Abstract: The presently-disclosed subject matter is directed to biosensors for detecting molecules of interest, and systems and methods for using same. The biosensors include an antibody and a probe covalently-linked to the antibody. The antibody has an antigen-binding site that selectively binds the molecule of interest and a purine-binding site, which is at a location distinct from that of the antigen-binding site. The probe includes a purine molecule, which is covalently bound at the purine-binding site to the antibody, and a label linked to the purine molecule. Upon binding of the molecule of interest to the biosensor antigen-binding site, the biosensor undergoes a conformational change, which detectably alters a signal of the label such that the molecule of interest can be detected.

Abstract: A method for diagnosing a neurological disease comprising detecting a neurological disease-specific biochemical marker macromolecule within a sample of extracted cerebral spinal fluid is disclosed. In particular, a radioactively labeled photoaffinity probe is used to diagnose a neurological disease. For instance, Alzheimer's disease can be diagnosed by detecting a disease-specific protein having a molecular weight of about 42,000 daltons, i.e., glutamine synthetase.