Surface imprinting

Bulk and surface imprinting strategies are straightforward tools to generate artificial antibodies. Combined with transducers such as QCM (quartz crystal microbalance), SAW (surface acoustic wave resonator), IDC (interdigital capacitor) or SPR (surface plasmon resonator) they yield powerful chemical sensors for a very broad range of analytes. 

Recently, an in-depth review on molecular imprinted membranes has been published by Piletsky et al. [4]. Four preparation strategies for MIP membranes can be distinguished (i) in-situ polymerization by bulk crosslinking (ii) preparation by dry phase inversion with a casting/solvent evaporation process [45-51] (iii) preparation by wet phase inversion with a casting/immersion precipitation [52-54] and (iv) surface imprinting. 

Silica particles surface-imprinted with a TSA of a-chymotrypsin were applied for the enantio-selective hydrolyzation of amides. Surprisingly, the particles showed reverse enantio-selectivity, i. e., the sol-gel imprinted with the L-isomer of the enzyme s TSA showed a higher selectivity for the D-isomer of the substrate [125]. Also Ti02 gels have been imprinted, e.g., with 4-(4-propyloxypheny-lazo)benzoic acid. QCM coated with ultrathin films of this gel were prepared by an immersion process and showed selective binding of the template [ 126]. These examples demonstrate once more the broad applicability of the concept of molecular imprinting. 

Ko DY, Lee HJ, Jeong B. Surface-imprinted, thermosensitive, core-shell nanosphere for molecular recognition. Macromolecular Rapid Communications 2006, 27, 1367-1372. 

Yang and coworkers also used a surface imprinting approach to prepare nanotube membranes that exhibit selectivity for the molecule estrone.77 In this study, the silica nanotubes with pore diameters of 100 nm were synthesized within the cylindrical pores of nanopore alumina membranes. A covalent assembly approach was used to prepare the imprint.77 Zhang and coworkers have also recently shown how silica nanotubes can be used as an imprinting scaffold.78 In this example, trinitrotoluene (TNT)... 

Whitcombe et al. concentrated on the synthesis of hydrophobic surface imprints in particles with a hydrophilic surface layer. To achieve hydrophilicity of the particles surface they chose divinylbenzene as crosslinker and an additional polymerizable surfactant (PS) (Fig. 4) with a charged end group for the shell polymerization. Thereby, imprinted particles of submicrometer scale, with good monodispersity and high surface area could be prepared. A schematic diagram of the design of hydrophobic surface imprints in particles with a hydrophilic surface layer is shown in Fig. 5. 

Fig. 5. Schematic diagram of the creation of hydrophobic surface imprints in particles with a hydrophilic surface layer (adapted from [28])...

Emulsion polymerization was successfully employed for the preparation of nano-scale MIPs by synthesizing core-shell latexes with an imprinted shell. The use of a template with surfactant properties led to enhanced surface imprinting. Magnetic cores were synthesized to render MIPs which could be manipulated by magnetic fields in suspension, thereby facilitating the separation of the colloidal solid phase from the suspending solution. 

Molecular imprinting polymerisation of Cu -IDA monomer (4)- )w-imidazole template assemblies on this reactive polymer surface enabled the creation of surface confined metal-complexing polymeric receptors. Faster kinetics for substrate and metal ion removal and reloading were observed with these imprinted polymers when compared to their bulk polymerised counterparts. The substrate recognition capabilities of both kinds of polymers were found to be comparable. This surface imprinting procedure is illustrated in Fig. 6.2. 

Fig. 6.2. Synthetic strategy for the preparation of surface imprinted metal-coordinating polymers using poly(TRIM) particles.

Fig. 6.3. Elution profile for fiM-imidazole substrates on a column packed with surface imprinted metal-coordinating silica particles prepared by using i -imidazole (4) as the template.

Fig. 8.7. Surface imprinting with a covalently coupled diimine template has been used to position two amines onto a flat silica surface in an effort to isolate the effect of functional group placement in molecular imprinting. The rectangular spacer between the imines represents either a phenyl or diphenylmethane. Adapted from [37].

Surface imprinting has recently been used in our laboratory to prepare phosphate and phosphonate receptors in silica xerogels [38]. In an effort to obtain faster on/off binding kinetics and gain thermodynamic control of the host-guest interaction, we positioned the receptor sites as close as possible to the gel surface. This resulted in observed equilibration binding times of less than a minute. 

Other results involving liquid chromatography separations with imprinted metal oxides have been published in recent years. Norrlow et al. prepared surface imprinted silica gels functionalised with boronic acids that could form covalent linkages with riboses via boronate ester formation [43]. The gels were imprinted with templates containing two (nicotinamide adenine dinucleotide (NAD)) or four ribose units (bis-NAD 1, bis-NAD II). Columns were packed with the imprinted... 

The concept of surface imprinting by the use of seed emulsion polymerisation... 

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