High-contrast paramagnetic fluorescent mesoporous silica nanorods as a multifunctional cell-imaging probe

Gadolinium oxide nanoparticles and aptamer-functionalized silver nanoclusters-based multimodal molecular imaging nanoprobe for optical/magnetic resonance cancer cell imaging

Multimodal molecular imaging has attracted more and more interest from researchers due to its combination of the strengths of each imaging modality. The development of specific and multifunctional molecular imaging probes is the key for this method. In this study, we fabricated an optical/magnetic resonance (MR) dual-modality molecular imaging nanoprobe, polyethylene glycol-coated ultrasmall gadolinium oxide (PEG-Gd2O3)/aptamer-Ag nanoclusters (NCs), for tracking cancer cells. To achieve this aim, PEG-Gd2O3 nanoparticles (NPs) as magnetic resonance imaging (MRI) contrast agent and aptamer functionalized silver nanoclusters (aptamer-Ag NCs) as fluorescence reporter were first synthesized by a one-pot approach, respectively. They were then conjugated by the covalent coupling reaction between the carboxyl group on the surface of PEG-Gd2O3 NPs and amino group modified on the 5'-end of AS1411 aptamer. With a suitable ratio, the fluorescence intensity of aptamer-Ag NCs and MR signal of PEG-Gd2O3 nanoparticles could both be enhanced after the formation of PEG-Gd2O3/aptamer-Ag NCs nanoprobe, which favored their application for multimodal molecular imaging. With this nanoprobe, MCF-7 tumor cells could be specifically tracked by both fluorescence imaging and magnetic resonance imaging in vitro.

Color Tunable Gd-Zn-Cu-In-S/ZnS Quantum Dots for Dual Modality Magnetic Resonance and Fluorescence Imaging

Inorganic nanoparticles have been introduced into biological systems as useful probes for in vitro diagnosis and in vivo imaging, due to their relatively small size and exceptional physical and chemical properties. A new kind of color tunable Gd-Zn-Cu-In-S/ZnS (GZCIS/ZnS) quantum dots (QDs) with stable crystal structure was successfully synthesized and utilized for magnetic resonance (MR) and fluorescence dual modality imaging. This strategy allows successful fabrication of GZCIS/ZnS QDs by incorporating Gd into ZCIS/ZnS QDs to achieve great MR enhancement without compromising the fluorescence properties of the initial ZCIS/ZnS QDs. The as-prepared GZCIS/ZnS QDs show high T₁ MR contrast as well as "color-tunable" photoluminescence (PL) in the range of 550-725 nm by adjusting the Zn/Cu feeding ratio with high PL quantum yield (QY). The GZCIS/ZnS QDs were transferred into water via a bovine serum albumin (BSA) coating strategy. The resulting Cd-free GZCIS/ZnS QDs reveal negligible cytotoxicity on both HeLa and A549 cells. Both fluorescence and MR imaging studies were successfully performed in vitro and in vivo. The results demonstrated that GZCIS/ZnS QDs could be a dual-modal contrast agent to simultaneously produce strong MR contrast enhancement as well as fluorescence emission for in vivo imaging.

Biosafe nanoscale pharmaceutical adjuvant materials

Thanks to developments in the field of nanotechnology over the past decades, more and more biosafe nanoscale materials have become available for use as pharmaceutical adjuvants in medical research. Nanomaterials possess unique properties which could be employed to develop drug carriers with longer circulation time, higher loading capacity, better stability in physiological conditions, controlled drug release, and targeted drug delivery. In this review article, we will review recent progress in the application of representative organic, inorganic and hybrid biosafe nanoscale materials in pharmaceutical research, especially focusing on nanomaterial-based novel drug delivery systems. In addition, we briefly discuss the advantages and notable functions that make these nanomaterials suitable for the design of new medicines; the biosafety of each material discussed in this article is also highlighted to provide a comprehensive understanding of their adjuvant attributes.

