Nanoscale Thermotropic Phase Transitions Enhance Photothermal Microscopy Signals

A. Nicholas G. Parra-Vasquez (1) , Laura Oudjedi (1) , Laurent Cognet (1) , Brahim Lounis (2)

1 LP2N - Laboratoire Photonique, Numérique et Nanosciences
2 lp2n-01,lp2n-12

The photothermal heterodyne imaging technique enabled studies of individual weakly absorbing nano-objects in various environments. It uses a photo-induced 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.

Mots clés: single molecule detection; Photothermal microscopy; nanoparticles; thermotropic phase transition; liquid crystals; single molecule detection.

Domaines: Autre [cond-mat.other]

A. Nicholas G. Parra-Vasquez, Laura Oudjedi, Laurent Cognet, Brahim Lounis. Nanoscale Thermotropic Phase Transitions Enhance Photothermal Microscopy Signals. Journal of Physical Chemistry Letters, 2012, 3 (10), pp.1400. ⟨10.1021/jz300369d⟩. ⟨hal-00735011⟩