ToF-SIMS 3D imaging unveils important insights on the cellular microenvironment during biomineralization of gold nanostructures

Abstract

The biomolecular imaging of cell-nanoparticle (NP) interactions using time-of-flight secondary ion mass spectrometry (ToF-SIMS) represents an evolving tool in nanotoxicology. In this study we present the three dimensional (3D) distribution of nanomaterials within biomolecular agglomerates using ToF-SIMS imaging. This novel approach was used to model the resistance of human alveolar A549 cells against gold (Au) ion toxicity through intra-and extracellular biomineralization. At low Au concentrations (≤1 mM HAuCl 4) 3D-ToF-SIMS imaging reveals a homogenous intracellular distribution of Au-NPs in combination with polydisperse spherical NPs biomineralized in different layers on the cell surface. However, at higher precursor concentrations (≥2 mM) supplemented with biogenic spherical NPs as seeds, cells start to biosynthesize partially embedded long aspect ratio fiber-like Au nanostructures. Most interestingly, A549 cells seem to be able to sense the enhanced Au concentration. They change the chemical composition of the extracellular NP agglomerates from threonine-O-3-phosphate aureate to an arginine-Au(I)-imine. Furthermore they adopt the extracellular mineralization process from spheres to irregular structures to nanoribbons in a dose-dependent manner with increasing Au concentrations. The results achieved regarding size, shape and chemical specificity were cross checked by SEM-EDX and single particle (sp-)ICP-MS. Our findings demonstrate the potential of ToF-SIMS 3D imaging to better understand cell-NP interactions and their impact in nanotoxicology. Au nano-or microparticles are promising candidates for both bioimaging and therapeutic applications 1. Recently, cell based biomineralization has been explored as a novel technique to synthesize versatile 0, 1, and 2 dimensional gold nanostructures under ambient synthesis conditions. For example, cancer cells are known to synthesize NPs de novo 2 from Au ions. However, little is known about how the surrounding chemical environment influences the extracellular biomineralization at the cell membrane interface and what effect this then has on uptake and biocompatibility. Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) is a versatile and noninvasive technique that allows for both label free imaging and analysis of the surface composition. Conventional scanning electron microscope-energy dispersive X-ray (SEM-EDX) imaging or fluorescence labelling of biological cells not only perturbs the cellular state but also limits the analysis to a specific number of fluorescence labeled targets. On the contrary, ToF-SIMS provides a more versatile method for the visualization of multiple chemicals or intracellular metabolites within individual cells 3. The submicron lateral resolution in combination with a high depth resolution for organic samples (down to 10 nm 3) enables the three dimensional (3D) label-free reconstruction of single cells. This makes ToF-SIMS a top emerging and evolving tool for studies relating to the chemical distribution within single cells 4. Here we app...

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