The development of highly efficient biocompatible photoluminescence nanomaterials or fluorophores in the biologically transparent Near-infrared windows (NIR 650 nm - 2500 nm) for non-invasive tumor cells diagnosing, detecting, and visualization in both in in vitro and in vivo has recently been a hot research topic, due to the simple and real-time testing features of fluorescence imaging technique. Currently, the only FDA approved NIR fluorophores for clinical use is indocyanine green (ICG), which shows certain limitations, such as poor photostability and low emission efficiency. Besides, drawbacks like concentration-dependent aggregation in aqueous solution, lack of targeting specificity may lead to quick clearance of ICG by the liver, which restricts its long-term in vivo imaging performance.
In pursuit of alternative fluorescence bioprobes to replace ICG, this thesis particularly focused on lanthanide-doped downconversion nanoparticles (DCNPs), a type of non-photobleaching nanomaterial emitting in the second biological window (NIR-II, 1000 nm-1700 nm), where the light scattering and autofluorescence from tissues and biological media can be significantly reduced, resulting in negligible interference from the background noise signal. Nevertheless, the development of highly efficient DCNPs is still in its infancy stage due to their quantum efficiency.
In this thesis, by employing Metal-enhanced Fluorescence (MEF) technique, plasmonic enhanced downconversion luminescence from DCNPs was for the first time demonstrated, by coupling a specially designed DCNPs with a 3-dimensional gold/silver hole-cap nanoarrays (Au/Ag HCNA). Furthermore, a satellite nanocomposite consisting of gold nanorods coupled with DCNPs was constructed, demonstrating the enhanced performance of plasmonically coupled DCNPs in solution phase. These findings suggest a promising pathway for overcoming the poor NIR-II luminescence efficiency of DCNPs and hold great potential for widespread applications in bioimaging and biosensing.