Nanoscale Thermotropic Phase Transitions Enhance Photothermal Microscopy Signals

TL;DR

This paper demonstrates that leveraging nanoscale thermotropic phase transitions in liquid crystals significantly enhances photothermal microscopy signals, enabling better detection of nano-objects.

Contribution

The study introduces a method to amplify photothermal signals using thermotropic phase transitions, achieving a 40-fold enhancement in imaging gold nanoparticles.

Findings

40-fold signal-to-noise ratio improvement in liquid crystals

Optimal enhancement depends on probe polarization, heating power, and temperature

Photothermal microscopy can detect local phase transitions at nanometer scales

Abstract

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.