Development of a molecular K+ probe for colorimetric/fluorescent/photoacoustic detection of K

The potassium ion (K + ) plays significant roles in many biological processes. To date, great efforts have been devoted to the development of K + sensors for colorimetric, fluorescent, and photoacoustic detection of K + separately. However, the development of molecular K + probes for colorimetric detection of urinary K + , monitoring K + fluxes in living cells by fluorescence imaging, and photoacoustic imaging of K + dynamics in deep tissues still remains an open challenge. Herein, we report the first molecular K + probe ( NK2 ) for colorimetric, fluorescent, and photoacoustic detection of K + . NK2 is composed of 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) as the chromophore and phenylazacrown-6-lariat ether (ACLE) as the K + recognition unit. Predominate features of NK2 include a short synthetic procedure, high K + selectivity, large detection range (5–200 mM), and triple-channel detection manner. NK2 shows good response to K + with obvious color changes, fluorescence enhancements (about threefold), and photoacoustic intensity changes. The existence of other metal ions (including Na + , Mg 2+ , Ca 2+ , Fe 2+ ) and pH changes (6.5–9.0) have no obvious influence on K + sensing of NK2 . Portable test strips stained by NK2 can be used to qualitatively detect urinary K + by color changes for self-diagnosis of diseases induced by high levels of K + . NK2 can be utilized to monitor K + fluxes in living cells by fluorescent imaging. We also find its excellent performance in photoacoustic imaging of different K + concentrations in the mouse ear. NK2 is the first molecular K + probe for colorimetric, fluorescent, and photoacoustic detection of K + in urine, in living cells, and in the mouse ear. The development of NK2 will broaden K + probes’ design and extend their applications to different fields. Graphical abstract