Photochemical design of stimuli-responsive nanoparticles prepared by supramolecular host–guest chemistry

We introduce the design of a thermoresponsive nanoparticle via sacrificial micelle formation based on supramolecular host–guest chemistry. Reversible addition–fragmentation chain transfer (RAFT) polymerization was employed to synthesize well-defined polymer blocks of poly(N,N-dimethylacrylamide) (poly(DMAAm)) (Mn,SEC = 10 700 g mol–1, Đ = 1.3) and poly(N-isopropylacrylamide) (poly(NiPAAm)) (Mn,SEC = 39 700 g mol–1, Đ = 1.2), carrying supramolecular recognition units at the chain termini. Further, 2-methoxy-6-methylbenzaldehyde moieties (photoenols, PE) were statistically incorporated into the backbone of the poly(NiPAAm) block as photoactive cross-linking units. Host–guest interactions of adamantane (Ada) (at the terminus of the poly(NiPAAm/PE) chain) and β-cyclodextrin (CD) (attached to the poly(DMAAm chain end) result in a supramolecular diblock copolymer. In aqueous solution, the diblock copolymer undergoes micellization when heated above the lower critical solution temperature (LCST) of the thermoresponsive poly(NiPAAm/PE) chain, forming the core of the micelle. Via the addition of a 4-arm maleimide cross-linker and irradiation with UV light, the micelle is cross-linked in its core via the photoinduced Diels–Alder reaction of maleimide and PE units. The adamantyl–cyclodextrin linkage is subsequently cleaved by the destruction of the β-CD, affording narrowly distributed thermoresponsive nanoparticles with a trigger temperature close to 30 °C. Polymer chain analysis was performed via size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, and dynamic light scattering (DLS). The size and thermoresponsive behavior of the micelles and nanoparticles were investigated via DLS as well as atomic force microscopy (AFM).

Visible light-driven cross-coupling reactions at lower temperatures using a photocatalyst of palladium and gold alloy nanoparticles

Palladium (Pd)-catalyzed cross-coupling reactions are among the most important methods in organic synthesis. We report the discovery of highly efficient and green photocatalytic processes by which cross-coupling reactions, including Sonogashira, Stille, Hiyama, Ullmann, and Buchwald–Hartwig reactions, can be driven with visible light at temperatures slightly above room temperature using alloy nanoparticles of gold and Pd on zirconium oxide, thus achieving high yields. The alloy nanoparticles absorb visible light, and their conduction electrons gain energy, which is available at the surface Pd sites. Results of the density functional theory calculations indicate that transfer of the light excited electrons from the nanoparticle surface to the reactant molecules adsorbed on the nanoparticle surface activates the reactants. When the light intensity was increased, a higher reaction rate was observed, because of the increased population of photoexcited electrons. The irradiation wavelength also has an important impact on the reaction rates. Ultraviolet irradiation can drive some reactions with the chlorobenzene substrate, while visible light irradiation failed to, and substantially improve the yields of the reactions with the bromobenzene substrate. The discovery reveals the possibility of using low-energy and -density sources such as sunlight to drive chemical transformations.

Copper nanoparticles on graphene support: An efficient photocatalyst for coupling of nitroaromatics in visible light

Copper is a low-cost plasmonic metal. Efficient photocatalysts of copper nanoparticles on graphene support are successfully developed for controllably catalyzing the coupling reactions of aromatic nitro compounds to the corresponding azoxy or azo compounds under visible-light irradiation. The coupling of nitrobenzene produces azoxybenzene with a yield of 90 % at 60 °C, but azobenzene with a yield of 96 % at 90 °C. When irradiated with natural sunlight (mean light intensity of 0.044 W cm−2) at about 35 °C, 70 % of the nitrobenzene is converted and 57 % of the product is azobenzene. The electrons of the copper nanoparticles gain the energy of the incident light through a localized surface plasmon resonance effect and photoexcitation of the bound electrons. The excited energetic electrons at the surface of the copper nanoparticles facilitate the cleavage of the NO bonds in the aromatic nitro compounds. Hence, the catalyzed coupling reaction can proceed under light irradiation and moderate conditions. This study provides a green photocatalytic route for the production of azo compounds and highlights a potential application for graphene.

