Morphine-imprinted polymers

Fig. 18.3. The graph illustrates the competitive morphine sensor response as a function of the morphine concentration (0-10 pgjm ) present in the solution. Three sensor types were examined, incorporating the morphine-imprinted polymer in agarose, reference polymer in agarose and agarose-only covered platinum electrodes.

Kriz D, Mosbach K. Competitive amperometric morphine sensor-hased on an agarose immobilized molecularly imprinted polymer. Anal Chim Acta 1995 300 71-75. 

The quantitative determination of drugs by radio-immunoassay techniques using imprinted polymers instead of natural antibodies was investigated by Mosbach. Theophyllin, Diazepam and Morphine were recognised and cross-reaction tests with other but sterical similar molecules, gave similar results like the established antibody reactions [449]. Eventually the expensive antibodies can be replaced by cheap synthetic imprinted polymers [474]. 

The most developed areas for imprinted polymers are for sequestration and separation. Several reported imprinted polymer sensors have in actuality been pretreatments by separation to allow a selective determination using a general detection method. The adaptation of this to an FIA system would be relatively simple. For example, Kriz et al. [31] report a sensor for morphine (see Chapter 18). The method of morphine detection involved two steps. The first step was to immobilise the morphine by loading it on the imprinted polymer. In the detection step, the morphine was released from the column by elution of an electro-inactive competitor (codeine) and the released morphine was detected by an amperometric method. The polymer was tested after exposure to extremes of heat and chemicals and proved resilient. This method would probably be suitable for automation as a flow injection technique. 

The MIPs have also been utilized as the recognition elements in pseudoimmunoassays. " In this approach, MIPs are substituted for antibodies to quantify the amount of analyte in a biological sample, such as blood plasma. Most MIP immunoassays are competitive binding studies in which a radio- or fluorescent-labeled analyte is added to a mixture of the MIP and imlabeled analyte. After equilibrium is reached, some fraction of the labeled species is bound to the polymer surface and thus can be separated from the supernatant. The supernatant is then analyzed via scintillation or fluorescence techniques to determine the concentration of the original unlabeled analyte. Mosbach et al. have demonstrated that MIP-based immunoassays can rival the selectivity of antibody-based assays. Imprinted polymers for the opioid receptor ligands enkephalin and morphine were prepared and showed submicromolar (pM) level selectivity in a radioligand competition assay in aqueous buffers. The analysis... 

Ho KC, Yeh WM, Tung TS, Liao JY (2005) Amperometric detection of morphine based on poly(3,4-ethylene dioxythiophene) immobilized molecularly imprinted polymer particles prepared by precipitation polymerization. Anal Chim Act 542(1 ) 90—96... 

Molecularly imprinted sorbent assays represent one of the most typical applications of biomimetic use, where imprinted polymers are used as substitutes of natural antibodies in immunoassays. The assays usually involve competitive binding of an analyte with a certain quantity of labeled ligands, in which the labeled ligand unbound is proportional to the analyte added. Because dissociation constants of common imprinted polymers are around 10 6-10 9 M, competitive binding assays could easily be performed. In practice, many molecularly imprinted sorbent assays have been developed for biologically active compounds, including theophylline, diazepam [26], S-propranolol [27], morphine, Leu-enkephalin [28], cyclosporin A [29], yohimbine [30], methyl-a-glucoside [31], corticosteroid [32], atrazine [33, 34], and 2,4-D [35]. 

Mayes, A. Lowe, C.R. Optimization of molecularly imprinted polymers for radio-ligand binding assays. Royal Society of Chemistry Cambridge, UK, 1998 Vol. 25, 28-36. Andersson, L.I. Muller, R. Vlatakis, G. Mosbach, K. Mimics of the binding sites of opioid receptors obtained by molecular imprinting of enkephalin and morphine. Proc. Natl. Acad. Sci. USA 1995, 92, 4788 792. 

Thus, Mayes and Lowe showed that an MIA for morphine worked equally well when the MIP was synthesized using a morphine MAA ratio of 1 500 as 1 5 [21], while Yilmaz et al. showed an MIA for theophylline worked equally well with a theophylline MAA ratio of 1 1000 as 1 4 [22] Theophylline-imprinted polymers employing only 2.5 pmol template per gram of monomers (compared with 151 pmol g in Vlatakis et al. s MIA [16]) were employed, and the MIA functioned well, with caffeine cross-reacting less than 0.1%. These works demonstrate that the oft-quoted drawback of MIPs, the cost of the template required for their preparation, may be overcome MIA is applicable even to expensive templates. 

Kriz, D. Mosbach, K. Competitive Amperometric Morphine Sensor Based on an Agarose Immobilized Molecularly Imprinted Polymer. Anal. Chim. Acta 1995, 300, 71-75. 

Yeh, W.-M., and K.-C. Ho. 2005. Amperometric morphine sensing using a molecularly imprinted polymer-modified electrode. Anal Chim Acta 542 76. 

D. Kriz and K. Mosbach, Competitive amperometric morphine sensor based on an agarose immobilised molecularly imprinted polymer. Anal. Chim. Acta, 300 (1-3) 71-75, 1995. 

D. Djozan and T. Baheri, Preparation and evaluation of solid-phase microextraction fibers based on monolithic molecularly imprinted polymers for selective extraction of diacetyl-morphine and analogous compounds, / Chromatogr. A, 1166 (1-2) 16-23,2007. 

Liquid fluorocarbon was used as continuous phase by Perez-Moral and Mayes [19] as well. They proposed a new method for rapid synthesis of MIP beads, in that they prepared 36 polymers imprinted for propranolol and morphine with different amounts of EDMA as a cross-linker and different functional monomers (MAA, acrylic acid, hydroxyethyl methacrylate, 4-vinylpyridine) directly in SPE cartridges. The properties of MIP microspheres prepared by this method were very similar in terms of size, morphology and extent of rebinding to microspheres prepared by conventional suspension polymerisation in perfluorocarbons as well as to bulk polymers prepared in the same solvent. The most notable advantages of this method are no waste production (no transfer of beads during washing steps) and possible direct use for a variety of screening, evaluation and optimisation experiments. 

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