Phase transfer of hydrophilic, cyclodextrin-modified gold nanoparticles to chloroform solutions

Recent Advances in the Pharmaceutical and Biomedical Applications of Cyclodextrin-Capped Gold Nanoparticles

The real problem in pharmaceutical preparation is drugs' poor aqueous solubility, low permeability through biological membranes, and short biological t_1/2. Conventional drug delivery systems are not able to overcome these problems. However, cyclodextrins (CDs) and their derivatives can solve these challenges. This article aims to summarize and review the history, properties, and different applications of cyclodextrins, especially the ability of inclusion complex formation. It also refers to the effects of cyclodextrin on drug solubility, bioavailability, and stability. Moreover, it focuses on preparing and applying gold nanoparticles (AuNPs) as novel drug delivery systems. It also studies the uses and effects of cyclodextrins in this field as novel drug carriers and targeting devices. The system formulated from AuNPs linked with CD molecules combines the advantages of both CD and AuNPs. Cyclodextrins benefit in increasing aqueous drug solubility, loading capacity, stability, and size control of gold NPs. Also, AuNPs are applied as diagnostic and therapeutic agents because of their unique chemical properties. Plus, AuNPs possess several advantages such as ease of detection, targeted and selective drug delivery, greater surface area, high loading efficiency, and higher stability than microparticles. In the present article, we tried to present the potential pharmaceutical applications of CD-derived AuNPs in biomedical applications including antibacterial, anticancer, gene-drug delivery, and various targeted drug delivery applications. Also, the article highlighted the role of CDs in the preparation and improvement of catalytic enzymes, the formation of self-assembling molecular print boards, the fabrication of supramolecular functionalized electrodes, and biosensors formation.

Fundamental Methods for the Phase Transfer of Nanoparticles

The utilization of nanoparticles for a variety of applications has raised much interest in recent years as new knowledge has emerged in nanochemistry. New and diverse methods for synthesis, characterization, and application of these particles have been discovered with differing degrees of ease and reproducibility. Post-synthetic modification of nanoparticles is often a required step to facilitate their use in applications. The reaction conditions and chemical environment for the nanoparticle synthesis may not support or may conflict with further reactions. For this reason, it is beneficial to have phase transfer methods for nanoparticles to allow for their dispersion in a variety of solvents. Phase transfer methods are often limited in the types and sizes of particles that can be effectively dispersed in an immiscible solvent. Currently, general transfer methods for a wide variety of nanoparticles have not been identified. New routes for phase transfer allow for utilization of a larger range of particles in applications which were previously limited by solubility and reactivity issues. In this work, we will describe the fundamental methods for the phase transfer of metallic nanoparticles. We will look at the major problems and pitfalls of these methods. The applications of phase transfer will also be reviewed, mainly focusing on catalysis and drug delivery.

Development of pH-responsive nanocomposites with remarkably synergistic antibiofilm activities based on ultrasmall silver nanoparticles in combination with aminoglycoside antibiotics

Bacterial biofilms are responsible for many chronic infections because antibacterial agents exhibit poor penetration into the dense matrix barrier and cannot easily reach the internal bacteria. Herein, we reported pH-responsive nanocomposites (PDA@Kana-AgNPs) that could penetrate and disperse biofilms, which were synthesized by the combination of ultrasmall silver nanoparticles (AgNPs) and kanamycin, and then coating with polydopamine. Confocal fluorescence imaging indicated that PDA@Kana-AgNPs could respond to the acidic microenvironment of biofilms, leading to biofilm-triggered on- demand drug release in situ. The zone of inhibition test and Resazurin assay showed that the combination of kanamycin and AgNPs had greater antimicrobial activity against test strains (Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Escherichia coli BL21) than when applied separately. The crystal violet staining test demonstrated that biofilms were effectively dispersed by the proposed nanocomposites. Biocompatibility was also evaluated, which showed that PDA@Kana-AgNPs were non-toxic to mammalian cells. Therefore, the proposed pH-responsive nanocomposites held great potential for efficient antibiotics delivery and showed synergistic antibacterial and antibiofilm activities. This strategy could also be used to encapsulate a variety of antibiotics in combination with other drugs or materials, thereby showing therapeutic potential in preventing biofilm-related infections and realizing fluorescence imaging in situ.

