Endogenous ratiometric fluorescence sensing of N-Methyl-4-nitroaniline based on Mn-doped carbon dots.

N-Methyl-4-nitroaniline (pMNA) is a critical stabilizer for solid rocket propellants. Herein, we develop a label-free ratiometric fluorescence probe based on manganese ion doped carbon dots (Mn-CDs) for the selective detection of pMNA. The Mn-CDs exhibit strong blue fluorescence under excitation at 320 nm. Upon addition of pMNA, the fluorescence intensity at 370 nm of the Mn-CDs was decreased due to an inner filter effect (IFE), while the emission at 470 nm remains unchanged, enabling a ratiometric fluorescence response. This probe shows a detection limit of 0.4 μM and excellent selectivity over various propellant related interferents. A hydrogel-based sensor was further fabricated by embedding the Mn-CDs into a PEGDA matrix, enabling convenient on site detection of pMNA when combined with smartphone-assisted RGB analysis. This work provides a simple and reliable method for rapid on-site monitoring of this propellant stabilizer.