Fully 3D-printed endomicroscopic objective for two-photon, multi-wavelength excitation microscopy

We present a fully 3D-printed, broadband endomicroscopic objective optimized for near-infrared two-photon fluorescence imaging, featuring a compact, alignment-free design. The objective provides a numerical aperture of 0.6 in water immersion over a 200 µm field of view and maintains near diffraction-limited performance across the 720-950 nm excitation band. Monolithically fabricated with multi-material via two-photon polymerization (2PP), the three-element refractive objective achieves a 2 mm lens mechanical diameter, a mechanical housing diameter of 3 mm, and a total length of 2.1 mm with an approximately 10-hour build time. A self-aligning architecture integrates the printed half-housing with the optics to minimize assembly error, yielding sub-10 µm element decenter and <0.1° element tilt. Optical performance was validated using a resolution target and biological specimens, with broadband excitation behavior assessed by two-photon imaging of pollen grains across multiple excitation wavelengths, and with autofluorescence imaging of fresh mouse liver confirming feasibility for in situ tissue imaging. This work demonstrates the potential of fully printed broadband objectives for compact, high-performance endomicroscopy and integrated biomedical optics.