CO₂ Laser Fabrication of PMMA Microfluidic Double T-Junction Device with Modified Inlet-Angle for Cost-Effective PCR Application

The formation of uniform droplets and the control of their size, shape and monodispersity are of utmost importance in droplet-based microfluidic systems. The size of the droplets is precisely tuned by the channel geometry, the surface interfacial tension, the shear force and fluid velocity. In addition, the fabrication technique and selection of materials are essential to reduce the fabrication cost and time. In this paper, for reducing the fabrication cost Polymethyl methacrylate (PMMA) sheet is used with direct write laser technique by VERSA CO₂ laser VLS3.5. This laser writing technique gives minimum channel width of about 160   μ m , which limit miniaturizing the droplet. To overcome this, modification on double T-junction (DTJ) channel geometry has been done by modifying the channel inlets angles. First, a two-dimensional (2D) simulation has been done to study the effect of the new channel geometry modification on droplet size, droplets distribution inside the channel, and its throughput. The fabricated modified DTJ gives the minimum droplet diameter of 39 ± 2   μ m , while DTJ channel produced droplet diameter of 48 ± 4   μ m at the same conditions. Moreover, the modified double T-junction (MDTJ) decreases the variation in droplets diameter at the same flow rates by 4.5 - 13 % than DTJ. This low variation in the droplet diameter is suitable for repeatability of the DNA detection results. The MDTJ also enhanced the droplet generation frequency by 8 - 25 % more than the DTJ channel. The uniformity of droplet distribution inside the channel was enhanced by 3 - 20 % compared to the DTJ channel geometry. This fabrication technique eliminates the need for a photomask and cleanroom environment in addition shortening the cost and time. It takes only 20   min for fabrication. The minimum generated droplet diameter is within 40   μ m with more than 1000 droplets per second (at 10   mL / h . oil flow rate). The device is a high-throughput and low-cost micro-droplet formation aimed to be as a front-end to a dynamic droplet digital PCR (ddPCR) platform for use in resource-limited environment.