A new nanoparticle test for dangerous bacteria such as Escherichia coli O157:H7 is so sensitive it can detect a single bacterial cell within minutes.

The new test consists of silica nanoparticles, each housing thousands of fluorescent dye molecules and each attached to an antibody for a given bacterium.

The nanoparticles are added to a solution of the test sample, such as ground beef. If the bacterium sought is present, the nanoparticles will quickly attach to it. The sample is then separated by weight in a centrifuge. The target bacteria, being heavier than the nanoparticles, will separate away from them. But those dye molecules already attached will fluoresce in this heavier sample, identifying the bacteria.

The new test differs from other dye tests in that thousands of dye molecules will fluoresce if only one bacterium is present because they are all attached to the same antibody.