Negatively charged gold nanoparticles as an intrinsic peroxidase mimic and their applications in the oxidation of dopamine

Artificial inorganic peroxidase is of great interest due to its intrinsic advantages over natural counterpart. Negatively charged gold nanoparticles (AuNPs) were discovered to function like a peroxidase in the present study. Two AuNPs in different size were prepared and characterized by TEM, and assayed for peroxidase activity. Its catalytic activity was found to follow Michaelis–Menten kinetics. The negative surface charge notably improves the affinity toward a substrate TMB, proved by the determined kinetic parameters. The particles expressed optimal catalytic activity under mildly acidic environment and resistance to elevated temperature and increased concentration of sodium azide. The origin of the activity was investigated tentatively. Hydrogen peroxide-treated AuNPs exhibited an enhanced activity. EDTA temporarily blocked the activity partially, while thiol groups permanently blocked the activity completely. Tests imply that it is the surface Au⁺ that provides the activity. The successful oxidation of dopamine, as an instance, under the action of AuNPs as a peroxidase was conducted. These studies would lead to a wide range of potential applications.     

Silver‐Assisted Synthesis of Gold Nanorods: the Relation between Silver Additive and Iodide Impurities

Seed‐mediated methods employing cetyltrimethylammonium bromide (CTAB) as a surfactant, and silver salts as additives, are the most common synthetic strategies for high‐yield productions of quality Au nanorods. However, the mechanism of these reactions is not yet fully understood and, importantly, significant lab‐to‐lab reproducibility issues still affect these protocols. In this study, the direct correlation between the hidden content of iodide impurities in CTAB reagents, which can drastically differ from different suppliers or batches, and the optimal concentration of silver required to maximize the nanorods yield is demonstrated. As a result, high‐quality nanorods are obtained at different iodide contents. These results are interpreted based on the different concentrations of CTAB and cetyltrimethylammonium iodide (CTAI) complexes with Ag⁺ and Au⁺ metal ions in the growth solution, and their different binding affinity and reduction potential on distinct crystallographic planes. Notably, the exhaustive conversion of CTAI–Au⁺ to CTAI–Ag⁺ appears to be the key condition for maximizing the nanorod yield.     

A Fast and Efficient Replacement of CTAB with MUA on the Surface of Gold Nanorods Assisted by a Water‐Immiscible Ionic Liquid

The synthesis and surface modification of gold nanorods (GNRs) is one of the most important and basic issues in nanoscience. Most of the widely investigated GNRs are coated with a cetyltrimethylammonium bromide(CTAB) bilayer. Here, a highly efficient method is proposed to replace CTAB from the surface of GNRs with a bifunctional 11‐mercaptoundecanoic acid in order to decrease the possible toxicity caused by CTAB. This ligand exchange is achieved in a biphasic mixture of an aqueous solution and a water‐immiscible ionic liquid (IL), [BMIM][Tf₂N]. That is, by mixing IL, mercaptoundecanoic acid (MUA)/IL (200 × 10^?3 m ) and a concentrated aqueous solution of GNRs together, followed by vortex stirring for 90 s, CTAB‐capped GNRs with varying aspect ratios can be turned into corresponding MUA‐capped GNRs with the same aspect ratio. Furthermore, the formed MUA‐capped GNRs can be obtained in a large quantity and stored as powders for easy use. The MUA‐capped GNRs with improved biocompatibility and colloidal stability are well suited for further biological functionalization and potential applications. This IL‐assisted ligand exchange can reverse the surface charge, enhance the stability of GNRs, and suppress its cytotoxicity.     

Synthesis and characterization of water-soluble <Emphasis Type="SmallCaps">l</Emphasis>-cysteine-modified ZnS nanocrystals doped with silver

The water-soluble Ag⁺-doped ZnS nanocrystals surface capped with cysteine (expressed as ZnS:Ag/Cys) were synthesized in aqueous solution by using l-cysteine as surface modifier. The crystal structure, size, shape, component, and spectral properties of ZnS:Ag/Cys nanocrystals were characterized by X-ray power diffraction, transmission electron microscope, energy dispersive X-ray analysis, inductively coupled plasma atomic emission spectrometry, infrared spectrum, UV–Vis absorption spectrum, and photoluminescence spectrum. The results show that the spherical ZnS:Ag/Cys nanocrystals with an average diameter of 2.6 nm have good fluorescent characteristics, their fluorescence intensity is enhanced greatly after doped with Ag⁺. And the sulfur atoms in cysteine molecules are coordinated with metal ions on the surface of the nanocrystals, the cysteine modified on the surface of ZnS:Ag/Cys nanocrystals renders the nanocrystals water soluble and biocompatible. The ZnS:Ag/Cys nanocrystals have potential applications in molecular assembly and biological fluorescence analysis.     

