Fig 1.
Fabrication workflow and experimental setup.
(A-H) Steps in fabricating the flow-cell. The steps are carried out left to right in two rows. (I) Cross-section along channel axis. The schematic is to scale for 1.5 mm channel width, 81 μm tape thickness and no. 1 thickness coverslips. (J) Cross-section through side of finished device showing the bottom and top glass coverslips, the PDMS barrier forming the inlet and the PDMS connector used for the outlet tubing. (K) Experimental setup for gravity driven perfusion. The device is secured on an (x,y) stage using stage clips and the outlet tubing leads to a large reservoir positioned on a height adjustable platform. The flow rate is adjusted by changing the height between the inlet and outlet reservoir or by changing the fluidic resistance of the system by adjusting the flow cell and tubing design geometry.
Fig 2.
Simple sequential exchange of solutions with a passive stop due to capillary action.
(A) Apparatus for generating gravity-driven flow. (B) The device was filled with purple dye solution to show the channel. The outlet tubing connects to an outlet reservoir 4 cm below the level of the inlet. (C) 10 μL green dye solution is added at the inlet using a pipette. (D) Solution flows through the device until (E) when the solution reaches the entrance and passively stops without experimenter input.
Fig 3.
(A) Computer aided design is used to fabricate a pattern in double-sided tape using a programmable cutting machine. (B) The device is assembled as in Fig 1 but with PDMS barriers for four separate inlets. (C) Bird’s eye view of device with multiple streams in laminar flow. (D) Magnified image defined by the dashed box in (C), showing the four separate laminar flow streams.
Fig 4.
Controllable addition of samples in a single-molecule DNA stretching experiment.
(A) Experimental schematic showing flow-cell together with magnets positioned at close proximity to the top cover slide to apply a fixed force. (B) DNA is tethered to the surface using a magnetic bead. At zero flow, the magnetic force acts away from the surface and stretches the DNA. When solution is added, the bead position is deflected due to the solution flow parallel to the channel axis. (C) Bead z-height as a function of time for the device using 20 cm of 0.51 mm inner diameter tubing with fluidic resistance calculated as 402 Pa.s.μL-1. The asterisks indicate timepoints where 10 μL of solution was manually added at the inlet. (D) Same experiment as (C) after adding 25 mm of 0.127 mm diameter narrow bore tubing to increase the calculated fluidic resistance to 3889 Pa.s.μL-1. (E) Using the device in the same configuration as (C)– 10 μL samples of solution were added and the height between the inlet and outlet reservoir levels was varied as indicated. (F) Comparison of flow rates through the device for the two different fluidic resistance configurations as a function of inlet and outlet reservoir height difference. The orange linear fit gave a value of Rfluidic = 3990 Pa.s.μL-1 and the blue linear fit gave a value of Rfluidic = 366 Pa.s.μL-1. (G) Experimental recording showing the addition of 10 μL solution samples separated by an interval of ~1 hr.
Fig 5.
Multiple channel design and reproducibility test.
(A-E) Key steps in fabricating the flow chamber. The steps are carried out left to right in two rows. (F) Image of flow chamber filled with four different dye solutions. (G) Flow sensor recordings from four channels on one device. Each channel was filled with deionised water and 30 μL deionised water was added at t = 10s. There is a brief transient at the beginning of the flow due to the fluidic capacitance of the device. (H) Flow rate values measured at t = 30s for 19 channels across five devices (one channel was blocked with PDMS and therefore not measured).