Direct casting of a PDMS substrate holder from a structured polymer film for lab-on-a-foil bonding

Abstract Lab-on-a-foil devices have recently attracted increasing attention, in which a thin and flexible polymer film is used as the substrate material. However, to protect the special three dimensional microfluidic structures on the polymer film from collapsing during the bonding process, a very elaborate substrate holder is required. In this work, we propose the use of a PDMS plate as the substrate holder for lab-on-a-foil bonding. The PDMS substrate holder is directly cast from the structured polymer film, hence it can perfectly match the polymer film and protect the microfluidic structures. This method is straightforward and low-cost, and obviates the difficulties of measuring the dimensions of the structured polymer film. Meanwhile, the stickiness of PDMS makes the positioning of the structured polymer film on the surface of the holder much easier, and the low modulus of PDMS contributes to obtaining a uniform bonding. As a demonstration, with the help of a PDMS substrate holder, a 240-μm-thick thermoformed polypropylene film was bonded with a 100-μm-thick aluminium foil to make a lab-on-a-foil device for gene expression analysis. The bonding qualities were examined, and the performances of the device were tested.