An ultrasensitive electrochemical immunosensor for CA72-4 based on a signal amplification strategy of MoS2 nanoflower-supported Au nanoparticles

Accurate detection of cancer antigen 72-4 (CA72-4), a tumor-associated glycoprotein, is of great significance for gastric cancer diagnosis and immunotherapy monitoring. Modification of noble metal nanoparticles on transition metal dichalcogenides can significantly enhance functions, such as electron transport. Molybdenum disulfide gold nanoparticles nanocomposites (MoS₂-Au NPs) were prepared in this study and a series of characterization studies were carried out. In addition, a label-free, highly sensitive electrochemical immunosensor molybdenum disulfide -Au nanoparticles/Glassy carbon electrode (MoS₂-Au NPs/GCE) was also prepared and used for the detection of CA72-4. The electrochemical performance of the immunosensor was characterized by electrochemical techniques, such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The results indicated that better MoS₂-Au NPs nanomaterials have been synthesized, and the prepared electrochemical immunosensor, MoS₂-Au NPs/GCE, showed excellent electrochemical performance. The sensor exhibited high detection sensitivity under optimal conditions, including an incubation time of 30 min, an incubation temperature of 25 °C, and a pH of 7.0. The electrochemical immunosensor also had a low detection limit of 2.0 × 10^?5 U/mL (S/N = 3) in a concentration range of 0.001–200 U/mL, with good selectivity, stability, and repeatability. In conclusion, this study provided a theoretical basis for the highly sensitive detection of tumor markers in clinical biological samples.     

Precise regulation of Ultra-thin platinum decorated Gold/Graphite carbon nitride photocatalysts by atomic layer deposition for efficient degradation of Rhodamine B under simulated sunlight

Atomic Layer Deposition (ALD) precise controlling ultra-thin platinum (Pt) modified Graphite carbon nitride (g-C₃N₄) photocatalysts, which had been doped with gold nanoparticles (Au NPs) by photodeposition, were successfully synthesized. The experimental results showed that precise regulation of platinum decorated C₃N₄-Au(C₃N₄-Au/nPt (n is the number of Pt ALD cycles, 1 Å per cycle)) exhibited excellent photocatalytic degradation ability for Rhodamine B (RhB). Under simulated sunlight irradiation, the degradation rate of 10 mg/L RhB(100 mL) by 1.5 mg C₃N₄-Au/10Pt catalysts was 95.8% within 60 min that is much better than other photocatalysts for the degradation of RhB. The efficient degradation mechanism of RhB by C₃N₄-Au/10Pt photocatalysts was studied and the experiments demonstrated the ·O₂^– as main active species played an important role in the photocatalytic process. Local surface plasmon resonance (LSPR) of Au NPs and Schottky barrier between Pt clusters and g-C₃N₄ may be the reasons for enhanced C₃N₄-Au/10Pt photocatalytic performances. Furthermore, the successive catalytic cycles revealed the excellent stability of C₃N₄-Au/10Pt photocatalyst.     

Bioinspired synthesis of multifunctional silver nanoparticles for enhanced antimicrobial and catalytic applications with tailored SPR properties

In the developing nanotechnology world, numerous attempts have been made to prepare the nobel metallic nanoparticles (NPs), which can improve their applicability in diverse fields. In the present work, the biosynthesis of silver (Ag) NPs has been successfully achieved through the medicinal plant extract (PE) of G. resinifera and effectively used for the catalytic and antibacterial applications. The size dependant tuneable surface plasmon resonance (SPR) properties attained through altering precursor concentrations. The X-ray and selected area diffraction pattern for Ag NPs revealed the high crystalline nature of pure Ag NPs with dominant (111) phase. The high-resolution TEM images show the non-spherical shape of NPs shifting from spherical, hexagonal to triangular, with wide particle size distribution ranging from 13 to 44 nm. Accordingly, the dual-band SPR spectrum is situated in the UV–Vis spectra validating the non-spherical shape of Ag NPs. The functional group present on the Ag NPs surface was analysed by FT-IR confirms the capping and reducing ability of methanolic PE G. resinifera. Further, the mechanism of antimicrobial activity studied using electron microscope showed the morphological changes with destructed cell walls of E. coli NCIM 2931 and S. aureus NCIM 5021 cells, when they treated with Ag NPs. The Ag NPs were more effective against S. aureus and E. coli with MIC 128 μg/ml as compared to P. aeruginosa NCIM 5029 with MIC 256 μg/ml. Apart from this, the reduction of toxic organic pollutant 4-NP to 4-AP within 20 min reveals the excellent catalytic activity of Ag NPs with rate constant k = 15.69 s^?1.     

