Former post-doc of Prof Paunov Dr Chun Xu worked as a Post-Doctoral Fellow in Paunov’s research group at the University of Hull 2001-2005. Supervisors: Prof Vesselin N. Paunov (PI) and Prof Paul Fletcher (Co-PI)

Research project 1:

Adsorption and hybridisation of DNA-surfactants at fluid surfaces and lipid bilayers

We have explored the properties of a new class of smart surfactants based on DNA. The DNA-based surfactants are prepared by conjugating a hydrophobic group to a short-chain oligonucleotide [1]. We show that DNA-surfactants can adsorb at the air–water surface and oil–water interfaces and can be incorporated within lipid bilayers (see Figs 1 ans 2). We demonstrated that once adsorbed the DNA-surfactants used remain on the liquid surface upon hybridisation with a complementary DNA chain. We also demonstrated that DNA-surfactants of a suitable hydrophobic group can hybridise with complementary DNA when adsorbed at an oil–water interface [2] (see also Figs 3 and 4). We showed that small liposomes functionalised with DNA-surfactants can be specifically deposited onto complementary DNA-patterns on solid substrates. Our results indicate that the deposited liposomes remain intact upon deposition on the DNA-pattern. We use complementary DNA surfactants to functionalise fluid surfaces and to program the interactions between them based on Watson–Crick pairing. By selecting the appropriate DNA base sequences the interaction between the fluid surfaces functionalised with DNA-surfactants can be programmed with the level of specificity of the enzyme–substrate interaction (Fig. 1). We also suggest a novel type of aqueous ink based on DNA-functionalised small liposomes for micropatterning of solid surfaces with DNA by a microcontact printing technique. We illustrate the capabilities of this technique by specific deposition of complementary DNA-functionalised liposomes onto DNA-micropatterned solid surfaces. 

Fig. 1. Schematic representation of the concept of the DNA-based surfactants and their properties. (A) DNA-surfactants are conjugates of a short-chain oligonucleotide, covalently bond to a hydrophobic group at its 3’- or 5’-end. (B) The DNA-based surfactant molecules can adsorb at various liquid surfaces, including air–water and oil–water interfaces as well as lipid bilayers. The DNA chain orientates with respect to the liquid interface. (C) Watson–Crick interaction between DNA-surfactant monolayers adsorbed at liquid surfaces or lipid bilayers can lead to specific programmable interactions between fluid surfaces.

Fig. 2 (A) Surface tension of the air–water surface vs. time for a solution of 150 μM (C₁₂-O)4-5’-GGGGGGAAAAAA-3’ in MilliQ water. (B) Dodecane–water interfacial tension vs. time for 230 μM solution of cholesteryl-5’-GGGGGGAAAAAA-3’ in MilliQ water. The measurements are conducted at 20 °C.

Fig. 3 Scheme of our experiment to check whether the DNA-surfactant remains adsorbed at the oil–water interface upon hybridization with a complementary DNA strand. (A) An oil drop deposited on a glass slide under water is exposed to a solution of DNA-surfactant. (B) The solution is replaced with a solution of complementary fluorescently-tagged DNA which can hybridise with the DNA-surfactant monolayer (C) adsorbed at the oil–water interface.

Fig. 4 (A) A confocal fluorescence microscope image of hexadecane drops deposited on a glass slide under water and treated (i) with 66 μM solution of cholesteryl-5’-GGGGGGAAAAAA-3’ followed by (ii) 85 μM solution of complementary TAMRA-5’-TTTTTTCCCCCC-3’. The image shows the fluorescent signal from TAMRA-DNA localised at the drop surface. Here the confocal plane is set close to the oil–glass boundary. (B) An optical microscope images of the same drops as (A) in transmitted light. (C) The control experiment: a confocal fluorescence microscope image of hexadecane drops deposited on a glass slide under water and treated (i) with a 66 μM solution of cholesteryl-5’-GGGGGGAAAAAA-3’ followed by (ii) 85 μM solution of a non-complementary TAMRA-5′-GGCCAGTCACTG-3′. Here the oil drops are darker than the background. No fluorescent signal is detected from TAMRA-DNA at the drop surface. (D) An optical microscope images of the same drops as (C) in transmitted light.

References

1. Xu, C., Taylor, P., Fletcher, P.D.I., Paunov, V.N., “Adsorption and Hybridisation of DNA-surfactants at Fluid Surfaces and Lipid Bilayers”, J. Mater. Chem., 15 (2005) 394-402.
2. Paunov, V.N., Xu, C., Taylor, P., Ersoz, M., Fletcher, P.D.I., “Properties and Applications of Novel DNA-Based Surfactants”, MRS Proceedings Fall 2004, volume 845, AA6.4.1-6.