All that glitters is gold: gold nanostars for enhanced fluroescence in the near infra-red window

Abstract

The second near infra-red (NIR-II) window holds great promise for enhanced resolution and imaging contrast in situ fluorescence imaging of biological tissue for preclinical and clinical applications. However, currently available NIR-II dyes display low quantum yields, thus limiting their biomedical applications. To address this issue, this thesis presents the design and synthesis of plasmonic nanomaterials, namely gold nanostars (AuNS) with a solid, polystyrene@gold and silica@gold core-shell composition, and investigates their fluorescence-enhancing capabilities in the NIR-II. Morphological and optical characterisation of the AuNS was done by Transmission electron microscopy (TEM), Selected area electron diffraction (SAED), Dynamic light scattering (DLS) and Ultraviolet-visible-near-infrared absorption spectroscopy (UV–Vis–NIR). Photoluminescence spectroscopy (PL) and Time-correlated single-photon counting (TCSPC) were performed to measure the fluorescence intensity and lifetime respectively and thus determine the extent of fluorescence enhancement achieved by the AuNS. Two commercially availiable dyes - IR-E1050 and ICG - as well as in-house synthesised silver sulfide quantum dots (QDs) were investigated as NIR-II dyes for fluroescence enhancement. It was found that tuning the AuNS to maximise the overlap between their plasmon resonances and the excitation and emission spectra of IR-E1050, ICG and the QDs resulted in far brighter fluorescent probes than that of free dye in solution. The biocompatibility of each AuNS-dye conjugate to two breast cancer cell lines - MCF-7 and MDA-MB-231 - was then investigated using Sulforhodamine B (SRB) assay work, and the cells were imaged using Confocal laser scanning microscopy (CLSM). In summary, this thesis developed super-bright fluorescent probes by conjugating AuNS to NIR-II fluorophores. This may lead to a paradigm shift in cancer diagnosis and surgical imaging, by employing a nanoscale engineered approach to enhance tumour detection sensitivity.