An efficient rose bengal based nanoplatform for photodynamic therapy

Organically modified mesoporous silica nanoparticles (MSNs) containing rose bengal (RB), a xanthene dye, were successfully synthesized. RB-modified MSNs have shown a relevant photostability and a high efficiency in the photoproduction and delivery of singlet oxygen ((1)O2), which is particularly promising for photodynamic therapy (PDT) applications. In vitro tests have evidenced that RB-MSNs are able to reduce cell proliferation in one of the most aggressive skin cancer types (SK-MEL-28) after green-light irradiation.

Biodegradable polysilsesquioxane nanoparticles as efficient contrast agents for magnetic resonance imaging

Polysilsesquioxane (PSQ) nanoparticles are crosslinked homopolymers formed by condensation of functionalized trialkoxysilanes, and provide an interesting platform for developing biologically and biomedically relevant nanomaterials. In this work, the design and synthesis of biodegradable PSQ particles with extremely high payloads of paramagnetic Gd(III) centers is explored, for use as efficient contrast agents for magnetic resonance imaging (MRI). Two new bis(trialkoxysilyl) derivatives of Gd(III) diethylenetriamine pentaacetate (Gd-DTPA) containing disulfide linkages are synthesized and used to form biodegradable Gd-PSQ particles by base-catalyzed condensation reactions in reverse microemulsions. The Gd-PSQ particles, PSQ-1 and PSQ-2, carry 53.8 wt% and 49.3 wt% of Gd-DTPA derivatives, respectively. In addition, the surface carboxy groups on the PSQ-2 particles can be modified with polyethylene glycol (PEG) and the anisamide (AA) ligand to enhance biocompatibility and cell uptake, respectively. The Gd-PSQ particles are readily degradable to release the constituent Gd(III) chelates in the presence of endogenous reducing agents such as cysteine and glutathione. The MR relaxivities of the Gd-PSQ particles are determined using a 3T MR scanner, with r1 values ranging from 5.9 to 17.8 mMs(-1) on a per-Gd basis. Finally, the high sensitivity of the Gd-PSQ particles as T1 -weighted MR contrast agents is demonstrated with in vitro MR imaging of human lung and pancreatic cancer cells. The enhanced efficiency of the anisamide-functionalized PSQ-2 particles as a contrast agent is corroborated by both confocal laser scanning microscopy imaging and ICP-MS analysis of Gd content in vitro.

Biocatalytic release of an anticancer drug from nucleic-acids-capped mesoporous SiO2 Using DNA or molecular biomarkers as triggering stimuli

DNA-gated mesoporous SiO2 nanoparticles, MP-SiO2 NPs, loaded with rhodamine B, RhB, act as "smart" materials that reveal complementary "sense" and "release" functionalities. The unlocking of the DNA pore-capping units is achieved by the biocatalytic cleavage of the DNA, and the unlocking process is amplified by the regeneration of the analyte-trigger. The RhB-loaded MP-SiO2 NPs are capped with nucleic acid hairpin structures that lock the RhB in the pores. Opening of the hairpin structures by a nucleic acid analyte trigger or by the formation of an aptamer-substrate (ATP) complex leads to the formation of duplex structures being cleaved by exonuclease III, Exo III, or the nicking enzyme, Nb. BbvCI. This results in the regeneration of the target analytes, the autonomous unlocking of the pores, and the release of RhB. The systems reveal selectivity, and one-, two-, three-base mutations in the target DNA, or substitution of ATP with other triphosphate nucleotides, prohibit the unlocking of the pores. In analogy to the biocatalytic release of the model fluorophore substrates, the anticancer drug camptothecin, CPT, was entrapped in the pores and locked by the 1 or 11 hairpin structures. The drug was released from the pores in the presence of the nucleic acid 2 or ATP and the Exo III, as biocatalyst. Similarly, CPT locked in the pores by the 6 or 12 hairpins were released from the pores in the presence of ATP and Nb. BbvCI, as nicking enzyme, respectively. The effects of the CPT-loaded MP-SiO2 NPs, capped with the ATP-dependent lock 6, on the viability of MDA-231 breast cancer cells and MCF-10a normal breast cells were examined. We find that after 48 h, 65% cell death was observed for the MDA-231 cancer cells, where only 25% cell death was observed for the normal cells. The higher cell death of the cancer cells correlates well with the enhanced metabolic synthesis of ATP in the cancerous cells.

