Self-Assembling Bilayer Lipid Membranes on Solid Support

17 Self-Assembling Bilayer Lipid Membranes on Solid Support Building Blocks of Future Biosensors and Molecular Devices Downloaded by FUDAN UNIV on March 11, 2017 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0240.ch017

1

2

3

A. Ottova-Leitmannova, T. Martynski, A. Wardak, and H . T. Tien* Membrane Biophysics Laboratory (Giltner Hall), Department of Physiology, Michigan State University, East Lansing, MI 48824

Planar bilayer lipid membranes (BLMs) have been widely used as a model for biomembranes. We first summarize certain BLM experiments with biosensors and molecular devices, after describing the conventional BLM system. These discussions will be followed by a description of a new BLM system based on self-assembling process of amphiphilic molecules. In recent years advances in microelectronics coupled with sustained interest in thin organic films have prompted a number of investigators to exploit the conventional BLM system as a basis for molecular devices as well as for the development of electrochemical sensors. The new supported BLMs (s-BLMs) have the requisite mechanical stability, besides possessing desired dynamic properties. Thus, the s-BLM system offers opportunities for basic studies as well as for technological applications.

TTHE CONCEPT OF THE LIPID BILAYER as the basic structure of biological membranes became generally known only in the late 1950s (1,2). Realizing the importance of the lipid bilayer, Rudin and his associates (3) and Tien (4) succeeded in 1960 in reconstituting a bimolecular or bilayer lipid membrane (BLM) between two aqueous solutions. Experimental BLMs (planar BLMs and the spherical liposomes that were developed shortly afterward by Bangham and co-workers, see reference 5), have 1

Current address: Slovak Technical University, Bratislava, Czechoslovakia/Slovakia Current address: Institute of Physics, Poznan Technical University, Poznan, Poland Current address: Department of Physics, Technical University of Lublin, Lublin, Poland * Corresponding author. 2 3

0065-2393/94/0240-0439$08.00/0

© 1994 American Chemical Society

Birge; Molecular and Biomolecular Electronics Advances in Chemistry; American Chemical Society: Washington, DC, 1994.

Downloaded by FUDAN UNIV on March 11, 2017 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0240.ch017

440

MOLECULAR AND BIOMOLECULAR ELECTRONICS

been extensively used as models of all sorts of biomembranes (4-11). It is now recognized that this universal bilayer structure exists because of the unique properties of lipid molecules. At one end of a lipid molecule is a hydrophobic fluid-hydrocarbon chain, and at the other end is a hydrophilic polar group. When lipid molecules are in aqueous media, this arrangement causes them to assemble spontaneously into a bilayer configuration (1, 4, 10, 12). Unmodified BLMs, like the closely related liposomes, are dynamic structures that can be easily modified by incorporating a variety of com pounds that will endow them with functional characteristics. The re sulting modified BLMs have proven since the 1960s to be ideal for in vestigating electrical, mechanical, immunological, photoelectrical, and a host of other properties associated with the lipid bilayer of biomem branes (10-15). Further, as evidenced by publications from a number of laboratories (JO, II, 15-20), the B L M system is of interest in solar energy transduction, biosensor development, and molecular electronic devices fabrication. BLMs formed in the conventional manner (i.e., by spreading a lipid solution across a small hole in a hydrophobic partition separating two aqueous compartments) are not very stable. These BLMs rarely last more than a few hours. For practical applications and for long-term studies, a durable B L M (lipid bilayer) is a prerequisite. In this chapter we de scribe a simple mechanical procedure for the self-assembly of lipid bilayers on solid supports (12, 21). These supported lipid bilayers have a long life, thereby offering opportunities for the preparation of a variety of probes with diverse applications in membrane biophysics, biochem istry, physiology, and biotechnology (22, 23). An overview of potentially BLM-based biosensor technology is given in Table I.