Rapidly Adaptive All-covalent Nanoparticle Surface Engineering

Emerging nanotechnologies demand the manipulation of nanoscale components with the same predictability and programmability as is taken for granted in molecular synthetic methodologies. Yet installing appropriately reactive chemical functionality on nanomaterial surfaces has previously entailed compromises in terms of reactivity scope, functionalization density, or both. Here, we introduce an idealized dynamic covalent nanoparticle building block for divergent and adaptive post-synthesis modification of colloidal nanomaterials. Acetal-protected monolayer-stabilized gold nanoparticles are prepared via operationally simple protocols and are stable to long-term storage. Tunable surface densities of reactive aldehyde functionalities are revealed on-demand, leading to a wide range of adaptive surface engineering options from one nanoscale synthon. Analytically tractable with molecular precision, interfacial reaction kinetics and dynamic surface constitutions can be probed in situ at the ensemble level. High functionalization densities combined with rapid equilibration kinetics enable environmentally adaptive surface constitutions and rapid nanoparticle property switching in response to simple chemical effectors.

Cyclodextrins and inorganic nanoparticles: Another tale of synergy

In this review, we summarize the recent research focused on the combination of inorganic nanoparticles and α-, β- and γ- cyclodextrins. Our intention is to highlight the most relevant publications on the synthesis of nanoparticle-cyclodextrin (NP-CD) nanohybrids, with CDs acting as reducing agents or through the post-synthetic modification of inorganic nanoparticles with CDs. We also discuss the new or enhanced properties that arise from the host-guest capabilities of the CDs and inorganic nanoparticles. Finally, we illustrate the potential applications of these materials in numerous research fields.

Discrimination of cysteamine from mercapto amino acids through isoelectric point-mediated surface ligand exchange of β-cyclodextrin-modified gold nanoparticles

A pI-mediated R6G-β-CD@AuNPs system was designed for the first time for the discrimination of CA from GSH/Cys/Hcy in human serum samples.

Complexes Formed by Hydrophobic Interaction between Ag-Nanospheres and Adsorbents for the Detection of Methyl Salicylate VOC

Surface-enhanced Raman spectroscopy (SERS) has been widely investigated in many applications. However, only little work has been done on using SERS for the detection of volatile organic compounds (VOCs), primarily due to the challenges associated with fabricating SERS substrates with sufficient hotspots for signal enhancement and with the surface interfacially compatible for the VOCs. This study investigated the phase transfer of Ag-nanospheres (AgNSs) from the aqueous phase to the non-aqueous phase by electrostatic interaction induced by cationic surfactants, and the feasibility of the transferred AgNSs as SERS substrates for the determination of methyl salicylate VOC. Results indicated that one of three cationic surfactants, tetraoctylammonium bromide (TOAB) dissolved in organic solvent showed successful phase transfer of the AgNSs confirmed by several characterization analyses. The complex formed by hydrophobic interaction between the transferred AgNSs and Tenax-TA adsorbent polymer was able to be utilized as a SERS substrate, and the volatile of methyl salicylate could be easily determined from SERS measurements at 4 h static volatile collection. Therefore, the proposed new techniques can be effectively employed to areas where many VOCs relevant to food and agriculture need to be analyzed.

Facile Transfer of Reverse Micelles from the Organic to the Aqueous Phase for Mimicking Enzyme Catalysis and Imaging-Guided Cancer Therapy

Reverse micelles (RMs) with confined water pools have been applied in many fields. However, the water insolubility of RMs seriously limits the scope of their application, especially those needed to operate in aqueous environments. Here, we report the first successful transfer of RMs from the organic phase to water phase without disturbing their confined water pools and hydrophobic alkyl region. This transfer was achieved by virtue of a mild host-guest interaction between the hydrophobic tails of interfacial cross-linked reverse micelles (ICRMs) and the hydrophobic cavity of (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD). Benefitting from the maintained confined water pools and the hydrophobic scaffold, the obtained water-soluble ICRMs served as multifunctional nanoplatforms for enzyme-mimicking catalysis and image-guided cancer therapy, which were impossible for normal RMs lacking water solubility or confined pool-buried water-soluble nanoparticles without a hydrophobic alkyl chain. This mild transfer approach thus surmounts the application obstacle of RMs and opens up new avenues for their application in aqueous environments.

