Bendable graded index lens-based laser-scanning optical-resolution photoacoustic microendoscopy

Minimally invasive, three-dimensional (3D), flexible in-situ optical microendoscopy with cellular resolution has the potential to elucidate key biological mechanisms inaccessible with conventional approaches. Developing such microendoscopy is, however, still technically challenging. To this end, we recently proposed a bendable graded index (bGRIN) lens two-photon microendoscopy, with imaging quality resistant to lens bending. In this Letter, we improve on this bGRIN lens microendoscopy with another complementary modality-photoacoustic imaging. This distal scan-free bGRIN lens photoacoustic microendoscopy (bGRIN-PAM) has optical resolutions of ~2 μm (lateral) and ~60 μm (axial), with a lateral field of view of 100.6 μm and a maximum penetration depth of 600 μm. We have demonstrated microendoscopic imaging of mouse hairs using our bGRIN-PAM.