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Surface functionalization of polydimethylsiloxane (PDMS) is important in developing high-performance microfluidic devices. This work applied the thermal chemical vapor deposition (t-CVD) of Parylene-C onto PDMS to caulk the molecular network while retaining the original surface properties for the oxygen plasma bonding. The very low deposition rates (for example, a nominal rate of 0.12 A min-1 at 135 °C) of Parylene-C at elevated substrate temperatures enabled the reactive Parylene-C monomers to penetrate into the PDMS matrix up to 4.6 ± 0.1 μm (135 °C), which was verified for the first time by a scanning electron microscope with an energy dispersive X-ray analysis (SEM-EDAX). The Parylene-C caulked in the molecular network of PDMS matrix guaranteed an excellent resistance to small molecule permeations. Meanwhile, only discrete nucleation islands were formed on the top surface rather than a continuous Parylene-C layer as observed under the AFM scan, which made the processed PDMS surface ready for device assembly. This surface functionalization method has better long-term stability than the other wet-type rivals. The barrier for oxygen plasma bonding in previously reported dry surface treatments was also avoided, thereby, facilitating the device assembly. The present work successfully developed a novel pcPDMS (Parylene-C caulked PDMS) technique, which overcame the bonding difficulty in the previous works but retained the low small molecule permeability as before. Caulking a molecular network through the t-CVD of Parylene-C also demonstrated a new strategy of functionalizing polymer surfaces and preparing new hybrid materials for wide lab-on-a-chip applications.

This note introduced a complete fabrication strategy of Parylene C-caulked PDMS (pcPDMS) for low permeability required microfluidics applications. The bonding issue enrolled in the pcPDMS fabrication was solved based on careful surface analyses of the Parylene C caulked status in the PDMS matrix.

Here we report an approach utilizing a suspended nanoparticle crystal (S-NPC) as an electrical read-out biosensor based on a nanofluidic electrokinetics principle. As a preliminary demonstration, streptavidin-modified S-NPC with a particle diameter of 520 nm was used to detect biotin in a PBS buffer. The present result indicated that the detection range of biotin by this nanofluidics-based biosensor was about 1 nM-10 muM (in 10(-4)x PBS) with a sensitivity of 160 nS/nM. Being easy to get established, low-cost, and having large electrical read-out signal, the present S-NPC is believed to be a promising biosensing scheme in the micro total analysis system.