Laser Ablation Sample Transfer for Localized LC-MS/MS Proteomic Analysis of Tissue

F. Donnarumma, F. Cao, K.K. Murray, Laser Ablation with Vacuum Capture for MALDI Mass Spectrometry of Tissue, J. Am. Soc. Mass Spectrom. 27 (2016) 108–116. doi:10.1007/s13361-015-1249-0.

Abstract: We have developed a laser ablation sampling technique for matrix-assisted laser desorption ionization (MALDI) mass spectrometry and tandem mass spectrometry (MS/MS) analyses of in-situ digested tissue proteins. Infrared laser ablation was used to remove biomolecules from tissue sections for collection by vacuum capture and analysis by MALDI. Ablation and transfer of compounds from tissue removes biomolecules from the tissue and allows further analysis of the collected material to facilitate their identification. Laser ablated material was captured in a vacuum aspirated pipette-tip packed with C18 stationary phase and the captured material was dissolved, eluted, and analyzed by MALDI. Rat brain and lung tissue sections 10 μm thick were processed by in-situ trypsin digestion after lipid and salt removal. The tryptic peptides were ablated with a focused mid-infrared laser, vacuum captured, and eluted with an acetonitrile/water mixture. Eluted components were deposited on a MALDI target and mixed with matrix for mass spectrometry analysis. Initial experiments were conducted with peptide and protein standards for evaluation of transfer efficiency: a transfer efficiency of 16% was obtained using seven different standards. Laser ablation vacuum capture was applied to freshly digested tissue sections and compared with sections processed with conventional MALDI imaging. A greater signal intensity and lower background was observed in comparison with the conventional MALDI analysis. Tandem time-of-flight MALDI mass spectrometry was used for compound identification in the tissue. Graphical Abstract ᅟ.

Laser Ablation Sample Transfer for Localized LC-MS/MS Proteomic Analysis of Tissue. J. Mass Spectrom. 2016, 51, 261
J. Mass Spectrom. 2016, 51, 261–268.
Laser Ablation with Vacuum Capture for MALDI Mass Spectrometry of Tissue

Lab Panoramas

Panorama photos of the Murray Group lab in Choppin Hall at LSU.

Murray lab in 335 Choppin Hall at LSU: mid-infrared optical parametric oscillator system (center) and laser ablation particle sizing system (right).
Murray lab in 335 Choppin Hall at LSU: mid-infrared optical parametric oscillator system (center) and laser ablation particle sizing system (right).

Murray lab in 333 Choppin Hall at LSU: quadrupole time-of-flight mass spectrometer (left), mid-infrared laser ablation (center), and future home of the near-field atomic force microscope laser ablation system (right).
Murray lab in 333 Choppin Hall at LSU: quadrupole time-of-flight mass spectrometer (left), mid-infrared laser ablation (center), and future home of the near-field atomic force microscope laser ablation system (right).

Laser desorption sample transfer for gas chromatography/mass spectrometry

C.A. Seneviratne, S. Ghorai, K.K. Murray, “Laser desorption sample transfer for gas chromatography/mass spectrometry,” Rapid Commun. Mass Spectrom. 30 (2016) 89–94. doi:10.1002/rcm.7419.

Abstract
Rationale: Ambient mass spectrometry can detect small molecules directly, but complex mixtures can be a challenge. We have developed a method that incorporates small molecule separation based on laser desorption with capture on a solid‐phase microextraction (SPME) fiber for injection into a gas chromatography/mass spectrometry (GC/MS) system.
Methods: Samples on a metal target were desorbed by a 3 µm mid‐infrared laser focused to a 250 µm spot and 1.2 mJ pulse energy. The desorbed material was aspirated into a metal tube suspended 1 mm above the laser spot and captured on a SPME fiber. The collected material was injected into a GC/MS instrument for analysis.
Results: We have developed a versatile approach for ambient laser desorption sampling onto SPME for GC/MS analysis. The performance of the laser desorption SPME capture GC/MS system was demonstrated for small molecule standards, a mixture of nitroaromatic explosives, and collected cigarette smoke.
Conclusions: The utility of ambient laser desorption sampling onto SPME for GC/MS was demonstrated. The performance of the method was evaluated by preparing calibration standards of caffeine over a range from 200 to 1000 ng. Laser desorption ambient sampling of complex mixtures was accomplished using SPME GC/MS.

