Reversible phase transfer of (CdSe/ZnS) quantum dots between organic and aqueous solutions

Magnetic aerogels from FePt and CoPt3 directly from organic solution

Here the synthesis of magnetic aerogels from iron platinum and cobalt platinum nanoparticles is presented. The use of hydrazine monohydrate as destabilizing agent triggers the gelation directly from organic solution, and therefore a phase transfer to aqueous media prior to the gelation is not necessary. The aerogels were characterized through Transmission Electron Microscopy, Scanning Electron Microscopy, Powder X-Ray Diffraction Analysis and Argon Physisorption measurements to prove the formation of a porous network and define their compositions. Additionally, magnetization measurements in terms of hysteresis cycles at 5 K and 300 K (M-H-curves) as well as zero field cooled-field cooled measurements (ZFC-FC measurements) of the dried colloids and the respective xero- and aerogels were performed, in order to analyze the influence of the gelation process and the network structure on the magnetic properties.

Controlling Trapping, Release, and Exchange Dynamics of Micellar Core Components

Whereas the formation and overall stability of hierarchically organized self-assembled supramolecular structures have been extensively investigated, the mechanistic aspects of subcomponent dynamics are often poorly understood or controlled. Here we show that the dynamics of polyamidoamine (PAMAM) dendrimer based micelles can be manipulated by changes in dendrimer generation, pH, and stoichiometry, as proven by NMR and FRET. For this, dendrimers were functionalized with either fluorescein (donor) or rhodamine (acceptor) and encapsulated into separate micelles. Upon mixing, exchange of dendrimers is revealed by an increase in FRET. While dendrimicelles based on dendrimer generations 4 and 5 show a clear increase in FRET in time, revealing the dynamic exchange of dendrimers between micellar cores, generation 6 based micelles appear to be kinetically trapped systems. Interestingly, generation 6 based dendrimicelles prepared at a pH of 7.8 rather than 7.0 do show exchange dynamics, which can be attributed to about 25% less charge of the dendrimer, corresponding to the charge of a virtual generation 5.5 dendrimer at neutral pH. Changing the pH of dendrimicelle solutions prepared at a pH of 7.8 to 7.0 shows the activated release of dendrimers. High-resolution NMR spectra of the micellar core are obtained from a 1.2 GHz spectrometer with sub-micromolar sensitivity, with DOSY discriminating released dendrimers from dendrimers still present in the micellar core. This study shows that dendrimer generation, charge density, and stoichiometry are important mechanistic factors for controlling the dynamics of complex coacervate core micelles. This knowledge can be used to tune micelles between kinetically trapped and dynamic systems, with tuning of exchange and/or release speeds, to be tailored for applications in, e.g., material science, sensors, or drug delivery.

CO2-Driven reversible transfer of amine-functionalized ZIF-90 between organic and aqueous phases

Phase transfer of metal-organic frameworks is highly desired in many areas, which remains a challenge. Herein, we present for the first time a CO₂-driven reversible transfer of amine-functionalized ZIF-90 between organics and water. A mechanistic study showed that the switching is ascribed to the reversible generation of hydrophilic ammonium salts from the reaction of CO₂ with the amines on ZIF-90. This unique system has been used for the coupling of trans-esterification reactions, product separation and component recycling for green sustainable processes. This work opens up a new avenue for performing reactions effectively with an easy separation process.

Positive Sorption Behaviors in the Ligand Exchanges for Water-Soluble Quantum Dots and a Strategy for Specific Targeting

