Influence of a dual-stabiliser formed by 3-morpholinoethanesulfonic and 3-mercaptopropionic acids on the photophysical, electrochemical and electrochemiluminescent properties of aqueous soluble CdSe quantum dots

In order to obtain an emitter nanoprobe for applications in aqueous solutions, we synthesised quantum dots of CdSe (CdSe QDs) in aqueous solutions, which were stabilised with 3-morpholinoethanesulfonic (MES) and 3-mercaptopropionic (MPA) acids. Comprehensive photophysical and electrochemical studies were carried out in order to determine the optimum MPA:MES ratio that produces the highest electrogenerated chemiluminescence (ECL) intensity. We found that the variation between the relationship of MPA and MES directly affected the surface, the size and properties of the CdSe QDs. Characteristic parameters of CdSe QDs were determined by conventional photophysical and electrochemical techniques, where an excellent correlation between the two methods was found. In addition, diameter, quantum yield (ϕNC), bandgap (Eg) and lifetime of CdSe QDs were determined. It was also observed that as the proportion of MPA in the capping increased, the ϕNC increased, and that an increase in the proportion of MES in the capping increased the intensity of ECL. The surface state of quantum dots is responsible for the difference in the behaviour between fluorescence and electrochemiluminescence properties. These results allowed us to infer that the choice of dual-stabiliser will depend on the applications of the resulting quantum dots as nanoprobe emitters.