Lipid bilayer-based sensors and biomolecular electronics.

The lipid bilayer postulated as the basic structural matrix of biological membranes is widely accepted. Experiments in the early 1960s have made direct studies of lipid bilayers possible. At present, the planar bilayer lipid membrane (BLM) together with spherical lipid bilayers (liposomes), upon suitable modification, serves as a most appropriate model for biological membranes. In recent years, advances in microelectronics and interest in ultrathin organic films, including BLMs, have resulted in a unique fusion of ideas toward the development of biosensors and transducers. Furthermore, recent trends in interdisciplinary studies in chemistry, electronics, and biology have led to a new field of research: biomolecular electronics. This exciting new field of scientific-technological endeavor is part of a more general approach toward the development of a new, postsemiconductor electronic technology, namely, molecular electronics with a long-term goal of molecular computers. Experimental BLMs have been mainly used in the past as models of biological membranes. The methods of BLM studies may not be familiar to those outside biomedical research. Therefore, a brief description of the experimental techniques will be given in Section IV. Recently, it has been demonstrated that BLMs, after suitable modification, can function as electrodes and exhibit nonlinear electronic properties. These and other experimental findings relevant to sensor development and to "biomolecular electronic devices" (BED) will be covered in Section V, after a brief description of biomembranes which have been suggested as nature's molecular devices (Section III). In the last section, the potential use of the BLM system together with its modifications in the development of a new class of organic diodes, switches, biosensors, electrochemical photocells, and biofuel cells will be presented (Section VI). Additionally, this paper, besides presenting a review of our work and those of others on BLMs and liposomes in relation to biosensors and molecular electronics, reports a novel technique for obtaining BLMs (or lipid bilayers) on solid supports. The presence of solid support on one side of the BLM greatly enhances its mechanical stability, while retaining the dynamic properties of the lipid bilayer. Advantages of the new technique for self-assembling amphiphilic molecules on rigid substrates are discussed in terms of their possible uses. That is, the new BLM system (s-BLMs) is potentially useful for technological applications in the area of biosensors, enzyme electrodes, and molecular electronics as well as biochips (Section IV.C). The dividing line between the present microscopic and the future molecular electronics is 1 micron.(ABSTRACT TRUNCATED AT 400 WORDS)