High-Resolution Two-Photon Fluorescence Microscope Imaging of Nanodiamond Containing Nv Color Centers

Fluorescent nanodiamond containing nitrogen-vacancy (NV) color centers plays an important role in nanoscale sensing for its unique properties, including extraordinary photon stability, bio-compatibility, and chemical inertness at room temperature. Two-photon fluorescence imaging of fluorescent nanodiamonds (FNDs) has been studied with a picosecond pulsed laser operating at 1032 nm. We observed an imaging resolution of 270 nm at nearly a quarter of the excitation wavelength. In this case, the resolution was improved by 2.6-fold, compared with diffraction-limited resolution of the near-infrared (NIR) single-photon confocal microscopic imaging. The fluorescence spectra of visible and near-infrared excitation of FNDs are similar, suggesting that the energy levels involved in the two processes are the same. With the unique advantages of high spatial resolution, high signal-to-noise ratio (SNR), infrared window matching, two-photon excitation microscope image of FNDs is conducive to its more suitable application in biology, physics, and materials sciences