Synergistic integration of Au nanoparticles, Co-MOF and MWCNT as biosensors for sensitive detection of low-concentration nitrite

Nitrite has been widely existed in food and natural environment systems. To protect the environmental safety and human health, non-enzymatic nitrite sensor with reasonable linear response range, low detection limit (LOD) and excellent storage stability are highly desirable. Herein, we designed a hierarchical structure including the multiwalled carbon nanotube (MWCNT) as substrates, Co-based metal-organic framework (Co-MOF) and high-dispersed small Au nanoparticles (AuNPs) (denoted as AuNPs/Co-MOF/MWCNT). Small Co-MOF nanoplates were firstly grown on the surface of MWCNT, and then provides abundant adsorption sites for catching Au ions. The Co-MOF plays a crucial role in controlling the growth and dispersion of AuNPs, and limits particle growth during the reduction process. Combining MWCNT with Co-MOF can significantly improve the electron transport capability of Co-MOF. On the other hand, small and uniform AuNPs distributed on Co-MOF can reduce the operating voltage and significantly enhance their catalytic activity for nitrite oxidation. Owing to the intriguing synergy between the components, the obtained nitrite sensor device exhibits a broad linear response range from 1 to 1000 µM and a LOD of 0.4 µM (S/N = 3) with a fast response balance (the response time ≈ 3.5 s) at a voltage of 0.72 V. Moreover, this sensor remains 94.5% of their initial response after 20 days of storage at room temperature in air. These results suggested that the AuNPs/Co-MOF/MWCNT nanocomposite has a good application prospect in the amperometric determination of nitrite.