CdTe Quantum Dot/Dye Hybrid System as Photosensitizer for Photodynamic Therapy

Table 2 FCS and zeta measurements results for 2.8-nm nanocrystals’ set

Sample name	Diffusion constant (μm²/s)	Hydrodynamic size (nm)	Zeta potential (mV)
A	259.6	4.33	−39.1
B	183.3
C	160.9
D	158.3
E	Fluorescence too low: Zeta potential and size measurements were taken instead	4.53	−34.1
F		4.85	−31.3

The diffusion constant was calculated from the FCS curves. It was found to decrease at increasing methylene blue concentrations, which is in accordance with dye molecules adsorbing onto NCs (NCs become heavier). For low fluorescing samples E and F, an increase in the hydrodynamic size of nanocrystals and a decrease in the amplitude of the zeta potential were observed. These results are also in agreement with the adsorption of positively charged methylene blue molecules onto negatively charged nanocrystals’ surface