Synthesis of Fe3O4@SiO2-Au/Cu magnetic nanoparticles and its efficient catalytic performance for the Ullmann coupling reaction of bromamine acid

Over bimetallic Au/Cu catalyst supported on magnetic Fe₃O₄ nanoparticles, water-mediated bromamine acid could be selectively converted into 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid (DAS) with a yield of 88.67%. The magnetic catalyst could be readily separated and reused.     

On demand release of ionic silver from gold-silver alloy nanoparticles: fundamental antibacterial mechanisms study

Synthesis and biomedical research of bimetallic gold-silver nanoparticles (Au–Ag NPs) have gained much attention due to their unique properties. Antibacterial mechanism of gold-silver nanoparticles is a current topic of interest in nanomedicine engineering. We used three routes in the synthesis of Au–Ag NPs alloy: i) Co-reduction of [HOOC-4-C₆H₄NN]AuCl₄/AgNO₃, ii) Seeding of AuNPs-COOH/AgNO₃ and iii) immobilization of AgNPs over the parent AuNPs-COOH. Two mild reducing agents, NaBH₄ and 9-BBN (9-borabicyclo(3.3.1)nonane), were used. Colloidal alloy nanoparticles structure was confirmed using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The particles reduced using NaBH₄ were larger (~20 nm) than those synthesized using 9-BBN (<10 nm). The synthesized nanoparticles showed high stability under notoriously leaching conditions of chloride-containing electrolytes. Moreover, we studied the Au–Ag NPs antibacterial activity against the growth of Gram-negative Escherichia coli ATCC strain 25922 and Gram-positive Staphylococcus aureus ATCC strain 29213. The antibacterial mechanisms were evaluated by studying the time-dependent generation of reactive oxygen species (ROS). A major destruction of the bacterial cell wall and leakage of cell components were observed by scanning electron microscopy (SEM), which is clearly visible towards E. coli more than S. aureus bacterial strain. The destruction of the bacterial cell wall was further confirmed by detecting the DNA leakage using gel electrophoresis. The synergistic effect of gold enhanced the antibacterial properties, however, with low cytotoxicity to human dermal fibroblast cells. This study deals with the important aspects of time-dependent mechanisms of the antibacterial action of Au–Ag NPs since the leaching out of Ag ion is slow compared to AgNPs. The Au–Ag NPs alloy efficiently tackles microbial activity that can be controlled to minimize cytotoxicity and thus opens their future applications as antibacterial agents.     

Constructing magnetic Fe3O4‐Au@CeO2 hybrid nanofibers for selective catalytic degradation of organic dyes

Au nanoparticles (Au NPs) play a vital role in heterogeneous catalytic reactions. However, pristine Au NPs usually suffer from poor selectivity and difficult recyclability. In this work, Fe₃O₄‐Au@CeO₂ hybrid nanofibers were prepared via a simple one‐pot redox reaction between HAuCl₄ and Ce (NO₃)₃ in the presence of Fe₃O₄ nanofibers. CeO₂ shell was uniformly coated on the surface of Fe₃O₄ nanofibers to form a unique core‐shell structure, while Au NPs were encapsulated inside the CeO₂ shell. The as‐prepared Fe₃O₄‐Au@CeO₂ hybrid nanofibers have been proved to be positively surface charged due to the formation of CeO₂ shell, enabling them to be good candidates for predominant selective catalytic activity towards the degradation of negatively charged organic dyes. In addition, the Fe₃O₄‐Au@CeO₂ hybrid nanofibers showed magnetic properties, offering them excellent recyclable usability. This work presents a facile and effective solution to prepare magnetic noble metal/metal oxide hybrid nanomaterials with unique chemical structure and surface characteristic for promising applications in heterogeneous catalysis.     

