Quantum Imaging of Bone Tissue Using Entangled Two-Photon Microscopy.

Tracking the progression of the bone resorption process is important for clinical research and development of pharmaceuticals for bone-related diseases. Although fluorescence imaging is found to be one of the powerful tools for studying bone, conventional fluorescence microscopy relies on extremely high excitation powers that induce photobleaching and phototoxic effects on biological samples, preventing long-term observations. To overcome these limitations, we propose a quantum light-based approach using entangled two-photon fluorescence microscopy (ETPFM). We demonstrate ETPFM for imaging fixed demineralized unstained and Hoechst- and DAPI-stained bone sections at photon fluxes nearly 6 orders of magnitude lower than classical two-photon excitation. This quantum-correlated light preserves tissue integrity, eliminates photobleaching, and reveals microstructures with high contrast. Endogenous fluorescence is detected without exogenous dyes, and osteoclast cells are clearly resolved in the stained bone sections. ETPFM thus provides a minimally invasive, quantum-enhanced approach for long-term imaging of bone microenvironments.