Optical Sensitivity Comparison of Multiblock Gold–Silver Nanorods Toward Biomolecule Detection: Quadrupole Surface Plasmonic Detection of Dopamine

In this work, we tested multiblock nanorods (NRs) with Au and Ag segments for the surface plasmonic detection of dopamine (DA). A change in the quadrupole surface plasmon mode was found to be sensitive to the Au/Ag block length and relative block ratio in a single NR. The surfaces of the NRs were decorated with monoclonal antibody (Mab) against DA. By comparing the results for pure Au NRs with those obtained for multiblock Au–Ag–Au NRs, we found that the magnitude of peak-shifting for the multiblock NRs was much larger than that for pure Au NRs. This result was attributed to the higher sensitivity of Ag to a change in the dielectric constant of the surrounding medium when compared to Au and the sensitive surface plasmon coupling at the junction between Au and Ag blocks. The magnitude of peak-shifting was tuned as a function of both the length of the Ag block and the number of repeating units of Au and Ag in the NRs.