Ratiometric Sensing of Alkaline Phosphatase Based on the Catalytical Activity from Mn-Fe Layered Double Hydroxides Nanosheets
Two-dimensional (2D) Mn-Fe layered double hydroxides (LDH) nanosheets are firstly examined to mediate O-phenylenediamine (OPD) based fluorescent switch in the presence of ascorbic acid (AA). On one hand, Mn-Fe LDH mimicked the functions of oxidase to catalyze the oxidation of OPD to OPDox, emitting the fluorescence at 565 nm. On the other hand, Mn-Fe LDH acts as the superior catalyst for the reaction between AA and OPD to generate the 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxalin-1(3H)-one (N-heterocyclic compound) with an emergence of the maximum emission at 425 nm (ca. 6 folds). The presence of AA not only induces the enhanced emission at 425 nm from N-heterocyclic compound, but also leads to the fluorescence at 565 nm decreased due to the decomposition of Mn-Fe LDH nanosheets. On the basis of the reversed fluorescent response at 425 and 565 nm, ratiometric fluorescent sensing methods (ΔF425 nm/ΔF565 nm) are developed for the determination of AA. With the assistance of alkaline phosphatase (ALP), the activity of ALP can be monitored using the ratiometric platform based on the hydrolyzing ascorbic acid 2-phosphate to yield AA with the detection limit of 0.16 mU/mL. Different from the traditional ratiometric sensing platform, where two fluorescent probes are often introduced, the present ratiometric system derived from one signal precursor holds great potential in developing the facile platform and broadens the application of 2D nanomaterials in biological field.