Juenguo

The exterior surface of nanoparticles (NPs) dictates the behavior of these systems with the outside world. Understanding the interactions of the NP surface functionality with biosystems enables the design and fabrication of effective platforms for therapeutics, diagnostics, and imaging agents. In this review, we highlight the role of chemistry in the engineering of nanomaterials, focusing on the fundamental role played by surface chemistry in controlling the interaction of NPs with proteins and cells.

Surface chemistry of nanoparticles (NPs) is an essential factor that governs the interactions of nanoparticles with biosystems. Comprehensive knowledge of how NP surface chemistry affects the interactions with biomolecules, cells, and tissues can be used to design useful delivery and imaging systems.

A novel pH- and redox- dual-responsive tumor-triggered targeting mesoporous silica nanoparticle (TTTMSN) is designed as a drug carrier. The peptide RGDFFFFC is anchored on the surface of mesoporous silica nanoparticles via disulfide bonds, which are redox-responsive, as a gatekeeper as well as a tumor-targeting ligand. PEGylated technology is employed to protect the anchored peptide ligands. The peptide and monomethoxypolyethylene glycol (MPEG) with benzoic-imine bond, which is pH-sensitive, are then connected via “click” chemistry to obtain TTTMSN. In vitro cell research demonstrates that the targeting property of TTTMSN is switched off in normal tissues with neutral pH condition, and switched on in tumor tissues with acidic pH condition after removing the MPEG segment by hydrolysis of benzoic-imine bond under acidic conditions. After deshielding of the MPEG segment, the drug-loaded nanoparticles are easily taken up by tumor cells due to the exposed peptide targeting ligand, and subsequently the redox signal glutathione in tumor cells induces rapid drug release intracellularly after the cleavage of disulfide bond. This novel intelligent TTTMSN drug delivery system has great potential for cancer therapy.

A novel pH- and redox- dual-responsive mesoporous silica nanoparticle is demonstrated for tumor-triggered targeting drug delivery in tumor cells. Upon the acidic condition, the targeting property is switched on for enhanced tumor cell internalization. Once entering tumor cell, the loaded drug can be released quickly due to the removal of peptide capping. This intelligent tumor-triggered targeting mesoporous silica nanoparticle (TTTMSN) will find great potential for cancer treatment.

Exosomes are a class of naturally occurring nanomaterials that play crucial roles in the protection and transport of endogenous macromolecules, such as microRNA and mRNA, over long distances. Intense effort is underway to exploit the use of exosomes to deliver synthetic therapeutics. Herein, transmission electron microscopy is used to show that when spherical nucleic acid (SNA) constructs are endocytosed into PC-3 prostate cancer cells, a small fraction of them (<1%) can be naturally sorted into exosomes. The exosome-encased SNAs are secreted into the extracellular environment from which they can be isolated and selectively re-introduced into the cell type from which they were derived. In the context of anti-miR21 experiments, the exosome-encased SNAs knockdown miR-21 target by approximately 50%. Similar knockdown of miR-21 by free SNAs requires a ≈3000-fold higher concentration.

Spherical nucleic acid (SNA) constructs can be naturally sorted into exosomes when endocytosed into PC-3 prostate cancer cells. The exosome-encased SNAs are secreted into the extracellular environment from which they can be isolated and selectively re-introduced into the cell type from which they were derived as potent microRNA regulation agents.

Temperature changes in the vicinity of a single absorptive nanostructure caused by local heating have strong implications in technologies such as integrated electronics or biomedicine. Herein, the temperature changes in the vicinity of a single optically trapped spherical Au nanoparticle encapsulated in a thermo-responsive poly(N-isopropylacrylamide) shell (Au@pNIPAM) are studied in detail. Individual beads are trapped in a counter-propagating optical tweezers setup at various laser powers, which allows the overall particle size to be tuned through the phase transition of the thermo-responsive shell. The experimentally obtained sizes measured at different irradiation powers are compared with average size values obtained by dynamic light scattering (DLS) from an ensemble of beads at different temperatures. The size range and the tendency to shrink upon increasing the laser power in the optical trap or by increasing the temperature for DLS agree with reasonable accuracy for both approaches. Discrepancies are evaluated by means of simple models accounting for variations in the thermal conductivity of the polymer, the viscosity of the aqueous solution and the absorption cross section of the coated Au nanoparticle. These results show that these parameters must be taken into account when considering local laser heating experiments in aqueous solution at the nanoscale. Analysis of the stability of the Au@pNIPAM particles in the trap is also theoretically carried out for different particle sizes.

