The fabrication of sub-100 nm feature sizes in large-scale three-dimensional (3D) geometries by two-photon polymerization requires a precise control of the polymeric reactions as well as of the intensity distribution of the ultrashort laser pulses. The authors, therefore, investigate the complex interplay of photoresist, processing parameters, and focusing optics. New types of inorganic– organic hybrid polymers are synthesized and characterized with respect to achievable structure sizes and their degree of crosslinking. For maintaining diffraction-limited focal conditions within the 3D processing region, a special hybrid optics is developed, where spatial and chromatic aberrations are compensated by a diffractive optical element. Feature sizes below 100 nm are demonstrated.

This study presents the development of post-processing steps for microfluidics fabricated with selective laser etching (SLE) in fused silica. In a first step, the SLE surface-even inner walls of microfluidic channels—can be smoothed by laser polishing. In addition, two-photon polymerization (2PP) can be used to manufacture polymer microstructures and microcomponents inside the microfluidic channels. The reduction in the surface roughness by laser polishing is a remelting process. While heating the glass surface above softening temperature, laser radiation relocates material thanks to the surface tension. With laser polishing, the RMS roughness of SLE surfaces can be reduced from 12 µm down to 3 nm for spatial wavelength λ < 400 µm. Thanks to the laser polishing, fluidic processes as well as particles in microchannels can be observed with microscopy. A manufactured microfluidic demonstrates that SLE and laser polishing can be combined successfully. By developing two-photon polymerization (2PP) processing in microchannels we aim to enable new applications with sophisticated 3D structures inside the microchannel. With 2PP, lenses with a diameter of 50 µm are processed with a form accuracy rms of 70 nm. In addition, this study demonstrates that 3D structures can be fabricated inside the microchannels manufactured with SLE. Thanks to the combination of SLE, laser polishing and 2PP, research is pioneering new applications for microfluidics made of fused silica

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Integrated passive and active devices are the key components in current and future information technology. In order to fulfill requirements in miniaturization for (integrated) optical or electronic devices, nano-scaled materials with a good compatibility to high-resolution processing techniques are needed. According to these requirements, multi-photon techniques attract much attention by providing a resolution far beyond the diffraction limit. The patterning of the inorganic-organic hybrid polymers, which are synthesized by catalytically controlled hydrolysis/polycondensation reactions, will be discussed with respect to the underlying photochemical processes. Emphasis will be on the direct writing of structures using femtosecond laser pulses, making use of two- and three-photon absorption (TPA/3PA) processes with visible or IR light, which also allows one to write arbitrary 3D structures. Due to the very sharp threshold fluence for these processes and its non-linear beh avior, features down to 100 nm can be realized by choosing a suitable combination of material formulation and patterning parameters. Voxel arrays were written, whereas the resulting voxel sizes are compared to a growth model, and the influence of radical diffusion and chain propagation is discussed. In order to determine the TPA cross-section and to estimate the role of the photoinitiator, a z-scan experiment was realized. The initiators' cross-sections will be correlated to the resulting voxel sizes

Molecular motor-driven filament systems have been extensively explored for biomedical and nanotechnological applications such as lab-on-chip molecular detection or network-based biocomputation. In these applications, filament transport conventionally occurs in two dimensions (2D), often guided along open, topographically and/or chemically structured channels which are coated by molecular motors. However, at crossing points of different channels the filament direction is less well determined and, though crucial to many applications, reliable guiding across the junction can often not be guaranteed. We here present a three-dimensional (3D) approach that eliminates the possibility for filaments to take wrong turns at junctions by spatially separating the channels crossing each other. Specifically, 3D junctions with tunnels and overpasses were manufactured on glass substrates by two-photon polymerization, a 3D fabrication technology where a tightly focused, femtosecond-pulsed laser is scanned in a layer-to-layer fashion across a photo-polymerizable inorganic–organic hybrid polymer (ORMOCER®) with µm resolution. Solidification of the polymer was confined to the focal volume, enabling the manufacturing of arbitrary 3D microstructures according to computer-aided design data. Successful realization of the 3D junction design was verified by optical and electron microscopy. Most importantly, we demonstrated the reliable transport of filaments, namely microtubules propelled by kinesin-1 motors, across these 3D junctions without junction errors. Our results open up new possibilities for 3D functional elements in biomolecular transport systems, in particular their implementation in biocomputational networks.

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The two-photon photopolymerization of resins by focused laser light in principle enables the fabrication of structures with details below the diffraction limit. However, the method can be highly susceptible to aberrations, which hinders the fabrication of structures that are larger than, e.g., the working distance of the microscope objective. Here, two-photon polymerization is extended to the fabrication of macroscopic structures by making use of medium numerical-aperture microscope objectives. By introducing a substrate holder movable in the axial direction it is possible to keep the focusing conditions constant and to fabricate very large structures with heights that are not limited by the working distance of the objective. Moreover, the constant focusing conditions enable us to quantify spherical aberrations by experimental mapping of the optical point-spread function, which manifests itself in the shape of singe photo-polymerized voxels. By monitoring such shapes it is possible to minimize aberrations. Effective aberration control enables us to fabricate large but detailed biomedical scaffolds with interconnected pores, e.g., in the shape of a human stirrup bone.