Surface Tailoring of Nanoparticles via Mixed‐Charge Monolayers and Their Biomedical Applications

The recent convergence of nanomaterials and medicine has provided an expanding horizon for people to achieve encouraging advances in many biomedical applications such as cancer diagnosis and therapy. However, to realize desirable functions in the rather complex biological systems, a suitable surface coating is greatly in need for nanoparticles (NPs), regardless of the species. In this review, a recently developed surface modification strategy is highlighted—mixed‐charge monolayers—with an emphasis on the nanointerfaces of inorganic NPs. Two typical mixed‐charge gold NPs (AuNPs) prepared from surface modifications with different combinations of oppositely charged alkanethiols are shown as detailed examples to discuss how the mixed‐charge monolayer can help NPs meet the criteria for in vitro and in vivo biomedical applications, including those critical issues like colloidal stability, nonfouling properties, and smart responses (pH‐sensitivity) for tumor targeting.     

Control of colloidal behavior of polystyrene latex nanoparticles and their cytotoxicity toward yeast cells using water-soluble polymers

Positively charged polystyrene latex (PSL) nanoparticles (NPs) dispersed in physiological saline (154?mM NaCl solution) are taken up by yeast cells. However, in low ionic strength solutions, the yeast cells are covered with the NPs, leading to cell death. The environmental conditions under which NPs are taken up are therefore limited. In this study, we attempted to control the uptake of positively charged PSL NPs by Saccharomyces cerevisiae in 5?mM NaCl solution using a water-soluble polymer. Addition of a small amount of anionic sodium carboxymethylcellulose (CMC), which has a carboxyl group, to 5?mM NaCl solution allowed the uptake of PSL NPs by living yeast cells. In contrast, non-ionic methylcellulose did not affect the NP behavior. This is because the negatively charged CMC adhered to the positively charged PSL NP surfaces and the surface charge changed from positive to negative. Atomic force microscopy using a single-NP probe consisting of one NP immobilized on the flattened end of the silicon nitride tip showed that CMC significantly reduced the interaction force between a negatively charged living yeast cell and a positively charged PSL NP.     

Charge-driven selective localization of fluorescent nanoparticles in live cells

Covalent grafting of amino groups onto the carboxylic acid functionalities, naturally covering the surface of fluorescent nanoparticles produced from silicon carbide (SiC NPs), allowed tuning of their surface charge from negative to highly positive. Incubating 3T3-L1 fibroblast cells with differently charged SiC NPs demonstrates the crucial role of the charge in cell fluorescent targeting. Negatively charged SiC NPs concentrate inside the cell nuclei. Close to neutrally charged SiC NPs are present in both cytoplasm and nuclei while positively charged SiC NPs are present only in the cytoplasm and are not able to move inside the nuclei. This effect opens the door for the use of SiC NPs for easy and fast visualization of long-lasting biological processes taking place in the cell cytosol or nucleus as well as providing a new long-term cell imaging tool. Moreover, here we have shown that the interaction between charged NPs and nuclear pore complex plays an essential role in their penetration into the nuclei.     

Amphiphilic star block copolymers as gene carrier Part I: Synthesis via ATRP using calix[4]resorcinarene-based initiators and characterization

In this work, a cationic star polymer [poly(2-dimethylamino)ethyl methacrylate (PDMAEMA)] was prepared via atom transfer radical polymerization (ATRP), using brominated calix[4]resorcinarene as an initiator. Hydrophobic moieties, methyl methacrylate (MMA) and butyl acrylate (BA), were further incorporated via “one-pot” method. Well-defined eight-armed star block copolymers bearing hydrophilic blocks inside and hydrophobic blocks outside were synthesized. The molecular weight, particle size, electrophoretic mobility and apparent charge density were determined by gel permeation chromatography (GPC), dynamic light scattering (DLS), phase analysis light scattering (PALS) and colloidal titration, respectively. The zeta potentials and apparent charge densities of the products exhibited the characteristics of polyelectrolyte. The incorporation of hydrophobic moieties generated electrostatic screening effect. The as-synthesized amphiphilic star copolymer is promising as a thermo-sensitive gene carrier for gene therapy.     