Experimental Details Materials. The BLMs on solid substrates described in this study were formed from various lipid solutions, for example, different concentrations of phosphatidylcholine (PC) in n-octane; 5% lecithin, PC (Walgreen Lab oratories, Inc.) in n-decane (Aldrich Chemical Company); 50% PC in ndecane; 1% glycerol monooleate (GMO) (Κ & Κ Laboratories, Inc., Roch ester, NY), in squalene (Eastman Kodak Co., Rochester, NY); oxidized cho lesterol in η-octane; and glycerol dioleate (GDO) (Κ & Κ Laboratories, Inc., Rochester, NY), in squalene. Supported BLMs were also formed from a GDO solution saturated with zinc phthalocyanine (Zn PLC) (Strem Chemical Company) orfrom4-n-octyl-4'-cyanobiphenyl (8-CB) (BDH Chemicals, Ltd.) dissolved in squalene (1:5 or 1:10 v/v) and saturated with 7,7,8,8-tetracyanop-quinodimethane (TCNQ) (Aldrich Chemical Company). The bathing so lution was 0.1 M KC1. All chemical compounds (KCl, NaCl, AICI3, MgS0 , ascorbic acid, K Fe(CN) , K Fe(CN) , and Pb(N0 ) were obtained com mercially and were used without further purification. In some experiments 4

3

6

4

6

3

2


17.

Bilayer Lipid Membranes

OTTOVA-LEITMANNOVA ET AL.

441

Table I. An Overview of the s-BLM-Based Biosensor Technology Type of Transducer

Type of Measurement

Oxygen electrode Ion-selective electrode Modified metal electrode Field effect transistor Conductimeter Spectrophotometry Laser light scattering Opticalfiberscombined with absorption and fluorescence Surface plasmon resonance Thermistors Piezoelectric crystal Surface acoustic wave device


Electrochemical : Potentiometry Amperometry Conductiometry Impediometry Photometric

Thermometric Acoustic

NOTE: TO be developed as a future technology. SOURCE: Adapted from references 22 and 23.

the following buffer solutions were used: phthalate buffer (pH 4.0), phoshate buffer (pH 7.0), and carbonate buffer (pH 10.0) (all were obtained om Altex, CA). Double distilled water in the preparation of all solutions was used (24-27). For solid substrates, metallic wires of Pt, Ag, and stainless steel (ss), of consisted of different concentrations of PC in η-octane or of 1% GMO, or 1% GDO in squalene. In some experiments the lipid solutions were modified with chlorophylls, TCNQ, and other modifiers promoting redox reactions of redox couples such as ferro- and ferricyanide, KI, and ascorbate. The aim of these experiments was to demonstrate two points: (1) for mation of a structure with the electrical parameters of a B L M on a solid support and (2) modification of this structure so that it is sensitive to the bathing solution (0.1 M KCl). The membrane-forming solutions wet the ss wire and Sn0 surfaces better than the electrolyte solution does. Although no direct measurements of thickness was performed, the similarities of the electrical parameters—resistance (R) and capacitance (C)—to those for lipid bilayers suggest that a bilayer arrangement was probably formed in the present system. To show some possibilities for modification of the supported BLM, we used several modifiers that promote redox reactions. The currentvoltage relationship for S n 0 - G D O in squalene, chlorophyll-ferricyanide, and K C l - S n 0 in a two-electrode system (SnO -covered glass as a reference electrode) is not symmetrical. The system is sensitive for l-μΜ ferricyanide. The same system modified with T C N Q was less sensitive. Further studies were done for the changes in the current-voltage relationship in the pres ence of 1-mM K Fe(CN) for the same system as described previously but with TCNQ as the modifier (Sn0 -GDO in squalene, TCNQ-ferricyanide, and KCl-Sn0 ). Also in this case, the current-voltage curve is not sym metrical. For more details see reference 26. As stated there, the purpose of the redox-reaction experiments was to demonstrate the potential of this system. No attempt was carried out to investigate the electrochemistry of the occurring reactions. The significance of these experiments is that the s-

