SERS active substrates of gold nanoparticles embedded in the pool of 5-CB liquid crystal molecules organized in Langmuir-Reverse Schaefer films: A facile fabrication route to make the topological defects useful

摘要

This paper reports for the first time, fabrications of SERS active substrates I and II from Langmuir Reverse Schaefer (L-R Sh) films of 5-CB nematic liquid crystal molecules immersed in gold nanocolloids for 36 and 48 h respectively. Under parallel or slightly crossed polarizations, the POM images of these two substrates exhibit micro aggregated textures embedded in the pool of 5-CB molecules. Under crossed polarizations, the aggregated textures disappear with the appearance of bright birefringent defects of various sizes and shapes. The rationale behind the evolution of such micro aggregated textures and spatial locations of birefringent defects in these substrates are suggested. The FESEM images of the substrates exhibit distinctive patterns driven by the birefringent defects and confirm trapping of gold nanoparticles within the defect sites. The instabilities appeared in the patterns are estimated from statistical considerations in terms of Hurst exponent and phase space trajectories. The chaotic domains prevailing in these substrates are confirmed from the Lyapunov exponents. The efficacies of both the substrates as efficient SERS sensing platform have been tested to detect 4-MPy molecules at trace concentration. The as prepared substrates can be used as "lab on a chip" for chemical and biochemical sensing at ultralow concentrations.