Metal‐Ion‐Modified Black Phosphorus with Enhanced Stability and Transistor Performance

Black phosphorus (BP), a burgeoning elemental 2D semiconductor, has aroused increasing scientific and technological interest, especially as a channel material in field‐effect transistors (FETs). However, the intrinsic instability of BP causes practical concern and the transistor performance must also be improved. Here, the use of metal‐ion modification to enhance both the stability and transistor performance of BP sheets is described. Ag⁺ spontaneously adsorbed on the BP surface via cation–π interactions passivates the lone‐pair electrons of P thereby rendering BP more stable in air. Consequently, the Ag⁺‐modified BP FET shows greatly enhanced hole mobility from 796 to 1666 cm² V^?1 s^?1 and ON/OFF ratio from 5.9 × 10⁴ to 2.6 × 10⁶. The mechanisms pertaining to the enhanced stability and transistor performance are discussed and the strategy can be extended to other metal ions such as Fe³⁺, Mg²⁺, and Hg²⁺. Such stable and high‐performance BP transistors are crucial to electronic and optoelectronic devices. The stability and semiconducting properties of BP sheets can be enhanced tremendously by this novel strategy.     

Gold functionalised attapulgite for discrimination of hydrogen peroxide and oxidising ions

Aiming to monitor hydrogen peroxide and oxidizing ions in aqueous circumstance, functionalized attapulgite [i.e. gold‐modified attapulgite nanocomposites (Au/ATP NCs)] as peroxidase mimics were prepared by loading β‐cysteamine‐capped gold nanoparticles onto attapulgite with the use of electrostatic interactions. As‐prepared Au/ATP NCs were used for the detection of H₂ O₂. The linear range and detection limit for H₂ O₂ were determined by quantitative experiments emerging excellent stability and recyclability. The peroxidase‐like activity of Au/ATP NCs could be expanded for the detection of some oxidative ions (Fe³⁺ and Ag⁺) was also been discovered. Based on the absorption spectrum and steady‐state kinetics, the mechanism for peroxidase mimic reaction is investigated. This work represents the first example of multitarget detection for molecule and cations (H₂ O₂, Fe³⁺ and Ag⁺) using Au/ATP NCs as peroxidase enzyme mimics and holds a promise for future biomedical and analytical applications.Inspec keywords: hydrogen compounds, chemical sensors, nanocomposites, nanosensors, electrostatics, goldOther keywords: Au, H₂ O₂ , biomedical application, enzyme, cation detection, molecule detection, steady‐state kinetics, absorption spectrum, recyclability, stability, electrostatic interaction, β‐cysteamine‐capped gold nanoparticle, peroxidase, Au‐ATP NC, goldmodified attapulgite nanocomposite, oxidising ion, hydrogen peroxide, gold functionalised attapulgite     

Tuning photoluminescence of ZnS nanoparticles by silver

We report the results of investigation of the interaction of silver with presynthesized ZnS nanoparticles (NPs) that was stabilized by cetyl trimethyl ammonium bromide (CTAB). The photoluminescence properties of ZnS NPs were followed in the presence of Ag⁺ ions, Ag NPs and by the synthesis of Ag@ZnS core-shell nanoparticles. We observed that CTAB stabilized ZnS NPs emitted broadly in the region from 350–450 nm, when excited by 309 nm light. In the presence of Ag⁺ ions the emission peak intensity up to 400 nm was reduced, while two new and stronger peaks at 430 nm and 550 nm appeared. Similar results were obtained when Ag NPs solution was added to ZnS solution. However, when Ag@ZnS NPs were synthesized, the emission in the 350–450 nm region was much weaker in comparison to that at 540 nm, which itself appeared at a wavelength shorter than that of Ag⁺ ion added ZnS NPs. The observations have been explained by the presence of interstitial sulfur and Zn²⁺, especially near the surface of the nanocrystals and their interaction with various forms of silver. In addition, our observations suggest that Ag⁺ ions diffuse into the lattice of the preformed ZnS NPs just like the formation of Ag⁺ doped ZnS NPs and thus changes the emission characteristics. We also have pursued similar experiments with addition of Mn²⁺ ions to ZnS and observed similar results of emission characteristics of Mn²⁺ doped ZnS NPs. We expect that results would stimulate further research interests in the development of fluoremetric metal ion sensors based on interaction with quantum dots.     

