[en] Highlights: • Sacrificial layer assisted microfabrication method was developed for CO₂ laser engraving. • Six thermoplastics were found compatible with sacrificial layer assisted laser engraving technique. • Microchannel width as small as ∼ 40 μm was attainable by a laser beam that was 5 times larger in diameter. • Inherent bulging issue of laser engraved microchannel has been solved such that good bonding quality can be achieved. - Abstract: Since polydimethylsiloxane (PDMS) is notorious for its severe sorption to biological compounds and even nanoparticles, thermoplastics become a promising substrate for microdevices. Although CO₂ laser engraving is an efficient method for thermoplastic device fabrication, it accompanies with poor bonding issues due to severe bulging and large feature size determined by the diameter of laser beam. In this study, a low-cost microfabrication method is proposed by reversibly sealing a 1 mm thick polymethylmethacrylate (PMMA) over an engraving substrate to reduce channel feature size and minimize bulges of laser engraved channels. PMMA, polycarbonate (PC), polystyrene (PS), perfluoroalkoxy alkane (PFA), cyclic-olefin polymers (COP) and polylactic acid (PLA) were found compatible with this sacrificial layer assisted laser engraving technique. Microchannel width as small as ∼40 μm was attainable by a laser beam that was 5 times larger in diameter. Bulging height was significantly reduced to less 5 μm for most substrates, which facilitated leak proof device bonding without channel deformation. Microdevices with high aspect ratio channels were prepared to demonstrate the applicability of this microfabrication method. We believe this fast and low-cost fabrication approach for thermoplastics will be of interest to researchers who have encountered problem with polydimethylsiloxane based microdevices in their applications.

[en] It is known for hydrophobic small molecules and proteins to be strongly adsorbed on the surface of polydimethylsiloxane (PDMS) based microdevices. However, no systematic studies have addressed issues related to the sorption of nanoparticles (NPs) on PDMS surfaces. The authors have used carboxylate-modified polystyrene nanoparticles (PS NPs), with sizes of <100 nm and prepared in different curing agent ratios, to study their sorption by native PDMS of different brands. It is found that both dynamic coating with sodium dodecyl sulfate and sol-gel modification can relieve the sorption issues, but only the co-treatment with both species gives satisfactory results in terms of suppressing bulk absorption. This combined coating strategy was further testified by an on-chip separation of a mixture of PS NPs (of 20 nm, 50 nm and 500 nm average diameter) based on a linear node array with enhanced mixing and diffusion-biased recovery of smaller nanoparticles. Instead of changing device design, optimal parameters for nano-separation can be achieved by changing the flow rate between a pair of syringe pumps. A more than 10-fold enrichment of 20 nm NPs was obtained when analyzing a mixture of nanoparticles. Since PDMS is still the preferred choice as a microfluidic substrate, this combined coating strategy is perceived to be highly beneficial in on-chip nano-separation and nanosynthesis using PDMS based microdevices. < Image>.