Initial adhesion and surface growth of Pseudomonas aeruginosa on negatively and positively charged poly(methacrylates)

The infection risk of biomaterial implants is determined by an interplay of bacterial adhesion and surface growth of the adhering organisms. In this study, we compared initial adhesion and surface growth of Pseudomonas aeruginosa AK1 (zeta potential –7 mV) on negatively charged (PMMA/MAA, zeta potential –18 mV) and positively charged (PMMA/TMAEMA-Cl, zeta-potential +12 mV) methacrylate copolymers in situ in a parallel plate flow chamber. Initial adhesion was measured using phosphate-buffered saline and subsequent surface growth of the adhering bacteria using nutrient broth as growth medium. Initial adhesion was twice as fast on the positively charged methacrylate than on the negatively charged copolymer. Surface growth, however, was absent on the positively charged copolymer, while on the negatively charged methacrylate the number of bacteria increased exponentially during surface growth with a generation time of 32 min. From the results of this study it can be concluded that positively charged biomaterial surfaces might show reduced risks of biomaterials-centred infections, despite being more adhesive.     

Facilitated and site-specific assembly of functional polystyrene microspheres on patterned porous films

Functional patterned materials have received considerable attention because of their potential applications in biochips, sensors, and optical or electronic materials. Here, we report a versatile approach to functional patterned films based on facilitated and site-specific assembly of microspheres. This method includes the hierarchical formation of honeycomb-patterned porous films from amphiphilic block copolymers and the assembly of functional polystyrene microspheres driven by the gravity and the electrostatic interaction. Polystyrene microspheres containing carboxyl groups with a narrow size distribution were synthesized by dispersion polymerization. Honeycomb-patterned porous films were prepared from polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA) by the breath figure method and then quaternized. We found that direct deposition of the microspheres on the patterned films reaches high filling ratio only when using ethanol dispersions that can wet the film pores. Plasma treatment of the films improves the hydrophilicity and introduces charged species to the external surface as well as the pore surface, leading to nonspecific assembly of microspheres. Negatively charged microspheres dispersed in buffer solution show a facilitated and site-specific assembly on the quaternized film. The electrostatic interaction as well as the gravity facilitates the assembly and the suborder arrangement of the hydrophilic PDMAEMA block around the pores is responsible for the site-specific assembly. In addition, we demonstrate the applicability of this method in preparing photoluminescent patterns by the assembly of porphyrinated microspheres, which is useful in various fields such as intelligent sensing.     

Fabrication of moth eye structures via charged nanoparticle lithography with size and density control

We have developed and demonstrated an effective method for fabricating the moth eye structures formed by charged nanoparticle lithography (cNPL). We attached high-density gold nanoparticles (Au NPs) to GaN without aggregation by making the surface of Au NPs negatively charged and GaN positively charged. Au NPs were effectively used as an etching mask, and the moth eye structures of GaN were formed by inductively coupled plasma reactive ion etching. The moth eye structures with various sizes and densities were fabricated by the cNPL, and the moth eye structures reduced the reflectance. The cNPL, as a simple technique with size and density control, will provide high potential to optical device applications.     

Aggregation of cyanine dyes at Langmuir-Blodgett monolayers

Cyanine dyes are adsorbed from aqueous solution to Langmuir-Blodgett (LB) films, forming monolayers of Scheibe or J aggregates, whereas the dye in solution is in monomeric state. As well as J aggregates other types of aggregates (H, H^* aggregates, oligomers, dimers) can form and interchange at the LB interface depending on conditions and the structures of the dyes and amphiphiles. Reflection spectroscopy proved to be a useful method for studying aggregates and kinetic processes at the air-water interface as the bulk subphase is not recorded by this method.

