Preparation of longitudinal sections of hair samples for the analysis of cocaine by MALDI-MS/MS and TOF-SIMS imaging

Matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) for the analysis of intact hair is a powerful tool for the detection of drugs of abuse in toxicology and forensic applications. Here we present a quick, easy, and reproducible method of preparing longitudinal sections of single hairs. This method improves the accessibility of chemicals embedded in the hair matrix for molecular imaging with mass spectrometry. The images obtained from a single, sectioned hair sample show molecular distributions in the exposed medulla, cortex, and a portion of the cuticle observed as a narrow layer surrounding the cortex. Using MALDI-MS/MS imaging, the distribution of cocaine was observed throughout five longitudinally sectioned drug-user hair samples. The images showed the distribution of the product ion at m/z 182, derived from the precursor ion of cocaine at m/z 304. MetA-SIMS images of longitudinally sectioned hair samples showed a more detailed distribution of cocaine at m/z 304, benzoylecgonine the major metabolite of cocaine at m/z 290 and other drugs such as methadone which was observed at m/z 310. Chronological information of drug intake can be obtained more sensitively. The chronological detail is in hours rather than months, which is of great interest in clinical as well as forensic applications. Copyright © 2015 John Wiley & Sons, Ltd.status: publishe

Core-Shell Plasmonic Nanohelices

We introduce core-shell plasmonic nanohelices, highly tunable structures that have a different response in the visible for circularly polarized light of opposite handedness. The glass core of the helices is fabricated using electron beam induced deposition and the pure gold shell is subsequently sputter coated. Optical measurements allow us to explore the chiral nature of the nanohelices, where differences in the response to circularly polarized light of opposite handedness result in a dissymmetry factor of 0.86, more than twice of what has been previously reported. Both experiments and subsequent numerical simulations demonstrate the extreme tunability of the core-shell structures, where nanometer changes to the geometry can lead to drastic changes of the optical responses. This tunability, combined with the large differential transmission, make core-shell plasmonic nanohelices a powerful nanophotonic tool for, for example, (bio)sensing applications.QN/Kuipers LabQN/Quantum Nanoscienc

Core–Shell Plasmonic Nanohelices

We introduce core–shell plasmonic nanohelices, highly tunable structures that have a different response in the visible for circularly polarized light of opposite handedness. The glass core of the helices is fabricated using electron beam induced deposition and the pure gold shell is subsequently sputter coated. Optical measurements allow us to explore the chiral nature of the nanohelices, where differences in the response to circularly polarized light of opposite handedness result in a dissymmetry factor of 0.86, more than twice of what has been previously reported. Both experiments and subsequent numerical simulations demonstrate the extreme tunability of the core–shell structures, where nanometer changes to the geometry can lead to drastic changes of the optical responses. This tunability, combined with the large differential transmission, make core–shell plasmonic nanohelices a powerful nanophotonic tool for, for example, (bio)­sensing applications

Photon bunching reveals single-electron cathodoluminescence excitation efficiency in InGaN quantum wells

Cathodoluminescence spectroscopy is a key analysis technique in nanophotonics research and technology, yet many aspects of its fundamental excitation mechanisms are not well understood on the single-electron and single-photon level. Here, we determine the cathodoluminescence emission statistics of InGaN quantum wells embedded in GaN under 6-30-keV electron excitation and find that the light emission rate varies strongly from electron to electron. Strong photon bunching is observed for the InGaN quantum well emission at 2.77 eV due to the generation of multiple quantum well excitations by a single primary electron. The bunching effect, measured by the g(2)(t) autocorrelation function, decreases with increasing beam current in the range 3-350 pA. Under pulsed excitation (p=2-100ns; 0.13-6 electrons per pulse), the bunching effect strongly increases. A model based on Monte Carlo simulations is developed that assumes a fraction γ of the primary electrons generates electron-hole pairs that create multiple photons in the quantum wells. At a fixed primary electron energy (10 keV) the model explains all g(2) measurements for different beam currents and pulse durations using a single value for γ=0.5. At lower energies, when electrons cause mostly near-surface excitations, γ is reduced (γ=0.01 at 6 keV), which is explained by the presence of a AlGaN barrier layer that inhibits carrier diffusion to the buried quantum wells. The combination of g(2) measurements in pulsed and continuous mode with spectral analysis provides a powerful tool to study optoelectronic properties and may find application in many other optically active systems and devices.QN/Conesa-Boj La