Effective absorption coefficient and effective thickness in attenuated total reflection spectroscopy.

Since the introduction of attenuated total reflection (ATR) spectroscopy for the characterization of materials, attempts have been made to relate the measured reflectivity (R) to the absorption coefficient (α) of the absorbing material of interest. The common approach is limited to the low absorption case under the assumption R∼exp(-αde), where de is an effective thickness, which is evaluated for the lossless case. In this Letter, a more detailed derivation leads to R=exp(-ßdp/2), enabling the definition of an ATR-effective absorption coefficient ß and the penetration depth dp of the electric field in the absorbing material. It is found that ß∼4πε2/λ, where ε2 is the imaginary part of the complex dielectric function of the absorbing material, and λ is the wavelength. An alternative formulation is R=exp(-αdef), where def is a generalized effective thickness for arbitrary strength of absorption which reduces to de in the low absorption limit. The experimental data for water, the biopolymer chitosan, and soda-lime glass prove the reliability of the ATR-effective absorption coefficient in the infrared range.

Combined antibacterial/tissue regeneration response in thermal burns promoted by functional chitosan/silver nanocomposites.

We report the combined antibacterial/tissue regeneration responses to thermal burns promoted by functional chitosan/silver nanocomposites (CS/nAg) with ultralow silver content (0.018wt.%, 7-30nm). Our approach allows one to produce CS/nAg nanocomposites without silver nanoparticles (nAg) agglomeration, with bactericide potency higher than 1wt.% of nAg (ca. 10nm) content and, promoting the healing process in controlled thermal burns. CS/nAg films exhibit high antibacterial activity against S. aureus and P. aeruginosa after 1.5h of incubation, demonstrating the bacterial penetration into hydrated films and their interaction with nAg. Additionally, exceptional healing of induced thermal burns was obtained by increasing myofibroblasts, collagen remodeling, and blood vessel neoformation. These factors are associated with epiderma regeneration after 7days of treatment with no nAg release. Our results corroborate the controlled synthesis of nAg embedded in CS matrix with combined antibacterial/biocompatibility properties aiming to produce functional nanocomposites with potential use in wound dressing and health care applications.