Extreme ultraviolet laser ablation mass spectrometer for molecular imaging at the nanoscale
Date
2018
Authors
Kuznetsov, Ilya, author
Menoni, Carmen, advisor
Rocca, Jorge, committee member
Crick, Dean, committee member
Bernstein, Elliot, committee member
Krapf, Diego, committee member
Journal Title
Journal ISSN
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Abstract
The demand for high-precision analytical instrumentation in modern science and technology is exploding. The quality of questions to be answered sets the requirements for a given piece of technology. The type of analytical instrumentation that enables users to unambiguously identify, quantify, and map the chemical structure of a solid is imaging mass spectrometry (IMS). Most common commercially available instruments include desorption electrospray ionization (DESI), matrix-assisted laser desorption and ionization (MALDI), and secondary ion mass spectrometry (SIMS) as well as their derivatives. Each of these methods possesses a set of capabilities that define its use for one or another research task. None of them, however, enables scientists to map a solid's molecular composition in three dimensions at the nanoscale. We have developed an extreme ultraviolet laser ablation time-of-flight mass spectrometer (EUV TOF) that relies on sample probing by a 46.9 nm wavelength laser. In this work, the unique interaction of EUV light with matter was experimentally assessed and compared to SIMS TOF. It was found that the spatial resolution can be as small as 80 nm in molecular and atomic analysis in organic and inorganic materials respectively. Depth resolution is as high as 20 nm as measured on an organic bilayer. Sensitivity of the EUV TOF reaches ~0.02 amol, which is estimated to be 20× better than that of SIMS TOF in the sample of the amino acid alanine. Sensitivity in other units—sample utilization efficiency (SUE)—was found to be similar to SIMS TOF when assessed by means of detecting trace actinides in a glass matrix. It was shown that it can be further improved by means of post-ablation ionization (PI) with a secondary UV laser source. Using vacuum ultraviolet (VUV) laser light can increase the mass range of molecular detection. For instance, an intact cholesterol molecule was first detected by EUV TOF operating in VUV PI mode. This approach opens a range of opportunities to use the technique for biological studies. EUV TOF is capable to image chemical composition. This capability is demonstrated by imaging the 3D nanoscale spatial distribution of low mass fragments in a single mycobacterium. With additional instrumental modifications, it will be possible to achieve sub-cellular imaging of the molecular structure of a single microorganism without the need for using externally applied ionization-promoting matrix. Such capabilities may help to steer the development of new drugs in pharmacology and identify the signature isotope pattern of the miniscule bits of material examined by nuclear scientists.
Description
Rights Access
Subject
extreme ultraviolet laser
mass spectrometry
time of flight
laser ablation
nanoscale molecular imaging
3D imaging