Design of a multi-dopamine-modified polymer ligand optimally suited for interfacing magnetic nanoparticles with biological systems

Mussel-Inspired Multifunctional Polyethylene Glycol Nanoparticle Interfaces

Nanoparticles (NPs) are receiving increasing interest in biomedical applications. However, due to their large surface area, in physiological environments, they tend to interact with plasma proteins, inducing their agglomeration and ultimately resulting in a substantial efficiency decrease in diagnostic and therapeutic applications. To overcome such problems, NPs are typically coated with a layer of hydrophilic and biocompatible polymers, such as PEG chains. However, few examples exist in which this property could be systematically fine-tuned and combined with added properties, such as emission. Herein, we report a novel mussel-inspired catechol-based strategy to obtain biocompatible and multifunctional coatings, using a previously developed polymerization methodology based on the formation of disulfide bridges under mild oxidative conditions. Two families of NPs were selected as the proof of concept: mesoporous silica NPs (MSNPs), due to their stability and known applications, and magnetite NPs (Fe3O4 NPs), due to their small size (<10 nm) and magnetic properties. The PEG coating confers biocompatibility on the NPs and can be further functionalized with bioactive molecules, such as glucose units, through the end carboxylic acid moieties. Once we demonstrated the feasibility of our approach to obtaining PEG-based coatings on different families of NPs, we also obtained multifunctional coatings by incorporating fluorescein functionalities. The resulting coatings not only confer biocompatibility and excellent cell internalization, but also allow for the imaging and tracking of NPs within cells.

Conjugation of gold nanoparticles with multidentate surfactants for enhanced stability and biological properties

This work originated from the need to functionalize surfactant-coated inorganic nanoparticles for biomedical applications, a process that is limited by excess unbound surfactant. These limitations are connected to the bioconjugation of targeting molecules that are often in equilibrium between the free aliquot in solution and that which binds the surface of the nanoparticles. The excess in solution can play a role in the biocompatability in vitro and in vivo of the final nanoparticles stock. For this purpose, we tested the ability of common surfactants - monothiolated polyethylene glycol and amphiphilic polymers - to colloidally stabilize nanoparticles as excess surfactant is removed and compared them to newly appearing multidentate surfactants endowed with high avidity for inorganic nanoparticles. Our results showed that monothiolated polyethylene glycol or amphiphilic polymers have an insufficient affinity to the nanoparticles and as the excess surfactant is removed the colloidal stability is lost, while multidentate high-avidity surfactants excel in the same regard, possibly allowing improvement in an array of nanoparticle applications, especially in those stated.

Clickable Polymer Ligand-Functionalized Iron Oxide Nanocubes: A Promising Nanoplatform for 'Local Hot Spots' Magnetically Triggered Drug Release

Exploiting the local heat on the surface of magnetic nanoparticles (MNPs) upon exposure to an alternating magnetic field (AMF) to cleave thermal labile bonds represents an interesting approach in the context of remotely triggered drug delivery. Here, taking advantages of a simple and scalable two-step ligand exchange reaction, we have prepared iron oxide nanocubes (IONCs) functionalized with a novel multifunctional polymer ligand having multiple catechol moieties, furfuryl pendants, and polyethylene glycol (PEG) side chains. Catechol groups ensure a strong binding of the polymer ligands to the IONCs surface, while the PEG chains provide good colloidal stability to the polymer-coated IONCs. More importantly, furfuryl pendants on the polymer enable to click the molecules of interest (either maleimide-fluorescein or maleimide-doxorubicin) via a thermal labile Diels-Alder adduct. The resulting IONCs functionalized with a fluorescein/doxorubicin-conjugated polymer ligand exhibit good colloidal stability in buffer saline and serum solution along with outstanding heating performance in aqueous solution or even in viscous media (81% glycerol/water) when exposed to the AMF of clinical use. The release of conjugated bioactive molecules such as fluorescein and doxorubicin could be boosted by applying AMF conditions of clinical use (16 kAm^-1 and 110 kHz). It is remarkable that the magnetic hyperthermia-mediated release of the dye/drug falls in the concentration range 1.0-5.0 μM at an IONCs dose as low as 0.5 g_Fe/L and at no macroscopical temperature change. This local release effect makes this magnetic nanoplatform a potential tool for drug delivery with remote magnetic hyperthermia actuation and with a dose-independent action of MNPs.

Versatile Coating Platform for Metal Oxide Nanoparticles: Applications to Materials and Biological Science

In this feature article, we provide an overview of our research on statistical copolymers as a coating material for metal oxide nanoparticles and surfaces. These copolymers contain functional groups enabling noncovalent binding to oxide surfaces and poly(ethylene glycol) (PEG) polymers for colloidal stability and stealthiness. The functional groups are organic derivatives of phosphorous acid compounds R-H₂PO₃, also known as phosphonic acids that have been screened for their strong affinity to metals and for their multidentate binding ability. Herein we develop a polymer-based coating platform that shares features with the self-assembled monolayer (SAM) and layer-by-layer (L-b-L) deposition techniques. The milestones of this endeavor are the synthesis of PEG-based copolymers containing multiple phosphonic acid groups, the implementation of simple protocols combining versatility with high particle production yields, and the experimental evidence of the colloidal stability of the coated particles. As a demonstration, coating studies are conducted on cerium (CeO₂), iron (γ-Fe₂O₃), aluminum (Al₂O₃), and titanium (TiO₂) oxides of different sizes and morphologies. We finally discuss applications in the domain of nanomaterials and nanomedicine. We evaluate the beneficial effects of coatings on redispersible nanopowders, contrast agents for in vitro/vivo assays, and stimuli-responsive particles.

