α-Cyanostilbene fluorophores as versatile dual-function imaging agents: from imaging lipid droplet dynamics in live cells to selective Gram-positive bacterial detection.

The development of fluorescent probes that function effectively in both eukaryotic and prokaryotic systems remains a major challenge in chemical biology. We report three α-cyanostilbene fluorophores with different structures: pyrene (P1), naphthalene (P2), and triphenylamine (P3). We investigated their use in biological imaging. The molecules exhibit intramolecular charge transfer, polarity-dependent emission changes, and aggregation-induced emission (AIE) features. In live COS-7 cells, these molecules target lipid droplets while causing little to no cytotoxicity. The probe P3, which contains triphenylamine, exhibited the strongest AIE response and the best cellular performance, maintaining stable lipid droplet retention for over 6 hours without relocating to other organelles. P3 allowed us to visualize changes in lipid droplets during LPS-induced inflammatory stress and tunicamycin-induced ER stress. This showed a 2.2-fold increase in lipid droplet number during ER stress. For bacterial imaging, P2 and P3 selectively stain Gram-positive bacteria, such as S. aureus and C. glutamicum, and exhibit very little fluorescence with Gram-negative species. This suggests that staining selectivity arises from barriers in the outer membrane rather than from bacterial viability. Overall, these findings indicate that α-cyanostilbene fluorophores provide a valuable dual-function imaging tool, linking eukaryotic lipid droplet imaging with Gram-positive bacterial detection within a single molecular framework.