Nanoceria based electrochemical sensor for hydrogen peroxide detection

Oxidative stress is a condition when the concentration of free radicals and reactive molecular species rise above certain level in living systems. This condition not only perturbs the normal physiology of the system but also has been implicated in many diseases in humans and other animals. Hydrogen peroxide (H₂O₂) is known to be involved in induction of oxidative stress and has also been linked to a variety of ailments such as inflammation, rheumatoid arthritis, diabetes, and cancer in humans. It is one of the more stable reactive molecular species present in living systems. Because of its stability and links with various diseases, sensing the level of H₂O₂ can be of great help in diagnosing these diseases, thereby easing disease management and amelioration. Nanoceria is a potent candidate in free radical scavenging as well as sensing because of its unique redox properties. These properties have been exploited, in the reported work, to sense and quantify peroxide levels. Nanoceria has been synthesized using different capping agents: Hexamethylene-tetra-amine (HMTA) and fructose. CeO₂-HMTA show rhombohedral and cubic 6.4 nm particles whereas CeO₂-fructose are found to be spherical with average particle diameter size 5.8 nm. CeO₂-HMTA, due to the better exposure of the active (200) and (220) planes relative to (111) plane, exhibits superior electrocatalytic activity toward H₂O₂ reduction. Amperometric responses were measured by increasing H₂O₂ concentration. The authors observed a sensitivity of 21.13 and 9.6 μA cm⁻² mM⁻¹ for CeO₂-HMTA and CeO₂-fructose, respectively. The response time of 4.8 and 6.5 s was observed for CeO₂-HMTA and CeO₂-fructose, respectively. The limit of detection is as low as 0.6 and 2.0 μM at S/N ratio 3 for CeO₂-HMTA and CeO₂-fructose, respectively. Ceria-HMTA was further tested for its antioxidant activity in an animal cell line in vitro and the results confirmed its activity.