Preparation of monolithic polymers with controlled porous properties for microfluidic chip applications using photoinitiated free‐radical polymerization

Abstract

A broad variety of monolithic macroporous polymers with both controlled chemistry and porous properties was prepared using UV‐initiated free‐radical polymerization. The chemistry of the monoliths is defined by the composition of the monomer mixture used for the polymerization. The use of functional methacrylate monomers such as glycidyl methacrylate, 2‐hydroxyethyl methacrylate, butyl methacrylate, 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid, and [2‐(methacryloyloxy) ethyl] trimethylammonium chloride enabled the preparation of monoliths with reactive, hydrophilic, hydrophobic, and ionizable functionalities, respectively. The porous properties of these monoliths were mainly affected by the choice of the porogenic solvent system. Because the UV polymerization was carried out at room temperature, even low molecular weight alcohols and other low boiling point solvents could safely be used to create a versatile series of binary porogenic mixtures. Monoliths were prepared in spatially defined positions using the photolithographic technique within a fused silica capillary and on microfluidic chips, and the former was demonstrated with the separation of derivatized amines by means of capillary electrochromatography in the reversed‐phase mode. Similarly, a monolith prepared in the microchip format was used to demonstrate a microextraction with enrichment of a solution of green fluorescent protein by a factor of 1000. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 755–769, 2002; DOI 10.1002/pola.10155

Why the move to microfluidics for protein analysis?

“…The outstanding surface-tovolume ratio of microchannels (typically 80 000 m À1 compared with 500 m À1 for a microtiter plate well) allows elution of samples in incomparably small volumes after capture on a solid-phase extraction (SPE) sorbent [4,5] (see Figure 2). Yu et al further increased the intrinsically high surface-to-volume ratio of their microfluidic device by incorporating a monolith within the microchannel [6]; by eluting green fluorescent protein in a very small volume they were able to reach 1000-fold preconcentration [7].…”

Optimization of the porous structure and polarity of polymethacrylate‐based monolithic capillary columns for the LC‐MS separation of enzymatic digests

“…Polymer-based monoliths are typically prepared in-situ from a liquid precursor [15,16], a feature that makes the monolithic stationary phases very attractive for their use in narrow bore capillaries and microfluidic devices. Both the chemistry and the porous properties of the monoliths, which have a direct effect on their chromatographic performance, are readily controlled by the composition of the polymerization mixture and conditions used for the in situ polymerization [17][18][19][20].…”

Mixing in polymeric microfluidic devices.

“…Porous mixers are considered passive mixers and are often compared with packed bed mixers or with mixers that use structures within the microchannels. Common fabrication techniques for porous monoliths uses phase separation photopolymerization [36][37][38][39][40]. These studies have focused on controlling the pore properties within the monoliths.…”