A reversible calix[4]arene armed phenolphthalein based fluorescent probe for the detection of Zn2+ and an application in living cells

A reversible and easy assembled fluorescent sensor based on calix4]arene and phenolphthalein (C4P) was developed for selective zinc ion (Zn²⁺) sensing in aqueous samples. The probe C4P demonstrated high selective and sensitive detection towards Zn²⁺ over other competitive metal ions. Interaction of Zn²⁺ with a solution of C4P resulted in a considerable increment in emission intensity at 440 nm (λ_ex = 365 nm) due to the suppression of photoinduced electron transfer (PET) process and the restriction of C=N isomerization . The binding constant (K_a) of C4P with Zn²⁺ was calculated to be 4.50 × 10¹¹ M^?2 and also the limit of detection of C4P for Zn²⁺ was as low as 0.108 μM (at 10^?7 M level). Moreover, the fluorescence imaging in the human colon cancer cells suggested that C4P had great potential to be used to examine Zn²⁺ in vivo.