Temperature changes in the vicinity of a single absorptive nanostructure caused by local heating have strong implications in technologies such as integrated electronics or biomedicine. Laser irradiation of Au nanoparticles requires precise control over parameters that may lead to deviations in the expected local heating, such as variations in the thermal conductivity or the viscosity of the surrounding medium. To address the temperature changes in the vicinity of a single nanostructure, Au NPs encapsulated in thermo-responsive shells are individually optically trapped.

Virus-like theranostic nanoparticles: virus-like poly(amino acid) nanoparticles are synthesized that can be internalized via receptor-mediated endocytosis, resulting in encapsulated pH-activatable fluorescence probes that can be turned on in acidic environments but otherwise remain undetectable. The encapsulated anticancer drugs are also released into cytosol by endosome disruption.

Copper sulfide (CuS) nanoparticles have attracted increasing attention from biomedical researchers across the globe, because of their intriguing properties which have been mainly explored for energy- and catalysis-related applications to date. This focused review article aims to summarize the recent progress made in the synthesis and biomedical applications of various CuS nanoparticles. After a brief introduction to CuS nanoparticles in the first section, we will provide a concise outline of the various synthetic routes to obtain different morphologies of CuS nanoparticles, which can influence their properties and potential applications. CuS nanoparticles have found broad applications in vitro, especially in the detection of biomolecules, chemicals, and pathogens which will be illustrated in detail. The in vivo uses of CuS nanoparticles have also been investigated in preclinical studies, including molecular imaging with various techniques, cancer therapy based on the photothermal properties of CuS, as well as drug delivery and theranostic applications. Research on CuS nanoparticles will continue to thrive over the next decade, and tremendous opportunities lie ahead for potential biomedical/clinical applications of CuS nanoparticles.

Copper sulfide (CuS) nanoparticles have attracted increasing attention from biomedical researchers because of their intriguing properties. This focused review article aims to summarize the progress made to date in the synthesis and biomedical applications of CuS nanoparticles. Both in vitro and in vivo applications will be described, and challenges and future directions will be discussed. Research on CuS nanoparticles will continue to thrive over the next decade, and tremendous opportunities lie ahead for potential biomedical/clinical applications of these intriguing nanoparticles.

It is generally believed that intravenous application of cationic vectors is limited by the binding of abundant negatively charged serum components, which may cause rapid clearance of the therapeutic agent from the blood stream. However, previous studies show that systemic delivery of cationic gene vectors mediates specific and efficient transfection within the lung, mainly as a result of interaction of the vectors with serum proteins. Based on these findings, a novel and charge-density-controllable siRNA delivery system is developed to treat lung metastatic cancer by using cationic bovine serum albumin (CBSA) as the gene vector. By surface modification of BSA, CBSA with different isoelectric points (pI) is synthesized and the optimal cationization degree of CBSA is determined by considering the siRNA binding and delivery ability, as well as toxicity. The CBSA can form stable nanosized particles with siRNA and protect siRNA from degradation. CBSA also shows excellent abiliies to intracellularly deliver siRNA and mediate significant accumulation in the lung. When Bcl2-specific siRNA is introduced to this system, CBSA/siRNA nanoparticles exhibit an efficient gene-silencing effect that induces notable cancer cell apoptosis and subsequently inhibits the tumor growth in a B16 lung metastasis model. These results indicate that CBSA-based self-assembled nanoparticles can be a promising strategy for a siRNA delivery system for lung targeting and metastatic cancer therapy.

Cationic bovine serum albumin based self-assembled nanoparticles are developed to deliver therapeutic siRNA to treat lung metastatic cancer. Interaction between the vehicles and the negatively charged blood components mediates an immediate aggregate formation. This aggregation leads to a primary lung accumulation via the filter effect of capillary beds and the simultaneous dissolution of the aggregates facilitates efficient intracellular siRNA delivery within the lung.