Construction of Cuprous Oxide Electrodes Composed of 2D Single‐Crystalline Dendritic Nanosheets

An unusual anisotropic growth of Cu₂O is stabilized via the electrochemical synthesis of Cu₂O in the presence of Ag⁺ ions, which results in the formation of Cu₂O electrodes composed of 2D sheetlike crystals containing complex dendritic patterns. It is quite unusual for Cu₂O to form a 2D morphology since it has a 3D isotropic cubic crystal structure where the a, b, and c axes are equivalent. Each Cu₂O sheet is single‐crystalline in nature and is grown parallel to the {110} plane, which is rarely observed in Cu₂O crystal shapes. A various set of experiments are performed to understand the role of Ag⁺ ions on the 2D growth of Cu₂O. The results show that Ag⁺ ions are deposited as silver islands on already growing Cu₂O crystals and serve as nucleation sites for the new growth of Cu₂O crystals. As a result, the growth direction of the newly forming Cu₂O crystals is governed by the diffusion layer structure created by the pre‐existing Cu₂O crystals, which results in the formation of 2D dendritic patterns. The thin 2D crystal morphology can significantly increase the surface‐to‐volume ratio of Cu₂O crystals, which is beneficial for enhancing various electrochemical and photoelectrochemical properties of the electrodes. The photoelectrochemical properties of the Cu₂O electrodes composed of 2D dendritic crystals are investigated and compared to those of 3D dendritic crystals. This study provides a unique and effective route to maximize the {110} area per unit volume of Cu₂O, which will be beneficial for any catalytic/sensing abilities that can be anisotropically enhanced by the {110} planes of Cu₂O.     

Palm‐Sized Ag+ Ion Emission Gun Operated at Room Temperature in Non‐Vacuum Atmosphere

Ion implantation is an effective method for changing surface properties and inducing various functionalities. However, a high vacuum is generally necessary for ion implantation, which limits the range of applications. Here, we describe a palm‐sized Ag⁺ ion emission gun produced using a solid electrolyte. AgI–Ag₂O–B₂O₃ glass, known as a super‐ion‐conducting glass, has a Ag⁺ ion conductivity higher than 5 × 10^?3 S cm^?1 at room temperature. In addition, the melted glass has suitable viscous flow, and a sharp glass‐fiber emitter with a pyramid‐like apex can be obtained. Ag⁺ ion emission is observed from the tip of the glass fiber at accelerating voltages corresponding to electric fields above 20 kV cm^?1, even at room temperature in a non‐vacuum atmosphere. Ag nanoparticles of size 50–350 nm are precipitated on a Si target substrate. Other glass components such as boron and iodine are not detected. Electrochemical quartz crystal microbalance (EQCM) measurements show that the mass of Ag nanoparticles estimated from the emission current using Faraday's law of electrolysis is in good agreement with that estimated from the QCM frequency shift.

