Nanostructure Imaging Mass Spectrometry: The Role of Fluorocarbons in Metabolite Analysis and Yoctomole Level Sensitivity

Abstract

Nanostructure Imaging mass spectrometry (NIMS) has become an effective technology for generating ions in the gas phase, providing high sensitivity and imaging capabilities on small molecules, metabolites, drugs, and drug metabolites. Specifically, laser desorption from the nanostructure surfaces results in efficient energy transfer, low background chemical noise, and the nondestructive release of analyte ions into the gas phase. The modification of nanostructured surfaces with fluorous compounds, either covalent or non-covalent, has played an important role in gaining high efficiency/sensitivity by facilitating analyte desorption from the non-adhesive surfaces, and minimizing the amount of laser energy required. In addition, the hydrophobic fluorinated nanostructure surfaces have aided in concentrating deposited samples into fine micrometer sized spots, a feature that further facilitates efficient desorption/ionization. These fluorous nanostructured surfaces have opened up NIMS to very broad applications including enzyme activity assays and imaging, providing low background, efficient energy transfer, nondestructive analyte ion generation, super-hydrophobic surfaces, and ultra-high detection sensitivity.

Application of Black Silicon for Nanostructure-Initiator Mass Spectrometry

“…However, the limit of detection for verapamil on the most sensitive black silicon surface (6.5 min at −80 °C, SF 6 /O 2 30/20 sccm/sccm) was many orders of magnitude higher (attomole level, Figure ). Although this value is much higher than that of the electrochemically etched surfaces (Supporting Information), many applications do not require such high sensitivity and the benefit of preparing surfaces using standard plasma etching equipment that does not require custom equipment and use of HF will outweigh this loss of sensitivity. We also anticipate that the sensitivity of the plasma etched surfaces can be further increased given the large parameter space in the ICP etching process.…”

“…NIMS substrates from HF electrochemical etching approach have been shown to have extreme sensitivity for verapamil with sensitivity in the yactomole range providing an important benchmark for comparison of this new plasma etching process. We were able to obtain the yactomole sensitivity for verapamil on our TOF/TOF mass spectrometer (Supporting Information).…”

“…In matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS), the efficient cocrystallization process of matrix-analyte is necessary in order to desorb/ionize analytes by energy transfer from the matrix to analytes. − The anticipated signals of analyte ions (<500 Da) can be buried by high background noise from abundant matrix molecules. − Matrix-free desorption/ionization is an approach developed to overcome some of the limitations of MALDI, especially for small molecule analysis. , A great diversity of nanostructured surfaces, such as porous silicon, , nanopost/nanowire arrays, − and surfaces with immobilized nanoparticles, − can be used to support small molecule analysis. Nanostructure-initiator mass spectrometry (NIMS) has high sensitivity and low background of direct analysis of a wide range of samples, such as biofluids, tissues, and single cells. − NIMS is based on trapping of a liquid “initiator” within the nanostructured surface, which is thought to desorb/ionize from surface during its vaporization with laser irradiation and subsequent heating of the NIMS surface. , …”

Mapping insoluble indole metabolites in the gastrointestinal environment of a murine colorectal cancer model using desorption/ionisation on porous silicon imaging

“…One NIMS variant, desorption ionisation on porous silicon (DIOS), relies on an electrochemically etched porous silicon (pSi) substrate with a high surface area (up to 800 m 2 /g) and a high UV cross-section 7 . The advantages of DIOS for imaging complex tissue include improved signal intensity 5 , reduced background spectral noise 8,9 , high efficiency desorption of ions and sensitivity down to yoctomole quantities 10 . The key advantage of DIOS, as compared to other drug metabolite discovery methods, is the capacity to detect and map metabolites that are not amenable to other pharmacokinetic approaches 11 .…”

Morphology-Driven Control of Metabolite Selectivity Using Nanostructure-Initiator Mass Spectrometry

“…To overcome the limitations of MALDI, the surface-assisted laser desorption ionization (SALDI) technique that utilizes nanostructured surfaces instead of a conventional matrix to assist analyte laser desorption ionization (LDI) has been developed to expand the detectable mass range of metabolites. ,, A large diversity of nanomaterials, such as porous surfaces, , carbon nanotubes, , nanowires, nanopost arrays (NAPA), ,, and thin films, , have been reported as functional interfaces to promote the analyte desorption/ionization process. As one of the most tested SALDI techniques, NIMS has demonstrated the capability to analyze a broad range of molecules and biological tissues. − This surface-based mass analysis technique relies on its liquid “initiator”-coated nanostructure surface to efficiently absorb and transfer laser energy to analyte ions during initiator vaporization …”