Activated Plasmonic Nanoaggregates for Dark-Field in Situ Imaging for HER2 Protein Imaging on Cell Surfaces

Dark-field microscopy (DFM) based on localized surface plasmon resonance (LSPR) was used for observation of experimental phenomena, which is a hopeful nondamaging and non-photobleaching biological imaging technique. In this strategy, plasma nanoaggregates with stronger scattering efficiency were formed in the presence of the target, causing a "turn-on" phenomenon, when asymmetry modified AuNPs were introduced as probes with zero LSPR background. First, Au₁-N₃ probe and Au₂-C≡C probe were designed for the cycloaddition between azide and alkyne to form AuNP dimers under catalytic action by Cu⁺, which was obtained from the reduction of Cu²⁺ by sodium ascorbate. The two kinds of probes were successfully used for the detection of Cu²⁺ in rat serum. Then, to apply this concept to protein on cells, DNA and antibody were modified on the probes. DNA1/Au₁-N₃ probe and anti-HER2/Au₂-C≡C probe were proposed for HER2 protein DFM on cells. By designing an aptamer sequence in primer, the rolling circle amplification (RCA) was introduced in HER2 DFM on cells, and the image signal was much brighter than that from no-RCA. The unique design made it easier to discriminate the target signal from background noise in cell DFM. This method might be used in the fields of molecular diagnostics and cell imaging.