Molecularly Imprinted Polymers at the Nanometric Scale: Synthetic Receptors for Chemical Sensors

In this thesis, polymerisation techniques or deposition methods have been developed permitting the creation of thin molecularly imprinted polymer (MIP) films or patterns and their interfacing with transducer surfaces for biosensor applications.

The creation of ultra thin films has been achieved using two different techniques, spin-coating and in-situ polymerization of thin films of monomers containing a sacrificial polymeric porogen, and autoassembly of MIP nanoparticles with the aid of an associative linear polymer. These films were then used in an optical sensor based on reflectometric interference spectroscopy. Reproducible results were obtained upon measurements on both types of films and concentrations of the target analyte atrazine in the lower ppm range were possible. We were also able to elucidate the pore-forming mechanism in the case of the spin-coated films.

Patterning of surfaces with MIPs in the form of micro and nano dots were achieved by a novel deposition method using fountain pen nanolithography, a scanning probe microscopy technique able to create nanoscale patterns due to its high spatial precision. Fluorescein was chosen as model analyte which enabled direct fluorescent microscopic detection of the MIP dots. The fluorescence variations of the dots upon washing and rebinding steps clearly proved that the nanofountanin pen is a very promising technique to create nanobiomimetic structures on a surface.

In order to specifically detect the molecular template or the target analyte in such small structures, Raman spectroscopy was chosen as the method of choice, as it was able to detect the weak signals obtained upon binding with these small structures. In addition, the high information content of the Raman signal often allows the binding molecule to be identified. A feasibility study was performed and Raman spectroscopy was used to detect the presence of a model template, S?propranolol, in MIP nanostructures, and to follow its extraction from and binding to the MIP.

In environmental analytical chemistry, there is growing interest in using MIPs as synthetic receptors for the detection of endocrine disrupting compounds. We have done a comparative study with the biological estrogen receptor and with MIPs against estradiol and testosterone, to evaluate whether MIPs can be used not only for detection but also to screen new substances for a possible endocrine disrupting effect. The data revealed a certain similarity in the cross-reaction profiles between MIP and biological receptor, even if the high selectivity of the MIPs prevented certain endocrine disruptors from being detected.