Polysalt ligands achieve higher quantum yield and improved colloidal stability for CsPbBr3 quantum dots

Colloidal lead halide perovskite quantum dots (PQDs) are relatively new semiconductor nanocrystals with great potential for use in optoelectronic applications. They also present a set of new scientifically challenging fundamental problems to investigate and understand. One of them is to address the rather poor colloidal and structural stability of these materials under solution phase processing and/or transfer between solvents. In this contribution, we detail the synthesis of a new family of multi-coordinating, bromide-based polysalt ligands and test their ability to stabilize CsPbBr₃ nanocrystals in polar solutions. The ligands present multiple salt groups involving quaternary cations, namely ammonium and imidazolium as anchors for coordination onto PQD surfaces, along with several alkyl chains with varying chain length to promote solubilization in various conditions. The ligands provide a few key benefits including the ability to repair damaged surface sites, allow rapid ligand exchange and phase transfer, and preserve the crystalline structure and morphology of the nanocrystals. The polysalt-coated PQDs exhibit near unity PLQY and significantly enhanced colloidal stability in ethanol and methanol.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Ultrasmall Alloy Nanozyme for Ultrasound- and Near-Infrared Light-Promoted Tumor Ablation

The therapeutic effect of chemodynamic therapy (CDT) is significantly restricted by the stern reaction conditions and slow reaction rate of the Fenton reaction (pH 3-4). Herein, we report an ultrasmall trimetallic (Pd, Cu, and Fe) alloy nanozyme (PCF-a NEs) possessing dynamic active-site synergism, thus exhibiting a cascade glutathione peroxidase and peroxidase (POD) mimicking activities in circumneutral pH. PCF-a NEs exhibit photothermally augmented POD property and high photothermal conversion efficiency (62%) for synergistic tumor cell apoptosis. In addition, ultrasound can also enhance the mass transfer at active catalytic sites of PCF-a NEs, in turn accelerating Fenton-like reaction for tumor-specific CDT. This work provides a strategy for engineering alloy nanozymes in a bioinspired way for the amplification of intratumor reactive oxygen species in response to external stimuli, demonstrating enhanced efficiency for the inhibition of tumor growth in vitro and in vivo.

Bioinspired double self-adhesion coating based on dopamine, coating resin and phosphorylcholine for surface lubrication and antifouling functionalization

Implanted medical devices that have poor friction property or biofilm formation can limit their service life and cause discomfort in patients. Recently, some zwitterionic coatings have been studied to modify the biomaterials surface for lubricating function, but the grafting methods of coatings are complicated and also seldom take the bacterial antiadhesion property into account at the same time. In our studies, motivated by the properties of nature mussels and human articular, we firstly successfully synthesized double adhesion protection of self-adhesive ternary polymer coating and achieved the excellent lubrication and antifouling functionalization of the medical devices surface. In details, the X-ray photoelectron spectroscopy, scanning electron microscope and the water contact angles could characterize the successful modification on the surface of titanium substrate. Additionally, the tribological tests carried out by atomic force microscope verified the ternary polymer could enhance the lubrication property owing to the hydration lubrication mechanism. Meanwhile, it also possessed the bacterial antiadhesion property for the initial 24 h attributed to the hydration repulsive force. We believe that, as a simple and universal preparation method, the ternary polymer could make a great significance for improving the surface function of biomaterials and alleviating patients' discomfort.

The Effect of Surface Coating of Iron Oxide Nanoparticles on Magnetic Resonance Imaging Relaxivity

Iron oxide nanoparticles (IONPs) with acceptable biocompatibility and size-dependent magnetic properties can be used as efficient contrast agents in magnetic resonance imaging (MRI). Herein, we have investigated the impact of particle size and surface coating on the proton relaxivity of IONPs, as well as engineering of small IONPs' surface coating as a strategy for achieving gadolinium-free contrast agents. Accordingly, polymer coating using poly(isobutylene-alt-maleic anhydride) (PMA) with overcoating of the original ligands was applied for providing colloidal stability to originally oleic acid–capped IONPs in aqueous solution. In case of replacement of the original ligand shell, the polymer had been modified with dopamine. Furthermore, the colloidal stability of the polymer-coated IONPs was evaluated in NaCl and bovine serum albumin (BSA) solutions. The results indicate that the polymer-coated IONPs which involved replacement of the original ligands exhibited considerably better colloidal stability and higher proton relaxivity in comparison to polymer-coated IONPs with maintained ligand shell. The highest r2/r1 we obtained was around 300.

Luminescent Quantum Dots Stabilized by N-Heterocyclic Carbene Polymer Ligands

We have tested the ability of N-heterocyclic carbene (NHC)-modified ligands to coordinate and stabilize luminescent CdSe-ZnS core-shell quantum dot (QD) dispersions in hydrophilic media. In particular, we probed the effects of ligand structure and coordination number on the coating affinity to the nanocrystals. We find that such NHC-based ligands rapidly coordinate onto the QDs (requiring ∼5-10 min of reaction time), which reflects the soft Lewis base nature of the NHC groups, with its two electrons sharing capacity. Removal of the hydrophobic cap and promotion of carbene-driven coordination on the nanocrystals have been verified by ¹H NMR spectroscopy, while ¹³C NMR was used to identify the formation of carbene-Zn complexes. The newly coated QD dispersions exhibit great long-term colloidal stability over a wide range of conditions. Additionally, we find that coordination onto the QD surfaces affects the optical and spectroscopic properties of the nanocrystals. These include a size-dependent red-shift of the absorption and fluorescence spectra and a pronounced increase in the measured fluorescence intensity when the samples are stored under white light exposure compared to those stored in the dark.

