Fluorinated oil (HFE7500, 3 M, USA) supplemented with 0.5% (w/w) surfactant (RAN Biotechnologies, USA) was used as the continuous phase. To visually differentiate the two sets of droplets, deionized (DI) water was used as the first dispersed phase to generate large droplets, while 12 mM fluorescent dye solution (Rhodamine 6 G, Sigma‒Aldrich, USA) was used as the second dispersed phase to generate small droplets. The interfacial tension is 6.8 mN/m. During droplet synchronization, the interfacial tension forces help resist changes in droplet shape, preventing droplet breakup.
For enzymatic reactions, glucose oxidase (G7141), D-(+)-glucose (G7021), 4-AAP (A4382), and TOPS (E8506) were all purchased from Sigma‒Aldrich, and HRP (31490) was purchased from Thermo Scientific. The concentrations of glucose oxidase, HRP, 4-AAP, and TOPS were maintained at 200 U/mL, 1200 U/mL, 0.6 mol/L, and 1 mol/L, respectively, while the concentration of glucose was set at 100, 200, 300, and 400 mg/dL.
Mouse myeloma cells (SP2/0 cell line) were used as the model cells for cell-bead pairing. They were cultured in Roswell Park Memorial Institute (RPMI) 1640 Medium (Life Technologies, USA) supplemented with 10% fetal bovine serum (FBS, A4766801, Gibco, USA) and 100 U/mL penicillin/streptomycin (Gibco, USA) in a humidified atmosphere with 5% CO2 at 37 °C. After trypsin treatment, the cells were resuspended in 2 μM Calcein AM (C3100MP, Invitrogen, USA) in FBS-free cell culture medium for 30 min to enable live cell staining. Then, the cells were centrifuged, and 15% (v/v) OptiPrep (D1556, Sigma‒Aldrich, USA) in cell culture medium, which had the same density as the SP2/0 cells, was used for resuspension of the cells.
For enzymatic reactions, glucose oxidase (G7141), D-(+)-glucose (G7021), 4-AAP (A4382), and TOPS (E8506) were all purchased from Sigma‒Aldrich, and HRP (31490) was purchased from Thermo Scientific. The concentrations of glucose oxidase, HRP, 4-AAP, and TOPS were maintained at 200 U/mL, 1200 U/mL, 0.6 mol/L, and 1 mol/L, respectively, while the concentration of glucose was set at 100, 200, 300, and 400 mg/dL.
Mouse myeloma cells (SP2/0 cell line) were used as the model cells for cell-bead pairing. They were cultured in Roswell Park Memorial Institute (RPMI) 1640 Medium (Life Technologies, USA) supplemented with 10% fetal bovine serum (FBS, A4766801, Gibco, USA) and 100 U/mL penicillin/streptomycin (Gibco, USA) in a humidified atmosphere with 5% CO2 at 37 °C. After trypsin treatment, the cells were resuspended in 2 μM Calcein AM (C3100MP, Invitrogen, USA) in FBS-free cell culture medium for 30 min to enable live cell staining. Then, the cells were centrifuged, and 15% (v/v) OptiPrep (D1556, Sigma‒Aldrich, USA) in cell culture medium, which had the same density as the SP2/0 cells, was used for resuspension of the cells.
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