N,N,N',N'-Tetramethylethylenediamine (TMEDA) and ethylenediamine (EDA) were investigated in-depth in the ligand exchanges for water-soluble CdSe quantum dots (QDs). TMEDA could assist the phase transfer of QDs from apolar solvents to the aqueous solutions as stabilized by mercaptopropionic acid (MPA). We successfully maintained the stability of a series of MPA-capped QDs of different ligand densities for NMR characterizations in aqueous solutions. The proton NMR spectroscopies of MPA of the binding state were used to analyze the ligand densities on the surface of QDs, which were not explored in the past. The binding thermodynamics of the surface ligands of QDs, as analyzed using the Hill equation, demonstrated a positive promoting effect and possible interactions between ligands. EDA in the purification process underwent a spontaneous adsorption with two-stage thermodynamic behaviors as characterized by isothermal titration calorimetry. Due to the positive role of the already adsorbed ligands, excess EDA would further attach to the surface of QDs in the form of non-bonded physisorption, greatly improving the quantum yield (QY) of QDs, and the ligand of this part would almost not change the stability of QDs. We proposed a strategy for the preparation of aqueous QDs with a high QY, followed by fluorescence quenching-enhancement cycles caused by purification-adsorption operations. The strategy made it possible for the preparation of functional QDs with small molecules after purification operations. Kinetics of the sorption of ligands on the surface of QDs were determined by fluorescence spectroscopy. Modified pseudo-second-order kinetics after consideration of the ligand-ligand interaction effect could well analyze the kinetic data. This kinetic model had advantages over the previous ligand exchange model in terms of accuracy, reproducibility, and physical significance. Finally, we used the above strategy for the design of fluorescent QDs for bioimaging of lysosomes, mitochondria, and cancer cells. This work can simplify the preparation of multifunctional fluorescent QDs and avoid complicated ligand design.

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.

Amorphous Selenium Nanoparticles Improve Vascular Function in Rats With Chronic Isocarbophos Poisoning via Inhibiting the Apoptosis of Vascular Endothelial Cells

AIM

This study aimed to investigate the preventive effect and possible mechanism of amorphous selenium nanoparticles (A-SeQDs) on isocarbophos induced vascular dysfunction.

METHODS

A-SeQDs was made by auto redox decomposition of selenosulfate precursor. Male rats were given isocarbophos (0.5 mg/kg/2 days) by intragastric administration for 16 weeks to induce vascular dysfunction. During the course, A-SeQDs (50 mg/kg/day) was added to the water from week 5. Then, the rats were killed to observe and test the influence of A-SeQDs on the vascular dysfunction induced by isocarbophos. Finally, human umbilical vein endothelial cells (HUVECs) were treated with 10% DMEM of isocarbophos (100 μM) for 5 days to detect the related indexes. Before the use of isocarbophos treatment, different drugs were given.

RESULTS

A-SeQDs could reduce total carbon dioxide, MDA, VCAM-1, ICAM-1, IL-1, and IL-6 while increasing oxygen saturation, NO content, and SOD activity in rats. A-SeQDs also resulted in relatively normal vascular morphology, and the expression of sodium hydrogen exchanger 1 (NHE1) and caspase-3 decreased in rats. Furthermore, in HUVECs treated with isocarbophos, A-SeQDs maintained mitochondrial membrane potential, inhibited the cleaved caspase-3 expression, and released cytochrome c from mitochondria to cytosol.

CONCLUSION

A-SeQDs can inhibit the apoptosis of HUVECs through the mitochondrial pathway, and effectively treat the impairment of vascular endothelial function caused by isocarbophos, which is NHE1-dependent.

Photocross-Linkable Hole Transport Materials for Inkjet-Printed High-Efficient Quantum Dot Light-Emitting Diodes

Efficient approach based on the photochemistry of benzophenone has been developed for the cross-linking of the polymer hole-transporting layer (HTL). The cross-linked poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4'-(N-(4-butylphenyl) (TFB) thin films showed high solvent stability, smooth surface morphology, and improved charge-carrier mobility. The solution-processed red, green, and blue (RGB) quantum dot light-emitting diodes (QLEDs) based on the cross-linked HTLs showed much better performances than the corresponding devices based on the pristine TFB HTLs. The spin-coated red QLEDs based on the cross-linked HTLs showed the maximum current efficiency (CE), the maximum power efficiency (PE), and the peak external quantum efficiency (EQE) of 32.3 cd A^-1, 42.3 lm W^-1, and 21.4%, respectively. The inkjet-printed red QLEDs with the cross-linked HTLs exhibited the CE, PE, and EQE of 26.5 cd A^-1, 37.8 lm W^-1, and 18.1%, respectively. The high-performance HTLs were obtained by significantly reducing the amount of cross-linking agents.

