Fe-doped CeO₂ nanorods for enhanced peroxidase-like activity and their application towards glucose detection

The construction of highly efficient inorganic mimetic enzymes (nanozymes) is much needed to replace natural enzymes due to their instability and high cost. Recently, nanoscale CeO₂ has been attracting significant interest due to its unique properties such as facile redox behaviour (Ce⁴⁺↔ Ce³⁺) and surface defects. In the present work, various amounts of Fe³⁺-doped CeO₂ nanorods (NRs) (with 3, 6, 9, and 12% Fe doping) were synthesized using a facile hydrothermal method and investigated for peroxidase-like activity and glucose detection. The peroxidase-like activity results revealed that 6 at% doping is the optimal Fe doping level to demonstrate superior catalytic performance over un-doped and Fe³⁺-doped CeO₂ NRs. Steady state kinetic analysis also confirms that the 6% Fe³⁺-doped CeO₂ (6Fe/CeO₂) NRs exhibited excellent catalytic performance towards 3,3',5,5'tetramethylbenzidine (TMB) oxidation with a K_m and V_m of 0.176 mM and 8.6 × 10^-8 M s^-1, respectively, as compared to horseradish peroxidase (HRP) enzymes (0.434 mM and 10.0 × 10^-8 M s^-1). Typical colour reactions arising from the catalytic oxidation of the TMB substrate over 6Fe/CeO₂ NRs with H₂O₂ have been utilized to establish a simple sensitive and selective colorimetric assay for the determination of glucose concentration in buffer, diluted fruit juices and foetal bovine serum samples. The superior catalytic performance of 6Fe/CeO₂ NRs could be attributed to abundant surface defects, high surface area and pore volume, and preferential exposure of the highly reactive (110) planes.