In aqueous solutions the spectral-kinetic parameters of quantum dots (QD) based on a mixture of semiconductors of groups I–III–VI, namely Ag–In–S and Ag–In–S2, with a layer of ZnS (AIS/ZnS QD), show a specific dependence on pH and on the local polarity caused by interaction with polyelectrolytes (spectral shifts, hyperchromism, and hypochromism in the absorption and photoluminescence spectra, changes of the average photoluminescence life time). It was found that the change in the properties of the AIS/ZnS QDs with variation of the pH of the solution is caused by reversible recharging of ampholyte ion groups, which alters the structure of the Helmholtz double layer at the surface of the QD covered by glutathione molecules. It was shown that the second derivative of the QD absorption spectra both in an acidic medium and during interaction with polyelectrolytes corresponds to a linear Stark effect due to the formation of an induced dipole moment in the QD. The obtained results can be used to develop selective markers based on AIS/ZnS QDs for testing local pH and polarity in biomedicine.
