Micro-droplet-based calibration for quantitative elemental bioimaging by LA-ICPMS

Andreas Schweikert,Debora Wernitznig,Anna Schoeberl,Sophie Neumayer,Gunda Koellensperger,Martin Schaier,Sarah Theiner,Bernhard K Keppler

doi:10.1007/s00216-021-03357-w

Abstract

In this work, a novel standardization strategy for quantitative elemental bioimaging is evaluated. More specifically, multi-element quantification by laser ablation-inductively coupled plasma-time-of-flight mass spectrometry (LA-ICP-TOFMS) is performed by multi-point calibration using gelatin-based micro-droplet standards and validated using in-house produced reference materials. Fully automated deposition of micro-droplets by micro-spotting ensured precise standard volumes of 400 ± 5 pL resulting in droplet sizes of around 200 μm in diameter. The small dimensions of the micro-droplet standards and the use of a low-dispersion laser ablation setup reduced the analysis time required for calibration by LA-ICPMS significantly. Therefore, as a key advance, high-throughput analysis (pixel acquisition rates of more than 200 Hz) enabled to establish imaging measurement sequences with quality control- and standardization samples comparable to solution-based quantification exercises by ICP-MS. Analytical figures of merit such as limit of detection, precision, and accuracy of the calibration approach were assessed for platinum and for elements with biological key functions from the lower mass range (phosphorus, copper, and zinc). As a proof-of-concept application, the tool-set was employed to investigate the accumulation of metal-based anticancer drugs in multicellular tumor spheroid models at clinically relevant concentrations.Graphical abstract

Highlights

Laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) has become an established technique for bioimaging applications as it is characterized by multielement analysis capabilities, limits of detection at the sub-μg g−1 level, and a high spatial resolution down to the low micrometer level
Gelatin from cold water fish skin was selected as a matrix because it does not solidify at ambient temperature, thereby avoiding blockage of the capillary
A quantification strategy based on gelatin micro-droplets was presented for multi-element analysis in biological samples using LA-ICP-TOFMS

Summary

Introduction

Laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) has become an established technique for bioimaging applications as it is characterized by multielement analysis capabilities, limits of detection at the sub-μg g−1 level, and a high spatial resolution down to the low micrometer level. This work describes a calibration approach based on gelatin micro-droplet standards generated by a micro-droplet spotter for multi-element quantification in bioimaging applications by LA-ICPMS. The concentrations of the investigated elements in the gelatin standards were confirmed using solution-based ICP-MS analysis.

Results

Conclusion