Food Nanotechnology: Current Developments and Future Prospects
381
bearings, car parts, medical devices, sports equipment, and industrial food-processing equipment (Spice, 1999; Gorman, 2003; Zhan et al., 2003). Recent studies suggest the use of carbon nanotubes for biological purposes, such as crystallization of proteins, building of bioreactors and biosensors (Huang et al., 2002). However, for biological applications, the insolubility of carbon nanotubes in aqueous media needs to be overcome. A research group at University of California solubilized single-wall carbon nanotubes (SWNT) in aqueous iodine–starch solutions (Dagani, 2002), while a research group in Israel obtained a similar result using aqueous solutions of gum arabic (Bandyopadhyaya et al., 2002). Other solutions for solubilization of SWNT consist of functionalizing the tubes with glucosamine (Pompeo and Resasco, 2002) or bovine serum albumin (Huang et al., 2002). In another example, nanotubes are formed by the self-assembly of phospholipid bilayers capable of entrapping active compounds. Due to their biocompatibility, such tubules are ideal for delivery in biological systems (Jelinski, 1999). Carbon nanotubes, particularly multi-wall nanotubes (MWNT) with well-defined nanostructures, can also be used to build sensors. Manufacturing of nanotube membranes is an area with significant potential for use in food systems. High-selectivity nanotube membranes can be used for analytical purposes, as part of the sensors for molecular recognition of enzymes, antibodies, various proteins and DNA, or for the membrane separation of biomolecules, such as proteins (Lee and Martin, 2002; Rouhi, 2002). The selectivity and yield of membranes currently used in the food industry are not fully satisfactory, mainly due to the limited control of their structure and chemical affinity. By functionalizing nanotubes in a desired manner, membranes could be tailored to efficiently separate molecules both on the basis of their molecular size and shape, and on their chemical affinity. Lee and Martin (2002) developed membranes that contain monodisperse gold nanotubes with inside diameters smaller than 1 nm; such membranes can be used either for the separation of molecules or for the transport of ions. The same authors were able to make the interior of the nanotubes hydrophobic, which allowed the nanotube membrane to preferentially extract and transport neutral hydrophobic molecules. While such technologies are still too expensive for commercial-scale food applications, as the technology is further developed such membranes might be used in the future for the isolation of food biomolecules with unique functional properties. Another area of carbon-nanotube-based applications is the development of electrically conductive membranes. The high length per diameter ratio of carbon nanotubes can be used to turn ordinary synthetic polymers, which are typically electrical insulators, into conducting polymers. In addition to