Efficient Auger scattering in Landau-quantized graphene

We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene

Antimicrobial activity of novel mouthrinses against planktonic cells and biofilms of pathogenic microorganisms

Background: Oral diseases pose major public health problems on a global scale. Such diseases have considerable impact on individuals and communities by causing pain and suffering, impairment of function and reduced quality of life. The objective of this study was to evaluate the antimicrobial activity of five mouthrinses against a variety of microorganisms associated with infections of the oral cavity and other body sites. Methods: Mouthrinse formulations were Chlorhexidine (0.2%), Citrox (1%; PerioplusTM/Hyaluronic acid (0.2%)®, Chlorhexidine (0.2%)/Citrox (1%; PerioplusTM), Chlorhexidine (0.2%)/Phenoxetol (0.1%)® and Citrox (1%; Oralclens)TM (Oraldent Ltd; UK). The test microorganisms were the bacteria, Actinomyces viscosus ATCC 1598; Actinomyces odontolyticus NCTC 9935, Clostridium difficile R8651, Prevotella intermedia NCTC 13070T, Prevotella denticola R20771, Porphyromonas gingivalis NCTC 11834T, Streptococcus gordonii ATCC 10558T, Streptococcus sanguinis NCTC 7863, and the fungi, Candida albicans ATCC 90028, Candida dubliniensis CD36, Candida krusei ATCC 6258, Candida glabrata ATCC 2001, Candida tropicalis ATCC 750 and Candida parapsilosis ATCC 22019. Determination of mouthwash antifungal and antibacterial properties was done using a microtitre plate assay. In vitro biofilms were constructed using 96-well plates and exposed to a range of mouthrinse concentrations. The minimum biofilm eradication concentration (MBEC) was established by examining subsequent re-growth of biofilm cells. Results were compared with the minimum inhibitory concentrations (MICs) obtained for planktonic cells cultured in 96-wells plates in various mouthrinse concentrations. Results: Planktonic cells of aerobic microorganisms were inhibited by all mouthrinses at concentrations ≤2% (v/v) of the stock preparation. Chlorhexidine (0.2%)/Citrox (1%)TM had the highest antimicrobial activity, followed by Citrox (1%)TM, 0.2% Chlorhexidine, Chlorhexidine (0.2%)/Phenoxetol (0.1%)® and Citrox (1%)/Hyaluronic acid (0.2%)®. Some anaerobic bacteria (Actinomyces odontolyticus, Clostridium difficile, Prevotella intermedia) exhibited higher MICs for all 5 mouthwashes. There was a noticeable increase (up to 16-fold) in tolerance to the mouthwashes by the majority of aerobic microorganisms when the minimum biofilm eradication concentration was compared to the minimum inhibitory concentration. Conclusion: The results highlight enhanced antimicrobial activity using a combined preparation of Chlorhexidine/Citrox compared with Chlorhexidine alone

Microscopic understanding of ultrafast charge transfer in van-der-Waals heterostructures

Van-der-Waals heterostructures show many intriguing phenomena including ultrafast charge separation following strong excitonic absorption in the visible spectral range. However, despite the enormous potential for future applications in the field of optoelectronics, the underlying microscopic mechanism remains controversial. Here we use time- and angle-resolved photoemission spectroscopy combined with microscopic many-particle theory to reveal the relevant microscopic charge transfer channels in epitaxial WS$_2$/graphene heterostructures. We find that the timescale for efficient ultrafast charge separation in the material is determined by direct tunneling at those points in the Brillouin zone where WS$_2$ and graphene bands cross, while the lifetime of the charge separated transient state is set by defect-assisted tunneling through localized sulphur vacanices. The subtle interplay of intrinsic and defect-related charge transfer channels revealed in the present work can be exploited for the design of highly efficient light harvesting and detecting devices.Comment: 37 pages, 16 figure

Strain-dependent exciton diffusion in transition metal dichalcogenides

Monolayers of transition metal dichalcogenides have a remarkable excitonic landscape with deeply bound bright and dark exciton states. Their properties are strongly affected by lattice distortions that can be created in a controlled way via strain. Here, we perform a joint theory-experiment study investigating exciton diffusion in strained tungsten disulfide (WS2) monolayers. We reveal a non-trivial and non-monotonic influence of strain. Lattice deformations give rise to different energy shifts for bright and dark excitons changing the excitonic landscape, the efficiency of intervalley scattering channels and the weight of single exciton species to the overall exciton diffusion. We predict a minimal diffusion coefficient in unstrained WS2 followed by a steep speed-up by a factor of 3 for tensile biaxial strain at about 0.6% strain - in excellent agreement with our experiments. The obtained microscopic insights on the impact of strain on exciton diffusion are applicable to a broad class of multi-valley 2D materials

In vitro interaction of chronic wound bacteria in biofilms

Objective: To use in vitro biofilm models of wound bacterial isolates and compare the biofilms produced for different combinations of wound bacterial species. Method: In vitro biofilms, generated by Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus oralis and Micrococcus luteus in microtitre plates and a constant depth film fermentor (CDFF), were studied. The tested isolates all originated from chronic venous leg ulcers. Biofilms of individual and dual combinations of these species were generated in microtitre plate wells at 37°C for 24-96 hours and also in the CDFF for 7 days. The extent of biofilm formation from these systems was then measured using crystal violet staining and/or total viable counts. Results: All the chronic wound bacteria formed biofilms (both individually and in mixed culture) in these models. In mixed species microtitre plate biofilms, both P. aeruginosa and S. aureus appeared to antagonise biofilm formation by S. oralis and M. luteus, with P. aeruginosa completely inhibiting the growth of these organisms. Similar effects were evident in the CDFF model, when all four bacterial species were added simultaneously, with M. luteus being 'out-competed' by the other organisms present and occurring at numbers at the limits of detection; however, there was an apparent increase in the numbers of S. oralis compared with its single culture equivalent. Conclusion: The study highlighted differences in biofilm formation ability for the tested species in both closed and open model systems. Using dual species biofilms, distinct species antagonism was observed with apparent antagonism of pathogenic species over 'commensal' ones. Such a finding provides insight into possible bacterial interactions during development of 'non-healing' wound biofilms

Development of an antimicrobial urinary catheter to inhibit urinary catheter encrustation.

