Deep-UV plasmonic resonators of aluminum for surface-enhanced circular dichroism and asymmetric photocatalysis
Embargo Date
2027-08-04
OA Version
Citation
Abstract
Chirality is a fundamental concept in stereochemistry that pertains to molecules that cannot be superimposed on their mirror images. The two enantiomers of a chiral molecule interact differently with circularly polarized light of opposite handedness, and the disparity in the absorption of left- and right-handed circularly polarized light defines circular dichroism. The electronic absorption bands of key biomolecules and pharmaceutical compounds typically lie within the UV range, between 180 nm and 280 nm—a range that does not overlap with the localized surface plasmon resonances of conventional gold or silver nanoparticle antennas. Aluminum nanostructures, however, support resonances in the UV range, generating significant interest in utilizing UV-resonant, nanostructured Al substrates to enhance the sensitivity of chiroptical spectroscopies, such as CD enhancement and asymmetric synthesis.In this dissertation, we demonstrated that large-area Al nanoparticle arrays, fabricated using hole-mask colloidal lithography, support size-tunable plasmonic resonances across the UV spectrum. The experimental CD enhancement of 2,2’-Bis(di-p-tolylphosphino)-1,1’-binaphthyl on the Al NP array was greater than that observed on the Ag NP array. Simulation-based analysis of the relative contributions of induced and inherent CD in both Al and Ag nanostructures—using the dissipated power in the films and nanostructures—revealed that the increase in CD for the UV-resonant Al NPs arose from both induced and inherent CD in the chiral film, while the induced CD in both Al and Ag NPs was comparable.
The subsequent section of this dissertation illustrates that large-area chiral Al NPs generated through glancing angle deposition exhibit strong UV resonance and distinct chirality. Previous studies have reported asymmetric photosynthesis of chiral molecules on chiral noble metal NPs. In this work, we showed that the fabricated chiral Al NPs possessed strong chirality and better spectral overlap with the reaction wavelength range. Experimental fluorescence data for tyrosine on chiral Al NPs with opposite handedness revealed that the photoreaction rates of tyrosine varied, with either slower or faster rates depending on the handedness of the chiral LSPRs on the Al NPs.
The strength of near-fields on nanoparticles decreases dramatically as the distance from the nanoparticle surface increases. As such, the primary hotspot for the interaction between chiral molecules and resonators is the surface of the resonators. However, this limitation can be addressed through the use of nanogaps. Nanogaps generate strong near-fields in the space between the gaps, rather than just on the surface, allowing interactions with chiral molecules away from the surface and thereby increasing the number of molecules detected by the near-fields. Nanogap-rich aluminum nanoholes were fabricated using colloidal lithography. The deep-UV resonances of the aluminum nanoholes exhibited good overlap with the absorption bands and CD spectrum peaks of the riboflavin film. A comparison of the CD response of riboflavin on the Al nanogaps, versus that on quartz without nanostructures or on silver nanogaps, highlights the advantages of the Al nanogaps. Simulation analysis of Al nanogaps using the dissipation power theorem further explained the enhancement of riboflavin CD, driven by the significant effect of inherent CD in the nanogaps.
Description
2025