L.D. Yu

Ion beam induced Deoxyribose Nucleic Acid transfer

We report our observations of the interaction of energetic ions with bacterial cells, inducing direct deoxyribose nucleic acid (DNA) transfer into Escherichia coli (E. coli). Argon- and nitrogen-ion beams were used to bombard the bacteria E. coli in a vacuum with energy of 26 keV and fluence in the range 0.5–4×1015u2002ions/cm2. Three DNA plasmids, pGEM2, pGEM-T easy, and pGFP, carrying different marker genes, were subsequently transferred (separately) into the appropriately ion-bombarded bacteria and successfully expressed. The results of this study indicate that ion beams with an energy such that the ion range is approximately equal to the cell envelope thickness, at a certain range of fluence, are able to generate pathways for macromolecule transfer through the envelope without irreversible damage.

A study of low-energy ion beam effects on outer plant cell structure for exogenous macromolecule transferring

Abstract The aim of this study was to investigate low-energy ion beam effects on inducing exogenous macromolecule transfer through cell walls into cells and the related dependence. The experiment focused on 20–30 keV Ar ion implantation in various plant tissues to doses ranging from 1014 to 1016 ions/cm2. Auxiliary 15–30 keV N ion implantation in the plant tissues as well as 25 keV Ar ion implantation in bacteria of E. coli was also carried out. The effects of ion beam bombardment on the outer cell structure and the ability of transferring large exogenous molecules of Trypan blue (TB) and plasmid DNA were investigated. Typical results show that the 20 keV Ar ion implantation only leads to retaining of the TB dye in the cell wall whereas the 30 keV Ar ion implantation can allow the dye to enter the cell. A discussion based on simulations of the ion implantation processes indicates that the cell wall composed of cellulose microfibrils is in a porous structure so that ions at certain low energies with appropriate doses can increase permeability of the cell wall and induce exogenous macromolecule transferring.

Ion penetration depth in the plant cell wall

Abstract This study investigates the depth of ion penetration in plant cell wall material. Based on the biological structure of the plant cell wall, a physical model is proposed which assumes that the wall is composed of randomly orientated layers of cylindrical microfibrils made from cellulose molecules of C6H12O6. With this model, we have determined numerical factors for ion implantation in the plant cell wall to correct values calculated from conventional ion implantation programs. Using these correction factors, it is possible to apply common ion implantation programs to estimate the ion penetration depth in the cell for bioengineering purposes. These estimates are compared with measured data from experiments and good agreement is achieved.

Characteristics of heavy ion beam-bombarded bacteria E. coli and induced direct DNA transfer

Abstract The goal of the work described here was to study ion beam interactions with bacteria and thus develop an understanding of the mechanisms involved in ion bombardment-induced direct gene transfer into bacterial cells. Ar ion beams at an energy of 26 keV and fluences ranging from 5×10 14 to 4×10 15 ions/cm 2 were used to bombard bacterial cells of Escherichia coli strain DH5α. The bacteria were able to survive the low-temperature and low-pressure treatment conditions for at least a few hours. The ion bombardment created novel crater-like structures on the surface of the bacterial cell envelope, as observed by scanning electron microscopy. Four variously sized DNA plasmids carrying the ampicillin resistance gene were transferred and expressed in E. coli cells bombarded with ion fluences of 1×10 15 and 2×10 15 ions/cm 2 . The dependence of the DNA transfer on the plasmid DNA size, ion fluence and incubation time all suggests that the ion beam-induced surface crater-like structures provide the pathway for the mechanism that is responsible for the ion beam-induced DNA transfer.

Some investigations of ion bombardment effects on plant cell wall surfaces

Abstract Recent developments in the field of ion beam bioengineering, for example our own work demonstrating ion beam-induced transfer of exogenous macromolecules into the interior cell region, have underscored the need for a better understanding of the effects of ion bombardment on the cell wall material. We describe here, our investigations of ion beam sputtering of plant cell wall material and ion beam-induced damage to the cell wall. The presently available ion implantation simulation programs are not adequate, and experimental results are not available, either. We have indirectly estimated the surface sputtering yield of plant cell wall composed of C6H12O6-compound by remodeling the cell wall material so as to use partial mass densities and surface binding energies in the available ion implantation programs. For bombardment with a 30-keV Ar-ion beam, the sputtering yield from the cell wall is estimated to be approximately 10 atoms/ion, which is somewhat greater than the value predicted by direct program simulation, but in good agreement with experimental results. We have also performed electron microscopy on the ion-bombarded cell walls. The micrographs show novel microcrater-like structures on the cell wall subsequent to ion bombardment, which could be the ion beam-generated pathways for exogenous macromolecule transfer.

