Surface‐assisted laser desorption ionization mass spectrometry techniques for application in forensics

Abstract

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is an excellent analytical technique for the rapid and sensitive analysis of macromolecules (>700 Da), such as peptides, proteins, nucleic acids, and synthetic polymers. However, the detection of smaller organic molecules with masses below 700 Da using MALDI-MS is challenging due to the appearance of matrix adducts and matrix fragment peaks in the same spectral range. Recently, nanostructured substrates have been developed that facilitate matrix-free laser desorption ionization (LDI), contributing to an emerging analytical paradigm referred to as surface-assisted laser desorption ionization (SALDI) MS. Since SALDI enables the detection of small organic molecules, it is rapidly growing in popularity, including in the field of forensics. At the same time, SALDI also holds significant potential as a high throughput analytical tool in roadside, work place and athlete drug testing. In this review, we discuss recent advances in SALDI techniques such as desorption ionization on porous silicon (DIOS), nano-initiator mass spectrometry (NIMS) and nano assisted laser desorption ionization (NALDI™) and compare their strengths and weaknesses with particular focus on forensic applications. These include the detection of illicit drug molecules and their metabolites in biological matrices and small molecule detection from forensic samples including banknotes and fingerprints. Finally, the review highlights recent advances in mass spectrometry imaging (MSI) using SALDI techniques.

Pyrylium Salts as Reactive Matrices for MALDI-MS Imaging of Biologically Active Primary Amines

“…However, different MALDI matrices have different ionization/desorption characteristics and may not enable adequate ionization of the target analyte. More complex techniques and tools have, therefore, been developed, which include nanostructure initiator mass spectrometry (NIMS) [11,12], ionic matrices [13,14], desorption ionization from porous silicon (DIOS) [15,16], and surface-assisted laser desorption ionization [17][18][19]. Despite some successes, these methods have never been as widely used as conventional MALDI because of technical and practical limitations, some of which are particularly problematic in imaging applications.…”

Laser desorption ionization mass spectrometry: Recent progress in matrix‐free and label‐assisted techniques

“…The AP‐DIOS was superior to AP‐MALDI at MW below 1100; however, at higher MW values AP‐MALDI was shown to produce better data. Clearly, the use of DIOS is strongly dependent on a wide range of properties of the silica surface . A recent study examined different silica surface structures and modifications to determine the requirements of the sample target to produce the optimal signal .…”

Nanomaterials as Assisted Matrix of Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for the Analysis of Small Molecules

“…Matrix-assisted laser desorption/ionization (MALDI), a powerful soft ionization method developed by Tanaka [1] and Karas [2], coupled with time-of-flight mass spectrometry (TOF MS) has become an indispensable analytical tool in complex sample analysis [3,4,5,6,7,8]. Due to its inherent properties including high-throughput, high sensitivity, high tolerance towards salts, fast analysis ability, small sample consumption, simple sample preparation, and no or little fragmentations, over 38,000 related papers have been published in the past three decades.…”