Colorimetric Biosensor Vesicles for Biotechnological Applications
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Colorimetric Biosensor Vesicles for Biotechnological Applications. Revital Halevy1, Sofiya Kolusheva1, Robert E.W. Hancock2 Raz Jelinek1. 1 Department of chemistry, Ben-Gurion University of the Negev, Beersheva,84105 Israel. 2 Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada. ABSTRACT Supramolecular assemblies of vesicles composed of natural lipids embedded in a matrix of polydiacetylene are shown to undergo blue-to-red color changes related to specific interactions between the lipids or recognition elements and biomolecules. The colorimetric transitions observed in the vesicles are due to structural modifications within the conjugated PDA polymer backbone. This colorimetric assay could serve as a membrane-mimicking environment for detection of interfacial processes, such as peptide-membrane interactions, antibody-antigen binding, enzymatic catalysis, and detection of physiological ions. The lipid/PDA mixed vesicles are robust and can be readily applied to diagnosis of physiological molecules and rapid screening of biological and chemical libraries. INTRODUCTION PDA-based vesicles have been previously shown to undergo blue-to-red color transitions induced by a variety of interfacial processes. The color transitions observed in the vesicles are believed to originate from structural changes at the conjugate PDA polymer backbone [1]. Previous studies have shown that biological processes leading to structural perturbations at the PDA vesicle interface, including enzymatic catalysis [2], pH- changes [3], or ligand-receptor recognition [4], also induce blue-to-red transitions occurring in the vesicle assemblies. We have recently demonstrated that PDA vesicles incorporating a high percentage of lipid molecules [Figure 1] similarly undergo colorimetric transitions and could be used for studying biological and chemical processes [5-8]. In the following we demonstrate some applications of the system.
Figure 1 Schematic representation of the lipid/PDA vesicles, indicating a part of the assembly of lipids and polydiacetylene. PC denotes the phosphatidylcholine headgroup.
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EXPERIMENTAL DETAIL Mixed vesicles composed of physiological lipids and PDA were prepared using approximately 40% (mole ratio) lipids, such as dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG), and 60% polydiacetylene (PDA) lipids. Following sonication and polymerization, the lipids form organized assemblies that exhibit an intense blue color due to the conjugated backbone of the PDA polymer. The macrocyclic receptor homooxacalixarene triether [9] was inserted into the lipid moieties within DMPC/PDA following the polymerization step without disruption of the liposome organization or chromatic properties. UV-vis measuremen
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