Multifunctional Gadolinium-Doped Manganese Carbonate Nanoparticles for Targeted MR/Fluorescence Imaging of Tiny Brain Gliomas

Fluorescent Probes for Disease Diagnosis

The identification and detection of disease-related biomarkers is essential for early clinical diagnosis, evaluating disease progression, and for the development of therapeutics. Possessing the advantages of high sensitivity and selectivity, fluorescent probes have become effective tools for monitoring disease-related active molecules at the cellular level and in vivo. In this review, we describe current fluorescent probes designed for the detection and quantification of key bioactive molecules associated with common diseases, such as organ damage, inflammation, cancers, cardiovascular diseases, and brain disorders. We emphasize the strategies behind the design of fluorescent probes capable of disease biomarker detection and diagnosis and cover some aspects of combined diagnostic/therapeutic strategies based on regulating disease-related molecules. This review concludes with a discussion of the challenges and outlook for fluorescent probes, highlighting future avenues of research that should enable these probes to achieve accurate detection and identification of disease-related biomarkers for biomedical research and clinical applications.

Folate Receptor Targeting Mn(II) Complex Encapsulated Porous Silica Nanoparticle as an MRI Contrast Agent for Early-State Detection of Cancer

Cancer is recognized as one of the major causes of mortality, however, early-stage detection can increase the survival chance greatly. It is recognized that folate receptors are gradually overexpressed in the cellular membrane with the progress of cancer from stage 1 to stage 4. Utilizing the fact, herein, developed a porous silica nanoparticle system C1@SiO2-FA-NP; A) impregnated with thermodynamically stable Mn(II) complex (1) molecules within the core of the nanoparticle, and B) surface functionalized with folate units. It exhibited a high longitudinal relaxivity value r1 = 21.45 mM-1s-1 that substantially increased to r1 = 40.97 mM-1s-1 in the presence of 0.67 mM concentration of BSA under the physiological condition. The in vitro fluorescent images after surface conjugation of C1@SiO2-FA-NP with FITC (fluorescein isothiocyanate) buttressed the inclusion of the nanoparticle exclusively within the cancerous HeLa cells than that of healthy HEK293 cells. The importance of the surface-bound folate unit in the nanoparticle is further established by comparing the fluorescent images of HeLa cells in the absence of the group. Finally, the applicability of C1@SiO2-FA-NP as the T1-weighted MRI contrast agent for early-stage cancer diagnosis is established within C57BL/6 mice after infecting the mice with HeLa cells.

Carbon Dots for Multiuse Platform: Intracellular pH Sensing and Complementary Intensified T1-T2 Dual Imaging Contrast Nanoprobes

Measurement of pH in living cells is a great and decisive factor for providing an early and accurate diagnosis factor. Along with this, the multimodal transverse and longitudinal relaxivity enhancement potentiality over single modality within a single platform in the magnetic resonance imaging (MRI) field is a very challenging issue for diagnostic purposes in the biomedical field of application. Therefore, this work aims to design a versatile platform by fabricating a novel nanoprobe through holmium- and manganese-ion doping in carbon quantum dots (Ho-Mn-CQDs), which can show nearly neutral intracellular pH sensing and MRI imaging at the same time. These manufactured Ho-Mn-CQDs acted as excellent pH sensors in the near-neutral range (4.01-8.01) with the linearity between 6.01 and 8.01, which could be useful for the intracellular pH-sensing capability. An innumerable number of carboxyl and amino groups are present on the surface of the prepared nanoprobe, making it an excellent candidate for pH sensing through fluorescence intensity quenching phenomena. Cellular uptake and cell viability experiments were also executed to affirm the intracellular accepting ability of Ho-Mn-CQDs. Furthermore, with this pH-sensing quality, these Ho-Mn-CQDs are also capable of acting as T1-T2 dual modal imaging contrast agents in comparison with pristine Ho-doped and Mn-doped CQDs. The Ho-Mn-CQDs showed an increment of r1 and r2 relaxivity values simultaneously compared with only the negative contrast agent, holmium in holmium-doped CQDs, and the positive contrast agent, manganese in manganese-doped CQDs. The above-mentioned observations elucidate that its tiny size, excitation dependence of fluorescence behavior, low cytotoxicity, and dual modal contrast imaging capability make it an ideal candidate for pH monitoring in the near-neutral range and also as a dual modal MRI imaging contrast enhancement nanoprobe at the same time.

