Involving High School Students in Computational Physics University Research: Theory Calculations of Toluene Adsorbed on Graphene.

To increase public awareness of theoretical materials physics, a small group of high school students is invited to participate actively in a current research projects at Chalmers University of Technology. The Chalmers research group explores methods for filtrating hazardous and otherwise unwanted molecules from drinking water, for example by adsorption in active carbon filters. In this project, the students use graphene as an idealized model for active carbon, and estimate the energy of adsorption of the methylbenzene toluene on graphene with the help of the atomic-scale calculational method density functional theory. In this process the students develop an insight into applied quantum physics, a topic usually not taught at this educational level, and gain some experience with a couple of state-of-the-art calculational tools in materials research.

Uptake of gold nanoparticles in healthy and tumor cells visualized by nonlinear optical microscopy.

Understanding the mechanism underlying the interactions between inorganic nanostructures and biological systems is crucial for several rapidly growing fields that rely on nano-bio interactions. In particular, the further development of cell-targeted drug delivery using metallic nanoparticles (NP) requires new tools for understanding the mechanisms triggered by the contact of NPs with membranes in different cells at the subcellular level. Here we present a novel concept of multimodal microscopy, enabling three-dimensional imaging of the distribution of gold NPs in living, unlabeled cells. Our approach combines multiphoton induced luminescence (MIL) with coherent anti-Stokes Raman scattering (CARS) microscopy. Comparison with transmission electron microscopy (TEM) reveals in vivo sensitivity down to the single nanostructure. By monitoring the incorporation of NPs in human healthy epidermal keratinocytes and squamous carcinoma cells (SCC), we address the feasibility of noninvasive delivery of NPs for therapeutic purposes. While neutralizing PEG coating was confirmed to prevent NP integration in SCCs, an unexpectedly efficient integration of NPs into keratinocytes was observed. These results, independently validated using TEM, demonstrate the need for advanced surface modification protocols to obtain tumor selectivity for NP delivery. The CARS/MIL microscopy platform presented here is thus a promising tool for noninvasive study of the interaction between NPs and cell.

Corticosteroid solubility and lipid polarity control release from solid lipid nanoparticles.

Solid lipid nanoparticles (SLN) show promise as a drug delivery system for skin administration. The solid state of the lipid particle enables efficient drug encapsulation and controlled drug release. The present study addresses the influence of lipid composition and drug substance lipid solubility on the in vitro release profile of corticosteroids from SLN for topical administration. Firstly, the effect of lipid composition on the lipid solubility and in vitro release of betamethasone-17-valerate (BMV) was determined by varying the lipid monoglyceride content and the chain length of the fatty acid moiety. Secondly, the effect of drug substance physicochemical properties was determined by studying five different corticosteroid derivatives with different lipophilicity. A high concentration of monoglyceride in SLN increased the amount of BMV released. The corticosteroid release rate depended on the drug substance lipophilicity and it was clear that the release profiles depended on drug partitioning to the aqueous phase as indicated by zero order kinetics. The results emphasize that the corticosteroid solubility in the lipid phase greatly influence drug distribution in the lipid particles and release properties. Thus knowledge of drug substance solubility and lipid polarity contributes to optimize SLN release properties.

High-resolution microspectroscopy of plasmonic nanostructures for miniaturized biosensing.

