Glycol Nanoparticles Research Articles

Experimental investigation of forced convective heat transfer coefficient in nanofluids of Al 2O 3/EG and CuO/EG in a double pipe and plate heat exchangers under turbulent flow

Nanofluid is the term applied to a suspension of solid, nanometer-sized particles in conventional fluids; the most prominent features of such fluids include enhanced heat characteristics, such as convective heat transfer coefficient, in comparison to the base fluid without considerable alterations in physical and chemical properties. In this study, nanofluids of aluminum oxide and copper oxide were prepared in ethylene glycol separately. The effect of forced convective heat transfer coefficient in turbulent flow was calculated using a double pipe and plate heat exchangers. Furthermore, we calculated the forced convective heat transfer coefficient of the nanofluids using theoretical correlations in order to compare the results with the experimental data. We also evaluated the effects of particle concentration and operating temperature on the forced convective heat transfer coefficient of the nanofluids. The findings indicate considerable enhancement in convective heat transfer coefficient of the nanofluids as compared to the base fluid, ranging from 2% to 50%. Moreover, the results indicate that with increasing nanoparticles concentration and nanofluid temperature, the convective heat transfer coefficient of nanofluid increases. Our experiments revealed that in lower temperatures, the theoretical and experimental findings coincide; however, in higher temperatures and with increased concentrations of the nanoparticles in ethylene glycol, the two set of results tend to have growing discrepancies.

Self-assembly of Pt nanoparticles on highly graphitized carbon nanotubes as an excellent oxygen-reduction catalyst

Platinum nanoparticles/graphitic carbon nanotubes (GCNTs) nanocomposites are fabricated with electrostatic self-assembly technology. Pt precursors are uniformly distributed on poly(diallyldimethylammonium chloride)-functionalized GCNTs surface (PDDA-GCNTs) via the electrostatic interaction and then in situ reduced to Pt nanoparticles in ethylene glycol, where PDDA is not only used as the wrapping polymer for GCNTs to preserve the integrity and the electronic structure of GCNTs, but also facilitates the uniform distribution of Pt nanoparticles on the surface of GCNTs. X-ray diffraction patterns and transmission electron microscope images reveal that Pt nanoparticles with an average size of ∼2.7nm are uniformly dispersed on highly graphitized GCNTs. Significant enhancement in the electrocatalytic activity on Pt/PDDA-GCNTs catalyst towards oxygen reduction reaction (ORR) has been demonstrated. In addition, this catalyst also shows enhanced electrochemical durability due to the high graphitization degree of GCNTs. This provides a facile and eco-friendly approach to large-scale production of high performance fuel cell eletrocatalysts.

Nanochemoprevention: Sustained Release of Bioactive Food Components for Cancer Prevention

Chemoprevention, especially through the use of naturally occurring phytochemicals capable of impeding the process of carcinogenesis at one or more steps, is an ideal approach for cancer management. Despite accomplished outcomes in preclinical settings, its applicability to humans has met with limited success for many reasons including inefficient systemic delivery and bioavailability of promising chemopreventive agents. We have recently introduced a novel concept of “nanochemoprevention” that utilizes nanotechnology for enhancing the outcome of chemoprevention (Cancer Res 69, 1712–1716, 2009). To establish the usefulness of nanochemoprevention in cancer management, we studied the efficacy of a well identified chemopreventive agent epigallocatechin-3-gallate (EGCG) encapsulated in polylactic acid (PLA) and polyethylene glycol (PEG) nanoparticles (hereafter referred to as nano-EGCG) in preclinical settings. Nano-EGCG was found to retain its biological effectiveness, with over 10-fold dose advantage compared to nonencapsulated EGCG for exerting its cell growth inhibition, proapoptotic, and angiogenic inhibitory effects. Nano-EGCG was also observed to be effective in inhibiting tumor cell growth in athymic nude mice, with over 10-fold dose advantage compared to nonencapsulated EGCG. The rate of degradation of nonencapsulated EGCG was rapid, with a complete degradation within 4 h, whereas nano-EGCG had a significantly longer half-life. This study provides a foundation for the use of nanoparticle-mediated delivery of natural products to enhance the bioavailability of active agents for their enhanced effective and chemopreventive potential. In doing this, it is hoped that perceived toxicity concerns associated with prolonged use of agents could also be minimized. Oral consumption is the most desirable and acceptable form of delivery of chemopreventive agents. One disadvantage of using PLA-PEG nanoparticles is its unstable nature in acidic environment; and therefore, it is not recommended for oral consumption. To overcome this obstacle, it will be important to develop nanoparticles encapsulating phytochemicals that are suitable for oral consumption.

