Charge Stabilized Silver Nanoparticles Applied as Antibacterial Agents.

Monodisperse silver nanoparticle sols were synthesized via chemical reduction processes in aqueous environment without using polymeric stabilizing agents or surfactants. The sols obtained using various reducing agents; inorganic cell permeabilizers and organic phenolic compounds; inter alia gallic acid (GA) and tannin (TA) were thoroughly characterized by various physicochemical methods such as TEM, SEM, AFM, DLS and micro-electrophoresis. The antibacterial activity of the sols against two E. coli strains was characterized via the determination of the Minimum Bactericidal Concentration (MBC). All sols exhibited a pronounced bactericidal effect against the standard K12 strain, especially the GA and TA sols showing MBC concentration as low as 1-5 mg L(-1). In the case of the antibiotic resistant strain the highest activity (MBC of 10 mg L(-1)) was observed for the sol synthesized using sodium hypophosphate and sodium tripolyphosphate. Additionally, interactions of silver nanoparticles with bacteria cell were studied using TEM and AFM imaging. It was shown that the silver particles attach to the bacteria surface inducing disintegration, which enables their penetration inside the bacteria. Our measurements confirmed that the surface chemistry of silver nanoparticles can play a decisive role.

Adsorption of tannic acid on polyelectrolyte monolayers determined in situ by streaming potential measurements.

Physicochemical characteristics of tannic acid (tannin) suspensions comprising its stability for a wide range of ionic strength and pH were thoroughly investigated using UV-vis spectrophotometry, dynamic light scattering and microelectrophoretic measurements. These studies allowed to determine the hydrodynamic diameter of the tannic acid that was 1.63 nm for the pH range 3.5-5.5. For pH above 6.0 the hydrodynamic diameter significantly decreased as a result of the tannin hydrolysis. The electrophoretic mobility measurements confirmed that tannic acid is negatively charged for these values of pH and ionic strength 10(-4)-10(-2) M. Therefore, in order to promote adsorption of tannin molecules on negatively charged mica, the poly(allylamine hydrochloride) (PAH) supporting monolayers were first adsorbed under diffusion transport conditions. The coverage of polyelectrolyte monolayers was regulated by changing bulk concentration of PAH and the adsorption time. The electrokinetic characteristics of bare and PAH-covered mica were determined using the streaming potential measurements. The zeta potential of these PAH monolayers was highly positive, equal to 46 mV for ionic strength of 10(-2) M. The kinetics of tannin adsorption on these PAH supporting monolayers was evaluated by the in situ the streaming potential measurements. The zeta potential of PAH monolayers abruptly decreases with the adsorption of tannin molecules that was quantitatively interpreted in terms of the three-dimensional electrokinetic model. The acid-base characteristics of tannin monolayers were acquired via the streaming potential measurements for a broad range of pH. The obtained results indicate that it is possible to control adsorption of tannin on positively charged surfaces in order to designed new multilayer structures of desirable electrokinetic properties and stability.

Prenatal care in northwestern Wisconsin.

The purposes of this study were to identify the components of prenatal care given by family practice physicians and obstetricians in a rural area and determine whether they were in agreement with standards of care advanced by the American College of Obstetricians and Gynecologists (ACOG). We surveyed 76 physicians (family physicians with and without residency training and obstetricians) and identified 40 components of regular prenatal care; they were consistent with 94% of the ACOG recommendations. Few differences were found in prenatal care practices by type of family practice training. Although the number of obstetricians was small, these specialists appeared more likely to agree with ACOG guidelines. Risk assessment instruments were not routinely used by most physicians, and the services of public health nurses were not generally recommended as part of prenatal care. The findings have implications for continuing medical education programs.