Fluorescein as a Visible‐Light‐Induced Oxidase Mimic for Signal‐Amplified Colorimetric Assay of Carboxylesterase by an Enzymatic Cascade Reaction

Abstract

We have found that fluorescein possesses high visible-light-induced oxidase mimetic activity and could transform colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB) without unstable and destructive H O under visible-light illumination. Instead, fluorescein uses oxygen as a mild and green electron acceptor, and its activity can be easily controlled by the switching "on/off" of visible light. In addition, the visible-light-induced catalytic mechanism was elucidated in detail and, as the main reactive species h and O accounted for TMB oxidation. Based on the fact that fluorescein diacetate (FDA) possessed no activity and generated active fluorescein in situ in the presence of carboxylesterase (CaE), a signal-amplified sensing platform through a cascade reaction for CaE detection was constructed. Our proposed sensing system displayed excellent analytical performance for the detection of CaE in a wide linear range from 0.040 to 20 U L with a low detection limit of 0.013 U L . This work not only changes the conventional concept that fluorescein is generally considered to be photocatalytically inert, but also provides a novel sensing strategy by tailoring the enzyme mimetic activity of fluorescein derivatives with analyte.

In Situ Enzyme Immobilization with Oxygen‐Sensitive Luminescent Metal–Organic Frameworks to Realize “All‐in‐One” Multifunctions

“…The value of K M (glucose) determined with the GOx@MAF‐2 composite is lower than that of free GOx (20±2 m m ) obtained previously (see Table S4) . As K M represents the substrate concentration at which half of the active sites of the enzyme are occupied by the substrate, the lower K M value suggests a higher substrate affinity for GOx@MAF‐2 compared with free GOx. This might be attributable to the increased folding stability of GOx in the confined spaces of MAF‐2 favoring a shift of the equilibrium from the unfolded state to the native state .…”

A Minireview of Recent Reported Carboxylesterase Fluorescent Probes: Design and Biological Applications

“…Zheng et al. constructed a carboxylesterase detecting platform based on fluorescein diacetate (FDA), which exhibit no activity in normal situation (Figure f) . In the presence of carboxylesterase, however, FDA generated active fluorescein.…”

CeO2‐Encapsulated Hollow Ag–Au Nanocage Hybrid Nanostructures as High‐Performance Catalysts for Cascade Reactions

“…However, poor stability and high cost in preparation and purification of biological enzymes make it difficult to be widely used . Inspired by natural enzymes, many researchers expect to achieve multistep complex reactions by hybrid materials with easy storage, low‐cost of preparation, flexibility in composition, and stable structure . Besides, on account of the improvement of atomic efficiency, the cascade reactions usually can achieve more than one‐step reaction.…”