Aggregation of dyes seems to be controlled by Coulomb interactions and the surface structure of the interacting monolayers. Cationic cyanine dyes are adsorbed only at negatively charged monolayers (e.g. fatty acids) whereas cyanine dyes with negative net charge form aggregates only at positively charged monolayers (e.g. amphiphilic ammonium salts).

Aggregation of cyanine dyes has also been found at LB monolayers of amphiphilic nucleic acids which have been synthesized for the first time. Aggregates of adsorbed cyanine dyes can be transferred to solid substrates by the LB method and investigated by other spectroscopic methods or microscopy.

Adsorption of cyanine dyes at vesicle bilayers has been reported; this was studied by absorption spectroscopy of vesicular dye solutions. Comparison of these spectra with reflection spectra of corresponding LB films reveals significant differences between the effects in LB monolayers and those in vesicular bilayers.     

Conformal Nanocoatings with Uniform and Controllable Thickness on Microstructured Surfaces: A General Assembly Route

Assembling nanoparticles (NPs) on various surfaces are intensively investigated for the construction of functional nanocoatings; however, it is still a challenge to fabricate conformal nanocoatings uniformly on surfaces having micro‐ or nanostructures. Herein, it is demonstrated that the negatively charged SiO₂ NPs and the positively charged silicon coupling agent can be assembled layer‐by‐layer on the microstructures based on the combination of electrostatic interaction and condensation reaction. Conformal nanocoatings with controllable thickness are formed on the microstructured surfaces with different compositions and morphologies. The formation mechanism is confirmed by using quartz crystal microbalance with dissipation (QCM‐D) to study the assembly process in real time. The universality of this method is illustrated by using other reactive building blocks with opposite charge to build up the conformal nanocoatings. Application in the preparation of antireflective nanocoatings on nonplanar optical materials is demonstrated. This simple, versatile, and scalable strategy for the preparation of conformal nanocoatings is promising for practical applications.     

Synthesis of crosslinked poly(styrene-<Emphasis Type="Italic">co</Emphasis>-divinylbenzene-<Emphasis Type="Italic">co</Emphasis>-sulfopropyl methacrylate) nanoparticles by emulsion polymerization: Tuning the particle size and surface charge density

We have synthesized highly charged, crosslinked poly (styrene-co-divinylbenzene-co-sulfopropyl methacrylate) copolymer colloidal particles using emulsion polymerization. The effects of concentration of the emulsifier and the initiator on the particle size and the charge density of the colloidal particles are studied. Colloidal particle size is highly dependent upon the concentration of the emulsifier and the initiator. The colloidal particle diameter decreases with increasing concentration of the emulsifier and increases with increasing concentration of the initiator in the polymerization mixture. Number of particles, surface charge density and charges per particle are also functions of both the emulsifier and the initiator concentration. The surface charge density and the number of charges per sphere increase with increasing particle diameter. These copolymer colloid particles self assemble readily and diffract visible light. Polymer hydrogel imbibed with these colloids shows the light diffraction.     

Interaction of silver nanoparticles with an environmentally beneficial bacterium, Pseudomonas chlororaphis

This study explores the potential antimicrobial mechanisms of commercial silver nanoparticles (Ag NPs) in the environmental bacterium, Pseudomonas chlororaphis O6. The 10nm size NPs aggregated in water, as demonstrated by atomic force microscopy. Solubility of the NPs at 10mg/L was 0.28 mg/L (pH 6) and 2.3mg/L (pH 7); release from 10mg/L bulk Ag was below detection. The NPs eliminated cell culturability at 3mg/L, whereas no effect was observed at 10mg/L bulk Ag. Zeta potential measurements revealed that the NPs were negatively charged; unlike Ag ions, their addition to the negatively charged cells did not change cell charge at pH 6, but showed a trend to reduce cell charge at pH 7. Isolated extracellular polymeric substances (EPS) from PcO6 was polydisperse, with negative charge that was neutralized by Ag ions, but not by the NPs. Addition of EPS eliminated Ag NP's toxicity in cells lacking EPS. Intracellular accumulation of OH was not detected in NP-treated cells; however, the use of scavengers suggested the NPs caused extracellular H(2)O(2) production. No evidence was found for loss of membrane integrity upon treatment with the NPs. Our findings indicate that growth of environmental bacteria could be impaired by Ag NPs, depending on the extent of EPS production.     