Background: Encrustation of urinary catheters is a frequent problem in patients with long-term indwelling catheters colonised with urease-positive bacteria such as Proteus mirabilis. Catheter blockage may follow catheter encrustation, potentially leading to systemic infection. Prevention of encrustation is difficult and avoidance of recurrence often unsuccessful. One possible preventative strategy is to use a catheter with an antimicrobial surface and development and assessment of such a surface was the aim of this research. Methods: Initial experiments assessed the antimicrobial activity of silicone impregnated with plant-derived antimicrobials and triclosan using agar diffusion. The longevity of activity of each antimicrobial silicone was examined over a period of 11 weeks following soaking individual pieces of antimicrobial silicone in an artificial urine solution before using agar diffusion to test remaining antimicrobial activity. Live/Dead staining of bacteria colonising the surface of each antimicrobial silicone was employed to determine the bactericidal properties of each antimicrobial silicone. Selected antimicrobial silicones were subsequently evaluated for their ability to prevent catheter encrustation in an in vitro bladder model. Results: Results showed that antimicrobial activity was obtained using 1% triclosan-impregnated silicone and that this antimicrobial activity was long-lasting (up to 11 weeks). Use of a dip coat silicone formulation, containing 0.2% triclosan, proved effective at delaying catheter encrustation with P. mirabilis metabolites in vitro. In 8 out of 13 independent experiments using dip-coated catheters, no catheter blockage occurred over 7 days, whilst all control catheters blocked during this period. Only on one occasion was delayed encrustation not evident with the treated catheters. Conclusions: In summary, a dip-coat silicone containing triclosan proved effective in preventing in vitro catheter encrustation caused by P. mirabilis infection. Further studies with triclosan silicone dip coat formulation are warranted, including those that investigate potential host cell toxicity and long-term benefits following its application to indwelling urinary catheters in clinical settings

Rapid screening of the antimicrobial efficacy of Ag zeolites

A semi-quantitative screening method was used to compare the killing efficacy of Ag zeolites against bacteria and yeast as a function of the zeolite type, crystal size and concentration. The method, which substantially reduced labor, consumables and waste and provided an excellent preliminary screen, was further validated by quantitative plate count experiments. Two pairs of zeolite X and zeolite beta with different sizes (ca. 200 nm and 2 m for zeolite X and ca. 250 and 500 nm for zeolite beta) were tested against Escherichia coli (E. coli) and Candida albicans (C. albicans) at concentrations in the range 0.05–0.5 mg ml−1. Reduction of the zeolite crystal size resulted in a decrease in the killing efficacy against both microorganisms. The semi-quantitative tests allowed convenient optimization of the zeolite concentrations to achieve targeted killing times. Zeolite beta samples showed higher activity compared to zeolite X despite their lower Ag content, which was attributed to the higher concentration of silver released from zeolite beta samples. Cytotoxicity measurements using peripheral blood mononuclear cells (PBMCs) indicated that Ag zeolite X was more toxic than Ag zeolite beta. However, the trends for the dependence of cytotoxicity on zeolite crystal size at different zeolite concentrations were different for the two zeolites and no general conclusions about zeolite cytotoxicity could be drawn from these experiments. This result indicates a complex relationship, requiring the necessity for individual cytotoxicity measurements for all antimicrobial applications based on the use of zeolites

Relaxation dynamics of carbon nanotubes of enriched chiralities

In our work we combined experimental and theoretical investigations of the relaxation dynamics of the single wall carbon nanotubes (SW-CNTs) in solution samples with enriched chiralities of (7,5) and (7,6) species. In two-color pump-probe studies we observe three-exponential decay in the differential transmission spectra in the range of few picoseconds, tens of picoseconds, and hundreds of picoseconds. Decay curves are very similar for both SW-CNT chiralities under resonant excitation and probing of excited and ground state transition energies, respectively. Both types of tubes exhibit no changes in decay for the different excitation energies in the range ±50meV around the excited state. By tuning the probe pulse towards energies higher then ground state (up to +350meV) we observe acceleration of the first decay component from 5.8ps down to 1.6ps. Our experimental results are supported by time resolved microscopic calculations based on carbon nanotube Bloch equations proving the fast decay component behavior being dominated through scattering with acoustic phonons

The denture microbiome in health and disease: an exploration of a unique community

The United Nations suggests the global population of denture wearers (an artificial device that acts as a replacement for teeth) is likely to rise significantly by the year 2050. Dentures become colonized by microbial biofilms, the composition of which is influenced by complex factors such as patient’s age and health, and the nature of the denture material. Since colonization (and subsequent biofilm formation) by some micro-organisms can significantly impact the health of the denture wearer, the study of denture microbiology has long been of interest to researchers. The specific local and systemic health risks of denture plaque are different from those of dental plaque, particularly with respect to the presence of the opportunist pathogen Candida albicans and various other nonoral opportunists. Here, we reflect on advancements in our understanding of the relationship between micro-organisms, dentures, and the host, and highlight how our growing knowledge of the microbiome, biofilms, and novel antimicrobial technologies may better inform diagnosis, treatment, and prevention of denture-associated infections, thereby enhancing the quality and longevity of denture wearers