Effective replacement of cetyltrimethylammonium bromide (CTAB) by mercaptoalkanoic acids on gold nanorod (AuNR) surfaces in aqueous solutions
Autor
Del Caño-Ochoa, Rafael
Gisbert-González, José M.
González Rodríguez, José
Sánchez-Obrero, Guadalupe
Madueño, Rafael
Blázquez, Manuel
Pineda, Teresa
Editor
Royal Society of ChemistryFecha
2020Materia
GoldHigh resolution transmission electron microscopy
Infrared devices
Nanorods
Near infrared spectroscopy
X ray photoelectron spectroscopy
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The highly packed cetyltrimethylammonium bromide (CTAB) bilayer built up on the surface of gold nanorods (AuNRs) when
synthetized by the seed-mediated procedure hampers the complete ligand exchange under experimental conditions that
preserve the stability of the dispersions. In the present work, a ligand exchange protocol by using carboxy-terminated
alkanethiols of different chain length by means of a green approach that use only aqueous solutions is presented. The
protocol is based on the kwnoledge of the stability in aqueous solution of both, the starting CTAB-AuNRs and the final
products that help in the choice of the experimental conditions used for ligand exchange. The characterization of the CTAB
protective layer as well as the study of its colloidal estability in solution have helped us to design the appropriate
methodology. Cyclic voltammetry of CTAB-AuNRs demonstrates the high stability of the bilayer showing the existence of a
two-dimensional phase transition from a highly ordered to a less organized phase. Other techniques such as XPS, FT-IR and
Raman spectroscopies inform about the structure of the layer and UV-visible-NIR spectroscopy stablishes the stability
conditions in aqueous solution. We have chosen an exchange procedure for 11-mercaptoundecanoic acid (MUA) and 16-
mercaptohexadecanoic acid (MHDA) based in a one-pot methodology under conditions where all the species involved are
stable. The protocol, however, can be extended to different chemical functionalities that are considered useful to be applied
in living systems. Under these conditions the complete exchange of CTAB by the mercaptoderivatives was successful as
demonstrated by the different characterization techniques used: UV-visible-NIR, FT-IR, Raman, XPS spectroscopy, cyclic
voltammetry and transmission electron microscopy (TEM).