Mesoporous silica with fibrous morphology: a multifunctional core-shell platform for biomedical applications

Multifunctional mesoporous silica nanocomposites are attractive carriers for targeted drug delivery in nanomedicine. Although promising developments have been made in the fabrication of multifunctional mesoporous silica nanocomposites, the design and mass production of novel multifunctional carriers are still challenging. This paper reports the facile one-pot fabrication of a multifunctional inorganic composite composed of superparamagnetic Fe3O4 nanoparticles and coated dye-functionalized mesoporous silica with a high specific surface area. The resulting composite particles had a tunable particle size, special open pore channels with high specific surface area, which is quite favorable for drug loading and release properties, as well as luminescent and superparamagnetic properties suitable for targeted drug delivery and tracking. This composite exhibited low toxicity, suggesting potential biomedical applications.

Color Doppler ultrasound and gamma imaging of intratumorally injected 500 nm iron-silica nanoshells

Perfluoropentane gas filled iron-silica nanoshells have been developed as stationary ultrasound contrast agents for marking tumors to guide surgical resection. It is critical to establish their long-term imaging efficacy, as well as biodistribution. This work shows that 500 nm Fe-SiO2 nanoshells can be imaged by color Doppler ultrasound over the course of 10 days in Py8119 tumor bearing mice. The 500 nm nonbiodegradable SiO2 and biodegradable Fe-SiO2 nanoshells were functionalized with diethylenetriamine pentaacetic acid (DTPA) ligand and radiolabeled with (111)In(3+) for biodistribution studies in nu/nu mice. The majority of radioactivity was detected in the liver and kidneys following intravenous (IV) administration of nanoshells to healthy animals. By contrast, after nanoshells were injected intratumorally, most of the radioactivity remained at the injection site; however, some nanoshells escaped into circulation and were distributed similarly as those given intravenously. For intratumoral delivery of nanoshells and IV delivery to healthy animals, little difference was seen between the biodistribution of SiO2 and biodegradable Fe-SiO2 nanoshells. However, when nanoshells were administered IV to tumor bearing mice, a significant increase was observed in liver accumulation of SiO2 nanoshells relative to biodegradable Fe-SiO2 nanoshells. Both SiO2 and Fe-SiO2 nanoshells accumulate passively in proportion to tumor mass, during intravenous delivery of nanoshells. This is the first report of the biodistribution following intratumoral injection of any biodegradable silica particle, as well as the first report demonstrating the utility of DTPA-(111)In labeling for studying silica nanoparticle biodistributions.

Effects of Mesoporous Silica Coating and Post-Synthetic Treatment on the Transverse Relaxivity of Iron Oxide Nanoparticles

Mesoporous silica nanoparticles have the capacity to load and deliver therapeutic cargo and incorporate imaging modalities, making them prominent candidates for theranostic devices. One of the most widespread imaging agents utilized in this and other theranostic platforms is nanoscale superparamagnetic iron oxide. Although several core-shell magnetic mesoporous silica nanoparticles presented in the literature have provided high T₂ contrast in vitro and in vivo, there is ambiguity surrounding which parameters lead to enhanced contrast. Additionally, there is a need to understand the behavior of these imaging agents over time in biologically relevant environments. Herein, we present a systematic analysis of how the transverse relaxivity (r₂) of magnetic mesoporous silica nanoparticles is influenced by nanoparticle diameter, iron oxide nanoparticle core synthesis, and the use of a hydrothermal treatment. This work demonstrates that samples which did not undergo a hydrothermal treatment experienced a drop in r₂ (75% of original r₂ within 8 days of water storage), while samples with hydrothermal treatment maintained roughly the same r₂ for over 30 days in water. Our results suggest that iron oxide oxidation is the cause of the r₂ loss, and this oxidation can be prevented both during synthesis and storage by the use of deoxygenated conditions during nanoparticle synthesis. The hydrothermal treatment also provides colloidal stability, even in acidic and highly salted solutions, and a resistance against acid degradation of the iron oxide nanoparticle core. The results of this study show the promise of multifunctional mesoporous silica nanoparticles but will also likely inspire further investigation into multiples types of theranostic devices, taking into consideration their behavior over time and in relevant biological environments.

