Quantum efficiency of excitonic enhancement in nanosensors by rainbow nonlinear optical spectroscopy

Quantum dots (QD) constitute a novel generation of fluorescent probes due to their confined size in the 1-10 nm range. In this field, nanosensors sensitivity is of pivotal importance to target biomolecules. We focus here on the grafting of organic ligand-coated CdTe QDs monolayers on glass surfaces to address the environmental problem and cost of nanosensors. QD monolayers samples are pre-characterized by UV-VIS absorption and (Time-resolved) fluorescence emission, evidencing the success of transferring the QD optoelectronic properties from colloidal solution to amine-terminated aliphatic organosilane monolayer-modified glass samples. Moreover, from time-resolved fluorescence spectroscopy, the effect of chemical structure of monolayers are seen from a fast-quenching phenomenon in relation to colloidal QD solution. Afterwards, an advanced surface-specific spectroscopic tool, non-linear optical Two-Colour IR-Visible Sum-Frequency Generation spectroscopy (2C-SFG), is used to probe and evidences the dipolar coupling between QD excitons and their molecular surroundings, which improves the nanosensor’s detection threshold. This electro-optical coupling (inorganic-organic charge transfer) is modelled in an original formalism we developed and based on Feynman loop-diagrams.