Elsevier

Biosensors and Bioelectronics

Volume 20, Issue 7, 15 January 2005, Pages 1373-1379
Biosensors and Bioelectronics

Conducting polymer polypyrrole supported bilayer lipid membranes

https://doi.org/10.1016/j.bios.2004.06.001Get rights and content

Abstract

Electrochemically synthesized conducting polymer polypyrrole (PPy) film on gold electrode surface was used as a novel support for bilayer lipid membranes (BLMs). Investigations by surface plasmon resonance (SPR) suggest that dimyristoyl-l-alpha-phosphatidylcholine (DMPC) and dimyristoyl-l-alpha-phosphatidyl-l-serine (DMPS) can form BLMs on PPy film surface but dimyristoyl-l-alpha-phosphatidylglycerol (DMPG) and didodecyldimethylammonium bromide (DDAB) can not do so, indicating the formation of PPy supported bilayer lipid membranes (s-BLMs) is dependent on the chemical structure of the lipids used. The self-assembly of DMPC induces a smoother topography than the PPy layer with rms roughness decreasing from 4.484 to 2.914 nm convinced by atomic force microscopy (AFM). Impedance spectroscopy measurements confirm that the deposition of BLM substantially increases the resistance of the system indicating a very densely packed BLM structures. The little change of PPy film in capacitance shows that solvent and electrolyte ions still retain within the porous PPy film after BLM deposition. Therefore, the PPy supported BLM is to some extent comparable to conventional BLM with aqueous medium retaining at its two sides. As an example and preliminary application, horseradish peroxidase (HRP) reconstituted into the s-BLM shows the expected protein activity and can transfer electron from or to the underlying PPy support for its response to electrocatalytic reduction of hydrogen peroxide in solution. Thus the system maybe possesses potential applications to biomimetic membrane studies.

Introduction

Bilayer lipid membranes (BLMs) have been extensively used in recent years as models for biological membranes. It is often necessary to immobilize lipid bilayers on solid supports for long-term basic studies. BLMs formed on supports are known as supported BLMs (s-BLMs). Up to now, several types of solids or cushions, for example, metal with nascent surface (Tien and Salamon, 1989), glass fiber (Nikolelis and Pantoulias, 2001, Siontorou et al., 2000), agar (Lu et al., 1996), protein (Schuster et al., 2001), self-assembly monolayer of alkanethiolates (Lahiri et al., 2000, Raguse et al., 1998, Cornell et al., 1997) and nonconducting polymers (Hillebrandt et al., 1999, Lang et al., 1994, Seitz et al., 2000, Naumann et al., 1995, Sackmann, 1996) have been used as supports.

The promising support for BLM with potentially extended applications should possess such properties as facilitating, tightly linking to substrates and easily controlling its thickness as well as retaining hydrophilicity. For these purposes, however, the previously reported supports usually need complex pretreatments and synthesis procedures (Raguse et al., 1998). Additionally, an electric phenomenon is one of the basic natures of biomembranes in vivo cell. In order to carry out electrochemical studies on the electronic properties of BLMs, investigators always hope the supports between the electrode and the BLMs possess electronic conductivity besides their hydrophilicity. Ideally, electronically conducting polymers could easily meet the requirements. Previous studies have proven that PPy shows some interesting properties with respect to biomimetic applications. The negatively charged multilamellar vesicles in aqueous solution can be included into a polypyrrole matrix by eletrophoretic copolymerization (Belamie et al., 2001). Interestingly, this electrically conducting polymer can represent a type of culture substrate which provides a noninvasive means to control the shape and function of mammalian cells by electrochemically adjusting its redox state (Wong et al., 1994). Additionally, Tien and his colleagues (Kotowski and Tien, 1989) have made significative results on conventional BLMs with polypyrrole as a modifier within BLM. Hianik and his coworkers used the method of spontaneous thinning of cephalin/decane mixtures on polypyrrole (Hianik et al., 1998, Nikolelis et al., 1999) but the usage of organic solvent should make the spontaneously incorporated proteins keep less activity. Up to now, the model of PPy film supported BLM itself has not been experimentally proved. Herein, we first studied the deposition of BLM onto PPy film surface by vesicle fusion and investigated interactions between them with surface plasmon resonance (SPR) combined with AFM and electrochemistry. Our work mainly aimed to understand the basal aspects of the BLM supported by conducting polymers.

Section snippets

Reagents and materials

Pyrrole was purified by passage through an activated alumina column until it became colorless. 1 mg ml−1 vesicle stocking solution containing dimyristoyl-l-alpha-phosphatidylcholine (DMPC, Sigma, 99%), dimyristoyl-l-alpha-phosphatidylglycerol (DMPG, Sigma, 99%), dimyristoyl-l-alpha-phosphatidyl-l-serine (DMPS, Sigma, 99%), or didodecyldimethylammonium bromide (DDAB, Acros, 99%) was directly dissolved in water by sonication after treatment with chloroform according to the procedure (Pierrat et

Formation of PPy film

The formation of conducting polymer film is usually attained by means of electrochemically induced polymerization of monomer in aqueous solution for biosensor and biomolecular immobilization (Schuhmann, 1995, Cosnier, 1999). The applied electropolymerization potential, together with the temperature, the monomer concentration, the solvent used and the nature of the incorporated counter-anion, has an important effect on average length of the resulted polymer chains and the morphology of the

Conclusions

We have demonstrated a simple method of assembly of bilayer lipid membranes deposited onto electronically conducting polymer surface by vesicles fusion. The practicability of vesicles fusion onto the PPy surface to form s-BLM shows a dependence on the chemical structure of the lipids used. The deposition of BLM markedly changes the electronic properties of the electrode convinced by impedance spectroscopy. Therefore, electrochemically synthesized PPy film can be served as a novel support for

Acknowledgements

We gratefully acknowledge the special funds from Major State Basic Research of China (2002CB713803) and the National Natural Science Foundation of China (no. 20275036 and 20211130506) for supports of this research.

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