Nanoscale and Biomolecular Imaging
Particle Manipulation and Sample Delivery to Lasers
Nondestructive characterization and alignment of aerodynamically focused particle beams using single particle charge detection
We describe the first experimental measurements of aerodynamically focused particle beams using single particle image-charge detection. An aerodynamic lens produces particle beams, which at times is not aligned with the bore of the lens, thus complicating the process of aligning a particle beam with the focus of a laser beam. A key result of this work is the development of a non-optical technique for aiming a beam of particles in vacuum into the focus of a laser beam. In the present application, the laser beam is fixed in space by the geometry of a large stationary vacuum system and it is necessary to blindly aim a narrowly focused particle beam across the laser beam.
Our aiming device is based on the non-destructive detection of electrically charged particles as they pass through a small metal tube that picks up the image charge of the transiting particle. Individual electrosprayed particles larger than 70 nm produce an electrical pulse that can be thresholded and counted. The duration of the detector signal provides a way to measure particle velocity and the amplitude of the signal is proportional to particle charge. The rate of particle injection into vacuum, single particle velocity and charge and particle beam shape and position can be measured with the charge detector. We show data for aiming and focusing electrosprayed polystyrene latex spheres ranging in size from 70 to 190 nm. Particle injection rates as high as 3000 per second and particle beam diameters as small as image were achieved by using the charge detector to optimize the performance of the aerodynamic lens to focus the particles before they entered. We also describe how this detector and injector system will be implemented for real-time particle analysis for aerosol mass spectrometry and single particle X-ray diffractive imaging.
Detection of Mycobacterium tuberculosis in respiratory effluent by single particle aerosol mass spectrometry
Two similar mycobacteria, Mycobacteria tuberculosis H37Ra and Mycobacteria smegmatis are rapidly detected and identified within samples containing a complex background of respiratory effluents using single-particle aerosol mass spectrometry (SPAMS). M. tuberculosis H37Ra (TBa), an avirulent strain, is used as a surrogate for virulent tuberculosis; M. smegmatis (MSm) is utilized as a near-neighbor confounder for TBa. Bovine lung surfactant and human exhaled breath condensate are used as first-order surrogates for infected human lung expirations from patients with pulmonary tuberculosis. This simulated background sputum is mixed with TBa or MSm and nebulized to produce conglomerate aerosol particles, single particles that contain a bacterium embedded within a background respiratory matrix. Mass spectra of single conglomerate particles exhibit ions associated with both respiratory effluents and mycobacteria. Spectral features distinguishing TBa from MSm in pure and conglomerate particles are shown. SPAMS pattern matching alarm algorithms are able to distinguish TBa-containing particles from background matrix and MSm for >50% of the test particles, which is sufficient to enable a high probability of detection and a low false alarm rate if an adequate number of such particles are present. These results indicate the potential usefulness of SPAMS for rapid, reagentless tuberculosis screening.
Aerosol sample preparation methods for X-ray diffractive imaging: Size-selected spherical nanoparticles on silicon nitride foils
We have demonstrated the methodology for reducing the size polydispersity of commercially available polystyrene spheres and dispersing them onto silicon nitride membranes. The solution of spheres is electrosprayed to create an aerosol of individual spheres that are size selected by differential mobility and captured via electrostatic precipitation. We validated the sphere sizes with the Mie scattering ALS. These size standards are used every run at FLASH, form the foundation for theoretical calculations of X-ray material interactions, are the basis of novel exploding optics techniques and are also used to tune the particle injection apparatus. This work is the underlying technology behind recent manuscripts from our group in Nature, Nature Photonics, J. Electron Spectrosc. Related Phenom., J. Aerosol Science & Nano Letters, with more forthcoming.
MALDI-TOF-MS analysis of droplets prepared in an electrodynamic balance: "Wall-less" sample preparation
We have demonstrated mass spectrometric characterization micrometer-sized droplets containing biomaterials that were prepared in an electrodynamic balance. This patented and licensed technology provides low sample consumption and low detection limits for mass spectrometry of proteins by overcoming the limitations of the wetting of capillary walls in ultra-low volume sample preparation. It has motivated novel analytical mass spectrometric methodologies based on arrays of closely spaced micrometer-sized sample spots and direct sampling of levitated droplets.
Other references:Bogan MJ et al, "Single particle coherent diffractive imaging with a soft x-ray FEL: Towards soot aerosol morphology" J Phys B: Atom, Mol, Optics 43, 194013, 2010
McJimpsey, E.; Jackson, W.; Lebrilla, C.; Tobias, H.; Bogan, M.; Gard, E.; Frank, M.; Steele, P. "Parameters contributing to efficient ion generation in aerosol MALDI mass spectrometry" Journal of the American Society for Mass Spectrometry, 2008, 19, 315-324
Bogan, M.; Patton, E.; Srivastava, A.; Martin, S.; Fergenson, D.; Steele, P.; Tobias, H.; Gard, E.; Frank, M.; "Aerosol mass spectrometry of single micrometer-sized particles containing poly(ethylene glycol)" Rapid Communications in Mass Spectrometry, 2007, 21, 1214-1220.
PULSE Research Nanoscale & Biomolecular Imaging • Publications • Scientific Staff