Liposome-based sensors

Ultrasound-assisted preparation of liposome-based sensors... 

Roberts, M. A. and Durst, R. A. (1995). Investigation of Liposome Based Immunomigration Sensors for the Detection of Polychlorinated-Biphenyls. Anal. Chem. 67 482-491. 

The conjugation of a lipid to a pesticide allows its incorporation into a liposome structure, leading to competitive liposome lA-based sensor. The use of piezoelectric crystals as physical sensors is a continuously developing research direction. Other physical sensors are optical, such as surface plasmon resonance (SPR), interferometric, or grating couplers. 

The sensors discussed so far are based on ligands covalently bound to the polymer backbone. Other methods of detection - often referred to as mix and detect methods - work by simple noncovalent incorporation of the polymer with the ligand of interest. Reichert et al. generated liposomes of polydiacetylene with sialic acid for the same purpose of detection as Charych s surface-bound polymers, but realized that covalent functionalization of the polymer was not necessary [17]. Through simple mixing of the lipid-bound sialic acid with the polymer before sonication and liposome formation, they were able to form a functional colorimetric recognition system (Fig. 8). 

In both of these cases, the ligand (sialic acid) for the analyte of interest (influenza vims) was covalently linked to the PDA backbone generated upon photopolymerization. Functional sensors based on ligands that are noncovalently incorporated into liposomes have also been reported (Charych et al. 1996 Pan and Charych 1997). Mixed liposomes as well as mixed thin films on glass containing a combination of the ganglioside GMl and diacetylene lipids detect the presence of cholera toxin, a protein that binds to GMl. 

Although the bulk of PDA sensors involve vesicles and Langmuir monolayers, a few examples of responsive PDA assemblies based on bolaamphiphiles and diyne silica nanocomposites have been reported (Lu et al. 2001 Song et al. 2001, 2004 Yang et al. 2003 Peng et al. 2006). Although these materials have not been broadly utilized for analyte sensing, they do exhibit the thermochromic, solvatochro-mic, and pH responsive behavior seen with monolayers and liposomes and hold promise for future development. 

Study binding of 78 compounds to liposomes POPC and Avanti-blend captured on sensor chip [18]. Using an automatized SPR-based biosensor it is possible to develop a screening method to rank and characterize the binding of compoimds to captured hposomes of different properties based on binding responses, as shown in the histogram (Fig. 11b). 

Reisberg, S Dang, L.A., Nguyen, Q.A. et al. (2008) Label-free DNA electtochemical sensor based on a PNA-functionalized conductive polymer. Talanta, 76 (1), 206-210. Chumbimuni-Torres, K.Y., Wu, J., Clawson, C. et al. (2010) Amplified potentiomet-ric transduction of DNA hybridization using ion-loaded liposomes. Analyst, 135 (7), 1618-1623. 

The ability to identify particular sequences of DNA, both quickly and precisely has become of increasing importance in recent years. Current DNA detection methods are limited by their need for the DNA in the sample to be chemically labelled before analysis. In this poster, the biosensor described does not. In fact, the detector is the DNA mimic, peptide nucleic acid (PNA) whilst the sensor is based on polydiacetylene (PDA) liposomes. It is envisaged that when the PNA detector binds to its target gene, the PDA sensor will be induced to change colour from blue to red. It is anticipated that this response will be detected visually and quantified through UVA/is spectroscopy. In order to improve the hydrophilic character of the liposomes, a hydrophilic spacer has been included. Here, we report our progress to date on the preparation and evaluation of PNA-functionalised PDA liposomes as potential, novel colorimetric nucleic acid biosensors. 

Biosensors based on neuroreceptors can measure toxins or other chemical agents used in warfare. The use of acetylcholine receptors enables the determination of acetylcholine by the detection of a specific impedance compared with other neurotransmitters [93]. This receptor is associated with immobilized acetylcholinesterase, and is sensitive to its inhibitors, organophosphorus compounds and carbamates. The receptor is physically adsorbed onto a suitable sensor by immersing the sensitive tip of the sensor in a liposome solution containing the receptor. 

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