A microfabricated glass chip containing fluidic channels filled with polymer monolith has been developed for reversed-phase electrochromatography. Acrylate-based porous polymer monoliths were cast in the channels by photopolymerization to serve as a robust and uniform stationary phase. UV light-initiated polymerization allows for patterning of polymer stationary phase in the microchip, analogous to photolithography, using a mask and a UV lamp for optimal design of injection, separation, and detection manifolds. The monoliths are cast in situ in less than 10 min, are very reproducible with respect to separation characteristics, and allow easy manipulation of separation parameters such as charge, hydrophobicity, and pore size. Moreover, the solvent used to cast the polymer enables electroosmotic flow, allowing the separation channel to be conditioned without need for high-pressure pumps. The microchip was used for separation of bioactive peptides and amino acids labeled with a fluorogenic dye (naphthalene-2,3-dicarboxaldehyde) followed by laser-induced fluorescence detection using a Kr+ ion laser. The microchip-based separations were fast (six peptides in 45 s), efficient (up to 600,000 plates/m), and outperformed the capillary-based separations in both speed and efficiency. We have also developed a method for complete removal of polymer from the channels by thermal incineration to regenerate the glass chips.

We have developed porous polymer monoliths (PPMs) that are versatile and robust reversed-phase chromatography media. The PPMs are cast-to-shape, UV-cured polymers that form uniform packings within pretreated glass capillaries and fused-silica chips. No applied pressure is ever needed to flush the PPMs since they support electroosmotic flow as cast. Such characteristics make the PPMs useful for chip-based devices. Our results show efficiencies greater than or equal to 150,000 plates/m for both capillary and chip-based separations of polycyclic aromatic hydrocarbons. By changing the monomers, the hydrophobicity of the polymers, and the direction of the electroosmotic flow can be altered without degrading chromatographic performance. We describe here the development of these acrylate-based materials along with both physical and chromatographic characterization.

Poly(n-butyl isoeyanlde): yellow-brown solid; IR (KBr) 1639 (C=N) cm-1; 'H NMR (CC14) 0.95-1.45 (br, 7 H, (CH2)2CH3), 3.35 (br, 2 H, NCH2).Poly(3-pentyl isocyanide): pale yellow solid; IR (KBr) 1623 (C=N) cm"1.Poly (benzyl isocyanide): brown solid; IR (KBr) 1630 (C=N) cm"1; NMR (CDClt) 4.0-5.0 (br, 2 H, CH2), 6.5-7.S (br, 5 H, ArH). Polv( , -dimethylbenzy 1 isocyanide): pale yellow solid; IR (KBr) 1620 (C=N) cm"1; NMR (CDC13) 2.60 (br, 6 H, CH3), 6.3 (br, 5 H, ArH).Poly(phenyl isocyanide): yellow solid; IR (KBr) 1643 (C=N) cm"1; with the dominant theme being modification of the Koga macrocycle (Figure 1). The most easily transformed region is the "linker", ®, and several workers have varied this unit. Koga varied the length of the linker [( CH2)"] and its rigidity,5b Lehn7 8*and Koga5c introduced chirality by using tartrate-derived linkers, and Vógtle83 built an entirely carbocyclic host with carboxylates as solubilizing units. Diederich first introduced spiropiperidinium units emanating from the diphenylmethane carbon in an effort to remove the charge from the binding region. Later modifications by Diederich included the introduction of further spiropiperidinium units and methyl groups on the aromatic rings.93 Further development continues, and other designs have also received considerable attention.10 Design of a New Class of Hydrophobic Binding Sites. Several years ago we set out to develop a new class of water-soluble molecules with hydrophobic binding sites. Our initial goal, too, was to start with the Koga system-a structure known to bind organic molecules-and modify it in several important ways to enhance binding and the potential utility of the structures for applications in catalysis, transport, etc. The specific improvements we sought were as follows.(9) (a) Diederich, F.;

Chip-level integration of microdialysis membranes is described using a novel method for in situ photopatterning of porous polymer features. Rapid and inexpensive fabrication of nanoporous microdialysis membranes in microchips is achieved using a phase separation polymerization technique with a shaped UV laser beam. By controlling the phase separation process, the molecular weight cutoffs of the membranes can be engineered for different applications. Counterflow dialysis is used to demonstrate extraction of low molecular weight analytes from a sample stream, using two different molecular weight cutoff (MWCO) membranes; the first one with MWCO below 5700 for desalting protein samples, and the second one with a higher MWCO for size-based fractionation of proteins. Modeling based on a simple control volume analysis on the microdialysis system is consistent with measured concentration profiles, indicating both that membrane properties are uniform, well-defined, and reproducible and that diffusion of subcutoff analytes through the membrane is rapid.

Spatial patterning of thin polyacrylamide films bonded to self-assembled monolayers on silica microchannels is described as a means for manipulating cell-adhesion and electroosmotic properties in microchips. Streaming potential measurements indicate that the zeta potential is reduced by at least two orders of magnitude at biological pH, and the adhesion of several kinds of cells is reduced by 80-100%. Results are shown for cover slides and in wet-etched silica microchannels. Because the polyacrylamide film is thin and transparent, this film is consistent with optical manipulation of cells and detection of cell contents. The spatial patterning technique is straightforward and has the potential to aid on-chip analysis of single adherent cells.