Andrew G. Mayes

MOLECULARLY IMPRINTED POLYMERS : USEFUL MATERIALS FOR ANALYTICAL CHEMISTRY?

Abstract Molecular imprinting is a technique for producing chemically selective binding sites, which recognize a particular molecule, in a macroporous polymer matrix. This paper reviews recent advances in imprinting methodology, particularly emphasizing some recently introduced functional monomers and methods which directly yield polymeric material suitable for chromatography. Following this, attempts to incorporate imprinted polymers into a range of analytical methodologies are critically discussed, with some pointers to likely directions for future research.

A holographic sensor based on a rationally designed synthetic polymer.

A new silver halide‐containing holographic recording material has been designed and developed specifically for holographic chemical sensors. The hologram enables very small volume changes to be measured in a polymer layer throughout which the hologram is located. The holographic film is based on a fine–grain silver bromide emulsion suspended in a poly(vinyl alcohol) matrix crosslinked with Cr(III) ions. Crosslinking gives the material sufficient spatial integrity to allow a holographic image to be recorded, while maintaining adequate porosity and elasticity of the polymer matrix for sensing applications. The new material has been characterized with respect to its response to pH and compared with a traditional gelatin holographic film. The response to some ions and small molecules typically found in analytical samples has also been measured. Functional groups introduced covalently into the poly(vinyl alcohol) matrix transform the base matrix into a pH‐responsive polymer with predictable swelling properties and which can be further derivatized to incorporate specific ligands. A rationally designed holographic sensor for trypsin has been developed from chemically synthesized artificial polymers. A trypsin substrate, the poly(amino acid) poly(L‐lysine), was incorporated into poly(vinyl alcohol) holograms to create a ‘designed’ holographic material which was degraded in a concentration‐dependent manner by trypsin. Extensions of this approach to other hydrolytic enzymes are briefly discussed. Copyright

A diffusion method for making silver bromide based holographic recording material

AbstractA simple diffusion method for the distribution of ultrafine silver bromide grains in pre-coated gelatin and customized polymeric films for holographic recording has been developed. The method involves two steps: immersion of the pre-formed film in a solution of a silver salt, followed by agitation of the film in a solution of a bromide salt containing sensitizing dye. Repetition of the operation on the same film with different sensitizing dyes in the bromide bath enables the production of film with a panchromatic response. Transmission electron microscopy reveals a grain structure very suitable for use in holography. A reflection hologram made by this method has a similar brightness under the same exposure and processing conditions to one made from a proprietary hologram recording material currently available.

A hologram biosensor for proteases

Abstract The concept of using a hologram as the interactive element in a one-shot biosensor is presented. The theoretical basis for a directly observed optical response to biological molecules is introduced. The most immediate application of such a device, restricted to the detection of proteases, is described in this paper. Using spectrographic measurements, a reflection hologram in gelatin in particular has been applied to the detection of 20 μg ml −1 trypsin and 23 μg ml −1 chymotrypsin, showing a greater sensitivity to trypsin. Enhanced specificity to trypsin has been shown following treatment of the hologram with bovine pancreatic trypsin inhibitor (BPTI), although measurements of pancreatin have yielded only a non-calibrated response. Sensitivity to trypsin down to 0.04 μg ml −1 has been shown. The sensitivities described are relevant to normal trypsin levels in duodenal fluid and faeces, suggesting that a holographic biosensor of this type will be useful as a low-cost quantitative screening test for pancreatic disorders manifest by low levels of enzyme. Improvement in specificity and extension of the concept to other types of analytes is likely to require modified gelatin or hologram-bearing materials other than gelatin.