Design of manganese-based nanomaterials for pharmaceutical and biomedical applications

In the past few years, manganese-based nanostructures have been extensively investigated in the biomedical field particularly to design highly biocompatible theranostics, which can not only act as efficient diagnostic imaging contrast agents but also deliver the drugs to the target sites. The nanoscale size, large surface area-to-volume ratio, availability of cheap precursors, flexibility to synthesize nanostructures with reproducible properties and high yield, and easy scale up are the major reasons for the attraction towards manganese nanostructures. Along with these properties, the nontoxic nature, pH-sensitive degradation, and easy surface functionalization are additional benefits for the use of manganese nanostructures in biomedical and pharmaceutical sciences. Therefore, in this review, we discuss the recent progress made in the synthesis of manganese nanostructures, describe the attempts made to modify their surfaces to impart biocompatibility and stability in biological fluids, and critically discuss their use in magnetic resonance imaging, drug and gene delivery, hyperthermia, photothermal/photodynamic, immunotherapy, biosensing and tumor diagnosis.

Manganese-Based Nanotheranostics for Magnetic Resonance Imaging-Mediated Precise Cancer Management

Manganese (Mn)-based magnetic resonance imaging (MRI) has become a competitive imaging modality for cancer diagnosis due to its advantages of non-invasiveness, high resolution and excellent biocompatibility. In recent years, a variety of Mn contrast agents based on different material systems have been synthesized, and a series of multi-purpose Mn nanocomposites have also emerged, showing satisfactory relaxation efficiency and MRI performance thus possess the transformation and application value in MRI-synergized cancer diagnosis and treatment. This tutorial review starts from the classification and properties of Mn-based nanomaterials, and then summarizes various preparation and functionalization strategies of nanosized Mn contrast agents, especially focuses on the latest progress of Mn contrast agents in MRI-synergized precise cancer theranostics. In addition, present review also discusses the current clinical transformation obstacles such as unclear molecular mechanisms, potential nanotoxicity, and scale production constraints. This paper provides evidence-based recommendations about the future prospects of multifunctional nanoplatforms, as well as technical guidance and panoramic expectations for the design of clinically meaningful cancer management programs.

Dynamic Nuclear Polarization of Selectively 29Si-Enriched Core@shell Silica Nanoparticles

²⁹Si silica nanoparticles (SiO₂ NPs) are promising magnetic resonance imaging (MRI) probes that possess advantageous properties for in vivo applications, including suitable biocompatibility, tailorable properties, and high water dispersibility. Dynamic nuclear polarization (DNP) is used to enhance ²⁹Si MR signals via enhanced nuclear spin alignment; to date, there has been limited success employing DNP for SiO₂ NPs due to the lack of endogenous electronic defects that are required for the process. To create opportunities for SiO₂-based ²⁹Si MRI probes, we synthesized variously featured SiO₂ NPs with selective ²⁹Si isotope enrichment on homogeneous and core@shell structures (shell thickness: 10 nm, core size: 40 nm), and identified the critical factors for optimal DNP signal enhancement as well as the effective hyperpolarization depth when using an exogenous radical. Based on the synthetic design, this critical factor is the proportion of ²⁹Si in the shell layer regardless of core enrichment. Furthermore, the effective depth of hyperpolarization is less than 10 nm between the surface and core, which demonstrates an approximately 40% elongated diffusion length for the shell-enriched NPs compared to the natural abundance NPs. This improved regulation of surface properties facilitates the development of isotopically enriched SiO₂ NPs as hyperpolarized contrast agents for in vivo MRI.

Synergistic Effect of Oxygen- and Nitrogen-Containing Groups in Graphene Quantum Dots: Red Emitted Dual-Mode Magnetic Resonance Imaging Contrast Agents with High Relaxivity

