2D Co 3 O 4 modified by IrO 2 nanozyme for convenient detection of aqueous Fe 2+ and intercellular H 2 O 2 .

A portable sensor for visual monitoring of Fe 2+ and H 2 O 2 , two-dimensional Co 3 O 4 modified by nano-IrO 2 (IrO 2 @2D Co 3 O 4 ) was prepared in this work, for the first time, with the help of microwave radiation at 140 °C, which was further stabilized onto common test strips. The present IrO 2 @2D Co 3 O 4 possessed superior dual-function enzyme-like activity with low toxicity and excellent biocompatibility. Especially, trace Fe 2+ and H 2 O 2 could exclusively alter their enzyme-like catalytic activity with discriminating hyperchromic or hypochromic effect, i.e., from blue to colorless or to dark blue for both IrO 2 @2D Co 3 O 4 dispersion and its functionalized test strips. The linear regression equations were A 652  = 0.5940 - 0.00041 c Fe 2+ (10 -8  M, R 2  = 0.9927) for Fe 2+ and ∆A 652  = 0.0023 c H2O2  + 0.00025 (10 -7  M, R 2  = 0.9982) for H 2 O 2 , respectively. When applied to visual monitoring of aqueous Fe 2+ and intercellular H 2 O 2 , the recoveries were 101.2 ~ 102.5% and 95.8 ~ 103.7% with detection limits of 1.25 × 10 -8  mol/L and 1.02 × 10 -7  mol/L, respectively, far below the permitted values in drinking water set by the World Health Organization. The mechanisms for the enhancing enzyme-mimetic activity of IrO 2 @2D Co 3 O 4 and its selective responses to Fe 2+ and H 2 O 2 were investigated in detail.