Synthesis of size monodisperse water-soluble metal nanoclusters for protein quantification by elemental mass spectrometry

The use of metal immunoprobes, defined as recognition molecules (e.g. antibodies) labelled with metal tags, constitutes an interesting strategy for the analysis of proteins in biological samples. Detection of such immunoprobes by elemental mass spectrometry (MS) allows not only the qualitative analysis of the proteins but also their absolute quantification [1].

In this context, fluorescent and biocompatible metal nanoclusters (MNCs) have been recently established as an alternative not only to conventional fluorophores but also to commercial elemental tags (e.g MAXPAR) or larger metal nanoparticles for elemental detection. MNCs, composed by hundreds of metal atoms, allow achieving high signal enhancement of low abundant proteins (pM range), meanwhile the small nucleus size (< 3 nm) of MNCs avoids the blocking of the antibody recognition sites. We have achieved the synthesis of thiolated AuNCs, AgNCs and PtNCs and they have been successfully employed as labels for specific proteins determination in biological fluids. Moreover, the combination of MNCs labelled immunoprobes with laser ablation (LA) coupled to elemental MS, allowed the quantitative imaging of proteins along tissue structures [2].

The proteins concentration is given by the average of MNCs measured per acquisition point by elemental MS. Therefore, the deviation associated to the MNCs polydispersity will limit the analytical precision, particularly in those samples were the concentrations of the sought protein is very low, such as in the case of single cell analysis. Thus, in this presentation it will be described our efforts to synthesise size monodisperse MNCs aiming to obtain accurate and precise quantification of specific proteins in single cells.

[1] A. Lores-Padín, P. Menero-Valdés, B. Fernández, R. Pereiro, Anal. Chim. Acta, 1128 (2020) 251-268

[2] A. Lores-Padín, B. Fernández, L. Álvarez, H. González-Iglesias, I. Lengyel, R. Pereiro, Talanta 221 (2021) 121489