Rational Design of Fluorogenic and Spontaneously Blinking Labels for Super-Resolution Imaging

Abstract

Rhodamine dyes exist in equilibrium between a fluorescent zwitterion and a nonfluorescent lactone. Tuning this equilibrium toward the nonfluorescent lactone form can improve cell-permeability and allow creation of “fluorogenic” compounds—ligands that shift to the fluorescent zwitterion upon binding a biomolecular target. An archetype fluorogenic dye is the far-red tetramethyl-Si-rhodamine (SiR), which has been used to create exceptionally useful labels for advanced microscopy. Here, we develop a quantitative framework for the development of new fluorogenic dyes, determining that the lactone–zwitterion equilibrium constant ( K _L–Z) is sufficient to predict fluorogenicity. This rubric emerged from our analysis of known fluorophores and yielded new fluorescent and fluorogenic labels with improved performance in cellular imaging experiments. We then designed a novel fluorophore—Janelia Fluor 526 (JF ₅₂₆)—with SiR-like properties but shorter fluorescence excitation and emission wavelengths. JF ₅₂₆ is a versatile scaffold for fluorogenic probes including ligands for self-labeling tags, stains for endogenous structures, and spontaneously blinking labels for super-resolution immunofluorescence. JF ₅₂₆ constitutes a new label for advanced microscopy experiments, and our quantitative framework will enable the rational design of other fluorogenic probes for bioimaging.

Abstract

We developed a general rubric for creating fluorogenic stains, resulting in the novel fluorophore JF ₅₂₆. This dye can be used in numerous imaging modalities including super-resolution microscopy.