SALDI-MS and SERS Multimodal Imaging: One Nanostructured Substrate to Rule Them Both

Abstract

Imaging techniques based on mass spectrometry or spectroscopy methods inform in situ about the chemical composition of biological tissues or organisms, but they are sometimes limited by their specificity, sensitivity, or spatial resolution. Multimodal imaging addresses these limitations by combining several imaging modalities; however, measuring the same sample with the same preparation using multiple imaging techniques is still uncommon due to the incompatibility between substrates, sample preparation protocols, and data formats. We present a multimodal imaging approach that employs a gold-coated nanostructured silicon substrate to couple surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) and surface-enhanced Raman spectroscopy (SERS). Our approach integrates both imaging modalities by using the same substrate, sample preparation, and data analysis software on the same sample, allowing the coregistration of both images. We transferred molecules from clean fingertips and fingertips covered with plasticine modeling clay onto our nanostructure and analyzed their chemical composition and distribution by SALDI-MS and SERS. Multimodal analysis located the traces of plasticine on fingermarks and provided chemical information on the composition of the clay. Our multimodal approach effectively combines the advantages of mass spectrometry and vibrational spectroscopy with the signal enhancing abilities of our nanostructured substrate.

Use of Nanoparticle Decorated Surface-Enhanced Raman Scattering Active Sol–Gel Substrates for SALDI-MS Analysis

“…Many of these spectral features are attributed to silver adducts of substrate-related compounds given the characteristic silver isotope patterns. Previous work using TiO 2 substrates with immobilized Au NPs for SALDI-MS analysis alone and Au on blackened silicon substrates for SERS and SALDI-MS, also feature low chemical background. Though the chemical background is large for the silver substrates, the magnitude of [heme] + signal is comparable to that of the gold substrate.…”

“…The sequential analysis has been shown for nanostructures such as gold-decorated titania nanotubes, 7 silver colloids, 8 silver dendrites, 9 SiO 2 /TiO 2 (core/shell) NPs, 10 silver NP functionalized glass fiber 11 and Au sputtered black silicon. 12 This type of bimodal analysis resulted in complementary information in the analysis of lipidome-relevant species, small isomeric molecules such as p-, m-, and opyridinecarboxylic acid, and drug-related compounds. 7,8,10 Here, we demonstrate metal nanoparticle decorated SiO 2 sol−gel substrates to have dual SERS and SALDI-MS capabilities, primarily focusing on blood as a model system with potential forensic impact.…”

“…A combination of SERS and SALDI-MS for sequential analysis can increase the chemical coverage that cannot be analyzed by a single tool. The sequential analysis has been shown for nanostructures such as gold-decorated titania nanotubes, silver colloids, silver dendrites, SiO 2 /TiO 2 (core/shell) NPs, as well as silver NP functionalized glass fiber and Au sputtered black silicon . This type of bimodal analysis resulted in complementary information in the analysis of lipidome-relevant species, small isomeric molecules such as p -, m -, and o -pyridinecarboxylic acid, and drug-related compounds. ,, …”

Interpol review of fingermarks and other body impressions (2019 – 2022)

“…Drugs and explosives – Brief overview of the studies aiming at detecting the presence of drugs or explosive traces in fingermarks: imaging of drug- and explosive-contaminated fingermarks using LADI-MSI [ 179 ]; imaging of drug- and clay-contaminated fingermarks using a gold-coated nanostructured silicon substrate compatible with SALDI-MSI and SERS [ 180 , 181 ]; imaging of explosive-contaminated fingermarks using DART-HRMS and MALDI-MSI [ 182 ]; detection of drugs and lead in contaminated fingermarks using Raman spectroscopy [ 183 ] and SALDI-MS [ 184 ]; detection of explosives in contaminated fingermarks using O-PTIR spectromicroscopy [ 185 ]; detection of hypolipidemic drugs in fingermarks spiked post-deposition, using UPLC-Q-TRAP-MS [ 186 ]; detection of caffeine, lead, lead oxide, and titanium dioxide in fingermarks using XPS [ 187 ]; detection of cutting agents in drug-contaminated fingermarks using HPLC-ESI-qToF-MS [ 188 ]; detection of amphetamine in contaminated fingermarks lifted by adhesives and analysed by ToF-SIMS [ 189 ]; detection of metoprolol and its metabolite in contaminated fingermarks using LC-MS/MS [ 190 ].…”

“…Preliminary/Pilot studies – Airflow-assisted DESI-MSI to image sebum-rich and contaminated fingermarks on paper [ 197 ]; LADI-MSI to image sebum-rich or contaminated fingermarks [ 179 ]; MALDI-FT-ICR-MSI to image fingermarks previously covered with blood [ 215 ]; use of carbon-based black powder [ 195 ] or titanium dioxide-based white powder [ 196 ] as matrixes to image sebum-rich or contaminated fingermarks by HRMS-MALDI-MSI; combined use of DART-HRMS and MALDI-MSI to image contaminated fingermarks [ 182 ]; Raman imaging to visualize fingermarks detected by lysozyme-specific aptamer-coated gold nanoparticles [ 216 ]; Sagnac UV FT imaging spectroscopy to image fingermarks spiked with vitamins C and B6 [ 217 ]; use of a gold-coated nanostructured silicon substrate compatible with SALDI-MSI and SERS [ 180 , 181 ]; SECM imaging of fingermarks previously transferred to a nitrocellulose membrane [ 218 , 219 ]; SERS imaging of fingermarks previously detected by SMD II [ 220 ]; ToF-SIMS to flatten fingermarks left on cartridge cases [ 221 ]; ToF-SIMS combined with a neural network to separate overlapped fingermarks [ 222 ]; XPS to image the presence of lead, lead oxide, titanium dioxide, and caffeine in fingermarks [ 187 ].…”