The oxidase-like activity of iridium nanoparticles, and their application to colorimetric determination of dissolved oxygen

Iridium nanoparticles (IrNPs) with intrinsic oxidase-like activity were synthesized by using sodium citrate as the stabilizer and NaBH4 as the reducing agent. The IrNPs have an average diameter of 2.5 +/- 0.5 nm and exhibit excellent oxidase-like property. Under the catalytic action of the IrNPs, 3,3', 5,5'-tetramethylbenzidine (TMB) is oxidized by dissolved oxygen (DO) to form a blue product with an absorption maximum at 652 nm. The catalytic activity is ascribed to the production of superoxide anion radical (O-2(-)center dot). The chromogenic reaction is exploited for the determination of DO. The method exhibits a wide calibration range from 12.5 to 257.5 mu M of DO and a limit of detection as low as 4.7 mu M. Compared to other methods, this method presented here shows improved precision and faster response time.