The effect of temperature and freeze-thaw processes on gold nanorods.

An application of increasing importance is the use of gold nanorods (AuNRs) as nanosensors and nanoprobes. We explored the possibility of using AuNRs as detectors for various temperature exposures. We measured the effects of freeze-thaw processes on AuNRs in aqueous solution by visual inspection (thermochromism), transmission electron microscopy (TEM; morphological reshaping and aggregation), and absorbance spectroscopy (plasmon peak shifts). TEM images revealed that AuNRs coalesced after prolonged exposures to -20 degrees C. The results suggest that solute rejection and cetyltrimethylammonium bromide (CTAB) bilayer crystallization underlie the mechanism of AuNR aggregation during freezing. This non-reversible aggregation appears to be unique to CTAB-protected AuNRs. Due to their unique freezing properties, we propose that AuNRs may have utility as freeze-thaw temperature nanoprobes.