Electrochemical synthesis of copper-arabinoxylan nanocomposite for applications as antimicrobial agent and CO2 conversion catalyst

This study reports the electrochemical synthesis, antimicrobial and catalytic activity of copper-arabinoxylan nanocomposite. The synthesis was achieved without use of any hazardous reducing and stabilizing agent. The spherical copper nanoparticles (size approx. 40 nm) dispersed in the arabinoxylan matrix as they formed and got stabilized. In the absence of arabinoxylan the particles rapidly converted to copper oxide suggesting a high stability for the composite. Electrolysis was carried out with copper plate as the sacrificial anode, carbon rod as the cathode and sodium nitrate (1.00 % in 1 % arabinoxylan suspension) as an electrolyte. The copper nanoparticles dispersed in arabinoxylan were characterized by surface plasmon resonance spectroscopy, X-ray diffraction, electron microscopy and zeta potential measurements. The synthesized composite exhibited good antimicrobial activity against P. aeruginosa, Staph. aureus and E. coli and a catalytic activity in conversion of CO₂ to methanol.     

Lime peel extract induced NiFe2O4 NPs: Synthesis to applications and oxidative stress mechanism for anticancer,antibiotic activity

Nanobiotechnology, joined with green science, has incredible potential for the advancement of novel and important products that benefit human health, climate, and industries. Green chemistry of materials from synthesis to diverse biomedical applications is a talk of town in today’s sustainable ideal world. Green synthesized nickel ferrites nanoparticles via biogenic lime peel extract (LPE) are investigated with precision and complete trail has been reported as multiple efficacies. The fcc crystal structure with the crystallite size (31 nm) were accessed by the XRD, magnetic properties using VSM, and FTIR for the functional group analysis of NiFe₂O₄ nanoparticles mediated by Lime peel extract (NiFe₂O₄@LPE NPs). From TEM and SEM analysis the average diameter of the NPs was observed in the range of 31–35 nm. In 3D view, the surface morphology was analyzed by the AFM. NiFe₂O₄@LPE NPs were used to assess cytotoxicity and cellular morphological alterations in In Vitro cervical cancerous cells (HeLa). Nanosized NiFe₂O₄@LPE accompanied the considerable NPs topology induced dose dependent MMP in HeLa cells unlike the previous interpretation of controlled metabolism anticancer activity for HeLa cancerous cells. Therefore, it is referred by oxidative stress and reduction phenomena for anticancer effects and inactivation of carcinogen. Moreover, Antioxidant DPPH radical scavenging method and antibacterial Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus activity were observed in the synthesized nickel ferrites NPs.     

Biosynthesized Zinc Oxide Nanoparticles as Efficient Photocatalytic and Antimicrobial Agent

This work reports an innovative, effortless and inexpensive method for the preparation of ZnO nanoparticles by green approach using leaf extract of Piper betleas a reducing-stabilizing negotiator. The prepared ZnO NPs were characterized through XRD, FTIR, UV–Visible spectroscopy, and EDX etc. The band gap energy of the sample was estimated as 3.41 eV which is larger than the bulk ZnO (E_g?=?3.37 eV). The observed blue shift is attributed to the quantum confinement of excitons. FTIR analysis showed the presence of alkaloids, flavonoids, polyphenols, and terpenoid. TEM analysis showed that each nanoparticle comprised of 1 to 2 nano-crystallites. Photocatalytic activity results revealed that ZnO-NPs prepared through green synthesis route were found to be efficient in the degradation of toxic reactive red dye with degradation efficiency of 96.4% having high photodegradation rate-constant of 1.6?×?10^–2 min^?1. As an antimicrobial agent, the ZnO NPs are effective against both gram-positive (Bacillus subtilis) and negative bacteria (Escherichia coli), with the zones of clearance as 16.4 and 14.3 mm, respectively. Therefore, present research signifies an effective approach to utilize as-prepared ZnO NPs as efficient photocatalysts as well as antimicrobial agent.

     

Synthesis,characterization and application of Cr2O3 nanoparticles as an efficient antibacterial agent

This study focuses on the microwave-assisted synthesis of Cr₂O₃ nanoparticles for the development of antibacterial materials. Characterization techniques including FT-IR spectroscopy, UV–vis spectroscopy, SEM-EDX, and XRD, were employed to analyze the nanoparticles' properties. The antibacterial efficacy against E. coli, S. aureus, B. subtilis, and P. aeruginosa was evaluated, with significant activity observed against all pathogens, highlighting their potential as antibacterial materials. The novelty of this study lies in the synthesis of Cr₂O₃ nanoparticles and their application as potent antibacterial agents against various pathogens. The results of XRD study concludes the average size of Cr₂O₃ nanoparticles as 49.96 nm. The synthesized Cr₂O₃ nanoparticles demonstrated a good zone of inhibition against E. coli (22 mm), S. aureus (19 mm), B. subtilis (18 mm), and P. aeruginosa (21 mm). The findings of the study suggest that Cr₂O₃NPs have potential as a novel antibacterial agent, and further research in this area could lead to the development of new and effective treatments for bacterial infections.     

