Polyurethane-based MIPs

Dickert and co-workers [18] have made an innovative advance by applying polyurethane-based MIPs to quartz crystals for the selective detection of solvent vapours (see also Section 20.2.5.8. and Chapter 21). Electrodes may be attached to quartz crystals to form quartz crystal microbalances (QCMs), wherein minute increases in the mass of the device (for example, upon adsorption of solvent vapour) result in a decrease of the resonant frequency of the crystal. For crystals... 

The protocol below outlines the steps used to create polyurethane-based MIP micromonoliths covalently attached to a silicon wafer support. The imprinting system was adapted from Dickert and Thierer [60], Dickert and Tortschanoff [61] and has not been optimized for the porosity required for flow-through monolith applications. 

To date, MIP microstructures have been successfully fabricated with dimethyl-formamide (DMF) as a solvent in both an acrylate-based [55] and a polyurethane based [59] imprinting system. While this solvent still swells PDMS, its effect is small. Other imprinting systems that utilize water and alcohols as the solvent may be possible since these solvents do not swell the PDMS stamps. Alcohols are the best as they have alow surface tension and wet the surface of the PDMS well. Water, however, has a high surface tension and does not wet the surface of the hydrophobic PDMS stamps. Possible solutions may be to render the stamp more hydrophilic by O2 plasma or UY irradiation to add a small percentage of alcohol ( 5 %) to the aqueous solution to wet the surface, or to use a small vacuum-assisted pump to fill the channels. 

Polycyclic aromatic hydrocarbons were also used for imprinting polyurethanes based on Van der Waals interactions, and the resulting MIPs were used for the recognition of the templates [80]. Cholesterol has also been used as the template in the polymeriza-ton of (3-cyclodextrin with diisocyanates in dimethyl sulfoxide [81]. In another work, the vinyl monomer of 6-0-a-D-glucosyl-(3-cyclodextrin was imprinted with dipeptides [82] or cyclodextrin [83]. Other examples include imprinting acryloylamylose with bisphenol A and alkylphenols [84]. 

Dickert et al. [58-61] had introduced the in situ synthesis of polyurethanes as very versatile system for the preparation of thin MIP films, especially due to the excellent film forming properties of the polymer. These materials had been especially successful for imprinting of templates without a distinct functional group, i.e., recognition was based mainly on shape complementarity. This system could also be useful for imprinting large templates such as cells [61]. 

---