Ionic Liquid-Responsive Phase Transfer of Gold Nanoparticles: Anionic Metathesis

In this work, a fresh approach has been proposed for the efficient transfer of gold nanoparticles (AuNPs) from an aqueous to organic phase by the metathesis reaction or anion exchange reaction. Here, we synthesized ionic liquid 1-butyl 3-hexadecyl imidazolium bromide [C₄C₁₆Im]Br-stabilized AuNPs which exhibit excellent stability in solution. Transfer of Au@[C₄C₁₆Im]Br from an aqueous to organic phase was investigated by the metathesis reaction with different hydrophobic ionic liquid-forming salts such as LiNTf₂, LiClO₄, and KPF₆. The anionic exchange process in ionic liquids at the AuNP surface to make hydrophilic to hydrophobic AuNPs is demonstrated. It was found that hydrophobic ionic liquids provide the most effective transfer of AuNPs from the aqueous to organic phase. Interestingly, we have noticed no change in color, size, and shape of AuNPs for more than a month, indicating more efficient transfer of AuNPs in organic solvents, which remained stable for over a month. The ionic liquids with anions NTf₂^-, ClO₄^-, and PF₆^- make the AuNP surface hydrophobic, indicating their good dispersibility in nonpolar solvents. Finally, these AuNPs exhibit excellent sensitivity toward the refractive index of organic solvents, which is correlated with the surface plasmon resonance (SPR) λ_SPR bands.

Simultaneous and Reversible Triggering of the Phase Transfer and Luminescence Change of Amidine-Modified Carbon Dots by CO2

The ability to reversibly manipulate the surface nature of luminescent nanoparticles upon external stimulation enables the development of advanced optical probes for biological sensing and data encoding. Herein, we report the synthesis of a new class of smart carbon dots (CDs) via surface modification of amine-enriched CDs with CO₂-responsive groups of amidine. We present that alternative CO₂ and N₂ bubbling can not only lead to a reversible phase transfer of the CDs between an organic phase and an aqueous phase but also give rise to a corresponding reversible luminescence change between blue and cyan-green. We attribute these observations to changes in both the surface chemistry and the emission states of the CDs triggered by the alternative CO₂/N₂ introduction. We also find a similar luminescence change of the CDs upon alternative exposure to a humid vapor of CO₂ and a mixture of NH₃ and N₂ at room temperature, allowing them to be used as a new class of optical materials for optical encoding.

pH-Responsive Mercaptoundecanoic Acid Functionalized Gold Nanoparticles and Applications in Catalysis

Mercaptoundecanoic acid (MUA) functionalized gold nanoparticles (AuNP-MUA) were synthesized and demonstrated to possess pH-triggered aggregation and re-dispersion, as well as the capability of phase transfer between aqueous and organic phases in response to changes in pH. The pH of aggregation for AuNP-MUA is consistent with the pK_a of MUA (pH ~4) in solution, while AuNP-MUA phase transition between aqueous and organic phases occurs at pH ~9. The ion pair formation between the amine group in octadecylamine (ODA), the carboxylate group in MUA, and the hydrophobic alkyl chain of ODA facilitates the phase transfer of AuNP-MUA into an organic medium. The AuNP-MUA were investigated as a reusable catalyst in the catalytic reduction of 4-nitrophenol by borohydride—a model reaction for AuNPs. It was determined that 100% MUA surface coverage completely inhibits the catalytic activity of AuNPs. Decreasing the surface coverage was shown to increase catalytic activity, but this decrease also leads to decreased colloidal stability, recoverability, and reusability in subsequent reactions. At 60% MUA surface coverage, colloidal stability and catalytic activity were achieved, but the surface coverage was insufficient to enable redispersion following pH-induced recovery. A balance between AuNP colloidal stability, recoverability, and catalytic activity with reusability was achieved at 90% MUA surface coverage. The AuNP-MUA catalyst can also be recovered at different pH ranges depending on the recovery method employed. At pH ~4, protonation of the MUA results in reduced surface charge and aggregation. At pH ~9, ODA will form an ion-pair with the MUA and induce phase transfer into an immiscible organic phase. Both the pH-triggered aggregation/re-dispersion and aqueous/organic phase transfer methods were employed for catalyst recovery and reuse in subsequent reactions. The ability to recover and reuse the AuNP-MUA catalyst by two different methods and different pH regimes is significant, based on the fact that nanoparticle-catalyzed reactions may occur under different pH conditions.

