Mixed monolayer-protected gold nanoclusters as selective peptide extraction agents for MALDI-MS analysis.

Cationic and anionic nanoparticles selectively target peptides with low and high isoelectric points, respectively. Additionally, their high surface area-to-volume ratios make these nanoparticles (approximately 2-nm core diameter) very efficient extraction and concentration agents. Upon extraction, the peptide-bound nanoparticles can be analyzed by MALDI-MS to provide highly sensitive detection of the targeted peptides. We demonstrate that MALDI-MS can detect peptide concentrations as low as 500 pM from 250-microL solutions using these nanoparticle scaffolds as extraction and concentration agents.