Three new mixed‐ligand copper(II) complexes containing glycyl‐l‐valine and N,N‐aromatic heterocyclic compounds: Synthesis,characterization, DNA interaction,cytotoxicity and antimicrobial activity

Three novel copper(II) complexes, [Cu(Gly‐l ‐Val)(HPBM)(H₂O)]·ClO₄·H₂O ( 1 ), [Cu(Gly‐l ‐Val)(TBZ)(H₂O)]·ClO₄ ( 2 ) and [Cu(Gly‐l ‐Val)(PBO)(H₂O)]·ClO₄ ( 3 ) (Gly‐l ‐Val = glycyl‐l ‐valine anion, HPBM = 5‐methyl‐2‐(2′‐pyridyl)benzimidazole, TBZ = 2‐(4′‐thiazolyl)benzimidazole, PBO = 2‐(2′‐pyridyl)benzoxazole), have been prepared and characterized with elemental analyses, conductivity measurements as well as various spectroscopic techniques. The interactions of these copper complexes with calf thymus DNA were explored using UV–visible, fluorescence, circular dichroism, thermal denaturation, viscosity and docking analyses methods. The experimental results showed that all three complexes could bind to DNA via an intercalative mode. Moreover, the cytotoxic effects were evaluated using the MTT method, and the antimicrobial activity of these complexes was tested against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. The results showed that the activities are consistent with their DNA binding abilities, following the order of 1 > 2 > 3 .     

Biogenic synthesis of husked rice-shaped iron oxide nanoparticles using coconut pulp (Cocos nucifera L.) extract for photocatalytic degradation of Rhodamine B dye and their in vitro antibacterial and anticancer activity

In this present study, photocatalytic and in-vitro biological properties of biogenic preparation of husked rice-shaped iron oxide nanoparticles (Fe₂O₃ NPs) are investigated. Fe₂O₃ NPs have been prepared by the reduction of iron chloride (FeCl₃) using coconut pulp (Cocos nucifera L.) extract. The Fe₂O₃ NPs were characterized by various analytical techniques such as FE-SEM, TEM, XRD, FT-IR, TGA, VSM, PL, and UV-DRS. Based on the characterization results, the as-prepared Fe₂O₃ NPs are in husked rice shape and exhibit rhombohedral crystal phase and also show an excellent stability. The prepared Fe₂O₃ NPs was investigated as a catalyst for the photocatalytic degradation of Rhodamine B solution. The photocatalytic results indicated that the Fe₂O₃ NPs catalyst possesses good activity with efficiency of 92% after 50 min under visible-light irradiation. In addition, the Fe₂O₃ NPs showed good antibacterial and anticancer properties against Gram-negative Escherichia coli and Gram-positive, Staphylococcus aureus and HepG2 cell lines, resulting in effective antibacterial and anticancer activity. The prepared Fe₂O₃ NPs, thus, proved to be a potential material for environmental remediation and biological applications.     

Synthesis of MnO2/CdTiO3 nano‐structure for high performance photocatalysis and antimicrobial application

A MnO₂/CdTiO₃ is prepared by a simple chemical method. The organic compound such as antibiotics is a contaminant found in large amounts in pharmaceutical industrial wastewater. Pharmaceutical compounds are toxic. The nano‐product was characterized by SEM, XRD, XPS, DLS and UV–vis DRS revealed that the MnO₂ nanoparticles were supported on the CdTiO₃ surface. The crystallite size was found as 72.11 nm, and 38.13 nm for CdTiO₃, and MnCdTi‐1 nanocomposites, respectively. The prepared catalyst was used for photo‐degradation of cephalexin under UV light irradiation. The result implies the complete degradation of cephalexin was carried out at 80 min for MnCdTi‐2 nanocomposites (88.88%) due to this catalyst has the lowest band gap compared to the other catalyst. The MnO₂/CdTiO₃ was selected for fungicidal and bactericidal efficiency against Aspergillus flavus, and candida albicans and Escherichia coli, and Staphylococcus aureus. The MnO₂/CdTiO₃–2 has great activity is compared with the other MnO₂/CdTiO₃–0 and MnO₂/CdTiO₃–1 samples.     

