Acaricidal efficacy of ultraviolet-C irradiation of Tetranychus urticae adults and eggs using a pulsed krypton fluoride excimer laser

Background Pulsed ultraviolet (UV)-C light sources, such as excimer lasers, are used in emerging non-thermal food-decontamination methods and also have high potential for use in a wide range of microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using female adults and eggs of a model organism, the two-spotted spider mite Tetranychus urticae. Methods UV-C light was generated by a pulsed krypton fluoride excimer laser operating at 248-nm emission wavelength. The pulse energy and pulse repetition rate were 5 mJ and up to 100 Hz, respectively. The distance from the light source to the target was 150 mm; the target surface area was 2.16 cm2. The exposure time for the mites and fresh eggs varied from 1 to 4 min at 5–300 mW, which corresponded to UV doses of 5–80 kJ/m2. Post-irradiation acaricidal effects (mite mortality) were assessed immediately and also measured at 24 h. The effects of UV-C irradiation on the hatchability of eggs were observed daily for up to 12 days post-irradiation. Results The mortality of mites at 5 and 40 kJ/m2 was 26% and 92%, respectively. Mite mortality reached 98% at 80 kJ/m2. The effect of exposure duration on mortality was minimal. The effect of irradiation on egg hatchability was even more significant than that on adult mite mortality, i.e. about 100% egg mortality at an accumulated dose of as little as 5 kJ/m2 for each exposure time. Conclusions A high rate of mite mortality and lethal egg damage were observed after less than 1 min of exposure to 5 mJ UV-C pulsed irradiation at 60 Hz. Pending further developments (such as beam steering, beam shaping and miniaturisation) and feasibility studies (such as testing with mites in real-life situations), the reported results and characteristics of the UV-C generator (modulation of energy output and adaptability to varying spot sizes) open up the use of this technology for a vast field of acaricidal applications that require long-range radiation. Graphical Abstract

Acaricidal Activity of UV-C irradiation on Tetranychus urticae and eggs using pulsed krypton fluoride excimer laser

Background While pulsed UV-C light sources such as excimer lasers are used in emerging non-thermal food decontamination method, they also have a high potential for a wide range of other microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using two-spotted spider mite female adults Tetranychus urticae and eggs as a model. Methods The UV-C light source was generated by a pulsed krypton fluoride (KrF) excimer laser operating at 248 nm emission wavelength. Pulse energy and pulse repetition rate were 5mJ, and up to 100Hz rate, respectively. Distance from light source to target was 150 mm with a target surface of 21.6 cm². The exposure time of the mite and fresh eggs varied from 1 to 4 minutes at a power of 300 mW. The post-irradiation acaricidal effects (mites’ mortality) were assessed immediately and measured 24 h post-irradiation. Effects on the hatchability of irradiated eggs were observed daily post-irradiation for up to 12 days. Results The mortality of mites observed with an energy amount of 5 and 40 mJ/mm² was 26% and 90%, respectively. The mortality at 80 mJ/mm² reached 99%. The effect of exposure duration on mortality was minimal. The effect of irradiation of eggs hatchability was even more important, with about 100% mortality with as little as 5 mJ/mm² for each exposure time. Conclusions A high mite mortality and lethal egg damage was already observed after less than 1 min exposure to UV-C pulsed irradiation. Pending further developments and feasibility studies, the current results and features of the UV-C generator (energy output modulation and applicability to varying spot sizes) open up a large field of germicidal applications requiring long-range radiation.

Nanostructured Polystyrene Doped with Acetylsalicylic Acid and Its Antibacterial Properties

Homogeneous polystyrene foils doped with different concentrations of acetylsalicylic acid were prepared by the solvent casting method. The surface morphology and surface chemistry of as-prepared foils were characterized in detail. Excimer laser (krypton fluoride, a wavelength of 248 nm) was used for surface nanopatterning of doped polystyrene foils. Certain combinations of laser fluence and number of laser pulses led to formation of laser-induced periodic surface structures (LIPSS) on the exposed surface. Formation of the pattern was affected by the presence of a dopant in the polystyrene structure. Significant differences in surface chemistry and morphology of laser-treated foils compared to both pristine and doped polystyrene were detected. The pattern width and height were both affected by selection of input excimer exposure conditions, and the amount of 6000 pulses was determined as optimal. The possibility of nanostructuring of a honeycomb-like pattern doped with acetylsalicylic acid was also demonstrated. Selected nanostructured surfaces were used for study the antibacterial properties for a model bacteria strain of S. aureus. The combination of altered surface chemistry and morphology of polystyrene was confirmed to have an excellent antibacterial properties.

LIPSS Structures Induced on Graphene-Polystyrene Composite

A laser induced periodic surface structure (LIPSS) on graphene doped polystyrene was prepared by the means of a krypton fluoride (KrF) laser with the wavelength of 248 nm and precisely desired physico-chemical properties were obtained for the structure. Surface morphology after laser modification of polystyrene (PS) doped with graphene nanoplatelets (GNP) was studied. Laser fluence values of modifying laser light varied between 0–40 mJ·cm−2 and were used on polymeric PS substrates doped with 10, 20, 30, and 40 wt. % of GNP. GNP were incorporated into PS substrate with the solvent casting method and further laser modification was achieved with the same amount of laser pulses of 6000. Formed nanostructures with a periodic pattern were examined by atomic force microscopy (AFM). The morphology was also studied with scanning electron microscopy SEM. Laser irradiation resulted in changes of chemical composition on the PS surface, such as growth of oxygen concentration. This was confirmed with energy-dispersive X-ray spectroscopy (EDS).

Characteristics of target polarization by laser ablation

Experimental results are obtained concerning the target polarization, which aptly characterizes the laser ablation. The charge separation in the laser-produced plasma, structure of the ion front, and the current of fast electrons expanding into the vacuum chamber ahead of ions are of crucial importance for the interpretation of multi-peak structure of target currents appearing much later than the laser pulse. Of particular interest is the correlation between the partial maxima in the time-resolved target current and the square root of mass number of ionized species. The late-time negative charging of targets provides evidence for production of very slow ions by ionization of neutrals ablated at the target crater by radiation from plasma produced by 23 ns excimer krypton fluoride laser.