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%.

Direct cation exchange of surface ligand capped upconversion nanocrystals to produce strong luminescence

We develop a facile and rapid cation exchange method for upconversion nanocrystals (UCNCs) without removing surface ligands.

Size-controlled and water-soluble gold nanoparticles using UV-induced ligand exchange and phase transfer

Oleylamine-capped gold nanoparticles (AuNPs) with sizes ranging from 5 to 13 nm and narrow size distributions (<10%) are synthesized by using a seeded growth approach. Water-solubility is achieved by using a UV-induced ligand exchange approach.

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.

Phase Transfer of Nanoparticles Using an Amphiphilic Ionic Liquid

The phase transfer of nanoparticles (NPs) from water to organic solvents by an amphiphilic room-temperature ionic liquid (IL) was reported. The geminal IL modified with Pluronic P123 stabilizes a variety of NPs of different size and nature, such as Pd, Au, Ag, and SiO₂ NPs. Their phase transfer into a hydrophobic environment was realized by raising the temperature and adding salts (such as NaCl and KBr), both of which have a common effect of breaking the hydrogen bonds of the IL with H₂O. A more straightforward method of using an organic solvent working as a hydrogen bond donor (such as butyl alcohol) was then proposed. In this case, NaCl was no longer required. To further apply this strategy to the organic solvents that are generally incapable of forming hydrogen bonds (e.g., toluene), a small quantity of benzoic acid was added to the organic phase. By forming hydrogen bonds from benzoic acid to the IL, an even more facile approach was provided. FT-IR confirmed the hydrogen bonding between them. The phase-transfer protocol does not rely on coordination bonding of ligands with a specific metal and is capable of the phase transfer of objects with large sizes and different natures. Thus, it has the potential for wide application.

Stimuli-Responsive Extraction and Ambidextrous Redispersion of Zwitterionic Amphiphile-Capped Silver Nanoparticles

Citrate-stabilized silver nanoparticles (AgNPs) were functionalized with a pH-responsive amphiphile, 3-[(2-carboxy-ethyl)-hexadecyl-amino]-propionic acid (C16CA). At pH ∼ 4, the zwitterionic C16CA assembled into lamellar structures due to the protonation of the amine groups of the amphiphile that neutralized the anionic charge of the carboxylate groups. The lamellar supramolecules incorporated the AgNPs into their 3D network and extracted them from water. C16CA supramolecules dissolved into water (at pH > 6) and organic solvents; consequently, the recovered C16CA-AgNPs were redispersed not only to water but also to chloroform and tetrahydrofuran without any additional functionalization. C16CA acted as a pH-responsive stabilizer of AgNPs and formed a solvent-switchable molecular layer such as a bilayered structure in water and densely packed monolayer in chloroform and tetrahydrofuran. Redispersion of the AgNPs was achieved in different solvents by changing the solvent affinity of the adsorbed C16CA molecular layer based on the protonation of the amine groups of the pH-responsive amphiphile. The morphology of redispersed AgNPs did not change during the recovery and redispersion procedure, due to the high steric effect of the network structure of C16CA supramolecules. These observations can lead to a novel solvent-exchange method for nanocrystals without aggregation and loss of nanocrystals, and they enable effective preparations of stimuli-responsive plasmonic nanomaterials.

