In Situ High‐Resolution Imaging of Live <i>Treponema pallidum</i> Using Catalyst‐Free Bioorthogonal Strategy

ABSTRACT Treponema pallidum ( T. pallidum ) causes syphilis, a sexually transmitted disease that leads to multi‐organ complications and even death. The lack of technology for tracing live T. pallidum greatly impedes understanding of the pathogenesis of T. pallidum . Herein, we firstly designed and developed an in situ high‐resolution imaging strategy to trace live T. pallidum using catalyst‐free bioorthogonal labeling with aggregation‐induced emission luminogens (AIEgens). An activated alkyne‐containing AIEgen, 5‐(4‐(diphenylamino) phenylthiophene‐2‐ynylidene) ketone (named TPA‐TA), was directly reacted with the proteins of T. pallidum through metal‐free click chemistry, without affecting T. pallidum ’s activity. Specially, TPA‐TA enables high‐resolution imaging of live T. pallidum with low background. Both whole phcagocytosis of T. pallidum by THP‐1 cells and dissemination in lesions could be monitored in real time, which helped clarify the interaction between the immune clearance and escape of T. pallidum . In conclusion, this catalyst‐free bioorthogonal labeling strategy enriches the toolkit for exploring and understanding syphilis‐related pathologies.