Utilizing low-energy ion beams to study living organisms

In the present study, the survival potentials of two kinds of water-abundant living organisms, the mammalian AL cell, and the nematode Caenorhabditis elegans, were investigated in an effort to improve their tolerance of the high-vacuum conditions required for ion implantation experiments. Samples were subjected to the vacuum at a pressure of 2–5 × 10− 2 Pa for a period of 90–150 s, and their surviving fractions were analyzed subsequently. The ion beam bioengineering facility, which makes use of a differential pumping system to minimize the sampleʹs vacuum duration time (less than 5 min for most implantation experiments), provided the physical foundation. Analyses on the cell status during vacuum exposure indicated that decrease of temperature and desiccation are the main causes (or at least parts of them), for cell inactivation. Glycerol, one of the most popular cryo-agents, in combination with proper pre-treatment protocols, was adopted to enhance the organismsʹ vacuum tolerance. The survival fraction of AL cells, assayed by PI-Flow Cytometry, manifested a PI-negative (indication of living cells) fraction of 12.7 ± 3.37% at 20% (v/v) glycerol pre-treatment. C. elegans, a self-organized animal, having much larger body volume compared with the former species, displayed a better anti-vacuum potential when an adaptation to glycerol at long-term (> 1 h) and low-concentration (2%, v/v) was applied prior to being processed with high-concentration (15%, v/v) glycerol. The final vacuum survival rate of C. elegans averaged at 40.4 ± 15.35%, which was evidently superior to that of the worms without glycerol protection. Though the poor vacuum tolerance has long been a trouble for researchers who have a strong desire to study these organisms by ion beam technology, we have every confidence that any such improvement will enable new directions for research in this field.