Saliva-coated titanium biosensor detects specific bacterial adhesion and bactericide caused mass loading upon cell death.

Bacteria adhering to implanted medical devices can cause invasive microbial infections, of e.g. skin, lung or blood. In dentistry, Streptococcus gordonii is an early oral colonizer initiating dental biofilm formation and also being involved in life-threatening infective endocarditis. To treat oral biofilms, antibacterial mouth rinses are commonly used. Such initial biomaterial-bacteria interactions and the influence of antibacterial treatments are poorly understood and investigated here in situ by quartz crystal microbalance with dissipation monitoring (QCM-D). A saliva-coated titanium (Ti) biosensor is applied to analyze possible specific signal patterns indicating microbial binding mechanisms and bactericide-caused changes in bacterial film rigidity or cell leakage caused by a clinically relevant antibacterial agent (ABA), i.e., a mouth rinse comprising chlorhexidine (CHX) and cetylpyridinium chloride (CPC). Apparent missing mass effects during the formation of microscopically proven dense and vital bacterial films indicate punctual, specific binding of S. gordonii to the saliva-coated biosensor, compared to unspecific adhesion to pure Ti. Coincidentally to ABA-induced killing of surface-adhered bacteria, an increase of adsorbed dissipative mass can be sensed, contrary to the prior mass-loss. This suggests the acoustic sensing of the leakage of cellular content caused by bacterial cell wall rupturing and membrane damage upon the bactericidal attack. The results have significant implications for testing bacterial adhesion mechanisms and cellular integrity during interaction with antibacterial agents.

Modeling of light scattering in different regimes of surface roughness.

The light scattering of rough metallic surfaces with roughness levels ranging from a few to several hundred nanometers is modeled and compared to experimental data. Different modeling approaches such as the classical Rayleigh-Rice vector perturbation theory and the new Generalized Harvey-Shack theory are used and critically assessed with respect to ranges of validity, accuracy, and practicability. Based on theoretical calculations and comparisons with Rigorous Coupled Wave Analysis for sinusoidal phase gratings, it is demonstrated that the approximate scatter models yield surprisingly accurate results and at the same time provide insight into light scattering phenomena. For stochastically rough metal surfaces, the predicted angles resolved scattering is compared to experimental results at 325 nm, 532 nm, and 1064 nm. In addition, the possibilities of retrieving roughness information from measured scattering data for different roughness regimes are discussed.

Definition of roughness structures for superhydrophobic and hydrophilic optical coatings on glass.

With specific modeling, measurement, and analysis procedures, it is possible to predict, define, and control roughness structures for tailored wetting properties of optical coatings. Examples are given for superhydrophobic and hydrophilic sol-gel layers on glass substrate.