Gold nanoparticle-enhanced secondary ion mass spectrometry and its bio-applications

Enhancement of signals in time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies is necessary to many biological applications. We have developed an efficient method of enhancing the signals of secondary ions from peptides using gold nanoparticles (AuNPs) attached to a well-controlled surface such as self-assembled monolayers (SAMs). AuNPs function as both signal enhancers and effective binding sites for peptides, which allow the high signal intensity from the peptides to produce well-contrasted ToF-SIMS images of peptides that are micropatterned on the surface of the AuNPs. For application, this AuNP-enhanced SIMS (NE-SIMS) provided the basis for the spectrum and images to assay protein kinases and their inhibitors. Phosphorylation efficiency and inhibitor effect were quantified by detecting mass change of the peptide substrates by kinase reaction. Maximum efficiency of phosphorylation was achieved from cysteine-tethered peptides with a spacer linker, indicating that accessibility of kinase was dependent on the surface orientation and length of the peptide substrate on the three-dimensional AuNPs. The activities of other enzymes such as phosphatase and protease could also be assayed using NE-SIMS. Our study shows that NE-SIMS can be applied as a useful tool for enzyme assay in biochip surfaces.