     

Size‐Dependent Toxicity of Gold Nanoparticles on Human Embryonic Stem Cells and Their Neural Derivatives

This study explores the use of human embryonic stem cells (hESCs) for assessing nanotoxicology, specifically, the effect of gold nanoparticles (AuNPs) of different core sizes (1.5, 4, and 14 nm) on the viability, pluripotency, neuronal differentiation, and DNA methylation of hESCs. The hESCs exposed to 1.5 nm thiolate‐capped AuNPs exhibit loss of cohesiveness and detachment suggesting ongoing cell death at concentrations as low as 0.1 μg mL^?1. The cells exposed to 1.5 nm AuNPs at this concentration do not form embryoid bodies but rather disintegrate into single cells within 48 h. Cell death caused by 1.5 nm AuNPs also occur in hESC‐derived neural progenitor cells. None of the other nanoparticles exhibit toxic effects on the hESCs at concentrations as high as 10 μg mL^?1 during a 19 d neural differentiation period. Thiolate‐capped 4 nm AuNPs at 10 μg mL^?1 cause a dramatic decrease in global DNA methylation (5 mC) and a corresponding increase in global DNA hydroxymethylation (5 hmC) of the hESC's DNA in only 24 h. This work identifies a type of AuNPs highly toxic to hESCs and demonstrates the potential of hESCs in predicting nanotoxicity and characterizing their ability to alter the DNA methylation and hydroxymethylation patterns in the cells.     

Facile fabrication of hierarchically flowerlike Ag microstructure for SERS application

Hierarchically flowerlike Ag microstructure with uniform silver nanosheets as building blocks has been facilely prepared on a composite film surface via in situ reduction of Ag⁺ by a polyaniline component. The morphology of the as-prepared Ag microstructure is determined by the reaction duration, not the concentration of Ag⁺ in the reaction process. The complex geometry, rough surface, and interlaced nanosheets of the hierarchical Ag microstructure create interstitial sites and thus result in enhanced Raman signals.     

TGF‐β1 Conjugated to Gold Nanoparticles Results in Protein Conformational Changes and Attenuates the Biological Function

Gold nanoparticles (AuNPs) are widely used as carriers or therapeutic agents due to their great biocompatibility and unique physical properties. Transforming growth factor‐beta 1 (TGF‐β1), a member of the cysteine‐knot structural superfamily, plays a pivotal role in many diseases and is known as an immunosuppressive agent that attenuates immune response resulting in tumor growth. The results reported herein reflect strong interactions between TGF‐β1 and the surface of AuNPs when incubated with serum‐containing medium, and demonstrate a time‐ and dose‐dependent pattern. Compared with other serum proteins that can also bind to the AuNP surface, AuNP–TGFβ1 conjugate is a thermodynamically favored compound. Epithelial cells undergo epithelial–mesenchymal transition (EMT) upon treatment with TGF‐β1; however, treatment with AuNPs reverses this effect, as detected by cell morphology and expression levels of EMT markers. TGF‐β1 is found to bind to AuNPs through S–Au bonds by X‐ray photoelectron spectroscopy. Fourier transform infrared spectroscopy is employed to analyze the conformational changes of TGF‐β1 on the surface of AuNPs. The results indicate that TGF‐β1 undergoes significant conformational changes at both secondary and tertiary structural levels after conjugation to the AuNP surface, which results in the deactivation of TGF‐β1 protein. An in vivo experiment also shows that addition of AuNPs attenuates the growth of TGF‐β1‐secreting murine bladder tumor 2 cells in syngeneic C3H/HeN mice, but not in immunocompromised NOD‐SCID mice, and this is associated with an increase in the number of tumor‐infiltrating CD4⁺ and CD8⁺ T lymphocytes and a decrease in the number of intrasplenic Foxp3(+) lymphocytes. The findings demonstrate that AuNPs may be a promising agent for modulating tumor immunity through inhibiting immunosuppressive TGF‐β1 signaling.     

High‐Yield Synthesis of Hollow Octahedral Silver Nanocages with Controllable Pack Density and Their High‐Performance Sers Application

Nanoparticle‐assembled octahedral Ag nanocages with sharp edges have been successfully synthesized through a Cu₂O‐based template‐assisted strategy. In the reaction system, Ag nanoparticles can be self‐assembled on the surface of Cu₂O octahedrons, which is accomplished by the reduction of Ag⁺ by NaBH₄ in the presence of sodium citrate as a capping agent. The hollow octahedral Ag nanocages are obtained after removing the inner Cu₂O cores with acetic acid. According to the scanning electron microscopy (SEM) and transmission electron microscopy characterization, the Ag nanocages are weaved by small nanoparticles, the rough surfaces are bestrewed with pores and sharp edges. It is found that the pack density of Ag nanoparticles strongly affects the surface enhanced Raman scattering (SERS) activities. The as‐prepared 1.05‐Ag cages with optimal pack density have suitable interparticle distance and suitable size of pores, which significantly enhance SERS signals. The SERS signals of rhodamine 6G (R6G) molecules can be detected at an ultralow concentration of 10^?14 m when 1.05‐Ag cages are used as substrates. In addition to sensitivity, 1.05‐Ag cages also exhibit good reproducibility. It is expected that the ultrahigh sensitivity will endow the Ag nanocages to become a promising candidate as high‐performance SERS‐based chemical sensor.     

