In this paper, microdialysis sampling was combined with an enzymatic assay of glucose level in rat brain. A novel amperometric glucose biosensor based on ferrocene-doped silica (FcDS) nanoparticles conjugated with a biopolymer chitosan (CHIT) membrane was developed. These uniform FcDS nanoparticles (about 15 +/- 3 nm) were prepared by a water-in-oil (W/O) microemulsion method and were characterized by TEM and electrochemical technology. The nanosilica surface exhibited high biocompatability and the ferrocene doped inside maintained its high electron-transfer efficiency as a mediator. The glucose biosensor showed a detection limit of 2.0 x 10(-6) mol L-1 with a linear range from 5.0 x 10(-6) to 1.2 x 10(-2) mol L-1. Coupled to microdialysis, it was used to determine the glucose concentration in rat brain. The result was in satisfactory agreement with the literature. (C) 2004 Published by Elsevier B.V.