Glucose oxidase (GO(x)) has been covalently immobilized onto chemically synthesized thiolated gold nanoparticles (5-8 nm) via N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The lower value of the Michaelis-Menton constant obtained for the immobilized (3.74 mM) GO(x) compared with that for the free (5.85 mM) GO(x) suggests significant enhancement in the activity of GO(x) attached to thiolated gold nanoparticles. The covalently immobilized GO(x) thiolated nanoparticles exhibit a response time of 30 s, a shelf life of more than 6 months, and improved tolerance to both pH and temperature.