In Situ Conversion of MnO Nanoparticles with Excellent Oxidase-like Activity in Building a Fluorescence Sensing Platform for Cysteine and Cu²⁺ Sequential Detection

Abstract

Consecutive detection of cysteine (Cys) and Cu2+ in the same condition is in great demand to shorten the detection time and simplify the measurement process. In this study, MnO nanoparticles supported on porous carbon (MnO NPs/PC) were prepared by the in situ conversion of MnO2 nanobelts and explored as a robust oxidase mimic to initiate Amplex Red (AR) oxidation with the generation of the strong fluorescent product resorufin. Cys shows an obvious suppression effect on the oxidase-like activity of MnO NPs/PC with a decline in the fluorescence of resorufin, while Cu2+ alleviates such inhibition and causes partial fluorescence recovery; as a result, the MnO NPs/PC-AR system can be used as an “off–on” fluorescence sensing platform to realize the sequential detection of Cys and Cu2+. Benefiting from the high activity of MnO NPs/PC and the commercial availability of AR, the proposed sensing platform holds the merits of high sensitivity and facile construction. This work not only explores the oxidase mimetic activity of MnO NPs/PC in triggering AR oxidation but also provides a convenient and sensitive “off–on” fluorescence sensing platform for Cys and Cu2+ sequential detection.