Exosomes are small vesicles (typically 30-120 nm), formed through the inward budding of endocytic compartments and secreted through fusion of these vesicle-containing endosomes with the plasma membrane. Increasing evidence suggests that exosomes play an important role in cell-to-cell communication through the transport and delivery of cellular components such as lipids, proteins, and nucleic acids. Exosomes preferably accumulate at solid tumor sites due to leaky vasculature and abnormal lymphatic drainage, making them an attractive candidate for detecting cancer.

In recent years, nanoparticles have paved pathway to detect exosomes by incorporating of targeting functionality onto nanoparticle surfaces of the nanoparticles. Among various nanoparticles, Gold nanostars possess interesting tunable properties that can be exploited in different nanomedicine applications including drug delivery systems, thermal-ablation, and image contrast agents. 

As nanoparticle properties are directly related to their size and shape, it is a fundamental criterion to ensure high control and precision during the synthesis to obtain anisotropic nanoparticles with desired properties. Gold nanostars were synthesized by seed-mediated method using biocompatible capping agents to control and stabilize nanoparticle morphology during the reactions. First step was to obtain small gold nanoparticles that served as seeds for the growth of branches to finally obtain nanoparticles with the desired star-shape. Gold seeds were obtained by chemical reaction method incorporating citrate as capping agent; monodisperse colloidal nanoparticles (30 ± 5 nm core diameter) were efficiently obtained. Characterization showed that gold seeds possessed a well-defined spherical structure. Silver nitrate was added to the growth solution which acts as a catalyst to activate the site for the formation of branches. 

However, in most cases these nanostars possess poor long-term stability, short branch length, polydispersity and suffer from aggregation. In order to address these issues, this thesis focuses characterization of physical properties such as size and morphology using numerical and experimental methods to enhance the synthesis and stabilization of gold nanostars for Localized Surface Plasmon Resonance (LSPR) based biosensing of exosomes. The results show a highly sensitive biosensing platform with prolonged shelf life of more than a year. Biomolecule such as Streptavidin, Biotin, PEGylated (PEG) and Vn peptide (Vn96) were used as surface functionalization molecules on gold nanostars for detecting exosomes. The results show great promise in comparison to standard spherical nanoparticles.