Nanoscale Thermotropic Phase Transitions Enhancing Photothermal Microscopy Signals.
The photothermal heterodyne imaging technique enables studies of individual weakly absorbing nano-objects in various environments. It uses a photoinduced change in the refractive index of the environment. Taking advantage of the dramatic index of refraction change occurring around a thermotropic liquid-crystalline phase transition, we demonstrate a 40-fold signal-to-noise ratio enhancement for gold nanoparticles imaged in 4-cyano-4'-pentylbiphenyl (5CB) liquid crystals over those in a water environment. We studied the photothermal signal as a function of probe laser polarization, heating power, and sample temperature quantifying the optimal enhancement. This study established photothermal microscopy as a valuable technique for inducing and/or detecting local phase transitions at the nanometer scales.
†Université Bordeaux, LP2N, F-33405 Talence, France.
A Nicholas G
AN
Parra-Vasquez
†Université Bordeaux, LP2N, F-33405 Talence, France.
Laura
L
Oudjedi
†Université Bordeaux, LP2N, F-33405 Talence, France.
Laurent
L
Cognet
†Université Bordeaux, LP2N, F-33405 Talence, France.
Brahim
B
Lounis
liquid crystals; nanoparticles; photothermal microscopy; single-molecule detection; thermotropic phase transition