Contrast agents (CAs) in magnetic resonance imaging generally involve the dissociative Gd³⁺. Because of the limited ligancy of Gd³⁺, the balance between Gd³⁺ coordination stability (reducing the concentration of dissociative Gd³⁺) and increases in the number of coordination water molecules (enhancing the relaxivity) becomes crucial. Herein, the key factor of the synergistic effect between the O- and N-containing groups of graphene quantum dots for the structural design of CAs with both high relaxivity and low toxicity was obtained. The nitrogen-doped graphene quantum dots (NGQDs) with an O/N ratio of 0.4 were selected to construct high-relaxivity magnetic resonance imaging (MRI)-fluorescence dual-mode CAs. The coordination stability of Gd³⁺ can be increased through the synergetic coordination of O- and N-containing groups. The synergetic coordination of O- and N-containing groups can result in the short residency time of the water ligand and achieve high relaxivity. The resulting CAs (called NGQDs-Gd) exhibit a high relaxivity of 32.04 mM^-1 s^-1 at 114 μT. Meanwhile, the NGQDs-Gd also emit red fluorescence (614 nm), which can enable the MRI-fluorescence dual-mode imaging as the CAs. Moreover, the bio-toxicity and tumor-targeting behavior of NGQDs-Gd were also evaluated, and NGQDs-Gd show potential in MRI-fluorescence imaging in vivo.

Recent development of contrast agents for magnetic resonance and multimodal imaging of glioblastoma

Glioblastoma (GBM) as the most common primary malignant brain tumor exhibits a high incidence and degree of malignancy as well as poor prognosis. Due to the existence of formidable blood–brain barrier (BBB) and the aggressive growth and infiltrating nature of GBM, timely diagnosis and treatment of GBM is still very challenging. Among different imaging modalities, magnetic resonance imaging (MRI) with merits including high soft tissue resolution, non-invasiveness and non-limited penetration depth has become the preferred tool for GBM diagnosis. Furthermore, multimodal imaging with combination of MRI and other imaging modalities would not only synergistically integrate the pros, but also overcome the certain limitation in each imaging modality, offering more accurate morphological and pathophysiological information of brain tumors. Since contrast agents contribute to amplify imaging signal output for unambiguous pin-pointing of tumors, tremendous efforts have been devoted to advances of contrast agents for MRI and multimodal imaging. Herein, we put special focus on summary of the most recent advances of not only MRI contrast agents including iron oxide-, manganese (Mn)-, gadolinium (Gd)-, ¹⁹F- and copper (Cu)-incorporated nanoplatforms for GBM imaging, but also dual-modal or triple-modal nanoprobes. Furthermore, potential obstacles and perspectives for future research and clinical translation of these contrast agents are discussed. We hope this review provides insights for scientists and students with interest in this area.

Albumin-templated manganese carbonate nanoparticles for precise magnetic resonance imaging of acute myocardial infarction

Myocardial infarction (MI) is a major cause of death worldwide. Early and precise diagnosis of myocardial viability after MI is extremely important for effective treatment and prognosis evaluation. Herein, we developed the BSA-templated manganese carbonate (MnCO₃@BSA) nanoparticles as an MR imaging contrast agent for accurate detection of the infarcted regions. The chemophysical features, targeting capability toward the infarct, and biocompatibility were evaluated. The nanoparticles showed superior chemical stability. In vitro study suggested that the MnCO₃@BSA nanoparticles do not enter normal cardiomyocytes. MR imaging indicated that the MnCO₃@BSA with a high longitudinal (r₁) relaxivity of 5.84 mM^-1s^-1 at physiological condition specifically accumulated into the infarcted regions of myocardial ischemia/reperfusion (I/R) mice. In addition, the MnCO₃@BSA nanoparticles exhibited low cytotoxicity to cardiomyocytes, no damage to organs and good hemocompatibility. Thereby, the MnCO₃@BSA nanoparticles manifested great potential as an extracellular contrast agent of MR imaging for sensitive and specific detection of the infarcted regions during acute myocardial I/R injury.

Advances in magnetic resonance imaging contrast agents for glioblastoma-targeting theranostics

Glioblastoma (GBM) is the most aggressive malignant brain tumour, with a median survival of 3 months without treatment and 15 months with treatment. Early GBM diagnosis can significantly improve patient survival due to early treatment and management procedures. Magnetic resonance imaging (MRI) using contrast agents is the preferred method for the preoperative detection of GBM tumours. However, commercially available clinical contrast agents do not accurately distinguish between GBM, surrounding normal tissue and other cancer types due to their limited ability to cross the blood–brain barrier, their low relaxivity and their potential toxicity. New GBM-specific contrast agents are urgently needed to overcome the limitations of current contrast agents. Recent advances in nanotechnology have produced alternative GBM-targeting contrast agents. The surfaces of nanoparticles (NPs) can be modified with multimodal contrast imaging agents and ligands that can specifically enhance the accumulation of NPs at GBM sites. Using advanced imaging technology, multimodal NP-based contrast agents have been used to obtain accurate GBM diagnoses in addition to an increased amount of clinical diagnostic information. NPs can also serve as drug delivery systems for GBM treatments. This review focuses on the research progress for GBM-targeting MRI contrast agents as well as MRI-guided GBM therapy.

