Sensitivity and enzyme stability are the main targets in the biosensors improvement. This work achieves both by means of the combination of two efficient electrocatalysts: ferrocene and gold nanoparticles (AuNPs). The AuNPs were electrodeposited onto a polyferrocenyl polycyclosiloxane polymer (FPP) in order to obtain an electrocatalytic framework for the covalent immobilization and direct electrochemistry of horseradish peroxidase (HRP). The developed surface is like that obtained with graphene modified electrodes, with very high specific area. The kinetic study of electrodes modified with and without HRP showed that the FPP/AuNPs system greatly improves other more complex systems based on the direct HRP electro-reduction by AuNPs, allowing the use of lower measuring potentials, with improved sensitivity, wider linear ranges and lower detection limits. The obtained apparent Michaelis-Menten constant, K-M,K-app, was 0.32 mM, significantly lower than the intrinsic K-M, revealing the very high enzymatic efficiency of the developed device. The HRP/AuNPs/FPP/Pt electrode was used as biosensor for hydrogen peroxide with two wide linear ranges of 0-200 mu M and 200-6800 mu M, and a high sensitivity of 685.71 mu A mM(-1) cm(-2), a low detection limit of 50 nM and long-term stability. The new device has been successfully used too as for the determination of organic hydroperoxides. (C) 2016 The Electrochemical Society. All rights reserved.