The mammalian olfactory system provides great inspiration for the design of intelligent sensors. To this end, we have developed a bioinspired phage nanostructure-based color sensor array and a smartphone-based sensing network system. Using a M13 bacteriophage (phage) as a basic building block, we created structural color matrices that are composed of liquid-crystalline bundled nanofibers from self-assembled phages. The phages were engineered to express cross-responsive receptors on their major coat protein (pVIII), leading to rapid, detectable color changes upon exposure to various target chemicals, resulting in chemical- and concentration-dependent color fingerprints. Using these sensors, we have successfully detected 5-90% relative humidity with 0.2% sensitivity. In addition, after modification with aromatic receptors, we were able to distinguish between various structurally similar toxic chemicals including benzene, toluene, xylene, and aniline. Furthermore, we have developed a method of interpreting and disseminating results from these sensors using smartphones to establish a wireless system. Our phage-based sensor system has the potential to be very useful in improving national security and monitoring the environment and human health.
We report a simple method to prepare individual electric arc-produced single-walled carbon nanotubes (SWNTs) in aqueous solution on a large scale through three steps of processing: refluxing in concentrated HNO(3), low speed centrifugation, and high speed centrifugation. The bulk production (10 g of starting SWNTs) results in a concentration of 0.2 mg/mL individual SWNTs stably dispersed in DI-H(2)O without any external protection. The atomic force microscopy images show that the aqueous dispersion contained approximately 80% individual SWNTs with lengths ranging from 500 nm to 1 micrometer. It is found that the stable individual SWNT dispersion has an absolute zeta potential value of approximately 72 mV with a concentration of 0.05 mg/mL at pH 5. We believe that it is this high zeta potential resulting from an electrical double layer which produces the repulsion to overcome the van der Waals attraction thereby keeping the SWNTs individually dispersed. The free-standing film prepared from the individual SWNT dispersion exhibits a 4-probe electrical conductivity of approximately 2000 S/cm and a transmittance of 60% at 550 nm.
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