Smart mesoporous SiO2 nanoparticles for the DNAzyme-induced multiplexed release of substrates

The fluorescent dyes methylene blue, MB(+), and thionine, Th(+), can be trapped in the pores of mesoporous silica, MP-SiO(2), by means of functional nanostructures consisting of the Mg(2+)- or Zn(2+)-dependent DNAzyme sequences. In the presence of Mg(2+) or Zn(2+) ions the respective DNAzymes are activated, leading to the specific cleavage of the respective caps, and the selective release of MB(+) or Th(+). The enlargement of the conserved loop domains of the Mg(2+)- or Zn(2+)-dependent DNAzyme sequences with foreign nucleotides prohibits the formation of active DNAzymes and eliminates the release of the respective dyes. This is due to the flexibility of the loops that lacks affinity for the association of the ions. The insertion of aptamer sequences (e.g., the adenosine-5'-triphosphate (ATP) aptamer) or ion-binding sequences (e.g., T-rich Hg(2+) ion-binding domains) as foreign components to the loop regions allows the formation of active Mg(2+)- or Zn(2+)-dependent DNAzyme structures through the cooperative formation of aptamer-ATP complexes or T-Hg(2+)-T bridges. These aptamer-substrate complexes or T-Hg(2+)-T bridges allosterically stabilize and activate the DNAzymes, thus allowing the selective release of the fluorescent substrates MB(+) or Th(+). The metal ion-driven DNAzyme release of substrates from the pores of MP-SiO(2), and particularly the allosteric activation of the DNAzymes through cooperative aptamer-substrate complexes or metal-ion bridges, has important future nanomedical implications for targeted release of drugs. This is demonstrated with the triggered release of the anticancer drug, doxorubicin, by the Mg(2+)-DNAzyme-locked pores or by the aptamer-ATP complex-triggered activation of the Mg(2+)-dependent DNAzyme.

Evaluation of the antibacterial activity and biocompatibility for silver nanoparticles immobilized on nano silicate platelets

Silver nanoparticles (AgNPs) are known for their bactericidal abilities. The antibacterial potency is dependent on the particle size and dispersion status. In this study, we synthesized AgNP/NSP nanohybrids in two different weight ratios (1/99 and 8/92) using the fully exfoliated clay, i.e., nanosilicate platelets (NSP), as a dispersing agent and carrier for AgNPs. Due to the size of NSP, the immobilized AgNPs do not enter cells readily, which may lower the risk associated with the cellular uptake of AgNPs. The biocompatibility, immunological response, and antimicrobial activities of AgNP/NSP hybrids were evaluated. The results revealed that AgNP/NSP hybrids elicited merely mild inflammatory response and retained the outstanding antibacterial activity. The hybrids were further embedded in poly(ether)urethane (PEU) to increase the biocompatibility. At the same silver content (20 ppm), the PEU-AgNP/NSP nanocomposites were nontoxic to mouse skin fibroblasts, while simultaneously exhibiting nearly complete bacterial growth reduction (99.9%). PEU containing the same amount of free AgNPs did not display such an effect. Our results verify the better biosafety of the AgNPs/NSP hybrids and their polymer nanocomposites for further clinical use.

The application of super paramagnetic iron oxide-labeled mesenchymal stem cells in cell-based therapy

Mesenchymal stem cell (MSC)-based therapy has great potential for tissue regeneration. However, being able to monitor the in vivo behavior of implanted MSCs and understand the fate of these cells is necessary for further development of successful therapies and requires an effective, non-invasive and non-toxic technique for cell tracking. Super paramagnetic iron oxide (SPIO) is an idea label and tracer of MSCs. MRI can be used to follow SPIO-labeled MSCs and has been proposed as a gold standard for monitoring the in vivo biodistribution and migration of implanted SPIO-labeled MSCs. This review discusses the biological effects of SPIO labeling on MSCs and the therapeutic applications of local or systemic delivery of these labeled cells.

