Cell populations in all biological systems are well-known for their heterogeneous nature. In fact, individual cells of the same line, under same physiological conditions and external stimuli, may show different biomolecule expression. Therefore, differences among cell populations can be difficult to elucidate unless biological systems are studied on a cell-by-cell basis. At present, there is a need for innovative analytical techniques that allow for the determination of elements and biomolecules in individual cells. In this work, LA-ICP-MS and single cell (sc) ICP-MS are presented as complementary strategies for the determination of specific proteins in cell cultures. On the one hand, LA-ICP-MS has demonstrated a huge potential for determining the spatial distribution of metals in individual cells. Although the bioimaging of endogenous cellular proteins still remains a challenge, an immunoassay in fixated cells using immunoprobes conjugated with an elemental label can be employed for proteins detection. On the other hand, sc-ICP-MS has been proposed for high-throughput cell-by-cell quantitative determination of target proteins within cell cultures [1]. Therefore, combining these two techniques it is possible to determine the concentration of sought proteins in single cells as well as to obtain their spatial distribution along the cell structures. In the proposed methodology, well characterized small iridium nanoclusters (IrNCs) providing a high signal amplification were employed as labels for the bioimaging of membrane and cytosolic proteins in individual retinal pigment epithelia cells (ARPE-19 cell line) by LA-ICP-MS (NWR193 laser equipped with a TwoVol2 ablation cell and DCI interface coupled to a 7900 ICP-MS). Protein quantification in individual cells was studied by sc-ICP-MS (microFAST Single Cell system coupled to a 7900 ICP-MS) and the proteins distribution was evaluated by LA-ICP-MS. The novel approach was based on immunoassays (cells fixed on chamber slides for LA-ICP-MS and cell suspensions for sc-ICP-MS) using IrNCs conjugated to specific antibodies for determination of the sought proteins under control and stress conditions (glucose treatment, 100 mM).

This work was financially supported through project PID2019-107838RB-I00 Agencia Estatal de Investigación (AEI)/10.13039/501100011033) and project AYUD/2021/51289 - FICYT. P. Menero- Valdés acknowledges the FPU Grant (Ref. FPU19/00556; Ministry of Education).

Resumen del trabajo presentado en el 15th European Workshop on Laser Ablation (EWLA 2022), celebrado en Berna (Suiza), del 12 al 15 de julio de 2022