Optical Transduction Schemes for Molecularly Imprinted Polymer Sensors
- PDF / 127,289 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 51 Downloads / 235 Views
G5.1.1
Optical Transduction Schemes for Molecularly Imprinted Polymer Sensors George M. Murray and Glen E. Southard Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099 ABSTRACT Molecular imprinting is a useful technique for making a chemically selective binding site. [1] The method involves building a synthetic polymeric scaffold of molecular compliments containing the target molecule with subsequent removal of the target to leave a cavity with a structural “memory” of the target. Molecularly imprinted polymers can be employed as selective adsorbents of specific molecules or molecular functional groups. Sensors for specific molecules can be made using optical transduction through chromophores residing in the imprinted site. The use of metal ions as chromophores can improve selectivity due to directional bonding. The combination of molecular imprinting and spectroscopic selectivity can result in sensors that are highly sensitive and nearly immune to interferences. [2] INTRODUCTION Spectroscopic sensing requires that a chromophore must be available and be influenced by the rebinding of the imprinted analyte. This can be accomplished in a variety of ways, the simplest of which is when the analyte is a chromophore itself. Sensors based on intrinsic analyte chromophores benefit from molecular imprinting by both selectivity and sensitivity enhancement. In terms of selectivity, molecules similar to the analyte are likely to have similar spectroscopic parameters that could be the source of interference in a conventional sensing strategy. The inability of an interferent to bind to the imprinted polymer allows discrimination. In terms of sensitivity, the analyte molecules can be effectively concentrated from the solution by the imprinted polymer. The degree of such concentration is controlled by the relevant binding constant. The target chromophore can be shielded from quenchers by the polymer matrix. The inclusion of non-complexing monomers isolates the chromophore, eliminates crosstalk and reduces concentration quenching. In the case of metal ion luminescence, the use of appropriate complexing ligands can enhance the intensity by several orders of magnitude through a variety of mechanisms. Many metal ions are intrinsic chromophores and can be sensed by absorbance or luminescence. The transition metals exhibit colors based on inter-configurational d electron transitions. The intensity and the positions of the spectral bands can be influenced with a judicious choice of coordinating ligand. The molar absorptivities are less than those of organic chromophores due to the "forbidden" nature of the inter-configurational transitions, but proper choice of coordinating ligands can improve the absorptivity. Metal ions in the d block exhibit directed bonding and can provide both transduction and a proper geometry for analyte binding making useful extrinsic chromophores. By using an adducting strategy that changes the geometry of the reporter complex, significant changes in optical absorbance can be obtained. Lan
Data Loading...
