Gold-nanoparticle-coated magnetic beads for concentration and ionization of analytes for laser desorption/ionization mass spectrometry

Rationale Magnetic particles coated with gold nanoparticles (Au NPs) (Au-MAGs) were developed and used (1) for sample concentration and (2) as a solid matrix for laser adsorption/desorption mass spectrometry (LDI-MS). Methods The Au-MAGs were prepared by (1) coating polystyrene on iron oxide NPs (PS-MNPs), (2) coating poly-l-lysine on the PS-MNPs (PLL-coated PS-MNPs), and (3) coating negatively charged Au NPs on the PLL-coated PS-MNPs (Au-MAGs). Results The Au-MAGs were used to concentrate the target analyte by means of electrostatic interactions between the positively charged GHP9 and the negatively charged Au-MAGs as well as selective interactions (such as gold-sulfur interactions) between glutathione (GSH) and Au-MAGs. Then, the concentrated analyte could be ionized for LDI-MS. Conclusions The Au-MAGs were demonstrated (1) to concentrate the target analyte in a sample solution, tested by electrostatic interactions and selective interactions between gold and sulfur and (2) to ionize the concentrated analyte for LDI-MS.