Highly sensitive electrochemical analysis of tunnel structured MnO₂ nanoparticle-based sensors on the oxidation of nitrite

Three MnO₂ nanoparticles with different tunnel structures, α-, β-, and γ-MnO₂, were synthesized and characterized. We demonstrated and compared their capabilities on the electrochemical oxidation of nitrite, providing a new perspective for MnO₂ or MnO₂ based materials on sensing application. α-MnO₂ exhibited higher electrochemical reactivity than β- or γ-MnO₂, which was ascribed to its higher conductivity, more exposure to MnO₆ edges, longer average Mn–O bond length, and lower Mn average oxidation state(AOS). We hereby reported the first α-MnO₂ nanoparticle-based electrochemical sensor for nitrite sensing. A highly controlled micro-plotter was used to deposit the MnO₂ nanoparticles for the sensor fabrication, providing a micro-pattern of the sensing surface area of MnO₂ and ensuring the reproducibility and sensitivity of this MnO₂ based sensor. Using differential pulse voltammetry, a detection range of 10–800 μM of nitrite was accomplished along with a sensitivity of 17.1 μA μM⁻¹ and a detection limit of 0.5 μM.