Tuning optical properties of perovskite nanocrystals by supermolecular mercapto-β-cyclodextrin

This study reports a host-guest interaction strategy for systematically manipulating the optical properties of cesium lead halide perovskite nanocrystals (CsPbBr₃ NCs) by protectant-mediated mercapto-β-cyclodextrin (SH-β-CD). The fluorescence of CsPbBr₃ NCs can be adjusted over 405-510 nm with the quantum yields (QY) maintained at 50-90%.

Continuum tuning of nanoparticle interfacial properties by dynamic covalent exchange

Dynamic covalent modification of the surface-stabilizing monolayer accesses a continuum of nanoparticle properties from a single starting point.

Surface chemical composition is fundamental to determining properties on the nanoscale, making precise control over surface chemistry critical to being able to optimise nanomaterials for virtually any application. Surface-engineering independent of the preparation of the underlying nanomaterial is particularly attractive for efficient, divergent synthetic strategies, and for the potential to create reactive, responsive and smart nanodevices. For monolayer-stabilised nanoparticles, established methods include ligand exchange to replace the ligand shell in its entirety, encapsulation with amphiphilic (macro)molecules, noncovalent interactions with surface-bound biomolecules, or a relatively limited number of covalent bond forming reactions. Yet, each of these approaches has considerable drawbacks. Here we show that dynamic covalent exchange at the periphery of the nanoparticle-stabilizing monolayer allows surface-bound ligand molecular structure to be substantially modified in mild and reversible processes that are independent of the nanoparticle–molecule interface. Simple stoichiometric variation allows the extent of exchange to be controlled, generating a range of kinetically stable mixed-monolayer compositions across an otherwise identical, self-consistent series of nanoparticles. This approach can be used to modulate nanoparticle properties that are defined by the monolayer composition. We demonstrate switching of nanoparticle solvent compatibility between widely differing solvents – spanning hexane to water – and the ability to tune solubility across the entire continuum between these extremes, all from a single nanoparticle starting point. We also demonstrate that fine control over mixed-monolayer composition influences the assembly of discrete, colloidally stable nanoparticle clusters. By carefully assessing monolayer composition in each state, using both in situ and ex situ methods, we are able to correlate the molecular-level details of the nanoparticle-bound monolayer with system-level properties and behaviour. These empirically determined relationships contribute fundamental insights on nanoscale structure–function relationships, which are currently beyond the capabilities of ab initio prediction.

Thiourea functionalized β-cyclodextrin as green reducing and stabilizing agent for silver nanocomposites with enhanced antimicrobial and antioxidant properties

Rapid development of microbial resistance against traditional antibiotics has generated a need for the synthesis of new more potent, less toxic, target specific, cost effective and biodegradable antimicrobial agents.

Dispersing hydrophilic nanoparticles in nonaqueous solvents with superior long-term stability

We report a general and robust polymerization–dissolution strategy for phase transfer of hydrophilic nanoparticles into nonaqueous solvents with a 100% transfer efficiency.

