The Interplay of Size and Surface Functionality on the Cellular Uptake of Sub-10 nm Gold Nanoparticles

Toxic Effects of Size-tunable Gold Nanoparticles on Caenorhabditis elegans Development and Gene Regulation

We utilized size-tunable gold nanoparticles (Au NPs) to investigate the toxicogenomic responses of the model organism Caenorhabditis elegans. We demonstrated that the nematode C. elegans can uptake Au NPs coated with or without 11-mercaptoundecanoic acid (MUA), and Au NPs are detectable in worm intestines using X-ray microscopy and confocal optical microscopy. After Au NP exposure, C. elegans neurons grew shorter axons, which may have been related to the impeded worm locomotion behavior detected. Furthermore, we determined that MUA to Au ratios of 0.5, 1 and 3 reduced the worm population by more than 50% within 72 hours. In addition, these MUA to Au ratios reduced the worm body size, thrashing frequency (worm mobility) and brood size. MTT assays were employed to analyze the viability of cultured C. elegans primary neurons exposed to MUA-Au NPs. Increasing the MUA to Au ratios increasingly reduced neuronal survival. To understand how developmental changes (after MUA-Au NP treatment) are related to changes in gene expression, we employed DNA microarray assays and identified changes in gene expression (e.g., clec-174 (involved in cellular defense), cut-3 and fil-1 (both involved in body morphogenesis), dpy-14 (expressed in embryonic neurons), and mtl-1 (functions in metal detoxification and homeostasis)).

A systematic electron microscopic study on the uptake of barium sulphate nano-, submicro-, microparticles by bone marrow-derived phagocytosing cells

Nanoparticles can act as transporters for synthetic molecules and biomolecules into cells, also in immunology. Antigen-presenting cells like dendritic cells are important targets for immunotherapy in nanomedicine. Therefore, we have used primary murine bone marrow-derived phagocytosing cells (bmPCs), i.e. dendritic cells and macrophages, to study their interaction with spherical barium sulphate particles of different size (40 nm, 420 nm, and 1 µm) and to follow their uptake pathway. Barium sulphate is chemically and biologically inert (no dissolution, no catalytic effects), i.e. we can separate the particle uptake effect from potential biological reactions. The colloidal stabilization of the nanoparticles was achieved by a layer of carboxymethylcellulose (CMC) which is biologically inert and gives the particles a negative zeta potential (i.e. charge). The particles were made fluorescent by conjugating 6-aminofluoresceine to CMC. Their uptake was visualized by flow cytometry, confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and correlative light and electron microscopy (CLEM). Barium sulphate particles of all sizes were readily taken up by dendritic cells and even more by macrophages, with the uptake increasing with time and particle concentration. They were mainly localized inside phagosomes, heterophagosomes, and in the case of nanoparticles also in the nearby cytosol. No particles were found in the nucleus. In nanomedicine, inorganic nanoparticles from the nanometer to the micrometer size are therefore well suited as transporters of biomolecules, including antigens, into dendritic cells and macrophages. The presented model system may also serve to describe the aseptic loosening of endoprostheses caused by abrasive wear of inert particles and the subsequent cell reaction, a question which relates to the field of nanotoxicology. STATEMENT OF SIGNIFICANCE: The interaction of particles and cells is at the heart of nanomedicine and nanotoxicology, including abrasive wear from endoprostheses. It also comprises the immunological reaction to different kinds of nanomaterials, triggered by an immune response, e.g. by antigen-presenting cells. However, it is often difficult to separate the particle effect from a chemical or biochemical reaction to particles or their cargo. We show how chemically inert barium sulphate particles with three different sizes (nano, sub-micro, and micro) interact with relevant immune cells (primary dendritic cells and macrophages). Particles of all three sizes are readily taken up into both cell types by phagocytosis, but the uptake by macrophages is significantly more prominent than that by dendritic cells. The cells take up particles until they are virtually stuffed, but without direct adverse effect. The uptake increases with time and particle concentration. Thus, we have an ideal model system to follow particles into and inside cells without the side effect of a chemical particle effect, e.g. by degradation or ion release.

Size, Shape, and Protein Corona Determine Cellular Uptake and Removal Mechanisms of Gold Nanoparticles

Size, shape, and protein corona play a key role in cellular uptake and removal mechanisms of gold nanoparticles (Au NPs). The 15 nm nanoparticles (NP1), the 45 nm nanoparticles (NP2), and the rod-shaped nanoparticles (NR) enter into cells via a receptor-mediated endocytosis (RME) pathway. The star-shaped nanoparticles (NS) adopt not only clathrin-mediated, but also caveolin-mediated endocytosis pathways. However, the 80 nm nanoparitcles (NP3) mainly enter into the cells by macropinocytosis pathway due to the big size. Furthermore, the results indicate that the presence of protein corona can change the uptake mechanisms of Au NPs. The endocytosis pathway of NP1, NP2, and NS changes from RME to macropinocytosis pathway and NR changes from RME to clathrin and caveolin-independent pathway under the non-fetal bovine serun (FBS)-coated condition. Both FBS-coated and non-FBS-coated of five types of Au NPs are released out through the lysosomal exocytosis pathway. The size, shape, and protein corona have an effect on the exocytosis ratio and amount, but do not change the exocytosis mechanism. The systematic study of the endocytosis and exocytosis mechanism of Au NPs with different sizes and shapes will benefit the toxicology evaluation and nanomedicine application of Au NPs.