Multifunctional PES fabrics modified with colloidal Ag and TiO2 nanoparticles

This study is aimed to highlight the possibility of engineering the multifunctional textile nanocomposite material based on the polyester (PES) fabric modified with colloidal Ag and TiO₂ nanoparticles (NPs). The effects of concentration of NPs as well as the order of Ag and TiO₂ NPs loading on antimicrobial, UV protective, and photocatalytic properties of PES fabrics were examined. The antimicrobial activity of differently modified PES fabrics was tested against Gram‐negative bacterium Escherichia coli, Gram‐positive bacterium Staphylococcus aureus, and fungus Candida albicans. The concentration of Ag colloid and the order of Ag and TiO₂ NPs loading considerably affected the antimicrobial efficiency of PES fabrics. The fabrics provided maximum UV protection upon surface modification with Ag and TiO₂ NPs. Ag NPs enhanced Ag NPs enhanced the photodegradation activity of TiO₂ NPs and total photodegradation of methylene blue was achieved after 24 hr of UV illumination. Copyright © 2010 John Wiley & Sons, Ltd.     

MnO<Subscript>2</Subscript> Nanoparticles and Carbon Nanofibers Nanocomposites with High Sensing Performance Toward Glucose

By combining the advantages of manganese dioxide nanoparticles (MnO₂ NPs) and carbon nanofibers (CNFs), a biosensing electrode surface as a high-performance enzyme biosensor is designed in this work. MnO₂ NPs and CNFs nanocomposites (MnO₂–CNFs) were prepared by using a simple hydrothermal method and then were characterized by scanning electron microscopy, powder X-ray diffraction, fourier transform infrared spectroscopy, energy dispersive spectrometry and electrochemisty. The results showed that MnO₂ NPs are uniformly attached to the surface of CNFs. Meanwhile, the MnO₂–CNFs nanocomposites as a supporting matrix can provide an efficient and advantageous platform for electrochemical sensing applications. On the basis of the improved sensitivity of MnO₂–CNFs modified electrode toward H₂O₂ at low overpotential, a MnO₂–CNFs based glucose biosensor was fabricated by monitoring H₂O₂ produced by an enzymatic reaction between glucose oxidase and glucose. The constructed biosensor exhibited a linear calibration graph for glucose in a concentration range of 0.08–4.6 mM and a low detection limit of 0.015 mM. In addition, the biosensor showed other excellent characteristics, such as high sensitivity and selectivity, short response time, and the relative low apparent Michaelis–Menten constant. Analysis of human urine spiked with glucose at different concentration levels yielded recoveries between 101.0 and 104.8%.     

Research article green synthesis of zirconium oxide nanoparticles (ZrO2NPs) using Helianthus annuus seed and their antimicrobial effects

Monoclinic Zirconia (ZrO₂NPs) nanoparticles were successfully prepared by non-toxic and low-cost production using green synthesis analysis from the methanolic extract of Helianthus annuus (sunflower) seeds as the reducing agent. Mechanism of the chemical reaction has shown the reduction and which confirmed the formation of nanoparticles via chemical bonding in the IR spectrum at 502-498 ​cm^-1 ZrO₂ nanoparticles were characterized as sharp peak at 275 ​nm in the UV-Vis spectrum with 3.7eV in photon energy bandgap, it confirms the monoclinic crystal structure, as well as x-ray diffractometry, reveals zirconia crystallite is 40.59 ​nm. The internal morphology of crystal structure is exhibited by Scanning Electron Microscopy (SEM), and Transmission Electron Microscope (TEM). The stability of nanoparticles is represented in terms of zeta potential (-9.32 ​mV) and particle size distribution (~331 ​nm). Biosynthesized ZrO₂NPs were indicated as superior antimicrobial activity for biomedical applications.     

Enhancement of ethanol electrooxidation on plasmonic Au/TiO2 nanotube arrays

Novel electrocatalysts Au/TiO₂ nanotube arrays (Au/TiO₂NTs) were prepared by loading low-content(1.9 at.%) of Au nanoparticles (AuNPs) onto highly ordered TiO₂ nanotube arrays (TiO₂NTs). Ethanol electrooxidation indicates that visible-light (λ > 400 nm) irradiation can significantly enhance the activity as well as resistpoisoning of Au/TiO₂NTs electrocatalysts that are activated by plasmon resonance. Au/TiO₂NTs catalysts calcinated at 300 °C display the highest performance due to the strong synergistic interactions between TiO₂ and Au NPs. The combination of visible-light irradiation with a controllable potential offers a new strategyfor enhancing the performance of anodes in direct ethanol fuel cell (DEFC).     

