The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules

Beams of atoms and molecules are stalwart tools for spectroscopy and studies of collisional processes. The supersonic expansion technique can create cold beams of many species of atoms and molecules. However, the resulting beam is typically moving at a speed of 300-600 m/s in the lab frame, and for a large class of species has insufficient flux (i.e. brightness) for important applications. In contrast, buffer gas beams can be a superior method in many cases, producing cold and relatively slow molecules in the lab frame with high brightness and great versatility. There are basic differences between supersonic and buffer gas cooled beams regarding particular technological advantages and constraints. At present, it is clear that not all of the possible variations on the buffer gas method have been studied. In this review, we will present a survey of the current state of the art in buffer gas beams, and explore some of the possible future directions that these new methods might take

High-Affinity Capture of Proteins by Diamond Nanoparticles for Mass Spectrometric Analysis

Carboxylated/oxidized diamond nanoparticles (nominal size 100 nm) exhibit exceptionally high affinity for proteins through both hydrophilic and hydrophobic forces. The affinity is so high that proteins in dilute solution can be easily captured by diamonds, simply separated by centrifugation, and directly analyzed by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). No preseparation of the adsorbed molecules from diamonds is required for the mass spectrometric analysis. Compared to conventional MALDI-TOF-MS, an enhancement in detection sensitivity by more than 2 orders of magnitude is achieved for dilute solution containing cytochrome c, myoglobin, and albumin because of preconcentration of the probed molecules. The lowest concentration detectable is 100 pM for a 1-mL solution. Aside from the enhanced sensitivity, the overall performance of this technique does not show any sign of deterioration for highly contaminated protein solutions, and furthermore, no significant peak broadening and band shift were observed in the mass spectra. The promise of this new method for clinical proteomics research is demonstrated with an application to human blood serum. Matrix-assisted laser desorption/ionization (MALDI) 1 time-offlight (TOF) mass spectrometry (MS) is a mainstream tool in current high-throughput mass analysis of biopolymers. 2 The MALDI technique, however, suffers from the shortcoming that it lacks sample specificity and its performance deteriorates markedly for samples containing multiple components and excessive amounts of salts or surfactants. 3 Surface-enhanced laser desorption/ ionization (SELDI) is one of the techniques 4-10 developed to circumvent these problems. In this method, 4 micrometer-sized (typically 80-300 µm in diameter) agarose beads made for affinity chromatography columns were used to capture proteins of interest in crude sample solutions. The microbeads were then recovered, washed, placed on the LDI probe tip, and analyzed with regular MALDI-TOF-MS. Unfortunately, direct analysis of the surfacebound proteins is often accompanied with undesired decrease in mass resolution as well as mass accuracy ascribed to the interference from the beads in ion formation and extraction. One solution to this problem is to directly immobilize proteins onto the surface of the LDI probe without use of the microbeads. 7 The approach again suffers from the shortcoming that the number of binding sites is quite limited, ∼1 × 10 13 molecules/cm 2 or ∼160 fmol/mm 2 for a single layer of proteins on the probe surface. The obstacle was later removed by immobilization of the proteins to high molecular weight dextrans precoated covalently on the LDI probe. 8 An approximate 500 times more sample could be loaded, although the dextran immobilization process is rather timeconsuming. We have previously shown 11 that diamond is an exceptional platform for protein adsorption and immobilization. The optical transparency, chemical inertness, and biological compatibility of the material endow diamond nanoparticles with novel and promising biotechnological applications. Preliminary tests with cytochrome c physisorbed to carboxylated/oxidized diamond particles of 5 and 100 nm in size indicate that the specially prepared diamond surfaces exhibit remarkably high affinity for proteins containing amino acid residues with basic side chains. This unique feature along with the fact that diamond is optically transparent up to the UV region motivated us to explore the possibility of using diamond nanoparticles for SELDI-TOF-MS. The advantage of using nanoparticles over microbeads is manyfold. First, nanoparticles have a much larger surface area-to-mass ratio, nearly 3 orders of magnitude higher than that of microbeads; second, the extent to which nanoparticles interfere with the laser desorption/ ionization process is diminished because of the smallness of the particles; third, nanoparticles can be embedded more firmly in the LDI matrix crystals than microbeads, thereby reducing material loss during sample preparation and analysis. There have been several applications of metallic, semiconducting as well as polymeric nanoparticles for mass spectrometric analysis of biopoly

Quantitative Measurements of Cell−Cell Signaling Peptides with Single-Cell MALDI MS

Cell-to-cell signaling peptides play important roles in neurotransmission, neuromodulation, and hormonal signaling. Significant progress has been achieved in qualitative investigations of signaling peptides in the nervous system using single cell matrix-assisted laser desorption/ionization mass spectrometry. However, quantitative information about signaling peptides is difficult to obtain with this approach because only small amounts of analytes are available for analysis. Here we describe several methods for quantitative microanalysis of peptides in individual Aplysia californica neurons and small pieces of tissue. Stable isotope labeling with d0- and d4-succinic anhydride and iTRAQ reagents has been successfully adopted for relative quantitation of nanoliter volume samples containing the Aplysia insulin Cβ peptide. Comparative analysis of the Cβ peptide release site, the upper labial nerve, and its synthesis location, the F- and C-clusters, shows that the release site possesses almost three times more of this compound. The method of standard addition permits absolute quantitation of the physiologically active neuropeptide cerebrin from small structures, including nerves and neuronal clusters, in the femtomole range with a limit of detection of 19 fmol. The simplicity of these methods and the commercial availability of the reagents allow quantitative measurements from a variety of small-volume biological samples

Accurate peak list extraction from proteomic mass spectra for identification and profiling studies

<p>Abstract</p> <p>Background</p> <p>Mass spectrometry is an essential technique in proteomics both to identify the proteins of a biological sample and to compare proteomic profiles of different samples. In both cases, the main phase of the data analysis is the procedure to extract the significant features from a mass spectrum. Its final output is the so-called peak list which contains the mass, the charge and the intensity of every detected biomolecule. The main steps of the peak list extraction procedure are usually preprocessing, peak detection, peak selection, charge determination and monoisotoping operation.</p> <p>Results</p> <p>This paper describes an original algorithm for peak list extraction from low and high resolution mass spectra. It has been developed principally to improve the precision of peak extraction in comparison to other reference algorithms. It contains many innovative features among which a sophisticated method for managing the overlapping isotopic distributions.</p> <p>Conclusions</p> <p>The performances of the basic version of the algorithm and of its optional functionalities have been evaluated in this paper on both SELDI-TOF, MALDI-TOF and ESI-FTICR ECD mass spectra. Executable files of MassSpec, a MATLAB implementation of the peak list extraction procedure for Windows and Linux systems, can be downloaded free of charge for nonprofit institutions from the following web site: <url>http://aimed11.unipv.it/MassSpec</url></p