Research group of Kermit Murray at Louisiana State University where we use lasers for sampling and imaging and study the chemistry and physics of laser ablation.
X. Fan, K.K. Murray, “UV laser irradiation of IR laser generated particles ablated from nitrobenzyl alcohol,” Appl. Surf. Sci.255 (2009) 6297–6302. doi:10.1016/j.apsusc.2009.02.005.
Abstract: Particles generated by 2.94 µm pulsed IR laser ablation of liquid 3-nitrobenzyl alcohol were irradiated with a 351 nm UV laser 3.5 mm above and parallel to the sample target. The size and concentration of the ablated particles were measured with a light scattering particle sizer. The application of the UV laser resulted in a reduction in the average particle size by one-half and an increase in the total particle concentration by a factor of nine. The optimum delay between the IR and UV lasers was between 16 and 26 µs and was dependent on the influence of the IR laser: higher influence led to a more rapid appearance of particulate. The ejection velocity of the particle plume, as determined by the delay time corresponding to the maximum two-laser particle concentration signal, was 130 m/s at 1600 J/m^2 IR laser influence and increased to 220 m/s at 2700 J/m^2. The emission of particles extended for several ms. The observations are consistent with a rapid phase change and emission of particulate, followed by an extended emission of particles ablated from the target surface.
Particle size distribution for IR laser ablation and UV post-irradiation of 3- nitrobenzyl alcohol at UV laser delay times of (a) 0, (b) 18, (c) 20, (d) 28, (e) 100, (f) 1000 µs and (g) 15 ms. The IR and UV fluences were 1900 and 2400 J/m2, respectively.
Surface plot of fluence dependence of particle concentration for ablation of glycerol at wavelengths from 2.60 to 3.80 μm.
Particles were generated from glycerol that was irradiated at atmospheric pressure using a mid-infrared optical parametric oscillator at wavelengths between 2.6 and 3.8 μm. The size distribution and quantity of ejected particles with diameters larger than 300 nm were measured using an aerodynamic particle sizer. At a given fluence, the particle concentration roughly tracked the infrared absorption spectrum of liquid glycerol. The threshold fluence for particle formation varied between 1000 and 5000 J/m2throughout the measured wavelength range and the minimum fluence corresponds to the IR absorption maxima of glycerol. The mean particle size roughly tracks the inverse of the IR absorption and smaller particles are observed at the greatest IR absorption. The material ejection mechanism is interpreted as an explosive boiling process in the stress confinement regime.
J.S. Sampson, K.K. Murray, D.C. Muddiman, Intact and Top-Down Characterization of Biomolecules and Direct Analysis Using Infrared Matrix-Assisted Laser Desorption Electrospray Ionization Coupled to FT-ICR Mass Spectrometry, J. Am. Soc. Mass Spectrom.20 (2009) 667–673. doi:10.1016/j.jasms.2008.12.003.
Abstract
We report the implementation of an infrared laser onto our previously reported matrix-assisted laser desorption electrospray ionization (MALDESI) source with ESI post-ionization yielding multiply charged peptides and proteins. Infrared (IR)-MALDESI is demonstrated for atmospheric pressure desorption and ionization of biological molecules ranging in molecular weight from 1.2 to 17 kDa. High resolving power, high mass accuracy single-acquisition Fourier transform ion cyclotron resonance (FT-ICR) mass spectra were generated from liquid- and solid-state peptide and protein samples by desorption with an infrared laser (2.94 µm) followed by ESI post-ionization. Intact and top-down analysis of equine myoglobin (17 kDa) desorbed from the solid state with ESI post-ionization demonstrates the sequencing capabilities using IR-MALDESI coupled to FT-ICR mass spectrometry. Carbohydrates and lipids were detected through direct analysis of milk and egg yolk using both UV- and IR-MALDESI with minimal sample preparation. Three of the four classes of biological macromolecules (proteins, carbohydrates, and lipids) have been ionized and detected using MALDESI with minimal sample preparation. Sequencing of O-linked glycans, cleaved from mucin using reductive β-elimination chemistry, is also demonstrated.
