<p>The&#xa0;development is shown&#xa0;of rod-shaped manganese-based metal–organic frameworks (Mn-MOFs) as hot- and cold-adapted oxidase-like nanozymes, with strong magnetic properties. These Mn-MOFs enable highly sensitive detection of nitrite ions, utilizing both convenient colorimetric ratio analysis and a visual instrument-free-based approach compatible with smartphone-based detection. The Mn-MOF showed multi-functional activity, such as cold/hot-adapted and magnetic oxidase-like activity, catalyzing the oxidation of chromogenic substrates 3,3′,5,5′-tetramethylbenzidine (TMB)&#xa0;to blue oxidized TMB (oxTMB). Mn-MOF shows high oxidase activity with&#xa0;<i>V</i>max&#xa0;of 1.39 × 10⁻⁸&#xa0;M/s and <i>K</i>m of&#xa0;0.068&#xa0;mM for TMB oxidation. Nitrite ions further react with oxTMB to form a yellow color via diazotization resulting in the ratiometric change in absorbance (A₆₅₂/A₄₆₁). The color ratio is also quantified through the naked eye and/or smartphone app by analyzing RGB values, providing a rapid, portable, and cost-effective method for on-site detection. When applying Mn-MOF for smartphone-based nitrite detection, it performs excellent detection, with a linear range of 5.0–55.0&#xa0;µM and a limit of detection of 0.18&#xa0;µM, superior to most of the oxidase nanozyme-based nitrite sensing platforms. The detection platforms develop sensing probes using a reusable nanozyme that enables highly sensitive and selective detection of nitrite, featuring a broad linear range and a low limit of detection.</p> Graphical Abstract <p></p>