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMA_x-b-AEMA_y/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.     

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

Abstract

We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMA_x-b-AEMA_y/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.     

Layer-by-layer self-assembly of multilayer films based on humic acid

Multilayer films consisting of negatively charged humic acid and positively charged polyelectrolyte have been fabricated on various substrates using the layer-by-layer self-assembly technique. The thickness (linearly increasing with the square root of NaCl concentration) and refractive index of the films determined by ellipsometry can be regulated by ionic strength through adjusting the coiling of the polyelectrolyte chains for assembly. The cone-shaped features on surface obtained by atomic force microscope are derived from the negatively charged colloidal humic acid binding with polyelectrolyte cation. The smooth features are corresponding to the dissociated humic acid with carboxylate ion (―COO⁻) electrostatically attracted on polyelectrolyte cation. These results are verified by Fourier transform infrared spectra. The linear dependence of the peak current on the square root of the scan rate revealed by the cyclic voltammetry indicates that the redox process at the electrode surface is diffusion-limited and the charge transport does not involve the film itself.     

Influence of the size and charge of nonstoichiometric silver sulfide nanoparticles on their interaction with blood cells

Silver sulfide (Ag₂S) nanoparticles synthesized using different precursors have been characterized by dynamic light scattering measurements and high-resolution transmission electron microscopy. In addition to Ag₂S nanoparticles, we have detected Ag₂S/Ag heterostructures. Using optical microscopy, we have examined interaction of the nanoparticles with red cells of peripheral blood. The results of the interaction have been shown to depend on the particle size and charge. A red cell solution containing large, negatively charged particles coagulated, whereas small, positively charged Ag₂S nanoparticles were concentrated around red cells.     

P(LMA-MA)两亲性梳型聚合物的合成与表征

采用溶液聚合方式,合成了具有两亲性梳型结构的聚甲基丙烯酸十二酯-马来酸酐共聚物P(LMA-MA)。使用傅里叶变换红外光谱(FT-IR)、核磁共振(1H-NMR)等检测手段对聚合物的组成结构进行了表征。在选择性溶剂(水)中制备了P(LMA-MA)两亲性梳型聚合物的胶束,通过Zeta电位粒径分析仪和透射电子显微镜(TEM)探讨了两亲性梳型聚合物在胶束化过程中胶束形态和尺寸的影响因素。实验表明,由于两亲性梳型聚合物的结构特点,P(LMA-MA)形成200nm以上尺寸的胶束;在浓度范围0.5 g/L-1.75 g/L、温度范围25℃-50℃和pH值范围4-8时,胶束可稳定形成和存在。     

A facile assay for direct colorimetric visualization of lipopolysaccharides at low nanomolar level

We report a facile assay for the rapid visual detection of lipopolysaccharide (LPS) molecules down to the low nanomolar level by taking advantage of the electrostatic interaction between LPS molecules and cysteamine-modified gold nanoparticles (CSH-Au NPs). The large amount of negatively charged groups on the LPS molecules make LPS highly negatively charged. Thus, when modified with cysteamine, the positively charged gold nanoparticles can aggregate in the presence of trace amounts of LPS. The probe is simple, does not require any advanced instrumentation, and the limit of detection (LOD) was determined to be as low as 3.3 × 10⁻¹⁰ mol/L. To the best of our knowledge, it is the most sensitive synthetic LPS sensor reported so far.      