Direct photocatalytic conversion of aldehydes to esters using supported gold nanoparticles under visible light irradiation at room temperature

Visible light can drive esteri fi cation from aldehydes and alcohols using supported gold nanoparticles (Au/Al 2 O 3 ) as photo- catalysts at ambient temperatures. The gold nanoparticles (AuNPs) absorb visible light due to the localized surface plasmon resonance (LSPR) e ff ect, and the conduction electrons of the AuNPs gain the energy of the incident light. The energetic electrons, which concentrate at the NP surface, facilitate the activation of a range of aldehyde and alcohol substrates. The photocatalytic e ffi ciencies strongly depend on the Au loading, particle sizes of the AuNPs, irradiance, and wavelength of the light irradiation. Finally, a plausible reaction mechanism was proposed, and the Au/Al 2 O 3 catalysts can be reused several times without signi fi cantly losing activity. The knowledge acquired in this study may inspire further studies in new e ffi cient recyclable photocatalysts and a wide range of organic synthesis driven by sunlight.

Direct photocatalysis for organic synthesis by using plasmonic-metal nanoparticles irradiated with visible light

Recent advances in direct-use plasmonic-metal nanoparticles (NPs) as photocatalysts to drive organic synthesis reactions under visible-light irradiation have attracted great interest. Plasmonic-metal NPs are characterized by their strong interaction with visible light through excitation of the localized surface plasmon resonance (LSPR). Herein, we review recent developments in direct photocatalysis using plasmonic-metal NPs and their applications. We focus on the role played by the LSPR of the metal NPs in catalyzing organic transformations and, more broadly, the role that light irradiation plays in catalyzing the reactions. Through this, the reaction mechanisms that these light-excited energetic electrons promote will be highlighted. This review will be of particular interest to researchers who are designing and fabricating new plasmonic-metal NP photocatalysts by identifying important reaction mechanisms that occur through light irradiation.

Efficient photocatalytic Suzuki cross-coupling reactions on Au-Pd alloy nanoparticles under visible light irradiation

We report herein highly efficient photocatalysts comprising supported nanoparticles (NPs) of gold (Au) and palladium (Pd) alloys, which utilize visible light to catalyse the Suzuki cross-coupling reactions at ambient temperature. The alloy NPs strongly absorb visible light, energizing the conduction electrons of NPs which produce highly energetic electrons at the surface sites. The surface of the energized NPs activates the substrates and these particles exhibit good activity on a range of typical Suzuki reaction combinations. The photocatalytic efficiencies strongly depend on the Au:Pd ratio of the alloy NPs, irradiation light intensity and wavelength. The results show that the alloy nanoparticles efficiently couple thermal and photonic energy sources to drive Suzuki reactions. Results of the density functional theory (DFT) calculations indicate that transfer of the light-excited electrons from the nanoparticle surface to the reactant molecules adsorbed on the nanoparticle surface activates the reactants. The knowledge acquired in this study may inspire further studies of new efficient photocatalysts and a wide range of organic syntheses driven by sunlight.

Viable photocatalysts under solar-spectrum irradiation: Nonplasmonic metal nanoparticles

Supported nanoparticles (NPs) of nonplasmonic transition metals (Pd, Pt, Rh, and Ir) are widely used as thermally activated catalysts for the synthesis of important organic compounds, but little is known about their photocatalytic capabilities. We discovered that irradiation with light can significantly enhance the intrinsic catalytic performance of these metal NPs at ambient temperatures for several types of reactions. These metal NPs strongly absorb the light mainly through interband electronic transitions. The excited electrons interact with the reactant molecules on the particles to accelerate these reactions. The rate of the catalyzed reaction depends on the concentration and energy of the excited electrons, which can be increased by increasing the light intensity or by reducing the irradiation wavelength. The metal NPs can also effectively couple thermal and light energy sources to more efficiently drive chemical transformations.

Electrochemical mechanism of eugenol at a Cu doped gold nanoparticles modified glassy carbon electrode and its analytical application in food samples

A simple one-step electrodeposition method was used to construct a glassy carbon electrode (GCE), which has been modified with Cu doped gold nanoparticles (GNPs), i.e. a Cu@AuNPs/GCE. This electrode was characterized with the use of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The eugenol was electrocatalytically oxidized at the Cu@AuNPs/GCE. At this electrode, in comparison with the behavior at the GCE alone, the corresponding oxidation peak current was enhanced and the shift of the oxidation potentials to lower values was observed. Electrochemical behavior of eugenol at the Cu@AuNPs/GCE was investigated with the use of the cyclic voltammetry (CV) technique, and additionally, in order to confirm the electrochemical reaction mechanism for o-methoxy phenols, CVs for catechol, guaiacol and vanillin were investigated consecutively. Based on this work, an electrochemical reaction mechanism for o-methoxy phenols was suggested, and in addition, the above Cu@AuNPs/GCE was successfully employed for the analysis of eugenol in food samples.

