How Quantum Dots Aggregation Enhances Förster Resonant Energy Transfer

Abstract

As luminescent quantum dots (QDs) are known to aggregate themselves through their chemical activation by carbodiimide chemistry and their functionalization with biotin molecules, we investigate both effects on the fluorescence properties of CdTe QDs and their impact on Förster Resonant Energy Transfer (FRET) occurring with fluorescent streptavidin molecules (FA). First, the QDs fluorescence spectrum undergoes significant changes during the activation step which are explained thanks to an original analytical model based on QDs intra-aggregate screening and inter-QDs FRET. We also highlight the strong influence of biotin in solution on FRET efficiency, and define the experimental conditions maximizing the FRET. Finally, a free-QD-based system and an aggregated-QD-based system are studied in order to compare their detection threshold. The results show a minimum concentration limit of 80 nM in FA for the former while it is equal to 5 nM for the latter, favouring monitored aggregation in the design of QDs-based biosensors.

Two-Dimensional Layers of Colloidal CdTe Quantum Dots: Assembly, Optical Properties, and Vibroelectronic Coupling

“…We thus conclude that the samples obtained by chemisorption are subject to an aggregation of QDs, even once grafted on the substrate. The action of the EDC-NHS couple as it was observed and described in [28] apply here even though CdTe QDs are transferred on a silanized substrate. To quantify this effect, we calculate for each sample the standard deviation A440nm of the absorbance at 440 nm, as defined and detailed in Supporting Information (section II): it is expressed as a percentage of the initial value A440nm (t = 0).…”

“…Since the pKa of amines is around 10 [27], we expect the protonated form of APTES to be predominant in the aqueous medium, when the silanized substrates are immersed in the colloidal solution of QDs (pH 5.5). As the surface of COOH-conjugated CdTe QDs is negatively charged (their zeta potential is -36 mV [28]), there exist significant attractive ionic forces between the carboxylates of the QDs and the terminal NH3 + of APTES ( Figure 1d). As observed on Figure 3, such a Glass-APTES-QD sample presents the same optical properties that the colloidal QDs solution.…”

A Unified Mathematical Formalism for First to Third Order Dielectric Response of Matter: Application to Surface-Specific Two-Colour Vibrational Optical Spectroscopy

“…This means that UV-visible and infrared spectroscopies, which consist of measuring the quantity − log I(x, ω) I(0, ω) as a function of the wavelength λ = 2πc/ω or the wavenumber σ = 1/λ, are sensitive to light scattering. For instance, UV-visible spectroscopy allows highlighting and quantifying the aggregation of metallic or semiconductor nanoparticles when this indeed occurs [9,10].…”

Spatial Dependence of the Dipolar Interaction between Quantum Dots and Organic Molecules Probed by Two-Color Sum-Frequency Generation Spectroscopy

“…With diameters ranging between 1 and 10 nm, QDs are able to absorb and emit light over the visible range [1][2][3][4][5]. Hence, they are largely employed within various scientific fields such as photovoltaics [6,7], photocatalysis [8][9][10], fluorescence spectroscopy [11,12], biomedical imaging [13][14][15], and biosensing [16][17][18][19][20][21]. In the later case, QDs are often used as fluorescent probes.…”

“…In the later case, QDs are often used as fluorescent probes. Indeed, their spectral and temporal emission properties are highly sensitive to their chemical environment, including capping ligands, solvent, pH, ion concentration, cross-linking molecules, and biomolecules [12,[22][23][24][25][26][27][28][29]. As a result, the literature extensively reports how the chemical medium of QDs influence their optical properties, especially within the framework of biosensors.…”