PNIPAM-based extracellular K+ fluorescent sensor for high-throughput analysis

Abstract We report on the fabrication of K+ fluorescent sensor P2 based on thermoresponsive poly(N-isopropylacrylamide) and small molecule K+ fluorescent sensor KS. P2 changed its size with a range from 35 °C to 42 °C and exhibited lower critical solution temperature (LCST) at 38 °C. The LCST affected the polymer’s nanostructures and microenvironment of KS, which in turn affected P2’s fluorescence intensities and responses to K+. Furthermore, P2 exhibited high selectivity and sensitivity to K+ with a dynamic response range from 1 to 20 mM, enabling its suitableness for extracellular K+ analysis. The sensor was further used to in situ monitor the K+ fluctuation of Escherichia coli and B. Subtilis 168 bacteria under lysozyme stimulation in 96 well plate by a high throughput analysis approach, and cell species dependent K+ release was observed. The PNIPAM-based K+ sensor P2 shows potential application in antimicrobial drugs/peptides screening.