Detecting, visualizing, and measuring gold nanoparticle chirality using helical pitch measurements in nematic liquid crystal phases.
Chirality at the nanoscale, or more precisely, the chirality or chiroptical effects of chiral ligand-capped metal nanoparticles (NPs) is an intriguing and rapidly evolving field in nanomaterial research with promising applications in catalysis, metamaterials, and chiral sensing. The aim of this work was to seek out a system that not only allows the detection and understanding of NP chirality but also permits visualization of the extent of chirality transfer to a surrounding medium. The nematic liquid crystal phase is an ideal candidate, displaying characteristic defect texture changes upon doping with chiral additives. To test this, we synthesized chiral cholesterol-capped gold NPs and prepared well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism spectropolarimetry and polarized light optical microscopy revealed that all three gold NPs induce chiral nematic phases, and that those synthesized in the presence of a chiral bias (disulfide) are more powerful chiral inducers than those where the NP was formed in the absence of a chiral bias (prepared by conjugation of a chiral silane to preformed NPs). Helical pitch data here visually show a clear dependence on the NP size and the number of chiral ligands bound to the NP surface, thereby supporting earlier experimental and theoretical data that smaller metal NPs made in the presence of a chiral bias are stronger chiral inducers.
Liquid Crystal Institute, Chemical Physics Interdisciplinary Program, Kent State University , Kent, Ohio 44242, United States.
Anshul
A
Sharma
Taizo
T
Mori
Huey-Charn
HC
Lee
Matthew
M
Worden
Eric
E
Bidwell
Torsten
T
Hegmann
D002784:Cholesterol / Q000737:chemistry; D002942:Circular Dichroism; D006046:Gold / Q000737:chemistry*; D050866:Liquid Crystals / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D008853:Microscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D013237:Stereoisomerism
D006046:Gold; D002784:Cholesterol
chirality; helical pitch; liquid crystals; nanoparticles