Upconverting nanoparticles: pushing theory and technology towards biomedical applications

Souza Matias, Jean

Upconverting nanoparticles: pushing theory and technology towards biomedical applications

dc.contributor.advisor	Andersson-Engels, Stefan
dc.contributor.advisor	Melgar Villeda, Silvia
dc.contributor.author	Souza Matias, Jean	en
dc.contributor.funder	Science Foundation Ireland	en
dc.date.accessioned	2023-09-14T09:22:18Z
dc.date.available	2023-09-14T09:22:18Z
dc.date.issued	2023
dc.date.submitted	2023
dc.description.abstract	Biophotonics faces a significant challenge in developing non-invasive imaging and interrogation techniques with high spatial resolution and penetration depth for precise diagnosis and treatment. These techniques rely on non-ionising radiation and non-toxic contrast agents possessing excellent photo and chemical stabilities. Among the various non-ionising wavelengths, the near-infrared (NIR) optical window offers the highest tissue penetration due to its minimal scattering and absorption in living tissues. Upconverting nanoparticles (UCNPs) possess the desirable properties of absorbing and emitting NIR light, making them ideal contrast agents for biomedical applications. UCNPs have shown promise in deep tissue imaging, optogenetics, photodynamic therapy, temperature sensing, drug delivery, and super-resolution microscopy. However, the efficiency of upconversion (UC) in UCNPs, as quantified by the quantum yield (QY), remains a significant challenge, particularly at low excitation power densities (PDs) where the non-linearity of upconversion luminescence (UCL) dominates. Furthermore, the lack of commercially available devices and standardised protocols that account for the crucial parameters affecting PD-dependent QY further complicates accurate characterisation of these materials. To address these issues, this thesis presents the design and construction of a comprehensive, broad-band, multi-variable QY characterisation system. This opto-electronically engineered setup enables simultaneous measurement of absorption and luminescence at two selected wavelengths. In addition, the fully automated system incorporates capabilities for characterising excitation beam profiles, scattering, and the emission spectrum of luminescent compounds in aqueous solutions. Accurate characterisation of the excitation beam profile is of particular importance due to its influence on the PD-dependent QY behaviour of UCNPs. Varying beam profiles lead to distinct QY values, necessitating beam profile compensation to derive an intrinsic QY property of the material independent of measurement configuration. However, achieving this compensation requires a comprehensive understanding of the mechanisms governing each UC emission wavelength, which has not yet been extensively studied across a wide range of PDs. Consequently, this thesis also includes a detailed theoretical study based on the rates of populating and depopulating the electronic energy states involved in UC processes. The investigation successfully quantifies the transition points at which the UCL transitions from non-linear behaviour of different orders to linearity. The theoretical model is validated using experimental UCL data acquired from two distinct UCNP compounds at various wavelengths. These combined theoretical and experimental studies are of utmost importance for the accurate characterisation and engineering of optimal UCNPs, representing a crucial advancement in the development of high-resolution, deep-penetration biomedical techniques and devices.	en
dc.description.status	Not peer reviewed	en
dc.description.version	Accepted Version	en
dc.format.mimetype	application/pdf	en
dc.identifier.citation	Souza Matias, J. 2023. Upconverting nanoparticles: pushing theory and technology towards biomedical applications. PhD Thesis, University College Cork.
dc.identifier.endpage	199
dc.identifier.uri	https://hdl.handle.net/10468/14979
dc.language.iso	en	en
dc.publisher	University College Cork	en
dc.relation.project	info:eu-repo/grantAgreement/SFI/SFI Research Professorship Programme/15/RP/2828/IE/Novel applications and techniques for in vivo optical imaging and spectroscopy/	en
dc.rights	© 2023, Jean Souza Matias.
dc.rights.uri	https://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject	Upconversion
dc.subject	Upconverting nanoparticle
dc.subject	UCNP
dc.subject	Quantum yield
dc.subject	Biophotonics
dc.subject	Power density
dc.title	Upconverting nanoparticles: pushing theory and technology towards biomedical applications
dc.type	Doctoral thesis	en
dc.type.qualificationlevel	Doctoral	en
dc.type.qualificationname	PhD - Doctor of Philosophy	en