Rational Design of a Polymer-Based Ratiometric K + Indicator for High-Throughput Monitoring Intracellular K + Fluctuations.

Highly selective fluorescent K + sensors are of great importance for monitoring K + fluctuations in various biological processes. In particular, highly efficient ratiometric K + sensors that can emit in dual wavelengths and facilitate the quantitative determination of K + are highly anticipated. Herein, we present the first polymer-based ratiometric fluorescent K + indicator ( PK1 ) for quantitatively detecting K + in aqueous solutions and high-throughput monitoring K + fluctuations in living cells. PK1 was synthesized by conjugating a small molecular K + probe and a red emission reference dye to a hydrophilic polymer skeleton. The newly synthesized PK1 can form highly stable nanoparticles in aqueous solutions and work in 100% water without the aid of any organic solvents or surfactants. PK1 is sensitive to K + with a fluorescence enhancement of sevenfold after interactions with K + at 1000 mM and inert to other metal ions, physiological pH, or dye concentration vibrations. More importantly, the fluorescence intensity ratio at 572 and 638 nm is linearly correlated with log [K + ] in the range of 2-500 mM ( R 2 = 0.998), which will facilitate the quantitative detection of K + . Practical application of PK1 in detecting different K + -rich samples demonstrates its great potential in quantitative detection of K + . PK1 can be quickly internalized by live cells and shows no obvious cytotoxicity. We also demonstrate that PK1 could be used for monitoring K + fluctuations under different stimulations by using a confocal microscope and especially a microplate reader, which is high throughput and time saving. The rational design of PK1 will broaden the design concept of ratiometric fluorescent K + sensors and facilitate the quantitative detection of K + .