Dynamic molecular imaging using nanoparticle plasmon resonance coupling

Distance dependant coupling of plasmon resonances between closely spaced metal nanoparticles offers an attractive alternative for the imaging of molecular interactions. Here we analyzed interactions between molecular specific gold nanoparticles and live cells using a combination of dark-field reflectance and hyperspectral imaging. The results of optical imaging were correlated with transmittance electron microscopy of cell slices and theoretical simulations of optical properties of gold aggregates. We showed that nanoparticles targeted to epidermal growth factor receptor (EGFR) form closely spaced assemblies in the presence of the target molecule. Our experiments with living cells showed that receptor mediated assembly and plasmon coupling of gold bioconjugates result in a spectral shift of more than 100 nm in plasmon resonance frequency of the nanoparticles giving a very bright red signal. We demonstrated that plasmon coupling can be used for imaging of EGFR activation and trafficking as formation of EGFR dimers and further intracellular uptake in early and late endosomes is associated with progressive color changes from green to red, respectively, with each stage of EGFR cycle being associated with a distinct color of EGFR bound nanoparticles. This approach can allow imaging of molecular interactions ranging from protein pairs to multi-protein complexes with sensitivity and SNR that cannot be currently achieved with any other method.