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A New Nano Based Real-time Aflatoxin Detector

Gilligan, Thomas
Sensor Development Corp
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Sensor Development Corp intends to demonstrate the sensitivity and selectivity of its proprietary nanocrystalline tin oxide solid state gas phase sensor for detecting ppb levels of certain signature gases given off during mold growth in grain. The initial target mold is Aspergillus flavus which produces aflatoxin. The target grain is corn. The FDA has an action limit for aflatoxin of 20 ppb. SDC believes a signature gas for Aspergillus flavus mold growth has been identified. With the sensitivity and selectivity of our systems, it could provide real-time management of grain storage and reduce the losses. Since our sensor system measures the signature gas from mold, it does not rely on grain sampling with its inherent potential for inaccuracy and the cost/delay of the sampling process. Temperature and carbon dioxide measurements could indicate mold growth. In a later phase, we would attempt correlation of these measurements with our signature gas measurements. Selectivity for the signature gas in the presence of other gases typical in grain storage environments is necessary and SDC will test a variety of active coatings, chip operating conditions and chip signal processing software to give the optimum performance for Aspergillus flavus. SDC believes there will be a unique set of parameters for each distinct signature gas. SDC will use combinatorial chemistry to fabricate a number of active coatings using sol-gel techniques. This nanocrystalline active coating will be screened in a laboratory test system that was developed and qualified earlier for assessment of indoor air quality. This system will use simulant gases of known composition for our measurements. Initial operating conditions will be based on earlier work, while the data analysis software to be evaluated will be commercially available platforms adapted to our application. The hardware and test operating software are already in place and should require minimal modification to complete the Phase I objective of developing a sensor chip with a high sensitivity and high selectivity for the signature gas for aflatoxin production in corn, performing under optimized chip operating conditions, and successfully using commercial software adapted for this application. The second objective for the Phase I program will be to test this sensor system in a real world environment by collaborating with Purdue University. Purdue possesses expertise in mold growth in corn both at the lab scale and 500 bushel bin scale. They will grow the mold on corn in the lab scale, and measure the gases produced using the optimized sensor from our lab scale work. Following completion of this task, we will evaluate the overall sensor performance in preparation for Phase II which would involve field-testing first in pilot bins at Purdue and then at beta test sites at major grain handling firms. Successful completion of this Phase I will open up other mold based applications in grain storage, such as DON produced by Fusarium, and other food supplies such as peanuts and wheat. In fuel ethanol production, aflatoxin in the DDG would also be a serious problem.
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NON-TECHNICAL SUMMARY: Mold growth in grain can produce deadly mycotoxins. SDCÆs nanocrystalline, solid state tin dioxide gas sensor will allow detection a signature gas given off during mold growth. This high sensitivity, high selectivity sensor system will allow real-time monitoring of grain in storage bins and during transportation. The initial target is detecting the growth of Aspergillus flavus in corn which produces aflatoxin. The FDA has a 20 ppb action limit on aflatoxin to insure food/feed safety. This project will optimize SDCÆs nanocrystalline gas phase sensors system. Sol gel coating of tin dioxide on an alumina substrate will produce a large number of active sites. Combinatorial chemistry will be used to add other compounds to the sol gel to improve selectivity to the signature gas given off by Aspergillus flavus. The operating conditions of the chip will be varied to further enhance sensitivity and selectivity. Commercial data analysis software will be adapted to further refine the detection system. Initially chips will be tested in a lab scale systems using know concentrations of signature gas and typical interferent gases. A lower detection limit of 1 ppb for the signature gas will be sought. Once optimized in the lab, a prototype will be evaluated in a real world environment using corn and Aspergillus flavus. Success will lead to beta site testing and the application to other mycotoxins, such as DON and other corps such as wheat and peanuts.

APPROACH: Sensor Development Corp will use its platform technology, a nanocrystalline tin dioxide solid state gas phase sensor system, to detect a signature gas for the presence of aflatoxin in corn storage. The Phase I effort will start with the fabrication of a number of sensor chips. These chips will be made by spin coating an alumina substrate with tin dioxide sol gels and then calcining under controlled temperature and time conditions. This will produce a nanocrystalline surface with numerous reaction sites, hence the high sensitivity. The composition of the sol gel will be modified by adding additional active metals to enhance selectivity in the presence of interferent gases. In addition to adding these metals to the sol gel, the composition of the sol gel can be varied. A combinatorial chemistry approach will be used to optimize performance of the sensors. The chip will have a platinum heater element printed, on its backside for chip heating, and a temperature sensor on the front side to monitor chip operating temperature. Chip fabrication will be done at Case Western Reserve University, using state-of-the-art equipment and experienced personnel. For sensors optimization, the fabricated chip will be evaluated in a lab test system which will expose the chip to controlled gas concentrations and compositions. Measurements of the specific net conductance (SNC), the change of the sensor in response to exposure to a test gas, will later be used to determine the concentration of the target gases. The system uses LabVIEW (National Instruments) to control the test operation and monitor the data output. During testing, the gas concentrations and compositions are varied along with the operating conditions. The optimum performance will be established from the variables of active coating composition, operating conditions, and data analysis. Software from commercial data analysis platforms will be used to analyze the data and correct for drift and noise if present. This optimized chip will then be installed in a test device, already prototyped by FloCell and delivered to Purdue University where it will be incorporated in a laboratory scale system for measuring the signature gas from actual mold growth in corn. The sensor chip, protected from dust, will be used to measure the concentration of the gas present. Knowing the bin volume and gas exchange rate, the high sensitivity of the system will allow comparison of the diluted signature gas with that determined by conventional analysis, the latter requiring representative sampling of the corn, then sample preparation and finally, reacting the resultant analyte with mycotoxin specific antibodies. The color change indicates the mycotoxin concentration. This method, Enzyme Link Immunosorbent Assay (ELISA), is approved by (GIPSA). Depending on the results from single chip testing in Phase I, multiple chips in an array format can be used to enhance the selectivity in Phase II. Each chip will have a different active coating or operating condition. Software manipulation of the data will further enhance the selectivity.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Nuts, Seeds