Functional silica nanoparticles for redox-triggered drug/ssDNA co-delivery

A mesoporous silica nanoparticle (MSNP) based co-delivery system is developed in order to deliver simultaneously drug and single strand DNA (ssDNA) in a controlled manner. Negatively charged ssDNA as a model gene is immobilized onto the surface of positively charged ammonium-functionalized MSNPs through electrostatic interaction, effectively blocking the loaded drugs within the mesopores of MSNPs. When the pre-installed disulfide bond on the ammonium unit is broken by the addition of the reducing agent such as dithiothreitol or glutathione, the ssDNA network on the surface is freed, leading to the release of the loaded drug molecules from the mesopores. The cell investigations indicate that the functional nanoparticles have a very low cytotoxicity under the concentrations measured. The doxorubicin-loaded and ssDNA-coated nanoparticles show an enhanced cellular internalization, leading to a successful drug/ssDNA co-delivery in vitro for significant apoptosis of Hela cancer cells as compared with that of free doxorubicin. The obtained experimental results indicate promising applications of the functional nanoparticles in cancer treatment.

In vitro biocompatibility of calcined mesoporous silica particles and fetal blood cells

Background:

The biocompatibility of two forms of calcined mesoporous silica particles, labeled as MCM41-cal and SBA15-cal, with fetal blood mononuclear cells was assessed in vitro.

Methods and results:

Fetal mononuclear cells were isolated from umbilical cord blood and exposed to 0.5 mg/mL of MCM41-cal or SBA15-cal for several hours. Transmission electron micrographs confirmed the presence of particles in the cytosol of macrophages, neutrophils, and lymphocytes without noticeable damage to the cellular organelles. The particles (especially MCM41-cal) were in close proximity to plasma, and nuclear and mitochondrial membranes. Biocompatibility was assessed by a functional assay that measured cellular respiration, ie, mitochondrial O₂ consumption. The rate of respiration (k_c, in μM O₂ per minute per 10⁷ cells) for untreated cells was 0.42 ± 0.16 (n = 10), for cells treated with MCM41-cal was 0.39 ± 0.22 (n = 5, P > 0.966) and for cells treated with SBA15-cal was 0.44 ± 0.13 (n = 5, P > 0.981).

Conclusion:

The results show reasonable biocompatibility of MCM41-cal and SBA15-cal in fetal blood mononuclear cells. Future studies are needed to determine the potential of collecting fetal cells from a fetus or neonate, loading the cells in vitro with therapeutic MCM41-cal or SBA15-cal, and reinfusing them into the fetus or neonate.

Magnetic and optical properties of multifunctional core-shell radioluminescence nanoparticles

When X-rays irradiate radioluminescence nanoparticles, they generate visible and near infrared light that can penetrate through centimeters of tissue. X-ray luminescence tomography (XLT) maps the location of these radioluminescent contrast agents at high resolution by scanning a narrow X-ray beam through the tissue sample and collecting the luminescence at every position. Adding magnetic functionality to these radioluminescent particles would enable them to be guided, oriented, and heated using external magnetic fields, while their location and spectrum could be imaged with XLT and complementary magnetic resonance imaging. In this work, multifunctional monodispersed magnetic radioluminescent nanoparticles were developed as potential drug delivery carriers and radioluminescence imaging agents. The particles consisted of a spindle-shaped magnetic γ-Fe2O3 core and a radioluminescent europium-doped gadolinium oxide shell. Particles with solid iron oxide cores displayed saturation magnetizations consistent with their ~13% core volume, however, the iron oxide quenched their luminescence. In order to increase the luminescence, we partially etched the iron oxide core in oxalic acid while preserving the radioluminescent shell. The core size was controlled by the etching time which in turn affected the particles' luminescence and magnetic properties. Particles with intermediate core sizes displayed both strong magnetophoresis and luminescence properties. They also served as MRI contrast agents with relaxivities of up to 58 mM-1s-1 (r2) and 120 mM-1s-1 (r2*). These particles offer promising multimodal MRI/fluorescence/X-ray luminescence contrast agents. Our core-shell synthesis technique offers a flexible method to control particle size, shape, and composition for a wide range of biological applications of magnetic/luminescent nanoparticles.

