Au nanorings for enhancing absorption and backscattering monitored with opticalcoherence tomography

Abstract

Preparation of a high-concentration Au nanoring (NR) water solution and its applicationsto the enhancement of image contrast in optical coherence tomography (OCT) and thegeneration of the photothermal effect in a bio-sample through localized surface plasmon(LSP) resonance are demonstrated. Au NRs are first fabricated on a sapphiresubstrate with colloidal lithography and secondary sputtering of Au, and thentransferred into a water solution through a liftoff process. By controlling the NRgeometry, the LSP dipole resonance wavelength in tissue can cover a spectralrange of 1300 nm for OCT scanning of deep tissue penetration. The extinctioncross sections of the fabricated Au NRs in water are estimated to give levels of10 − 10–10 − 9 cm2 near their LSP resonance wavelengths. The fabricated Au NRs are then delivered into pigadipose samples for OCT scanning. It is observed that, when resonant Au NRs aredelivered into such a sample, LSP resonance-induced Au NR absorption results in aphotothermal effect, making the opaque pig adipose cells transparent. Also, the deliveredAu NRs in the intercellular substance enhance the image contrast of OCT scanningthrough LSP resonance-enhanced scattering. By continuously OCT scanning a sample,both photothermal and image contrast enhancement effects are observed. However, bycontinually scanning a sample with a low scan frequency, only the image contrastenhancement effect is observed.