Polycaprolactone solution-based ink for designing microfluidic channels on paper via 3D printing platform for biosensing application

This work reports a novel fabrication technique for development of channels on paper-based microfluidic devices using the syringe module of a 3D printing syringe-based system. In this study, printing using polycaprolactone (PCL)-based ink (Mw 70 000-90 000) was employed for the generation of functional hydrophobic barriers on Whatman qualitative filter paper grade 1 (approximate thickness of 180 mu m and pore diameter of 11 mu m), which would effectively channelize fluid flow to multiple assay zones dedicated for different analyte detection on a microfluidic paper-based analytical device (mu PAD). The standardization studies reveal that a functional hydrophilic channel for sample conduction fabricated using the reported technique can be as narrow as 460.7 +/- 20 mu m and a functional hydrophobic barrier can be of any width with a lower limit of about 982.2 +/- 142.75 mu m when a minimum number of two layers of the ink is extruded onto paper. A comparison with the hydrodynamic model established for writing with ink is used to explain the width of the line printed by this system. A fluid flow analysis through a single channel system was also carried out to establish its conformity with the Washburn model, which governs the fluid flow in two-dimensional mu PAD. The presented fabrication technique proves to be a robust strategy that effectively taps the advantages of this 3D printing technique in the production of mu PADs with enhanced speed and reproducibility.