Versatile Surface Functionalization of Water-Dispersible Iron Oxide Nanoparticles with Precisely Controlled Sizes

The synthesis of highly water-dispersible iron oxide nanoparticles with surface functional groups and precisely controlled sizes is essential for biomedical application. In this paper, we report a one-pot strategy for versatile surface functionalization. The iron oxide nanoparticles are first synthesized by thermal decomposition of iron(III) acetylacetonate (Fe(acac)₃) in diethylene glycol (DEG), and their surfaces are modified by adding the surface ligands at the end of the reaction. The size of iron oxide nanoparticles can be precisely controlled in nanometer scale by continuous growth. This facile synthesis method enables the surface modification with different coating materials such as dopamine (DOPA), polyethylene glycol with thiol end group (thiol-PEG), and poly(acrylic acid) (PAA) onto the iron oxide nanoparticles, introducing new surface functionalities for future biomedical application. From transmission electron microscopy (TEM) and X-ray diffraction (XRD), the morphology and crystal structure are not changed during surface functionalization. The attachment of surface ligands is studied by Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). The surface functional groups are confirmed by X-ray Photoelectron Spectroscopy (XPS). In correlation with the change of hydrodynamic size, PAA coated nanoparticles are found to exhibit outstanding stability in aqueous solution. Furthermore, we demonstrate that the functional groups are available for conjugating with other molecules such as fluorescent dye, showing potential biological applications. Lastly, the magnetic resonance phantom studies demonstrate that iron oxide nanoparticles with PAA coating can be used as T₁ and T₂ dual-modality contrast agents. Both r₁ and r₂ relaxivities significantly increase after surface functionalization with PAA, indicating improved sensitivity.

Yolk–shell magnetic composite Fe3O4@Co/Zn-ZIF for MR imaging-guided chemotherapy of tumors in vivo

The yolk–shell composites Fe₃O₄@Co/Zn-ZIF exhibited high doxorubicin loading capacity, pH-responsive release characteristics, and strong T₂-weighted MR imaging contrast enhancement, and were used for MR imaging-guided chemotherapy of tumors in vivo.

Probing the Consequences of Cubic Particle Shape and Applied Field on Colloidal Crystal Engineering with DNA

In a magnetic field, cubic Fe₃ O₄ nanoparticles exhibit assembly behavior that is a consequence of a competition between magnetic dipole-dipole and ligand interactions. In most cases, the interactions between short hydrophobic ligands dominate and dictate assembly outcome. To better tune the face-to-face interactions, cubic Fe₃ O₄ nanoparticles were functionalized with DNA. Their assembly behaviors were investigated both with and without an applied magnetic field. Upon application of a field, the tilted orientation of cubes, enabled by the flexible DNA ligand shell, led to an unexpected crystallographic alignment of the entire superlattice, as opposed to just the individual particles, along the field direction as revealed by small and wide-angle X-ray scattering. This observation is dependent upon DNA length and sequence and cube dimensions. Taken together, these studies show how combining physical and chemical control can expand the possibilities of crystal engineering with DNA.

Cation Exchange Protocols to Radiolabel Aqueous Stabilized ZnS, ZnSe, and CuFeS2 Nanocrystals with 64Cu for Dual Radio- and Photo-Thermal Therapy

Here, cation exchange (CE) reactions are exploited to radiolabel ZnSe, ZnS, and CuFeS2 metal chalcogenide nanocrystals (NCs) with 64Cu. The CE protocol requires one simple step, to mix the water-soluble NCs with a 64Cu solution, in the presence of vitamin C used to reduce Cu(II) to Cu(I). Given the quantitative cation replacement on the NCs, a high radiochemical yield, up to 99%, is reached. Also, provided that there is no free 64Cu, no purification step is needed, making the protocol easily translatable to the clinic. A unique aspect of the approach is the achievement of an unprecedentedly high specific activity: by exploiting a volumetric CE, the strategy enables to concentrate a large dose of 64Cu (18.5 MBq) in a small NC dose (0.18 µg), reaching a specific activity of 103 TBq g-1. Finally, the characteristic dielectric resonance peak, still present for the radiolabeled 64Cu:CuFeS2 NCs after the partial-CE reaction, enables the generation of heat under clinical laser exposure (1 W cm-2). The synergic toxicity of photo-ablation and 64Cu ionization is here proven on glioblastoma and epidermoid carcinoma tumor cells, while no intrinsic cytotoxicity is seen from the NC dose employed for these dual experiments.