Ultrasmall Pb:Ag2S Quantum Dots with Uniform Particle Size and Bright Tunable Fluorescence in the NIR‐II Window

Ag₂S quantum dots (QDs) are well‐known near‐infrared fluorophores and have attracted great interest in biomedical labeling and imaging in the past years. However, their photoluminescence efficiency is hard to compete with Cd‐, Pb‐based QDs. The high Ag⁺ mobility in Ag₂S crystal, which causes plenty of cation deficiency and crystal defects, may be responsible mainly for the low photoluminescence quantum yield (PLQY) of Ag₂S QDs. Herein, a cation‐doping strategy is presented via introducing a certain dosage of transition metal Pb²⁺ ions into Ag₂S nanocrystals to mitigate this intrinsic shortcoming. The Pb‐doped Ag₂S QDs (designated as Pb:Ag₂S QDs) present a renovated crystal structure and significantly enhanced optical performance. Moreover, by simply adjusting the levels of Pb doping in the doped nanocrystals, Pb:Ag₂S QDs with bright emission (PLQY up to 30.2%) from 975 to 1242 nm can be prepared without altering the ultrasmall particle size (≈2.7–2.8 nm). Evidently, this cation‐doping strategy facilitates both the renovation of crystal structure of Ag₂S QDs and modulation of their optical properties.     

Sensitive,Quantitative Naked‐Eye Biodetection with Polyhedral Cu Nanoshells

One of the most heavily used methods in chemical and biological labeling, detection, and imaging is based on silver shell‐based enhancement on Au nanoparticles (AuNPs) that is useful for amplifying Rayleigh scattering, colorimetric signal, surface‐enhanced Raman scattering, and electrical signal, but poor structural controllability and nonspecific growth of silver shells have limited its applications, especially with respect to signal reproducibility and quantification. Here, a highly specific, well‐defined Cu nanopolyhedral shell overgrowth chemistry is developed with the aid of polyethyleneimine (PEI) on AuNPs, and the use of this PEI‐mediated Cu polyhedral nanoshell (CuP) chemistry is shown as a means of light‐scattering signal enhancement for the development of naked‐eye‐based highly sensitive and quantitative detections of DNA and viruses. Remarkably, these CuPs are exclusively formed on AuNPs in a controllable manner, with no noticeable nonspecific CuP growth. The findings enable to acquire clearly visible signals without analytic instrumentation, detectable down to 8 × 10^?15m of DNA (anthrax sequence) and 2700 copies of viruses (noroviruses in clinical stool samples) with broad dynamic ranges on archetypal assay platforms. This new method provides a general platform in controlling Cu shell nanostructures and their optical signals, and opens up revenues for highly reliable, quantitative onsite naked‐eye biodetection.     

Probing Adsorption Behaviors of BSA onto Chiral Surfaces of Nanoparticles

Chiral properties of nanoscale materials are of importance as they dominate interactions with proteins in physiological environments; however, they have rarely been investigated. In this study, a systematic investigation is conducted for the adsorption behaviors of bovine serum albumin (BSA) onto the chiral surfaces of gold nanoparticles (AuNPs), involving multiple techniques and molecular dynamic (MD) simulation. The adsorption of BSA onto both L‐ and D‐chiral surfaces of AuNPs shows discernible differences involving thermodynamics, adsorption orientation, exposed charges, and affinity. As a powerful supplement, MD simulation provides a molecular‐level understanding of protein adsorption onto nanochiral surfaces. Salt bridge interaction is proposed as a major driving force at protein–nanochiral interface interaction. The spatial distribution features of functional groups (? COO^?, ? NH₃⁺, and ? CH₃) of chiral molecules on the nanosurface play a key role in the formation and location of salt bridges, which determine the BSA adsorption orientation and binding strength to chiral surfaces. Sequentially, BSA corona coated on nanochiral surfaces affects their uptake by cells. The results enhance the understanding of protein corona, which are important for biological effects of nanochirality in living organisms.     

