Single particle inductively coupled plasma mass spectrometry imaging of immunochemically labeled
                                         spheroid sections

Svojanovský V ^1, Stiborek M ^1, Stráník J ^1, Jindřichová L^1, Krásenský P ^1, Kroupa J ^2, Houška
                 P ^2, Barbora P ^1, Navrátilová J ^1, Kanický V ^1, Preisler J ^1

                                                 ^

1 Faculty of Science, Department of Chemistry, Masaryk University, Kamenice 5, 625 00 Brno, Czech
Republic

2 Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69 Brno,
Czech Republic ​


Spheroids are one of the 3D biological models whose arrangement of proliferating and necrotic cells
resembles the tumor microenvironment. One of the markers of proliferation is Ki-67 protein, which
is expressed by cells in the active phase of the cell cycle. Immunohistochemical labeling with a
primary antibody and a fluorophore-labeled secondary antibody followed by fluorescence microscopy
analysis is commonly used for two- and three-dimensional imaging of the target protein in spheroid
sections.

We have successfully switched from fluorophore labeling of KI-67 to nanoparticle labeling combined
with
LA ICP MS. Recently, gold nanoparticles were used as very sensitive immunochemical tags in
conventional UV laser ablation ICP MSI.^1 In our approach 20-nm gold nanoparticles tags were
desorbed from the spheroid section with 2940 nm laser ablation system. In comparison to UV, IR
laser allows tissue ablation and desorption of intact nanoparticle tags, allowing their precise
counting leading to high sensitivity. Finally, our technique is compared to mainstream imaging
techniques such as confocal fluorescence microscopy or UV LA ICP MS.

Keywords: imaging, nanoparticle, single particle, SP ICP MS, LA ICP MS, laser ablation


1.        Tvrdonova, M., Vlcnovska, M., Vanickova, L.P. et al. Gold nanoparticles as labels for
immunochemical analysis using laser ablation inductively coupled plasma mass spectrometry. Anal
Bioanal Chem 411, 559–564 (2019).




The authors gratefully acknowledge the financial support of the Czech Science Foundation (18-16583S
and 21-12262S), Masaryk University, Brno, Czech Republic (MUNI/A/1325/2021), European Regional
Development Fund - Project ENOCH (CZ.02.1.01/0.0/16_019/0000868), the project National Institute
for Cancer Research (Programme EXCELES, ID Project No. LX22NPO5102) - funded by the European Union
- Next Generation EU, and MEYS CR infrastructure project LM2018127 of CIISB, Instruct-CZ Centre of
Instruct-ERIC EU consortium for the financial support of the measurements at the CF CRYO.