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The design of responsive luminescent probes and sensors Cite this: Chem. Soc. Rev., 2021, 50, 8193 David Parker, *ab Jack D. Fradgleya and Ka-Leung Wong b

The principles of the design of responsive luminescent probes and sensors based on lanthanide emission are summarised, based on a mechanistic understanding of their mode of action. Competing kinetic pathways for deactivation of the excited states that occur are described, highlighting the need to consider each of the salient quenching processes. Such an analysis dictates the choice of both the ligand and its integral sensitising moiety for the particular application. The key aspects of quenching involving electron transfer and vibrational and electronic transfer are highlighted and exemplified. Responsive systems for pH, pM,

pX and pO2 and selected biochemical analytes are distinguished, according to the nature of the optical signal observed. Signal changes include both simple and ratiometric intensity measurements, emission lifetime variations and the unique features associated with the observation of circularly polarised

Creative Commons Attribution 3.0 Unported Licence. luminescence (CPL) for chiral systems. A classification of responsive lanthanide probes is introduced.

Examples of the operation of probes for reactive oxygen species, citrate, bicarbonate, a1-AGP and pH are used to illustrate reversible and irreversible transformations of the ligand constitution, as well as the reversible changes to the metal primary and secondary coordination sphere that sensitively perturb the Received 29th March 2021 ligand field. Finally, systems that function by modulation of dynamic quenching of the ligand or metal DOI: 10.1039/d1cs00310k excited states are described, including real time observation of endosomal acidification in living cells, rapid urate analysis in serum, accurate temperature assessment in confined compartments and high throughput rsc.li/chem-soc-rev screening of drug binding to G-protein coupled receptors. This article is licensed under a

a Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK. E-mail: [email protected] b

Open Access Article. Published on 01 June 2021. Downloaded 10/8/2021 4:26:47 AM. Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China

David Parker FRSC FRS was Jack Fradgley graduated in 2017 educated in the state sector and with a First Class Honours degree read Chemistry at Oxford in Chemistry from Durham University (1974–1978), where he University, working for his final studiedwithJohnBrownfora year project with Gareth Williams DPhil (1980) before taking up a on luminescent noble metal NATO Fellowship with Jean-Marie coordination complexes. He gained Lehn in Strasbourg. He was his PhD working with David Parker appointed in the autumn of 1981 in 2021, working on pH responsive as a Lecturer in Chemistry at chiral complexes. During Durham University, rising to this period he worked closely with Professor in 1992 and served Cisbio Bioassays in France, and David Parker twice as Head of Department. He Jack D. Fradgley was a co-inventor on a patent has gained several national and application in 2020. international awards and prizes for his multidisciplinary research that has embraced the design of a wide variety of sensing systems, the creation of targeted imaging and therapeutic agents and conjugates, as well as major contributions to chiral analysis. In each domain his work has been characterized by incisive mechanistic studies.

This journal is © The Royal Society of Chemistry 2021 Chem. Soc. Rev., 2021, 50, 8193–8213 | 8193 View Article Online Review Article Chem Soc Rev 1. Introduction

The low molar absorption coefficients of the lanthanide ions, associated with the forbidden nature of f