A.J. Dugas, K.K. Murray, On-target digestion of collected bacteria for MALDI mass spectrometry, Anal. Chim. Acta.627 (2008) 154–161. doi:10.1016/j.aca.2008.07.028.
Abstract
Representation of the use of a mini-well to an impacted MALDI target.
An on-target protein digestion system was developed for the identification of microorganisms in collected bioaerosols using off-line matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Bacteria analysis techniques based on MALDI-MS were adapted for use with an orthogonal MALDI quadrupole-time-of-flight mass spectrometer. Bioaerosols were generated using a pneumatic nebulizer and infused into a chamber for sampling. An Andersen N6 single-stage impactor was used to collect the bioaerosols on a MALDI target. On-target digestion was carried out inside temporary mini-wells placed over the impacted samples. The wells served as miniature reactors for proteolysis. Collected test aerosol particles containing the protein cytochrome c and E. coli bacteria were proteolyzed in situ using trypsin or cyanogen bromide. A total of 19 unique proteins were identified for E. coli. Using the TOF-MS spectra of the digested samples, peptide mass mapping was performed using the MASCOT search engine and an iterative search technique.
H. Musyimi, S.A. Soper, K.K. Murray, On-line versus off-line analysis from a microfluidic device, in: S. Le Gac & A. van den Berg (Eds.), Miniaturization and Mass Spectrometry, Royal Society of Chemistry, 2008.
Abstract
Capillary gel microfluidic chip interfaced to laser desorption/ionization (LDI) mass spectrometry with a time-of-flight mass analyzer.
Micro-total analysis systems (μTAS) are novel platforms that address the need for high throughput and automated analysis achieved through miniaturization, integration, and multiplexing of processing and analysis elements. Integration of sample processing steps reduces analysis time, prevents sample loss, contamination and false positives while miniaturization affords the assembly of dedicated modular devices that are portable. Fast and parallel analysis of small samples volumes, using low cost disposable polymeric microfluidic devices have the potential to revolutionize point-of-care testing for clinical and diagnostic screening. The majority of emerging microfluidic devices are capable of integrated and highly multiplexed sample processing. Chemical and biochemical analyses often probe qualitative, structural and quantitative information and many efforts continue to progress towards realizing the full potential of these devices by integration with existing analytical detectors. A long term challenge lies in scaling-down traditional analytical techniques into miniaturized platforms without compromising their utility and system performance.
We have used an infrared laser for desorption of material and ionization by interaction with electrosprayed solvent. Infrared laser-assisted desorption electrospray ionization (IR LADESI) mass spectrometry was used for the direct analysis of water-containing samples under ambient conditions. An ion trap mass spectrometer was modified to include a pulsed Er:YAG laser at 2.94 µm wavelength coupled into a germanium oxide optical fiber for desorption at atmospheric pressure and a nanoelectrospray source for ionization. Analytes in aqueous solution were placed on a stainless steel target and irradiated with the pulsed IR laser. Material desorbed and ablated from the target was ionized by a continuous stream of charged droplets from the electrosprayed solvent. Peptide and protein samples analyzed using this method yield mass spectra similar to those obtained by conventional electrospray. Blood and urine were analyzed without sample pretreatment to demonstrate the capability of IR LADESI for direct analysis of biological fluids. Pharmaceutical products were also directly analyzed. Finally, the role of water as a matrix in the IR LADESI process is discussed.
F. Huang, X. Fan, K.K. Murray, Matrix-assisted laser desorption ionization of infrared laser ablated particles, Int. J. Mass Spectrom.274 (2008) 21–24. doi:10.1016/j.ijms.2008.04.006.
Abstract
Schematic layout of the IR/UV two-laser matrix-assist laser desorption ionization linear time-of flight mass spectrometer. From “Infrared laser ablation for biological mass spectrometry”; Identifier etd-04182012-204238; Fan Huang, Louisiana State University and Agricultural and Mechanical College
An infrared (IR) laser was used to ablate particles that were subsequently ionized by matrix-assisted laser desorption ionization (MALDI). Infrared light from a pulsed optical parametric oscillator (OPO) laser system was directed at a solid sample under vacuum containing a 2,5-dihydroxybenzoic acid (DHB) matrix and peptide or protein analyte. A pulsed 351 nm ultraviolet (UV) excimer laser that was directed 1.4 mm above and parallel to the sample surface was used to irradiate the ablated material in the desorption plume. Ions created by post-ablation ionization were detected with a linear time-of-flight (TOF) mass spectrometer. Mass spectra of the peptide bradykinin and proteins bovine insulin and cytochrome c were recorded. Under these conditions, two simultaneous mass spectra were generated: an IR–MALDI mass spectrum from the OPO and a UV post-ablation spectrum generated by irradiating material in the plume. Factors affecting the two-laser ion yield were studied, including the delay time between the laser pulses and the fluence of the IR and UV laser.