Nanoparticle-plant interaction: Implications in energy, environment, and agriculture

In the recent techno-scientific revolution, nanotechnology has gained popularity at a rapid pace in different sectors and disciplines, specifically environmental, sensing, bioenergy, and agricultural systems. Controlled, easy, economical, and safe synthesis of nanomaterials is desired for the development of new-age nanotechnology. In general, nanomaterial synthesis techniques, such as chemical synthesis, are not completely safe or environmentally friendly due to harmful chemicals used or to toxic by-products produced. Moreover, a few nanomaterials are present as by-product during washing process, which may accumulate in water, air, and soil system to pose serious threats to plants, animals, and microbes. In contrast, using plants for nanomaterial (especially nanoparticle) synthesis has proven to be environmentally safe and economical. The role of plants as a source of nanoparticles is also likely to expand the number of options for sustainable green renewable energy, especially in biorefineries. Despite several advantages of nanotechnology, the nano-revolution has aroused concerns in terms of the fate of nanoparticles in the environment because of the potential health impacts caused by nanotoxicity upon their release. In the present panoramic review, we discuss the possibility that a multitudinous array of nanoparticles may find applications convergent with human welfare based on the synthesis of diverse nanoparticles from plants and their extracts. The significance of plant-nanoparticle interactions has been elucidated further for nanoparticle synthesis, applications of nanoparticles, and the disadvantages of using plants for synthesizing nanoparticles. Finally, we discuss future prospects of plant-nanoparticle interactions in relation to the environment, energy, and agriculture with implications in nanotechnology.

Cellular Uptake of Nanoparticles versus Small Molecules: A Matter of Size

The primary function of the cell membrane is to protect cells from their surroundings. This entails a strict regulation on controlling the exchange of matter between the cell and its environment. A key factor when considering potential biological applications of a particular chemical structure has to do with its ability to internalize into cells. Molecules that can readily cross cell membranes are frequently needed in biological research and medicine, since most therapeutic entities are designed to modulate intracellular components. However, the design of molecules that do not penetrate cells is also relevant toward, for example, extracellular contrast agents, which are most widely used in clinical diagnosis. Small molecules have occupied the forefront of biomedical research until recently, but the past few decades have seen an increasing use of larger chemical structures, such as proteins or nanoparticles, leading to unprecedented and often unexpectedly novel research. Great achievements have been made toward understanding the rules that govern cellular uptake, which show that cell internalization of molecules is largely affected by their size. For example, macromolecules such as proteins and nucleic acids are usually unable to internalize cells. Intriguingly, in the case of nanoparticles, larger sizes seem to facilitate internalization via endocytic pathways, through which the particles remain trapped in lysosomes and endosomes. In this Account, we aimed at presenting our personal view of how different chemical structures behave in terms of cell internalization due to their size, ranging from small drugs to large nanoparticles. We first introduce the properties of cell membranes and the main mechanisms involved in cellular uptake. We then discuss the cellular internalization of molecules, distinguishing between those with molecular weights below 1 kDa and biological macromolecules such as proteins and nucleic acids. In the last section, we review the biological behavior of nanoparticles, with a special emphasis on plasmonic nanoparticles, which feature a high potential in the biomedical field. For each group of chemical structures, we discuss the parameters affecting their cellular internalization but also strategies that can be applied to achieve the desired intracellular delivery. Particular attention is paid to approaches that allow conditional regulation of the cell internalization process using external triggers, such as activable cell penetrating peptides, due to the impact that these systems may have in drug delivery and sensing applications. The Account ends with a "Conclusions and Outlook" section, where general lessons and future directions toward further advancements are briefly presented.

Promoting intracellular delivery of sub-25 nm nanoparticles via defined levels of compression

Many investigations into the interactions between nanoparticles and mammalian cells entail the use of culture systems that do not account for the effect of extracellular mechanical cues, such as compression. In this work, we present an experimental set-up to systematically investigate the combined effects of nanoparticle size and compressive stress on the cellular uptake and intracellular localization of poly(ethylene glycol)-coated gold nanoparticles (Au-PEG NPs). Specifically, we employ an automated micromechanical system to apply defined levels of compressive strain to an agarose gel, which transmits defined amounts of unconfined, uniaxial compressive stress to a monolayer of C2C12 mouse myoblasts seeded underneath the gel without compromising cell viability. Notably, uptake of Au-PEG NPs smaller than 25 nm by compressed myoblasts is up to 5-fold higher than that by uncompressed cells. The optimal compressive stress for maximizing the cellular uptake of sub-25 nm NPs monotonically increases with NP size. With and without compression, the Au-PEG NPs enter C2C12 cells via energy-dependent uptake; they also enter compressed cells via clathrin-mediated endocytosis as the major pathway. Upon cellular entry, the Au-PEG NPs more readily reside in the late endosomes or lysosomes of compressed cells than uncompressed cells. Results from our experimental set-up yield mechanistic insights into the delivery of NPs to cell types under extracellular compression.

A Versatile AuNP Synthetic Platform for Decoupled Control of Size and Surface Composition

While a plethora of protocols exist for the synthesis of sub-10-nm gold nanoparticles (AuNPs), independent control over the size and surface composition remains restricted. This poses a particular challenge for systematic studies of AuNP structure-function relationships and the optimization of crucial design parameters. To this end, we report on a modular two-step approach based on the synthesis of AuNPs in oleylamine (OAm) followed by subsequent functionalization with thiol ligands and mixtures thereof. The synthesis of OAm-capped AuNPs enables fine-tuning of the core size in the range of 2-7 nm by varying the reaction temperature. The subsequent thiol-for-OAm ligand exchange allows a reliable generation of thiol-capped AuNPs with target surface functionality. The compatibility of this approach with a vast library of thiol ligands provides detailed control of the mixed ligand composition and solubility in a wide range of solvents ranging from water to hexane. This decoupled control over the AuNP core and ligand shell provides a powerful toolbox for the methodical screening of optimal design parameters and facile preparation of AuNPs with target properties.

