Low cost polymeric on-chip flow sensor with nanoliter resolution

Highly integrated polymeric microliquid flow controller for droplet microfluidics

“…It is composed of two monolithically integrated modular components, a flow-regulating pneumatic microvalve and a post-produced on-chip calorimetric thermal flow sensor in a bypass configuration for high flow rates. These two components have been successfully demonstrated in previous works as stand-alone components (Etxebarria et al 2014(Etxebarria et al , 2016.…”

“…d Close-up image of a finished microvalve filled with a green-coloured solution, which highlights the different parts of the structure, being the membrane diameter 3 mm, actuating membrane 100 µm, seat diameter 1 mm, and membrane gap 20 µm. Further information on single component architecture and working principle is addressed in previous publications (Etxebarria et al 2014(Etxebarria et al , 2016 Fig. 2 Block diagram of the LFCS working principle, where the flow sensor (FT) sends the flow rate value to the PID controller, which modulates the pressure (PR) on the valve (⊗) to minimize the error (e±) between the measured flow rate and the set point defined by the user An equilibration time is necessary to obtain droplets that are stable in size, and the stabilization depends on the nature of the imposed flow rates or the materials used in the whole system, since depending on the elasticity of the fluidic system (syringe, tube, device) and their deformability under pressure changes the stabilization time may vary considerably (Bertholle and Velvé Casquillas).…”

“…In short, the general method consists in (1) replicating the valve and the sensor structures by hot embossing, (2) sealing these structures with a COP membrane by a solvent bonding that ensures a smooth surface and (3) metal deposition on top of the covering membrane (Etxebarria et al 2014(Etxebarria et al , 2016.…”

“…The process starts by cleaning the surface of the finalized device with oxygen plasma treatment for 2 min at 90 W. Next, OIR-positive photo-resist is spin-coated and softbaked under IR for 12 min at 95 W. The resist is exposed to a UV dose of 350 mJ cm −2 to define the sensor elements, developed in a bath of positive resist developer and rinsed with DIW. Prior to Ni sputtering, the wafer is again cleaned with oxygen plasma for 2 min at 90 W. Next, a layer of 100 nm of Ni is deposited and a lift-off performed (Etxebarria et al 2016). The LFCS devices …”

“…The best ratio of output signal to flow rate was obtained for Design D12, for a heater operating at 50 °C, 2.5 mm long, 20 µm thick and sensors 2 mm long and 20 µm thick, with a distance between the elements of 60 µm. This configuration provides the highest sensitivity by maximizing heat transfer to the fluid and sensing area and minimizing cross-talk between sensors (Etxebarria et al 2016). The flow sensor requires a bypass construction to widen its detection range and thus match with the flow range that the microvalve can regulate.…”