Time Gated Luminescence Imaging of Immunolabeled Human Tissues

Multiplexed immunofluorescence imaging of formalin-fixed, paraffin-embedded tissues is a powerful tool for investigating proteomic profiles and diagnosing disease. However, conventional immunofluorescence with organic dyes is limited in the number of colors that can be simultaneously visualized, is made less sensitive by tissue autofluorescence background, and is usually incompatible with commonly used hematoxylin and eosin staining. Herein, we demonstrate the comparative advantages of using time-gated luminescence microscopy in combination with an emissive Tb(III) complex, Lumi4-Tb, for tissue imaging in terms of sensitivity, multiplexing potential, and compatibility with common immunohistochemistry protocols. We show that time-gated detection of millisecond-scale Tb(III) emission increases signal-to-noise ratio relative to conventional steady-state detection of organic dye fluorescence and permits visualization of low-abundance tissue markers such as Bcl-6 or MSH-6. In addition, temporal separation of long- and short-lifetime (∼nanosecond) signals adds a second dimension for multiplexing and also permits detection of intermolecular Tb(III)-to-dye Förster resonance energy transfer. Furthermore, we demonstrate that the Lumi4-Tb complex is compatible with tyramide signal amplification and, unlike conventional organic dyes, can be reliably used on tissue stained with hematoxylin and eosin. Our results indicate that time-gated luminescence microscopy using Tb(III) labels can provide a sensitive and robust method to perform multiplexed immunofluorescence on archived or clinical tissue specimens.