Visible‐Light‐Induced Electron Transport from Small to Large Nanoparticles in Bimodal Gold Nanoparticle‐Loaded Titanium(IV) Oxide

A key to realizing the sustainable society is to develop highly active photocatalysts for selective organic synthesis effectively using sunlight as the energy source. Recently, metal‐oxide‐supported gold nanoparticles (NPs) have emerged as a new type of visible‐light photocatalysts driven by the excitation of localized surface plasmon resonance of Au NPs. Here we show that visible‐light irradiation (λ>430 nm) of TiO₂‐supported Au NPs with a bimodal size distribution (BM‐Au/TiO₂) gives rise to the long‐range (>40 nm) electron transport from about 14 small (ca. 2 nm) Au NPs to one large (ca. 9 nm) Au NP through the conduction band of TiO₂. As a result of the enhancement of charge separation, BM‐Au/TiO₂ exhibits a high level of visible‐light activity for the one‐step synthesis of azobenzenes from nitrobenzenes at 25 °C with a yield greater than 95 % and a selectivity greater than 99 %, whereas unimodal Au/TiO₂ (UM‐Au/TiO₂) is photocatalytically inactive.     

Crystallographic interface control of the plasmonic photocatalyst consisting of gold nanoparticles and titanium(iv) oxide

A big question in the field of plasmonic photocatalysis is why a typical photocatalyst consisting of gold nanoparticles and rutile titanium(iv) oxide (Au/R-TiO₂) usually exhibits activity much higher than that of Au/anatase TiO₂ (Au/A-TiO₂) under visible-light irradiation. Shedding light on the origin should present important guidelines for the material design of plasmonic photocatalysts. Au nanoparticles (NPs) were loaded on ordinary irregular-shaped TiO₂ particles by the conventional deposition precipitation method. Transmission electron microscopy analyses for the Au/TiO₂ particles ascertain that faceting of Au NPs is induced on R-TiO₂ by using a domain-matching epitaxial junction with the orientation of (111)_Au//(110)_R-TiO2, whereas non-faceted hemispherical Au NPs are exclusively formed on A-TiO₂. The faceting probability of Au NPs (P_f) on R-TiO₂ increases with decreasing Au particle size (d_Au) to reach 14% at d_Au = 3.6 nm. A clear positive correlation between the photocatalytic activity and P_f in several test reactions indicates that the heteroepitaxial junction-induced faceting of Au NPs is the principal factor for governing the plasmonic photocatalytic activity of Au/TiO₂. In light of this finding, R-TiO₂ nanorods with a high percentage (95%) of {110} facets were hydrothermally synthesized and used for the support of Au NPs. Consequently, the P_f value increases to as much as 94% to enhance the photocatalytic activity with respect to that of Au/R-TiO₂ with P_f = 14% by factors of 2.2–4.4 depending on the type of reaction.

In the represented plasmonic photocatalyst consisting of Au nanoparticles (NPs) and TiO₂, the combination of crystal facet engineering of TiO₂ and atom-level-interface control between Au NP and TiO₂ gives rise to a drastic activity enhancement.     

Formation of gold nanoparticles in diblock copolymer micelles with various reducing agents

Gold nanoparticles (Au NPs) were prepared by the reduction of HAuCl₄ acid incorporated into the polar core of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) copolymer micelles dissolved in toluene. The formation of Au NPs was controlled using three reducing agents with different strengths: hydrazine (HA), triethylsilane (TES), and potassium triethylborohydride (PTB). The formation of Au NPs was followed by transmission electron microscopy, UV–Vis spectroscopy, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS). It was found that the strength of the reducing agent determined both the size and the rate of formation of the Au NPs. The average diameters of the Au NPs prepared by reduction with HA, TES, and PTB were 1.7, 2.6, and 8 nm, respectively. The reduction of Au(III) was rapid with HA and PTB. TES proved to be a mild reducing agent for the synthesis of Au NPs. DLS measurements demonstrated swelling of the PS-b-P2VP micelles due to the incorporation of HAuCl₄ and the reducing agents. The original micellar structure rearranged during the reduction with PTB. ITC measurements revealed that some chemical reactions besides Au NPs formation also occurred in the course of the reduction process. The enthalpy of formation of Au NPs in PS-b-P2VP micelles reduced by HA was determined.