Near-Infrared-Light-Activatable Nanomaterial-Mediated Phototheranostic Nanomedicines: An Emerging Paradigm for Cancer Treatment

Cancer is one of the most deadly diseases threatening the lives of humans. Although many treatment methods have been developed to tackle cancer, each modality of cancer treatment has its own limitations and drawbacks. The development of minimally invasive treatment modalities for cancers remains a great challenge. Near-infrared (NIR) light-activated nanomaterial-mediated phototherapies, including photothermal and photodynamic therapies, provide an alternative means for spatially and temporally controlled minimally invasive treatments of cancers. Nanomaterials can serve as nanocargoes for the delivery of chemo-drugs, diagnostic contrast reagents, and organic photosensitizers, and can be used to directly generate heat or reactive oxygen species for the treatment of tumors without the need for organic photosensitizers with NIR-light irradiation. Here, current progress in NIR-light-activated nanomaterial-mediated photothermal therapy and photodynamic therapy is summarized. Furthermore, the effects of size, shape, and surface functionalities of nanomaterials on intracellular uptake, macrophage clearance, biodistribution, cytotoxicities, and biomedical efficacies are discussed. The use of various types of nanomaterials, such as gold nanoparticles, carbon nanotubes, graphene, and many other inorganic nanostructures, in combination with diagnostic and therapeutic modalities for solid tumors, is briefly reviewed.

Nanoparticle-Cell Interaction: A Cell Mechanics Perspective

Progress in the field of nanoparticles has enabled the rapid development of multiple products and technologies; however, some nanoparticles can pose both a threat to the environment and human health. To enable their safe implementation, a comprehensive knowledge of nanoparticles and their biological interactions is needed. In vitro and in vivo toxicity tests have been considered the gold standard to evaluate nanoparticle safety, but it is becoming necessary to understand the impact of nanosystems on cell mechanics. Here, the interaction between particles and cells, from the point of view of cell mechanics (i.e., bionanomechanics), is highlighted and put in perspective. Specifically, the ability of intracellular and extracellular nanoparticles to impair cell adhesion, cytoskeletal organization, stiffness, and migration are discussed. Furthermore, the development of cutting-edge, nanotechnology-driven tools based on the use of particles allowing the determination of cell mechanics is emphasized. These include traction force microscopy, colloidal probe atomic force microscopy, optical tweezers, magnetic manipulation, and particle tracking microrheology.

Intracellular Transport of Silver and Gold Nanoparticles and Biological Responses: An Update

Medicine, food, and cosmetics represent the new promising applications for silver (Ag) and gold (Au) nanoparticles (NPs). AgNPs are most commonly used in food and cosmetics; conversely, the main applications of gold NPs (AuNPs) are in the medical field. Thus, in view of the risk of accidentally or non-intended uptake of NPs deriving from the use of cosmetics, drugs, and food, the study of NPs⁻cell interactions represents a key question that puzzles researchers in both the nanomedicine and nanotoxicology fields. The response of cells starts when the NPs bind to the cell surface or when they are internalized. The amount and modality of their uptake depend on many and diverse parameters, such as NPs and cell types. Here, we discuss the state of the art of the knowledge and the uncertainties regarding the biological consequences of AgNPs and AuNPs, focusing on NPs cell uptake, location, and translocation. Finally, a section will be dedicated to the most currently available methods for qualitative and quantitative analysis of intracellular transport of metal NPs.

Stable and oxidant responsive zwitterionic nanoclusters

Zwitterions are promising ligands for the fabrication of non-toxic and non-interacting biomaterials. Sulfonamide-based monothiol zwitterionic ligands on gold nanocluster (AuNC) surfaces provide nanomaterials with stable colloidal properties and intense red emission in biological environments. The fluorescence intensity of the nanocluster can be modulated by reactive oxygen species (e.g. ˙OH), allowing for quantitative and selective sensing of antioxidants (e.g. ascorbic acid) in real time.

Label-free in-flow detection of receptor recognition motifs on the biomolecular corona of nanoparticles

Nanomedicine, nanotargeting and nanotherapeutics have in the last few years faced several difficulties in translating the promising results obtained in vitro to an in vivo scenario. The origin of this discrepancy might be found in the lack of a detailed and realistic characterization of the biological surface of nanoparticles. Despite the capability to engineer nanomaterials with a great variety and a precise control of the surface functionalization, the targeting capability is lost when the nanoparticles are embedded in complex biological media, due to the formation of a biological layer (biomolecular corona). This biological layer represents the ultimate nanoparticle surface, likely to interact with the cell machinery. Therefore, in addition to traditional nanoparticle characterization techniques, a more insightful investigation of the biomolecular corona is needed, including the capability to assess the orientation and functionality of specific key molecular features. Here we present a method for the rapid screening of exposed protein recognition motifs on the surface of nanoparticles exploiting quartz crystal microbalance (QCM). We quantify accessible functional epitopes of transferrin-coated nanoparticles and correlate them to differences in nanoparticle size and functionalization. The target recognition occurs label free in flow, thereby pushing our investigation into a more in vivo-like scenario. Our method is applicable to a wide array of nanoparticles and therefore holds the potential to become an advanced technique for the classification of all kinds of nanobioconstructs based on their biological external functionality.

Structure-Property Relationships of Amphiphilic Nanoparticles That Penetrate or Fuse Lipid Membranes

The development of synthetic nanomaterials that could embed within, penetrate, or induce fusion between membranes without permanent disruption would have great significance for biomedical applications. Here we describe structure-function relationships of highly water-soluble gold nanoparticles comprised of an ∼1.5-5 nm diameter metal core coated by an amphiphilic organic ligand shell, which exhibit membrane embedding and fusion activity mediated by the surface ligands. Using an environment-sensitive dye anchored within the ligand shell as a sensor of membrane embedding, we demonstrate that particles with core sizes of ∼2-3 nm are capable of embedding within and penetrating fluid bilayers. At the nanoscale, these particles also promote spontaneous fusion of liposomes or spontaneously embed within intact liposomal vesicles. These studies provide nanoparticle design and selection principles that could be used in drug delivery applications, as membrane stains, or for the creation of novel organic/inorganic nanomaterial self-assemblies.