Nickel Nanoparticles Catalyzed Knoevenagel Condensation of Aromatic Aldehydes with Barbituric Acids and 2-Thiobarbituric Acids

An efficient route for the Knoevenagel condensation of aromatic aldehydes with barbituric acids and 2-thiobarbituric acids in the presence of polyvinyl pyrrolidone (PVP) stabilized Ni nanoparticles in ethylene glycol has been reported. A range of biologically important arylidene barbiturates were obtained in high yields (82–97%) in a very short reaction time. A novel and highly efficient PVP-stabilized Ni nanoparticles catalyzed synthesis of arylidene barbiturates and arylidene 2-thiobarbiturates has been described.

Synthesis and characterisation of silver nanoparticles in viscous solvents and its transfer into non-polar solvents

Room temperature synthesis of silver nanoparticles has been successfully achieved by adding NaOH acting as an accelerator for the reduction of silver ions in ethylene glycol and glycerol without adding any external reducing agent. Highly monodisperse silver particles are obtained in the presence of various stabilisers such as PVP, SiO2 and SDS. Nanoparticles with a mean diameter of 25 nm and a mean deviation of 2 nm could be obtained under experimental conditions. The silver nanoparticles so obtained could be easily transferred to chloroform containing CTAB, giving rise to CTAB stabilised silver nanoparticles having sizes of around 25 nm. The newly found role of OH− stabilisation was used to formulate a mechanism for the formation of silver nanoparticles in ethylene glycol and glycerol. In this mechanism, silver nanoparticles are stabilised in ethylene glycol by the adsorbed OH− ions.

Immunization of Guinea Pigs with Novel Hepatitis B Antigen as Nanoparticle Aggregate Powders Administered by the Pulmonary Route

Novel nanoparticle-aggregate formulations containing recombinant hepatitis B surface antigen (rHBsAg) were administered to the lungs of guinea pigs and antibodies generated to this antigen evaluated. Preparations of dry powders of: (a) rHBsAg encapsulated within poly(lactic-co-glycolic acid) (PLGA)/polyethylene glycol (PEG) nanoparticles (antigen nanoparticles, AgN(SD)), (b) rHBsAg in a physical mixture with blank PLGA/PEG nanoparticles (antigen nanoparticle admixture (AgNA(SD)), and (c) rHBsAg encapsulated in PLGA/PEG nanoparticles plus free rHBsAg (antigen nanoparticles and free antigen), were generated by spray drying with leucine. Control groups consisted of alum with adsorbed rHBsAg (AlumAg); reconstituted suspensions of spray-dried rHBsAg-loaded PLGA/PEG nanoparticles with leucine; and rHBsAg-loaded PLGA/PEG nanoparticles (AgN). Control preparations were administered by intramuscular injection; AgN was also spray instilled into the lungs. The IgG titers were measured in the serum for 24 weeks after the initial immunization; IgA titers were measured in the bronchio-alveolar lavage fluid. While the highest titer of serum IgG antibody was observed in guinea pigs immunized with AlumAg administered by the IM route, animals immunized with powder formulations via the pulmonary route exhibited high IgA titers. In addition, guinea pigs immunized with AgNA(SD) via the pulmonary route exhibited IgG titers above 1,000 mIU/ml in the serum (IgG titers above 10 mIU/ml is considered protective). Thus, the disadvantages observed with the existing hepatitis B vaccine administered by the parenteral route may be overcome by administering them as novel dry powders to the lungs. In addition, these powders have the advantage of eliciting a high mucosal immune response in the lungs without traditional adjuvants.

Abstract 5708: Anti-proliferative and pro-apoptotic effects of (−)-epigallocatechin-3-gallate encapsulated in chitosan nanoparticles on human melanoma Mel 928 cells