Gold nanoparticles (AuNP) have been widely used for drug delivery and have recently been explored for applications in cancer immunotherapy. Although AuNPs are known to accumulate heavily in the spleen, the particle distribution within immune cells has not been thoroughly studied. Here, cellular distribution of Cy5 labeled 50 nm AuNPs is characterized within the immune populations of the spleen from naïve and tumor bearing mice using flow cytometry. Surprisingly, approximately 30% of the detected AuNPs are taken up by B cells at 24 h, with about 10% in granulocytes, 18% in dendritic cells, and 8% in T cells. In addition, 3% of the particles are detected within myeloid derived suppressor cells, an immune suppressive population that could be targeted for cancer immunotherapy. Furthermore, it is observed that, over time, the particles traveled from the red pulp and marginal zone to the follicles of the spleen. Taking into consideration that the particle cellular distribution does not change at 1, 6 and 24 h, it is highly suggestive that the immune populations carry the particles and migrate through the spleen instead of the particles migrating through the tissue by cell-cell transfer. Finally, no difference is observed in particle distribution between naïve and tumor bearing mice in the spleen, and nanoparticles are detected within 0.7% of dendritic cells of the tumor microenvironment. Overall, these results can help inform and influence future AuNP delivery design criteria including future applications for nanoparticle-mediated immunotherapy.

Gold nanoparticles (AuNPs) are promising vehicles for immunotherapy. However, there is little understanding of the distribution of AuNPs within cells of the immune system. This study characterizes the distribution of Cy5 labeled 50 nm gold nanoparticles within the spleen and tumor microenvironment, illustrating that AuNPs associate with a range of immune cells, including B cells, granulocytes, dendritic cells, and macrophages.

Hydrogen peroxide (H₂O₂) is a prominent member of the reactive oxygen species family and plays crucial roles in living organisms, thus detecting H₂O₂ and elucidating its biological functions has become an important area of biological and biomedical research. Herein, a multifunctional fluorescent nanoprobe is demonstrated for detecting mitochondrial H₂O₂. The nanoprobe is prepared by covalently linking a mitochondria-targeting ligand (triphenylphosphonium, TPP) and a H₂O₂ recognition element (PFl) onto carbon dots (CDs). For this nanoprobe, the CD serves as the carrier and the FRET donor. In the presence of H₂O₂, the PFl moieties on a CD undergo structural and spectral conversion, affording the nanoplatform a FRET-based ratiometric probe for H₂O₂. The nanoprobe displays excellent water dispersibility, high sensitivity and selectivity, satisfactory cell permeability, and very low cytotoxicity. Following the living cell uptake, this nanoprobe can specifically target and stain the mitochondria; and it can detect the exogenous H₂O₂ in L929 cells, as well as the endogenously produced mitochondrial H₂O₂ in Raw 264.7 cells upon stimulation by PMA. This study shows that CDs can serve as promising nano-carriers for fabricating practical multifunctional fluorescent nanosensors.

Targeted and ratiometric nanoprobe for sensing mitochondrial H₂O₂ in living cells: A FRET-based ratiometric and mitochondria-targeted nanoprobe for H₂O₂ is fabricated with carbon-dot as carrier, which features excellent cell permeability and little cytotoxicity. The nanoprobe can selectively target mitochondria and ratiometrically image the exogenous H₂O₂ and endogenously produced mitochondrial H₂O₂.

Using highly functional ‘building-blocks’ of AuNPs mono-conjugated to three-dimensional DNA ‘rung’ structures, both discrete and extended linear assemblies are controllably prepared via addition of various templating backbone strands. This unique approach presents a facile alternative to other methods of AuNP organization through DNA, and has potential utility in the fields of nanophotonics and nanoelectronics.

Multimodal imaging offers the potential to improve diagnosis and enhance the specificity of photothermal cancer therapy. Toward this goal, gadolinium-conjugated gold nanoshells are engineered and it is demonstrated that they enhance contrast for magnetic resonance imaging, X-ray, optical coherence tomography, reflectance confocal microscopy, and two-photon luminescence. Additionally, these particles effectively convert near-infrared light to heat, which can be used to ablate cancer cells. Ultimately, these studies demonstrate the potential of gadolinium-nanoshells for image-guided photothermal ablation.

When conjugated to gadolinium, near-infrared resonant gold-silica nanoshells can be employed for image-guided photothermal ablation of cancer. These particle conjugates demonstrate positive contrast across length scales with a variety of imaging modes, including magnetic resonance, X-ray, optical coherence tomography, reflectance confocal microscopy, and two-photon luminescence.

