Quantum dots have the potential to revolutionize biological imaging due to their exceptional photophysical properties. However, precise control over the interfacial chemistry between QDs and other biomolecules remains a significant synthetic challenge limiting their broad application in biology. Common strategies for preparing QD-biomolecule conjugates generate products with poorly defined valency, relatively large hydrodynamic size, and limited modularity. To address these issues and hence to establish higher-performance and more versatile QD imaging probes, we propose an innovative synthetic approach, termed "steric exclusion". The method uses a functionalized steric-exclusion oligonucleotide designed to wrap the QD as it reacts and thereby limits the extent of the reaction to a species of fixed valency. We propose to (i) perform the single-step complete conversion of QDs to bioimaging probes that are small (<12 nm), modular, highly-specific, and monovalent;and (ii) demonstrate the utility of these probes in a challenging single- molecule imaging application by elucidating the dynamics of Notch and its processing intermediates on the surface of live cells. Ultimately, we propose to transform QDs from "probes for special purposes" to "versatile and ready-to-use bioprobes," accessible to scientists from any discipline.
The proposed optical probes with extreme brightness, high-resolution, and photostability will provide specific and sensitive diagnostic tools. Moreover, Notch signaling is an important protein involving development and many diseases such as cancer, multiple sclerosis, lymphoma, and other diseases, and thus understanding of Notch dynamics will be beneficial for diagnostic and therapeutic purposes.