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molecular species within a single experiment [1, 2]. Although it has somewhat
lower spatial resolution than microscopy, IMS enables the detection of a wide range
of biological species at increased molecular coverage with high spatial resolution
and sensitivity using advanced data processing techniques. Herein, we present upto- date examples of the current technologies of MALDI IMS.
7.2 Spatial Resolution Improvements in IMS
The spatial resolution of an IMS experiment determines the level of structural detail
and differentiation among regions of a sample in the resulting ion images. Most
commercial IMS instruments are limited to a spatial resolution (and sampling diameter) of about 10 μm as determined by the incident spot size of a focused laser beam
on a sample. Laser focusing approaches to achieve smaller ablation diameter and
stage pitch reduction are important instrumental considerations for high spatial resolution IMS. Recent advances in IMS instrumentation have allowed for spatial resolution at or below 1 μm [3]. As such, molecular information using IMS can be
acquired that allows comparison with common staining techniques.
A tight laser focus for high spatial resolution IMS is achieved using objective
lenses placed above a sample surface. However, high power objectives can interfere
with transmission of ions to the mass analyzer (Fig. 7.1, frontside geometry). An
ablation diameter below 5 μm is possible with special modifications of the laser
Fig. 7.1 MALDI ion sources available on commercial instruments (frontside geometry) allow for
a laser ablation diameter down to 10 μm. A smaller ablation diameter can be achieved with objective lenses closer to the sample. The transmission geometry optical path allows for use of high
numerical aperture lenses close to the sample such that the laser can travel through a transparent
substrate and can be focused on the sample to achieve an ablation diameter of about 1 μm. (Adapted
with permission from McMillen et al. [10])
J. C. McMillen et al.
molecular species within a single experiment [1, 2]. Although it has somewhat
lower spatial resolution than microscopy, IMS enables the detection of a wide range
of biological species at increased molecular coverage with high spatial resolution
and sensitivity using advanced data processing techniques. Herein, we present upto- date examples of the current technologies of MALDI IMS.
7.2 Spatial Resolution Improvements in IMS
The spatial resolution of an IMS experiment determines the level of structural detail
and differentiation among regions of a sample in the resulting ion images. Most
commercial IMS instruments are limited to a spatial resolution (and sampling diameter) of about 10 μm as determined by the incident spot size of a focused laser beam
on a sample. Laser focusing approaches to achieve smaller ablation diameter and
stage pitch reduction are important instrumental considerations for high spatial resolution IMS. Recent advances in IMS instrumentation have allowed for spatial resolution at or below 1 μm [3]. As such, molecular information using IMS can be
acquired that allows comparison with common staining techniques.
A tight laser focus for high spatial resolution IMS is achieved using objective
lenses placed above a sample surface. However, high power objectives can interfere
with transmission of ions to the mass analyzer (Fig. 7.1, frontside geometry). An
ablation diameter below 5 μm is possible with special modifications of the laser
Fig. 7.1 MALDI ion sources available on commercial instruments (frontside geometry) allow for
a laser ablation diameter down to 10 μm. A smaller ablation diameter can be achieved with objective lenses closer to the sample. The transmission geometry optical path allows for use of high
numerical aperture lenses close to the sample such that the laser can travel through a transparent
substrate and can be focused on the sample to achieve an ablation diameter of about 1 μm. (Adapted
with permission from McMillen et al. [10])
J. C. McMillen et al.