Localized surface plasmon resonance sensing of lipid-membrane-mediated biorecognition events

Supported phospholipid bilayers (SPBs) have emerged as important model systems for studies of the natural cell membrane and its components, which are essential for the integrity and function of cells in all living organisms, and also constitute common targets for therapeutic drugs and in disease diagnosis. However, the preferential occurrence of spontaneous SPB formation on silicon-based substrates, but not on bare noble-metal surfaces, has so far excluded the use of the localized surface plasmon resonance (LSPR) sensing principle for studies of lipid-membrane-mediated biorecognition reactions. This is because the LSPR phenomenon is associated with, and strongly confined to, the interfacial region of nanometric noble-metal particles. This problem has been overcome in this study by a self-assembly process utilizing localized rupture of phospholipid vesicles on silicon dioxide in the bottom of nanometric holes in a thin gold film. The hole-induced localization of the LSPR field to the voids of the holes is demonstrated to provide an extension of the LSPR sensing concept to studies of reactions confined exclusively to SPB-patches supported on SiO2. In particular, we emphasize the possibility of performing label-free studies of lipid-membrane-mediated reaction kinetics, including the compatibility of the assay with array-based reading (approximately 7 x 7 microm2) and detection of signals originating from bound protein in the zeptomole regime.     

Tobacco smoke chemistry 3. Aromatic acids of cigarette smoke condensate

A fraction containing mainly aromatic acids has been isolated from cigarette smoke condensate. Gas chromatographic and mass spectral analysis of the corresponding methyl esters and comparison with reference compounds, many of which were synthesized for this purpose, made possible the identification of 27 constituents (Table 1). Eighteen of these have not been detected in tobacco smoke condensate before.     

Chemical compositional studies of archaeological artifacts: Comparison of LA-ICP-MS to INAA measurements

Summary Multielement analysis of archaeological artifacts for the purpose of correlating chemical composition in an effort to determine provenience has become a well-known and accepted procedure. In this study, inductively coupled plasma-mass spectrometry with laser ablation probe (LA-ICP-MS) for the direct study of solids was used to generate elemental data for comparison with existing instrumental neutron activation analysis (INAA) data. Matrix element Al was used as an internal standard in the ICP work to normalize for variations in sample density and sample mass ablated. While absolute accuracy and precision for the ICP data are inferior to INAA, multivariate statistical analysis of data resulting from the two methods demonstrates a high degree of comparability. Sample cluster assignments differed in only 4.7% (4 out of 86) of the cases. Results show a clear usefulness for LA-ICP-MS in archaeological compositional analysis.     

Sample pretreatment on a microchip with an integrated electrospray emitter

This study presents a microbead-packed PDMS microchip with an integrated electrospray emitter for sample pretreatment prior to sheathless ESI-MS. We prove the concept of analytical functions integrated onto a cm-sized area of a single bulk material. The microchip consists of two PDMS substrates replicated from SU-8 fabricated silicon wafer masters, bonded together after oxidation by corona discharge treatment. The channel within the microchip contains a grid structure that was used to trap 5 microm hypercross-linked polystyrene beads. The beads acted as a medium for sample desalting and enrichment. Electrical contact for the sheathless ESI process was achieved by coating the integrated emitter with conductive graphite powder after applying a thin layer of PDMS as glue. The coating as well as the bond of the PDMS structures showed excellent durability. A continuous spray was obtained from the microchip for over 800 h in a long-term electrospray stability experiment. Desalting and enrichment of neuropeptides from a physiological salt solution was successful by loading the sample onto the packed beads, followed by a washing and an eluting step. The results were obtained and evaluated using a TOF MS. An LOD of approximately 20 fmol (loaded onto the beads) for angiotensin II was obtained from a sample of neuropeptides dissolved in physiological salt solution.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Distribution patterns of Mimbres ceramics using INAA and multivariate statistical methods

The distribution patterns of Classic Mimbres black-on-white bowls and jars were determined by instrumental neutron activation analysis to identify vessel movement between geographically defined regions and between villages within individual regions of southwestern New Mexico. The data set produced and utilized by the various multivariate statistical treatments included multielement neutron activation analysis results for 288 ceramic and clay samples from 15 sites in the Gila, Mimbres and Rio Grande valleys of southwest New Mexico. The results indicate that bowls were more frequently exchanged than jars and distribution frequencies between regions were lower than between villages. Two statistical approaches to the data were compared. In one, cluster analysis of the compositional data was used to form homogeneous groups and the distribution of those groups across sites and regions was examined. In the second, discriminant analysis was used to look for significant differences in composition between regions and sites. The significance of predetermining groups based on collection location as opposed to blind group formation from hierarchical cluster analysis was evaluated in terms of its potential to lead to different interpretations of the data.