High resolution imaging apparatus and method
The present invention relates to the high resolution imaging of samples using imaging mass spectrometry (IMS) and to the imaging of biological samples by imaging mass cytometry (IMCTM) in which labelling atoms are detected by IMS. LA-ICP-MS (a form of IMS in which the sample is ablated by a laser, the ablated material is then ionised in an inductively coupled plasma before the ions are detected by mass spectrometry) has been used for analysis of various substances, such as mineral analysis of geological samples, analysis of archaeological samples, and imaging of biological substances. However, traditional LA-ICP-MS systems and methods may not provide high resolution. Described herein are methods and systems for high resolution IMS and IMC.
1. A method of analyzing a sample by imaging mass spectrometry, comprising:
radiating the sample in a sample chamber with a first energy source to release material from the sample;
allowing the material to expand past the point of significant charge neutralization once ionized;
ionizing the expanded material with an ionizing laser to:
form a microplasma near the sample surface, and
generate elemental ions; and
analyzing the elemental ions by mass spectrometry.
2. The method of claim 1 , wherein allowing the material to expand comprises allowing the material to expand into a partial vacuum in the sample chamber.
3. The method of claim 2 , wherein the partial vacuum is 10-10,000 Pa.
4. The method of claim 1 , wherein allowing the material to expand comprises allowing the material to expand for 100 ps to 10 ns before ionizing.
5. The method of claim 1 , wherein the ionizing laser is an IR laser or a visible laser.
6. The method of claim 1 , wherein the ionizing laser is a picosecond laser or a femtosecond laser.
7. The method of claim 1 , further comprising directing ions resulting from the microplasma using ion optics positioned near the sample.
8. The method of claim 1 , wherein analyzing is by a time-of-flight mass spectrometer or a magnetic sector mass spectrometer.
9. The method of claim 1 , further comprising analyzing the sample by imaging mass cytometry.
10. The method of claim 1 , wherein the first energy source is a laser.
11. The method of claim 10 , wherein the laser has a wavelength of less than 300 nm.
12. The method of claim 10 , wherein the laser is focused with an objective lens of numerical aperture of at least 0.9.
13. The method of claim 10 , wherein the laser is focused to a spot size of 250 nm or less.
14. The method of claim 10 , wherein the laser is positioned on the opposite side of a sample stage from the sample.
15. The method of claim 1 , wherein the first energy source is an ion beam.
16. The method of claim 1 , wherein the first energy source is an electron beam.
17. The method of claim 1 , further comprising ablating the material from the sample using the first energy source, wherein the first energy source comprises a first laser source and a second laser source.
18. The method of claim 1 , wherein the sample is a biological sample.
19. The method of claim 18 , wherein the biological sample is a tissue sample that has a thickness of 100 nm or below.
20. The method of claim 18 , wherein the biological sample comprises labelling atoms.