A contrast marker for indicating a presence of a target cell in an environment comprises a fluorophore, an NMP, and a short spacer and a long spacer linking the fluorophore to the NMP. The short spacer holds the fluorophore at a quenching distance from the NMP and the long spacer holds the fluorophore at a fluorescence enhancing distance from the NMP. The short spacer is configured to be cleaved by a molecule characterizing the target cells.