Ag2S nanodots for advanced biological applications through luminescence thermometry and fluorescence images

Abstract

Remarkable investigations/discoveries were performed/found out throughout the development of this thesis motivated by the needs of updated technologies that support basic human well-being and survival. Hybrid nanostructures based on the semiconductor of silver sulfide nanodots (Hereafter, Ag2S nanodots) have been employed for carrying out different challenging tasks because of their unique and superb performance as a florescent agent of multifunctional character, acting as nanoheaters, thermal sensors, biolabelings and biomarkers. Based on these well-known outstanding features of nanostructures of Ag2S nanodots, one major challenge in this thesis was to focus on their synthesis production, aiming to improve structural and fluorescence properties, their biocompatibilities and to achieve suitable surface decoration to specific purposes. Furthermore, their fluorescence emission lies in the so-called second biological window (II-BW), conducting to higher penetration depths of emitted photons and reducing autofluorescence due to the barely scattering and absorption of these energy photons in living tissues. Another remarkable advantage is that this material is well-excited under 800 nm of excitation photons, which is also weakly absorbed by living tissues. All these terrific features working in partnership with its multifunctional character open up the possibility of realizing so dreamed applications concerning preclinical assay. Among them, we could deal with some as can be briefly mentioned: Ex-vivo experiments were projected to provide detailed information about thermal gradients in subcutaneous studies based on the temperature dependency of the time-resolved fluorescence dynamics of our synthesized (or purchased) Ag2S, in other words, exploiting its thermal sensing talent. Concerning its thermal sensing ability based on the luminescence properties, it also enabled us to perform an efficient detection of a tumor and even providing a well accurate prediction of its stage. During the progress of this thesis we also produced a new version of Ag2S nanodots by far the brightest contrast agent reported in literature so far. We named them as Ag2S superdots and some preclinical assay were carried out, enabling us to monitor, for example, its in vivo bio-distribution after low-dose intravenous administration and using the lowest power density dose so far reported.