Non-polydimethylsiloxane devices for oxygen-free flow lithography

Abstract

Flow lithography has become a powerful particle synthesis technique. Currently, flow lithography relies on the use of polydimethylsiloxane microchannels, because the process requires local inhibition of polymerization, near channel interfaces, via oxygen permeation. The dependence on polydimethylsiloxane devices greatly limits the range of precursor materials that can be processed in flow lithography. Here we present oxygen-free flow lithography via inert fluid-lubrication layers for the synthesis of new classes of complex microparticles. We use an initiated chemical vapour deposition nano-adhesive bonding technique to create nonpolydimethylsiloxane-based devices. We successfully synthesize microparticles with a subsecond residence time and demonstrate on-the-fly alteration of particle height. This technique greatly expands the synthesis capabilities of flow lithography, enabling particle synthesis, using water-insoluble monomers, organic solvents, and hydrophobic functional entities such as quantum dots and single-walled carbon nanotubes. As one demonstrative application, we created near-infrared barcoded particles for real-time, label-free detection of target analytes.

Inertio-elastic focusing of bioparticles in microchannels at high throughput

“…Microscopic video imaging also shows that these particles rotate freely when suspended in a Newtonian fluid. To investigate the effect of particle shape on inertio-elastic focusing in HA solution at high Reynolds numbers, we used cylindrical cross-linked poly(ethylene glycol) (PEG) particles synthesized via flow lithography 45 . For a given PEG particle, we measured the lateral position z p (with channel centerline defined by z = 0 µm) and the instantaneous orientation angle θ p of the particle (with stream wise alignment defined by θ = 0°) in the original HA solution at Q = 20 ml min −1 (Fig.…”

“…Fluorescently labelled WBCs were centrifuged and suspended in PBS, low-molecular weight HA solution (357 kDa, 0.1% w/v, PBS) or high-molecular weight HA solution (1,650, kDa, 0.1% w/v, PBS) at a concentration of 5 × 10 6 cells ml −1 . Anisotropic (cylindrical) hydrogel particles were synthesized via stop-flow lithography 45 from prepolymer solutions of 60% poly(ethylene glycol) diacrylate (PEG-DA 700, Sigma-Aldrich), 30% poly(ethylene glycol) (PEG 200, Sigma-Aldrich), 10% 2-hydroxy-2-methylpropiophenone (Sigma-Aldrich), and 3 mg ml −1 rhodamine acrylate (Polysciences). Fluorescently labelled PEG particles (20-µm length, 10-µm cross-sectional diameter) were collected and washed in Tween-20 solution (0.1% v/v, PBS) before dilution in HA solution (1,650 kDa, 0.1% w/v, water).…”

Synthesis of colloidal microgels using oxygen-controlled flow lithography

“…We note that the use of inert sheath ows is insufficient as the minimum gap height achievable is $2 mm (ref. 34) for any reasonable polymerization time due to diffusive mixing at the uid interfaces.…”

Flow lithography in ultraviolet-curable polydimethylsiloxane microfluidic chips

“…Therefore, photocrosslinked microparticles drift away from the site of UV exposure so that free-floating microparticles can be collected at downstream of the microchannel. 1,21 Unless one introduces inert layers that preclude photocrosslinking with a microchannel constructed with oxygen-impermeable materials, 22 it is imperative to satisfy this criterion. Second, the materials have to be optically transparent so that UV light penetrates through them and traverses the microchannel.…”

“…33 However, the nanoadhesive layer has been yet unsuitable for FL due to oxygen-impermeability. 22 Here, we propose the utilization of UV-curable PDMS for FL as a more optimal alternative material to conventional PDMS. Specifically, we were able to fabricate microfluidic chips simply by placing a micropatterned replica (fully cured by UV) on a partially cured layer, without any heat or plasma treatments.…”