Fig. 4. Parallelizing pH-gated molecular state encoding.

(A) Epifluorescence intensity versus pH for an aqueous fluorescein solution (10 μM). (B) On-chip measured pixel-center OCP and pH as a function of time in an example stimulated pixel. (C) Epifluorescence imaging and on-chip pH imaging juxtaposed side by side (left and middle). In each of the pixels selected for stimulation, an appreciable fraction of fluorescein molecules enter state “1” every time acidic pH voxels are formed (e.g., pH 5.54 converts approximately 20% to state 1), while nearly all molecules are left in state 0 in each of the unstimulated pixels. In the state matrix (right), matrix element 1 refers to a pixel’s collective status where an appreciable fraction of fluorescein molecules are in state 1, whereas matrix element 0 refers to the status where nearly all molecules are in state 0. The ceiling height is about 14 μm. a.u., arbitrary units.