thermal
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CuS nanoparticles: clinically favorable materials for photothermal applications? “Despite their promise for photothermal applications, gold nanostructures are not widely embraced...” Keywords: CuS • drug delivery • nanoparticle • photothermal therapy
Interest in the development of photothermal agents for clinical applications has passed several milestones. The first description of thermal-based treatment dates back to 1700 BC, when a glowing tip of a firedrill was employed for breast cancer therapy [1] . Since then, a variety of thermal sources (e.g., radiofrequency, microwaves and ultrasound waves) were developed; however, these sources have the limitation of nonselectivity, resulting in the same extent of damaging surrounding healthy tissues. In 1960, the first application of laser light as a thermal source represented a turning point. The collimation characteristics of laser light resulted in a narrow and high intensity beam with minimal damage to the healthy tissue [2] . Nevertheless, laser-induced thermal therapy requires high power density of laser output to achieve efficient tissue oblation in the clinic [3] . To overcome this limitation, photothermal agents with high capabilities of light-to-heat conversion were utilized, thus greatly reducing the laser energy requirement [4] . Traditional photothermal agents include photoabsorbing chromophores or dye molecules (e.g., indocyanine green and naphthalocyanines); however, these molecules are readily photobleached under laser irradiation. Interest in nanostructures, especially gold nanostructures (e.g., gold nanospheres [5] , gold nanorods [6] , gold nanoshells [7] and gold nanocages [8]) as photothermal agents has surged in the last decade. These nanostructures take the advantage of surface plasmon resonance (SPR) oscillations, and exhibit four to five orders of magnitude stronger absorption in the visible and near infrared (NIR) regions than conventional photoabsorbing molecules, thus
10.2217/NMM.14.2 © 2014 Future Medicine Ltd
enabling effective laser therapy at relatively lower energies. Additionally, these nanostructures present high photostability against photobleaching. All of these features formed the foundation for the clinical translation of first-in-man gold nanoshells (AuroLase™, Nanospectra Biosciences, Inc., TX, USA) for photothermal cancer therapy [9,10] . Despite their promise for photothermal applications, gold nanostructures are not widely embraced due to their shape-dependent photothermal effects, relatively high costs of synthesis and nondegradability. As an alternative to gold analogs, CuS nanoparticles (NPs) have emerged as a new class of photothermal agents in the past 3 years [11–13] . Compared with gold nanostructures, CuS NPs afford two major advantages in terms of their translational applications: consistent NIR absorption and low cost. The NIR light absorption of CuS NPs derives from the d–d energy band transition of Cu2+ ions instead of the SPR effects, and thus the absorption wavelength of CuS NPs is not affected by the particle shape, size and surrounding environment [11] . This feature benefits the applications of CuS NPs in several ways. First, the synthesis of CuS NPs does not require stringent control of morphology or shape (e.g., hollow nanospheres, nanoshells or nanorods) to retain SPR effects, contributing to an easy scale-up process. Second, photothermal CuS NPs can be formulated with a rather smaller size (
Editorial For reprint orders, please contact: [email protected]
CuS nanoparticles: clinically favorable materials for photothermal applications? “Despite their promise for photothermal applications, gold nanostructures are not widely embraced...” Keywords: CuS • drug delivery • nanoparticle • photothermal therapy
Interest in the development of photothermal agents for clinical applications has passed several milestones. The first description of thermal-based treatment dates back to 1700 BC, when a glowing tip of a firedrill was employed for breast cancer therapy [1] . Since then, a variety of thermal sources (e.g., radiofrequency, microwaves and ultrasound waves) were developed; however, these sources have the limitation of nonselectivity, resulting in the same extent of damaging surrounding healthy tissues. In 1960, the first application of laser light as a thermal source represented a turning point. The collimation characteristics of laser light resulted in a narrow and high intensity beam with minimal damage to the healthy tissue [2] . Nevertheless, laser-induced thermal therapy requires high power density of laser output to achieve efficient tissue oblation in the clinic [3] . To overcome this limitation, photothermal agents with high capabilities of light-to-heat conversion were utilized, thus greatly reducing the laser energy requirement [4] . Traditional photothermal agents include photoabsorbing chromophores or dye molecules (e.g., indocyanine green and naphthalocyanines); however, these molecules are readily photobleached under laser irradiation. Interest in nanostructures, especially gold nanostructures (e.g., gold nanospheres [5] , gold nanorods [6] , gold nanoshells [7] and gold nanocages [8]) as photothermal agents has surged in the last decade. These nanostructures take the advantage of surface plasmon resonance (SPR) oscillations, and exhibit four to five orders of magnitude stronger absorption in the visible and near infrared (NIR) regions than conventional photoabsorbing molecules, thus
10.2217/NMM.14.2 © 2014 Future Medicine Ltd
enabling effective laser therapy at relatively lower energies. Additionally, these nanostructures present high photostability against photobleaching. All of these features formed the foundation for the clinical translation of first-in-man gold nanoshells (AuroLase™, Nanospectra Biosciences, Inc., TX, USA) for photothermal cancer therapy [9,10] . Despite their promise for photothermal applications, gold nanostructures are not widely embraced due to their shape-dependent photothermal effects, relatively high costs of synthesis and nondegradability. As an alternative to gold analogs, CuS nanoparticles (NPs) have emerged as a new class of photothermal agents in the past 3 years [11–13] . Compared with gold nanostructures, CuS NPs afford two major advantages in terms of their translational applications: consistent NIR absorption and low cost. The NIR light absorption of CuS NPs derives from the d–d energy band transition of Cu2+ ions instead of the SPR effects, and thus the absorption wavelength of CuS NPs is not affected by the particle shape, size and surrounding environment [11] . This feature benefits the applications of CuS NPs in several ways. First, the synthesis of CuS NPs does not require stringent control of morphology or shape (e.g., hollow nanospheres, nanoshells or nanorods) to retain SPR effects, contributing to an easy scale-up process. Second, photothermal CuS NPs can be formulated with a rather smaller size (
