An Ultrasensitive Bioassay for the Detection of Furocoumarins and Other Photosensitizing Molecules

A photobiological assay based upon inhibition of growth in the DNA repair‐deficient bacterium E. coli B s‐1 , is described for the analysis of a number of photosensitizing agents. The lower limits of detection were as follows: psoralen 5 × 10 ‐11 g; 5‐methoxypsoralen 1 × 10 ‐9 g; 8‐methoxypsoralen 1 × 10 ‐9 g; 4,5',8‐trimethylpsoralen 1 × 10‐ 11 g; angelicin 5 × 10 ‐9 g; 5,7‐di‐methoxycoumarin 1 × 10 ‐7 g; isoimperatorin 5 × 10 ‐9 g; dictamnine 1 × 10 ‐8 g; oxypeucedanin 5 × 10 ‐7 g; 5‐nitroxanthotoxin 5 × 10 ‐7 g; and α‐terthienyl 1 × 10 ‐6 g. All active compounds with the exception of α‐terthienyl were more easily detected by several orders of magnitude by E. coli B s‐1 than with the normal wild type E. coli. 5—Geranoxypsoralen and isopimpinellin were not active. The application of this technique, after TLC, to the analysis of complex mixtures from lemon oil, oil of bergamot, Heracleum lanatum, Angelica dawsonii , and celery and parsnip is illustrated. The bioassay described is more rapid and sensitive than previously published methods, permits replica plates to be made, and allows tentative identification of the photosensitized molecular target.