An OFF–ON chemosensor for biological and environmental applications: sensing Cd2+ in water using catanionic vesicles and in living cells

Abstract

A new OFF–ON fluorescent chemosensor (L¹) for Cd²⁺ recognition based on a 5-chloro-8-hydroxyquinoline pendant arm derivative of 1,4,7-triazacyclononane ([9]aneN₃) will be presented and its photochemical features in an MeCN–H₂O 1 : 1 (v/v) mixture, in pure water, after inclusion within catanionic vesicles, and in living cells will be discussed. The coordination properties of L¹ both in solution and in the solid state were preliminarily studied and its selectivity towards Cd²⁺versus a set of different metal ions (Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Al³⁺, Hg²⁺, Co²⁺, Ni²⁺, Mn²⁺, Mg²⁺, K⁺, Ca²⁺, Ag⁺, and Na⁺) was verified in MeCN–H₂O 1 : 1 (v/v). In water, upon addition of increasing amounts of Cd²⁺ to L¹ an enhancement of the fluorescence emission was detected. To overcome this serious drawback, L¹ was dissolved in an innovative catanionic vesicular solution based on sodium bis(2-ethylhexyl) sulfosuccinate, a traditional surfactant, and 1-dodecyl-3-methylimidazolium bromide, an ionic liquid. When enclosed within the vesicle bilayers in water, L¹ restored its fluorescence emission property upon addition of Cd²⁺. Remarkably, L¹ enters the cellular membrane of living cells thus allowing the detection of intracellular Cd²⁺. These findings encourage the application of this new fluorescent chemosensor in real samples for histological and environmental analyses.