Magnetic field enhanced cell uptake efficiency of magnetic silica mesoporous nanoparticles

The advantages of using magnetic mesoporous silica nanoparticles (M-MSNs) in biomedical applications have been widely recognized. However, poor uptake efficiency may hinder the potential of M-MSNs in many applications, such as cell tracking, drug delivery, fluorescence and magnetic resonance imaging. An external magnetic field may improve the cellular uptake efficiency. In this paper, we evaluated the effect of a magnetic field on the uptake of M-MSNs. We found that the internalization of M-MSNs by A549 cancer cells could be accelerated and enhanced by a magnetic field. An endocytosis study indicated that M-MSNs were internalized by A549 cells mainly through an energy-dependent pathway, namely clathrin-induced endocytosis. Transmission electron microscopy showed that M-MSNs were trafficked into lysosomes. With the help of a magnetic field, anticancer drug-loaded M-MSNs induced elevated cancer cell growth inhibition.

In vivo biodistribution and pharmacokinetics of silica nanoparticles as a function of geometry, porosity and surface characteristics

The in vivo biodistribution and pharmacokinetics of silica nanoparticles (SiO(2)) with systematically varied geometries, porosities, and surface characteristics were investigated in immune-competent CD-1 mice via the intravenous injection. The nanoparticles were taken up extensively by the liver and spleen. Mesoporous SiO(2) exhibited higher accumulation in the lung than nonporous SiO(2) of similar size. This accumulation was reduced by primary amine modification of the nanoparticles. High aspect ratio, amine-modified mesoporous nanorods showed enhanced lung accumulation compared to amine-modified mesoporous nanospheres. Accumulation of the nanoparticles was mainly caused by passive entrapment in the discontinuous openings in the endothelium of the liver and spleen or in the pulmonary capillaries, and was highly dependent on nanoparticle hydrodynamic size in circulation. The SiO(2) were likely internalized by the reticulo-endothelial system (RES) following physical sequestration in the liver and spleen. The nanoparticles that were transiently associated with the lung were re-distributed out of this organ without significant internalization. Pharmacokinetic analysis showed that all SiO(2) were rapidly cleared from systemic circulation. Amine-modified or nonporous nanoparticles possessed a higher volume of distribution at steady state than their pristine counterparts or mesoporous SiO(2). In all, surface characteristics and porosity played important roles in influencing SiO(2) biodistribution and pharmacokinetics. Increasing the aspect ratio of amine-modified mesoporous SiO(2) from 1 to 8 resulted in increased accumulation in the lung.

Visualizing dynamics of sub-hepatic distribution of nanoparticles using intravital multiphoton fluorescence microscopy

Nanoparticles that do not undergo renal excretion or in vivo degradation into biocompatible debris often accumulate in the reticuloendothelial system, also know as the mononuclear phagocyte system, with undesired consequences that limit their clinical utility. In this work, we report the first application of intravital multiphoton fluorescence microscopy to dynamically track the hepatic metabolism of nanoparticles with subcellular resolution in real time. Using fluorescently labeled mesoporous silica nanoparticles (MSNs) in mice as a prototypical model, we observed significant hepatocyte uptake of positively charged, but not negatively charged, moieties. Conversely, in vivo imaging of negatively charged, but not positively charged, MSNs reveals an overwhelming propensity for the former's rapid uptake by Kupffer cells in liver sinusoids. Since the only prerequisite for these studies was that nanoparticles are fluorescently labeled and not of a specific composition or structure, the techniques we present can readily be extended to a wide variety of nanoparticle structures and surface modifications (e.g., shape, charge, hydrophobicity, PEGylation) in the preclinical assessment and tailoring of their hepatotoxicities and clearances.

