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

Microfluidic devices hold considerable promise for miniaturizing and automating laboratory scale workflows involving sample preparation and biomarker analysis. By-and-large microfluidic automation has been implemented using polydimethyl siloxane (PDMS) - a material that presents challenges for scalable manufacturing. In this paper, we fabricated an automated microfluidic device composed of thermoplastic material, poly (methyl methacrylate) (PMMA), and demonstrated a sophisticated workflow consisting of plasma extraction, sample aliquoting and sample-reagent mixing steps performed in the device. 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, our device included features designed to address challenges arising from the gas impermeable nature of PMMA. These features included a bubble trap and air micro-tanks to supply O2 for enzymatic reactions. We rigorously characterized the performance of the microfluidic device and demonstrated that the quality of plasma extracted in the device is comparable to a standard plasma isolation method involving centrifugation. We also showed close agreement between glucose levels measured in the device and by standard assay. As a final demonstration of utility, we loaded 5 {micro}L of blood, isolated plasma and detected three analytes simultaneously - glucose, lactate and H2O2. In addition to minimizing the volume of blood and eliminating standard laboratory equipment (e.g., centrifuge), our device enabled a rapid response (<10 min). The use of thermoplastic materials may pave the way for inexpensive, mass-produced automated microfluidic devices for rapid detection of blood biomarkers at the point of care.