Nanoscale structures are becoming increasingly important because they provide the basis for devices with dramatically reduced power and mass, while simultaneously having enhanced capabilities, and previous patent applications have disclosed the advantageous use of such nanostructures in a number of different real-time, molecule specific sensors.
However, very often airborne and waterborne microbiological entities, such as macro-biomolecules, spores, bacteria, etc. occur in such low concentrations that real-time detectors are ineffective at sensing them. In addition, the identification of these particulates often requires some form of intrusive analysis (tagging, DNA extraction, etc.), which cannot be accomplished if the particulate is free to move away from the location of the detector. Finally, while many of the current nano-sensors are very sensitively tuned to capture and identify one particular species (DNA strands, Salmonella etc.), the devices may miss all the other particulates of interest present in the environment.
To solve these problems a system is needed to trap all molecules of interest for later analysis by a more conventional detection means. One conventional method of filtering, or trapping small particles is to use high surface area charcoal. Indeed, the ancient Egyptians understood the beneficial properties of charcoal as a filter, which was used to improve the quality of drinking water.
The modern successor of charcoal is activated carbon. Activated carbon is a carbonaceous adsorbent with high internal porosity, and hence a large internal surface area of 500 up to 1500 m^2/g. Activated carbon mainly consists of elementary carbon in a graphite-like structure. It can be produced by heat treatment, or “activation”, of raw materials such as wood, coal, peat and coconuts. During the activation process, the unique internal pore structure is created, and it is this pore structure which provides activated carbon its outstanding adsorptive properties. Activated carbon finds uses in a myriad of applications, from adsorption or chemisorption, to removal of chlorine through reduction reactions, as a carrier of catalytic agents, as a support material for biofilters, or as a chemical carrier for the slow release of coloring agents.
For example, since 1991, activated carbon adsorption has been widely adopted for dioxin removal from waste incinerators in Europe and Japan. Because of the higher bond energy between dioxin and activated carbon than other sorbents, the removal efficiency for dioxin by activated carbon is much higher than other sorbents, including clays, pillared clays, gamma-alumina, and zeolites.
However, although high surface area activated charcoal is an excellent trapping material, the three-dimensional nature of the high surface area matrix makes it very difficult to use standard detection schemes, laser diagnostics techniques (UV fluorescence and other non-linear light scattering techniques) to actually distinguish the particles of interest (such as those containing proteins, nucleic acids, and coenzymes) from other organic and inorganic particulate contaminants.
Accordingly, a need exists for improved nanoscale material for use as a trapping material for concentrating low concentrations of airborne and waterborne particles for detection by highly sensitive, robust, and cost-effective in situ sensors.
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