MAGNETIC NANOPARTICLE LABELING OF CULTURED CANCER CELL LINE WITHOUT TRANSFECTION AGENT

Magnetic nanoparticle (MNP) labeling of stem cell has been proved its efficacy for cell trafficking. Most of the labeling technique requires mixture of iron oxide nanoparticles and transfection agent. Stem cells with ionic MNP without the aid of transfection agent were labeled previously. The possibility of high efficiency labeling of cultured cancer cell, HeLa cell, by using ionic MNP is proposed. The labeled cell morphology was observed and the intracellular iron content was determined by spectrophotometry. The cell character change was evaluated by flow cytometry where front scattering count and side scattering count (SSC) were recorded. The imaging ability of the labeling method was determined by T2 weighted magnetic resonance (MR) imaging. Labeled MNPs were accumulated at cytoplasm is observed and the iron content of labeled cell could reach 27 pg/cell. There is no cell diameter change but the cell granularity increased according to SSC data from flow cytometry. Under clinical 1.5T MR imaging, we could detect labeled cells easily were detected at the cell number of 1 × 105. It is concluded that labeling of cancer cell with ionic MNPs without transfection agent is an efficient labeling method which will provide non-invasive imaging method for monitoring cancer behavior.

Influence of geometry, porosity, and surface characteristics of silica nanoparticles on acute toxicity: their vasculature effect and tolerance threshold

Silica nanoparticles (SiO(2)) are widely used in biomedical applications such as drug delivery, cell tracking, and gene transfection. The capability to control the geometry, porosity, and surface characteristics of SiO(2) further provides new opportunities for their applications in nanomedicine. Concerns however remain about the potential toxic effects of SiO(2) upon exposure to biological systems. In the present study, the acute toxicity of SiO(2) of systematically varied geometry, porosity, and surface characteristics was evaluated in immune-competent mice when administered intravenously. Results suggest that in vivo toxicity of SiO(2) was mainly influenced by nanoparticle porosity and surface characteristics. The maximum tolerated dose (MTD) increased in the following order: mesoporous SiO(2) (aspect ratio 1, 2, 8) at 30-65 mg/kg < amine-modified mesoporous SiO(2) (aspect ratio 1, 2, 8) at 100-150 mg/kg < unmodified or amine-modified nonporous SiO(2) at 450 mg/kg. The adverse reactions above MTDs were primarily caused by the mechanical obstruction of SiO(2) in the vasculature that led to congestion in multiple vital organs and subsequent organ failure. It was revealed that hydrodynamic sizes of SiO(2) post-protein exposure had an important implication in relating SiO(2) physicochemical properties with their vasculature impact and resultant tolerance threshold, as the larger the hydrodynamic size in the presence of serum protein, the lower the MTD. This study sheds light on the rational design of SiO(2) to minimize in vivo toxicity and provides a critical guideline in selecting SiO(2) as the appropriate system for nanomedicine applications.

Mesoporous silica nanoparticles: synthesis, biocompatibility and drug delivery

In the past decade, mesoporous silica nanoparticles (MSNs) have attracted more and more attention for their potential biomedical applications. With their tailored mesoporous structure and high surface area, MSNs as drug delivery systems (DDSs) show significant advantages over traditional drug nanocarriers. In this review, we overview the recent progress in the synthesis of MSNs for drug delivery applications. First, we provide an overview of synthesis strategies for fabricating ordered MSNs and hollow/rattle-type MSNs. Then, the in vitro and in vivo biocompatibility and biotranslocation of MSNs are discussed in relation to their chemophysical properties including particle size, surface properties, shape, and structure. The review also highlights the significant achievements in drug delivery using mesoporous silica nanoparticles and their multifunctional counterparts as drug carriers. In particular, the biological barriers for nano-based targeted cancer therapy and MSN-based targeting strategies are discussed. We conclude with our personal perspectives on the directions in which future work in this field might be focused.