Engineering the Bio-Nano Interface Using a Multifunctional Coordinating Polymer Coating

In the past three decades, interest in using nanoparticles as diagnostic tools to interrogate various biosystems has witnessed remarkable growth. For instance, it has been shown that nanoparticle probes enable the study of cellular processes at the single molecule level. These advances provide new opportunities for understanding fundamental problems in biology, innovation in medicine, and the treatment of diseases. A multitude of nanoparticles have been designed to facilitate in vitro or in vivo sensing, imaging, and diagnostics. Some of those nanoparticle platforms are currently in clinical trials or have been approved by the U.S. Food and Drug Administration. Nonetheless, using nanoparticles in biology is still facing several obstacles, such as poor colloidal stability under physiological conditions, nonspecific interactions with serum proteins, and low targeting efficiency in biological fluids, in addition to issues of uncontrolled biodistribution and cytotoxicity. All these problems are primarily controlled by the surface stabilizing coating used.In this Account, we summarize recent progress made in our laboratory focused on the development of multifunctional polymers as coordinating ligands, to tailor the surface properties of nanoparticles and facilitate their application in biology. We first detail the advantageous features of the coating strategy, followed by a discussion of the key parameters in the ligand design. We then describe the synthesis and use of a series of multicoordinating polymers as ligands optimized for coating quantum dots (QDs), gold nanoparticles (AuNPs), and magnetic nanoparticles (MNPs), with a focus on (i) how to improve the colloidal stability and antifouling performance of materials in biological conditions; (ii) how to design highly compact coating, without compromising colloidal stability; and (iii) how to tailor the surface functionalities to achieve conjugation to target biomolecules. We also highlight the ability of a phase transfer strategy, mediated by UV irradiation, to promote rapid ligand exchange while preserving the integrity of key functional groups. We then summarize the bioconjugation approaches applied to polymer-coated nanoparticles, with emphasis on the ability of metal-histidine self-assembly and click chemistry, to control the final nanoparticle bioconjugates. Finally, we demonstrate the use of polymer-coated nanoparticles for sensor design based on redox-active interactions and peptide-mediated intracellular delivery. We anticipate that the coating design presented in this Account would advance the integration of nanoparticles into biology and medicine.

Continuous growth phenomenon for direct synthesis of monodisperse water-soluble iron oxide nanoparticles with extraordinarily high relaxivity

The direct synthesis of highly water-soluble nanoparticles has attracted intensive interest, but systematic size control has not been reported. Here, we developed a general method for synthesizing monodisperse water-soluble iron oxide nanoparticles with nanometer-scale size increments from 4 nm to 13 nm in a single reaction. Precise size control was achieved by continuous growth in an amphiphilic solvent, diethylene glycol (DEG), where the growth step was separated from the nucleation step by sequential addition of a reactant. There was only one reactant in the synthesis and no need for additional capping agents and reducing agents. This study reveals the "living growth" character of iron oxide nanoparticles synthesised in an amphiphilic solvent. The synthetic method shows high reproducibility. The as-prepared iron oxide nanoparticles are extremely water soluble without any surface modification. Surprisingly, the synthesized 9 nm iron oxide nanoparticles exhibit extremely high transversal and longitudinal relaxivities of 425 mM-1 s-1 and 32 mM-1 s-1 respectively, which is among the highest transversal relaxivity in the literature for sub-10 nm spherical nanoparticles. This study will not only shed light on the continuous growth phenomenon of iron oxide nanoparticles in an amphiphilic solvent, but could also stimulate the synthesis and application of iron oxide nanoparticles. The continuous growth method could be further extended to other materials for the controlled synthesis of water-soluble nanoparticles.

Substrate-independent Cu(0)-mediated controlled radical polymerization: grafting of block copolymer brushes from poly(dopamine) modified surfaces

A method is presented combining poly(dopamine) chemistry and surface-initiated Cu(0)-mediated controlled radical polymerization (SI-CuCRP). Polymer brushes and block copolymer brushes are grafted independent of the original surface properties.

Photo-induced copper mediated copolymerization of activated-ester methacrylate polymers and their use as reactive precursors to prepare multi-dentate ligands for the water transfer of inorganic nanoparticles

Polymers bearing activated ester groups are synthesized using photo-ATRP and used as precursors for direct synthesis of multi-phosphonic acid functionalized ligands which are able to transfer different nanoparticles with distinct cores into water.

Bioinspired Surface Functionalization of Titanium for Enhanced Lubrication and Sustained Drug Release

Titanium and its alloys have long been used as implantable biomaterials in orthopedics; however, to the best of our knowledge, few studies were reported to investigate surface functionalization of titanium for enhanced lubrication and sustained drug release. In the present study, titania nanotube arrays (TNTs) were prepared by anodization as effective drug nanocarriers, using titanium as the substrate. Meanwhile, motivated by articular cartilage-inspired superlubricity and mussel-inspired adhesion, a copolymer containing both dopamine methacrylamide and 2-methacryloyloxyethyl phosphorylcholine was synthesized (DMA-MPC) and spontaneously grafted onto the TNT surface, which was validated by characterization techniques such as scanning electron microscopy, water contact angle measurements, and X-ray photoelectron spectroscopy. Additionally, the lubrication test showed that copolymer-grafted TNTs have remarkably reduced friction coefficients compared with bare TNTs. Furthermore, the drug release test demonstrated that copolymer-grafted TNTs inhibited burst drug release and achieved sustained drug release in comparison with bare TNTs. In conclusion, the bioinspired surface functionalization strategy developed here, namely DMA-MPC copolymer-grafted TNTs, can be applied to modify orthopedic biomaterials (such as titanium) for enhanced lubrication and sustained drug release.

