Surface Modified

QDs have particularly interesting fluorescence properties, the emission wavelength depends strongly on the particle size and the nature of the corresponding phase, it is possible then to excite them in a wide wavelengths range below the wavelength of fluorescence. Their fluorescence performance exceeds those of conventional organic dyes. In addition to that, the quantum yield fluorescence and emission wavelength are greatly influenced by the particle size, which is directly related to their method of preparation, the nature and proportion of the doping element.

Structuring agents (ligands) as organic molecules play a key role in the stability of the nanocrystals, they surround the surface of the nanocrystals by steric repulsion between particles, allowing them suspended in a suitable solvent, a lack of ligands leads to particle aggregation. The affinity of ligands with particle surface depends on the interaction of their functional groups and their chain length with the surface.

The ligands are not linked to the surface, but they are in constant exchange between the free and the bound forms which allows the particles to grow during synthesis. In general, the ligands have growth control ability, several types of ligands can be used in the syntheses, and their relative affinity to the surface is the parameter which scientists use to modify the reactivity of different crystal faces to obtain particular sizes and shapes of nanocrystals. The ligands may also play a direct role in the reaction mechanism, leading to different crystal structures.

Nevertheless, ligands have a capacity to burn off the ability of the nanocrystals surface, the dangling bonds due to surface atoms can create loads that cannot be compensated by neutral ligands. In addition, the ligands form an insulating layer that can be used to confine the charges in the nanocrystal and protect their fluorescence even without shell.

Surface modified Znse/Znsquantu dots have cubic zinc blende structure. The enhancement of the luminescent ZnSe/Zns QD by doping the  main phase using various elements as metals, transition metals and halides can serve for imaging of the positive cells especially used for cancer identification cells and life cell imaging. The application was based on conjugated ZnS using folic acid to detect cancer in lung fibroblast cell.