Evidence of the Disassembly of α-Cyclodextrin-octylamine Inclusion Compounds Conjugated to Gold Nanoparticles via Thermal and Photothermal Effects

Cyclodextrin (CD) molecules form inclusion compounds (ICs), generating dimers that are capable of encapsulating molecules derived from long-chain hydrocarbons. The aim of this study is to evaluate the structural changes experienced by ICs in solution with increasing temperatures. For this, a nuclear magnetic resonance (¹H-NMR) titration was performed to determinate the stoichiometric α-cyclodextrin (α-CD):octylamine (OA) 2:1 and binding constant (k = 2.16 M⁻²) of ICs. Solution samples of α-CD-OA ICs conjugated with gold nanoparticles (AuNPs) were prepared, and ¹H-NMR spectra at different temperatures were recorded. Comparatively, ¹H-NMR spectra of the sample irradiated with a laser with tunable wavelengths, with plasmons of conjugated AuNPs, were recorded. In this work, we present evidence of the disassembly of ICs conjugated with AuNPs. Thermal studies demonstrated that, at 114 °C, there are reversible rearrangements of the host and guests in the ICs in a solid state. Migration movements of the guest molecules from the CD cavity were monitored via temperature-dependent ¹H-NMR, and were verified comparing the chemical shifts of octylamine dissolved in deuterated dimethylsulfoxide (DMSO-d₆) with the OA molecule included in α-CD dissolved in the same solvent. It was observed that, at 117 °C, OA exited the α-CD cavity. CD IC dimer disassembly was also observed when the sample was irradiated with green laser light.

Synthesis and application of colloidal beta-cyclodextrin-decorated silver nanoparticles for rapid determination of malachite green in environmental water using surface-enhanced Raman spectroscopy

A series of AgNPs were synthesized by silver mirror reaction in the presence of CDs. Combined with SERS, a rapid method for the determination of MG was established successfully.

Spectral, morphological and antibacterial studies of β-cyclodextrin stabilized silver - Chitosan nanocomposites

The aim of the study is to investigate the antibacterial properties and characterization of β-cyclodextrin (β-CD) stabilized silver - chitosan nanocomposite (Ag-Cts NCs). An effective and eco-friendly technique for the synthesis of Ag-Cts NCs in the presence of a strong stabilizing agent β-CD is described. The well formed nanocomposites were characterized by the Ultraviolet Visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Photoluminescence spectroscopy (PL), Scanning electron microscope (SEM/EDS), Atomic force microscope (AFM), High resolution transmission electron microscope (HR-TEM) and Zeta potential measurement (ZP). The results confirmed that the poly dispersed Ag-Cts NCs are less than 15nm in size with spherical shape and show good stability. The antibacterial activity was also investigated and β-CD coated Ag-Cts NCs showed a promising bacterial activity against gram negative Escherichia coli (E. coli) and gram positive Staphylococcus aureus (S. aureus) micro-organism.

Particle self-assembly at ionic liquid-based interfaces

This review presents an overview of the nature of ionic liquid (IL)-based interfaces and self-assembled particle morphologies of IL-in-water, oil- and water-in-IL, and novel IL-in-IL Pickering emulsions with emphasis on their unique phenomena, by means of experimental and computational studies. In IL-in-water Pickering emulsions, particles formed monolayers at ionic liquid-water interfaces and were close-packed on fully covered emulsion droplets or aggregated on partially covered droplets. Interestingly, other than equilibrating at the ionic liquid-water interfaces, microparticles with certain surface chemistries were extracted into the ionic liquid phase with a high efficiency. These experimental findings were supported by potential of mean force calculations, which showed large energy drops as hydrophobic particles crossed the interface into the IL phase. In the oil- and water-in-IL Pickering emulsions, microparticles with acidic surface chemistries formed monolayer bridges between the internal phase droplets rather than residing at the oil/water-ionic liquid interfaces, a significant deviation from traditional Pickering emulsion morphology. Molecular dynamics simulations revealed aspects of the mechanism behind this bridging phenomenon, including the role of the droplet phase, surface chemistry, and inter-particle film. Novel IL-in-IL Pickering emulsions exhibited an array of self-assembled morphologies including the previously observed particle absorption and bridging phenomena. The appearance of these morphologies depended on the particle surface chemistry as well as the ILs used. The incorporation of particle self-assembly with ionic liquid science allows for new applications at the intersection of these two fields, and have the potential to be numerous due to the tunability of the ionic liquids and particles incorporated, as well as the particle morphology by combining certain groups of particle surface chemistry, IL type (protic or aprotic), and whether oil or water is incorporated.

