results in a logical TRUE value," lead researcher Yaakov Benenson, of Federal Institute of Technology in Zurich, said in a statement.

The researchers, including a team from the Massachusetts Institute of Technology in the US, tested the biocomputer with HeLa cells, a prolific type of cervical cancer cell.

They studied the cells' microRNA, which regulates gene expression by destroying messenger RNA, the substance that brings the DNA blueprint to the rest of the cell. They eventually pinpointed one microRNA combo that was unique to HeLa cells.

Once they had the right combination, the researchers designed a synthetic gene which codes for a protein that promotes apoptosis, or programmed cell death. The special gene would turn on in the presence of miRNA levels that match the HeLa profile.

If the miRNA levels were too high or too low, the gene would not switch on, and the cell would not be killed. Healthy cells, which would also lack the HeLa profile, would be similarly left alone, the researchers said.

The next step, they said, would be to test this system in a living animal, but this will be difficult. Current methods use viruses or chemicals to bring foreign DNA inside cells, but these make permanent changes, which could have their own complications.

So the method is still far from being usable for cancer treatment, they said, but added that it is an important step toward building a single-cell-level diagnostic method.