Good question :)

The basic concept is an electrical detection of the complex antigen-antibody. For example, you can fabricate a small grapheme transistor with covalent attached antibody on the gate. After incubation into solution with virus antigen the complexes will be on the gate and the capacity will be change. It is possible (theoretically! :)) to detect them by simple electronic system.

Unfortunately, in real life all processes are very difficult - the real clinical samples are not pure and there are a lot of artifacts. For practical using a chip must be better than classical diagnostic kits - it must be cheap, simple in use, fast and precise. It is very difficult task and its solvability is not obvious...

I am not sure about graphene, but there are a lot of articles about biochips with classical silicon structures, just google "chip virus detection".  

The techniques of conjugation are described in some classical books, for example: Bioconjugate Techniques, Greg T. Hermanson

Good luck! 

http://dx.doi.org/10.1080/10408436.2014.1002604

Graphen peer see cannot detect analyte in samples. Also hepatites is broad concept. You mean hepatite virus? inflammation?

If is virus as said Denis you need to detect antibody or genome. Graphene only increase the sensibility of biosensors.  

Thanks Sitansu Sekhar Nanda  and Denis Korneev  for your valuable comments.