Graded Shell Peptide-Coated Nanoparticles for Bioimaging

The patent applies local quality by creating a graded shell structure where the composition varies spatially from the core outward. The shell transitions from CdSe-rich regions near the core to ZnS-rich regions at the surface, with intermediate CdS layers. This gradual compositional change allows different regions to serve different functions: the CdSe-rich regions maintain high photoluminescence quantum yield, while the ZnS-rich surface regions provide stable peptide binding and water solubility. This resolves the contradiction by allowing peptide coating to confer biofunctionality without requiring the entire shell to have high peptide affinity, thus preserving photoluminescence in the interior regions.

The patent employs parameter changes by systematically varying the shell thickness and compositional gradient. The graded shell structure allows optimization of the thickness parameter: a thin graded shell (e.g., 2-5 nm total thickness) provides sufficient photostability and peptide binding capability without excessive size increase. The gradual compositional transition within this thin shell maintains quantum yield while the outer ZnS-rich layer ensures stable peptide attachment. This resolves the contradiction by demonstrating that a thin graded shell can simultaneously achieve photostability, high quantum yield, and minimal steric hindrance for intracellular applications.

The patent applies segmentation by dividing the shell formation process into discrete compositional zones. The graded shell is constructed with distinct regions: an inner CdSe-rich zone, intermediate CdS zones with varying compositions, and an outer ZnS-rich zone. Each zone can be formed through controlled sequential addition of precursors or by adjusting reaction conditions during shell growth. This segmentation approach maintains manufacturing feasibility through stepwise synthesis while achieving the desired photoluminescence properties, as each compositional zone contributes specific functions that collectively enhance quantum yield compared to uniform non-graded shells.