In this article, we demonstrate how to perform microscale spectroscopy of plasmonic nanostructures in order to minimize the noise when determining the resonance peak wavelength. This is accomplished using an experimental setup containing standard optical components mounted on an ordinary light microscope. We present a detailed comparison between extinction spectroscopy in transmission mode and scattering spectroscopy under dark field illumination, which shows that extinction measurements provide higher signal-to-noise in almost all situations. Furthermore, it is shown that rational selection of nanostructure, hardware components, and data analysis algorithms enables tracking of the particle plasmon resonance wavelength from a 10 microm x 50 microm area with a resolution of 10(-3) nm in transmission mode. We investigate how the temporal resolution, which can be improved down to 17 ms, affects the noise characteristics. In addition, we show how data can be acquired from an area as small as 2 microm x 10 microm (approximately 240 particles) at the expense of higher noise on longer time scales. In comparison with previous work on macroscopic sensor designs, this represents a sensor miniaturization of 5 orders of magnitude, without any loss in signal-to-noise performance. As a model system, we illustrate biomolecular detection using gold nanodisks prepared by colloidal lithography. The microextinction measurements of nanodisks described here provide detection of protein surface coverages as low as 40 pg/cm(2) (<0.1% of saturated binding). In fact, the miniaturized system provides a detection limit in terms of surface coverage comparable to state of the art macroscopic sensors, while simultaneously being as close to single protein molecule detection as sensors based on a single nanoparticle.

Controlling plasmon line shapes through diffractive coupling in linear arrays of cylindrical nanoparticles fabricated by electron beam lithography.

The effect of diffractive coupling on the collective plasmon line shape of linear arrays of Ag nanoparticles fabricated by electron beam lithography has been investigated using Rayleigh scattering spectroscopy. The array spectra exhibit an intricate multi-peak structure, including a narrow mode that gains strength for interparticle distances that are close to the single particle resonance wavelength. A version of the discrete dipole approximation method provides an excellent qualitative description of the observed behavior.

Confined plasmons in nanofabricated single silver particle pairs: experimental observations of strong interparticle interactions.

We report on the optical properties of single isolated silver nanodisks and pairs of disks fabricated by electron beam lithography. By systematically varying the disk size and surface separation and recording elastic scattering spectra in different polarization configurations, we found evidence for extremely strong interparticle interactions. The dipolar surface plasmon resonance for polarization parallel to the dimer axis exhibited a red shift as the interdimer separation was decreased; as expected from previous work, an extremely strong shift was observed. The scattering spectra of single particles and pairs separated by more than one particle radius can be well described by the coupled dipole approximation (CDA), where the particles are approximated as point dipoles using a modified dipole polarizability for oblate spheroids. For smaller particle separations (d < 20 nm), the simple dipole model severely underestimates the particle interaction, indicating the importance of multipolar fields and finite-size effects. The discrete dipole approximation (DDA), which is a finite-element method, describes the experimental results well even at d < 20 nm, including particles that have metallic bridges.

Experimental design as a tool when evaluating stationary phases for the capillary electrochromatographic separation of basic peptides.

Two different capillary electrochromatography (CEC) stationary phases, Hypersil phenyl and Hypersil C(18), have been characterised with respect to their ability to separate the four basic peptides H-Tyr-(D)Ala-Phe-Phe-NH(2) (TAPP), H-Tyr-(D)Ala-Phe-NH(2) (TAP), H-Phe-Phe-NH(2) (PP) and H-Phe-NH(2) (P). Optimal separation conditions were first established separately for the two phases by applying experimental design in a stepwise procedure. The first step comprised a study to acquire basic knowledge about the variables, their influence on the response and their respective experimental domains for each of the two stationary phases. The second step was screening the significant variables and the third step was an optimisation with response surface modelling (RSM) to locate the optimum separation conditions for each stationary phase. The experimental procedure was identical for both stationary phases, but their respective experimental domains were different. The response functions were peak resolution and peak efficiency. This procedure enables specific optimal experimental conditions to be identified for each of the two stationary phases. The optimal conditions identified for the separation on the phenyl stationary phase were to use 50% ACN, 20% 50 mM Tris(hydroxymethyl)aminomethane (TRIS) pH 7.5, 30% H(2)O as BGE, operating at 20 degrees C and 20 kV high voltage. For the C(18) stationary phase optimal separation was achieved using a BGE with 80% ACN, 20% 30 mM TRIS pH 8.5, again operating at 20 degrees C and 20 kV high voltage. Results show that the phenyl stationary phase is better suited for the separation of basic, hydrophilic peptides.