Tandem electrostatic lens as a zoom system to achieve ultra-high magnification in microscope imaging mass spectrometry

A zoom system was developed for a projection-type microscope imaging mass spectrometer to achieve an ultra-high magnification of up to 650. The zooming effect was accomplished by assembling a series of two Einzel lenses. Here, the first lens works as conventional ion microscope optics, providing a typical magnifying power of 20, and the second lens relays the imaginary image formed by the first lens to the detector by delivering over 30 times additional magnifying power without losing the alignment of the optical axis for final image production. In our experiments, gridded dye samples in a 25.4 μm pitch were imaged onto a DLD (delay line detector). The ionized dye of crystal violet was detected in spatially well-resolved grids with a magnifying power of 650.9. In addition, we imaged HeLa cells. Three ionized molecules of m/z 88, m/z 136, and m/z 344 were detected in sub-cellular structures with the magnifying power of 98.3. These magnification levels appeared sufficient to visualize ion distribution patterns within a single spot irradiated using a scanning laser probe in conventional MALDI mass spectrometers. Indeed, ion optical simulation predicted a detection capability of up to 100 nm in size of structure for our zoom system and suggested that this level of spatial resolution would be achievable in experiments, mostly by minimizing the effect of initial energy dispersion with increased acceleration voltages.