Multilayered skyscraper microchips fabricated by hybrid “all-in-one” femtosecond laser processing

Multilayered microfluidic channels integrated with functional microcomponents are the general trend of future biochips, which is similar to the history of Si-integrated circuits from the planer to the three-dimensional (3D) configuration, since they offer miniaturization while increasing the integration degree and diversifying the applications in the reaction, catalysis, and cell cultures. In this paper, an optimized hybrid processing technology is proposed to create true multilayered microchips, by which “all-in-one” 3D microchips can be fabricated with a successive procedure of 3D glass micromachining by femtosecond-laser-assisted wet etching (FLAE) and the integration of microcomponents into the fabricated microchannels by two-photon polymerization (TPP). To create the multilayered microchannels at different depths in glass substrates (the top layer was embedded at 200 μm below the surface, and the underlying layers were constructed with a 200-μm spacing) with high uniformity and quality, the laser power density (13~16.9 TW/cm2) was optimized to fabricate different layers. To simultaneously complete the etching of each layer, which is also important to ensure the high uniformity, the control layers (nonlaser exposed regions) were prepared at the upper ends of the longitudinal channels. Solvents with different dyes were used to verify that each layer was isolated from the others. The high-quality integration was ensured by quantitatively investigating the experimental conditions in TPP, including the prebaking time (18~40 h), laser power density (2.52~3.36 TW/cm2) and developing time (0.8~4 h), all of which were optimized for each channel formed at different depths. Finally, the eight-layered microfluidic channels integrated with polymer microstructures were successfully fabricated to demonstrate the unique capability of this hybrid technique.Microfluidics: 3D chips to power next-gen experimentsNewly-developed manufacturing technologies enable the construction of powerful microfluidics chips. Just as how silicon computer chips leaped in capability thanks to the development of three-dimensional circuitry, microfluidics chips—which conduct experiments on liquids in micrometer-sized channels—stand to benefit from the same development. Researchers led by Dong Wu, from the University of Science and Technology of China, and Koji Sugioka, from Japan’s RIKEN Center for Advanced Photonics, developed a methodology that leverages femtosecond laser pulses to fabricate multi-layer glass microfluidics channels. The team validated their process by creating an eight-layered glass microfluidics device with layers of channels separated by just 200 µm. 3D microfabrication technologies such as this have the capacity to enable point-of-care diagnostics, the modeling of multiple organ systems, and complex studies involving particle mixing and separation.