Preventing biological activity of Ulocladium sp spores in artifacts using 157-nm laser

Abstract

High resolution atomic force microscopy images of immobilized Ulocladium sp cultures on silicon wafers reveal the cessation of biological activity after laser illumination at 157 nm. Laser light dissociates the external multilayered proteinaceous membrane of the spores, reducing their thickness to a critical value prior to cell explosion due to the high internal pressure of the nucleus. The population of a monolayer culture was successfully destroyed following illumination with 150 laser pulses at the fluence of 1 mJ/cm² per pulse. A thin layer of 0.3 nm was removed on the average from the external membrane per pulse, and a thin layer of 45 nm had to be removed from the external membrane before cell explosion. Thus, the use of a 157-nm laser is an effective and controllable method for stopping biological activity of Ulocladium sp spores in artifacts. This finding supports previous results of using 157-nm lasers against foxing in historic paper preservation.