Preparation of SiO2@Ag Composite Nanoparticles and Their Antimicrobial Activity.

At normal atmospheric temperature, the modified sol­gel method was employed to synthesize SiO2 nanospheres (SiO2 NSs) whose average size was about 352 nm. Silver nanoparticles (Ag NPs) were uniformly distributed on the surface of SiO2 nanospheres (SiO2 NSs) by applying chemical reduction method at 95 °C and the size of silver nanoparticles (Ag NPs) could be controlled by simply tuning the reaction time and the concentration of sodium citrate. Besides, the size, morphology, structure and optical absorption properties of SiO2@Ag composite nanoparticles were measured and characterized by laser particle size analyzer (LPSA), transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) and ultraviolet visible absorption spectrometer (UV-Vis), respectively. Furthermore, antimicrobial effect experiments that against gram-negative bacteria (E. coli) and gram-positive bacteria (S. aureus) were carried out to characterize the antibacterial activity of synthesized SiO2@Ag composite nanoparticles. The results show that the prepared SiO2@Ag composite nanoparticles have strong antimicrobial activity, which is associated with the size of silver nanoparticles.

Enhancement and regulation of fluorescence emission from NaYF4:Yb3+, Er3+ nanocrystals by codoping Mn2+ ions.

NaYF4:Yb3+, Er3+, Mn2+ nanocrystals with cubic crystal phase were obtained by a facile solvothermal method through doping a proper amount of Mn2+ ions to the nanocrystals. The results of XRD and TEM showed that the as-prepared samples were well crystallized and their average size was about 25 nm. Under excitations at 978.5 nm and at 532 nm, obvious enhancement and regulation of upconversion and downconversion fluorescence were obtained. Upconversion emission spectra indicate that these effects were independent of doped concentrations of Er3+ and Yb3+, excitation power, and the excitation wavelength in the current study. It is concluded that the enhancement of fluorescence emissions is mainly due to the change of local symmetry around Er3+ ions, while the regulation of red-to-green ratios was caused by efficient energy transfer between Er3+ and Mn2+ ions. This kind of upconversion material has a great potential in bioimaging and drug delivery since the excitation and emission falls into the region of "optical window" of biological tissues.

Fluorescence enhancement of modified silver nanoparticles.

Surface enhanced fluorescence (SEF) effect of acridine orange fluorophore in the proximity of silver nanoparticles (NPs) has been investigated experimentally in the aqueous solution system. It was found that the SEF effect could be influenced by the distribution of the NPs and the separation between the fluorophore molecule and metal surface. The fluorescence enhancement was improved significantly when Ag NPs was capped with 4-Aminothiophenol (PATP) that was acted as an isolating layer between the metal surface and fluorophore molecules. The results suggest that a proper distribution of metallic NPs and proper separation between fluorophore molecule and the particle surface are important for obtaining an optimal SEF effect.

Gold Nanorods as Saturable Absorber for Harmonic Soliton Molecules Generation.

Gold nanorods (GNRs) has been investigated in the field of chemistry, optoelectronics, and medicine for their tenability, compatibility, electromagnetics, and excellent photonics properties. Especially, GNRs, used to generate ultrashort pulse, have been studied recently. However, multiple pulses evolution based on GNRs needs to be further explored. In this article, GNRs are synthesized by seed-mediated growth method, characterized systematically and been chosen as saturable absorber (SA) to apply in ultrafast photonics. The GNRs SA presents a saturable intensity of 266 MW/cm2, modulation depth of 0.6%, and non-saturable loss of 51%. Furthermore, a passively mode-locked erbium-doped fiber laser based on GNRs SA with femtosecond pulse is demonstrated. Thanks to the excellent properties of GNRs, by adjusting the cavity polarization direction with the proposed GNRs SA, soliton molecules operation with spectrum modulation period of 3.3 nm and pulse modulation interval of 2.238 ps is directly obtained. For the most important, 9th-order harmonic soliton molecules have been generated in the laser cavity for the first time. It is demonstrated that GNRs can be a novel type of non-linear optical (NLO) device and have potential applications in the field of ultrafast photonics.

Effects of static magnetic fields on the physical and chemical properties of cell culture medium RPM1 1640.

RPMI 1640 culture medium was chosen to simulate body fluids, and after exposure to 0.085 approximately 0.092 T static magnetic fields (SMF), surface tension, pH, dissolved oxygen, and UV-visible spectrum were measured. Compared with the control group in the normal geomagnetic field, the pH value increased about 0.14 units, dissolved oxygen increased about 14%, and the UV-visible spectra were different in peak intensity but without a shift in the peak. Surface tension showed no significant difference in the two groups. This data suggests that SMF can change some of the physical and chemical properties of RPM1 1640 solution, and may contribute to understanding biological effects of SMF.