Thesis presented June 10, 2016

Abstract:
One of the many challenges modern medicine is facing today is the accurate and early diagnosis of diseases. Due to their unique photophysical properties semiconductor quantum dots (QDs) are promising fluorescent labels for biosensing. The major aim of this work is the development of QD antibody (AB) conjugates to be used in Förster resonance energy transfer (FRET) immunoassays for the detection of the tumor biomarker PSA (prostate specific antigen). In these assays, the QDs act as FRET acceptors in combination with terbium complex donors. Thanks to the specific luminescence properties of these two classes of fluorophores, time-gated detection of the QD signal allows for the fast and sensitive detection of biomarkers. We developed a novel two-step approach for QD functionalization and bioconjugation which yields ultra compact, stable and highly luminescent QD-AB conjugates maximizing FRET efficiency. In the first step aqueous phase transfer of lab-synthesized InP-based QDs emitting at 530 nm and of commercial CdSe-based QDs emitting at 605 nm and 705nm was achieved by surface ligand exchange with penicillamine. Then, post-functionalization with a heterobifunctional crosslinker, containing a lipoic acid group and a maleimide function, enabled the subsequent coupling to sulfhydryl groups of proteins. This was demonstrated by QD conjugation with fragmented antibodies (F(ab)); the obtained conjugates have a very low hydrodynamic diameter < 13 nm and long-term colloidal stability. The applicability of the obtained probes was confirmed by the detection of PSA in serum samples with detection limits (LODs) down to 0.8 ng/mL for the 705 nm emitting probes, whose absorption spectrum shows the largest overlap integral with the Tb emission. In addition, direct grafting of rare earth complexes on the QD surface has also been explored, giving access to dual-mode imaging agents (with Gd) or to biluminescent (with Eu, Yb) probes. In the latter case, the sensitization of Yb NIR luminescence by InP-based QDs has been firstly demonstrated. Finally, we carried out nanotoxicological studies on the different types of QDs used. In particular we investigated in vivo toxicity using the model organism Hydra vulgaris and in vitro toxicity using human keratinocyte cells comparing core and core/shell InP-based and CdSe-based QDs.

Keywords:
Functionalization, Nanocrystals, Fluoroimmunological analysis

On-line thesis.