Treatment of Streptococcus mutans biofilms with a nonthermal atmospheric plasma.

AIMS: A nonthermal atmospheric plasma, designed for biomedical applications, was tested for its antimicrobial activity against biofilm cultures of a key cariogenic bacterium Streptococcus mutans. METHODS AND RESULTS: The Strep. mutans biofilms were grown with and without 0.15% sucrose. A chlorhexidine digluconate rinse (0.2%) was used as a positive antimicrobial reference. The presence of sucrose and the frequency of plasma application during growth were shown to have a significant effect on the response to treatment and antibacterial activity. CONCLUSIONS: A single plasma treatment for 1 min on biofilms cultured without sucrose caused no re-growth within the observation period. However, with either single or repeated plasma treatments of 1 min, on biofilms cultured with 0.15% sucrose, growth was only reduced. SIGNIFICANCE AND IMPACT OF THE STUDY: In summary, there may be a role for nonthermal plasma therapies in dental procedures. Sucrose and associated growth conditions may be a factor in the survival of oral biofilms after treatment.

Electric discharge plasmas influence attachment of cultured CHO K1 cells.

Non-thermal plasmas can be generated by electric discharges in gases. These plasmas are reactive media, capable of superficial treatment of various materials. A novel non-thermal atmospheric plasma source (plasma needle) has been developed and tested. Plasma appears at the end of a metal pin as a submillimetre glow. We investigate the possibility of applying the plasma needle directly to living tissues; the final goal is controlled cell treatment in microsurgery. To resolve plasma effects on cells, we study cultured Chinese hamster ovarian cells (CHO-K1) as a model system. When these are exposed to the plasma, instantaneous detachment of cells from the surface and loss of cell-cell interaction is observed. This occurs in the power range 0.1-0.2 W. Cell viability is assessed using propidium iodide (PI) and cell tracker green (CTG) fluorescent staining utilizing confocal laser scanning microscopy (CLSM). Detached cells remain alive. Use of higher doses (plasma power >0.2 W) results in cell necrosis. In all cases, plasma-influenced cells are strictly localized in submillimetre areas, while no reaction in surrounding cells is observed. Due to its extreme precision, plasma treatment may be applicable in refined tissue modification.

Evolution of a dust void in a radio-frequency plasma sheath.

The onset and growth of a dust void are investigated in a radio-frequency (rf) sheath of a capacitively coupled argon plasma. A circularly symmetric void emerges and grows with increasing rf power and pressure in the central region of the dust cloud levitating in the sheath. Experimental measurements of the void diameter are compared with the predictions of a simple phenomenological theory, based on a balance of forces on dust grains.

Effects of crystal shape on the energy levels of zero-dimensional PbS quantum dots.

Nanometer-size PbS quantum dots have been made by electrodeposition on a Au(111) substrate. The deposited nanocrystals have a flattened cubic shape. We probed the single-electron energy-level spectrum of individual quantum dots by scanning tunneling spectroscopy and found that it deviates strongly from that of spherical PbS quantum dots. The measured energy-level spectrum is successfully explained by considering strong confinement in a flattened cubic box.

Threefold effect of peripheral precues: alertness, orienting, and response tendencies.

Three experiments were run revealing that peripheral cues exert an alerting and orienting effect. Novel is the finding that peripheral cues induce a (hidden) tendency to respond to the cued side, which interacts with the response tendency elicited by the subsequent following target. Compatible S-R mappings revealed either a reversed or no response tendency in cue conditions as compared to uncued conditions. Incompatible mappings mostly showed a decrease in response tendencies under influence of the peripheral cue. An increase of the interval between the cue and the target up to 500 ms resulted in a return to the baseline condition (without cue). The findings for the compatible mappings may be interpreted in terms of an extra recoding operation that was induced by peripheral cues. Inconsistencies found for incompatible S-R mappings might be attributed to the dual presence of recoding operations on account of the cue and the target.

Uncertainty and processing routes in the selection of a response: an S-R compatibility study.

Stimulus-response (S-R) pairs are usually processed faster when-they are presented in a series that consists entirely of compatible relations rather than incompatible relations. A mixture of the two pairs in a series, which induces uncertainty, increases processing speed for both pairs, but more so for compatible S-R pairs. The results of three choice reaction time (RT) tasks showed that presentation of a precue that only indicated either compatible or incompatible S-R pairs reduced the detrimental effect of mixing pairs more for the former than for the latter pairs. A similar asymmetric reduction was observed in the third experiment when either pair was preceded by the same pair or the same class of pairing. Analyses of RT bins revealed that decreases in RT for the mixed compatible S-R pairs occurred only for the faster responses. It was shown further that errors consisted primarily of a correct application of an incorrect S-R transformation rule. The results are interpreted within the framework of the dimensional overlap model of Kornblum et al. (1990) suggesting two sources of the S-R compatibility effect; interference of primed responses and the need to suppress response priming.

An additive factors analysis of the effect(s) of location cues associated with auditory stimuli on stages of information processing.

The additive factors method (AFM) was used as a tool for assessing the locus (or loci) of the detrimental effect of auditory location cues in the chain of (visual) information processing. In the first experiment the location variable was factorially combined with response specificity, which is assumed to affect the response adjustment stage. A second experiment was performed in which movement amplitude, assumed to affect the response programming stage, was manipulated in addition to the location variable and a different variety of response specificity. Finally, the location variable was combined with relative S-R frequency, which is also assumed to affect the response programming stage, in a third experiment. The results of these experiments showed additive effects of the location variable with motor variables. The remaining two experiments were designed to assess the effects of location cues on response selection. In these experiments the location variable was combined with the number of response alternatives. Response speed decreased with an increase in the number of response alternatives. However, the effects of the location variable and number of response alternatives were additive. According to the additive factor logic, then, the results of experiments 1, 2 and 3 seem to indicate that the locus of interference of the location cues is not in the later response stages of the reaction process. The results of the last two experiments were interpreted to suggest that the effects of location cues and the number of response alternatives affect either different processes within the response selection stage or affect different process stages. It was concluded that the latter alternative explains most of the data currently available and that the stimulus identification stage is the most likely candidate for the locus of the location effect.