Abstract We recently employed the use of nanotechnology to improve the outcome of bioactive food components for cancer chemoprevention and termed the concept as nanochemoprevention (Cancer Res. 2009; 69(5): 1712-6.). To demonstrate the proof-of-principle we encapsulated green tea polyphenol epigallocatechin-3-gallate (EGCG) in polylactic acid-polyethylene glycol (PLA-PEG) nanoparticles and showed that this formulation demonstrates greater than ten-fold dose advantage over non-encapsulated EGCG in human prostate cancer PC3 cells both in vitro and in vivo settings. Here we extended the work to human melanoma cells where we previously showed that EGCG exerts anti-proliferative and pro-apoptotic effects. Further, one disadvantage of PLA-PEG nanoparticles is the lack of its oral bioavailability. To overcome this obstacle we encapsulated EGCG in nanoparticles employing a naturally occurring polymer chitosan (hereafter referred to as nano-EGCG), a delivery system suitable for oral consumption. We first determined the usefulness of this unique formulated nano-EGCG for its cytotoxic response against human melanoma Mel 928 cells. MTT assay showed that treatment of cells with nano-EGCG, compared to EGCG in PBS, produced remarkably superior effects with an IC50 of 2.0 μM compared to 50 μM when delivered in PBS. Our next goal was to determine if nano-EGCG retains its mechanistic identity. Nano-EGCG treatment (2 μM) to the Mel 928 cells resulted in (i) a shift in Bax/Bcl-2 ratio in favor of apoptosis, (ii) an increase in PARP cleavage, (iii) a significant inhibition in caspase 3 and 9, other key regulators of apoptosis, (iv) a dramatic increase in the levels of annexin V, and (v) marked induction of p21 and p27 cyclin dependent kinase inhibitors. Importantly, 2 μM of EGCG delivered in PBS was without any effect on any of these responses. Next we determined EGCG release kinetics of the nanoformulation using simulated gastric and intestinal fluids. We observed that the EGCG release peaked at 2 hours post-incubation with 50% released into the intestinal fluid and 30% released into the gastric juice and the percent release thereafter was maintained at constant levels suggesting a sustained release phenomenon. Furthermore, to ascertain oral bioavailability of nano-EGCG compared to free EGCG, blood samples were collected from mice treated with EGCG and nano-EGCG at 1, 8 and 24 hrs post administration and the levels of EGCG were determined by LC/MS/MS. We observed a steady and sustained release of EGCG in the plasma of mice following oral administration. Several experiments indicated that this nano formulated EGCG exhibited a significant longer half-life compared to non-encapsulated EGCG when given orally to mice. Translation of these data to appropriate animal model systems could pave the way for developing new avenues for melanoma chemoprevention. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5708.

Nanochemoprevention by Bioactive Food Components: A Perspective

Chemoprevention through the use of bioactive food components is a practical approach for cancer control. Despite abundant efficacy data under preclinical settings, this strategy has resulted in limited success for human cancer control. Amongst many reasons, inefficient systemic delivery and bioavailability of promising chemopreventive agents are considered to significantly contribute to such a disconnect. We recently introduced a novel concept in which we utilized nanotechnology for enhancing the outcome of chemoprevention (Cancer Res. 2009; 69:1712-6) and termed it nanochemoprevention. To establish the proof-of-principle of nanotechnology for cancer management, we determined the efficacy of a well-known chemopreventive agent epigallocatechin-3-gallate (EGCG) encapsulated in polylactic acid (PLA)-polyethylene glycol (PEG) nanoparticles in preclinical settings and observed that, compared to non-encapsulated EGCG, nano-EGCG retained its biological efficacy with over 10-fold dose advantage both in cell culture system and in vivo settings in athymic nude mice implanted with human prostate cancer cells. This study laid the foundation of nanochemoprevention by bioactive food components. Since oral consumption is the most desirable and acceptable form of delivery of bioactive food components, it will be important to develop nanoparticles containing bioactive food components that are suitable for oral consumption for which experiments are underway in this laboratory.

