Doped Nanocrystals as Plasmonic Probes of Redox Chemistry

The use of nanostructured probes for chemical sensing has opened up the ability to detect ultra-low analyte volumes and achieve nanoscale spatial resolution. Metal nanoparticles exhibiting localized surface plasmon resonances (LSPRs) have been at the forefront of this research1–5 for two reasons: 1) LSPR scattering can be routinely measured from single nanoparticle probes and 2) the frequency of the LSPR band is highly sensitive to the local refractive index (nm) around the nanoparticle as per the resonance condition: εᵣ(ω) = 2nₘ² where εᵣ is the real part of the metal dielectric function as a function of optical frequency ω. Analytes, which induce a change in the local refractive index around the nanoparticle, are detected by shifts in the frequency of the LSPR scattering band. The method, while powerful, is limited: chemical events, which do not involve a large enough change in refractive index, go undetected.