Proton-Cluster-Beam Lethality and Mutagenicity in Bacillus subtilis Spores

The unique energy transfer characteristics of swift cluster ions have attracted the attention of many researchers working on the analysis or processing of material surfaces, but the effects on living organisms remain unclear. We irradiated B. subtilis spores with monomer and cluster proton beams and examined their lethality; the 2 MeV H2+ shows a clearly lower lethality than 340 keV H+, even though both have a comparable linear energy transfer. The 2 MeV H2+ dissociates into a pair of 1 MeV H+ by losing the bonding electrons at the target surface. The estimated internuclear distance and the radial dose distribution suggest that the spread of deposited total energy over two areas separated by just several nanometers greatly diminishes beam lethality and that the energy density in the very center of the trajectory, possibly within a 1 nm radius, has a great impact on lethality. We also performed a whole genome resequencing of the surviving colonies to compare the molecular nature of mutations but failed to find a clear difference in overall characteristics. Our results suggest that cluster beams may be a useful tool for understanding biological effects of high linear energy transfer radiation.

Mass separated particle flux from a laser-ablation metal cluster source

Flux waveforms of aluminum cluster beams supplied from a laser-ablation cluster source were precisely investigated under various source conditions such as background pressure, ablation laser intensity, and nozzle structure. A time-of-flight mass spectroscopy revealed that aluminum clusters with sizes up to 200 were generated and the amount of the clusters could be maximized by choosing a proper background pressure (~2 MPa) and an ablation laser fluence (~40 mJ/cm2). Flux waveforms of clusters having specific sizes were carefully reconstructed from the observed mass spectra. It is found that the pulse widths of the aluminum cluster beams were typically about 100 µs and much smaller than that of the monoatomic aluminum beam, indicating that the cluster formation was limited in a relatively small volume in the laser-ablated vapor. Introducing a conical nozzle having a large open angle was also found to enhance the cluster beam velocity and reduce its pulse width. A velocity measurement of particles in the cluster beam was conducted to examine the velocity spread of the supplied clusters. We found that the aluminum clusters were continuously released from the source for about 100 µs and this release time mainly determined the pulse width of the cluster beam, suggesting that controlling the behavior of an ablated vapor plume in the waiting room of the cluster source holds the key to drastically improving the cluster beam flux.

Comparative study of antibacterial properties of polystyrene films with TiO x and Cu nanoparticles fabricated using cluster beam technique

Background: Antibacterial materials are of high importance for medicine, and for the production and conservation of food. Among these materials, polymer films with metal nanoparticles (NPs) are of considerable interest for many practical applications. Results: The paper describes a novel approach for the formation of bactericidal polymer thin films (polystyrene in this case), produced by spin-coating, with Ti and Cu NPs deposited from cluster beams. Ti NPs are treated in three different ways in order to study different approaches for oxidation and, thus, efficiency in formation of the particles with semiconducting properties required for the catalytic formation of reactive oxygen species. Cu NPs are used as deposited. Partial NP embedding into polystyrene is realised in a controllable manner using thermal annealing in order to improve surface adhesion and make the particles resistant against wash-out. The formed composite films with TiO x and Cu species are tested as bactericidal media using E.coli bacteria as model microorganisms. Conclusion: The obtained results show considerable efficiency in destroying the bacteria and a good possibility of multiple re-use of the same composite films making the suggested approach attractive for the cases requiring reusable polymer-based antibacterial media.