Fig. 3: Spatial immobilization of functional materials on channel walls.

a (i, ii) Schematic showing the localized immobilization of functional materials on channel walls by attaching solutions to the channel. The large-sized solutes (radius or \({R}_{h}\) ≥ 3.0 nm) carrying electrostatic charges cannot penetrate membrane walls but can be electrostatically immobilized on the membranes. (iii, iv) Schematics showing the immobilization of negatively or positively charged solutes on channel walls; Confocal laser scanning microscope images showing channel walls immobilized with the positively charged FITC-labeled horseradish peroxidase (FITC-HRP, green) or negatively charged RhB-labeled glucose oxidase (RhB-GOx, red). Scale bars are 200 μm. b (i) Schematic and (ii) fluorescence microscope images showing the spatially arranged immobilization of the two enzymes on the channel walls. RhB-GOx-coated regions are visualized under RhB channel of the microscope, and FITC-HRP-coated regions are visualized under FITC channel of the microscope. Fluorescence images under RhB channel and FITC channel are collected, respectively, and merged into one. To obtain the three RhB-GOx-coated regions, region R1 is treated with 0.5 μL, 10 mg mL^–1 RhB-GOx solution; region R2 is treated with 0.5 μL, 4 mg mL^–1 RhB-GOx solution; region R3 is coated with 1 μL, 1 mg mL^–1 RhB-GOx solution. The left HRP-coated region is treated with 0.5 μL, 1 mg mL^–1 FITC-HRP aqueous solution, and the right region is coated with 1 μL, 4 mg mL^–1 FITC-HRP aqueous solution. The scale bar is 2 mm. (iii) RhB-GOx-coated regions treated with different concentrations of RhB-GOx solutions have different fluorescence intensities. The relative fluorescence intensities in arbitrary units (a.u.) are obtained by analyzing fluorescence microscope images under RhB channel. Source data are provided as a Source Data file.