Somatostatin Decorated Quantum Dots for Targeting of Somatostatin Receptors

Due to the unique optical properties like high brightness and narrow emission bands of Quantum dots, it is used as simple fluorescence materials in bio-imaging, immunoassays, microarrays, and other applications. To easy invistigate cell lines that overexpressed somtostatin receptors, somatostatin (SST) was conjugated with Quantum dots carrying PEG amine (Qdots-PEG-NH₂). The conjugation of SST to Qdots-PEG-NH₂ started with the thiolation of SST using Traut's reagent. Moreover, the Qdots-PEG-NH₂ were subsequently activated by 500-fold molar excess of sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) dissolved in phosphate buffer. The Qdots-PEG-NH₂-sulfo-SMCC was conjugated to the thiolated-SST to form Qdots-SST. The number of sulfhydryl groups can be controlled by the molar ratio of Traut´s reagent to SST. Thiolation was necessary for the conjugation of SST to Qdots-PEG-NH₂. This was achieved by reacting the SST with Traut's reagent in a 1:1 molar ratio. Ellman's reagent was used to determine the number of sulfhydryle groups. Furthermore, cellular uptake study on triple negative breast cancer cells (HCC-1806) showed that the numbers of Qdots-SST per cell were significantly higher compared to unmodified Qdots-PEG-NH₂ when quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES). Moreover, the binding of Qdots-SST to cells can be suppressed by addition of free SST, indicating that the binding of Qdots-SST to cells is due to receptor-specific binding.