Facile Counting of Ligands Capped on Nanoparticles via a Titration Chip of Moving Reaction Boundary Electrophoresis

Absolute quantification of ligand capped on the surface of nanoparticles (NPs) has faced a great challenge without the use of complex inner standards (CIS). Herein, we proposed a facile electrophoresis titration (ET) model, designed an ET device, and developed a relevant method for counting the ligand on NPs without the use of CIS, based on moving reaction boundary (MRB). Furthermore, we conducted the relevant ET runs by using 3-mercaptopropionic acid (MPA) and quantum dots (QDs) as the model ligand and NPs, respectively. The experiments revealed that the ligand content of 1518 ± 295 obtained via an ET was close to the one of 1408 ± 117 determined via NMR, validating the ET model. Moreover, the experiments showed fair stability (RSD < 5.62%) and simplicity of ET without the use of CIS. Evidently, the ET model opens a window for facile assay of ligand capped on NPs.