Abstract
Prussian blue (PB) is a coordination polymer studied since the early 18th century, historically known as a pigment. PB can be prepared in colloidal form with a straightforward synthesis. It has a strong charge-transfer absorption centered at ~700 nm, with a large tail in the Near-IR range. Irradiation of this band results in thermal relaxation and can be exploited to generate a local hyperthermia by irradiating in the so-called bio-transparent Near-IR window. PB nanoparticles are fully biocompatible (PB has already been approved by FDA) and biodegradable, this making them ideal candidates for in vivo use. While papers based on the imaging, drug-delivery and absorbing properties of PB nanoparticles have appeared and have been reviewed in the past decades, a very recent interest is flourishing with the use of PB nanoparticles as photothermal agents in biomedical applications. This review summarizes the syntheses and the optical features of PB nanoparticles in relation to their photothermal use and describes the state of the art of PB nanoparticles as photothermal agents, also in combination with diagnostic techniques.
Highlights
Prussian Blue (PB) is believed to be the oldest artificial coordination compound
In PB the Fe2+ cations are coordinated by the carbon atom of the cyanide (CN− ) ligand, that acts as a bridge with Fe3+ cations, that are octahedrally coordinated by 6 nitrogen atoms
Many of the papers describing the photothermal effect of PBnp propose a combined use of the photothermal properties coupled with imaging, drug delivery and chemotherapy functions
Summary
Prussian Blue (PB) is believed to be the oldest artificial coordination compound. It was accidentally prepared in the early 18th century by the colormaker Heinrich Diesbach from Berlin [1], its name following the geopolitical origin. The preparations of PB typically require mixing of Fe3+ salts with potassium hexacyanoferrate, K4 [Fe(CN)6 ], leading to different formula depending on the exact stoichiometry and preparation conditions Such formula may range from FeIII 4 [FeII (CN)6 ]3 ·xH2 O (x = 14–16) and KFeIII [FeII (CN)6 ]·xH2 O (x = 1–5) [1] that are commonly called ‘insoluble PB’ and ‘soluble PB’, respectively (oxidation states as roman superscripts are added for sake of clarity). In the latter case the obtained blue product historically received a different name, Turnbull a different name, Turnbull Blue, it is PB [4]: it forms after a redox reaction leading Blue, it is PB [4]: it forms after a redox reaction leading to Fe3+ and [FeII(CN)2+6]4−, to Fe3+ and [FeII (CN)6 ]4− , promoted by the coordination of the cyanide. C atoms ofIII thecenters cyanide[6]
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