The design and synthesis of biomimetic materials that are capable of binding target molecules with high specificity has been a longstanding goal in the analytical chemistry, biomedical and materials science fields. One of the most promising approaches towards producing such materials is molecular imprinting of synthetic polymers. This technique involves using a molecular template, which directs the self-assembly of functional monomers that are subsequently co-polymerized in the presence of an excess of cross-linking monomers. The resulting molecularly imprinted polymers (MIPs) possess binding properties that often rival those of antibodies and enzymes, but with far greater stability than their natural counterparts. These properties make MIPs potentially very suitable as recognition elements for chemical sensors, biosensors or biochips [1]. Recent advances in the field will be described, with special emphasis on biochips and biosensors. Biomimetic microchips were produced by depositing MIP microdot arrays on surfaces. MIP precursors with fluorescein as the template were deposited with a microcantilever array. A sacrificial polymeric porogen, poly(vinylacetate), was used to obtain porous dots. Fluorescence microscopy revealed specific binding of fluorescein to the MIP dots. With another MIP selective for the herbicide 2,4-D, competitive binding assays were performed using a coumarin derivative as fluorescent probe [2]. Integrated MIP-based acoustic sensors were developed based on matrices of piezoelectric membranes. Each membrane can be individually actuated by a piezoelectric thin film with two platinum electrodes, allowing for simultaneous actuation and detection of the resonant frequency of the membranes. A MIP precursor solution containing the template 2,4-D and non-imprinted control polymer precursor solution were deposited on the membranes by microspotting. The dots were polymerized under UV light. Polymerization was monitored by following the membrane's resonant frequency in real time. Following polymerization, dip-and-dry experiments were performed in order to validate the MIP's functionality. Elution of the template resulted in an increase of the resonant frequency. This demonstrats the extraction of the template 2,4-D from the dots. After incubation in a 2,4-D solution, frequencies close to the initial values were measured showing that the MIP's binding sites are progressively reoccupied by 2,4-D, a reversible process that could be repeated numerous times. For certain sensor designs, the combination of molecular imprints with nanostructured materials is of particular interest. The creation of polymer surfaces nanostructured at two levels by simultaneous nanomoulding and molecular imprinting is described. Polymer nanomoulding resulted in polymer surfaces carrying nanofilaments or other nanostructures with surface molecular imprints. The number and size of the nanostructures could be fine-tuned by adjusting the morphology of the initial template surface. The molecular imprinting effect was demonstrated using fluorescent ligand or radioligand binding. The usefulness of these molecularly imprinted surfaces as recognition layers in optical sensors was evaluated. The surfaces were also characterised with respect to additional features such as, wetting properties, by contact angle measurements and direct observation of the formation of water microdroplets using environmental scanning electron microscopy. It was found that nanostructuration rendered more hydrophobic a hydrophobic polymer, and more hydrophilic a hydrophilic one [3].

[1] K. Haupt, "Imprinted polymers - Tailor-made mimics of antibodies and receptors", Chem. Commun. 2, 171-178, 2003.

[2] F. Vandevelde, T. Leïchlé, C. Ayela, C. Bergaud, L. Nicu, K. Haupt, "Direct patterning of molecularly-imprinted microdot arrays for sensors and biochips", Langmuir 23, 6490-6493, 2007.

[3] Fanny Vandevelde, Anne-Sophie Belmont, Jacques Pantigny, Karsten Haupt (2007) Hierarchically nanostructured polymer films based on molecularly imprinted surface-bound nanofilaments. Advanced Materials (in press)

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1. Micro and nanofabrication of molecularly imprinted polymer synthetic receptors for sensing applications
2. Nanostructured molecularly imprinted polymers - synthetic receptors for protein recognition
3. Piezoelectric Microgravimetry for Determination of Some Biologically Important Compounds