Microfluidic capillary platform with hydrophilic PDMS for point-of-care immunoassays

Abstract

Point-of-care (PoC) devices offer the possibility of fast and easy to use testing platforms. Self-driven capillary devices are particularly interesting because they can function without external pumps. Microfluidic devices often rely on polydimethylsiloxane (PDMS) prototyping; however, for self-driven microfluidics, its hydrophobic nature makes its use challenging. Bulk modification of PDMS through copolymers with hydrophilic moieties could be a practical solution because the copolymer is added prior to PDMS baking in a single-step process. In this work, a PDMS bulk modification with dimethylsiloxane-(60–70 % ethylene oxide) block copolymer was used to render PDMS hydrophilic. The addition of 1 % (w/w) copolymer resulted in a hydrophilic PDMS which was then used to fabricate the capillary devices. The microfluidic design included a serpentine channel with reagent entry points connected to a capillary pump and was closed by a membrane layer with conical shaped reservoirs. The reservoirs were designed to allow the sequential entry of the solutions and the device sealing and robustness were improved through PMMA frames with integrated magnets. A proof-of-concept was performed with food colouring demonstrating the capability of the device to flow the solutions sequentially. Finally, an immunoassay to detect the presence of Infliximab, a therapeutic antibody for chronic inflammatory diseases, was used to demonstrate the functionality of the capillary device. The versatility of the device was also shown by performing a fluorescent indirect immunoassay and a colorimetric indirect-ELISA for the detection of Infliximab with both approaches detecting Infliximab in the clinical range of interest (between 3 and 7 μg/mL).