UV Raman detection of micro-organisms and their toxins in fish tissue

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It has been determined that domoic acid(DA) can be quantitated from homogenized shellfish tissue by means of resonance Raman spectra excited by 251 nm light. Detection limits have been found to be substantially below the 20 micrograms DA per gram tissue deemed by regulators to be unfit for human consumption. Clam tissue obtained from a supermarket has been prepared for analysis by direct homogenization for 2 minutes in a Waring blender. The homogenized samples were placed in a flow system and subjected to a 5-10 mw 251 nm excitation. Back-scattering collected for 20-30 seconds provided sufficient information for analysis. The method is extremely simple to use since the DA produces a single intense peak at 1652 cm-1. Because relatively-weak protein, nucleic acid and lipid spectra are excited from the tissue, background interference is surprisingly low. Bacteria can be detected using the same approach, but sensitivities are much lower primarily due to spectral interference from tissue nucleic acids.

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Proceedings of SPIE - The International Society for Optical Engineering