Solvent switchable nanostructures and the function of a π-amphiphile

This manuscript reports solvent tunable functional nano-assemblies of an unsymmetrical bola-shaped π-amphiphile (NDI-PY) which consists of a hydrophobic naphthalene-diimide (NDI) chromophore connected to a non-ionic hydrophilic wedge and a pyridine group at its two opposite arms. Importantly, it contains a hydrazide group located at the hydrophobic domain between the NDI-chromophore and the hydrophilic-wedge to drive the supramolecular assembly by directional H-bonding. NDI-PY exhibits spontaneous assembly in water as well as in a highly non-polar solvent like tetra-chloroethylene (TCE) by the synergistic effect of H-bonding and π-stacking interaction. Spectroscopy studies reveal almost identical self-assembly features in water and TCE with critical aggregation concentrations in the range of 0.3 mM, which matches the values obtained from the isothermal calorimetry (ITC) dilution experiment. Differential scanning calorimetry (DSC) experiments reveal a single endothermic peak at 31 °C (ΔH = -12.3 kJ mol^-1) and 40 °C (ΔH = -5.35 kJ mol^-1) for water and TCE, respectively, indicating marginally higher thermal stability in TCE, which is consistent with the FT-IR data, suggesting stronger H-bonding in TCE. Although the molecular assembly features appear to be similar, NDI-PY produces distinctly different mesoscopic structures in water and TCE. In water, it forms vesicles (D_h = 150-180 nm) with the pyridine groups displayed at the outer surface, while in TCE it generates a transparent gel (CGC = 8.0 mM) with a nanotubular (width ∼50 nm, wall thickness ∼10 nm) morphology. Powder X-ray diffraction studies show clearly different packing structures; in water a single sharp peak at the low angle (d = 19.3 Å, a little shorter than the extended length of the molecule) suggests the formation of a monolayer membrane, while in TCE several sharp peaks appear with the d values maintaining a ratio of 1 : 1/√3 : 1/2 : 1/√7 : 1/3 : 1/√12, indicating the formation of a 2D hexagonal lattice. Photoconductivity measurements reveal moderate electronic conduction in both cases. However, it shows a remarkable enhancement of the life time of the charge-carriers for the nanotubular structure compared to the vesicular morphology. On the other hand, the vesicles in water display antimicrobial activity against Gram-positive S. aureus with a highly promising MIC_LB value of 29.4 μg mL^-1. In contrast, it does not lyse human red blood cells even at as high a concentration as 2.5 mg mL^-1 (HC₅₀ > 2.5 mg mL^-1), implying high selectivity of the NDI-PY vesicles towards bacterial cells over mammalian cells. Display of the pyridine groups at the outer surface of the membrane enables molecular recognition by complementary H-bonding with a carboxylic acid group and thereby facilitates uptake of the attached pyrene chromophores in the NDI-membrane by charge-transfer interaction between the NDI acceptor and the pyrene donor. In fact a Job's plot experiment reveals maximum uptake at a 1 : 1 ratio of the NDI-PY and the pyrene guest, indicating all the pyridine groups are accessible at the vesicular surface.

Gold nanoparticles impair autophagy flux through shape-dependent endocytosis and lysosomal dysfunction

Gold nanospheres stimulate more autophagosome accumulation than gold nanorods due to their higher efficiency of cellular uptake.

Reduction-responsive diblock copolymer-modified gold nanorods for enhanced cellular uptake

Reduction-responsive polymer micelles are highly promising drug carriers with better tumor therapeutic effect, which can be achieved by controlled drug release under stimulation. Gold nanorods (AuNRs) have attracted considerable attention due to their unique optical and electronic properties when used for biomedical applications. Herein, the lipoic-acid-functionalized reduction-responsive amphiphilic copolymer poly(ε-caprolactone)-b-poly[(oligoethylene glycol) acrylate] (LA–PCL–SS–POEGA) with a disulfide group between the two blocks was prepared to modify AuNRs via Au–S bonds. The size and morphology of AuNRs@LA–PCL–SS–POEGA were measured by dynamic laser light scattering (DLS) and transmission electron microscopy (TEM) methods. The stabilities of AuNRs@LA–PCL–SS–POEGA in different types of media were studied by UV/vis spectroscopy and DLS techniques. The results show that AuNRs@LA–PCL–SS–POEGA gradually aggregate in a concentrated salt solution containing 150 mM dithiothreitol (DTT), but exhibit high stability in a non-reducing environment. Near infrared (NIR)-induced heating of AuNRs@LA–PCL–SS–POEGA was investigated in an aqueous solution under NIR laser irradiation (808 nm), revealing that AuNRs@LA–PCL–R–POEGA maintain excellent photothermal conversion efficiency after modification. When compared with non-reduction responsive AuNRs@LA–PCL–CC–POEGA, the in vitro internalization of AuNRs@LA–PCL–SS–POEGA demonstrates that the reduction-responsive polymer could enhance the cellular uptake of nanoparticles measured by inductively coupled plasma mass spectrometry (ICP-MS) and TEM.

Gold nanorod (AuNRs) modified by reduction-responsive amphiphilic copolymer poly(ε-caprolactone)-b-poly[(oligoethylene glycol)acrylate] (LA–PCL–SS–POEGA) can enhance the cellular uptake of AuNRs, presumably due to the aggregation under reducing environment in the cells.

