Fig. 7.

Spectral properties and potassium sensitivity of the APG4/AF568 PAMAM-PEG ratiometric nanosensor. (a) Schematic representation of the nanosensor design comprising a generation 5 (poly)amidoamine dendrimer (PAMAM; red) with a 1,4-diaminobutane core (DAB; black), as well a polyethyleneglycol (PEG; blue) outer shell, as depicted in Fig. 1. This dual-dye ratiometric version encapsulates the ${\mathrm{K}}^{+}$-sensitive indicator Asante Potassium Green 4 (APG4) and the ${\mathrm{K}}^{+}$-insensitive dye Alexa Fluor 568 (AF568) in a $1:1$ molar ratio. (b) Single-photon in vitro emission spectra (${\lambda }_{\mathrm{ex}}$ 515 nm) of the ratiometric nanosensor with a ${\mathrm{K}}^{+}$ titration in the range 0-50 mM, corrected for dilution.