Schematic representation of the experimental configuration for laser desorption sample transfer to SPME fiber. The heated transfer line is held 1 mm above the sample surface and the SPME fiber is inserted into a tee in the tube and exposed to the flow.

Laser Ablation with Vacuum Capture for MALDI Mass Spectrometry of Tissue

F. Donnarumma, F. Cao, & K. K. Murray, J. Am. Soc. Mass Spectrom. (2015) DOI: 10.1007/s13361-015-1249-0

Laser Ablation with Vacuum Capture for MALDI Mass Spectrometry of Tissue
Laser Ablation with Vacuum Capture for MALDI Mass Spectrometry of Tissue

We have developed a laser ablation sampling technique for matrix-assisted laser desorption ionization (MALDI) mass spectrometry and tandem mass spectrometry (MS/MS) analyses of in-situ digested tissue proteins. Infrared laser ablation was used to remove biomolecules from tissue sections for collection by vacuum capture and analysis by MALDI. Ablation and transfer of compounds from tissue removes biomolecules from the tissue and allows further analysis of the collected material to facilitate their identification. Laser ablated material was captured in a vacuum aspirated pipette-tip packed with C18 stationary phase and the captured material was dissolved, eluted, and analyzed by MALDI. Rat brain and lung tissue sections 10 μm thick were processed by in-situ trypsin digestion after lipid and salt removal. The tryptic peptides were ablated with a focused mid-infrared laser, vacuum captured, and eluted with an acetonitrile/water mixture. Eluted components were deposited on a MALDI target and mixed with matrix for mass spectrometry analysis. Initial experiments were conducted with peptide and protein standards for evaluation of transfer efficiency: a transfer efficiency of 16% was obtained using seven different standards. Laser ablation vacuum capture was applied to freshly digested tissue sections and compared with sections processed with conventional MALDI imaging. A greater signal intensity and lower background was observed in comparison with the conventional MALDI analysis. Tandem time-of-flight MALDI mass spectrometry was used for compound identification in the tissue.

Laser desorption sample transfer for gas chromatography/mass spectrometry

C. A. Seneviratne, S. Ghorai & K. K. Murray, Rapid Commun. Mass Spectrom. in press
DOI: 10.1002/rcm.7419

Schematic representation of the experimental configuration for laser desorption sample transfer to SPME fiber. The heated transfer line is held 1 mm above the sample surface and the SPME fiber is inserted into a tee in the tube and exposed to the flow.
Schematic representation of the experimental configuration for laser desorption sample transfer to SPME fiber. The heated transfer line is held 1 mm above the sample surface and the SPME fiber is inserted into a tee in the tube and exposed to the flow.

RATIONALE: Ambient mass spectrometry can detect small molecules directly, but complex mixtures can be a challenge. We have developed a method that incorporates small molecule separation based on laser desorption with 80 capture on a solid-phase microextraction (SPME) fiber for injection into a gas chromatography/mass spectrometry 81 (GCMS) system.

METHODS: Samples on a metal target were desorbed by a 3 μm mid-infrared laser focused to a 250 μm spot and 1.2 mJ pulse energy. The desorbed material was aspirated into a metal tube suspended 1 mm above the laser spot and captured 84 on a SPME fiber. The collected material was injected into a GC/MS instrument for analysis.

RESULTS: We have developed a versatile approach for ambient laser desorption sampling onto SPME for GC/MS analysis. The performance of the laser desorption SPME capture GC/MS system was demonstrated for small molecule 87 standards, a mixture of nitroaromatic explosives, and collected cigarette smoke.

CONCLUSIONS: The utility of ambient laser desorption sampling onto SPME for GC/MS was demonstrated. The performance of the method was evaluated by preparing calibration standards of caffeine over a range from 200 to 90 1000 ng. Laser desorption ambient sampling of complex mixtures was accomplished using SPME GC/MS.