Thin films of a molecularly imprinted sol-gel polymer with specific binding sites for parathion were developed. The films were cast on glass substrates and on glassy carbon electrodes and were used to detect parathion in aqueous solutions. Gas-phase binding measurements were performed on coated quartz crystal microbalance resonators. The binding of parathion to the imprinted films in the liquid phase was investigated by steady-state experiments with analysis by GC-FPD and cyclic voltammetry. The imprinted films showed high selectivity toward parathion in comparison to similar organophosphates. The binding was shown to be very sensitive to the type of functional monomer used for imprinting, and that rational design of the matrix components is an essential step in molecular imprinting. Specific binding in the gas phase proved to be less sensitive to the imprinting effect and exhibits relatively high nonspecific binding. The difference between molecular recognition in the gas-and liquidphase imprinted polymer is discussed.Organophosphate (OP) pesticides present a challenge for detection and identification in both the gas and liquid phase. The organophosphate esters are commonly used as persistent pesticides and nerve agents. Thus, it is highly desirable to develop methods for the detection of these compounds in ppb levels. The most common methods involve preconcentration of the organophosphate on a solid phase and subsequent detection by highperformance liquid chromatography or gas chromatography (GC), often coupled to MS. 1,2 Several studies used electrochemical methods to detect electroactive OP compounds 3-5 or applied electrochemical and gravimetric techniques in conjunction with enzymes, predominantly choline esterase and organophosphate hydrolase, to detect OP compounds. [6][7][8][9][10] The potential use of the molecular imprinting technique for sensing applications has been realized in several reviews. 11-14 A frequent issue that emerges from reviewing the relevant literature concerns the coupling between a sensitive transducer and a specific polymer film. Several transduction techniques have been coupled to molecularly imprinted polymers (MIPs), which include fluorescence, 12,15 electrochemical methods (voltammetric, 16 amperometric, 17 or conductometric 18 methods), and mass-sensitive sensors. 19,20 Most of these studies couple particles of acrylic-based MIP to the transducer. By this method the full potential of the MIP as a specific binding element is not exploited, since the diffusion into a particle is slow. Thus, methods for the preparation of films of MIP have been developed. The preparation of acrylic MIP films requires special experimental consideration. [20][21][22] Application of the sol-gel method to construct thin MIP films is favorable since control of the thickness, porosity, and surface area is easier, while the selectivity and diffusion are comparable and even better than acrylic polymer-based films. [23][24][25] Recently, the use of MIPs as specific preconcentration element or detection pl...

Enantioselective surfactant-templated thin films were fabricated through the sol-gel (SG) process. The enantioselectivity is general in the sense that it discriminates between pairs of enantiomers not used for the imprinting process. The chiral cationic surfactant (-)-N-dodecyl-N-methylephedrinium bromide (1) was used as the surfactant template, and after its extraction chiral domains were created. The chiral discriminative feature of these films was examined by challenging with pure enantiomer solutions for rebinding. Selective adsorption was shown using (R)- and (S)-propranolol, (R)-2 and (S)-2, respectively, and (R)- and (S)-2,2,2-trifluoro-1-(9-anthryl)ethanol, (R)-3 and (S)-3, respectively, as the chiral probes. The selective adsorption was measured by fluorescence analysis, and the chiral selectivity factors were found to be 1.6 for 2 and 2.25 for 3. In both cases, (R)-enantiomer was adsorbed preferably. The resulting material was characterized by transmission electron microscopy, by diffraction, and by surface area measurements, and was found to be semicrystalline with short-range ordered domains (50 A) of hexagonal symmetry.

Thin films with enantioselective properties for electrochemically active chiral probes were developed. Enantioselectivity was accomplished via molecular imprinting. The films were fabricated through the sol-gel technique and were spin-coated on ITO electrodes. The chiral selectivity recognition was detected using two enantiomer pairs: D- and L-3,4-dihydroxyphenylalanine (D- and L-dopa) and (R)- and (S)-N,N'-dimethylferrocenylethylamine [(R)-Fc and (S)-Fc]. A defined chiral cavity was obtained by selection of functional monomers that interact with the template molecule, followed by its removal. Chiral selection properties were measured by cyclic voltammetry and square wave voltammetry. For both template molecules, very good chiral recognition was revealed by electrochemical measurement. The nonspecific adsorption measured for reference nonimprinted films was negligible (less than 5%). Dopa imprinted films revealed both high sensitivity, by the detection of 1 nM (0.2 ppb) concentration, and excellent selectivity, when challenged with a series of catechol derivatives. Fc-imprinted films were able to detect ca. 2 ppm of the target molecule, with very good enantioselectivity and low nonspecific adsorption. To our knowledge, this is the first report of successful molecular imprinting of a ferrocene derivative.

Chirally imprinted sol-gel thin films were fabricated through the molecular imprinting technique. The films were spin coated on glass plate substrates. Enantioselective discrimination of these films was observed toward three different templates. In each case a different enantiomer pair was selected as a template and a sol mixture was tailored accordingly. By extracting the template molecule a defined chiral cavity was created. The enantiomer pairs were (R)-and (S)-propranolol, (R)-and (S)-2,2,2-trifluoro-1-(9-anthryl) ethanol, and D-and L-3,4-dihydroxyphenylalanine (D-and L-dopa). Selective adsorption properties of the resulted films toward the imprinted molecules were measured by radioactive and fluorescence analysis. In all cases, preferred adsorption of one enantiomer was revealed. This preference was due to configuration match between the cavity and the adsorbed molecule. Nonspecific adsorption was remarkably low and was measured for reference nonimprinted films.

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We review the different approaches that lead to chiral sol-gel materials. These methods include the use of silanes bearing a chiral group for silylating the surface of the porous sol-gel (SG) material, the use of such silanes as monomers or co-monomers in SG polycondensations, the physical entrapment of chiral molecules by SG procedures, the imprinting of SG materials with chiral templates and the creation of chiral pores, and the induction of chirality in the matrix skeleton itself. Analytical methods for detecting chirality are reviewed, including fluorescence methods, electrochemical methods, NMR, and induced CD. Applications are reviewed as well, including sensing, catalysis, chromatography, and optics. While most of the examples are focused on silicas and derivatized silicas, the methods and the analytical tools are generally applicable to other oxides and to preparation procedures other than sol-gel processes.

The molecular imprinting technique was applied on a model compound, propranolol, using two polymeric systems, acrylic and hybrid organic-inorganic sol-gels. The polymers were applied as thin films on glass substrates. The preparation of thin films of imprinted acrylic polymers required the development of a new polymerization system. The binding properties of the two polymers toward propranolol were characterized by radioactive and fluorimetric assay procedures. The acrylic system was found to have high uptake toward propranolol, but this was accompanied by a high degree of nonspecific binding. The sol-gel system had lower uptake, but remarkably lower nonspecific binding (<10%). The K d of the sol-gel matrix to propranolol is 80 ( 6 nM, a value that is common in biological systems. The binding was found to be solvent sensitiveswith high affinity and specificity in aqueous solution, which was completely lost in organic solvents. The uptake kinetics of the acrylic polymer was significantly slower than the sol-gel polymer, reaching saturation after 10 h, relative to <1 h for the sol-gel polymer. Imprinting of the sol-gel film with enantiomerically pure (S)propranolol resulted in its pronounced chiral recognition over the (R)-enantiomer.

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