Design and synthesis of a squaraine based near-infrared fluorescent probe for the ratiometric detection of Zn2+ ions

• A novel ratiometric near-infrared fluorescent probe (SQ-1) for Zn2+ has been first synthesized based on squaraine dye.
• SQ-1 can detect Zn2+ in acetone by a 22 nm red-shift and a remarkable enhancement of the fluorescence intensity.
• The detection identification for Zn2+ will not be impacted by the biologically ubiquitous ions such as Na+, K+, Mg2+ and Ca2+.

A squaraine based ratiometric near-infrared fluorescent probe with bipyridyl binding arms for Zn2+ (SQ-1) has been designed and synthesized. SQ-1 exhibits a selective fluorogenic response to Zn2+ in acetone by a 22 nm red-shift and a remarkable enhancement of the fluorescence intensity. Further study shows that the calculated detection limit for Zn2+ is 6.1 × 10−8 M (3σ/k) and the identification for Zn2+ will not be impacted by competing ions such as Na+, K+, Mg2+, Ca2+, Pb2+, Mn2+, Ba2+ and Hg2+. The binding mode between SQ-1 and Zn2+ has also been discussed.

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