TOKYO Hitachi Ltd. has developed a semiconductor biosensor chip that introduces electrical measurement for the first time into immunoassay, in place of light absorption measurement.
According to Hitachi, introducing the electric phenomena eliminates bulky optics, making it possible to build a low cost, portable immunoassay test system that can shrink in size from a refrigerator to a notebook PC.
Hitachi intends to offer an immunoassay measurement system using the biosensor in a few years. The company expects to offer the system at a tenth of current test system prices.
Rising health concerns have sparked increasing demand for a compact immunoassay test system that can test blood, food and bovine spongiform encephalopathy (BSE). Hitachi researchers believe that their biosensor-based test system can satisfy such a need.
Besides shrinking test system size, the chip also provides ten times higher sensitivity than present sensors. It can detect densities to 1 picogram per milliliter, according to Masao Kamahori, senior researcher of Hitachi Biosystems Research Department. The higher sensitivity allows detecting a much wider range of diseases, Kamahori said.
The biosensor chip consists of one gold anode and one field effect transistor. A prototype device is a 5mm x 2.5mm with one pair of sensors mounted on it. The anode is a gold plate measuring 400 x 400 microns and is 100 nm thick. The transistor's channel is 2400 micron wide and 5 microns long. The disposable sensor can be used to test various antigens (protein) without changing its structure.
From an immune reaction, a product called thiol compound is generated. The absorption of thiol at the anode produces current between the transistor's source and drain. The drain current change is proportional to the absorption speed.