  Low quantum yields of near infrared (NIR) fluorophores have limited their
capabilities as imaging probes in a transparent, low background imaging window.
Here for the first time we reported near-infrared fluorescence enhance (NIR-FE)
cell imaging using nanostructured Au substrate, which was employed as a general
platform for both single-walled carbon nanotubes (SWNTs) and organic
fluorescent labels in the NIR region. Fluorescence intensity, as well as cell
targeting specificity, was greatly improved by this novel imaging technique.
With NIR-FE imaging, we were able to image SWNT-stained cells at short exposure
time of 300ms, and push the detectable limit of SWNT staining of cells down to
an ultralow concentration of ~50 pM. Further, different degrees of fluorescence
enhancement for endocytosed, intracellular SWNTs vs. nanotubes on the cell
membrane at the cell/gold interface were observed, suggesting the possibility
of using this technique to track the transmembrane behavior of NIR
fluorophores.
