Thesis defences

PhD Oral Exam - Jun-Ray Macairan, Chemistry and Biochemistry

Development of Multisensing Imaging Probes Using Carbon Dots

Friday, April 23, 2021 (all day)

This event is free


School of Graduate Studies


Daniela Ferrer



When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.


Imaging probes serve as unique diagnostic tools in biomedical applications offering high sensitivity particularly in their ability to image cells and tissues, as well as for the study of various biological processes. These tools are becoming crucial for early detection and disease diagnostics especially with an increase in numbers of an aging population and the requirement for more efficient health care. Recent advancements in the field of nanomaterials have propelled research groups into investigating these nanoparticles for various biological applications including drug delivery, biosensing and bioimaging, among others. Indeed, several nanomaterials including polymer dots, quantum dots and lanthanide-doped upconverting nanoparticles have been studied for these applications. Recently, carbon dots have garnered significant attention owing to the fact that they can be prepared from simple synthetic routes using inexpensive precursors, offering tunable optical properties, low cytotoxicity and good biocompatibility. Their inherent fluorescent nature not only allows for fluorescence imaging, but also for sensing environmental changes (e.g. temperature and pH), which can provide additional insights for the development of novel diagnostic applications.

In this work, carbon dots are synthesized using a one-step microwave- and solvothermal-assisted reaction. The prepared dots are capable of simultaneously fluorescing in both the blue and the red regions of the electromagnetic spectrum. The carbon dots’ physico-optical properties are thoroughly studied to shed light on their fluorescence mechanism, which remains of topic of debate in the literature. It is demonstrated that the fluorescence of the carbon dots is tailored through manipulation of key synthesis parameters to determine the underlying effect on the observed optical signature. The dots’ unique optical properties are believed to derive from the carbon core- and molecular-states fluorescence mechanism. In brief, the blue fluorescence stems from the core of the dot, while the red counterpart originates from the molecular states that are typically localized on the surface.

With their unique fluorescence properties and our understanding of this phenomenon, these dots offer the possibility of sensing changes in temperature and pH, at subcellular resolution, using ratiometric approaches. In the case of former, the ratio of the red:blue fluorescence is observed to linearly increase with increasing temperature. As for the latter, the red fluorescence, centered at 680 nm, evidences a change with the appearance of a shoulder at 650 nm where an increase in pH of the surrounding environment results in a decreasing sigmoidal response in the 680:650 nm bands ratio. Both temperature and pH sensing measurements translate well from the cuvette to the cellular model. The change in physiological parameters are in agreement with the change in emission using epifluorescence and confocal microscopy. The ability to glean such information renders these nanoparticles into versatile diagnostic nanotools with the ability to shed new insights on disease mechanisms and can be foreseen as future tools for in vivo sensing applications.

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