E

2

2

2

a

3

6

2

2


442

MOLECULAR A N D BIOMOLECULAR

ELECTRONICS

BLM can be modified to achieve a particular function. This seems to be very important for the successful development of s-BLM-based biosensors diameters ranging from 0.02 to 0.2 mm, with and without Teflon coating (0.075 mm), were obtained from Medwire Corp., Mount Vernon, NY. In some experiments pure platinum wires (Pt, 99.95%) (AESAR Johnson Matthey, Inc., Ward Hill, MA), 0.5 -mm diameter, were used as metallic solid surfaces. Tubes made of Teflon (TEF, Berghof/America, Inc., Rochester, NY) were used as sleeves to coat Pt wires for the modified version of the original method of solid s-BLM formation. The inner and outer diameters were 0.52 and 1.2 mm, respectively. The use of BLMs supported on solid substrates like silver wires coated with Teflon and Sn0 on glass for analysis of sensor-development problems, with relevance to a possible novel type of biomolecular device is also described in our work. Downloaded by FUDAN UNIV on March 11, 2017 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0240.ch017

2

Methods. Electrical properties of supported BLMs were measured at room temperature (21 ± 1 °C) using the setup that consisted of a highimpedance electrometer (model 610 BR, Keithley Instruments Company, Taunton, MA), a picoammeter (model 417, Keithley Instruments Company, Taunton, MA), a low-level capacitance meter (model 1-6, IC Electronics, Taunton, MA). We also used an IBM (model EC/225) voltammetric analyzer in conjunction with a strip-chart recorder. In some experiments, namely in the case of the modified version of solid s-BLM formation also Potentiostat/ Galvanostat (model 173) with interface model 276 (EG&G, Princeton Applied Research, Princeton, NJ) connected to an IBM PC/XT computer with Headstart software (EG&G, Princeton Applied Research, Princeton, NJ) was used (24-27). In all of the experiments described here the s-BLM was used as a working electrode in a three-electrode setup in which a coil of Pt wire was used as the counter electrode. A calomel electrode with a salt-bridge served as a reference electrode. The bathing solution was usually 0.1 M KC1. The only exception was the case of s-BLM on solid substrates like silver wires that were coated with Teflon and of Sn0 on glass for analysis of biosensor development problems. In this case s-BLM was used as a working electrode in a two-electrode system. Ag-AgCl, saturated calomel electrode (SCE), or Sn0 -covered glass were used as reference electrodes (24-27). 2

2

Techniques for Spontaneous Assembly of an s-BLM. An s-BLM (or lipid bilayer) as described here is formed by two consecutive self-assembling steps: (1) placing lipid molecules in contact with a freshly fractured metal surface and (2) immersing the lipid layer that becomes adsorbed onto the metal surface in an aqueous solution. In this chapter we present a brief summary of the procedure described in detail elsewhere (24-27). Figure 1 portrays the most essential steps of our experimental procedure. In Figure 1 (left), the tip of a Teflon-coated wire (platinum, silver, or ss) has been cut with a sharp knife under a lipid solution, for example, a 1% glycerol dioleate in squalene. When the nascent metal surface is exposed in a lipid solution, a monolayer of lipid molecules is irreversibly bound onto its surface, as shown in Figure 1 (left). The adsorbed lipid monolayer with unattached hydrocarbon chains interacts with the hydrophobic chains of other lipid molecules. When the lipid-coated wire is immersed in an aqueous solution (e.g., 0.1 M KC1), as illustrated in Figure 1 (right), this immersion leads eventually (under favorable conditions) to the spontaneous formation



17,

OTTOVA-LETTMANNOVA ET AL.

Figure 1.

443


Self-assembling ofs-BLMs in two steps (12, 21,

24).

of an exceptionally stable, self-assembled lipid bilayer, as shown in Figure 1 (right). The precise arrangement and degree of ordering of the lipid molecules in the final structure shown in Figure 1 (right) is not known for certain. But it is highly probable that the bilayer nature of the assembly is a consequence of the thermodynamics of free-energy changes at the metal-lipid surface and at the lipid-aqueous solution interface 0-2). Our measurements of the electrical properties of s-BLMs are consistent with those of conventional BLMs and closely related systems (4, 28): In the series of our experiments, we have found that s-BLMs not only have desired electrochemical and optical properties but also have some areas of practical applications as well (2123). All of these results have demonstrated a simple and useful method of solid s-BLMs. For further improving both the reproducibility of obtaining BLM systems with similar electrochemical properties and of getting even longer lifetime of such s-BLMs, a modified version of the original method of s-BLM formation is presented. More details are given in reference 27. For the best cutting of Pt wire, we constructed a miniature guillotine where the sharp knife is moved vertically onto the wire placed on the flat base. The wire is then cut while immersed in a drop of lipid solution so that the initial contact of the newly exposed wire surface is with the lipid solution. The newly cut surface is almost perpendicular to the length of wire. This lipid-coated wire is then inserted into a small piece of Teflon tubing (TEF, 10 mm) that has been filled with lipid solution. This assembled Teflon-covered Pt wire is trans-