Bioinspired Surface Functionalization of Nanodiamonds for Enhanced Lubrication

The addition of nanoparticles to water-based lubricants is a commonly used method to improve lubrication, but to the best of our knowledge few studies have been reported to investigate the lubrication property of surface-modified nanodiamonds (ND) with polyzwitterionic brushes. In this study, a bioinspired copolymer containing dopamine and 2-methacryloyloxyethyl phosphorylcholine (MPC) was synthesized (DMA-MPC) and then spontaneously grafted onto the ND surface (ND-MPC) through simple stirring in order to enhance lubrication. The characterization of transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis indicated that the DMA-MPC was successfully modified on the ND surface. Furthermore, a series of tribological experiment were performed on a universal materials tester using glycerol, glycerol + ND, and glycerol + ND-MPC as the lubricants. It was found that the addition of ND to the lubricant (i.e., glycerol + ND and glycerol + ND-MPC) significantly reduced wear with a smaller wear scar and wear track on the tribopairs, and the coefficient of friction further decreased by about 40% when using glycerol + ND-MPC as the lubricant, which could be attributed to the hydration lubrication of the polyzwitterionic brushes modified on the ND surface and the rolling effect of nanoparticles. In conclusion, in this study a universal and versatile surface modification method was proposed on the basis of the synthesis of bioinspired copolymer DMA-MPC, which remarkably enhanced the lubrication property of ND nanoparticles when added to water-based lubricants.

Enhanced Mechanical Properties of Polymer Nanocomposites Using Dopamine-Modified Polymers at Nanoparticle Surfaces in Very Low Molecular Weight Polymers

While incorporation of nanoparticles in a polymer matrix generally enhances the physical properties, effective control of the nanoparticle/polymer interface is often challenging. Here, we report a dramatic enhancement of the mechanical properties of polymer nanocomposites (PNCs) using a simple physical grafting method. The PNC consists of low molecular weight poly(ethylene glycol) (PEG) and silica nanoparticles whose surfaces are modified with dopamine-modified PEG (DOPA-mPEG) brush polymers. With DOPA-mPEG grafting, the nanoparticle surface can be readily altered, and the shear modulus of the PNC is increased by a factor of 10⁵ at an appropriate surface grafting density. The detailed microstructure and mechanical properties are examined with small-angle X-ray scattering (SAXS) and oscillatory rheometry experiments. The attractive interactions between particles induced by DOPA-mPEG grafting dramatically improve the mechanical properties of PNCs even in an unentangled polymer matrix, which shows a much higher shear modulus than that of a highly entangled polymer matrix.

Stability and Mobility of Magnetic Nanoparticles in Biological Environments Determined from Dynamic Magnetic Susceptibility Measurements

Low tumor accumulation following systemic delivery remains a key challenge for advancing many cancer nanomedicines. One obstacle in engineering nanoparticles for high tumor accumulation is a lack of techniques to monitor their stability and mobility in situ. One way to monitor the stability and mobility of magnetic nanoparticles biological fluids in situ is through dynamic magnetic susceptibility measurements (DMS), which under certain conditions provide a measure of the particle's rotational diffusivity. For magnetic nanoparticles modified to have commonly used biomedical surface coatings, we describe a systematic comparison of DMS measurements in whole blood and tumor tissue explants. DMS measurements clearly demonstrated that stability and mobility changed over time and from one medium to another for each different coating. It was found that nanoparticles coated with covalently grafted, dense layers of PEG were the only ones to show good stability and mobility in all settings tested. These studies illustrate the utility of DMS measurements to estimate the stability and mobility of nanoparticles in situ, and which can provide insights that lead to engineering better nanoparticles for in vivo use.

Hypoxia-Triggered Nanoscale Metal-Organic Frameworks for Enhanced Anticancer Activity

The oxygen-dependent feature of most photosensitizers (PSs) and the aggravated hypoxia tumor microenvironment seriously impede the photodynamic therapy (PDT) effectiveness. However, this undesirable impediment can be utilized to further trigger the activation of hypoxia-sensitive prodrugs. Moreover, a combined therapy can be used by associating PDT with hypoxia-activated chemotherapy. Herein, a multifunctional Hf-porphyrin nanoscale metal-organic framework (NMOF) platform [Hf/tetra(4-carboxyphenyl)porphine (TCPP)] has been synthesized, with a high porphyrin loading capacity and a well-ordered coordination array preventing porphyrin self-quenching, thus greatly improving the generation efficiency of reactive oxygen species (ROS), which is helpful for PDT. As-synthesized Hf-TCPP nanoparticles possess more than 50 wt % of TCPP PS content, good crystallization, and a large Brunauer-Emmett-Teller surface for further loading the hypoxia-activated prodrug [tirapazamine (TPZ)] in a high-loading content. Additionally, subsequent surface modification with a dopamine-derived polymer (DOPA-PIMA-mPEG) significantly improves their dispersibility and structural stability, and the controlled release kinetics of TPZ. Such a nanoplatform can efficiently produce ROS for PDT upon irradiation, and also the depletion of the oxygen could further aggravate the hypoxic environment of tumors to induce the activation of TPZ for achieving an enhanced treatment efficacy. This work demonstrates the great advantages of an NMOF-based platform in antitumor therapies for combined PDT and hypoxia-activated chemotherapy.

Magnetic control of cellular processes using biofunctional nanoparticles

Remote control of cellular functions is a key challenge in biomedical research. Only a few tools are currently capable of manipulating cellular events at distance, at spatial and temporal scales matching their naturally active range. A promising approach, often referred to as 'magnetogenetics', is based on the use of magnetic fields, in conjunction with targeted biofunctional magnetic nanoparticles. By triggering molecular stimuli via mechanical, thermal or biochemical perturbations, magnetic actuation constitutes a highly versatile tool with numerous applications in fundamental research as well as exciting prospects in nano- and regenerative medicine. Here, we highlight recent studies, comment on the advancement of magnetic manipulation, and discuss remaining challenges.

