Herein we report a microfluidic device integrated with a PDMS membrane nano-filter for the size-based trapping of particles. We propose a novel cost-effective fabrication process to form submicron-sized nano-pore and slit arrays in the PDMS membrane by using a reusable three-dimensional silicon mold with the shape of microneedles and microblades. The PDMS is coated onto the silicon mold, etched, and detached from the mold to form nano-pores and slits in the PDMS membrane filter. The sizes of the nano-pores and slits could be adjusted in the range of several hundreds of nanometers by varying the etching time of the PDMS coated on the sharp silicon mold. The diameter of the pores and the width of the slits were controlled to be 354 +/- 79 nm and 389 +/- 84 nm, respectively, with PDMS etching times of 60 s. Moreover, it was confirmed that the deposition of a parylene-C thin film on the PDMS membrane filter can be effectively used to control the nano-slit size and improve the trapping efficiency. We have demonstrated size-based filtration of microbeads with diameters of 0.4, 0.8, 1.0, and 2.2 mu m using the proposed microfluidic device. In addition, the microfluidic device integrated with the proposed PDMS membrane filter was successfully applied to the trapping of submicron-sized E. coli bacteria with a filter recovery efficiency of 89.1%.