The in vivo fate of nanoparticles and nanoparticle-loaded microcapsules after oral administration in mice: Evaluation of their potential for colon-specific delivery

Anti-cancer drug loaded-nanoparticles (NPs) or encapsulation of NPs in colon-targeted delivery systems shows potential for increasing the local drug concentration in the colon leading to improved treatment of colorectal cancer. To investigate the potential of the NP-based strategies for colon-specific delivery, two formulations, free Eudragit® NPs and enteric-coated NP-loaded chitosan–hypromellose microcapsules (MCs) were fluorescently-labelled and their tissue distribution in mice after oral administration was monitored by multispectral small animal imaging. The free NPs showed a shorter transit time throughout the mouse digestive tract than the MCs, with extensive excretion of NPs in faeces at 5 h. Conversely, the MCs showed complete NP release in the lower region of the mouse small intestine at 8 h post-administration. Overall, the encapsulation of NPs in MCs resulted in a higher colonic NP intensity from 8 h to 24 h post-administration compared to the free NPs, due to a NP ‘guarding’ effect of MCs during their transit along mouse gastrointestinal tract which decreased NP excretion in faeces. These imaging data revealed that this widely-utilised colon-targeting MC formulation lacked site-precision for releasing its NP load in the colon, but the increased residence time of the NPs in the lower gastrointestinal tract suggests that it is still useful for localised release of chemotherapeutics, compared to NP administration alone. In addition, both formulations resided in the stomach of mice at considerable concentrations over 24 h. Thus, adhesion of NP- or MC-based oral delivery systems to gastric mucosa may be problematic for colon-specific delivery of the cargo to the colon and should be carefully investigated for a full evaluation of particulate delivery systems.

Multimodal polymer nanoparticles with combined 19F magnetic resonance and optical detection for tunable, targeted, multimodal imagingin vivo

Understanding the complex nature of diseased tissue in vivo requires development of more advanced nanomedicines, where synthesis of multifunctional polymers combines imaging multimodality with a biocompatible, tunable, and functional nanomaterial carrier. Here we describe the development of polymeric nanoparticles for multimodal imaging of disease states in vivo. The nanoparticle design utilizes the abundant functionality and tunable physicochemical properties of synthetically robust polymeric systems to facilitate targeted imaging of tumors in mice. For the first time, high-resolution 19F/1H magnetic resonance imaging is combined with sensitive and versatile fluorescence imaging in a polymeric material for in vivo detection of tumors. We highlight how control over the chemistry during synthesis allows manipulation of nanoparticle size and function and can lead to very high targeting efficiency to B16 melanoma cells, both in vitro and in vivo. Importantly, the combination of imaging modalities within a polymeric nanoparticle provides information on the tumor mass across various size scales in vivo, from millimeters down to tens of micrometers.

Airway cellularity, lipid laden macrophages and microbiology of gastric juice and airways in children with reflux oesophagitis

Background: Gastroesophageal reflux disease (GORD) can cause respiratory disease in children from recurrent aspiration of gastric contents. GORD can be defined in several ways and one of the most common method is presence of reflux oesophagitis. In children with GORD and respiratory disease, airway neutrophilia has been described. However, there are no prospective studies that have examined airway cellularity in children with GORD but without respiratory disease. The aims of the study were to compare (1) BAL cellularity and lipid laden macrophage index (LLMI) and, (2) microbiology of BAL and gastric juices of children with GORD (G+) to those without (G-). Methods: In 150 children aged <14-years, gastric aspirates and bronchoscopic airway lavage (BAL) were obtained during elective flexible upper endoscopy. GORD was defined as presence of reflux oesophagitis on distal oesophageal biopsies. Results: BAL neutrophil% in G- group (n = 63) was marginally but significantly higher than that in the G+ group (n = 77), (median of 7.5 and 5 respectively, p = 0.002). Lipid laden macrophage index (LLMI), BAL percentages of lymphocyte, eosinophil and macrophage were similar between groups. Viral studies were negative in all, bacterial cultures positive in 20.7% of BALs and in 5.3% of gastric aspirates. BAL cultures did not reflect gastric aspirate cultures in all but one child. Conclusion: In children without respiratory disease, GORD defined by presence of reflux oesophagitis, is not associated with BAL cellular profile or LLMI abnormality. Abnormal microbiology of the airways, when present, is not related to reflux oesophagitis and does not reflect that of gastric juices. © 2005 Chang et al; licensee BioMed Central Ltd.