Individually Stabilized, Superparamagnetic Nanoparticles with Controlled Shell and Size Leading to Exceptional Stealth Properties and High Relaxivities

Superparamagnetic iron oxide nanoparticles (SPION) have received immense interest for biomedical applications, with the first clinical application as negative contrast agent in magnetic resonance imaging (MRI). However, the first generation MRI contrast agents with dextran-enwrapped, polydisperse iron oxide nanoparticle clusters are limited to imaging of the liver and spleen; this is related to their poor colloidal stability in biological media and inability to evade clearance by the reticuloendothelial system. We investigate the qualitatively different performance of a new generation of individually PEG-grafted core-shell SPION in terms of relaxivity and cell uptake and compare them to benchmark iron oxide contrast agents. These PEG-grafted SPION uniquely enable relaxivity measurements in aqueous suspension without aggregation even at 9.4 T magnetic fields due to their extraordinary colloidal stability. This allows for determination of the size-dependent scaling of relaxivity, which is shown to follow a d2 dependence for identical core-shell structures. The here introduced core-shell SPION with ∼15 nm core diameter yield a higher R2 relaxivity than previous clinically used contrast agents as well as previous generations of individually stabilized SPION. The colloidal stability extends to control over evasion of macrophage clearance and stimulated uptake by SPION functionalized with protein ligands, which is a key requirement for targeted MRI.

Selection of affinity peptides for the purification potential of porcine circovirus type 2 (PCV2) Cap virus-like particles (VLPs)

In this study, we describe the use of a M13 phage-displayed random peptide library for screening novel peptide motifs that specifically recognize recombinant PCV2 Cap protein for the first time.

Sensitive detection of Listeria monocytogenes based on highly efficient enrichment with vancomycin-conjugated brush-like magnetic nano-platforms

Pathogens pose a significant threat to public health worldwide. Despite many technological advances in the rapid diagnosis of pathogens, sensitive pathogen detection remains challenging because target pathogenic bacteria usually exist in complex samples at very low concentrations. Here, the construction of multivalent brush-like magnetic nanoprobes and their application for the efficient enriching of pathogens are demonstrated. Brush-like magnetic nanoprobes were constructed by modification with poly-L-lysine (PLL) onto amino-modified magnetic beads, followed by coupling of PEG (amine-PEG₅₀₀₀-COOH) to the amine sites of PLL. Subsequently, vancomycin (Van), a small-molecule antibiotic with affinity to the terminal peptide (D-alanyl-D-alanine) on the cell wall of Gram-positive bacteria, was conjugated to the carboxyl of the PEG. The use of multivalent brush-like magnetic nanoprobes (Van-PEG-PLL-MNPs) results in a high enrichment efficiency (>94%) and satisfactory purity for Listeria monocytogenes (employed as a model) within 20min, even at bacterial concentrations of only 10²cfumL^-1. Integrated with the enrichment of the Van-PEG-PLL-MNP nano-platform and electrochemiluminescence (ECL) detection, Listeria monocytogenes can be rapidly and accurately detected at levels as low as 10cfumL^-1. The approach described herein holds great potential for realizing rapid and sensitive pathogen detection in clinical samples.

Preparation of Magnetic Iron Oxide Nanoparticles (MIONs) with Improved Saturation Magnetization Using Multifunctional Polymer Ligand

This paper describes the preparation of ultra-small magnetic iron oxide (Fe₃O₄) nanoparticles (MIONs) coated with water-soluble thioether end-functionalized polymer ligand pentaerythritol tetrakis 3-mercaptopropionate-polymethacrylic acid (PTMP-PMAA). The MIONs were prepared by co-precipitation of aqueous iron precursor solution at a high temperature. The polymer modified MIONs were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometery (VSM). It was found that these MIONs were successfully modified by this water-soluble polymer ligand with a fairly uniform size and narrow size distribution. The dried powder of MIONs could be stored for a long time and re-dispersed well in water without any significant change. Additionally, the polymer concentration showed a significant effect on size and magnetic properties of the MIONs. The saturation magnetization was increased by optimizing the polymer concentration. Furthermore, the 3-(4,5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide (MTT)-assay demonstrated that these MIONs were highly biocompatible and they could be successfully coupled with fluorescent dye Rhodamine due to the formation of amide bond between carboxylic acid groups of MIONs and amine groups of dye. The obtained results indicated that these multifunctional MIONs with rich surface chemistry exhibit admirable potential in biomedical applications.

Facile Coating Strategy to Functionalize Inorganic Nanoparticles for Biosensing

The use of inorganic nanoparticles (NPs) for biosensing requires that they exhibit high colloidal stability under various physiological conditions. Here, we report on a general approach to render hydrophobic NPs into hydrophilic ones that are ready for bioconjugation. The method uses peglyated polymers conjugated with multiple dopamines, which results in multidentate coordination. As proof-of-concept, we applied the coating to stabilize ferrite and lanthanide NPs synthesized by thermal decomposition. Both polymer-coated NPs showed excellent water solubility and were stable at high salt concentrations under physiological conditions. We used these NPs as molecular-sensing agents to detect exosomes and bacterial nucleic acids.