444



ferred into an aqueous bathing solution. We then let the system stand for a few minutes or hours. Supplied by diffusion within the lipid solution, the nascent platinum support surface will attract the polar groups of lipid mol ecules. To promote the process of self-assembling of BLM, one of the fol lowing two methods has been used: (1) by removing G D O solution from T E F sleeve simply with capillary forces or (2) by using a piston system (27). The final step is self-adjusting thinning and formation of the Plateau-Gibbs (P-G) border. During the time of self adjusting process, the change in ca pacitance of a layer was monitored. After 5-10 min the capacitance reaches a constant value and the bilayer structure has been formed. With these methods we are able to control both the rate of the BLM formation process and the ratio of BLM to the P - G border. These simple steps allow us to produce stable and very similar s-BLMs.

Results and Discussion In our experiments we showed that the time change of resistance in a s-BLM on platinum is very similar to that observed with a conventional single B L M (4, 12). This change means that the resistance decreases during the thinning process until it reaches a constant value on the order of 10 to ΙΟ Ω cm , for a variety of unmodified BLMs. The value for a platinum-supported 8-CB + T C N Q bilayer's resistance drops to ΙΟ Ω cm . The capacitance of a B L M , along with optical reflectance, is a wellestablished parameter for estimating the thickness of lipid bilayers (4, 10). Therefore, the capacitance measurements were used to monitor the B L M formation process and to estimate the thickness of the lipid bilayer. The capacitances were measured as a function of time. The thinning process was fairly rapid; the capacitance value reached a plateau in about 2 min, indicating corresponding thicknesses of 4.0 and 4.5 nm, respectively, for the supported BLMs formed from G D O and lecithin lipids. Characteristic values of the capacitance for s-BLMs are in the range of 0.2- to 0.5 uF c m " , which are fairly consistent with those of conventional BLMs. Other electrical measurements were made after completion of the thinning process. We measured a number of typical electrical parameters such as cyclic voltammograms (CV), potential (V), and capacitance (C). The C V curves for the s-BLMs are strongly asym metrical. Especially in the negative part of the curve, the current de pends on the type of ions in the bathing solution. To reduce this nega tivity, current influence of several ions has been tested: K C l , NaCl, M g S 0 , A1C1 in different concentrations from 0.001 to 0.1 M . The best shape of C V curves and the longest lifetime of the system were obtained for a 0.1 M A1C1 bathing solution. After a few C V measured between —100 and +700 mV at sweep rate of 100 mV s" , the C V curves became wider. Further, saturation of bathing solution with argon decreased the cathodic current even more, and the bilayer systems became even more stable. 6

7

2

5

2

2

4

3

3

1



17.

OTTOVA-LEITMANNOVA E T AL.


445

Further experiments were performed on s-BLMs with well-known redox compounds in the bathing solution (25). The C V for ascorbic acid shows two anodic peaks: one in the forward and one in the reverse potential scan (Figure 2). The peak in the forward potential scan, appearing for both a membrane-modified and a bare Pt electrode, is characteristic for the oxidation of ascorbic acid. The position of this peak, for the electrode modified with a lipid bilayer, was shifted toward morepositive potentials, as compared to the bare electrode. The peak on the reverse scan was recorded for the modified electrode only. The observed dependence of the positions of both peaks on the concentration of ascorbic acid is related to p H changes. In buffered solutions no dependence on the concentration of ascorbic acid was found, but a strong dependence on p H is observed. The peak current for the forward scan is linearly dependent on the concentration of ascorbic acid. The dependence for the reverse scan peak is linear only for lower concentrations. At higher concentrations of ascorbic acid, the dependence is sublinear

Figure 2. Dependence of the cyclic voltammograms on scan rate for a sBLM in 0.5 M KCl containing 1-mM ascorbic acid. (Reproduced with permission from reference 25. Copyright 1990 Elsevier Sequoia.)