Reduction in arterial wall strain with aggressive lipid-lowering therapy in patients with carotid artery disease

Background: Inflammation and biomechanical factors have been associated with the development of vulnerable atherosclerotic plaques. Lipid-lowering therapy has been shown to be effective in stabilizing them by reducing plaque inflammation. Its effect on arterial wall strain, however, remains unknown. The aim of the present study was to investigate the role of high- and low-dose lipid-lowering therapy using an HMG-CoA reductase inhibitor, atorvastatin, on arterial wall strain. Methods and Results: Forty patients with carotid stenosis >40% were successfully followed up during the Atorvastatin Therapy: Effects on Reduction Of Macrophage Activity (ATHEROMA; ISRCTN64894118) Trial. All patients had plaque inflammation as shown by intraplaque accumulation of ultrasmall super paramagnetic particles of iron oxide on magnetic resonance imaging at baseline. Structural analysis was performed and change of strain was compared between high- and low-dose statin at 0 and 12 weeks. There was no significant difference in strain between the 2 groups at baseline (P=0.6). At 12 weeks, the maximum strain was significantly lower in the 80-mg group than in the 10-mg group (0.085±0.033 vs. 0.169±0.084; P=0.001). A significant reduction (26%) of maximum strain was observed in the 80-mg group at 12 weeks (0.018±0.02; P=0.01). Conclusions: Aggressive lipid-lowering therapy is associated with a significant reduction in arterial wall strain. The reduction in biomechanical strain may be associated with reductions in plaque inflammatory burden.

Biophysical response of living cells to boron nitride nanoparticles: Uptake mechanism and bio-mechanical characterization

Boron nitride nanomaterials have attracted significant interest due to their superior chemical and physical properties. Despite these novel properties, investigation on the interaction between boron nitride nanoparticle (BN NP) and living systems has been limited. In this study, BN NP (100–250 nm) is assessed as a promising biomaterial for medical applications. The toxicity of BN NP is evaluated by assessing the cells behaviours both biologically (MTT assay, ROS detection etc.) and physically (atomic force microscopy). The uptake mechanism of BN NP is studied by analysing the alternations in cellular morphology based on cell imaging techniques. The results demonstrate in vitro cytocompatibility of BN NP with immense potential for use as an effective nanoparticle for various bio-medical applications.

Rapid isolation and detection of erythropoietin in blood plasma by magnetic core gold nanoparticles and portable Raman spectroscopy

Isolating, purifying, and identifying proteins in complex biological matrices is often difficult, time consuming, and unreliable. Herein we describe a rapid screening technique for proteins in biological matrices that combines selective protein isolation with direct surface enhanced Raman spectroscopy (SERS) detection. Magnetic core gold nanoparticles were synthesised, characterised, and subsequently functionalized with recombinant human erythropoietin (rHuEPO)-specific antibody. The functionalized nanoparticles were used to capture rHuEPO from horse blood plasma within 15 minutes. The selective binding between the protein and the functionalized nanoparticles was monitored by SERS. The purified protein was then released from the nanoparticles’ surface and directly spectroscopically identified on a commercial nanopillar SERS substrate. ELISA independently confirmed the SERS identification and quantified the released rHuEPO. Finally, the direct SERS detection of the extracted protein was successfully demonstrated for in-field screening by a handheld Raman spectrometer within 1 minute sample measurement time.

Occupational release of engineered nanoparticles: A review

Characterising the release of different types of Engineered Nanoparticles (ENPs) from various processes is of critical importance for the assessment of human exposure, as well as understanding the possible health effects of these particles. Therefore, the main aim of this chapter is to present a comprehensive review of studies which report on the release of airborne ENPs in different nanotechnology workplaces. The chapter will cover topics of relevance to the occupational characterisation of ENP emissions, ranging from the identification of different particle release sources and scenarios, to measurement methods and working towards a more uniform approach to characterisation. Furthermore, a brief review of ENP exposure control strategies, together with the application of mathematical modelling as an effective tool for the characterisation of emissions at nanotechnology workplaces is included.