Hydrophilicity-Differentiated Albumin Sensitivity of Polymethine Dyes <i>in Vivo</i> for Specialized Bioimaging

Polymethine dyes are invaluable tools for studying biological processes <i>in vivo</i> due to their superior fluorescence properties and biological functions. However, despite the availability of excellent polymethine dyes, their uncontrollable interactions with albumin often limits their applications to specialized contexts. In this study, we present a general strategy for modulating the albumin sensitivity of dyes through a hydrophilicity-differentiated bidirectional regulation approach. Experimental data and computational simulations demonstrate that sulfonate positioning is crucial for suppressing hydrophobic interaction-mediated albumin-dye binding. Furthermore, this effect is enhanced when coupled with an optimal length of the polymethine bridge, which governs the postbinding responsiveness of the dye. Together, these factors establish the regulatory basis for differentiating albumin-sensitive and insensitive dyes. Consequently, a hydrophilic and albumin-insensitive Cy5 was identified and constructed a probe, showing potential for detecting hepatic fibrosis in mice without albumin interference (a protein primarily produced in the liver). Conversely, an albumin-sensitive Cy5 was synthesized by reducing the hydrophilicity of a Cy5 framework with a high TICT tendency, which can monitor blood-brain barrier function <i>in vivo</i>.