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Posted: Feb 18, 2015
Gold nanotubes for theranostic applications
(Nanowerk News) Photothermal therapy, also known as photothermal ablation or optical hyperthermia, has been actively explored as a minimally invasive approach to cancer therapy. It utilizes photothermal conversion agents, which strongly absorb light and convert the absorbed light into heat, to generate rapid localized heating to preferentially ablate cancerous cells.
The development of gold nanostructures as contrast agents is based on the ability to tune their optical properties via control over the localized surface plasmon modes. The photoacoustic signal-to-noise ratio can be significantly improved by carefully choosing the excitation laser wavelength within NIR region to minimize the light attenuation.
Hence, considerable efforts have been made to develop Au nanostructures active in the NIR window, such as Au nanorods, Au nanoshells, hollow Au nanospheres, and Au nanocages. These NIR-absorbing gold nanostructures have been exploited as theranostic nanosystems that integrate targeting, imaging, and therapy (chemotherapy via drug delivery and photothermal therapy) into one platform.
As a novel nanostructure with promise for theranostic applications, Au nanotubes (NTs) offer potential advantages over their solid counterparts.
First, as open-ended tubes they have large inner voids that can be filled with suitable drugs from small molecules through to proteins.
Second, they have inner and outer surfaces, which might provide routes for differential surface functionalization enabling selective attachment of moieties to the inside (such as drugs and imaging agents) and outside (targeting moieties, antifouling agents).
Third, they have open ends that make the inner surface accessible and allow subsequent incorporation of species within the tubes and can be used as a gate to control drug release.
In addition, for photoacoustic imaging and photothermal therapy, the hollow core can lower the heat capacity to allow better pulse heating.
Compared to their spherical counterparts, the elongated nanostructures have longer blood circulation times and show multivalence effect, that is, multiple binding sites of a functionalized NT to one cell, leading to improved cell adhesion and more effective targeting.