Commentary [Research Highlights

Drug delivery to the central nervous system remains a vexing problem because of the presence of the blood-brain barrier (BBB), whose endothelial cell tight junctions limit the paracellular flux of hydrophilic molecules. One solution may be vector-mediated delivery to the brain. This employs chimeric peptide technology, wherein the drug is conjugated to a molecular carrier of protein nature (e.g. cationized albumin or a transferrin receptor antibody). Transferrin receptor antibodies selectively target BBB endothelium due to the high levels of receptor expressed by these cells, thereby triggering receptor-mediated transport across the BBB via transcytosis. Chitosan, a naturally occurring, abundant, and biocompatible polysaccharide has found widespread pharmaceutical application. In particular, the cationic nature of chitosan facilitates its interaction with negative charges on the brain endothelium, Building on their previous work on brain-deliverable chitosan-polyethylene glycol nanoparticles functionalized with monoclonal anti-transferrin antibody, Karatas and colleagues have now designed caspase-3 inhibitor-loaded chitosan nanospheres conjugated with an anti-mouse transferrin receptor monoclonal antibody that selectively recognizes the transferrin receptor type 1 on the cerebral vasculature. Caspase-3 has been implicated in neuronal cell death in cerebral ischemia, as well as in the pathophysiology of other neurological disorders. When given intravenously, the caspase-3-loaded nanospheres were rapidly transported across the BBB and dose-dependently decreased infarct volume, neurological deficit, and ischemiainduced caspase-3 activity in mice subjected to focal cerebral ischemia/reperfusion. Because significant opening of the BBB starts only 6 h after ischemia/reperfusion, the rapid transfer of nanospheres to the brain was not likely caused by an increased permeability of the BBB. Similarly, nanospheres inhibited physiological caspase-3 activity during development in the neonatal mouse cerebellum on postnatal day 17, after closure of the BBB. These observations convincingly demonstrate that transferrin monoclonal antibody-conjugated chitosan nanospheres are an efficient delivery system for bringing neuroprotective, small peptide drugs into the brain. This opens intriguing new avenues for the treatment of central nervous system disorders in which the administration of therapeutic agents is handicapped by insufficient diffusion across the BBB. Further studies are eagerly awaited to see if this technology will be applicable to polypeptide factors, for example, brain-derived neurotrophic factor and ciliary neurotrophic factor.

Polyelectrolyte nanoparticles based on water-soluble chitosan–poly( l-aspartic acid)–polyethylene glycol for controlled protein release

Water-soluble chitosan (WSC)–poly( l-aspartic acid) (PASP)–polyethylene glycol (PEG) nanoparticles (CPP nanoparticles) were prepared spontaneously under quite mild conditions by polyelectrolyte complexation. These nanoparticles were well dispersed and stable in aqueous solution, and their physicochemical properties were characterized by turbidity, FTIR spectroscopy, dynamic light scattering (DLS), transmission electron microscope (TEM), and zeta potential. PEG was chosen to modify WSC–PASP nanoparticles to make a protein-protective agent. Investigation on the encapsulation efficiency and loading capacity of the bovine serum albumin (BSA)-loaded CPP nanoparticles was also conducted. Encapsulation efficiency was obviously decreased with the increase of initial BSA concentration. Furthermore, its in vitro release characteristics were evaluated at pH 1.2, 2.5, and 7.4. In vitro release showed that these nanoparticles provided an initial burst release, followed by a slowly sustained release for more than 24 h. The BSA released from CPP nanoparticles showed no significant conformational change compared with native BSA, which is superior to the BSA released from nanoparticles without PEG. A cell viability study suggested that the nanoparticles had good biocompatibility. This nanoparticle system was considered promising as an advanced drug delivery system for the peptide and protein drug delivery.

Introducing Nanochemoprevention as a Novel Approach for Cancer Control: Proof of Principle with Green Tea Polyphenol Epigallocatechin-3-Gallate

Chemoprevention, especially through the use of naturally occurring phytochemicals capable of impeding the process of one or more steps of carcinogenesis process, is a promising approach for cancer management. Despite promising results in preclinical settings, its applicability to humans has met with limited success largely due to inefficient systemic delivery and bioavailability of promising chemopreventive agents. Here, we introduce the concept of nanochemoprevention, which uses nanotechnology for enhancing the outcome of chemoprevention. We encapsulated green tea polyphenol epigallocatechin-3-gallate (EGCG) in polylactic acid-polyethylene glycol nanoparticles and observed that encapsulated EGCG retains its biological effectiveness with over 10-fold dose advantage for exerting its proapoptotic and angiogenesis inhibitory effects, critically important determinants of chemopreventive effects of EGCG in both in vitro and in vivo systems. Thus, this study could serve as a basis for the use of nanoparticle-mediated delivery to enhance bioavailability and limit any unwanted toxicity of chemopreventive agents, such as EGCG.

Self-assembly of Nafion molecules onto silica nanoparticles formed in situ through sol–gel process

Self-assembly of Nafion onto in situ formed silica nanoparticles in ethylene glycol–water mixture solvent has been investigated in this study. It was found that the formation of silica nanoparticles depends on the concentration of Nafion in dispersions. At relatively low concentration, 0.8% in weight in this case, the existing Nafion is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the concentration of Nafion increased to 2% in weight, self-assembled Nafion layer on the surface stabilizes the initial formed silica nanoparticles and silica particles with average diameters of 4.2 ± 0.5 nm were found to be uniformly distributed in the dispersion. With further increasing the concentration of Nafion, the number of Nafion aggregates increases and silica nanoparticles were mainly formed inside the entangled Nafion chains, resulting in an observation of clusters of silica nanoparticles.