In vitro and Microbiological Assay of Functionalized Hybrid Nanomaterials To Validate Their Efficacy in Nanotheranostics: A Combined Spectroscopic and Computational Study

Functionalized nanoparticles reveal new frontiers in therapeutics and diagnostics, simultaneously referred to as theranostics. Functionalization of an inorganic nanoparticle (NP) with an organic ligand determines the interaction of the functionalized NPs with various cellular components, leading to the desired therapeutic effect, while diminishing adverse side effects. Apart from the therapeutic effect of the nanoparticles, other physical properties of the organic-inorganic complex (nanohybrid) including fluorescence, X-ray or MRI contrast offer diagnosis of the anomalous target cell. In this study we functionalized Mn₃ O₄ NPs with organic citrate (C-Mn₃ O₄ ) and folic acid (FA-Mn₃ O₄ ) ligands and investigated their antimicrobial activities using Staphylococcus hominis as a model bacteria, which can be remediated through their membrane rupture. While high-resolution transmission microscopy (HR-TEM), XRD, DLS, absorbance and fluorescence spectroscopy were used for structural characterisation of the functionalised NPs, zeta potential measurements and temperature-dependent reactive oxygen speices (ROS) generation reveal their drug action. We used high-end density functional theory (DFT) calculations to rationalise the specificity of the drug action of the NPs. Picosecond-resolved FRET studies confirm the enhanced affinity of FA-Mn₃ O₄ to the bacteria relative to C-Mn₃ O₄ , leading to enhanced antimicrobial activity. We have shown that the functionalised nanoparticles offer significant X-ray contrast in in-vitro studies, indicating the FA-Mn₃ O₄ NPs to be a potential theranostic agent against bacterial infection.

Tumor-Specific Activatable Nanocarriers with Gas-Generation and Signal Amplification Capabilities for Tumor Theranostics

Multifunctional nanotheranostics are typically designed by integrating multiple functional components. This approach not only complicates the preparation process but also hinders any bioapplication due to the potential toxic effects when each component is metabolized. Here, we report a safe, biodegradable, and tumor-specific nanocarrier that, once activated by the acidic tumor microenvironment (TME), has diagnostic and therapeutic functions suitable for tumor theranostics. Our nanocarrier is composed of biomineralized manganese carbonate (BMC) nanoparticles (NPs) that readily decompose to release Mn²⁺ ions and CO₂ gas in the acidic TME due to its intrinsic pH-dependent solubility. Mn²⁺ and CO₂ release permits magnetic resonance and ultrasound imaging of tumors, respectively. These NPs can be loaded with the anticancer drug doxorubicin (DOX): BMC-DOX has high tumor inhibition effects both in vitro and in vivo due to combined Mn²⁺-mediated chemodynamic therapy and DOX-induced chemotherapy. This tumor-specific actuating nanocarrier might be a promising candidate for clinical translation.

Immobilization of hemoglobin on MnCO3 sphere-loaded Au nanoparticles as highly efficient sensing platform towards hydrogen peroxide

In this paper, we report the synthesis of MnCO₃-Au hybrid microspheres and their application on the electrochemical biosensing of hydrogen peroxide (H₂O₂) based on the immobilization of hemoglobin (Hb). The characterization of MnCO₃-Au microspheres revealed that an abundance of Au nanoparticles (AuNPs) has been absorbed on the surface of the spherical MnCO₃ by the electrostatic assembly. The combined unique properties of MnCO₃-Au microspheres are beneficial for the realization of the direct electron transfer of Hb. Hb immobilized on the microspheres maintained its biological activity, showing a surface-controlled process with the heterogeneous electron transfer rate constant (k _s) of 2.63 s^-1. The fabricated biosensor displayed an excellent performance for the electrocatalytic reduction of H₂O₂. The linear range for the determination of H₂O₂ was from 0.06-40.0 μM with a detection limit of 0.015 µM (S/N = 3). The biosensor also exhibited high selectivity, good repeatability and long-term stability, which offers great potential for H₂O₂ detection in real sample analysis.

