Recent Advances in Developing Lanthanide Metal-Organic Frameworks for Ratiometric Fluorescent Sensing

Abstract

Fluorescent probes have attracted special attention in developing optical sensor systems due to their reliable and rapid fluorescent response upon reaction with the analyte. Comparing to traditional fluorescent sensing systems that employ the intensity of only a single emission, ratiometric fluorescent sensors exhibit higher sensitivity and allow fast visual screening of analytes because of quantitatively analyzing analytes through the emission intensity ratio at two or more wavelengths. Lanthanide metal-organic frameworks (LnMOFs) are highly designable multifunctional luminescent materials as lanthanide ions, organic ligands, and guest metal ions or chromophores are all potential sources for luminescence. They thus have been widely employed as ratiometric fluorescent sensors. This mini review summarized the basic concept, optical features, construction strategies, and the ratiometric fluorescent sensing mechanisms of dual-emitting LnMOFs. The review ends with a discussion on the prospects, challenges, and new direction in designing LnMOF-based ratiometric fluorescent sensors.

Keywords: dual emission; lanthanide; luminescence; metal–organic frameworks; ratiometric sensing.

FIGURE 1

Schematic representation of four possible emissive components (A), and three typical scenarios for the construction of dual-emitting ratiometric fluorescent sensors in LnMOFs (B–D).

FIGURE 2

In a dual-emitting system, analyte can be probed through the four commonly employed mechanisms. Analyte interacts with the sensor by suppressing (A–C) or enhancing (D–F) the antenna effect. Reproduced from Yu et al. (2020) with permission from American Chemical Society and Zhang et al. (2018) with permission from The Royal Society of Chemistry. The analyte may also change the coordination environment of Ln (G,H) or modulate the lanthanide-lanthanide energy transfer (I,J). Reproduced from Zeng et al. (2020a) with permission from American Chemical Society and Zhang et al. (2016a) with permission from The Royal Society of Chemistry.