The effect of surface charge on oral absorption of polymeric nanoparticles

Positively charged nanoparticles showed a favorable distribution in the small intestine, and significantly improved oral bioavailability.

In Vivo Pharmacokinetics of Magnetic Nanoparticles

Over the past few years, many papers have been published on the nanomedical applications of magnetic nanoparticles. However, most studies lack important information about the in vivo behavior of these nanoparticles, which is a critical aspect for their rational design. In this chapter we describe a simple protocol for the in vivo characterization of the pharmacokinetics of magnetic nanoparticles intravenously injected in mice, using basic MRI sequences.

Preparation of Gold Nanocomposites with Tunable Charge and Hydrophobicity via the Application of Polymer/Surfactant Complexation

During the synthesis of gold nanoparticle (NP) assemblies, the interfacial charge and hydrophobicity of the primary particles play a distinguished role. In the present article, we demonstrate that the association of poly(ethyleneimine) (PEI) capped gold NPs with sodium alkyl sulfates provide a powerful route for the manipulation of these interfacial properties. Dynamic light-scattering, electrophoretic mobility, UV-vis-near-infrared spectroscopy, nanoparticle tracking analysis, and transmission electron microscopy measurements were used to characterize the PEI/surfactant/gold nanoassemblies. The results indicate the formation of gold NPs surrounded by a PEI/surfactant shell with composition-dependent charge and hydrophobicity. The mean size and the aggregation of the nanoassemblies can be fine tuned by the amount of surfactant bound to the primary gold NPs as well as by the application of controlled mixing methods. The specific features of the prepared nanocomposites may be further exploited in next-generation applications.

Gold Nanorods Stabilized by Biocompatible and Multifunctional Zwitterionic Copolymer for Synergistic Cancer Therapy

A zwitterionic copolymer between methacryloyloxyethyl phosphorylcholine (MPC) and methacrylic acid (MA), PMAMPC is introduced as a potential versatile polymeric stabilizer for gold nanorods (AuNRs). The MA units in the copolymer serve as built-in feature for multiple functionalization, namely introducing additional thiol groups as active sites for binding with the AuNRs and conjugating with doxorubicin (DOX), an anticancer drug via acid-labile hydrazone linkage. The MPC units, on the other hand, provide biocompatibility and antifouling characteristics. The chemically modified PMAMPC can act as an effective stabilizer for AuNRs yielding PMAMPC-DOX-AuNRs with a fairly uniform size and shape with good colloidal stability. In vitro cytotoxicity suggested that PMAMPC can not only improve the AuNRs biocompatibility, but also decrease DOX toxicity to a certain extent. The PMAMPC-DOX-AuNRs were efficiently internalized inside cancer cells and localized in lysosomes, where DOX was presumably acid-triggered released as monitored by confocal laser scanning microscopic analysis and flow cytometry. Furthermore, the combined photothermal-chemo treatment of cancer cells using PMAMPC-DOX-AuNRs exhibited a higher therapeutic efficacy than either single treatment alone. These results suggested that the PMAMPC-DOX-AuNRs could potentially be applied in pH-triggered drug delivery for synergistic cancer therapy.

Peptide Brush Polymers and Nanoparticles with Enzyme-Regulated Structure and Charge for Inducing or Evading Macrophage Cell Uptake

Cellular uptake by macrophages and ensuing clearance by the mononuclear phagocyte system stands as a significant biological barrier for nanoparticle therapeutics. While there is a growing body of work investigating the design principles essential for imparting nanomaterials with long-circulating characteristics and macrophage evasion, there is still a widespread need for examining stimuli-responsive systems, particularly well-characterized soft materials, which differ in their physiochemical properties prior to and after an applied stimulus. In this work, we describe the synthesis and formulation of polymeric nanoparticles (NPs) and soluble homopolymers (Ps) encoded with multiple copies of a peptide substrate for proteases. We examined the macrophage cell uptake of these materials, which vary in their peptide charge and conjugation (via the N- or C-terminus). Following treatment with a model protease, thermolysin, the NPs and Ps undergo changes in their morphology and charge. After proteolysis, zwitterionic NPs showed significant cellular uptake, with the C-terminus NP displaying higher internalization than its N-terminus analogue. Enzyme-cleaved homopolymers generally avoided assembly and uptake, though at higher concentrations, enzyme-cleaved N-terminus homopolymers assembled into discrete cylindrical structures, whereas C-terminus homopolymers remained dispersed. Overall, these studies highlight that maintaining control over NP and polymer design parameters can lead to well-defined biological responses.

Reversible Modulation of the Electrostatic Potential of a Colloidal Quantum Dot through the Protonation Equilibrium of Its Ligands

This Letter describes the reversible modulation of the electrostatic potential at the interface between a colloidal PbS quantum dot (QD) and solvent, through the protonation equilibrium of the QD's histamine-derivatized dihydrolipoic acid (DHLA) ligand shell. The electrostatic potential is sensitively monitored by the yield of photoinduced electron transfer from the QD to a charged electron acceptor, 9,10-anthraquinone-2-sulfonate (AQ). The permeability of the DHLA coating to the AQ progressively increases as the average degree of protonation of the ligand shell increases from 0 to 92%, as quantified by ¹H NMR, upon successive additions of p-toluenesulfonic acid; this increase results in a decrease in the photoluminescence (PL) intensity of the QDs by a factor of 6.7. The increase in permeability is attributable to favorable electrostatic interactions between the ligands and AQ. This work suggests the potential of the combination of near-IR-emitting QDs and molecular quenchers as robust local H⁺ sensors.

