In this work we demonstrate the potential use of gold nanoparticles as contrast agents for the optical coherence tomography (OCT) imaging technique in dentistry. Here, a new in situ photothermal reduction procedure was developed, producing spherical gold nanoparticles inside dentinal layers and tubules. Gold ions were dispersed in the primer of commercially available dental bonding systems. After the application and permeation in dentin by the modified adhesive systems, the dental bonding materials were photopolymerized concurrently with the formation of gold nanoparticles. The gold nanoparticles were visualized by scanning electron microscopy (SEM). The SEM images show the presence of gold nanospheres in the hybrid layer and dentinal tubules. The diameter of the gold nanoparticles was determined to be in the range of 40 to 120 nm. Optical coherence tomography images were obtained in two- and three-dimensions. The distribution of nanoparticles was analyzed and the extended depth of nanosphere production was determined. The results show that the OCT technique, using in situ formed gold nanoparticles as contrast enhancers, can be used to visualize dentin structures in a non-invasive and non-destructive way.
Metal nanofabrication techniques have become increasingly important for photonic applications with rapid
developments in plasmonics, nanophotonics and metamaterials. While two-dimensional (2D) techniques to create high
resolution metal patterns are readily available, it is more difficult to fabricate 3D metal structures that are required for
new applications in these fields. We present a femtosecond laser technique for 3D direct-writing silver nanostructures
embedded inside a polymer. We induce the photoreduction of silver ions through non-linear absorption in a sample
doped with a silver salt. Utilizing nonlinear optical interactions between the chemical precursors and femtosecond
pulses, we limit silver-ion photoreduction processes to a focused volume smaller than that of the diffraction-limit. The
focal volume is scanned rapidly in 3D by means of a computer-controlled translation stage to produce complex patterns.
Our technique creates dielectric-supported silver structures, enabling the nanofabrication of silver patterns with
disconnected features in 3D. We obtain 300 nm resolution.