446

MOLECULAR A N D BIOMOLECULAR

and the peak is usually weakly pronounced. Both, the peak potentials and the peak currents are dependent on the scan rate (Figure 2). At high scan rates, the forward scan peak current increases while the reverse scan peak current decreases, and the peak is weakly pronounced. At low scan rates, the peak in the forward scan is shifted to lower potentials, and the peak in the reverse scan is shifted to higher potentials. For more details see reference 25. Also in ferri- and ferrocyanide solutions, oxidation and reduction peaks were recorded. The C V currents were dependent on the scan rate and on the concentration of K F e ( C N ) and K F e ( C N ) . No peaks were observed below 2 mM. The currents at 500 mV, that is, over the peak levels, were compared for bilayer electrodes and for bare electrodes. For the bilayer-covered electrodes, the currents were lower (Table II). At the same time, the positions of the peaks were changed and the peak-to-peak separation increased (Table II). For TCNQ-modified membranes the peaks were more pronounced than for unmodified membranes, and the peaks were recorded even at a concentration of 0.2 mM. Modification of s-BLMs increases the currents and decreases the peak-to-peak separation (Table II). The experiments described in the preceding paragraphs show that an electrode modified by supporting a lipid bilayer on it has some new features when compared with a bare electrode. Compared to conventional BLMs, BLMs supported on an electrode are much more stable. Their high stability is a feature that makes them very useful in analytical studies. The modified Pt electrode can presumably be used to study redox species to which the lipid membrane is highly sensitive. The appearance of characteristic peaks in C V and the linear dependence of peak currents on concentration make both qualitative and quantitative studies possible. Suitable modification of the membranes can make them even more sensitive. C V studies of a lipid bilayer supported (i.e., sBLM) on the working electrode can probably also provide some information about the transfer of species through the solution-lipid interface and through the bilayer interior, as well as about redox reactions at and in the membrane. 3


ELECTRONICS

Table II. Kind of s-BLM

Bare wire No modification With TCNQ

6

4

6

Properties of s-BLMs with and without Modification No. ofExpts.

9 11 11

Peak Separation (mV)

89 ± 4 365 ± 30 279 ± 40

l)lo

a

1 0.029 0.054

The ratio between the current of an electrode covered with lipid membrane and the current of a bare electrode. S O U R C E : Adapted from reference 25.

a


17.


447


A typical C V for a Pt-supported (8-CB + T C N Q ) bilayer in 0.1-M KC1 bathing solution at a sweep rate of 100 mV s e c exhibits three oxidation peaks, occurring at —650, —90, and +450 mV. The presence of more than two oxidation peaks indicates that a charge-transfer (CT) complex (8-CB TCNQ~) is formed, as indicated by a new peak. Taking into account previous C V results with T C N Q in different solvent, it can be assumed that the two peaks that occur at —650 and —90 mV are probably caused by the oxidation of T C N Q " ( T C N Q " T C N Q " + e) and T C N Q " ( T C N Q " T C N Q + e), respectively, whereas the third peak at +450 mV is a result of the C T complex (8-CB+TCNQ) oxidation (8-CB TCNQ8 - C B + T C N Q + e). -1

