Controlled fluorescence quenching by antibody-conjugated graphene oxide to measure tau protein.

We report an ultrasensitive immunoassay for tau protein-a key marker of Alzheimer's disease. This sensing platform relies on graphene oxide (GO) surfaces conjugated with anti-human tau antibody to provide quantitative binding sites for the tau protein. The GO quenches standard fluorescein isothiocyanate labelled tau (tau-FITC) when tau protein and tau-FITC are both present and compete for the binding sites. This change in fluorescence signal can be used to quantitate tau protein. In contrast with traditional enzyme-linked immunosorbent assay (ELISA), our method does not require enzyme-linked secondary antibodies for protein recognition nor does it require an enzyme substrate for optical signal generation. This requires fewer reagents and has less systematic error than the antigen-antibody recognition steps in ELISA. Our method has a tau protein detection limit of 0.14 pmol ml-1 in buffer. This approach could be developed into a promising biosensor for the detection of tau protein and may be useful in the clinical diagnosis of tau-induced neurodegeneration syndromes.