Lipid bilayers are biomembranes common to cellular life and constitute a continuous barrier between cells and their environment. Understanding the interaction of engineered nanomaterials (ENMs) with lipid bilayers is an important step toward predicting subsequent biological effects. In this study, we assess the effect of varying the surface functionality and concentration of 10 nm-diameter gold (Au) and titanium dioxide (TiO2) ENMs on the disruption of negatively charged lipid bilayer vesicles (liposomes) using a dye leakage assay. Our findings show that Au ENMs having both positive and negative surface charge induce leakage that reaches a steady state after several hours. Positively charged particles with identical surface functionality and different core composition show similar leakage effects and result in faster and greater leakage than negatively charged particles, which suggests that surface functionality, not particle core composition, is a critical factor in determining the interaction between ENMs and lipid bilayers. The results suggest that particles permanently adsorb to bilayers and that only one positively charged particle is required to disrupt a liposome and trigger leakage of its entire contents in contrast to mellitin molecules, the most widely studied membrane lytic peptide, which requires hundred of molecules to generate leakage.

The Raman and surface-enhanced Raman spectra (SERS) of flavone and three of its hydroxy derivatives, 3-hydroxyflavone (3-HF) and 5-hydroxyflavone (5-HF) and quercetin (3,5,7,3 ,4 pentahydroxyflavone) have been obtained. The normal Raman (NR) spectra were taken in the powder form. The SERS spectra were obtained both on Ag colloids and Ag electrode substrates. Assignments of the spectrally observed normal modes were aided by density functional theory (DFT) calculations using the B3LYP functional and the 6-31+G * basis, a split valence polarized basis set with diffuse functions. Excellent fits were obtained for the observed spectra with little or no scaling. The most intense lines of the NR spectra are those in the C O stretching region (near 1600 cm −1 ). These lines are often weakened by proximity to the surface, while other lines at lower wavenumbers, due to in-plane ring stretches, tend to be strongly enhanced. The SERS spectrum of flavone is weak both on the colloid and on the electrode, indicating weak attachment to the surface. In contrast, the SERS spectra of the hydroxy derivatives of flavone are intense, indicating the assistance of OH groups in attachment to the surface. The spectra of the various species are compared, and a case study of application to detection of a textile dye (Persian berries), which contains quercetin, is presented.

We present a method for the tunable production of monodisperse silver nanoparticles. Using monochromatic light of different laser wavelengths to irradiate an initial solution of seed crystals, the size and shape of the products can be controlled. By monitoring the absorption spectrum during growth, it is found that initially the absorption maximum shifts to longer wavelengths and broadens, indicating an increase in particle size and size dispersion. Remarkably, this effect comes to a halt and reverses, displaying a shift to shorter wavelengths and simultaneously narrower bandwidths until, on completion, a final size and relatively narrow distribution are reached. The final size and shape is found to depend on laser wavelength and power. Both discs and triangular prisms as well as pyramidal and pentagonal prisms may be produced. A mechanism based on a wavelength-dependent self-limiting process governed by the surface plasmon resonance controlling the photochemical reduction of particles is suggested.

Successfully using the solution phase, we have prepared, in large quantities, uniform hexagonal silver nanoplates developed from silver triangular nanoprims by employing a photoinduced technique. The growth process was characterized by ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscope (TEM), and high-resolution transmission electron microscope (HRTEM). The UV-vis spectra showed that three bands of hexagonal silver nanoplates appear at 341 (weak), 368 (medium), and 498 (strong) nm. TEM images showed that hexagonal silver nanoplates had an average edge size of 25.9 nm and thickness of 15.7 ( 1.0 nm. The mechanism of the conversion from triangular to hexagonal nanoplates has also been studied. Triangular silver nanoplates were at first fabricated through seed-mediated growth of silver particles in the presence of trisodium citrate. Subsequently, the truncation of triangular nanoplates led to the formation of hexagonal nanoplates.