Gold-Silver and Gold-Palladium Alloy Nanoparticles as Mass-Probes for Immunosensing

Silver or palladium shelled gold nanoparticles were fused into alloy nanoparticles by pulsed-laser irradiation. The alloy nanoparticles could carry antibodies on their surfaces without affecting their immune functionalities and interact selectively with antigens on a blotting membrane. Silver or palladium ions desorbed from the alloy nanoparticles as reporter ions upon the UV laser irradiation in a mass spectrometer.

Surface optimization of gold nanoparticle mass tags for the sensitive detection of protein biomarkers via immuno-capture LI-MS

HPV-induced cervical cancer is one of the most lethal cancers. Therefore, the development of a reliable and accurate method for the early diagnosis of HPV infections is highly important. Here, gold nanoparticles (AuNPs) were utilized as mass tags in an immuno-capture LI-MS assay for the detection of HPV marker proteins. Through the optimization of the amount of antibodies and surface charges on AuNPs, high antigen detection efficiency with minimal non-specific binding was achieved. With optimized antibody-conjugated AuNPs, low attomole amount of HPV proteins in HeLa cell lysate was quantified.

Imaging mass spectrometry of gold nanoparticles in a tissue section as an immunohistochemical staining mass probe

For analysis of low abundance peptides in a tissue section, immunohistochemical staining through antibody-antigen interaction is a usual technique. The antibody is conjugated with a probe moiety that aids in highly sensitive detection. Gold nanoparticles, which show excellent chemical stability and variation of surface modifications, are expected to act as a sensitive mass probe to desorb gold ions (Au⁺ , Au₂ ⁺ , Au₃ ⁺ ) that are distinguishable from fragment ions from organic molecules. Here, green fluorescent proteins (GFP) in a tissue section of a transgenic zebrafish were detected by the gold mass probe conjugated with antibodies. Due to the efficient ionization and desorption of gold ions, imaging mass spectrometry of Au₂ ⁺ ions indicated the distribution of gold nanoparticles stained in a tissue section, and the mass signal distribution was consistent with the area where the GFP-expressing cells were distributed. Conventional immunofluorescence techniques showed intense autofluorescence that come from intrinsic fluorophores in the tissue section. In contrast, the gold nanoparticles acted as an immunostaining mass probe that displayed significantly lower background signals.