Reversible phase transfer of nanoparticles based on photoswitchable host-guest chemistry

An azobenzene-containing surfactant was synthesized for the phase transfer of α-cyclodextrin (α-CD)-capped gold nanoparticles between water and toluene phases by host-guest chemistry. With the use of the photoisomerization of azobenzene, the reversible phase transfer of gold nanoparticles was realized by irradiation with UV and visible light. Furthermore, the phase transfer scheme was applied for the quenching of a reaction catalyzed by gold nanoparticles, as well as the recovery and recycling of the gold nanoparticles from aqueous solutions. This work will have significant impact on materials transfer and recovery in catalysis and biotechnological applications.

Selective nanodecoration of modified cyclodextrin crystals with gold nanorods

Gold nanorods (AuNRs) stabilized by cetyltrimethylammonium bromide (CTAB) were deposited onto crystals of α-cyclodextrin (α-CD) inclusion compounds (ICs) that contained octanethiol (OT) as guest molecules. The nanodecoration was produced specifically at the {001} crystal planes through interaction between the -SH groups of the ICs and the AuNRs.

Construction of nanoparticle superstructures on the basis of host-guest interaction to achieve performance integration and modulation

Creation of nanoparticle (NP) architectures via a self-assembly strategy is the current means to integrate and/or modulate the functionalities of NPs. In this paper, we demonstrate the capability for constructing NP spherical superstructures through the specific interaction between host and guest molecules, for instance the model system of α-cyclodextrin (α-CD) and oleic acid (OA), which are decorated on two different NPs beforehand. Subsequently, the OA-decorated hydrophobic NPs are dispersed in hexane, whereas the α-CD-decorated NPs are dispersed in water. The blending of these two immiscible solutions produces NP binary superstructures because of the multiple linkages between the α-CD- and OA-decorated NPs. Control experiments indicate that the self-assembly of NPs occurs either at the hexane/water interface to form hybrid films or in the aqueous phase to generate spherical architectures, which strongly depends on the amount and the size of α-CD-decorated NPs. The high ratio and small size of the α-CD-decorated NPs facilitate the formation of spherical architectures. Competitive experiments with the addition of host α-CD and guest sodium oleate clearly confirm that the main driving force for the NP co-assembly is the specific interaction between α-CD and OA. In addition, the flexible decoration of α-CD and OA on the NPs makes the current strategy generally applicable for a variety of NPs, such as the superstructures of Au/Fe(3)O(4), Pt/Fe(3)O(4), and Au/NaYF(4):Yb,Tm, which is expected to promote the further application of NPs in environmental and biological sciences.

Transfer of biosynthesized gold nanoparticles from water into an ionic liquid using alkyltrimethyl ammonium bromide: an anion-exchange process

Biosynthesized gold nanoparticles (GNPs) were transferred from water to a hydrophobic ionic liquid (IL), [Bmim]PF(6), with the assistance of alkyl trimethyl ammonium bromide. The phase transfer mechanism was illustrated through the exemplification of cetyltrimethyl ammonium bromide (CTAB). Interaction between GNPs and CTAB was demonstrated through zeta potential analysis. Moreover, an anion-exchange process was discovered between CTAB and IL. During the process, the hydrophobic CTAPF(6) formed in situ on the GNPs led to the hydrophobization and thus phase transfer of the GNPs. The phase transfer efficiency was found to be size-dependent.

Controlled transformation from nanorods to vesicles induced by cyclomaltoheptaoses (β-cyclodextrins)

A modified cyclomaltoheptaose (β-cyclodextrin) containing an anthraquinone moiety, mono[6-deoxy-N-n-hexylamino-(N'-1-anthraquinone)]-β-cyclodextrin (1), which can self-assemble into nanorods in aqueous solution, was synthesized. Interestingly, upon the addition of natural cyclodextrin, the nanorods could transform into bilayer vesicles, which were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), and epi-fluorescence microscopy (EFM). A transformation mechanism is suggested based on the results of (1)H NMR, 2D NMR ROESY, FTIR, and UV-vis spectra. The response of the vesicles to changing pH and adding Cu(2+) was also tested. Our research may pave the way to the development of new intelligent materials and biomaterials.