Bifunctional Pyrrolidin-2-one Terminated Manganese Oxide Nanoparticles for Combined Magnetic Resonance and Fluorescence Imaging

Multimodal probes are an asset for simplified, improved medical imaging. In particular, fluorescence and magnetic resonance imaging (MRI) are sought-after combined capabilities. Here, we show that pyrrolidin-2-one-capped manganese oxide nanoparticles (MnO^pyrr NPs) combine MRI with fluorescence microscopy to function as efficient bifunctional bio-nanoprobes. We employ a one-pot synthesis for ca. 10 nm MnO NPs, wherein manganese(II) 2,4-pentadionate is thermally decomposed using pyrrolidin-2-one as a solvent and capping ligand. The MnO^pyrr NPs are soluble in water without any further postsynthetic modifications. The r₁ relaxivity and r₂ /r₁ ratio indicate that these NPs are potential T₁ MRI contrast agents at clinical (3 T) and ultrahigh (9.4 T) magnetic fields. Serendipitously, the as-prepared NPs are photoluminescent. The unexpected luminescence is ascribed to the modification of the pyrrolidin-2-one during the thermal treatment. MnO^pyrr NPs are successfully used to enable fluorescence microscopy of HeLa cells, demonstrating bifunctional imaging capabilities. A low cytotoxic response in two distinct cell types (HeLa, HepG2) supports the suitability of MnO^pyrr NPs for biological imaging applications.

A multifunctional low-generation dendrimer-based nanoprobe for the targeted dual mode MR/CT imaging of orthotopic brain gliomas

An RGD peptide-targeted low-generation dendrimer nanoprobe can cross the blood-brain barrier for dual-modal MR/CT imaging of an orthotopic brain glioma.

Nanoparticle-based diagnostic and therapeutic systems for brain tumors

Many theranostic nanoparticles have been tailored for high-efficiency diagnostic or therapeutic agents or applied as carriers and might provide new possibilities for brain tumor diagnosis and treatment.

Aminopeptidase N (CD13) targeted MR and NIRF dual-modal imaging of ovarian tumor xenograft

The development of tumor-specific imaging nanoprobes with the potential to improve the accuracy of cancer diagnosis has become an area of intense research. Aminopeptidase N (CD13) predominantly expresses on the surface of ovarian tumor cells and can be specifically recognized by Asn-Gly-Arg (NGR) peptide. The applicability of CD13 as a target for specific ovarian tumor imaging, however, remains unexploited so far. In this study, Cy5.5-labeled, NGR-conjugated iron oxide nanoparticles (Cy5.5-NGR-Fe₃O₄ NPs) were prepared as an ovarian tumor specific bimodal imaging nanoprobe. It is demonstrated that the conjugation of NGR targeting moiety leads to a higher cellular uptake toward ES-2 cells, the human ovarian carcinoma cells that highly express CD13. Moreover, magnetic resonance imaging of ovarian tumor xenograft reveals that the Fe₃O₄-Cy5.5-NGR NPs results in a significant T₂* signal reduction in the tumor. Meanwhile, near infrared fluorescence imaging indicates a higher accumulation of Fe₃O₄-Cy5.5-NGR NPs in the tumor xenograft. Therefore, CD13 could be applied as a novel and efficient target for constructing ovarian tumor specific nanoprobes with improved accuracy for ovarian tumor diagnosis.

Manganese-Doped Carbon Dots for Magnetic Resonance/Optical Dual-Modal Imaging of Tiny Brain Glioma

Brain gliomas are life-threatening diseases with low survival rates. Early detection and accurate intraoperative location of brain gliomas is vital to improving the prognosis. Herein, we synthesized manganese (Mn)-doped carbon dots (CDs) as magnetic resonance (MR)/optical dual-modal imaging nanoprobes by a one-pot green microwave-assisted route. These ultra-small-sized Mn-doped CDs possess distinct excitation-dependent photoluminescent emissions, high r₁ relaxivity, and low cytotoxicity. The in vivo MR imaging and ex vivo optical imaging of mouse brain with tiny glioma demonstrate that the Mn-doped CDs could lead to an enhanced MR T₁ contrast effect in the tiny brain glioma region, disclosing the great promise of these Mn-doped CDs as MR/optical dual-modal imaging nanoprobes for detection and intraoperative location of tiny brain gliomas.

