Novel Cu2+-specific “Turn-ON” fluorescent probe based on [5]helicene with very large Stokes shift and its potential application in living cells

Abstract

A novel fluorescent sensor based on a [5]helicene dye bearing hydrazine (1) was synthesized through a simple reaction. The sensor was fully characterized by NMR, single crystal X-ray analysis, and HRMS spectrometry. Fluorescence technique was also employed to study the ability of 1 for the detection of Cu²⁺ among different ions. It was found that 1 exhibited a highly sensitive fluorescence response toward Cu²⁺ with a “Turn-ON” fluorescence enhancement and a very large Stokes shift of ∼183 nm. The sensor selectively bound to Cu²⁺ in the presence of various metal ions, such as Cd²⁺, Ag⁺, Pb²⁺, Zn²⁺, Ni²⁺, Hg²⁺, K⁺, Li⁺, Ba²⁺, Al³⁺, Fe²⁺, Co²⁺, Mn²⁺, Ca²⁺, Na⁺, and Mg²⁺ in aqueous acetonitrile solution. The Cu²⁺ detection limit was 2.6 ppb (3σ/slope), which was lower than the permissible concentration in drinking water determined by the US EPA and WHO. In addition, the sensor can enhance fluorescence from the intracellular area in the HepG2 cellular system. Hence, it has the potential for the detection of Cu²⁺ in biological samples.