Detection of presence of chemical precursors
Inventors
Li, Jing • Meyyappan, Meyya • Lu, Yijiang
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-7623972-B1
Publication Date
2009-11-24
Expiration Date
2025-07-08
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Abstract
Methods and systems for determining if one or more target molecules are present in a gas, by exposing a functionalized carbon nanostructure (CNS) to the gas and measuring an electrical parameter value EPV(n) associated with each of N CNS sub-arrays. In a first embodiment, a most-probable concentration value C(opt) is estimated, and an error value, depending upon differences between the measured values EPV(n) and corresponding values EPV(n;C(opt)) is computed. If the error value is less than a first error threshold value, the system interprets this as indicating that the target molecule is present in a concentration C≈C(opt). A second embodiment uses extensive statistical and vector space analysis to estimate target molecule concentration.
Core Innovation
The invention provides methods and systems for detecting one or more chemical precursors of a multi-component compound that may become unstable when fully combined. It uses functionalized carbon nanostructures (CNSs) loaded with different sensitizing substances that react with specific chemical precursors present in a gas. Upon exposure, electrical parameter values (EPVs) such as impedance, conductance, capacitance, or inductance are measured and compared with reference EPV sequences to estimate the presence and concentration of target molecules.
The problem addressed is the need for rapid detection of target chemical precursors, often present in unstable or sealed forms at very low concentrations (e.g., 1-100 ppm), especially relevant for detecting substances associated with terrorist activities. The system must detect oxidizers and energizers in a short time frame (about 5-15 seconds), with high sensitivity, a small physical footprint, and low energy consumption.
The system includes arrays of CNS sub-arrays, each functionalized differently, exposed to a gas suspected of containing target molecules. The changes in electrical parameters are modeled with linear or logarithmic relationships relative to concentration. Statistical and vector space analyses including eigenvalue decomposition and orthonormal vector construction identify linear combinations of sensor responses that distinguish different target molecules. The system estimates most probable concentrations and applies error thresholds to decide presence or absence of specific target molecules based on measured EPVs.
Claims Coverage
The claims cover a method for detecting target molecules in a gas using carbon nanostructure sub-arrays, focusing on the measurement and interpretation of electrical parameter values (EPVs) and estimation of concentrations with error thresholding.
Use of functionalized carbon nanostructure sub-arrays loaded with Au nanoparticles
The method employs N CNS sub-arrays each loaded with a sensitizing substance comprising Au nanoparticles to functionalize the sensors for detecting target molecules.
Estimation of concentration-dependent electrical parameter value relationships
The method estimates first and second functional relationships between concentration of first and second target molecules and measured electrical parameters, using logarithmic forms in low concentration ranges and linear forms in higher ranges, with selected real parameters defining these relationships.
Rapid exposure and measurement protocol
The CNS sub-arrays are exposed to the gas and electrical parameter values are measured in a short time interval not exceeding about 15 seconds, enabling rapid detection.
Computation of probable concentration values based on measured and reference EPVs
The method calculates probable concentration values for the first and second target molecules based on differences between measured EPVs and the estimated functional relationships for each molecule.
Error value computation and threshold-based interpretation
First and second error values are computed from differences between measured EPVs and reference EPVs adjusted to the probable concentrations. These error values are compared with selected thresholds to determine presence or absence of the target molecules and their concentrations.
The claims collectively define a method that integrates functionalized CNS sensors, modeled EPV-concentration relationships, rapid measurement, and statistical error-based decision-making to detect and estimate concentrations of at least two target molecules present simultaneously in a gas.
Stated Advantages
Enables detection of target chemical precursors at very low concentrations (as low as 1 ppm) within a short time interval (about 5-15 seconds).
Allows simultaneous detection of multiple target molecules, including oxidizers and energizers.
Operates with a relatively small physical footprint suitable for real-life environments.
Requires only small energy expenditure for operation.
Provides flexibility to detect any reasonable number of target molecules from a single set of measurements.
Documented Applications
Detection of chemical precursors associated with terrorist activities, such as oxidizers and energy sources for liquid explosives.
Rapid sensing of gases containing target molecules in sealed containers at low concentrations for security screening.
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