Pdms base and cross linker

Microfluidics devices were generated using a previously published design [121 ]. Soft lithography was performed using SU-8 2050 photoresist (MicroChem) on 4′′ silicon substrate to obtain a feature aspect depth of 90 μm. After overnight silanization (using chlorotrimethylsilane; Sigma), the wafer masks were used for microfluidics fabrication. Drop-seq chips were generated using silicon-based polymerization chemistry, according to a previously published protocol [122 ]. Briefly, polydimethylsiloxane (PDMS) base and cross-linker (Dow Corning) were mixed at a 10:1 ratio, and degassed before pouring the solution onto the Drop-seq master template. PDMS was cured on the master template, at 70 °C for 2 h. After incubation and cooling, PDMS monoliths were cut and the inlet/outlet ports were punched with 1.25-mm biopsy punchers (World Precision Instruments). The PDMS monolith was plasma-bonded to a clean microscopic glass slide using a Harrick plasma cleaner. After pairing the plasma-treated surfaces of the PDMS monolith and the glass slide, flow channels of the Drop-seq chip were subjected to a hydrophobicity treatment using 1H,1H,2H,2H-perfluorodecyltri-chlorosilane (in 2% v/v in FC-40 oil; Alfa Aesar/Sigma). After 5 min of treatment, excessive silane was blown through the inlet/outlet ports. Chips were further incubated at 80 °C for 15 min.

Microfluidics devices were generated on-site, using a technique described below, which is based on an earlier Drop-Seq protocol^{37 ,128 ,129 (link)}. Soft lithography was performed using SU-8 2050 photoresist (MicroChem) on a 4″ silicon substrate, to generate a 90 μm aspect depth feature. The wafer masks were subjected to silanization overnight using chlorotrimethylsilane (Sigma), before being used for the fabrication of microfluidics. Silicon-based polymerization chemistry was used to fabricate the Drop-Seq chips. In short, we prepared a 1:10 ration mix of polydimethylsiloxane (PDMS) base and cross-linker (Dow Corning), which was degassed and poured onto the Drop-Seq master template. PDMS was cured on the master template, at 70 °C for 2 h. After cooling, PDMS monoliths were cut and 1.25 mm biopsy punchers (World Precision Instruments) were used to punch out the inlet/outlet ports. Using a Harrick plasma cleaner, the PDMS monolith was then plasma bonded to a clean microscope glass slide. After the pairing of the PDMS monolith’s plasma-treated surfaces with the glass slide, we subjected the flow channels to a hydrophobicity treatment using 1H,1H,2H,2H-perfluorodecyltri-chlorosilane (in 2% v/v in FC-40 oil; Alfa Aesar/Sigma) for 5 min of treatment. Excess silane was removed by being blown through the inlet/outlet ports. Chips were then incubated at 80 °C for 15 min.