Fast and sensitive fluorescent and visual sensing of cysteine using Hg-metalated PCN-222

A porphyrinic metal-organic framework, PCN-222, was employed for the fast and sensitive determination of cysteine (Cys) based on its fluorescence (FL) property. A "turn-on" sensor was easily established based on the instant metalation of PCN-222 with Hg2+, and the sensing for Cys primarily derived from the strong binding between Hg and Cys, with the PCN-222 FL fast recovered via the rapid and efficient release of Hg. A more than two orders of magnitude in the linear dynamic range and a limit of detection as low as 60 nM were obtained by using the proposed method based on FL measurement. In particular, the sensing could also be accomplished in a visual manner, with the color change of Hg-metalated PCN-222 easily observed by naked eyes upon the addition of Cys as low as 100 nM. The proposed strategy for Cys sensing also showed advantages including facile preparation and cyclic usage of the probe, fast response (1 min) to Cys, high sensitivity for both FL and visual sensing, and no extra additives such as catalysts nor chromogenic substrates.