Multifunctional and High Affinity Polymer Ligand that Provides Bio-Orthogonal Coating of Quantum Dots

We detail the design of hydrophilic metal-coordinating ligands and their use for the effective coating of luminescent quantum dots (QDs). The ligand design exploits the specific, reagent-free nucleophilic addition reaction of amine-modified molecules toward maleic anhydride to introduce several lipoic acid metal anchors, hydrophilic zwitterion moieties, and specific reactive groups along a poly(isobutylene-alt-maleic anhydride) (PIMA) chain. Tunable reactive groups tested in this study include azide, biotin, carboxyl, and amine. Cap exchange with these multilipoic acid ligands via a photochemical ligation strategy yields homogeneous QD dispersions that are colloidally stable over several biologically relevant conditions and for extended periods of time. The zwitterionic coating yields compact nanoparticle size and imparts nonsticky surface properties onto the QDs, preventing protein absorption. The introduction of a controllable number of reactive groups allows conjugation of the QDs to biomolecules via bio-orthogonal coupling chemistries including (1) attachment of the neurotransmitter dopamine to QDs via amine-isothiocyanate reaction to produce a platform capable of probing interactions with cysteine in proteins, based on charge transfer interactions; (2) self-assembly of biotinylated QDs with streptavidin-dye; and (3) ligation of azide-functionalized QDs to cyclooctyne-modified transferrin via copper-free click chemistry, used for intracellular delivery. This ligand design strategy can be used to prepare an array of metal-coordinating ligands adapted for coating other inorganic nanoparticles, including magnetic and plasmonic nanomaterials.

A multi-coordinating polymer ligand optimized for the functionalization of metallic nanocrystals and nanorods

We report the design and use of a multi-coordinating polymer ligand that is ideally suited for functionalizing gold nanoparticles and nanorods, and promoting their steric stabilization in buffer media. The ligand is prepared via a one-step nucleophilic addition reaction between poly(isobutylene-alt-maleic anhydride) and amine-modified anchoring groups and hydrophilic moieties. Surface functionalization of gold nanoparticles and nanorods with this polymer yields nanocrystals that exhibit excellent long-term colloidal stability over a broad range of conditions, including pH changes and in growth media, as verified using dynamic light scattering measurements combined with agarose gel electrophoresis. This polymer coating can also prevent the formation of protein corona. These features bode well for use in biological applications where small size, reduced nonspecific interactions and colloidal stability are highly desired. Furthermore, this design can be easily expanded to functionalize a variety of other inorganic nanocrystals.

Facile synthesis of novel hydrophilic and carboxyl-amine functionalized superparamagnetic iron oxide nanoparticles for biomedical applications

We report a one-step facile synthesis of novel water-soluble and functionalized SPIONs, which could be promising candidates for cancer theranostics.

Click Synthesis of Hydrophilic Maltose-Functionalized Iron Oxide Magnetic Nanoparticles Based on Dopamine Anchors for Highly Selective Enrichment of Glycopeptides

The development of methods to isolate and enrich low-abundance glycopeptides from biological samples is crucial to glycoproteomics. Herein, we present an easy and one-step surface modification strategy to prepare hydrophilic maltose functionalized Fe3O4 nanoparticles (NPs). First, based on the chelation of the catechol ligand with iron atoms, azido-terminated dopamine (DA) derivative was assembled on the surface of magnetic Fe3O4 nanoparticles by sonication. Second, the hydrophilic maltose-functionalized Fe3O4 (Fe3O4-DA-Maltose) NPs were obtained via copper(I)-catalyzed azide-alkyne cycloaddition (click chemistry). The morphology, structure, and composition of Fe3O4-DA-Maltose NPs were investigated by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectrometer (XPS), and vibrating sample magnetometer (VSM). Meanwhile, hydrophilicity of the obtained NPs was evaluated by water contact angle measurement. The hydrophilic Fe3O4-DA-Maltose NPs were applied in isolation and enrichment of glycopeptides from horseradish peroxidase (HRP), immunoglobulin (IgG) digests. The MALDI-TOF mass spectrometric analysis indicated that the novel NPs exhibited high detection sensitivity in enrichment from HRP digests at concentration as low as 0.05 ng μL(-1), a large binding capacity up to 43 mg g(-1), and good recovery for glycopeptides enrichment (85-110%). Moreover, the Fe3O4-DA-Maltose NPs were applied to enrich glycopeptides from human renal mesangial cells (HRMC) for identification of N-glycosylation sites. Finally, we identified 115 different N-linked glycopeptides, representing 93 gene products and 124 glycosylation sites in HRMC.

A multifunctional polymer combining the imidazole and zwitterion motifs as a biocompatible compact coating for quantum dots

We introduce a set of multicoordinating imidazole- and zwitterion-based ligands suited for surface functionalization of quantum dots (QDs). The polymeric ligands are built using a one-step nucleophilic addition reaction between poly(isobutylene-alt-maleic anhydride) and distinct amine-containing functionalities. This has allowed us to introduce several imidazole anchoring groups along the polymer chain for tight coordination to the QD surface and a controllable number of zwitterion moieties for water solubilization. It has also permitted the introduction of reactive and biomolecular groups for further conjugation and targeting. The QDs capped with these new ligands exhibit excellent long-term colloidal stability over a broad range of pH, toward excess electrolyte, in cell-growth media, and in the presence of natural reducing agents such as glutathione. These QDs are also resistant to the oxidizing agent H2O2. More importantly, by the use of zwitterion moieties as the hydrophilic block, this polymer design provides QDs with a thin coating and compact overall dimensions. These QDs are easily self-assembled with full size proteins expressed with a polyhistidine tag via metal-histidine coordination. Additionally, the incorporation of amine groups allows covalent coupling of the QDs to the neurotransmitter dopamine. This yields redox-active QD platforms that can be used to track pH changes and detect Fe ions and cysteine through charge-transfer interactions. Finally, we found that QDs cap-exchanged with folic acid-functionalized ligands could effectively target cancer cells, where folate-receptor-mediated endocytosis of QDs into living cells was time- and concentration-dependent.