Carbon nanotubes as anti-bacterial agents

Multidrug-resistant bacterial infections that have evolved via natural selection have increased alarmingly at a global level. Thus, there is a strong need for the development of novel antibiotics for the treatment of these infections. Functionalized carbon nanotubes through their unique properties hold great promise in the fight against multidrug-resistant bacterial infections. This new family of nanovectors for therapeutic delivery proved to be innovative and efficient for the transport and cellular translocation of therapeutic molecules. The current review examines the latest progress in the antibacterial activity of carbon nanotubes and their composites.

Nanoparticle probes for quantifying supramolecular determinants of biosurface affinity

Interactions between macromolecular systems and biosurfaces are complicated by both the complexity of these multivalent interactions and challenges in quantifying affinities. A library of gold nanoparticles (AuNPs) as multivalent probes is used to quantify biosurface affinity, using hair as a model targeted substrate.

Gold nanoparticles with patterned surface monolayers for nanomedicine: current perspectives

Molecular self-assembly is a topic attracting intense scientific interest. Various strategies have been developed for construction of molecular aggregates with rationally designed properties, geometries, and dimensions that promise to provide solutions to both theoretical and practical problems in areas such as drug delivery, medical diagnostics, and biosensors, to name but a few. In this respect, gold nanoparticles covered with self-assembled monolayers presenting nanoscale surface patterns-typically patched, striped or Janus-like domains-represent an emerging field. These systems are particularly intriguing for use in bio-nanotechnology applications, as presence of such monolayers with three-dimensional (3D) morphology provides nanoparticles with surface-dependent properties that, in turn, affect their biological behavior. Comprehensive understanding of the physicochemical interactions occurring at the interface between these versatile nanomaterials and biological systems is therefore crucial to fully exploit their potential. This review aims to explore the current state of development of such patterned, self-assembled monolayer-protected gold nanoparticles, through step-by-step analysis of their conceptual design, synthetic procedures, predicted and determined surface characteristics, interactions with and performance in biological environments, and experimental and computational methods currently employed for their investigation.

Radiosensitization by gold nanoparticles: Will they ever make it to the clinic?

The utilization of gold nanoparticles (AuNPs) as radiosensitizers has shown great promise in pre-clinical research. In the current review, the physical, chemical, and biological pathways via which AuNPs enhance the effects of radiation are presented and discussed. In particular, the impact of AuNPs on the 5 Rs in radiobiology, namely repair, reoxygenation, redistribution, repopulation, and intrinsic radiosensitivity, which determine the extent of radiation enhancement effects are elucidated. Key findings from previous studies are outlined. In addition, crucial parameters including the physicochemical properties of AuNPs, route of administration, dosing schedule of AuNPs and irradiation, as well as type of radiation therapy, are highlighted; the optimal selection and combination of these parameters enable the achievement of a greater therapeutic window for AuNP sensitized radiotherapy. Future directions are put forward as a means to provide guidelines for successful translation of AuNPs to clinical applications as radiosensitizers.

Dual-Mode Mass Spectrometric Imaging for Determination of in Vivo Stability of Nanoparticle Monolayers

Effective correlation of the in vitro and in vivo stability of nanoparticle-based platforms is a key challenge in their translation into the clinic. Here, we describe a dual imaging method that site-specifically reports the stability of monolayer-functionalized nanoparticles in vivo. This approach uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) imaging to monitor the distributions of the nanoparticle core material and laser desorption/ionization mass spectrometry (LDI-MS) imaging to report on the monolayers on the nanoparticles. Quantitative comparison of the images reveals nanoparticle stability at the organ and suborgan level. The stability of particles observed in the spleen was location-dependent and qualitatively similar to in vitro studies. In contrast, in vivo stability of the nanoparticles in the liver differed dramatically from in vitro studies, demonstrating the importance of in vivo assessment of nanoparticle stability.

Quantitative Particle-Cell Interaction: Some Basic Physicochemical Pitfalls

There are numerous reports about particle-cell interaction studies in the literature. Many of those are performed in two-dimensional cell cultures. While the interpretation of such studies seems trivial at first sight, in fact for quantitative analysis some basic physical and physicochemical bases need to be considered. This starts with the dispersion of the particles, for which gravity, Brownian motion, and interparticle interactions need to be considered. The respective strength of these interactions determines whether the particles will sediment, are dispersed, or are agglomerated. This in turn largely influences their interaction with cells. While in the case of well-dispersed particles only a fraction of them will come into contact with cells in a two-dimensional culture, (agglomeration-induced) sedimentation drives the particles toward the cell surface, resulting in enhanced uptake.

Shedding light on zwitterionic magnetic nanoparticles: limitations for in vivo applications

Over the last few years several studies have dealt with the importance of the surface charge of nanoparticles in prolonging their blood circulation and minimizing their interaction with plasma proteins. These investigations claimed that zwitterionic nanoparticles exhibited a minimal macrophage response and long blood circulation times compared to nanoparticles with other surface charges. These differences in their in vivo behavior are mainly attributed to the interaction of nanoparticles with plasma proteins. Interestingly, most of these studies considered the total surface charge, instead of the outermost layer of the nanomaterial, as being mainly responsible for these undesirable interactions. However, the first contact with plasma proteins is most likely due to the outermost layer on the nanomaterials. Therefore, here we report a detailed study on the effect of the outermost surface charge of magnetic nanoparticles with regard to biodistribution, pharmacokinetics and bioavailability. Magnetic nanoparticles, coated with PEG chains functionalized with neutral, positive or zwitterionic groups, were intravenously injected into mice, followed in vivo by MRI and then quantified by ICP-MS in blood and the main organs. We found that neutral nanoparticles exhibited long blood circulation times, very good stealth properties and the highest bioavailability, whereas zwitterionic nanoparticles were readily recognized by the mononuclear phagocyte system and avidly taken up by the liver. Also, zwitterionic nanoparticles showed high non-specific cell internalization, whereas neutral nanoparticles showed the lowest cellular uptake, indicating that they require active transport to cross the plasma membrane, which is the desirable situation for therapeutic vehicles with low side effects. Thus, neutral nanoparticles exhibit very favorable characteristics for in vivo applications, whereas zwitterionic nanoparticles show important limitations.