Semiconductor quantum dot nanocrystals (QDs) for optical biosensing applications often contain thick polyethylene glycol (PEG)-based coatings in order to retain the advantageous QD properties in biological media such as blood, serum or plasma. On the other hand, the application of QDs in Förster resonance energy transfer (FRET) immunoassays, one of the most sensitive and most common fluorescence-based techniques for non-competitive homogeneous biomarker diagnostics, is limited by such thick coatings due to the increased donor-acceptor distance. In particular, the combination with large IgG antibodies usually leads to distances well beyond the common FRET range of approximately 1 to 10 nm. Herein, time-gated detection of Tb-to-QD FRET for background suppression and an increased FRET range is combined with single domain antibodies (or nanobodies) for a reduced distance in order to realize highly sensitive QD-based FRET immunoassays. The “(nano)²” immunoassay (combination of nanocrystals and nanobodies) is performed on a commercial clinical fluorescence plate reader and provides sub-nanomolar (few ng/mL) detection limits of soluble epidermal growth factor receptor (EGFR) in 50 μL buffer or serum samples. Apart from the first demonstration of using nanobodies for FRET-based immunoassays, the extremely low and clinically relevant detection limits of EGFR demonstrate the direct applicability of the (nano)^2- assay to fast and sensitive biomarker detection in clinical diagnostics.

Nano-squared: The combination of single domain antibodies (nanobodies) and semiconductor quantum dots leads to highly sensitive and homogeneous Förster resonance energy transfer (FRET) immunoassays for epidermal growth factor receptor (EGFR).

A new strategy for promoting endoplasmic gene delivery and nucleus uptake is proposed by developing intracellular microenvironment responsive biocompatible polymers. This delivery system can efficiently load and self-assemble nucleic acids into nano-structured polyplexes at a neutral pH, release smaller imidazole-gene complexes from the polymer backbones at intracellular endosomal pH, transport nucleic acids into nucleus through intracellular environment responsive multiple-stage gene delivery, thus leading to a high cell transfection efficiency.

A detection platform combining NIR emitting CdSeTe/CdS/ZnS quantum dot (QD)-encoded microbeads and flow cytometry with a 488 nm laser is described on page 3327 by W. Li, K. Sun, X. Chen, and co-workers. This platform is used to conduct a 2-plex hybridization assay for hepatitis B surface antigen, hepatitis Be antigen and a 3-plex hybridization assay for hepatitis B surface antibody, hepatitis Be antibody and hepatitis B core antibody, which suggests the promising application of NIR QDencoded microbeads for multiplexed immunoassays.

Upconversion nanoparticles (UCNPs) can convert tissue-penetrable nearinfrared light into UV emission, making them promising as transducers for photoactivation in biology. However, the choice of the UV emitting UCNPs is limited and their NIR-to-UV efficiency is low. G. Han and co-workers have addressed this issue by developing a family of CaF₂-coated UCNPs with tunable UV enhancement. As reported on page 3213, such design outperforms known optimal UCNPs and in situ realtime live-cell photoactivation is recorded for the first time with such nanoparticles. This result is a potential game changer in photoactivation in living systems and a new tool for other biophotonic applications.

An approach for manipulating single adherent cells is developed that is integrated with an enzymatic batch release. This strategy uses an array of releasable microfabricated mobile substrates, termed microplates, formed from a biocompatible polymer, parylene. A parylene microplate array of 10–70 μm in diameter can be formed on an alginate hydrogel sacrificial layer by using a standard photolithographic process. The parylene surfaces are modified with fibronectin to enhance cell attachment, growth, and stretching. To load single cells onto these microplates, cells are initially placed in suspension at an optimized seeding density and are allowed to settle, stretch, and grow on individual microplates. The sacrificial layer underneath the microplate array can be dissolved on a time-scale of several seconds without cytotoxicity. This system allows the inspection of selected single adherent cells. The ability to assess single cells while maintaining their adhesive properties will broaden the examination of a variety of attributes, such as cell shape and cytoskeletal properties.

A microplate array for culturing, releasing, and manipulating single adherent cells is described. Single-cell-laden microplates are enzymatically releasable in a batch process without cytotoxicity, enabling the collection and manipulation of targeted cells. Cells remain adherent to the growth substrate throughout the manipulation process. This method can significantly enhance the handling and viability of single adherent cells.

