Rotational behaviour of PEGylated gold nanorods in a lipid bilayer system

PEGylated gold nanorods are widely used as nanocarriers in targeted drug delivery and other nanotechnology applications due to the special optical and photo-thermal characteristics of gold nanorods. In this work, we employ coarse-grain molecular simulations to examine the pathway by which PEGylated gold nanorods enter and exit a dipalmitoylphosphatidylcholine lipid bilayer membrane and follow the behaviour of the system to investigate the consequences. We find that PEGylated gold nanorods rotate during permeation, lying down and straightening up as they make their way through the lipid membrane. We find that this rotational behaviour, irrespective of the initial orientation of the nanorod with respect to the membrane normal, is concomitant with the changing interactions of polyethylene glycol (PEG) beads with lipid head beads in both membrane leaflets. For a nanorod with hydrophilic ligands, such as PEG, lying down appears to be driven by favourable hydrophilic interactions with the phosphate and choline groups of the lipid. Mobility of the ligands offers mechanisms for these favourable interactions and for minimising unfavourable interactions with the hydrophobic lipid tails that constitute the inner section of the membrane; the PEG ligands can stretch out to reach the phosphate and choline groups of both leaflets and they can coil in and interact with each other and avoid the alkane lipid tails. Recently developed experimental techniques for imaging, orientation, and rotation of single gold nanorods may be able to observe this predicted rotational behaviour. We find that lipid flip-flop mechanisms do not differ significantly from a spherical gold nanoparticle to a gold nanorod, and PEGylated gold nanorods like their spherical counterparts do not remove lipid molecules from the bilayer membrane. Our results should be of interest to experimentalists who plan to use functionalised gold nanorods in biomedical applications

Measurement of the nue and Total 8B Solar Neutrino Fluxes with the Sudbury Neutrino Observatory Phase I Data Set

This article provides the complete description of results from the Phase I data set of the Sudbury Neutrino Observatory (SNO). The Phase I data set is based on a 0.65 kt-year exposure of heavy water to the solar 8B neutrino flux. Included here are details of the SNO physics and detector model, evaluations of systematic uncertainties, and estimates of backgrounds. Also discussed are SNO's approach to statistical extraction of the signals from the three neutrino reactions (charged current, neutral current, and elastic scattering) and the results of a search for a day-night asymmetry in the ?e flux. Under the assumption that the 8B spectrum is undistorted, the measurements from this phase yield a solar ?e flux of ?(?e) = 1.76+0.05?0.05(stat.)+0.09?0.09 (syst.) x 106 cm?2 s?1, and a non-?e component ?(? mu) = 3.41+0.45?0.45(stat.)+0.48?0.45 (syst.) x 106 cm?2 s?1. The sum of these components provides a total flux in excellent agreement with the predictions of Standard Solar Models. The day-night asymmetry in the ?e flux is found to be Ae = 7.0 +- 4.9 (stat.)+1.3?1.2 percent (sys.), when the asymmetry in the total flux is constrained to be zero

Measurement of CC interactions produced by8B solar neutrinos at SNO

The Sudbury Neutrino Observatory (SNO) is a 1000 tonne heavy water Cherenkov detector placed 2 km underground in Ontario, Canada. Its main purpose is the detection of solar neutrinos, but it is also sensitive to atmospheric and supernova neutrinos. In this paper we report our first measurement of the solar electron-type neutrino flux using the charged current interaction on deuterium, above an electron kinetic energy threshold of 6.75 MeV. This measurement, when compared with an electron scattering measurement from Super Kamiokande, provides the first evidence for non-electron neutrino types from the Sun implying flavor change of solar electron neutrinos. We also present an initial angular distribution of through-going muons, which shows that we can detect neutrino-induced muons from well above the horizontal. This will give us good sensitivity to neutrino oscillations in the atmospheric sector