Superparamagnetic nanoparticles (SPIONs) could enable cancer theranostics if magnetic resonance imaging (MRI) and magnetic hyperthermia treatment (MHT) were combined. However, the particle size of SPIONs is smaller than the pores of fenestrated capillaries in normal tissues because superparamagnetism is expressed only at a particle size <10 nm. Therefore, SPIONs leak from the capillaries of normal tissues, resulting in low accumulation in tumors. Furthermore, MHT studies have been conducted in an impractical way: direct injection of magnetic materials into tumor and application of hazardous alternating current (AC) magnetic fields. To accomplish effective enhancement of MRI contrast agents in tumors and inhibition of tumor growth by MHT with intravenous injection and a safe AC magnetic field, we clustered SPIONs not only to prevent their leakage from fenestrated capillaries in normal tissues, but also for increasing their relaxivity and the specific absorption rate. We modified the clusters with folic acid (FA) and polyethylene glycol (PEG) to promote their accumulation in tumors. SPION clustering and cluster modification with FA and PEG were achieved simultaneously via the thiol-ene click reaction. Twenty-four hours after intravenous injection of FA- and PEG-modified SPION nanoclusters (FA-PEG-SPION NCs), they accumulated locally in cancer (not necrotic) tissues within the tumor and enhanced the MRI contrast. Furthermore, 24 h after intravenous injection of the NCs, the mice were placed in an AC magnetic field with H = 8 kA/m and f = 230 kHz (Hf = 1.8×109 A/m∙s) for 20 min. The tumors of the mice underwent local heating by application of an AC magnetic field. The temperature of the tumor was higher than the surrounding tissues by ≈6°C at 20 min after treatment. Thirty-five days after treatment, the tumor volume of treated mice was one-tenth that of the control mice. Furthermore, the treated mice were alive after 12 weeks; control mice died up to 8 weeks after treatment.

Using a one-pot synthesis, thiol-organosilica nanoparticles (NPs) made from (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, and (3-mercaptopropyl)methyldimethoxysilane have been successfully prepared. We compared the synthesis processes of thiol-organosilica NPs made of these three kinds of organosilicates, as well as particles made from tetraethoxysilicate (TEOS), at concentrations varying between 6.25 and 200 mM. We examined three types of synthetic conditions: the Stöber method, in which particles are prepared in 65% ethanol, and two entirely aqueous solvent syntheses, containing either 2% or 27% ammonium hydroxide. The synthetic mixtures were examined using transmission electron microscopy (TEM) to evaluate the as-prepared NPs. The formation trends and rates for these organosilica NPs vary with differing organosilicate precursors, concentrations, and synthetic conditions. The Stöber method is not suitable for formation of thiol-organosilica NPs as compared with the case of TEOS, but the conditions without ethanol and with 27% ammonium hydroxide are suitable for the formation of thiol-organosilica NPs. The size distributions of the formed NPs were evaluated using TEM and dynamic light scattering. The mean diameters of NPs increase with increasing concentrations of silicate, but the size distributions of NPs prepared under various conditions also differ between silicate sources. Thiol-organosilica NPs internally functionalized with fluorescent dye were also prepared using a one-pot synthesis and were characterized using fluorescence microscopy. The thiol-organosilica NPs retain fluorescent dye maleimide very well. In addition, rhodamine B-doped thiol-organosilica NPs show higher fluorescence than thiol-organosilica NPs prepared with rhodamine red maleimide. The surface of thiol-organosilica NPs contains exposed thiol residues, allowing the covalent attachment of fluorescent dye maleimide and protein maleimide. This is the first report describing the synthesis of thiol-organosilica NPs made of three kinds of thiol-organosilicates, differences in nanoparticle formation due to the kinds and concentrations of thiol-organosilicate and due to synthetic conditions, and the advantages of thiol-organosilica NPs due to the existence of both interior and exterior thiol residues.

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We report the synthesis of smart nanoparticles (NPs) that generate heat in response to an alternating current magnetic field (ACMF) and that sequentially release an anticancer drug (doxorubicin, DOX). We further study the in vivo therapeutic efficacy of the combination of magnetic hyperthermia (MHT) and chemotherapy using the smart NPs for the treatment of multiple myeloma. The smart NPs are composed of a polymer with a glass-transition temperature (Tg) of 44°C, which contains clustered Fe3O4 NPs and DOX. The clustered Fe3O4 NPs produce heat when the ACMF is applied and rise above 44°C, which softens the polymer phase and leads to the release of DOX. The combination of MHT and chemotherapy using the smart NPs destroys cancer cells in the entire tumor and achieves a complete cure in one treatment without the recurrence of malignancy. Furthermore, the smart NPs have no significant toxicity.

Multifluorescent silica nanoparticles were synthesized by the Stöber method using conjugates of (3-aminopropyl)triethoxysilane and fluorescent dye-N-hydroxysuccinimide esters. The nanoparticles containing the fluorescent dyes were well dispersed and showed high, stable, and tunable fluorescence intensities. In addition, we prepared multifluorescent silica nanoparticles containing two kinds of fluorescent dyes and used the nanoparticles in biological applications. Flow cytometry analysis showed high and tuned fluorescence and multiple fluorescences from single nanoparticles with diameters of approximately 400 nm. Fluorescence microscopy analysis also showed high and tuned fluorescence, as well as multiple fluorescences from single nanoparticles and from cells labeled with multifluorescent silica nanoparticles. The intracellular distribution of nanoparticles was evaluated by confocal microscopy and electron microscopy. We discuss the advantages and demonstrate the usefulness of our nanoparticles in relation to commercially available fluorescent nanoparticles including quantum dots.