3D-printed micro-optical dark-field condenser

Optical microscopy is an essential tool in fields such as biology, material science, medicine, and nanotechnology, where resolution and contrast play a crucial role in sample analysis. Dark-field microscopy is fundamental for image contrast and edge enhancement, especially for nearly transparent or nanoscale samples. Dark-field microscopy, however, usually requires a bulky and expensive microscope setup. In this work, we demonstrate a miniaturized, millimeter-sized dark-field condenser fabricated by femtosecond two-photon polymerization 3D-printing. An annular absorbing aperture and a high-numerical aperture lens are combined on a glass substrate. This condenser provides an oblique illumination of the sample, necessary for dark-field imaging. We demonstrate excellent dark-field performance of the 3D-printed dark-field condenser by imaging USAF 1951 resolution test charts and on gold disks with diameters below 500 nm. Our work paves the way for the utilization of miniaturized microscopy techniques that can be rapidly prototyped for applications in medicine or biology. This could possibly lead to entire 3D-printed microscopes with enhanced dark-field imaging capability, for example, for microfluidic chips.