Smartbeam 2 uv laser

Experimental details about animals, tissue sectioning, and matrix application can be found in the Supporting Information. The rat sagittal brain slice was prepared and imaged to generate 39 775 pixels. MSI was performed on a solariX 7T MALDI FT-ICR mass spectrometer (Bruker Corp., Billerica, MA) equipped with an atmospheric pressure ionization dual ESI/MALDI source operating at ~2.65 mbar. A mass window of m/z 150–1200 was selected, yielding transients with 0.734 s duration, which resulted in a resolving power of 93 000 at m/z 700. MALDI mass spectra were acquired in positive-mode using a smartbeam-II UV laser (Bruker Corp.) in ‘minimum’ mode with a 50-μm raster width. Each MALDI acquisition consisted of 400 laser shots at a frequency of 1000 Hz. External calibration was performed using PepMix II (Bruker Corp.). The total time for data acquisition was 8 h and the entire imaging experiment took 15 h, with an ~0.85 s measurement overhead per pixel (e.g., time spent on multiple laser shots, ion accumulation, stage movement, and some online processing). The acquired dataset was used as the gold standard to evaluate the subspace approach. We would like to note that these measurement overheads are instrument- and experiment-dependent, and can be further reduced by optimizing various experimental parameters, but are not the focus of this paper.

Single-cell measurements as a comparison to the 21 T FTICR mass spectrometer were performed on a 7 T FTICR mass spectrometer (Bruker Corp., Billerica, MA) equipped with an APOLLO II dual MALDI/ESI source (Bruker). Data was collected at 1 M yielding a transient acquisition time of 0.721 s for m/z range 150–1,600 and 0.979 s for m/z range 200–1,600, respectively. Data was also collected at 2 M for m/z range 200–1,600 yielding a transient acquisition time of 1.478 s. The instrument was operated in positive-mode using a Smartbeam-II UV laser (Bruker) set to ‘Ultra mode’, which yields a 100-μm-diameter laser footprint. Each MALDI acquisition consisted of one accumulation comprising of 400 laser shots each, at a frequency of 1,000 Hz. Single-cell stage coordinates were generated using microMS as previously described ^{14 (link)}.