One-pot preparation of ferrocene-functionalized polymer brushes on gold substrates by combined surface-initiated atom transfer radical polymerization and "click chemistry"

A gold substrate with surface-grafted ferrocene functional polymer brushes, or Au-g-PFTMA surface [PFTMA = poly(5-ferrocene-triazolyl methacrylate)], was prepared by a combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and "click chemistry" in one pot, in the presence of 2-azidoethyl methacrylate (AzEMA), ethynyl ferrocene, CuBr catalyst, CuBr(2) deactivator, and pentamethyldiethylenetriamine ligand. Thus, SI-ATRP of AzEMA from the Au substrate (the "grafting from" process) and click chemistry of the ethynyl ferrocene to the azide functional group of AzEMA (the "grafting to" process) proceeded simultaneously to produce the functional PFTMA brushes on the Au surface. Kinetic studies suggest that the reaction involving simultaneous SI-ATRP and click chemistry is still consistent with a controlled/"living" process. The composition and physical properties of the modified gold surface were analyzed by X-ray photoelectron spectroscopy, water contact angle measurement, and cyclic voltammetry. The redox-responsive properties of the ferrocene-functionalized polymer brushes on the Au-g-PFTMA surface were demonstrated in the reversible loading-unloading step of the β-cyclodextrin polymer via host-guest interaction.

Light-triggered reversible phase transfer of composite colloids

Composite colloids were prepared via grafting optically responsive spiropyran polymer brushes onto silica colloids. Similar to spiropyran, the polymer brushes undergo a reversible inversion from a hydrophobic state to a hydrophilic state upon irradiation with UV light (or vice versa by visible light). The composite colloids can thus reversibly transfer between oil and water phases, and this can be remotely triggered using light. At intermediate stages of irradiation, both hydrophobic and hydrophilic components coexist, resulting in the amphiphilic performance of the composite colloids. Such amphiphilic composite colloids can be used as particulate emulsifiers.

Emerging methods for fabricating functional structures by patterning and assembling engineered nanocrystals

Inorganic nanocrystals and nanoparticles have aroused increasing attention in the last years due to their original optoelectronic, thermodynamic, mechanical and catalytic properties, which are extremely attractive for fundamental understanding as well as for their huge potential in applications. The ability to strongly exploit the original potential of such nano-objects and access their properties relies on the ability to bridge the gap between the nanoscopic and mesoscopic scale. Indeed, to integrate nanoparticles in structures, materials and finally devices, their incorporation in processable systems, and their organization in morphologically controlled assembly and/or ordered arrays is crucial. The fabrication of 2/3 D patterned micro- and nanostructure is a promising strategy for integrating the nanoparticles in macroscopic entities in order to properly exploit their unprecedented functionality for biomedical, electronic, catalytic materials and devices. In this paper, different and complementary strategies able to engineer inorganic colloidal nanocrystals due to their organization in original functional materials and structures will be described.

Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles

Inorganic colloidal nanoparticles are very small, nanoscale objects with inorganic cores that are dispersed in a solvent. Depending on the material they consist of, nanoparticles can possess a number of different properties such as high electron density and strong optical absorption (e.g. metal particles, in particular Au), photoluminescence in the form of fluorescence (semiconductor quantum dots, e.g. CdSe or CdTe) or phosphorescence (doped oxide materials, e.g. Y(2)O(3)), or magnetic moment (e.g. iron oxide or cobalt nanoparticles). Prerequisite for every possible application is the proper surface functionalization of such nanoparticles, which determines their interaction with the environment. These interactions ultimately affect the colloidal stability of the particles, and may yield to a controlled assembly or to the delivery of nanoparticles to a target, e.g. by appropriate functional molecules on the particle surface. This work aims to review different strategies of surface modification and functionalization of inorganic colloidal nanoparticles with a special focus on the material systems gold and semiconductor nanoparticles, such as CdSe/ZnS. However, the discussed strategies are often of general nature and apply in the same way to nanoparticles of other materials.