Effects of low-fluence swift iodine ion bombardment on the crystallization of ion-beam-synthesized silicon carbide

Ion beam synthesis using high-fluence carbon ion implantation in silicon in combination with subsequent or in situ thermal annealing has been shown to be able to form nanocrystalline cubic SiC (3C-SiC) layers in silicon. In this study, a silicon carbide layer was synthesized by 40-keV C12+ implantation of a p-type (100) Si wafer at a fluence of 6.5×1017u2009ions∕cm2 at an elevated temperature. The existence of the implanted carbon in Si substrate was investigated by time-of-flight energy elastic recoil detection analysis. The SiC layer was subsequently irradiated by 10–30 MeV I127 ions to a very low fluence of 1012u2009ions∕cm2 at temperatures from 80 to 800u2009°C to study the effect on the crystallization of the SiC layer. Infrared spectroscopy and Raman scattering measurement were used to monitor the formation of SiC and detailed information about the SiC film properties was obtained by analyzing the peak shape of the Si-C stretching mode absorption. The change in crystallinity of the synthesized layer was probed ...

The low-energy ion range in DNA

In fundamental studies of low-energy ion irradiation effects on DNA, calculation of the low-energy ion range, an important basic physical parameter, is often necessary. However, up to now a unified model and approach for range calculation is still lacking, and reported data are quite divergent and thus unreliable. Here we describe an approach for calculation of the ion range, using a simplified mean-pseudoatom model of the DNA target. Based on ion stopping theory, for the case of low-energy (< or = a few keV) ion implantation into DNA, the stopping falls in the low reduced energy regime, which gives a cube-root energy dependence of the stopping (E(1/3)). Calculation formulas of the ion range in DNA are obtained and presented to unify the relevant calculations. The upper limits of the ion energy as a function of the atomic number of the bombarding ion species are proposed for the low-energy case to hold. Comparison of the results of this approach with the results of some widely used computer simulation codes and with results reported by other groups indicates that the approach described here provides convincing and dependable results.

Friction modification of WC-Co by ion implantation

Abstract This study focuses on the effects of ion implantation on the friction modification of WC-Co cermet. Samples were implanted with Ar, C, N, O and B ions at 120–140 keV, and underwent tribological tests, mainly within the elastic region, against the cermet itself using varied loads. The experimental results show that the C ion implantation most significantly reduces the friction coefficient, and that the effect increases with the ion dose, whereas N, O and B ion implantations increase microhardness. A modified friction model suggests that the contributors to the friction modification are attributed to the compromise between microhardness and toughness, depending on the microstructure or phase and the ion-implantation-induced surface compression stress, which depends on the ion size.

Hardness, tribological behaviour and corrosion performance at the very near surface of nitrogen ion-implanted X5CrNi18.10 steel

Abstract The influence of nitrogen ion implantation on the hardness, tribological behaviour and corrosion performance at the very near surface of polished X5CrNi18.10 steel was studied. The specimens were implanted with 120 keV N + ions to four different fluences ranging from 10 16 to 10 18 ions cm −2 . It was found that hardness, tribological behaviour in terms of wear and friction, and corrosion resistance of the specimens strongly depend on the implantation conditions. The greatest improvement in the surface properties of the steel was achieved at doses between 1 × 10 17 and 5 × 10 17 ions cm −2 . Although hardness, wear resistance and friction behaviour were improved noticeably by the implantation, N ion implantation tended to reduce the corrosion resistance of the specimens in KNO 3 .

Improved antioxidant activity of BKOS Thai jasmine rice.

Thai jasmine rice (Oryza sativa L. cv. KDML105) is highly valued due to its subtle aroma, robust seed characteristics and high nutritional quality. Low-energy ion-beam bombardment was chosen to improve the quality of jasmine rice by mutation induction. One mutated variety, named BKOS, was found to exhibit a deep purple colour due to an increased accumulation of anthocyanin. The total phenolic content and antioxidant activities of cooked and uncooked rice extracts were compared with KDML105, BKOS and other rice mutants created by a low-energy ion beam. The BKOS extracts showed the highest total phenol content (0.140 and 0.096u2009mg of gallic acid equivalent (GAE)u2009g−1 dry extract from uncooked and cooked rice, respectively). The BKOS extracts also had improved antioxidant activities, determined using three standard methods: 2,2′-diphenyl-1-picrylhdrazyl (DPPH) free radical scavenging, ABTS radical cation (ABTS•+) decolourisation and ferric-reducing antioxidant power assays. BKOS extracts showed 2–2.5-fold increased levels for each method. Interestingly, there was no significant difference between the antioxidant activities of the cooked and uncooked BKOS rice extracts. The increased quantity of antioxidants in this anthocyanin-based natural product could allow antioxidants to be consumed by a wider population than what is currently possible.