Long-term multimodal imaging of tumor draining sentinel lymph nodes using mesoporous silica-based nanoprobes

The imaging of sentinel lymph nodes (SLNs), the first defense against primary tumor metastasis, has been considered as an important strategy for noninvasive tracking tumor metastasis in clinics. In this study, we report the development and application of mesoporous silica-based triple-modal nanoprobes that integrate multiple functional moieties to facilitate near-infrared optical, magnetic resonance (MR) and positron emission tomography (PET) imaging. After embedding near-infrared dye ZW800, the nanoprobe was labeled with T(1) contrast agent Gd(3+) and radionuclide (64)Cu through chelating reactions. High stability and long intracellular retention time of the nanoprobes was confirmed by in vitro characterization, which facilitate long-term in vivo imaging. Longitudinal multimodal imaging was subsequently achieved to visualize tumor draining SLNs up to 3 weeks in a 4T1 tumor metastatic model. Obvious differences in uptake rate, amount of particles, and contrast between metastatic and contra-lateral sentinel lymph nodes were observed. These findings provide very helpful guidance for the design of robust multifunctional nanomaterials in SLNs' mapping and tumor metastasis diagnosis.

Surface-Selective Solution NMR Studies of Functionalized Zeolite Nanoparticles

The surface chemistry of zeolite nanoparticles functionalized with the organosilane aminopropyldimethylmethoxysilane (APDMMS) was selectively probed using solution (1)H NMR spectroscopy. The use of solution NMR spectroscopy results in high-resolution NMR spectra, and the technique is selective for protons on the surface organic functional groups due to their motional averaging in solution. In this study, (1)H solution NMR spectroscopy was used to investigate the interface of the organic functional groups of APDMMS-functionalized silicalite nanoparticles (∼35 nm) in D2O. The pKa for the amine group of APDMMS-functionalized silicalite nanoparticles in D2O was determined using an NMR-pH titration method based on the variation in the proton chemical shift for the alkyl group protons closest to the amine group with pH. The resulting NMR spectra demonstrate the sensitivity of solution NMR spectroscopy to the electronic environment and structure of the surface functional groups.

Critical Considerations in the Biomedical Use of Mesoporous Silica Nanoparticles

Since the first report of mesoporous silica nanoparticles in 2001, many efforts have been made to develop them for biomedical applications. With the emergence of new designs and increasingly complex synthetic schemes, mesoporous silica nanoparticles have never been more promising. For this promise to be fulfilled, however, practical considerations for biomedical use must be carefully addressed. Many current mesoporous silica reports, even those reporting in vivo work, neglect the observation of nanoparticle size, pore structure, aggregation state, and biodegradability under biological conditions before administration. These critical considerations, beginning at synthetic stages, must be taken into account to make effective and safe mesoporous silica nanoparticles for biomedical use and timely application in clinical trials. Herein, we present a comprehensive review of mesoporous silica nanoparticle synthetic strategies, pointing out nanoparticle behavior under biological conditions and how it may affect in vitro and in vivo results.

Multifunctional mesoporous silica nanospheres with cleavable Gd(III) chelates as MRI contrast agents: synthesis, characterization, target-specificity, and renal clearance

Mesoporous silica nanospheres (MSNs) are a promising material for magnetic resonance imaging (MRI) contrast agents. In this paper multifunctional MSNs with cleavable Gd(III) chelates are synthesized and characterized, and their applicability as MRI contrast agents is demonstrated both in vitro and in vivo. The MSNs contain Gd(III) chelates that are covalently linked via a redox-responsive disulfide moiety. The MSNs are further functionalized with polyethylene glycol (PEG) and an anisamide ligand to improve their biocompatibility and target specificity. The effectiveness of MSNs as an MRI imaging contrast agent and their targeting ability are successfully demonstrated in vitro using human colon adenocarcinoma and pancreatic cancer cells. Finally, the capability of this platform as an in vivo MRI contrast agent is tested using a 3T scanner. The Gd(III) chelate was quickly cleaved by the blood pool thiols and eliminated through the renal excretion pathway. Further tuning of the Gd(III) chelate release kinetics is needed before the MSN system can be used as target-specific MRI contrast agents in vivo.