Background-Free 3D Nanometric Localization and Sub-nm Asymmetry Detection of Single Plasmonic Nanoparticles by Four-Wave Mixing Interferometry with Optical Vortices

Abstract

Single nanoparticle tracking using optical microscopy is a powerful technique with many applications in biology, chemistry and material sciences. Despite significant advances, localising objects with nanometric position accuracy in a scattering environment remains challenging. Applied methods to achieve contrast are dominantly fluorescence based, with fundamental limits in the emitted photon fluxes arising from the excited-state lifetime as well as photobleaching. Furthermore, every localisation method reported to date requires signal acquisition from multiple spatial points, with consequent speed limitations. Here, we show a new four-wave mixing interferometry technique, whereby the position of a single non-fluorescing gold nanoparticle is determined with better than 20 nm accuracy in plane and 1 nm axially from rapid single-point acquisition measurements by exploiting optical vortices. The technique is also uniquely sensitive to particle asymmetries of only 0.5% aspect ratio, corresponding to a single atomic layer of gold, as well as particle orientation, and the detection is background-free even inside biological cells. This method opens new ways of of unraveling single-particle trafficking within complex 3D architectures. * langbeinww@cardiff.ac.uk † borrip@cardiff.ac.uk arXiv:1707.04888v1 [physics.optics]

Imaging and tracking single plasmonic nanoparticles in 3D background-free with four-wave mixing interferometry

“…with ∂z/∂Φ = 37 nm/rad, as calibrated in our previous work . 11 Notably, we observed a peculiar behavior of z a function of time, as shown in Fig. 5, indicating that the NP 'jumps' over two pockets in the agarose gel, separated by about 80 nm.…”

“…9,10 More recently, we developed a latest generation of the technique comprising a new FWM detection modality that can determine the position of a single AuNP in the 15-30 nm radius range with shot-noise limited precision better than 20 nm in plane and 1 nm axially from scanless single-point background-free acquisition on a 1 ms time scale, by exploiting optical vortices of tightly focused light . 11 The technique is also uniquely sensitive to particle asymmetries down to 0.5% ellipticity, corresponding to a single atomic layer of gold.…”

Heterodyne dual-polarization epi-detected CARS microscopy for chemical and topographic imaging of interfaces

“…The phase difference can be attributed to the sensitivity of the epi-detected signal phase to the axial position of the signal source, similar to what we recently showed by measuring the heterodyne epi-detected resonant four-wave mixing of single gold nanoparticles . 24 The phase slope can be estimated as k signal + 2k Pump − k Stokes for plane wave excitation, resulting in 1.64 • /nm, using the glass refractive index of 1.518, and the wavelengths 665 nm, 820 nm, 1069 nm for signal, Pump, and Stokes beam, respectively. The phase slope measured in the experiment by moving the sample was found to be (1.4 ± 0.2) • /nm, somewhat smaller than the above estimate as expected due to the Gouy phase shift in the focus.…”

Imaging and Tracking Single Plasmonic Nanoparticles in 3D Background-Free with Four-Wave Mixing Interferometry

“…High-resolution DIC microscopy was available in the same instrument. Furthermore, the set-up enables simultaneous interferometric detection of the reflected probe field (for details see [12]). Figure 2(a) shows the DIC image of a group of HeLa cells on which reflection and FWM imaging was performed in the region highlighted by the dashed frame.…”

“…This was evident when measuring gold NPs immobilised onto a glass surface. We were able to model our experimental findings by assuming and ellipsoid nanoparticle in the dipole limit, and in turn calculating the pump-induced change of the particle polarizability probed by E 2 and interferometrically detected through its interference with a mode-matched reference field, as a function of the NP position in the sample focal plane (for more details see [12]). These calculations, and their comparison with experiments on a nominally spherical 30 nm radius NP are shown in Fig.4.…”