Enhanced thermal conductivity and viscosity of copper nanoparticles in ethylene glycol nanofluid

This study investigates the thermal conductivity and viscosity of copper nanoparticles in ethylene glycol. The nanofluid was prepared by synthesizing copper nanoparticles using a chemical reduction method, with water as the solvent, and then dispersing them in ethylene glycol using a sonicator. Volume loadings of up to 2% were prepared. The measured increase in thermal conductivity was twice the value predicted by the Maxwell effective medium theory. The increase in viscosity was about four times of that predicted by the Einstein law of viscosity. Analytical calculations suggest that this nanofluid would not be beneficial as a coolant in heat exchangers without changing the tube diameter. However, increasing the tube diameter to exploit the increased thermal conductivity of the nanofluid can lead to better thermal performance.

A New Chemical Route to Synthesise TM‐Doped (TM = Co, Fe) TiO2 Nanoparticles

AbstractSince the discovery of ferromagnetism well above room temperature in the Co‐doped TiO2 system, diluted magnetic semiconductors based on TiO2 doped with transition metals have generated great interest because of their potential use in the development of spintronic devices. The purpose of this paper is to report on a new and swift chemical route to synthesise highly stable anatase single‐phase Co‐ and Fe‐doped TiO2 nanoparticles, with dopant concentrations of up to 10 at.‐% and grain sizes that range between 20 and 30 nm. Complementary structural, microstructural and chemical analyses of the different nanopowders synthesised strongly support the hypothesis that a homogeneous distribution of the dopant element in the substitutional sites of the anatase structure has been achieved. Moreover, UV/Vis diffuse reflectance spectra of powder samples show redshifts to lower energies and decreasing bandgap energies with increasing Co or Fe concentration, which is consistent with n‐type doping of the TiO2 anatase matrix. Films of Co‐doped TiO2 were successfully deposited onto Si (100) substrates by the dip‐coating method, with suspensions of Ti1–xCoxO2 nanoparticles in ethylene glycol.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Green Synthesis of Ag and Pd Nanospheres, Nanowires, and Nanorods Using Vitamin B2: Catalytic Polymerisation of Aniline and Pyrrole

For the first time, we report green chemistry approach using vitamin B2 in the synthesis of silver (Ag) and palladium (Pd), nanospheres, nanowires, and nanorods at room temperature without using any harmful reducing agents, such as sodium borohydride (NaBH4) or hydroxylamine hydrochloride and any special capping or dispersing agent. Vitamin B2 was used as reducing agent as well as capping agent due to its high‐water solubility, biodegradability, and low‐toxicity compared with other reducing agents. The average particle size of nanoprticle was found to be Ag (average size 6.1±0.1 nm) and Pd (average size 4.1±0.1 nm) nanoparticles in ethylene glycol and Ag (average size 5.9±0.1 nm, and average size 6.1±0.1) nanoparticles in acetic acid and NMP, respectively. The formation of noble multiple shape nanostructures and their self assembly were dependent on the solvent employed for the preparation. When water was used as solvent media, Ag and Pd nanoparticles started to self‐assemble into rod‐like structures and in isopropanol Ag and Pd nanoparticles yielded wire‐like structures with a thickness in the range of 10 to 20 nm and several hundred microns in length. In acetone and acetonitrile medium, the Ag and Pd nanoparticles are self‐assembled into a regular pattern making nanorod structures with thicknesses ranging from 100 to 200 nm and lengths of a few microns. The so‐synthesized nanostructures were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X‐ray (EDX) analysis, and UV spectroscopy. The ensuing Ag and Pd nanoparticles catalyzed the reactions of aniline and pyrrole to generate polyaniline and polypyrrole nanofibers and may find various technological and biological applications. This single‐step greener approach is general and can be extended to other noble metals and transition metal oxides.

The thermal conductivity of alumina nanoparticles dispersed in ethylene glycol

The thermal conductivities of several nanofluids (dispersions of alumina nanoparticles in ethylene glycol) were measured at temperatures ranging from 298 to 411 K using a liquid metal transient hot wire apparatus. Our measurements span the widest range of temperatures that have been investigated to date for any nanofluid. A maximum in the thermal conductivity versus temperature behavior was observed at all mass fractions of nanoparticles, closely following the behavior of the base fluid (ethylene glycol). Our results confirm that additional temperature contributions inherent in Brownian motion models are not necessary to describe the temperature dependence of the thermal conductivity of nanofluids. Our results also show that the effect of mass or volume fraction of nanoparticles on the thermal conductivity of nanofluids can be correlated using the Hamilton and Crosser or Yu and Choi models with one adjustable parameter (the shape factor in the Hamilton and Crosser model, or the ordered liquid layer thickness in the Yu and Choi model).