Dual-emitting quantum dot/carbon nanodot-based nanoprobe for selective and sensitive detection of Fe(3+) in cells

A novel dual-emitting fluorescence probe is developed for rapid and ultrasensitive detection of Fe(3+). The nanoprobe is prepared by coating CdSe semiconductor quantum dots (SQDs) onto the surface of carbon nanodot (CND) doped TiO2 microspheres. The as-prepared nanoprobe exhibits the corresponding dual emissions at 436 and 596 nm for CNDs and CdSe, respectively, under a single excitation wavelength. The blue fluorescence of the CNDs is insensitive to Fe(3+), whereas the orange emission of the CdSe SQDs is functionalized to be selectively quenched by Fe(3+). The intensity ratio of I436/I596 shows a good linear relationship with the concentration of Fe(3+) in the range of 10(-9) to 10(-5) M. The nanoprobe provides an effective platform for the reliable detection of Fe(3+) with a detection limit as low as 10 nM. Besides, this ratiometric nanosensor exhibits good selectivity for Fe(3+) over other metal ions. The results reveal that the nanoprobe could provide a sensitive sensor for rapid detection of Fe(3+) with high selectivity and sensitivity. Moreover, 293T cells are used as models to achieve a potential application as a probe for monitoring Fe(3+) in cells. Thus, these dual-emitting nanoprobes could work as an alternative to conventional fluorescence probes for biolabeling, sensing and other applications.

Coinage metal coordination chemistry of stable primary, secondary and tertiary ferrocenylethyl-based phosphines

Ferrocene-based phosphines constitute an important auxiliary ligand in inorganic chemistry. Utilizing the (ferrocenylethyl)phosphines (FcCH2CH2)3-nHnP (Fc = ferrocenyl; n = 2, 1; n = 1, 2; n = 0, 3) the synthesis of a series of coordination complexes [(FcCH2CH2)3-nHnPCuCl]4 (n = 2, 1-CuCl; n = 0, 3-CuCl), [(FcCH2CH2)2HPCuCl] (2-CuCl), {[(FcCH2CH2)H2P]2AgCl}2 (1-AgCl), [(FcCH2CH2)2HPAgCl] (2-AgCl), [(FcCH2CH2)3PAgCl]4 (3-AgCl), [(FcCH2CH2)3PM(OAc)]4 (M = Cu, 3-CuOAc M = Ag, 3-AgOAc), [(FcCH2CH2)3-nHnPAuCl] (n = 1, 2-AuCl; n = 0, 3-AuCl), via the reaction between the free phosphine and MX (M = Cu, Ag and Au; X = Cl, OAc), is described. The reaction between the respective phosphine with a suspension of metal-chloride or -acetate in a 1 : 1 ratio in THF at ambient temperature affords coordinated phosphine-coinage metal complexes. Varying structural motifs are observed in the solid state, as determined via single crystal X-ray analysis of 1-CuCl, 3-CuCl, 1-AgCl, 3-AgCl, 3-CuOAc, 3-AgOAc, 2-AuCl and 3-AuCl. Complexes 1-CuCl and 3-CuCl are tetrameric Cu(i) cubane-like structures with a Cu4Cl4 core, whereas silver complexes with primary and tertiary phosphine reveal two different structural types. The structure of 1-AgCl, unlike the rest, displays the coordination of two phosphines to each silver atom and shows a quadrangle defined by two Ag and two Cl atoms. In contrast, 3-AgCl is distorted from a cubane structure via elongation of one of the ClAg distances. 3-CuOAc and 3-AgOAc are isostructural with step-like cores, while complexes 2-AuCl and 3-AuCl reveal a linear geometry of a phosphine gold(i) chloride devoid of any aurophilic interactions. All of the complexes were characterized in solution by multinuclear (1)H, (13)C{(1)H} and (31)P NMR spectroscopic techniques; the redox chemistry of the series of complexes was examined using cyclic voltammetry. This class of complexes has been found to exhibit one reversible Fe(ii)/Fe(iii) oxidation couple, suggesting the absence of electronic communication between the ferrocenyl units on individual phosphine ligands as well as between different phosphines on the polymetallic cores.

