Photothermal convection has been a major obstacle for stable particle trapping in plasmonic optical
tweezer at high optical power. Here, we demonstrate a strategy to suppress the plasmonic
photothermal convection by using vanishingly small thermal expansion coefficient of water at low
temperature. A simple square nanoplasmonic array is illuminated with a loosely Gaussian beam to
produce a two dimensional optical lattice for trapping of micro particles. We observe stable
particle trapping due to near-field optical gradient forces at elevated optical power at low temperature.
In contrast, for the same optical power at room temperature, the particles are convected away
from the center of the optical lattice without their accumulation. This technique will greatly
increase usable optical power and enhance the trapping capability of plasmonic optical tweezer.