Comparative toxicity and contrast enhancing assessments of Gd2O3@BSA and MnO2@BSA nanoparticles for MR imaging of brain glioma

The albumin-templated Gd₂O₃ and MnO₂ nanoparticles (NPs) have been developed as a new type of magnetic resonance (MR) T₁ contrast agents. However, their potential toxicity and applicability for MR imaging of brain gliomas has not been fully explored so far. In this study, we prepared Gd₂O₃@BSA and MnO₂@BSA nanoparticles (NPs) and investigated their toxicity comprehensively and comparatively by H&E staining, blood biochemical analysis, and adverse outcome pathways testing. It is revealed that both Gd₂O₃@BSA and MnO₂@BSA NPs are biocompatible at a rational dose level. Although the relaxivity of MnO₂@BSA NPs is less than that of Gd₂O₃@BSA NPs, the MnO₂@BSA NPs lead to a greater contrast enhancement in the brain glioma due to the controlled release of Mn ions under the acidic tumor microenvironmental conditions. These comparative toxicity and contrast enhancement data are of fundamental importance for the clinical translation of Gd₂O₃@BSA and MnO₂@BSA NPs as MR contrast agents for brain glioma diagnosis.

Polydopamine-Coated Manganese Carbonate Nanoparticles for Amplified Magnetic Resonance Imaging-Guided Photothermal Therapy

This study reports a multifunctional nanoparticle (NP) that can be used for amplified magnetic resonance image (MRI)-guided photothermal therapy (PTT) due to its surface coating with a polydopamine (PDA) shell. Importantly, by means of introducing the surface coating of PDA, large quantities of water can be trapped around the NPs allowing more efficient water exchange, leading to greatly improved MR contrast signals compared with those from NPs without the PDA coating. Further, a distinct photothermal effect can be obtained arising from the strong absorption of PDA in the near-infrared (NIR) region. By synthesizing multifunctional MnCO₃@PDA NPs, for example, we found that the longitudinal relaxivity (r₁) of MnCO₃ NPs can improve from 5.7 to 8.3 mM^-1 s^-1. Subsequently, in vitro MRI and PTT results verified that MnCO₃@PDA could serve as an excellent MRI/PTT theranostic agent. Furthermore, the MnCO₃@PDA NPs were applied as an MRI/PTT theranostic agent for in vivo MRI-guided photothermal ablation of tumors by intratumoral injection in 4T1 tumor-bearing mice. The MR imaging result shows a significantly bright MR image in the tumor site. The MnCO₃@PDA-mediated PTT result shows high therapeutic efficiency as a result of high photothermal conversion efficiency. The present strategy of amplified MRI-guided PTT based on PDA coating of NPs will be widely applicable to other multifunctional NPs.

Tuning of synthesis conditions by thermal decomposition towards gadolinium-doped manganese carbonate nanoparticles with uniform size and high relaxivity

A low temperature thermal decomposition method has been developed to synthesize uniform-sized Gd-doped MnCO₃ nanoparticles.

Quantitative Measurement of Ligand Exchange with Small-Molecule Ligands on Iron Oxide Nanoparticles via Radioanalytical Techniques

Ligand exchange on the surface of hydrophobic iron oxide nanoparticles is a common method for controlling surface chemistry for a desired application. Furthermore, ligand exchange with small-molecule ligands may be necessary to obtain particles with a specific size or functionality. Understanding to what extent ligand exchange occurs and what factors affect it is important for the optimization of this critical procedure. However, quantifying the amount of exchange may be difficult because of the limitations of commonly used characterization techniques. Therefore, we utilized a radiotracer technique to track the exchange of a radiolabeled ¹⁴C-oleic acid ligand with hydrophilic small-molecule ligands on the surface of iron oxide nanoparticles. Iron oxide nanoparticles functionalized with ¹⁴C-oleic acid were modified with small-molecule ligands with terminal functional groups including catechols, phosphonates, sulfonates, thiols, carboxylic acids, and silanes. These moieties were selected because they represent the most commonly used ligands for this procedure. The effectiveness of these molecules was compared using both procedures widely found in the literature and using a standardized procedure. After ligand exchange, the nanoparticles were analyzed using liquid scintillation counting (LSC) and inductively coupled plasma-mass spectrometry. The labeled and unlabeled particles were further characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS) to determine the particle size, hydrodynamic diameter, and zeta potential. The unlabeled particles were characterized via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and vibrating sample magnetometry (VSM) to confirm the presence of the small molecules on the particles and verify the magnetic properties, respectively. Radioanalytical determination of ¹⁴C-oleic acid was used to calculate the total amount of oleic acid remaining on the surface of the particles after ligand exchange. The results revealed that the ligand-exchange reactions performed using widely cited procedures did not go to completion. Residual oleic acid remained on the particles after these reactions and the reactions using a standardized protocol. A comparison of the ligand-exchange procedures indicated that the binding moiety, multidenticity, reaction time, temperature, and presence of a catalyst impacted the extent of exchange. Quantification of the oleic acid remaining after ligand exchange revealed a binding hierarchy in which catechol-derived anchor groups displace the most oleic acid on the surface of the nanoparticles and the thiol group displaces the least amount of oleic acid. Thorough characterization of ligand exchange is required to develop nanoparticles suitable for their intended application.

