Surface PEGylation of ionophore-based microspheres enables determination of serum sodium and potassium ion concentration under flow cytometry.

We present here an ionophore-based ion-selective optode (ISO) platform to detect potassium and sodium concentrations in serum through flow cytometry. The ion-selective microsensors were based on polyethylene glycol (PEG)-modified polystyrene (PS) microspheres (PEG-PS). Ratiometric response curves were observed using peak channel fluorescence intensities for K+ (10-6 M to 0.1 M) and Na+ (10-4 M to 0.2 M) with sufficient selectivity for clinical diagnosis. Due to the matrix effect, proteins such as albumin and immunoglobulin caused an obvious increase in response for serum sample determination. To solve this problem, 4-arm PEG chains were covalently attached onto the surface of PS microspheres through a two-step reaction, which improved the stability and combated pollution of microspheres. As a preliminary application, potassium and sodium concentrations in human serums were successfully determined by the PEG-PS microsensors through flow cytometry.