Gold Nanoparticle Size and Shape Effects on Cellular Uptake and Intracellular Distribution of siRNA Nanoconstructs

Gold nanoparticles (AuNPs) show potential for transfecting target cells with small interfering RNA (siRNA), but the influence of key design parameters such as the size and shape of the particle core is incomplete. This paper describes a side-by-side comparison of the in vitro response of U87 glioblastoma cells to different formulations of siRNA-conjugated gold nanoconstructs targeting the expression of isocitrate dehydrogenase 1 (IDH1) based on 13 nm spheres, 50 nm spheres, and 40 nm stars. 50 nm spheres and 40 nm stars showed much higher uptake efficiency compared to 13 nm spheres. Confocal fluorescence microscopy showed that all three formulations were localized in the endosomes at early incubation times (2 h), but after 24 h, 50 nm spheres and 40 nm stars were neither in endosomes nor in lysosomes while 13 nm spheres remained in endosomes. Transmission electron microscopy images revealed that the 13 nm spheres were enclosed and dispersed within endocytic vesicles while 50 nm spheres and 40 nm stars were aggregated, and some of these NPs were outside of endocytic vesicles. In our comparison of nanoconstructs with different sizes and shapes, while holding siRNA surface density and nanoparticle concentration constant, we found that larger particles (50 nm spheres and 40 nm stars) showed higher potential as carriers for the delivery of siRNA.

The Effect of shape on Cellular Uptake of Gold Nanoparticles in the forms of Stars, Rods, and Triangles

Gold nanomaterials have attracted considerable interest as vehicles for intracellular drug delivery. In our study, we synthesized three different shapes of methylpolyethylene glycol coated-anisotropic gold nanoparticles: stars, rods, and triangles. The cellular internalization of these nanoparticles by RAW264.7 cells was analyzed, providing a parametric evaluation of the effect of shape. The efficiency of cellular uptake of the gold nanoparticles was found to rank in the following order from lowest to highest: stars, rods, and triangles. The possible mechanisms of cellular uptake for the three types of gold nanoparticles were examined, and it was found that different shapes tended to use the various endocytosis pathways in different proportions. Our study, which has demonstrated that shape can modulate the uptake of nanoparticles into RAW264.7 cells and that triangles were the shape with the most efficient cellular uptake, provides useful guidance toward the design of nanomaterials for drug delivery.

Nanosalina: A Tale of Saline-Loving Algae from the Lake's Agony to Cancer Therapy

The nanoparticles (NPs) that contain the therapeutic agent within themselves without further modifications can be coined as "self-therapeutic" NPs. The development of these agents especially when derived from natural resources can lead to a paradigm shift in the field of cancer nanotechnology as they can immensely facilitate the complex chemistry procedures and the follow up biological complications. Herein, we demonstrate that inherently therapeutic NPs "integrating" β-carotene can be synthesized from Dunaliella salina microalgae in a single step without complicated chemistry. The facile synthesis involved microwave irradiation of aqueous suspension of algae which resulted in water dispersible NPs with hydrodynamic diameter of ∼80 nm. Subsequently, extensive physiochemical characterizations were performed to confirm the integrity of the particles. The pro-oxidant activities of the integrated β-carotene were triggered by photoexcitation under UV lamp (362 nm). It was demonstrated that after UV exposure, the C32 human melanoma cells incubated with NPs experienced extensive cell death as opposed to nonilluminated samples. Further cellular analysis revealed that the significant reactive oxygen species (ROS) and in particular singlet oxygen were responsible for the cells' damage while the mode of cell death was dominated by apoptosis. Moreover, detailed endocytic inhibition studies specified that UV exposure affected NPs' cellular uptake mechanism. These inherently therapeutic NPs can open new avenues for melanoma cancer treatment via ROS generation in vitro.

Cooperative Strategies for Enhancing Performance of Photothermal Therapy (PTT) Agent: Optimizing Its Photothermal Conversion and Cell Internalization Ability

Photothermal conversion ability (PCA) and cell internalization ability (CIA) are two key factors for determining the performance of photothermal agents. The previous studies mostly focus on improving the PCA by exploring new photothermal nanomaterials. Herein, the authors take the hybrids of graphene and gold nanostar (GGN) as an example to investigate the gradually enhanced phototherapy effect by changing the PCA and CIA of photothermal therapy (PTT) agent simultaneously. Based on the GGN, the GGN and the reduced GGN protected by bovine serum albumin (BSA) or BSA-FA (folic acid) are prepared, which are named as GGNB, rGGNB, and rGGNB-FA, respectively. The rGGNB showed an enhanced PCA compared to GGNB, leading to strong cell ablation. On the other hand, the 1,2-dioleoyl-3-trimethylammoniumpropan (DOTAP) can activate the endocytosis and promote the CIA of rGGNB, further help rGGNB to be more internalized into the cells. Finally, rGGNB-FA with the target ability can make itself further internalized into the cells with the aid of DOTAP, which can significantly destroy the cancer cells even at the low laser density of 0.3 W cm^-2 . Therefore, a new angle of view is brought out for researching the PTT agents of high performance.

Development of nanoparticle-based optical sensors for pathogenic bacterial detection

Background

Pathogenic bacteria contribute to various globally important diseases, killing millions of people each year. Various fields of medicine currently benefit from or may potentially benefit from the use of nanotechnology applications, in which there is growing interest. Disease-related biomarkers can be rapidly and directly detected by nanostructures, such as nanowires, nanotubes, nanoparticles, cantilevers, microarrays, and nanoarrays, as part of an accurate process characterized by lower sample consumption and considerably higher sensitivity. There is a need for accurate techniques for pathogenic bacteria identification and detection to allow the prevention and management of pathogenic diseases and to assure food safety.