Metal Nanoparticles as Targeted Carriers Circumventing the Blood-Brain Barrier

Metal nanoparticles have been proposed as a carrier and a therapeutic agent in biomedical field because of their unique physiochemical properties. Due to these physicochemical properties, they can be used in different fields of biomedicine. In relation to this, plasmonic nanoparticles can be used for detection and photothermal destruction of tumor cells or toxic protein aggregates, and magnetic iron nanoparticles can be used for imaging and for hyperthermia of tumor cells. In addition, both therapy and imaging can be combined in one nanoparticle system, in a process called theranostics. Metal nanoparticles can be synthesized to modulate their size and shape, and conjugated with different ligands, which allow their application in drug delivery, diagnostics, and treatment of central nervous system diseases. This review is focused on the potential applications of metal nanoparticles and their capability to circumvent the blood-brain barrier (BBB). Although many articles have demonstrated delivery of metal nanoparticles to the brain by crossing the BBB after systemic administration, the percentage of the injected dose that reaches this organ is low in comparison to others, especially the liver and spleen. In connection with this drawback, we elaborate the architecture of the BBB and review possible mechanisms to cross this barrier by engineered nanoparticles. The potential uses of metal nanoparticles for treatment of disorders as well as related neurotoxicological considerations are also discussed. Finally, we bring up for discussion a direct and relatively simpler solution to the problem. We discuss this in detail after having proposed the use of the intranasal administration route as a way to circumvent the BBB. This route has not been extensively studied yet for metal nanoparticles, although it could be used as a research tool for mechanistic understanding and toxicity as well as an added value for medical practice.

Dual-targeting superparamagnetic iron oxide nanoprobes with high and low target density for brain glioma imaging

A major limit of superparamagnetic iron oxide nanoparticles (SPIONs) as a magnetic resonance (MR) imaging nanoprobe in clinical applications is that the SPIONs are unable to reach sufficient concentrations at the tumor site by passive targeting to produce an obvious contrast effect for tumor imaging. Single-targeting SPIONs systems have been applied to improve the contrast effect. However, they still suffer from a lack of efficiency and specificity of the SPIONs to tumors. Herein, we developed folic acid (FA) and cyclic Arg-Gly-Asp-D-Tyr-Lys (c(RGDyK)) dual-targeting nanoprobes based on Cy5.5 labeled Fe3O4 nanoparticles (NPs). The synergistic targeting ability of the dual-targeting Fe3O4 NPs and the effect of the dual-target density on targeting specificity were investigated in brain glioma-bearing mice. In vivo T2-weighted MR imaging of brain glioma-bearing mice and ex vivo near-infrared imaging of brains harboring gliomas suggested that the combination of dual-target increased the uptake of NPs by glioma, consequently, enhanced the contrast effect. Moreover, it was revealed that the density of dual-target plays an important role in targeting specificity.

Formation mechanism of dysprosium-doped manganese carbonate nanoparticles by thermal decomposition

The formation mechanism of Dy-doped MnCO₃ NPs through the thermal decomposition method was elucidated and the potential of Dy-doped MnCO₃ NPs as an efficient MR contrast agent was demonstrated in the brain glioma-bearing mice.

RGD conjugated, Cy5.5 labeled polyamidoamine dendrimers for targeted near-infrared fluorescence imaging of esophageal squamous cell carcinoma

The early detection of esophageal squamous cell carcinoma (ESCC), one of the most common human neoplasms, is of great importance in improving prognosis.