Ligand exchange procedure for bimetallic magnetic iron-nickel nanocrystals toward biocompatible activities

Bimetallic magnetic iron-nickel (FeNi) nanocrystals (NCs) were synthesized through a one-pot synthetic wet chemistry method, and the morphology of the resulting NCs can be adjusted by changing the molar ratio of chemical attendees during the experimental processes. The obtained FeNi NCs can be redispersed in water medium though the phase works by using the ligand exchange procedures of cysteine (Cys), 5-aminovaleric acid (5AA), and glutathione (GSH), respectively. The synthesized NCs exhibited excellent magnetic properties with Hc (magnetic fields, ≈10(-3) T) and μa (initial permeability of up to 10(5)). Furthermore, linear sweep voltammetry (LSV) polarization curves revealed a low overpotential of -0.47, -0.44, and 0.15 V and a current of 105.7, 97.8, and 209 mA for the Cys-, 5AA-, and GSH-FeNi NCs, respectively. This indicated a relatively high catalytic activity of these NCs in the hydrogen evolution reaction (HER). The different cell lines (AGS, HepG2, MG63, NCI-H460, and SK-MEL-2) exposed to FeNi NCs for 5 days exhibited >87% viability at concentrations of up to 50 μg mL(-1), which was indicative of excellent biocompatibility. The resulting FeNi NCs offer a facile synthetic route to fabricate monodispersed NCs. The biocompatibility of these NCs should also enable their application in electrocatalysis and biological applications.

Photoligation of an amphiphilic polymer with mixed coordination provides compact and reactive quantum dots

We introduce a new set of multicoordinating polymers as ligands that combine two distinct metal-chelating groups, lipoic acid and imidazole, for the surface functionalization of QDs. These ligands combine the benefits of thiol and imidazole coordination to reduce issues of thiol oxidation and weak binding affinity of imidazole. The ligand design relies on the introduction of controllable numbers of lipoic acid and histamine anchors, along with hydrophilic moieties and reactive functionalities, onto a poly(isobutylene-alt-maleic anhydride) chain via a one-step nucleophilic addition reaction. We further demonstrate that this design is fully compatible with a novel and mild photoligation strategy to promote the in situ ligand exchange and phase transfer of hydrophobic QDs to aqueous media under borohydride-free conditions. Ligation with these polymers provides highly fluorescent QDs that exhibit great long-term colloidal stability over a wide range of conditions, including a broad pH range (3-13), storage at nanomolar concentration, under ambient conditions, in 100% growth media, and in the presence of competing agents with strong reducing property. We further show that incorporating reactive groups in the ligands permits covalent conjugation of fluorescent dye and redox-active dopamine to the QDs, producing fluorescent platforms where emission is controlled/tuned by Förster Resonance Energy Transfer (FRET) or pH-dependent charge transfer (CT) interactions. Finally, the polymer-coated QDs have been coupled to cell-penetrating peptides to facilitate intracellular uptake, while subsequent cytotoxicity tests show no apparent decrease in cell viability.

Monodispersity of magnetic immuno-nanoprobes enhances the detection sensitivity of low abundance biomarkers in one drop of serum

A streamlined protocol for biocompatible monodisperse magnetic nanoparticles for sensitive detection of low abundance protein biomarkers.

Dopamine functionalized polymeric nanoparticle for targeted drug delivery

A dopamine functionalized, polyaspartamide-based polymeric nanoparticle has been synthesized for selective delivery of drugs to human colon adenocarcinoma cells.

A mussel-inspired chitooligosaccharide based multidentate ligand for highly stabilized nanoparticles

A mussel-inspired poly(ethylene glycol)-grafted-chitooligosaccharide based multidentate ligand (ML) is designed for preparing robust biocompatible iron oxide nanoparticles. The successful in vivo MRI application confirmed their suitability for biomedical applications.

Strategies for interfacing inorganic nanocrystals with biological systems based on polymer-coating

A representative set of nanocrystals made of semiconductors, Au and iron oxide, surface-capped with polymer ligands presenting various metal-coordinating groups.

A multifunctional amphiphilic polymer as a platform for surface-functionalizing metallic and other inorganic nanostructures

We designed a new set of polymer ligands that combine multiple metal-coordinating groups and short polyethylene glycol (PEG) moieties in the same structure. The ligand design relies on the controlled grafting of a large number of amine-terminated histamines and PEG short chains onto a poly(isobutylene-alt-maleic anhydride) backbone,viaa one-step nucleophilic addition reaction. This addition reaction is highly efficient, can be carried out in organic media and does not require additional reagents. We show that when imidazole groups are used the resulting polymer ligand can strongly ligate onto metal nanostructures such as nanoparticles (NPs) and nanorods (NRs) made of gold cores. The resulting polymer-coated NPs and NRs exhibit good colloidal stability to pH changes and added electrolytes. This constitutes a departure from the use of thiol-based ligands to coordinate on Au surfaces. The present chemical approach also opens up additional opportunities for designing hydrophilic and reactive platforms where the polymer coating can be adjusted to various metal and metal oxide surfaces by simply modifying or combining the addition reaction with other metal coordinating groups. These could include iron oxide NPs and semiconductor QDs. These polymer-capped NPs and NRs can be used to develop biologically-active platforms with potential use for drug delivery and sensing.