Optimization of machining process on electrospun nanofibers for integration in microfluidic devices

The main goal of this thesis is to fabricate a PDMS-based microfluidic Lab-On-a-Chip (LOC) with polyacrylonitrile (PAN) nanofibers inside the channels to facilitate micro-RNA (miRNA) capture. The designed and developed device is oriented, in a viral detection context, to the execution of tests with RNA immobilization and amplification with an isothermal amplification method. The good properties of PDMS were exploited, namely the biocompatibility, the versatility and the stickiness it exhibits with a very wide range of materials, including polymer-type nanofibers. The main technological challenge was to integrate nanofibers inside the microfluidic channels, thus exploiting their intrinsic characteristics: high surface-to-volume ratio and high porosity per unit mass. These can substantially improve the performance of microfluidic devices addressed to virus detection, increasing their capture capability. A fabrication protocol was defined to allow LOC bonding in presence of the patterned nanofibers, which must be kept unaffected by the passage of test fluids and pass the leak tests. The reason why PAN was chosen for nanofibers deposition is related to the chemical nature of its surface, presenting amino groups which, activated by plasma treatments, facilitate the capture of miRNA. Another advantage is that PAN allows for the electrospinning of fibers in a controlled manner. As regards the layout, the LOC has a silicon base, on which nanofibers find place, and a PDMS top-cover which includes: a microfluidic channel concentration area (15.5 mm x 10.5 mm) with squared 500 μm x 500 μm channels; an inlet well for biological sample injection; an outlet for waste withdrawal. The layout of the device was designed using the software Rhinoceros (Robert McNeel & Associates) by first making the 2D model CAD and then the 3D model. The master mold, subsequently used for the PDMS chip replication, was printed using a poly-jet 3D printer (OBJET 30 from Stratasys). Before depositing the PAN nanofibers, the silicon substrate was spin-coated with a layer of PDMS. Then, by laser ablation, the same geometry of the microfluidics was patterned on the deposited PAN nanofibers. The PDMS chip replica was bonded via interlayer bonding technique and leakage tests were carried out. Leak tests in ethanol (at 60 °C for 10 minutes) were conducted to verify that the bonding technique allowed for proper adhesion of the PDMS replica to the underlying substrate. At the end, interlayer bonding turned out to be the right assembly technique. Moreover, the overall process ensured a good alignment of the nanofibers as well as their stability, even after fluidic tests as demonstrated through microscopic characterizations. This thesis work has been developed in the framework of a collaboration between the Politecnico di Torino-DISAT and Consiglio Nazionale delle Ricerche (Istituto dei Materiali per l’Elettronica ed il Magnetismo) and partially funded by the National grant VIRAD-C19 (Rilevazione VIrale RApiDa del COVID-19) FISR 2020 COVID (FISR2020IP_00044). The aim of this collaboration is to investigate a new rapid diagnostic tool for viral detection, specially addressed to robust detection of SARS COV-2.