Application of luminescent nanodiamonds to intracellular imaging

Imaging at the molecular level has recently become a reality, if specific molecular sites are tagged with "optical labels". In this case scenario, even individual molecules become visible in the cell. These optical labels can be engineered as fluorophores, e.g. fluorescent dyes or quantum dots. Unfortunately, photoinstability and toxicity of these labels limit the scope of optical imaging, especially in the context of tracking individual molecules in the cell.

An alternative optical label is luminescent nanodiamond (LND). It represents a diamond nanocrystal that features a colour centre. The luminescence properties of LND, including its lifetime and near-infrared emission band, ensure the LND high visibility in the cell, even on the background of the cell's own fluorescence, called autofluorescence. The scattering properties of highly refractile larger diamond nanocrystals (> 50 nm) render them visible in the cells. LND is extremely photostable. In virtue of their carbon composition, nanodiamonds are biologically compatible, and also, their surface functional groups are very common in the cellular environment, so that biomolecules can easily "talk" to LNDs.

We have carried out collaborative research into production, characterisation of luminescent nanodiamonds, and LND-assisted intracellular imaging. Some of our preliminary results are shown in Figures 1 and 2.

A PhD candidate will address optical imaging of LNDs on the crowded background of the cell using spectral and temporal filtering approaches.

Figure 1. Schematic diagram of the fluorescence confocal microscope for imaging luminescent nanodiamonds. PMT - photomultiplier tube; DM - dichroic mirror; LP - low-wavelength-pass filter with cutoff wavelength in nanometers.	Figure 2. Image of the 4-nm LND sample. The sample was spun-coated on a cover slip plate and imaged, as shown in Figure 1. The luminescence spectrum centered at 650 nm suggests nitrogen-associated colour centers.

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