Colloidal Polymer-Templated Formation of Inorganic Nanocrystals and their Emerging Applications

Inorganic nanocrystals possess unique physicochemical properties compared to their bulk counterparts. Stabilizing agents are commonly used for the preparation of inorganic nanocrystals with controllable properties. Particularly, colloidal polymers have emerged as general and robust templates for in situ formation and confinement of inorganic nanocrystals. In addition to templating and stabilizing inorganic nanocrystals, colloidal polymers can tailor their physicochemical properties such as size, shape, structure, composition, surface chemistry, and so on. By incorporating functional groups into colloidal polymers, desired functions can be integrated with inorganic nanocrystals, advancing their potential applications. Here, recent advances in the colloidal polymer-templated formation of inorganic nanocrystals are reviewed. Seven types of colloidal polymers, including dendrimer, polymer micelle, stare-like block polymer, bottlebrush polymer, spherical polyelectrolyte brush, microgel, and single-chain nanoparticle, have been extensively applied for the synthesis of inorganic nanocrystals. Different strategies for the development of these colloidal polymer-templated inorganic nanocrystals are summarized. Then, their emerging applications in the fields of catalysis, biomedicine, solar cells, sensing, light-emitting diodes, and lithium-ion batteries are highlighted. Last, the remaining issues and future directions are discussed. This review will stimulate the development and application of colloidal polymer-templated inorganic nanocrystals.     

Bioactive multilayer thin films of charged N,N-disubstituted hydrazine phosphorus dendrimers fabricated by layer-by-layer self-assembly

Charged N,N-disubstituted hydrazine phosphorus-containing dendrimers are deposited either as alternate all-dendrimers multilayers or alternating with linear polymers on 3-mercaptopropionic acid or 3-aminopropyldimethylethoxysilane coated surfaces via electrostatic layer-by-layer self-assembly. The behavior of the film formation is investigated by surface plasmon resonance spectroscopy and ellipsometry. Fetal cortical rat neurons were cultured on the dendrimer films in order to investigate the influence of the surface charge of the outermost layer on their adhesion and maturation. It was found that neurons attached preferentially and matured slightly faster on film surfaces terminated with positively charged dendrimers than on negatively charged surfaces.     

Positively and negatively charged liposomes as carriers for transdermal delivery of sumatriptan: in vitro characterization

Background: The influence of liposome composition, lamellarity, preparation method, and charge on the encapsulation efficiency, size, polydispersity, and surface charge of sumatriptan liposomes was studied. For this purpose, we studied multilamellar, unilamellar, and frozen and thawed liposomes. Positively or negatively charged liposomes were obtained using both phosphatidylcholine and cholesterol, in combination with stearylamine or dicetylphosphate. Liposomal formulations were characterized by confocal laser scanning microscopy and optical microscopy for vesicle formation, morphology, and lamellarity by dynamic laser light scattering for size distribution and polydispersity, and electrophoretic mobility for zeta potential determination. To obtain more information about the sumatriptan encapsulation, dynamic dialysis technique was employed. The sumatriptan amount was quantified by high-performance liquid chromatography. Results: Overall obtained results showed that liposomes may be interesting carriers for sumatriptan succinate. Statistical analysis evidenced that the preparation method does not affect the evaluated characterization parameters. However, the presence of charge inducer agents modified these characteristics. Highest loading efficiency of sumatriptan was exhibited for positively charged liposomes containing 6.58:10.34:3.73 mmolar ratio for phosphatidylcholine : cholesterol : stearylamine. The mean size was affected by the charge inducer, being smaller in positively charged liposomes. Logically, surface charge of liposomes varied as a function of the employed charged agent. Also, interesting results were obtained when vesicles were loaded with sumatriptan, showing a statistical significance between all pairs, comparing the formulations with and without drug. Conclusion: Results obtained revealed that the presence of sumatriptan into the vesicles has a different behavior in negatively and positively charged liposomes.