Isopropyl alcohol ipa

The microfluidic mold was initially designed with the software, AutoCAD 2018. The mold mainly consisted of double fiber grooves, double microlens channels and a detection channel. The geometrical length, width and height of the detection channel were designed as 60 mm, 250 μm and 250 μm, respectively. At the entrance and exit of the detection channel, circular chamfers were designed to prevent the dead zone at the corners. In this mold design, the axis of the 3D microlens was self-aligned with the direction of sample flow. The diameter of the microlens was designed as 250 μm and its thickness was optimized with the Ray Tracing Module in COMSOL. The CAD drawing file was converted into an STL printing file for the fabrication of the microfluidic mold using a two-photon stereolithographic 3D printer (Nanoscribe, Germany).
The main procedures of fabricating the 3D-MIMC are summarized in Fig. 1. Initially, the photoresist (IP-S, Nanoscribe, Germany) was dropped onto the indium tin oxide (ITO) coated glass substrate (Fig. 1a) and selectively polymerized to form the mold using an ultrafast 780 nm laser with 50 mW power. The main part of the mold (Fig. 1b) and critical optical structures including the mold of microlenses and all optical facets of the detection channel and fiber grooves (Fig. 1c) were fabricated separately using different values of printing parameters. The schematics of such hierarchical modular printing are presented in Fig. 1b z andc z , which show the magnified parts of Fig. 1b andc. A 25-fold objective was selected for printing due to its good combination of resolution and working range for printing optical structures without any block stitch. After finishing all printing work, the uncured photoresist was removed by rinsing with the developer (1-methoxy-2-propanol acetate, Sigma, USA) for 18 minutes and IPA (isopropyl alcohol, Sigma, USA) for 2 minutes in sequence (Fig. 1d). Before PDMS casting, the mold was thermally pretreated in an oven at 200 °C for 2 hours for the subsequent efficient separation of the PDMS replica. PDMS and its curing reagent (Sylgard 184, Dow Corning, Midland, USA) were well mixed at the standard ratio of 10 : 1 and then were preliminarily degassed in a vacuum desiccator. Afterwards, the homogeneous mixture was cast onto the microfluidic mold and thoroughly degassed to avoid any bubble cavity (Fig. 1e). After polymerization at 70 °C for 4 hours, the cured PDMS was carefully peeled off from the mold and then was punched to form holes (Fig. 1f). Finally, the PDMS layer was bound onto the glass substrate after the plasma treatment (Fig. 1g).