Near-infrared
(NIR) fluorescence provides a new avenue for biomedical
fluorescence imaging that allows for the tracking of fluorophore through
several centimeters of biological tissue. However, such fluorophores
are rare and, due to accumulation-derived toxicity, are often restricted
from clinical applications. Deep tissue imaging not only provided
by near-infrared fluorophores but also conventionally carried out
by magnetic resonance imaging (MRI) or computed tomography (CT) is
also hampered by the toxicity of the contrast agents. This work offers
a biocompatible imaging solution: cerium oxide (CeO2) nanocubes
doped with ytterbium or neodymium, and co-doped with gadolinium, showing
simultaneous potential for near-infrared (NIR) fluorescence and magnetic
resonance imaging (MRI) applications. A synthetic process described
in this work allows for the stable incorporation of ytterbium or neodymium,
both possessing emissive transitions in the NIR. As a biocompatible
nanomaterial, the CeO2 nanocubes act as an ideal host material
for doping, minimizing lanthanide fluorescence self-quenching as well
as any potential toxicity associated with the dopants. The uptake
of nanocubes by HeLa cells maximized at 12 h was monitored by hyperspectral
imaging of the ytterbium or neodymium NIR emission, indicating the
capacity of the lanthanide-doped nanocubes for in vitro and a potential for in vivo fluorescence imaging.
The co-doped nanocubes demonstrate no significant loss of NIR emission
intensity upon co-doping with 2 atomic % gadolinium and exhibit magnetic
susceptibilities in the range of known negative contrast agents. However,
a small increase to 6 atomic % gadolinium significantly affects the
magnetic susceptibility ratio (r
2/r
1), shifting closer to the positive contrast
range and suggesting the potential use of the CeO2 nanocube
matrix doped with selected rare-earth ions as a tunable MRI contrast
agent with NIR imaging capabilities.
We present optical studies of two different size distributions of silver triangular nanoprisms, one with a dipole resonance at 520 nm and the other with a dipole resonance at 650 nm, placed in different media. Significant wavelength-dependent depolarization of scattered light from the silver nanoprisms suspended in water indicates strong interference of multiple surface plasmon resonant modes in the same particle. We use this depolarization as a probe of light scattering by the nanoprisms in a lipid solution due to the rejection of a polarized background scattering. Also, the silver nanoprisms were embedded in a polyvinyl alcohol polymer matrix and oriented by stretching the polymer/nanoprism nanocomposite films. We observe significantly increased linear dichroism in the region associated with the plasmonic in-plane dipole mode upon stretching. Additionally, there is a weaker linear dichroism in the region associated with out-of-plane modes, which vanish in the extinction spectrum of the stretched nanocomposite film.
Europium-doped CeO2 nanomaterials have been investigated for a variety of sensing and biological applications, as doping enhances the catalytic activity of CeO2 and contributed visible fluorescence to the nanomaterial. However,...
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