Cellulosic micelles as nanocapsules of liposoluble CdSe/ZnS quantum dots for bioimaging

Sustainable light-emitting nanoaggregates obtained by encapsulating liposoluble CdSe/ZnS QDs in novel cellulosic micelles show promise in bioimaging.

Supramolecular tailoring of protein-nanoparticle interactions using cucurbituril mediators

Supramolecular modification of nanoparticle surfaces through threading of cucurbit[7]uril (CB[7]) onto surface ligands is used to regulate protein-nanoparticle interactions.

Interfacial tension-hindered phase transfer of polystyrene-b-poly(ethylene oxide) polymersomes from a hydrophobic ionic liquid to water

We examine the phase transfer of polystyrene-b-poly(ethylene oxide) (PS-PEO) polymersomes from a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), into water. The dependence of the phase transfer on the molecular weight and PEO volume fraction (fPEO) of the PS-PEO polymersomes was systematically studied by varying the molecular weight of PS (10,000-27,000 g/mol) as well as by varying the volume fraction of PEO (fPEO) between 0.1 and 0.3. We demonstrate a general boundary for the phase transfer in terms of a reduced tethering density for PEO (σPEO), which is independent of the molecular weight of the hydrophobic PS. The reduced PEO tethering density was controlled by changing the polymersome size (i.e., increased polymersome sizes increase σPEO), confirming that it is the driving force in the transfer of PS-PEO polymersomes at room temperature. The phase transfer dependence on σPEO was also analyzed in terms of the free energy of polymersomes in the biphasic system. The quality of the aqueous phase, which affects the interfacial tension of the PS membrane, influenced the phase transfer. We systematically reduced the interfacial tension by adding a water-selective solvent, THF, which has a similar effect to increasing σPEO. The results indicate that the interfacial tension between the membrane and water plays an important role in the phase transfer with the corona and that the phase transfer can be controlled either by the dimensions of the polymersomes or by the suitability of the solvent for the membrane. The interfacial tension-hindered phase transfer of polymersomes in the biphasic water-[EMIM][TFSI] system will inform the design of temperature-sensitive and reversible nanoreactors and the separation of polydisperse particles according to size by tuning the quality of the solvent.

Water-soluble Zn–Ag–In–Se quantum dots with bright and widely tunable emission for biomedical optical imaging

In this work, we synthesized water-soluble quaternary cadmium-free Zn–Ag–In–Se quantum dots with bright and widely tunable emission, and explored their potential in tumor-specific imaging in vitro and in vivo.

Nano-design of quantum dot-based photocatalysts for hydrogen generation using advanced surface molecular chemistry

A molecular linking strategy is demonstrated to achieve efficient electron transfer and hydrogen evolution using a (CdSe–ZnS)–TiO₂–(Au–Pt) photocatalyst.

pH-induced recovery and redispersion of shape-controlled gold nanorods for nanocatalysis

The pH-responsive amphiphile C16CA was used for the functionalization of gold nanorods. The pH-induced recovery–redispersion of gold nanorods using C16CA self-assembly was accomplished without affecting the catalytic activity of the nanorods.

Surface complexation reaction for phase transfer of hydrophobic quantum dot from nonpolar to polar medium

Chemical reaction between oleate-capped Zn(x)Cd(1-x)S quantum dots (Qdots) and 8-hydroxyquinoline (HQ) led to formation of a surface complex, which was accompanied by transfer of hydrophobic Qdots from nonpolar (hexane) to polar (water) medium with high efficiency. The stability of the complex on the surface was achieved via involvement of dangling sulfide bonds. Moreover, the transferred hydrophilic Qdots--herein called as quantum dot complex (QDC)--exhibited new and superior optical properties in comparison to bare inorganic complexes with retention of the dimension and core structure of the Qdots. Finally, the new and superior optical properties of water-soluble QDC make them potentially useful for biological--in addition to light emitting device (LED)--applications.

