Tip enhanced laser assisted sample transfer for biomolecule mass spectrometry
Disclosed are various embodiments for transferring molecules from a surface for mass spectrometry and other sample analysis methods, and the like. A laser is focused onto a tip of an atomic force microscope to remove and capture a quantity of molecules from the surface, so they can be transferred to a mass spectrometer or another instrument for analysis.
1. A method for transferring molecules from a film to a collection device for analysis via an atomic force microscope and a pulsed laser comprising:
positioning a gold-coated silicon tip of the atomic force microscope above the film to image a sample of the molecules, the gold-coated silicon tip having a radius of curvature and being positioned at a first distance from the film;
focusing the pulsed laser onto the gold-coated silicon tip of the atomic force microscope;
ablating the sample from a plurality of ablation spots on the film onto the collection device, the collection device being suspended at a first position relative to the gold-coated silicon tip, wherein a first amount of material from the sample is ablated from each of the ablation spots and transferred onto the collection device.
2. The method of claim 1 , wherein the collection device comprises a metal wire.
3. The method of claim 1 , wherein the molecules comprise at least one of: anthracene or rhodamine 6G, and wherein a metal wire is cut and affixed to a metal target using double-sided conductive tape, and wherein the molecules are analyzed by laser desorption ionization (LDI) using a commercial laser desorption time-of-flight mass spectrometer.
4. The method of claim 1 , wherein the molecules comprise at least one of: angiotensin II or bovine insulin, and wherein the molecules are dissolved in a saturated matrix solution and deposited on a target for matrix-assisted laser desorption ionization (MALDI) analysis.
5. The method of claim 1 , wherein the radius of curvature of the gold-coated silicon tip is about 30 nm and the first distance is about 10 nm.
6. The method of claim 1 , wherein the first position relative to the gold-coated silicon tip is located about 300 μm vertically from the gold-coated silicon tip and about 100 μm horizontally from the gold-coated silicon tip.
7. The method of claim 1 , wherein a polarization of a laser beam of the pulsed laser is adjusted via a half wave plate, the polarization of the laser beam being perpendicular at 355 nm or parallel at 532 nm.
8. The method of claim 7 , wherein the laser beam is focused with a 25 cm calcium fluoride (CaF 2 ) lens to irradiate the gold-coated silicon tip at an angle that is 83° from normal.
9. The method of claim 1 , further comprising engaging the gold-coated silicon tip in a tapping mode with the sample at an amplitude set point of 1 V.
10. The method of claim 1 , wherein the sample is ablated via about 30 laser shots at more than about 3 seconds per ablation spot.
11. The method of claim 1 , wherein the analysis is mass spectrometry.
12. The method of claim 11 , wherein the resonant frequency is about 300 kHz.
13. A system for capturing and transferring molecules from a surface for mass spectrometry comprising:
a pulsed laser configured to:
focus onto a gold-coated silicon tip of an atomic force microscope; and
ablate the molecules from a plurality of ablation spots on the surface; and
a collection device configured to:
capture the molecules ablated from the plurality of ablation spots, the collection device being suspended at a first position relative to the gold-coated silicon tip of the atomic force microscope.
14. The system of claim 13 , wherein the pulsed laser is a 355 nm or a 532 nm pulsed laser.
15. The system of claim 13 , wherein the pulsed laser is focused onto the gold-coated silicon tip at an angle of about 45° in a horizontal plane relative to the surface and at an angle of about 8° in a vertical plane relative to the surface.
16. The system of claim 13 , wherein the collection device comprises a capture wire.
17. The system of claim 16 , wherein the capture wire is a silver capture wire and a tip of the silver capture wire is flattened to produce a ribbon of about 400-500 μm in width.
18. The system of claim 13 , wherein the first position relative to the gold-coated silicon tip is located about 300 μm above the gold-coated silicon tip and about 100 μm horizontally from the gold-plated silicon tip.
19. The system of claim 13 , wherein a focal point of a laser beam of the pulsed laser is about 4 cm beyond the gold-coated silicon tip and a resulting diameter where the laser beam intersects the gold-coated silicon tip is about 600 μm.
20. The system of claim 19 , wherein a distance between the collection device and at least one of the plurality of ablation spots is about 100 μm.