Spatially confining copper atom in flowerlike CoFe hydroxides for smartphone based ratiometric colorimetric dual mode detection of nitrite

Great progress in nanozyme catalysis for distinct catalytic reactions have been made. However, more current nanozyme induced sensing platforms are depended on oxidase like nanozymes with multienzymatic catalytic behavior, which can affect the determination accuracy and reliability. Designing high active and stable advanced nanozymes for enzyme like catalysis remains a huge challenge for analytic chemistry. Herein, a three atom site catalyst of CoFeCu hydroxide nanozyme is rationally prepared for constructing sensing platform by utilizing oxidase like catalytic activity. The CoFeCu nanozyme can mimic the behavior of oxidase by trigging O2 into O2·− via its highly dispersed metal active sites, which exhibits good oxidase like activities with of 2.22 mM and of 3.69 × 10−8 M·s−1 toward 3, 3′, 5, 5′ tetramethylbenzidine (TMB). Specifically, the elaborate doping of low content Cu leads to higher catalytic activity and adequate detection sensitivity. Interestingly, with the addition of nitrite, a redox and diazotized reaction can be induced to generate visual color change from blue to yellow, resulting in the nitrite level related ratio variation for the absorbance intensity at 665 and 450 nm. Besides, to the realize the demand of point of care monitor of nitrite, a portable sensor was built containing a dark box by a UV lamp and an intelligent smartphone. In the colorimetry smartphone modes, the linear ranges of nitrite are 1–290, and 3.3–250 μM, with related detection limits of 0.9, and 2.96 μM, respectively. This strategy was further used to detect nitrite in river water with outstanding results with the dual mode. Therefore, the proposed dual mode detection approach provides promising potential for self-house monitor of nitrite, which will greatly improve the analysis efficiency and large scale determination in human life quality.