A graphene transistor works like a microscopic switch: a molecule lands on its surface, and the current changes. But a bare graphene surface catches nothing. You need a "bait"—antibodies that recognize only viral proteins. How do you attach them to graphene without damaging the sensor itself?
Scientists found a way: they coated the graphene with a carbon film one nanometer thick. It's like putting ultra-thin double-sided tape on a table. One side sticks to the graphene, the other to the antibodies. The film is applied in advance, and antibodies are added to the already working chip. This way, you can place different baits for different proteins on a single chip.
Fifteen such sensors were combined into a single chip with channels for liquid. A pump pushes the sample solution through, and electronics monitor each sensor's signal in real time. Everything is automated: no need to manually drip reagents and wait.
They tested it on coronavirus proteins — the spike (S) and nucleocapsid (N). The sensors detected them at concentrations as low as 10 attomoles. That's roughly six molecules per liter of water. The device distinguished the target proteins from similar ones and worked across a concentration range spanning ten thousandfold.
This approach isn't tied to one virus. Swap the antibodies, and the same chip hunts for other proteins, bacteria, or chemicals. It's a step toward portable labs that deliver answers in minutes, not days.
An attomole is one billionth of one billionth of a mole. If you dissolved a single drop of ink in Lake Baikal, the concentration would be about a million times higher than this chip's detection limit.