Navy

Fluidized bed detector (FBD) for continuous ultra-sensitive detection of biological and chemical materials

Reagent-less system for monitoring air, water, food, and agricultural areas provides immediate results

Sensors Environmental

There is a need for sensors for materials such as chemicals, bacterial toxins, and viruses at small concentrations in a large volume of media, where the media is a solvent, such as water, a solid, or a gas or a mixture of media such as food, which contains all three states.

Live bioassays have a number of issues that limit their use. For example, the living organism must be kept alive. This requires some care and feeding even when the sensor is not being actively used. And live bioassays that use complex organisms, such as canaries, may respond to other factors that do not cause appreciable concern for humans, such as temperature and transportation stress. And the interpretation of the response of the complex organism may be difficult in varying environments. For example, why did the canary die? Was it a toxic substance in the air, heat stress, or an avian virus that only affects canaries but not humans or other species? For cell-based live assays, the cells also must be kept alive and more importantly, some transduction mechanism must be engineered into the cells to identify the threat.

Schematic diagram of the fluidized bed detector, which has no rotating seals. The hoses are protected from twisting by a counter rotation at the base.

If the agent in question is known, specific detectors are possible. They may be either based on immunoassays, where the antibodies or other specific binding molecules such as peptides can act as the recognition element or nucleic acid detectors where specific sequences of DNA or RNA are sought. The major issue with many specific detectors is that the volume of liquid or air testable is quite small so that a preconcentration step is required. Without this preconcentration step, the likelihood of detection of a target species decreases with the concentration and the volume of material needed for the test. Because of this preconcentration step, the testing technology is often a grab-and-sample type of test, (the preconcentrator is run for a given amount of time, a sample of the concentrate is taken, and the sample tested.) This process can be repeated on a periodic timescale but as most tests are single-use where consumption of reagents can be substantial, the frequency of testing is often limited. Most immunoassays are single use; an example being the lateral-flow immunoassays used in home pregnancy testing.

Navy scientists have overcome these problems with a device for continuous detection of biological and chemical materials comprising a fluidized bed of detecting elements suspended in a continuous flow system. The detecting elements remain in the system when a force trying to move them to the bottom of the system is balanced with a force of a flowing gas or liquid trying to move the detecting elements to the top of the system. The target molecule in the flowing gas or liquid disrupts the balance of these forces causing the detecting element to exit the system. The release of the detecting element indicates the presence of the target molecule which may be captured and concentrated for further evaluation by other assays or other means.

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