Conclusion

The focus of this review is on the current nanoparticle-based techniques for pathogenic bacterial identification and detection using these applications.

Photoluminescent Gold Nanoclusters in Cancer Cells: Cellular Uptake, Toxicity, and Generation of Reactive Oxygen Species

In recent years, photoluminescent gold nanoclusters have attracted considerable interest in both fundamental biomedical research and practical applications. Due to their ultrasmall size, unique molecule-like optical properties, and facile synthesis gold nanoclusters have been considered very promising photoluminescent agents for biosensing, bioimaging, and targeted therapy. Yet, interaction of such ultra-small nanoclusters with cells and other biological objects remains poorly understood. Therefore, the assessment of the biocompatibility and potential toxicity of gold nanoclusters is of major importance before their clinical application. In this study, the cellular uptake, cytotoxicity, and intracellular generation of reactive oxygen species (ROS) of bovine serum albumin-encapsulated (BSA-Au NCs) and 2-(N-morpholino) ethanesulfonic acid (MES)-capped photoluminescent gold nanoclusters (Au-MES NCs) were investigated. The results showed that BSA-Au NCs accumulate in cells in a similar manner as BSA alone, indicating an endocytotic uptake mechanism while ultrasmall Au-MES NCs were distributed homogeneously throughout the whole cell volume including cell nucleus. The cytotoxicity of BSA-Au NCs was negligible, demonstrating good biocompatibility of such BSA-protected Au NCs. In contrast, possibly due to ultrasmall size and thin coating layer, Au-MES NCs exhibited exposure time-dependent high cytotoxicity and higher reactivity which led to highly increased generation of reactive oxygen species. The results demonstrate the importance of the coating layer to biocompatibility and toxicity of ultrasmall photoluminescent gold nanoclusters.

Effect of Gold Nanoparticle Size and Coating on Labeling Monocytes for CT Tracking

With advances in cell therapies, interest in cell tracking techniques to monitor the migration, localization, and viability of these cells continues to grow. X-ray computed tomography (CT) is a cornerstone of medical imaging but has been limited in cell tracking applications due to its low sensitivity toward contrast media. In this study, we investigate the role of size and surface functionality of gold nanoparticles for monocyte uptake to optimize the labeling of these cells for tracking in CT. We synthesized gold nanoparticles (AuNP) that range from 15 to 150 nm in diameter and examined several capping ligands, generating 44 distinct AuNP formulations. In vitro cytotoxicity and uptake experiments were performed with the RAW 264.7 monocyte cell line. The majority of formulations at each size were found to be biocompatible, with only certain 150 nm PEG functionalized particles reducing viability at high concentrations. High uptake of AuNP was found using small capping ligands with distal carboxylic acids (11-MUA and 16-MHA). Similar uptake values were found with intermediate sizes (50 and 75 nm) of AuNP when coated with 2000 MW poly(ethylene-glycol) carboxylic acid ligands (PCOOH). Low uptake values were observed with 15, 25, 100, and 150 nm PCOOH AuNP, revealing interplay between size and surface functionality. Transmission electron microscopy (TEM) and CT performed on cells revealed similar patterns of high gold uptake for 50 nm PCOOH and 75 nm PCOOH AuNP. These results demonstrate that highly negatively charged carboxylic acid coatings for AuNP provide the greatest internalization of AuNP in monocytes, with a complex dependency on size.

Insight into the interactions between nanoparticles and cells

This review summarizes the latest advances in nanoparticle (NP)–cell interactions. The influence of NP size, shape, shell structure, surface chemistry and protein corona formation on cellular uptake and cytotoxicity is highlighted in detail. Their impact on other cellular responses such as cell proliferation, differentiation and cellular mechanics is also discussed.

Size changeable nanosystems for precise drug controlled release and efficient overcoming of cancer multidrug resistance

Herein we demonstrate the rational design of a size changeable nanosystem for precise drug controlled release and efficient overcoming of cancer multidrug resistance in cancer cells by enhancing the cellular uptake and inhibiting the expression of ABC family proteins.

In vivo self-assembly induced retention of gold nanoparticles for enhanced photothermal tumor treatment

A simple route to fabricate peptide modified spherical gold nanoparticles with enhanced retention performance in tumor sites for improved photothermal treatment.

Sub-10 nm gold nanoparticles promote adipogenesis and inhibit osteogenesis of mesenchymal stem cells

Sub-10 nm Au NPs with an average size of 4 nm (Au4-mPEG NPs) had a promotive effect on the adipogenic differentiation and an inhibitive effect on the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs) due to the highly induced ROS level.

Pentacle gold-copper alloy nanocrystals: a new system for entering male germ cells in vitro and in vivo

Gold-based nanocrystals have attracted considerable attention for drug delivery and biological applications due to their distinct shapes. However, overcoming biological barriers is a hard and inevitable problem, which restricts medical applications of nanomaterials in vivo. Seeking for an efficient transportation to penetrate biological barriers is a common need. There are three barriers: blood-testis barrier, blood-placenta barrier, and blood-brain barrier. Here, we pay close attention to the blood-testis barrier. We found that the pentacle gold-copper alloy nanocrystals not only could enter GC-2 cells in vitro in a short time, but also could overcome the blood-testis barrier and enter male germ cells in vivo. Furthermore, we demonstrated that the entrance efficiency would become much higher in the development stages. The results also suggested that the pentacle gold-copper alloy nanocrystals could easier enter to germ cells in the pathological condition. This system could be a new method for theranostics in the reproductive system.