Figure 1. Schematic diagram illustrates the design of a “turn-on” molecular probe specific to vitamin C with long-lived luminescence suitable for time-gated luminescence microscopy (TGLM) system.

(a) The luminescence probe TOB-Eu³⁺ turns on in its hydroxylamine derivative form of TOHB-Eu³⁺ in the presence of vitamin C (photographs show luminescence colours of the complex solutions under a 365 nm UV lamp). (b) The TGLM system employs a rapid-switching flash lamp synchronized to a time-gated optical chopper in front of the camera. The camera is externally shut off during the excitation pulse period, and a short time delay is given to allow the short-lived autofluorescence to vanish before the chopper opens for long-lived luminescence detection in absence of optical backgrounds.