A low-cost, implantable electronic biosensor

June 12, 2013

Field effect transistor protein biosensor schematic. A sensing channel connects the source (S) and drain (D) with a reference electrode (RE). When a target analyte (protein) binds to the receptor, it induces charges in the substrate, causing a change in the current flow between the source and drain (a protein detection). (Credit: Ohio State University)

Ohio State University engineers are developing low-cost electronic devices that work in direct contact with living tissue inside the body.

The initial objective is to develop an in vivo biosensor to detect the presence of proteins that mark the first signs of organ rejection in the body. Such biosensors could also be used for detecting glucose, pH, and diseases such as cancer.

Doctors would insert a needle into the patient’s body near the site of the implanted organ. Silicon sensors on the needle would detect the protein, and doctors would know how to tailor the patient’s dosage of anti-rejection drugs based on the sensor readings.

Paul Berger, professor of electrical and computer engineering and physics at Ohio State, explained that one barrier to the development of implantable sensors is that most existing electronics are based on silicon, and charges on electrolytes in the body interfere with the electrical signals in silicon circuits, causing long-term electrical drifting and instability.

While other more exotic semiconductors might work in the body, they are more expensive, harder to manufacture, and may be toxic, he said. Also,silicon biosensors are preferred because they can be integrated onto a small chip atop a diagnostic needle.

Protective coating

A silicon circuit, coated with a protective layer and immersed in fluid that mimicks human body chemistry (credit: Ohio State University)

Berger’s Ohio State team found that electrolytes could be blocked from entering silicon by using a layer of aluminum oxide.

In tests, a silicon-based MOS capacitor coated with this material continued to function, even after 24 hours of immersion in a solution that mimicked typical body chemistry.

Other materials such as titanium could also work, and such coatings could even be tailored to boost the performance of sensors or other biomedical devices, Berger suggested.

The university will license this technology for further development.