Surface Modification and Functionalization Of CdSe and InP Quantum Dots Using Multidentate Polymer Ligands For Imaging of Single Protein Molecule

Abstract

Quantum dots (QDs) exhibit size‐dependent emission wavelengths, high brightness, and excellent photoluminescence quantum yields (PLQY), making them valuable fluorophores for various fields. Although ligand exchange enables QDs surface modification by replacing native hydrophobic ligands with hydrophilic alternatives, conventional monodentate ligands often suffer from poor colloidal stability and weak binding, ultimately limiting their use in biological environments. For reliable bio-applications, QDs must maintain stable aqueous dispersion, possess compact hydrodynamic size, and minimize nonspecific binding (NSB). To address these challenges, we designed and synthesized multidentate polymer ligands consisting of anchor (A), hydrophilic (H), and functional (F) groups. These polymers give good colloidal stability, increasing water solubility and giving bio- functionalization. In Chapter II, we applied this multidentate ligand to CdSe QDs and developed a two-step ligand- exchange procedure to obtain compact, water-soluble QDs with superior properties. The polymer- coated QDs showed excellent resistance to NSB and retained functional azido groups for strain- promoted click chemistry. Furthermore, Efficient antibody conjugation was achieved using DBCO- modified antibodies. Systematic electrophoretic mobility shift assays (EMSA) revealed that PEG itself induces XPA–DNA dissociation, independent of various factors. By tuning the relative fractions of A-, H-, and F-groups on the QD surface, we identified polymer compositions that do not induce XPA dissociation from DNA. Therefore, the optimized QDs enabled single-molecule visualization of XPA recognizing a specific site of DNA in DNA curtain assays. In Chapter III, we further expanded our surface-engineering platform by synthesizing diverse polymer ligands—P[LA-Z], P[LA-Z-PEG COOH], and P[LA-Z-PEG N₃]—for use on InP QDs. And also FT-IR, XPS, DLS, UV–vis, PL, XRD, and TRPL analyses confirmed successful ligand exchange to InP QDs surface, preserved crystal structure, and strong optical properties following surface modification. The preservation of functional groups (azide, carboxylic acid) on the polymer-coated InP QDs further confirms their broad utility as adaptable platforms for diverse bio-conjugation and biological applications.