Fluorescent chemosensors for copper(II) ion: Structure, mechanism and application

Among the transition metal ions, copper is the third most abundant essential trace metal element in human body, and is also required by many living organisms for normal physiological processes, while excessive levels of Cu2+ are highly toxic to organisms and generate enormous quantities of pollution to our living environment. It is an essential and key issue to devise more sensitive and selective fluorescent chemosensors to efficiently evaluate the Cu2+ levels in environmental and biological systems. This review summarizes the important advances in fluorescent chemosensors for Cu2+, mainly made in the recent five years. Three types of chemosensors, namely 'on-off, 'off-on' and 'ratiometric', are categorized according to fluorescence signal changes, and each type is further classified into several sections according to the molecular structure features and/or recognition mechanisms. Additionally, the Cu2+-promoted reaction based chemosensors are also discussed by the different reactions like hydrolysis, oxidation and reduction. The molecular structures, recognition mechanism and applications of the fluorescent chemosensors are emphatically discussed, and the future perspective is overviewed briefly. (C) 2017 Elsevier B.V. All rights reserved.