## 1 Introduction
A specific feature of laser-matter interaction, in particular when using ultrashort pulse lasers with pulse widths of several tens of femtosecond (fs) to several picoseconds (ps), offers the possibility to precisely control three-dimensional (3D) micro-/nanofabrication in transparent materials [14; 15; 16; 17; 18; 19; 20]. Indeed, tightly focused ultrashort pulse lasers can achieve very high peak intensities (\(\approx\)10 TW cm\({}^{-2}\)), resulting in strong nonlinear absorption phenomena in transparent materials to allow localized modification in volume with high precision [21]. The fundamental mechanisms of fs laser pulse interaction with the transparent materials were extensively explored in the literature [15; 17; 19; 21]. Some of the involved processes are competitive at different time scales and are strongly dependent not only on the laser irradiation parameters (pulse energy, pulse duration, laser wavelength, repetition rate, and focusing optics) but also on the physical-chemical properties of materials processed. The extensive studies of the laser-matter interaction together with new development of high-precision 3D CAD-CAM (computer-aided design/computer-aided manufacturing) stages potentiate the unique characteristics of ultrashort pulse lasers for 3D micro- and nanofabrication of the diverse materials. Advanced setups consisting of ultrashort pulse lasers and high-precision 3D translation stages have been developed for selective and precise generation of complex 3D microstructures embedded inside photosensitive glasses (PGs). The process is known as fs laser-assisted etching (FLAE) and was continuously optimized for concrete applications [22; 23; 24; 25; 26; 27]. It begins with laser direct writing (LDW) of PG in which the stage scanning speed, focusing position, and laser power are adjusted to achieve the desired 3D shape structure. An initial annealing treatment follows the laser irradiation, by which Ag atoms generated by the laser irradiation are clustering to form nuclei for the growth of a crystalline phase of lithium metasilicate at the laser-exposed regions. The wet chemical etching using hydrofluoric (HF) acid solution is then applied for selective removal of the crystalline phase to create 3D hollow structures. Consequently, microfluidic platforms with scale-down (\(\upmu\)m) and scale-up (mm) configurations can be achieved. A typical PG used with FLAE is commercially available Foturan glass. It exhibits high chemical stability, high transparency for optical interrogation, and biocompatibility. Advanced laser processing protocols of Foturan glass were described in details in [22; 28; 29; 30]. Pioneering FLAE of Foturan glass and the fabrication of complex 3D microfluidic structures with a high spatial resolution were reported by [PERSON] et al. [22]. Microstructures fabricated in Foturan glass proved to be useful for many applications due to good properties in terms of surface smoothness of created 3D structures [25; 31], capability of selective metallization [32; 33; 34], and good process efficiency [35]. Specifically, 3D microfluidic structures fabricated in Foturan glass by FLAE were successfully applied to fabricate nanoaquariums for microorganisms' studies (e.g., 3D monitoring of flagellum motion of _Euglena gracilis_[30] or gliding mechanism of _Phormidium cyanobacteria_[36]). A very recent study evidenced the possibility to generate submicrometer 3D channels inside Foturan by FLAE, for mimicking the intravasation-extravasation processes during chemotaxis-free cancer cells' migration inside confined nanospaces [37]. An alternative material used for microfluidic assays for multiple biological applications is a soft polymer polydimethylsiloxane (PDMS) due to its biocompatibility, transparency, high molding properties, tunable mechanical features, and low cost [38; 39]. However, it has been shown that biomolecule adsorption by PDMS is a current limitation, especially in case of biological testing such as particular drug response assays [40].