Metal nanoparticles and methods of making same

A method for making metal nanorods, the method comprising:

• combining a source of metal cations with at least one surfactant to form a mixture, wherein the metal cations are reduced and the metal nanorods are produced, the at least one surfactant comprises a first surfactant and a second surfactant, wherein one or more of the first surfactant and the second surfactant are different, and wherein the first surfactant is an amphoteric surfactant of formula (IV):
• wherein:
• R1 of formula (IV) represents a hydrophobic group, wherein the hydrophobic group comprises a substituted or unsubstituted hydrocarbon group, or a substituted or unsubstituted heterogeneous group;
• and
• R2 and R3 of formula (IV) are each independently selected from hydrogen or a substituted or unsubstituted hydrocarbon group, or a substituted or unsubstituted heterogeneous group;
• and the second surfactant is a zwitterionic surfactant of formula (I):
• wherein:
• R1 of formula (I) represents a hydrophobic group, wherein the hydrophobic group comprises a substituted or unsubstituted hydrocarbon group, or a substituted or unsubstituted heterogeneous group;
• R2 and R3 of formula (I) are each independently selected from hydrogen or a substituted or unsubstituted hydrocarbon group, or a substituted or unsubstituted heterogeneous group;
• and
• R4 of formula (I) is a substituted or unsubstituted hydrocarbon group, or a substituted or unsubstituted heterogeneous group,
• wherein the metal nanorods have an aspect ratio of from about 1.1 to about 10 and the metal nanorods exclude metal nanowires.