Thermoreversible partitioning of poly(ethylene oxide)s between water and a hydrophobic ionic liquid

We describe a poly(ethylene oxide) (PEO) homopolymer "shuttle" between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). PEO homopolymers with varying molecular weight transferred reversibly and quantitatively between water at room temperature and [EMIM][TFSI] at an elevated temperature. The temperature of the transfer from water to [EMIM][TFSI] shows a linear dependence on PEO molecular weight and a dependence on polymer concentration consistent with expectation based on Flory-Huggins theory. These results are also consistent with the previously observed lower critical solution temperature (LCST) behavior of PEO in water. Dynamic light scattering study of the concentration and temperature dependence of the swelling degree of PEO corona of polybutadiene (PB)-PEO block copolymer micelles indicates that the solvent quality of [EMIM][TFSI] for PEO remains essentially the same as a good solvent over the temperature range of the PEO shuttle. Fundamental understanding of the PEO shuttle is of significance in development of systems for phase transfer of reagents and reaction products between ionic liquids and water.

'One-pot' synthesis of multifunctional GSH-CdTe quantum dots for targeted drug delivery

A novel quantum dots-based multifunctional nanovehicle (DOX-QD-PEG-FA) was designed for targeted drug delivery, fluorescent imaging, tracking, and cancer therapy, in which the GSH-CdTe quantum dots play a key role in imaging and drug delivery. To exert curative effects, the antineoplastic drug doxorubicin hydrochloride (DOX) was loaded on the GSH-CdTe quantum dots through a condensation reaction. Meanwhile, a polyethylene glycol (PEG) shell was introduced to wrap the DOX-QD, thus stabilizing the structure and preventing clearance and drug release during systemic circulation. To actively target cancer cells and prevent the nanovehicles from being absorbed by normal cells, the nanoparticles were further decorated with folic acid (FA), allowing them to target HeLa cells that express the FA receptor. The multifunctional DOX-QD-PEG-FA conjugates were simply prepared using the 'one pot' method. In vitro study demonstrated that this simple, multifunctional nanovehicle can deliver DOX to the targeted cancer cells and localize the nanoparticles. After reaching the tumor cells, the FA on the DOX-QD-PEG surface allowed folate receptor recognition and increased the drug concentration to realize a higher curative effect. This novel, multifunctional DOX-QD-PEG-FA system shows great potential for tumor imaging, targeting, and therapy.

Toward structurally defined carbon dots as ultracompact fluorescent probes

There has been much discussion on the need to develop fluorescent quantum dots (QDs) as ultracompact probes, with overall size profiles comparable to those of the genetically encoded fluorescent tags. In the use of conventional semiconductor QDs for such a purpose, the beautifully displayed dependence of fluorescence color on the particle diameter becomes a limitation. More recently, carbon dots have emerged as a new platform of QD-like fluorescent nanomaterials. The optical absorption and fluorescence emissions in carbon dots are not bandgap in origin, different from those in conventional semiconductor QDs. The absence of any theoretically defined fluorescence color-dot size relationships in carbon dots may actually be exploited as a unique advantage in the size reduction toward having carbon dots serve as ultracompact QD-like fluorescence probes. Here we report on carbon dots of less than 5 nm in the overall dot diameter with the use of 2,2'-(ethylenedioxy)bis(ethylamine) (EDA) molecules for the carbon particle surface passivation. The EDA-carbon dots were found to be brightly fluorescent, especially over the spectral range of green fluorescent protein. These aqueous soluble smaller carbon dots also enabled more quantitative characterizations, including the use of solution-phase NMR techniques, and the results suggested that the dot structures were relatively simple and better-defined. The potential for these smaller carbon dots to serve as fluorescence probes of overall sizes comparable to those of fluorescent proteins is discussed.

