Search for: All records

Laser ablation electrospray ionization (LAESI) driven by mid-infrared laser pulses allows the direct analysis of biological tissues with minimal sample preparation. Dedicated remote ablation chambers have been developed to eliminate the need for close proximity between the sample and the mass spectrometer inlet. This also allows for the analysis of large or irregularly shaped objects, and incorporation of additional optics for microscopic imaging. Here we report on the characterization of a newly designed conical inner volume ablation chamber working in transmission geometry, where a reduced zone of stagnation was achieved by tapering the sample platform and the chamber outlet. As a result, the transmission efficiency of both large (>7.5 μm) and smaller particulates (<6.5 μm) has increased significantly. Improved analytical figures of merit, including 300 fmol limit of detection, and three orders of magnitude in dynamic range, were established. Particle residence time, measured by the FWHM of the analyte signal, was reduced from 2.0 s to 0.5 s enabling higher ablation rates and shorter analysis time. A total of six glucosinolates (sinigrin, gluconapin, progoitrin, glucoiberin, glucoraphanin, and glucohirsutin) were detected in plant samples with ion abundances higher by a factor of 2 to 8 for the redesigned ablation chamber. 

Mass spectrometry imaging (MSI) has become an important analytical tool for the label‐free chemical imaging of diverse molecules in biological specimens. This minireview surveys some emerging methods in the context of factors that can lead to inaccurate information in MSI, chemical and spatial aberrations, along with their common sources. Matrix‐assisted laser desorption ionization, based on organic matrices, has become the most widely used MSI technique for biomolecules. However, due to inherent limitations associated with the use of organic matrices, for example, heterogeneous matrix‐analyte cocrystallization, and spectral interferences due to the matrix, laser desorption ionization (LDI) from inorganic and nanophotonic platforms has emerged as an alternative MSI modality with complementary advantages. In this review, inorganic and nanophotonic platforms for LDI‐MSI, their applications in imaging, notable merits, and limitations are described.

 

Mass spectrometry imaging (MSI) enables simultaneous spatial mapping for diverse molecules in biological tissues. Matrix‐assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been a mainstream MSI method for a wide range of biomolecules. However, MALDI‐MSI of biological homopolymers used for energy storage and molecular feedstock is limited by, e.g., preferential ionization for certain molecular classes. Matrix‐free nanophotonic ionization from silicon nanopost arrays (NAPAs) is an emerging laser desorption ionization (LDI) platform with ultra‐trace sensitivity and molecular imaging capabilities. Here, we show complementary analysis and MSI of polyhydroxybutyric acid (PHB), polyglutamic acid (PGA), and polysaccharide oligomers in soybean root nodule sections by NAPA‐LDI and MALDI. For PHB, number and weight average molar mass, polydispersity, and oligomer size distributions across the tissue section and in regions of interest were characterized by NAPA‐LDI‐MSI.

 

Mass spectrometry imaging (MSI) enables simultaneous spatial mapping for diverse molecules in biological tissues. Matrix‐assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been a mainstream MSI method for a wide range of biomolecules. However, MALDI‐MSI of biological homopolymers used for energy storage and molecular feedstock is limited by, e.g., preferential ionization for certain molecular classes. Matrix‐free nanophotonic ionization from silicon nanopost arrays (NAPAs) is an emerging laser desorption ionization (LDI) platform with ultra‐trace sensitivity and molecular imaging capabilities. Here, we show complementary analysis and MSI of polyhydroxybutyric acid (PHB), polyglutamic acid (PGA), and polysaccharide oligomers in soybean root nodule sections by NAPA‐LDI and MALDI. For PHB, number and weight average molar mass, polydispersity, and oligomer size distributions across the tissue section and in regions of interest were characterized by NAPA‐LDI‐MSI.