Gold nanoshells improve LDI-MS tissue imaging

Plasmonic nanoshells have been accepted as effective nanomaterials for LDI-MS recognition of many small molecules, although their use in mass spectrometry imaging (MSI) is not well known. A study in the article ACS applied nanomaterials reported the development and optimization of [email protected] nanoshells with custom shell assemblies and structures for highly sensitive LDI-MS analysis and a variety of MSI bases applications.

Study: Plasmonic Gold Nanoshell Assisted Laser Desorption/Ionization Mass Spectrometry for Small Biomolecule Analysis and Tissue Imaging† Image Credit: Carl Dupont/Shutterstock.com

Mass spectrometry imaging

Mass spectrometry imaging (MSI) has become a popular label-free method that allows for the spatial clarity of a wide variety of analytes, including drugs, lipids, peptides, small biomolecules, and proteins present in various complex samples, such as individual cells and biological tissues.

Due to its superior Limit of Detection (LOD), high productivity, high salt tolerance and minimal sample consumption, Matrix Assisted Laser Desorption/Ionization (MALDI) has emerged as one of the essential methods for MSI.

Cons of MALDIA

Despite being widely used, the approach has a number of inherent drawbacks related to organic matrices, including poor spot-to-spot reproducibility, significant background interference ions in low-mass regions, and sometimes reduced ion yield to small molecules.

Due to heterogeneous co-crystallization, it is still difficult to implant a consistent film of organic matrices onto tissue coating, which can lead to reduced tissue imaging resolution.

Recrystallization is essential for addressing the extraction of weak analytes to achieve good ionization yields, and much attention has been paid to minimizing this phenomenon. Therefore, the creation of a matrix-free LDI technique with the combined advantages of improved tissue imaging and recognition sensitivity is particularly desirable with regard to mapping the spatial distribution of small molecules.

Ultraviolet Absorbing Inorganic Nanomaterials

Inorganic nanomaterials that absorb ultraviolet (UV) light, such as those based on silicon, carbon, composite nanomaterials, metal nanoparticles (NPs), metal oxide NPs, and metal-organic frameworks (MOFs), have attracted much attention. These newly developed nanomaterials have advantages such as low thermal conductivity, excellent light absorption, high electrical conductivity and high surface-to-volume ratio.

Although the fine architectures of nanomaterials vary regardless of spraying or sputtering, their nano properties often produce a homogeneous coating surface, making them suitable candidates for MSI testing and tissue imaging.

Metal-based nanoparticles

An effective alternative for monitoring endogenous metabolites present in animal and plant tissues is the use of metal oxide NPs. The high boiling and melting points of these NPs make them resistant to ionization, resulting in a clear mass spectrum with highly limiting background signals.

Plasmonic nanomaterials

To meet the growing demand for fast, targeted and sensitive detection of small biomolecules, composite nanomaterials with synergistic action have attracted much attention. Plasmonic nanomaterials have been extensively investigated for LDIMS and tissue imaging of various metabolites due to the characteristics of hot carriers and localized surface plasmon resonance (LSPR).

However, according to several studies, they have problems such as unavoidable aggregations and insufficient thermal conductivity. An ongoing effort has been made to create plasmonic core-shell nanoparticles for sensitive analysis of metabolites in a variety of biological samples to address these limitations.

Silicon-based nanomaterials

For effective LDI-MS for metabolites present in human biofluid samples, a variety of silica core nanoshells have been presented. To provide distinctive metabolic fingerprints, a number of plasmonic bimetallic/trimetallic alloys have also been produced. Despite considerable efforts, the excellent performance of plasmonic core-shell nanoparticles and high potential for LDI-MS and tissue imaging are not at all optimal in practical implementations.

In this work, a number of [email protected] core-shell NPs with controllable nanoshell frameworks were achieved by a multicyclic reduction reaction of Au3+ ions with the film of SiO2 bulbs. The production procedure is simple, repeatable and minimally reactive.

the SiO2@Au nanoshells show improved performance in the evaluation of numerous small compounds with significantly less background interference, compared to typical organic matrices, thanks to improved photoelectric effects, hot carrier generation and local heating.

Important findings

Three things could explain why these plasmonic gold nanoshells have better tissue imaging properties than current single composite nanomaterials. First, SiO2@Au nanoshells have a significantly high light-to-heat conversion efficiency. Second, the nanoscale roughness provides a certain gap region for specifically trapping cations and small molecules from complex biological mixtures. Finally, the negatively charged layer stimulates the formation of a layer of cations during the ionization procedure. All these factors contribute to a high ion yield.

The nanoscale size and homogeneous stratification of SiO allow lipid species and small molecule metabolites to be spatially observed in strawberry tissue, mouse brain tissue, and the body tissues of honeybees and zebrafish.2@Au nanoshells. These concrete evidences show that the capabilities of plasmon-based nanoscale materials can be enhanced for use in practical MSI applications.

Reference

Du, M., Chen, D. et al† (2022). Plasmonic Gold Nanoshell-Assisted Laser Desorption/Ionization Mass Spectrometry (LDI-MS) for Small Biomolecule Analysis and Tissue Imaging. Available at: https://doi.org/10.1021/acsanm.2c01850

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