Ligand Counting and Size Determination of Quantum Dots Using Electronegative Matrix-Assisted Laser Desorption...

Area of Science:

• Materials Science
• Analytical Chemistry
• Nanotechnology

Background:

• Surface ligands on quantum dots (QDs) are crucial for their properties and applications.
• Conventional characterization methods like UV-vis and TEM lack direct stoichiometric information on ligands.
• Traditional MALDI-MS often results in significant ligand loss during analysis.

Purpose of the Study:

• To develop a mass spectrometry (MS) method for accurate quantitative analysis of ligands on QDs.
• To overcome the limitations of traditional MALDI-MS in preserving ligands on QDs.
• To enable precise determination of QD core sizes and surface ligand stoichiometry.

Main Methods:

• Utilized a highly electronegative, fluorinated porphyrin (TPFP) as a soft MALDI matrix for CdSe QDs.
• Conducted comparative studies with conventional electron-transfer matrices (DCTB, 9-nitroanthracene, dithranol, pentacene).
• Employed TPFP-MALDI-MS to analyze carboxylate- and thiolate-capped QDs.

Main Results:

• TPFP matrix significantly reduced ligand loss and increased ion signals at lower laser power compared to other matrices.
• The method accurately determined QD core sizes and quantified the number of surface ligands.
• Ligand numbers and densities were evaluated for thiolate-capped QDs across various core sizes with improved resolution.

Conclusions:

• TPFP-MALDI-MS offers a reliable strategy for determining QD core size, counting ligands, and estimating surface coverage.
• The electron affinity of the MALDI matrix is critical for soft ionization and ligand preservation.
• This expands MS-based tools for comprehensive characterization of QD core and surface chemistry.