+

2

+

2

+

The C V of the system with 100 and 300 μΜ of P b ( N 0 ) in the bathing solution displays a reduction (at —608 mV) and oxidation peak (at —448 mV). A large separation potential between peaks indicates that the system is irreversible. The height of the oxidation peak increases sharply with an increasing concentration of lead ions. The peak height's dependence on concentration is linear over a micromolar range of leadion concentration, with the lowest detectable ion level around 100 μΜ. Although bare Pt wire of the same size, coated with Teflon but with out a B L M deposited on its surface, shows a much more reversible C V signal (voltage separation between peaks is 60-80 mV), the lowest con centration of Pb ions detected by such a system is three orders of mag nitude lower [100 mM of P b ( N 0 ) ] in the bathing solution. Thus, it is evident that the presence of a (8-CB + T C N Q ) bilayer on the surface of a Pt wire modifies a platinum electrode's behavior with respect to P b ions, significantly increasing its sensitivity to them and changing peak heights, peak potentials, and peak shapes, as well. When compared to results with a bare electrode, the increased sen sitivity (by three orders of magnitude) of a platinum electrode covered with a (8-CB + T C N Q ) bilayer seems to be a most significant finding. The observed increase in sensitivity indicates that (1) the interaction between the T C N Q present in a bilayer system and lead molecules is strong enough to keep a higher concentration of lead at the surface of a Pt-supported bilayer system than in the bulk solution, and (2) an ener getic barrier for an electron exchange between an (8-CB + T C N Q ) sys tem, and lead is probably lower than that between a bare Pt electrode and lead. To demonstrate further our novel method for self-organizing B L M formation on a solid substrate, a pigmented B L M from a G D O solution saturated with Zn P L C , according to the new procedure was formed. The properties of this organometallic complex containing B L M were characterized simultaneously by electrical and spectroscopic techniques. As it has been shown (24), the spectral sensitivity of a photocurrent corresponds well to the absorption spectrum of the Zn P C L in the B L M -


3

3

2

2 +


2


448


forming solution, and the magnitude of the photoresponse is linear to the light intensity used (at low light intensities). For details see Figure 3. A similar correspondence was found between the electrical properties of the supported B L M and those of B L M formed in the traditional manner. Thus, the findings provide clear evidence that the photoactive compound was incorporated into a supported B L M and that the photocurrent is a result of the Zn P L C photoexcitation. Our method for self-assembly of BLMs on solid supports complements the conventional B L M technique that has been used extensively in membrane reconstitution and in basic studies (21-28). The s-BLMs, owing to their stability and ease of formation, offer an approach especially useful in the research and development of lipid bilayer-based sensors and molecular devices (29-36). For example, to develop optical devices based on s-BLMs, we have incorporated semiconductor materials into BLMs (35), which not only displayed nonlinear electrical properties

[nm]

Figure 3. Photoelectric effect of a s-BLM containing Zn PLC. The photocurrent action spectrum (2) corresponds well with the absorption spectrum (1 ) ofthe lipid solution from which the s-BLM has been formed. (Reproduced with permission from reference 24. Copyright 1989 Elsevier Sequoia.)


17.

O T T O V A - L E I T M A N N O V A E T AL.


449

but also displayed photoactive properties in the presence and absence of dyes (35). These features seem promising for their technical applications. In one of our experiments we compared the peak current as a func tion of H 0 concentration in 0.1 M K C l for the following systems: bare ss wire, ss wire cut under P C + cholesterol lipid solution, ss-wire cut under lipid solution with T C N Q , and ss-wire cut under lipid solution containing molecular iodine. In all these experiments the forward as well as backward peak currents (Figures 4 and 5) showed a sigmoidshaped curve in dependence of H 0 concentration. The analyses of results show a strong closeness of bare-wire experiments with those of wire cut under lipids with I (Figure 6). The lipid conductivity exhibits similarity with those of s-BLM system containing I . To facilitate our delineation, we define "biosensors" as sensors that incorporate biomolecules as their principal sensing components. How ever, the word "biomolecule" is meant to include those compounds that exist in nature as well as in human-made analogues. It seems evident that, first of all, the key to the successful fabrication of supported B L M based biosensors is the ability to incorporate active biomolecules (re ceptors) into the lipid bilayer, so that they are anchored with their activity and specificity intact (Figure 7). However, the process of in corporation that takes place in natural receptors is not easy to imitate, requiring expert knowledge and experience of scientists of diverse backgrounds. This and other technological challenges in biosensor- and 2

2

2

2


2

2

I[MA]

V

0

2

4

6

8

10

12

14

1st

peak

• — ·

lipids f l

•—•

lipids + TCNQ V — V

• — •

PC + c h l .

