Two-Photon Endomicroscopy for Image-Guided Magnetic Micro-Agents

Magnetic microrobotics holds promise for minimally invasive biomedical applications, yet imaging in this field still relies predominantly on external modalities. Endoscopic imaging offers an alternative route for in situ visualization and micro-agent guidance, but its use in microrobotics has so far remained limited to standard endoscopic modalities. This study demonstrates two-photon endomicroscopy (TPE) for real-time fluorescence imaging of magnetically actuated micro-agents. Dynamic experiments under rotating magnetic fields support motion analysis across multiple actuation frequencies. In addition, dual-color imaging enables analysis of mixed magnetic and non-magnetic micro-agent populations labeled with distinct fluorescent dyes. Imaging through biological tissue shows that magnetic micro-agents remain detectable through a 140 $\mu m$ rat mammary gland tissue layer. The feasibility of image-guided re-centering of a HeLa cell spheroid within the TPE field of view is also shown, compensating for displacement induced by the magnetic micro-agents. These results extend TPE from passive observation to active image-guided functionality in microrobotic systems.