Systems and methods for detecting contaminants in a sample

Inventors

Chao, Kuanglin • Kim, Moon S. • Lefcourt, Alan M. • Tuschel, David • Olkhovyk, Oksana • Liu, Yongliang

Assignees

US Department of Agriculture USDA • ChemImage Technologies LLC

Abstract

System and method for determining the presence of a contaminant in a sample using Raman spectroscopic data. The sample may be food or feed and the contaminant may be melamine. The sample is illuminated with substantially monochromatic light to produce Raman scattered photons. The Raman scattered photons are collected to generate Raman spectroscopic data. The Raman spectroscopic data may comprise at least one of a Raman spectrum and a spatially accurate wavelength resolved Raman image. The Raman spectroscopic data is analyzed to determine the presence or absence of a contaminant in a sample. The concentration of the contaminant in the sample can also be determined by using a ratio algorithm.

Core Innovation

The invention provides systems and methods for the rapid, accurate, non-destructive, specific, and routine detection of contaminants, such as melamine, in food and feed samples using Raman spectroscopy and Raman chemical imaging. The method involves illuminating a sample with substantially monochromatic light to produce Raman scattered photons, collecting these photons to generate Raman spectroscopic data, and analyzing this data to determine the presence or absence of a contaminant. The concentration of the contaminant can also be determined using a ratio algorithm applied to the Raman spectra.

The problem addressed is the presence of melamine as a harmful contaminant intentionally added to animal feed and food products to falsely elevate apparent protein content. Existing detection methods rely on time-consuming in-vitro GC-MS and LC-MS/MS procedures that require chemical solvents, expensive mass spectrometry equipment, and labor-intensive steps. There is a need for a rapid, non-destructive, low-cost, and easy-to-operate detection method that requires minimal sample preparation and can be used routinely to ensure food/feed safety and security.

The invention takes advantage of the Raman Effect wherein molecular information is obtained by monitoring frequency shifts in scattered monochromatic light. Raman chemical imaging combines spectral and spatial imaging for molecular-specific analysis of heterogeneous samples, offering high spatial resolution and minimal sample preparation. The invention uses dominant and well-isolated Raman bands, particularly a melamine Raman peak at approximately 670 cm−1, as markers to detect contaminants at concentrations as low as 0.2% by weight. The approach includes wide-field illumination, use of excitation lasers at 785 nm or 1064 nm wavelengths, and integration of bright field imaging fused with Raman images to identify and analyze regions of interest.

Claims Coverage

The patent includes two independent claims that disclose methods for determining the presence of a contaminant in a sample using Raman chemical imaging with wide-field illumination and generating Raman images, and their analysis.

The independent claims focus on methods for detecting contaminants, including melamine and its derivatives, in non-aqueous macroscopic samples by applying wide-field illumination to generate Raman chemical images at specific wavelengths, and analyzing those images to determine contaminant presence and concentration with optional application of algorithms, using excitation laser sources around 785 nm or 1064 nm and employing tunable filters and specific Raman spectral peaks such as at approximately 670 cm−1.

Stated Advantages

Documented Applications