Bradykinin mass spectra with different laser conditions: (a) 2.94µm IR laser only and (b) IR and UV lasers att=50s; no signal was obtained with the 351 nm laser only.
“Two possibilities for ionization of biomolecules in the plume of desorbed and ablated material are the multiphoton ionization of free molecules and the ionization of particles containing matrix and analyte. The observation of biomolecules of the size of insulin and cytochrome c (Fig. 5) argues strongly against a multiphoton ionization mechanism. Molecules of this size are difficult to ionize through the absorption of multiple photons due to the efficient energy dissipation in the large number of vibrational degrees of freedom [10]. Instead, these results suggest that particles containing a UV MALDI matrix and analyte, when irradiated with the UV laser, form ions by a MALDI process. It has been observed that particles containing matrix and analyte, when sprayed into vacuum and irradiated with a UV laser, form ions by MALDI [11,17]. A particle MALDI mechanism has been suggested previously for IR laser ablated particles that were irradiated with a second IR laser. However, in this case, the absorption of the second IR laser energy by the analyte molecule [19] or waters of hydration [20] cannot be ruled out. The observation of ions from proteins by UV irradiation of the ablated material strongly suggests that the ionization mechanism is MALDI of the ablated particles. This hypothesis is supported by results of time-resolved fast-flash photography of the glycerol plume [21] and by measurements of the particle size and number ablated by an IR laser from a MALDI matrix [14],which shows a large number of particles in the IR ablation plume.”
IR/UV post ionization mass spectra of (a) cytochrome c at Δt=70 s and (b) insulin at Δt=60 s.
J. Dong, Y.H. Rezenom, K.K. Murray, Desorption electrospray ionization of aerosol particles, Rapid Commun Mass Spectrom.21 (2007) 3995–4000. doi:10.1002/rcm.3294.
Abstract
Schematic of the dry particle DESI setup. The electrospray emitter (a) was 4 mm away from the ion trap mass spectrometer (c). The angle between a and c was 60°. Nitrogen gas (N2) was used to assist the solvent (S) spray. Aerosol particles generated from a fluidized bed aerosol generator exited the tube (b). The angle between a and b was 90°.
We have applied desorption electrospray ionization to aerosol particles. Ions were formed from aerosols by merging suspended dry particles with an electrospray of solvent in a modified ion trap mass spectrometer. Dry aerosol particles were generated using a fluidized bed powder disperser and directed toward the inlet of the mass spectrometer. A nanospray source was used to create a spray of solvent droplets directed at the inlet and at a right angle with respect to the aerosol. Ions generated by the interaction of the particles and electrospray were transferred into the ion trap mass spectrometer. Using this method, pure samples of caffeine and erythromycin A were analyzed. In addition, commonly available food and drug powders including instant cocoa powder, artificial sweetener and ibuprofen were analyzed.
K.K. Murray, Mass spectrometry and Web 2.0, J. Mass Spectrom. 42 (2007) 1263–1271. doi:10.1002/jms.1315.
Abstract
The term Web 2.0 is a convenient shorthand for a new era in the Internet in which users themselves are both generating and modifying existing web content. Several types of tools can be used. With social bookmarking, users assign a keyword to a web resource and the collection of the keyword ‘tags’ from multiple users form the classification of these resources. Blogs are a form of diary or news report published on the web in reverse chronological order and are a popular form of information sharing. A wiki is a website that can be edited using a web browser and can be used for collaborative creation of information on the site. This article is a tutorial that describes how these new ways of creating, modifying, and sharing information on the Web are being used for on-line mass spectrometry resources.