0*··Ό

• — •

b a r e wire

Δ···^

c

t

m M

2nd O-.-O

2

l

Figure 4. Peak current (forward direction) as a function ofH 0 concen tration in 0.1-M KCl for different s-BLMs and for bare electrode (ss-wire). 2

2



450

MOLECULAR A N D BIOMOLECULAR ELECTRONICS

molecular-device development will be met eventually, since the basic design common to all such probes, based on a supported lipid bilayer, is now available for experimentation (21, 23, 28). In our experiments concerning these questions, we worked with sBLMs on metallic (silver wires coated with Teflon) and metal oxide (Sn0 on glass) surfaces (26). The significance of these experiments is that the supported B L M (s-BLM) can be modified to achieve a particular function. This seems to be very important for the successful development of sBLM-based biosensors in the near future. 2

Conclusions The B L M system has been extensively investigated as a model of biological membranes since the early 1960s. However, until recently, relatively few attempts have been made to exploit their potential in practical applications such as sensors and molecular devices. From the viewpoint of membrane biophysics and physiology, biological membranes are essentially the basic structure of nature's sensors and devices. For example, the thylakoid membrane of green plants functions as an energy transducer, converting sunlight into electrical and chemical energy; in visual perception, the photoreceptor membrane of a rod's outer segment detects photons; and the plasma membranes of cells and organelles possess the ability to sense ions (e.g., differentiating N a and K with great specificity). Furthermore, the plasma membrane provides sites for a +

+


17.


451



I[pA]

30

Ι

0

2.451

4.902

7.353

9.804

12.255

c

R

Q

[mM]

Figure 6. Typical sigmoid-shaped curves for the bare ss-wire electrode and for s-BLM containing I (solid line) and for s-BLMs containing TCNQ (dashed line). 2




452

Figure 7. A general scheme illustrating ligand (L) and receptor (R) contact interaction in a s-BLM formed in accordance to the procedure given in Figure 1. Conformational changes of imbedded species (e.g., biomolecules and redox compounds) may lead to alterations in the electrical parameters of s-BLM, that can then be detected, amplified, transduced, and displayed by appropriate state-of-the-art microelectronics technology. (Reproduced with permission from reference 21. Copyright 1990.)

host of ligand-receptor contact interactions such as antigen-antibody formation. In view of the fact that these and numerous other vital functions are associated with cell membranes, it is not surprising that the past two decades or so have witnessed an enormous research effort directed toward membranes. Reconstituted planar BLMs and spherical liposomes have played a primary role in this research. In our work a new B L M system is described—a s-BLM system, which, with its ease of formation, its stability, and its long life, offers new possibilities for applications in biosensors and molecular electronics.

Acknowledgments This work was supported by USARO Grant No. D A A L O 3 - 9 1 - G - 0 0 6 2 . We thank Robert Birge for organizing the Third International Symposium on Molecular Electronics and Biocomputing, held in New York City in 1991 in conjunction with the American Chemical Society Meeting.


17.



