Amplified Peroxidase-Like Activity in Iron Oxide Nanoparticles Using Adenosine Monophosphate: Application to Urinary...

Numerous compounds such as protein and double-stranded DNA have been shown to efficiently inhibit intrinsic peroxidase-mimic activity in Fe₃O₄ nanoparticles (NP) and other related nanomaterials. However, only a few studies have focused on finding new compounds for enhancing the catalytic activity of Fe₃O₄ NP-related nanomaterials. Herein, phosphate containing adenosine analogs are reported to enhance the oxidation reaction of hydrogen peroxide (H₂O₂) and amplex ultrared (AU) for improving the peroxidase-like activity in Fe₃O₄ NPs. This enhancement is suggested to be a result of the binding of adenosine analogs to Fe²⁺/Fe³⁺ sites on the NP surface and from adenosine 5'-monophosphate (AMP) acting as the distal histidine residue of horseradish peroxidase for activating H₂O₂. Phosphate containing adenosine analogs revealed the following trend for the enhanced activity of Fe₃O₄ NPs: AMP > adenosine 5'-diphosphate > adenosine 5'-triphosphate. The peroxidase-like activity in the Fe₃O₄ NPs progressively increased with increasing AMP concentration and polyadenosine length. The Michaelis constant for AMP attached Fe₃O₄ NPs is 5.3-fold lower and the maximum velocity is 2.7-fold higher than those of the bare Fe₃O₄ NPs. Furthermore, on the basis of AMP promoted peroxidase mimicking activity in the Fe₃O₄ NPs and the adsorption of protein on the NP surface, a selective fluorescent turn-off system for the detection of urinary protein is developed.