Determination of the effective thermal diffusivity of nanofluids by the double hot-wire technique

This paper introduces a new transient double hot-wire technique for the direct measurement of the thermal diffusivity of nanofluids. A correlation to be used with the double hot-wire technique to calculate the effective thermal diffusivity of nanofluids is also developed. Several types of nanofluids were prepared by suspending different volume percentages (1–5%) of titanium dioxide (TiO2), aluminium oxide (Al2O3) and aluminium (Al) nanoparticles in ethylene glycol and engine oil. The thermal diffusivities of these nanofluids determined directly by this technique were found to increase substantially with the increased volume fraction of nanoparticles in base fluids. Based on the calibration results obtained for the base fluids, ethylene glycol and engine oil, the measurement error is estimated to be within 1.2%. The measured thermal diffusivities of nanofluids were found to be significantly higher than those calculated from the thermal diffusivity expression (i.e. αeff = keff/(ρ cp)eff) by using the effective thermal conductivities and volumetric specific heats obtained from the conventional hot-wire method and from the volume fraction mixture rule, respectively.

Adriamycin release from poly(lactide-co-glycolide)-polyethylene glycol nanoparticles: synthesis, and in vitro characterization

The preparation, properties, and application in adriamycin delivery ofbiocompatible and biodegradable poly(lactide-co-glycolide)-polyethylene glycol (PLGA-PEG) nanoparticles are discussed. PLGA-PEG copolymers were synthesized by ring opening polymerization of the dl-lactide and glycolide in the presence of PEG1000. 1H-NMR and FT-IR spectrum were consistent with the structure of PLGA-PEG copolymers. The adriamycin-loaded nanoparticles could be prepared using a precipitation-solvent evaporation technique. The nanoparticles have been produced by a precipitation-solvent evaporation technique. The physical characteristics and drug loading efficiency of the PLGA-PEG nanoparticles were influenced by the composition of the PLGA-PEG copolymers used to prepare the nanoparticles. Particle sizes were between 65 and 100 nm for different compositions of PLGA-PEG copolymers. PLGA-PEG nanoparticles prepared from copolymers having relatively high PLGA/PEG ratios were smaller. Entrapment efficiency was 25%-33%. Adriamycin release from the nanoparticles at pH 7.4 showed an initial burst release and then sustained release phase. These results showed that PLGA-PEG nanoparticles could be an effective carrier for cancer therapy.

Electrochemical synthesis of free-standing CdS nanoparticles in ethylene glycol

A novel one-step electrochemical method for the preparation of capping-free cadmium sulfide nanoparticles is described. With gold as the working electrode, capping-free CdS nanoparticles are synthesized very conveniently at 70°C in the ethylene glycol (EG) solution of elementary sulfur, cadmium salt, and supporting electrolyte at −0.1 V. By carefully selecting the reductive potential, elementary sulfur is reduced while the reduction of Cd2+ is blocked by the formation of a sulfur monolayer on the gold electrode surface. The produced S2− reacts with cadmium cations in the solution to produce CdS. In this method, magnetic stirring can effectively prevent the deposition of CdS on the electrode surface. XRD analysis indicates that the product is pure cubic-phase CdS. The size and morphology of the particles are studied by TEM.

Molecular Mechanism of the Photochemical Generation of Gold Nanoparticles in Ethylene Glycol: Support for the Disproportionation Mechanism

It is found that replacement of the chloride ions in tetrachloroauric acid with bulky bromide ions inhibits the formation of gold nanoparticles in the photochemical reduction in ethylene glycol. However, the addition of silver ions to either the bromide or the chloride auric acid solution is found to enhance the rate of gold nanoparticle formation. These results are found to be accounted for by the previously proposed mechanism (Eustis, S.; Hsu, H.-Y.; El-Sayed, M. A. J. Phys. Chem. B 2005, 109, 4811) which involves disproportionation of the chloroauric complexes to generate free gold atoms and chloride ions. The steric effects of the bulky bromide ions inhibit the formation of the Au-Au bond needed in the electron transfer process of the disproportionation reaction. The addition of Ag+ ions results in the formation of insoluble silver halide, which shifts the disproportionation reaction toward the formation of gold atoms and thus the formation of gold nanoparticles.