Statistics
MERCAPTOCARBOXYLIC ACID
To narrow down the pool of data and eliminate extraneous variables, the Kruskal Wallis’ Test was used to find the dominant wavelengths, where fluorescence is maximised, for each of the ligands. For Quantum Dots coated with both Thioglycolic Acid and 11-Mercaptoundecanoic Acid, we found that (530, 590), (590, 645) and (530, 645) have fluorescence values significantly higher than the other wavelengths. Hence, these are the dominant wavelengths.
MERCAPTOAMINE
(530, 590), (530, 645) and (485, 590) were identified as the dominant wavelengths for the Quantum Dots coated with both the Cystamine and the 11-Amino-1-Undecanethiol.
Due to the fact that the Quantum Dots attached with the two types of ligands have different dominant wavelengths, they cannot be directly compared with each other.
COMPARISON OF LIGAND
For the dominant wavelengths, a Kruskal Wallis’ Test was run and it was found that quantum dots coated with ligands containing 2 carbon atoms (Thioglycolic Acid and Cystamine) have a significantly higher fluorescence than those coated with ligands containing 11 carbon atoms (11-Mercaptoundecanoic Acid and 11-Amino-1-Undecanethiol) for both the ligands with Carboxylic Acid and Amine functional groups.
Evidently, for both functional groups, the longer the hydrocarbon chain length, the lower the fluorescence. This is possibly because the longer the hydrocarbon chain, the greater the dipole interactions, hence causing more aggregation. As can be seen in the TEM images, there is a greater amount of aggregation of quantum dots when the length of the ligand attached is increased. Unfortunately, the effects of both functional on fluorescence could not be compared as the dominant wavelengths they produced in a Quantum Dot were different.