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

Abstract

Metal–organic frameworks (MOFs) for enzyme immobilization have already shown superior tunable and designable characteristics, however, their diverse responsive properties have rarely been exploited. In this work we integrated a responsive MOF into a MOF–enzyme composite with the purpose of designing an “all‐in‐one” multifunctional composite with catalytic and luminescence functions incorporated into a single particle. As a proof‐of‐concept, glucose oxidase (GOx) was encapsulated in situ within an oxygen (O2)‐sensitive, noble‐metal‐free, luminescent CuI triazolate framework (MAF‐2), denoted as GOx@MAF‐2. Owing to the rigid scaffold of MAF‐2 and confinement effect, the GOx@MAF‐2 composite showed significantly improved stability (shelf life of 60 days and heat resistance up to 80 °C) as well as good selectivity and recyclability. More importantly, owing to the O2 sensitivity of MAF‐2, the GOx@MAF‐2 composite exhibited a rapid and reversible response towards dissolved O2, thereby allowing direct and ratiometric sensing of glucose without the need for chromogenic substrates, cascade enzymatic reactions, or electrode systems. High sensitivity with a detection limit of 1.4 μm glucose was achieved, and the glucose levels in human sera were accurately determined. This strategy has led to a new application for MOFs that can be facilely extended to other MOF–enzyme composites due to the multifunctionality of MOFs.

Metal–Organic Framework-Based Enzyme Biocomposites

“…This can be easily performed by following the reaction with an O 2 probe. An interesting approach for detection of the consumed O 2 was developed by Xu et al, who used the luminescent properties of MAF-2 (Cu + and 3,5-diethyl-1,2,4-triazole) to create a glucose sensor by encapsulating GOx . The fluorescence of MAF-2 is quenched in the presence of O 2 .…”

“…An interesting approach for detection of the consumed O 2 was developed by Xu et al, who used the luminescent properties of MAF-2 (Cu + and 3,5-diethyl-1,2,4triazole) to create a glucose sensor by encapsulating GOx. 357 The fluorescence of MAF-2 is quenched in the presence of O 2 . Hence, the activity of GOx can be monitored by detecting an increase in fluorescence with decreasing O 2 .…”

Boosting Enzyme Activity in Enzyme Metal–Organic Framework Composites

“…Over the past decades, many glucose-sensing devices have been developed by coupling enzyme–MOF composites with colorimetric or fluorescent indicators . Recently, Xu et al encapsulated glucose oxidase in situ in an oxygen-sensitive and luminescent MOFs for ratiometric sensing of glucose . The composites, free of additional indicator, possess a detection limit of 1.4 μM glucose as well as improved shelf life and thermostability.…”

“… 109 Recently, Xu et al encapsulated glucose oxidase in situ in an oxygen-sensitive and luminescent MOFs for ratiometric sensing of glucose. 84 The composites, free of additional indicator, possess a detection limit of 1.4 μM glucose as well as improved shelf life and thermostability.…”

Recent Progress in Metal–Organic Framework (MOF) Based Luminescent Chemodosimeters

“…MOF-based luminescent chemosensors have shown great potential in the detection of various analytes, including volatile organic compounds [25,26,27], ions (especially for metal cations) [28,29,30,31], gases [32,33,34,35], as well as for monitoring pH [36,37,38,39,40,41,42], humidity [43,44,45], and temperature [46,47,48]. Compared to the relatively well-developed fluorescent MOFs chemosensors, MOF-based chemodosimeters are expected to be more efficient in terms of selectivity, as they exploit the specific reactivities of certain target analytes [24].…”