The synthesis of yolk–shell catalysts, consisting of platinum or gold–platinum cores and graphitic carbon shells, and their electrocatalytic stabilities are described. Different encapsulation pathways for the metal nanoparticles are explored and optimized. Electrochemical studies of the optimized AuPt, @C catalyst revealed a high stability of the encapsulated metal particles. However, in order to reach full activity, several thousand potential cycles are required. After the electrochemical surface area is fully developed, the catalysts show exceptionally high stability, with almost no degradation over approximately 30 000 potential cycles between 0.4 and 1.4 V_RHE.

Encapsulation of noble metals in graphitic hollow shells by hard templating is explored as a means for stabilizing fuel cell catalysts. Small platinum particles can be encapsulated, but the achievable loading is too small. Encapsulation of Au–Pt yolk–shell particles allows higher loading, and with such cores, stable catalysts could be produced.

Non-aqueous routes to inorganic nanoparticles are supposedly based on the absence of water; here, this view is partially challenged, showing that the presence of water (or moisture) is probably necessary, and is surely useful to achieve a precise control over the growth/aggregation phenomena leading to titanium dioxide nanoparticles. This study is focused on the preparation of size-controlled and ligand-free titania (anatase) nanoparticles in water dispersion. This is achieved through a three-step process: 1) production of primary (3–4 nm) nanoparticles from titanium alkoxides (Ti(OnPr)₄, Ti(OnBu)₄ or Ti(OⁱPr)₄) in benzyl alcohol through the controlled addition of water; 2) thermal growth phase, where the aggregation of primary nanoparticles at 80 °C leads to secondary nanoparticles with a typical fractal dimension of 2.2–2.4; the primary particles are still identifiable as the individual crystallites composing the secondary nanoparticles; 3) precipitation/re-dispersion in water, where secondary nanoparticles further agglomerate to yield tertiary nanoparticles. The size of the latter and their photocatalytic efficiency is primarily controlled by the nature of residual alkoxide chains; in particular, isopropoxide groups allow to produce anatase nanoparticles with an average size of 7–8 nm in water dispersion and in the absence of any stabilizing ligand, which is an unprecedented result.

A detailed control of the aggregation behavior in a three-step preparative process allows to produce water-dispersible anatase nanoparticles with a ligand-free surface and dimensions <10 nm.

It stems from the magnetism: The extraction of stem/progenitor cells from the brain of live animals is possible using antibodies conjugated to magnetic nanoparticles (Ab-MNPs). The Ab-MNPs are introduced to a rat's brain with a superfine micro-syringe. The stem cells attach to the Ab-MNPs and are magnetically isolated and removed. They can develop into neurospheres and differentiate into different types of cells outside the subject body. The rat remains alive and healthy.

Back and forth: The CO₂/N₂ trigger of a switchable surfactant (neutral amidine/cationic amidinium) was transferred to mineral nanoparticles through in situ hydrophobization in water. Switchable oil-in-water Pickering emulsions that entail a CO₂/N₂ trigger were obtained by using negatively charged silica nanoparticles and a trace amount of the switchable surfactant as the stabilizer.

Hard-shell case: Using a (RKK)₄D₈ peptide allows mineralization to occur under cytocompatible conditions. Thus individual Chlorella cells could be encapsulated within a SiO₂–TiO₂ nanoshell with high cell viability (87 %). The encapsulated Chlorella showed an almost threefold increase in their thermo-tolerance after 2 h at 45 °C.

Subtle differences: Two recent crystal structures have provided the first insight into nitrate/nitrite exchangers (example shown with bound nitrite), which are crucial to bacterial metabolism. A direct comparison of the structures reveals how the proteins can distinguish between their highly similar substrates and translate this into a conformational change to translocate ions across the membrane.

Particles and sheets: Polyaniline is used as a linker to couple metal oxides and hydroxides to graphene sheets. Hydrothermal treatment converts these coupled hybrids into nitrogen-doped 2D carbon nanosheets integrated with size-controlled metal nanoparticles. This structure gives these 2D nanohybrids promising electrochemical behavior in supercapacitors and oxygen-reduction reactions.

Fold me to hold me: A specific binding agent against the delta-like ligand 4 protein, which is expressed in angiogenesis, was identified by ribosome display. Specific tumor binding of this molecular imaging agent depends on the appropriate disulfide connectivity of its scaffold.

The “gold standard” for nanothermometry: The application of ultrasmall, near-IR-emitting fluorescent gold nanoclusters (AuNCs) for temperature sensing has been explored. AuNC-based fluorescent nanothermometry features excellent thermal sensitivity and simultaneous temperature sensing and imaging in HeLa cells.