What’s the News: One of biologists’ favorite fantasies is a doctor who can fit inside a cell. This tiny physician, likely a device built from DNA, would make diagnoses by sensing molecules floating around the body that are signatures of certain diseases and would then release the appropriate drug.

While that vision is still a long way off, scientists have taken a significant step in that direction with a system that detects problems at several levels of cells’ machinery.

What’s the Context:

Disease are frequently the result of malfunctioning proteins, which zip around taking care of the daily business of the body. Proteins are made using our DNA as templates; as described by the Central Dogma of biology, first DNA is transcribed into an mRNA molecule, which is then translated by cellular machinery into the protein. One way to tell whether a protein is abnormal is by checking the mRNA molecule for errors.
The researchers’ first “biocomputer,” which they developed seven years ago, did just that. It consisted of a strand of DNA and a DNA-snipping enzyme. The DNA was designed to bind to mRNAs of specific proteins known to be involved in ...