A Multimodal SIMS/MALDI Mass Spectrometry Imaging Source with Secondary Electron Imaging Capabilities for Use with timsTOF Instruments.

Mass spectrometry imaging (MSI) is a surface analysis technique that produces chemical images and is commonly used for biological and biomedical research. Multimodal imaging combines multiple imaging modes in order to get a more comprehensive view of a sample. Multimodal MSI images are often acquired using multiple MSI instruments, which leads to issues regarding image registration and increases the chance of sample damage or degradation during sample transfer. These problems can be solved by using a single instrument that can image in multiple modes. In order to improve the efficiency of multimodal imaging and investigate complementary modes of MSI, we have modified a prototype Bruker timsTOF fleX by adding secondary ion mass spectrometry (SIMS) and secondary electron (SE) imaging capabilities while preserving the ability to perform matrix-assisted laser desorption/ionization (MALDI). We show multimodal images collected on this instrument that required only trivial registration and were acquired without sample transfer between imaging trials. Furthermore, we characterize the performance of SIMS, SE, and MALDI imaging and compare the performance of the modified instrument to a commercial timsTOF fleX.

MALDI-2 on a Trapped Ion Mobility Quadrupole Time-of-Flight Instrument for Rapid Mass Spectrometry Imaging and Ion Mobility Separation of Complex Lipid Profiles.

Matrix-assisted laser desorption/ionization combined with laser-induced postionization (MALDI-2) is a recently introduced method for enhanced mass spectrometry imaging of numerous classes of biomolecules, including phospho- and glycolipids in tissue sections at high lateral resolution. Here we describe the first adaptation of the technology to a Bruker timsTOF fleX mass spectrometer. Upon use of a 1 kHz postionization laser, MALDI-2 produces a sizable increase in the number of detected features as well as in ion signal intensities. This enhancement is similar to that described previously for low repetition rate MALDI-2 systems, but now enables substantially enhanced measurement speeds. In our proof-of-concept study, we furthermore demonstrate, on examples of rat brain and testis tissue sections, that the combination of MALDI-2 with the trapped ion mobility spectrometry (TIMS) functionality of the instrument can crucially support unravelling the complex molecular composition of the lipidome. Numerous isomeric/isobaric ion species are successfully separated upon using the collisional cross section (CCS) as additional specific physical property. With the possibilities of high data acquisition speed or high separation powers in combination with the increased sensitivity of MALDI-2 available in one instrument, the described methodology could be a valuable tool in many areas of biological and medical research.

Optimizing UV laser focus profiles for improved MALDI performance.

Matrix assisted laser desorption/ionization (MALDI) applications, such as proteomics, genomics, clinical profiling and MALDI imaging, have created a growing demand for faster instrumentation. Since the commonly used nitrogen lasers have throughput and life span limitations, diode-pumped solid-state lasers are an alternative. Unfortunately this type of laser shows clear performance limitations in MALDI in terms of sensitivity, resolution and ease of use, for applications such as thin-layer sample preparations, acceptance of various matrices (e.g. DHB for glycopeptides) and MALDI imaging. While it is obvious that the MALDI process has some dependence on the characteristics of the laser used, it is unclear which features are the most critical in determining laser performance for MALDI. In this paper we show, for the first time, that a spatially structured laser beam profile in lieu of a Gaussian profile is of striking importance. This result enabled us to design diode-pumped Nd : YAG lasers that on various critical applications perform as well for MALDI as the nitrogen lasers and in some respects even better. The modulation of the beam profile appears to be a new parameter for optimizing the MALDI process. In addition, the results trigger new questions directing us to a better understanding of the MALDI process.