Fig. 3.

Single-photon fluorescence imaging of APG4 PAMAM-PEG immobilized in a silica sol-gel. (a) Image of a condensed sol-gel preparation containing the APG4 PAMAM-PEG nanosensor. During the process of condensation, the thin layer of silica sol-gel attached to the coverslip cracks into small fragments. (b) Fluorescence recording of the nanosensor embedded in sol-gels during superfusion of extracellular-like solutions containing 0, 5, 10, 15, or 20 mM ${\mathrm{K}}^{+}$, and showing the responsiveness and reversibility of sensor response.