Quantum dot bioconjugates for the detection of extracellular vesicles in saliva and breath
Nano-sized extracellular vesicles, released by most types of cells, contain information about the cell they originate from and have been shown to be involved in a variety of cellular processes. However, their detection and characterisation has been challenging and non-standardised, which makes comparisons across literature very challenging. While exosomes are known to exist in complex biological fluids such as saliva, breast milk, blood, and urine, their separation and identification from these media are time-consuming. Many researchers use techniques such as transmission electron microscopy for physical characterisation and western blot for protein identification, which are often not available in medical settings. Additionally, while these fluids can be easily obtained, acquiring similar samples from lung environments is a highly invasive procedure. While breath is known to transmit droplets from the lungs, the presence of exosomes in these condensates is unknown. In this project, functionalised InP/ZnS quantum dots (QDs) were used to target exosomes from a number of biological sources and provide a gateway to more fully characterise their ensemble properties. The InP/ZnS QDs were synthesised, and their size dependency on the band gap was investigated in accordance with the theoretical effective mass approximation model for quantum dots. The QDs were produced with hydrophobic oleylamine ligands, and therefore had to be ligand exchanged to be used in biological applications. A range of ligand exchange methods was surveyed to probe the best balance between retention of original quantum yields and best colloidal stability in aqueous systems.The QDs were further conjugated to an antibody specific for CD63, the protein found on exosomes. The conjugation was confirmed using dynamic light scattering and surface plasmon resonance. Finally, the binding of the QD-Antibody probe to the exosome was confirmed using surface plasmon resonance and confocal microscopy. Further modifications of the assay system could lead to multiplex-detection of the different proteins on the exosomes, their characterisation, and a method for the rapid detection of diseases.