Integrating microfluidic automation into thermoplastic devices for analysis of small volumes of blood

Microfluidic devices with built-in microvalves hold particular promise for minimizing sample volume requirements while automating sample preparation workflows. Such devices have typically been implemented in polydimethyl siloxane (PDMS) using multi-layer soft lithography. Both the material and assembly process of devices present challenges for scalable manufacturing and limit utilization of microfluidic automation at the point of care. Our work aims to address this challenge. It describes a microfluidic device composed of thermoplastic material, poly (methyl methacrylate) (PMMA) performing a sophisticated automated workflow of plasma extraction, sample aliquoting and sample-reagent mixing steps. Automation was accomplished using multiple on-board microvalves consisting of a pressure sensitive adhesive (PSA) membrane sandwiched between PMMA flow and control layers. In addition to novel microvalves, the device included features designed to circumvent issues arising from gas-impermeable nature of PMMA - a bubble trap and air micro-tanks to supply O₂ for enzymatic reactions. The performance of the microfluidic device was rigorously characterized. The quality of plasma extracted in the device was comparable to a standard plasma isolation method involving centrifugation. Close agreement was observed between glucose levels measured in the device and by a standard assay. As a final demonstration of utility, 5 μL of blood was loaded into the device, plasma was isolated, and three analytes-glucose, lactate and H₂O₂ were detected. In addition to minimizing the volume of blood and eliminating standard laboratory equipment (e.g., centrifuge), the device enabled a rapid response (<10 min). The use of thermoplastic materials may pave the way for inexpensive automated microfluidic devices for rapid detection of blood biomarkers at the point of care.