Block Copolymer-Encapsulated CaWO₄ Nanoparticles: Synthesis, Formulation, and Characterization

Abstract

We envision that CaWO4 (CWO) nanocrystals have the potential for use in biomedical imaging and therapy because of the unique ways this material interacts with high energy radiation (Figure 1). These applications, however, require development of nanoparticle (NP) formulations that are suitable for in vivo applications; primarily, the formulated nanoparticles should be sufficiently small, chemically and biologically inert, and stable against aggregation under physiological conditions. The present study demonstrates one such method of formulation, in which CWO nanoparticles are encapsulated in bio-inert block copolymer (BCP) micelles. For this demonstration, we prepared three different CWO nanocrystal samples having different sizes (3, 10 and 70 nm in diameter) and shapes (elongated vs. truncated rhombic). Depending on the specific synthesis method used, the as-synthesized CWO NPs contain different surfactant materials (citric acid, cetyl trimethylammonium bromide, or a mixture of oleic acid and oleylamine) in the coating layers. Regardless of the type of surfactant, the original surfactant coating can be replaced with a new enclosure formed by BCP materials using a solvent exchange method. Two types of BCPs have been tested: poly(ethylene glycol-block-n-butyl acrylate) (PEG-PnBA), and poly(ethylene glycol-block-D,L-lactic acid) (PEG-PLA). Both BCPs are able to produce fully PEGylated CWO NPs that are stable against aggregation under physiological salt conditions for very long periods of time (for at least three months). The optical and radio-luminescence properties of both BCP-encapsulated and surfactant-coated CWO NPs were extensively characterized. The study confirms that the BCP coating structure does not influence the luminescence properties of CWO NPs.

Technical Note: A simulation study on the feasibility of radiotherapy dose enhancement with calcium tungstate and hafnium oxide nano‐ and microparticles

“…CaWO 4 is a high Z, luminescent material first described by Thomas Edison in the Journal Nature in 1896, and is today being used in the search for Dark Matter due to its scintillation property . Our group has described a synthesis protocol for encapsulating a CaWO 4 NP in a bioinert block copolymer (BCP) micelle, while ensuring the fidelity of these encapsulated‐NPs luminescence under excitation . Lee et al measured the fluorescent peak at 420 nm (2.9 eV), with significant emission <400 nm into the UV spectrum.…”

Facile synthesis of alginate‐based calcium tungstate composite: A thermally stable blue emitting phosphor

“…[27][28][29] CaWO 4 possessing various morphologies have been successfully prepared by different approaches, including electrospinning, microemulsion technique, low-temperature nanocasting, sonochemical route, solvothermal method, and microwave irradiation. [30][31][32][33][34][35] However, most studies on the preparation of CaWO 4 were based on high-temperature treatment of the mixture of surfactants. Besides, it is difficult to tune the particle size and the aggregation of products.…”

“…Classically, the fluorescence effect of CaWO 4 is attributed to the electron transitions within WO 4 2− groups, in which the electron of O atoms is captured by the empty hole in W orbitals to arouse the luminescent behavior 27–29 . CaWO 4 possessing various morphologies have been successfully prepared by different approaches, including electrospinning, microemulsion technique, low‐temperature nanocasting, sonochemical route, solvo‐thermal method, and microwave irradiation 30–35 . However, most studies on the preparation of CaWO 4 were based on high‐temperature treatment of the mixture of surfactants.…”

Microemulsion‐Mediated Synthesis and Properties of Uniform Ln:CaWO4 (Ln = Eu, Dy) Nanophosphors with Multicolor Luminescence for Optical and CT Imaging

“…Much less attention has been paid to the synthesis of CaWO 4 -based particles in the nanometer-size range. In fact, only a few procedures have been reported on the formation of uniform nanospheres, [26] uniform nanorhomboids and nanocubes, [27] or nanoparticles with a less-defined shape, [28] most of them based on the use of cyclohexane/water microemulsions with cetyltrimethylammonium bromide (CTAB) as a stabilizing agent and different cosurfactants (hexanol, [27,28] penthanol [26] ). In this work, we demonstrate that by using cyclohexane/water-based microemulsions, with Triton X as the stabilizing agent and octanol as the cosurfactant, it is possible, under a certain set of experimental conditions, to obtain, for the first time, highly uniform nanoparticles with a new morphology (spindletype) for the CaWO 4 system.…”

“…Much less attention has been paid to the synthesis of CaWO 4 ‐based particles in the nanometer‐size range. In fact, only a few procedures have been reported on the formation of uniform nanospheres, uniform nanorhomboids and nanocubes, or nanoparticles with a less‐defined shape, most of them based on the use of cyclohexane/water microemulsions with cetyltrimethylammonium bromide (CTAB) as a stabilizing agent and different cosurfactants (hexanol,, penthanol).…”