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.
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 (ÎĽTAS) 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.
Presented at the 55th ASMS Conference on Mass Spectrometry, June 4, 2007, Indianapolis, Indiana
Mass Spectrometry on Wikipedia: Open Source and Peer Review, Mass Spectrometry on Wikipedia: Open Source and Peer Review
Goal
Develop a procedure for peer review of Wikipedia articles on mass spectrometry.
Introduction
Wikipedia is an on-line encyclopedia that anyone can edit. The site is maintained by hundreds of users who create, edit and organize articles, oversee quality and consistency, moderate disputes, and guard against abuse. Anyone can contribute as much or as little as he or she desires. On the English language Wikipedia in early 2007, there were 1.4 M articles being edited by more than 150,000 users who were creating about 2000 new articles each day. Of these articles, 70 were in the category “Mass Spectrometry.”
Why is Wikipedia Important?
The public face of mass spectrometry is determined by the information that can be found most easily on the web.
Content Development Models
In April 2007, the top ten hits for “mass spectrometry” on the search engine Google were
Wikipedia
ASMS (What is MS?)
ASMS
Michigan State University
University of Arizona
University of Leeds
University of Illinois, Chicago
Scripps Institute
Ionsource.com
Imass.com
and on Yahoo
Wikipedia
I-mass.com
Basepeak.com
Encyclopaedia Britannica
ASMS
Michigan State University
Wikipedia
GenomicGlossaries.com
Mass Spectrometry Blog
University of New Mexico
Wikipedia is the #1 hit for “Mass Spectrometry” on the top five search pages
Google
Yahoo
Ask.com
MSN Live Search
Altavista
Wikipedia is the way that the public learns about mass spectrometry on the web yet the information is not subject to peer review and it is not developed in conjunction with any mass spectrometry organization.
Content Development Models
Three basic content development models are presented with their advantages and disadvantages. Here, a Wikipedian is someone who understands the workings of Wikipedia and can create and edit content and work with Editors, Bureaucrats and Administrators. A mass spectrometrist is a person who has or is working toward an advanced degree in mass spectrometry or has the equivalent work experience.
Open Model
The Open Model is in effect today. Wikipedians, who may also be mass spectrometrists, openly edit mass spectrometry content on Wikipedia, drawing on mass spectrometry literature and web-based resources.
Wikipedia Open Model
Advantages and Disadvantages
The advantage of the open model is that it is already in place. There are mass spectrometry entries on Wikipedia and anyone can add content within the bounds of the Wikipedia community. Wikipedians with a knowledge of mass spectrometry, chemistry, physics and other areas provide an ad hoc peer review.
The disadvantages are the time required to learn the Wikipedia system to effectively generate content and the fact that the site tends to favor the persistent and tactically adroit over the subject expert. Further, content generated on Wikipedia is not credited to the student or academic and copyright is not retained.
Closed Model
In the closed model, content is generated by mass spectrometrists and in many cases subject to peer review. For example, the ASMS “What is Mass Spectrometry?” web page. Another example is mass spectrometry journals, all of which are on line and some of these are openly available.
Advantages and Disadvantages
The advantage of the closed model is that the content is created by experts and peer reviewed. The disadvantage is that the information is not generally available and is often presented at a level not suited to a general audience. Some excellent works have been generated in recent years, such as the documents created by the ASMS Education Committee, Michael A Grayson’s Measuring Mass: From Positive Rays to Proteins, and a wide range of excellent mass spectrometry textbooks. However, only a few of these works are openly available. Consider a high school student writing a report on mass spectrometry. Where will that student obtain the information for that report?
The Protected Fork Model
The material in Wikipedia is not copyrighted and it can therefore be “forked” – all or part of the material can be removed and independently modified as long as the derivative material is also made available with the same unrestricted license. This is the kind of reciprocal license principle that is applied to open source software.
A Wikipedia fork must be available by unrestricted license, but it need not be openly edited: the fork can be protected. Under this model, mass spectrometry content is taken from Wikipedia under the terms of the GNU Free Documentation License. This “Mass Spectrometry Wiki” can only be modified by a set of approved mass spectrometry editors whose work is reviewed by their peers. Non-wikipedian mass spectrometrists can participate without the need to learn the rules and language of generating Wikipedia content. Wikipedian mass spectrometrists can help to synchronize (or at least harmonize) the content between the two wikis.
Wikipedia protected fork model
Advantages and Disadvantages
The advantage of the Protected Fork Model is that it has the potential to bring in experts on a subject who may not otherwise be inclined to participate directly in Wikipedia. It offers the possibility of peer review within the Wikipedia construct. The disadvantage is the difficulty in synchronizing information (in both directions) and the need for experienced Wikipedians who are also experienced mass spectrometrists.
Conclusions
Wikipedia’s presentation of mass spectrometry has become a significant part of the way the public perceives the field. The mass spectrometry community should be aware of this fact and avenues for participation in Wikipedia should be encouraged and facilitated.
J. Dong, Y. H. Rezenom, and K. K. Murray, “Aerosol Desorption Electrospray Ionization,” Presented at the 55th ASMS Conference on Mass Spectrometry, June 4, 2007, Indianapolis, Indiana, Ambient Ionization I, MP 006.
