Fig. 2.

(A) SM fluorescent spots of 2 (verified by one-step photo-bleaching) in PVA film (532 nm excitation, 91 W cm⁻²). (B) Survival probability histogram of 2 doped into PVA films at nM concentrations with an average 71 000 detected photons, corresponding to an average of 1.7 × 10⁶ photons emitted by each SM. (C) Schematic of in vitro experiment where 4 (structure shown in Chart 1) was covalently attached to poly-lysine coverslips immersed in PBS buffer (pH 7.4) containing free NADH and NTR enzyme. Enzymatically generated fluorophores remained attached to surface lysines. (D) Bulk fluorescence at the surface after NADH and NTR addition. Inset: bulk fluorescence of 4 before NTR reaction (same contrast). Bulk fluorescence of all control incubation conditions is shown in Fig. S6.† sample and control details in ESI.†