Interfacial and phase transfer behaviors of polymer brush grafted amphiphilic nanoparticles: a computer simulation study

Nanoparticles' phase transfer behaviors at the oil-water interface have many respects in common with lipid bilayer crossing behavior and the Pickering emulsion formation. Hence, the interfacial behavior and phase transfer behavior are intuitive indicators for the application potential of nanoparticle materials, e.g., on the emulsion formation and biomedical applications. Polymer brush modification enables nanoparticles to behave differently in hydrophilic solvent, hydrophobic solvent, and their interface region. In the present work, phase transfer behaviors of triblock polymer brush modified gold nanoparticles are explored by using coarse-grained simulations. The nanoparticles grafted with hydrophobic/weak hydrophilic/hydrophobic triblock brushes are found to have the best phase transfer performance, and the enhanced flexibility and mobility of head blocks are found to be the most vital factors. The inherent mechanism of interfacial behavior and phase transfer process are investigated and explained as perturbation effect and traction effect. According to our results, middle blocks dominate the brush morphology and decide whether NPs can be transferred into another phase. However, the inner blocks show higher dominance for the phase transfer behavior of nanoparticles restricted in the interface region, while the outer ones shows higher dominance for the nanoparticles departing from the interface region. Otherwise, interesting flat-Janus morphologies are found. Special applications in two-phase interface including emulsion stabilization could be expected. This work could provide some guidance for the molecular design and applications of polymer-nanoparticle composite materials.

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.

Recent advances in quantum dot surface chemistry

Quantum dot (QD) surface chemistry is an emerging field in semiconductor nanocrystal related research. Along with size manipulation, the careful control of QD surface chemistry allows modulation of the optical properties of a QD suspension. Even a single molecule bound to the surface can introduce new functionalities. Herein, we summarize the recent advances in QD surface chemistry and the resulting effects on optical and electronic properties. Specifically, this review addresses three main issues: (i) how surface chemistry affects the optical properties of QDs, (ii) how it influences the excited state dynamics, and (iii) how one can manipulate surface chemistry to control the interactions between QDs and metal oxides, metal nanoparticles, and in self-assembled QD monolayers.

Stable single-photon emission by quantum dot/polymer hybrid particles

Colloidal quantum dots are well-established probes for quantum optical experiments. However, they possess a limited stability toward their environment. Herein, the generation of hybrid particles composed of a high optical quality quantum dot centered in a polymer particle by means of a miniemulsion polymerization procedure is reported. This embedding strongly enhances emission intensity and photochemical stability of these single-photon emitters. At the same time, their colloidal mobile nature is not compromised.

A mesoporous silica nanocomposite shuttle: pH-triggered phase transfer between oil and water

With a simple protocol, we synthesize a novel mesoporous silica nanocomposite shuttle that can reversibly transfer between an organic phase and water in response to the pH, due to the switchable surface hydrophobicity/hydrophilicity. Our synthesis protocol allows the phase transfer ability to be tuned in a controllable fashion. This nanocomposite shuttle exhibits a good ability to load various cargoes such as Pd(OAc)2, Pd nanoparticles, and organic molecules. The built-in properties of the nanocomposite shuttle lay the foundations for many innovative applications. As a proof of concept, we successfully demonstrate its application in separating and recycling Pd nanoparticle catalysts. The composite shuttle can take Pd nanoparticles to an organic phase for catalyzing hydrogenation of olefins and come back to an aqueous phase at the end of reaction, making in situ separation and recycling of nanocatalysts possible. This pH-driven round trip for catalysis can be repeated several times. Our investigations not only supply a novel nanocomposite shuttle with controllable properties but also open an innovative avenue to in situ separation and recycling of nanocatalysts, which can address the obstacles of the conventional methods such as centrifugation and filtration.