Plasmon-enhanced two-photon excitation fluorescence of rhodamine 6G and an Eu-diketonate complex by a picosecond diode laser

Two-photon excited fluorescence (TPEF) of rhodamine 6G (Rh6G) and tris(dibenzoylmethane) mono(5-aminophenanthroline) europium (Eu-TDPA) was measured using a pulsed diode laser head (<45 mW, 975 nm, 90 ps pulse width, 40 MHz). Fluorophores were cast on a glass slide modified with triangular silver nanoprisms. A photon-counting photomultiplier detected the TPEF of Rh6G on a glass substrate (1361 Hz) and on the nanoprisms (6322 Hz). On the other hand, Eu-TDPA did not exhibit TPEF on a glass substrate. TPEF was only observed when the extinction of the nanoprisms on the substrates was larger than 0.1. The nanoprisms enhanced the TPEF of these two fluorophores up to the detectable level using a low-power laser diode.

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.