Detection of glucose at 2 fM concentration

Abstract

We report the amperometric detection of glucose at 2 fM concentration in a physiological buffer solution at 1 atm O2 pressure. The sensitive assay is based on the close to absolute electroreductive stripping of O 2 from the solution near the glucose electrooxidizing anode. The glucose was detected by its electrooxidation on a stationary glassy carbon disk surrounded by an also stationary platinum ring. The disk was coated with a film of glucose oxidase (GOx), electrically "wired" with PVP-[Os(N,N′-dimethyl-2,2′-biimidazole)3] 2+/3+ (polymer I), having a redox potential of -0.19 V versus Ag/AgCl. The ring was coated with bilirubin oxidase (BOD) "wired" with PAA-PVI-[Os(4,4′-dichloro-2,2′-bipyridine)2Cl] +/2+ (polymer II), having a redox potential of + 0.36 V versus Ag/AgCl. The ring-disk electrode was held facing up, and a 30-μL drop was placed on it for the assay, with the ring poised at -0.3 V/AgAgCl and the disk poised at -0.1 V/Ag/AgCl. Even though the atmosphere over the drop was O 2 at 1 atm pressure, the wired BOD disk scavenged the O2 so effectively that the glucose-reduced FADH2 of GOx was not oxidized by O2, the natural cosubstrate of the enzyme.