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Dipicolinic Acid and Its Calcium Salt as Biomarker Compounds Determined by Raman Spectroscopy

Dipicolinic acid ( 2, 6-pyridine dicarboxylic acid) is a universal constituent of bacterial spores where it represents 5-15% of total mass, and it has never been detected in vegetetive cells. Spores also contain high concentaration of calcium ions that are mostly complexed with dipicolinic acid in equimolar amounts. It was suggested that these compounds serve a role in the heat and ultraviolet irradiation resistance. Dipicolinic acid is often used as a signal of sporulating bacteria presence, and variety of analytical techniques have been employed for its detection, e.g. fluorescence, colorimetry, polarography, GC and HPLC. Most methods involve extraction and derivatization of dipicolinic acid that increase anaylsis time. In this work, Raman spectroscopy was used as a modern and fast analysis tool to detect the presence of dipicolinic acid in synthetic samples and also in samples contain bacterial spores. The Raman spectra of pure dipicolinic acid and its isolated calcium salt were asigned. Surface-enhanced Raman scattering (SERS) technique using silver colloids of different paricle size was employed to detect the presence of dipicolinic acid in solutions of low concentration range. The obtained spectra of dipicolinic anion was asigned and compared with spectra of solids. Applicability of biomaker compounds detection in pure culture of Bacillus subtilis by Raman spectroscopy was also discussed.

Raman spectroscopy ; dipicolinic acid ; SERS ; biomarker compounds

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