453


References 1. Chemistry of Biosurfaces Surface; Hair, M. L., Ed.; Marcel Dekker: New York, 1971; Vol. 1, pp 234-348. 2. Electrical Double Layers in Biology; Blank, M., Ed.; Plenum: New York, 1986; pp 149-166. 3. Mueller, P.; Rudin, D. O.; Tien, H. T.; Wescott, W. C.J.Phys. Chem. 1963, 67, 534. 4. Tien, H. T. Bilayer Lipid Membranes (BLM): Theory and Practice; Marcel Dekker: New York, 1974. 5. Bangham, A. D. In Progress in Biophysics and Molecular Biology; Butler, J. Α. V.; Noble, D., Eds.; Pergamon: New York, 1968; Vol. 18, pp 29-95. 6. Antonov, V. F.; Rovin, Y. G.; Trofimov, L. T. A Bibliography of Bilayer Lipid Membranes; All Union Institute for Scientific Information: Moscow, Russia, 1976. 7. Antolini, R.; Gliozzi, Α.; Gorio, A. Transport in Membranes: Models Systems and Reconstitution; Raven: New York, 1982; p 57. 8. Fendler, J. H. Membrane Mimetic Chemistry; Wiley: New York, 1982. 9. Koryta, J. Ions, Electrodes and Membranes; Wiley: New York, 1982;p197. 10. Thin Liquid Films; Ivanov, I. B., Ed.; Marcel Dekker: New York, 1988; p 927. 11. Progress Surface Science; Davison, S. G., Ed.; Pergamon: New York, 1989; Vol. 30, p 1. 12. Surfactants in Solution; Mittal, K. L., Ed.; Plenum: New York, 1989; Vol. 8, p 133. 13. Robinson, J. N.; Cole-Hamilton, D. J. Chem. Soc. Rev. 1991, 20, 49. 14. Dryhurst, G.; Niki, K. Redox Chemistry and Interfacial Behavior of Biological Molecules; Plenum: New York, 1988. 15. Mauzerall, D. In Light-Induced Charge Separation in Biology and Chemistry; Gerischer, H.; Katz, J. J., Eds.; Springer-Verlag: Berlin, Germany, 1979; p 241. 16. Gerischer, H. In Topics in Applied Physics; Seraphin, Β. O., Ed.; SpringerVerlag: Berlin, Germany, 1979; pp 115-172. 17. Thompson, M.; Krull, V. J.; Bendell, L. I. In Proceedings of the International Meeting on Chemical Sensors; Seiyama, T.; Fueki, K.; Shiokawa, J.; Suzuki, S., Eds.; Elsevier-Kodansha: New York, 1983; p 576. 18. Janata, J. In Proceedings of the Symposium on Chemical Sensors; Turner, A. P. F., Ed.; The Electrochemical Society, Inc.: Pennington, NY, 1987; p 258; J. Anal. Chem. 1990, 62, 33R. 19. Ringsdorf, H.; Schlarb, B.; Venzmer, H. J. Angew. Chem. Int. Ed. Engl. 1988, 27, 113-158. 20. Krull, U. J.Anal.Chim. Acta 1987, 197, 203. 21. Tien, Η. T. Adv. Mater. 1990, 2, 316. 22. Tien, H. T.; Salamon, Z.; Kochev, V.; Ottova, Α.; Zviman, M. Symposium on Molecular Electronics: Biosensors and Biocomputers; Hong, F. T., Ed.; Plenum: New York, 1989; p 259. 23. Tien, H. T. J. Surf. Sci. Technol. 1988, 4, 1-21; J. Clin. Lab. Anal. 1988, 2, 256-264. 24. Tien, H. T.; Salamon, Z. Bioelectrochem. Bioenerg. 1989, 22, 211-218. 25. Wardak, Α.; Tien, Η. T. Bioelectrochem. Bioenerg. 1990, 24, 1-11. 26. Zviman, M.; Tien, H. T. Biosens. Bioelectron. 1991, 6, 37-42. 27. Martynski, T.; Tien, H. T. Bioelectrochem. Bioenerg. 1991, 25, 317-324.


454



28. Tien, H. T.; Salamon, Z.; Kutnik, J.; Krysinski, P.; Kotowski, J.; Ledermann, D.; Janas, T. J. Mol. Electron. 1988, 4, S1. 29. Molecular Electronic Devices: Proceedings of the Third International Sym posium; Carter, F. L.; Siatkowski, R. E.; Wohltjen, H., Eds.; North-Holland: Amsterdam, The Netherlands, 1988; pp 209-225. 30. Reichert, W. M.; Bruckner, J.; Joseph, J. Thin Solid Films 1987, 152, 345. 31. Cherny, V. V.; Mirsky, V. M.; Sokolov, V. S.; Markin, V. S. Bioelectrochem. Bioenerg. 1989, 21, 373. 32. Mountz, J. M.; Tien, H. T. Photochem.Photobiol.1978, 28, 395. 33. Yoshikawa, K.; Hayashi, H.; Shimooka, T.; Terada, H.; Ishii, T. Biochem. Biophys. Res. Commun. 1987, 145, 1092. 34. Fare, T. L.; Rusin, Κ. M.; Bey, P. P. Sens. Actuators 1991, 3, 51. 35. Kutnik, J.; Tien, H. T. Photochem. Photobiol. 1987, 46, 413. 36. Schuhmann, W.; Heyn, S.-P.; Gaub, H. E. Adv. Mater. 1991, 3, 388. RECEIVED for review March 12, 1992. ACCEPTED revised manuscript March 3, 1993.


Self-Assembling Bilayer Lipid Membranes on Solid Support

Recommend Documents