Tailoring Enzyme‐Like Activities of Gold Nanoclusters by Polymeric Tertiary Amines for Protecting Neurons Against Oxidative Stress

The cytotoxicity of nanozymes has drawn much attention recently because their peroxidase‐like activity can decompose hydrogen peroxide (H₂O₂) to produce highly toxic hydroxyl radicals (?OH) under acidic conditions. Although catalytic activities of nanozymes are highly associated with their surface properties, little is known about the mechanism underlying the surface coating‐mediated enzyme‐like activities. Herein, it is reported for the first time that amine‐terminated PAMAM dendrimer‐entrapped gold nanoclusters (AuNCs‐NH₂) unexpectedly lose their peroxidase‐like activity while still retaining their catalase‐like activity in physiological conditions. Surprisingly, the methylated form of AuNCs‐NH₂ (i.e., MAuNCs‐N⁺R₃, where R = H or CH₃) results in a dramatic recovery of the intrinsic peroxidase‐like activity while blocking most primary and tertiary amines (1°‐ and 3°‐amines) of dendrimers to form quaternary ammonium ions (4°‐amines). However, the hidden peroxidase‐like activity is also found in hydroxyl‐terminated dendrimer‐encapsulated AuNCs (AuNCs‐OH, inside backbone with 3°‐amines), indicating that 3°‐amines are dominant in mediating the peroxidase‐like activity. The possible mechanism is further confirmed that the enrichment of polymeric 3°‐amines on the surface of dendrimer‐encapsulated AuNCs provides sufficient suppression of the critical mediator ?OH for the peroxidase‐like activity. Finally, it is demonstrated that AuNCs‐NH₂ with diminished cytotoxicity have great potential for use in primary neuronal protection against oxidative damage.     

Silver-embedded zeolite crystals as substrates for surface-enhanced Raman scattering

This paper reports the preparation of a type of Ag-embedded zeolite crystals as surface-enhanced Raman spectroscopy (SERS) substrates by chemical reduction of Ag⁺-exchanged ZSM-5. Ag⁺ ions were loaded into the zeolite framework by ion exchange. Then the exchanged-Ag⁺ ions were reduced and metallic silver clusters formed inside the zeolite channel. The resulting Ag-embedded zeolite crystals are characterized by using a number of techniques including X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy to confirm silver formed inside the crystal channel. The fabricated Ag-embedded ZSM-5 zeolite substrates displayed strong and reproducible SERS activity for different Raman probe molecules such as Tris(2,2′-bipyridyl) ruthenium(II) chloride (RuBpy) and rhodamine 6G (R6G). Since silver embedded into the zeolite channel without changing the crystal surface property, the Ag–ZSM-5 zeolite crystal can be used to prepare different SERS-active substrate (SERS-tags), in which different probe molecules may be detected. Such Ag-embedded zeolite substrate would be useful in chemical and biological sensing and in the development of SERS-based analytical devices.     

Simultaneous Adjustment of Size and Helical Sense of Chiral Nanospheres and Nanotubes Derived from an Axially Racemic Poly(phenylacetylene)

Nanospheres and nanotubes with full control of their size and helical sense are obtained in chloroform from the axially racemic chiral poly(phenylacetylene) poly‐(R)‐ 1 using either Ag⁺ as both chiral inducer and cross‐linking agent or Na⁺ as chiral inducer and Ag⁺ as cross‐linking agent. The size is tuned by the polymer/ion ratio while the helical sense is modulated by the polymer/cosolvent (i.e., MeCN) ratio. In this way, the helicity and the size of the nanoparticles can be easily interconverted by very simple experimental changes.     

An analysis of the electrical conductivity in BaSO4-added Ag2SO4 solid electrolyte system

The compositions (1 −x)Ag₂SO₄−(x)BaSO₄, wherex=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba²⁺ in Ag₂SO₄ was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained using a detailed impedance analysis. The partial substitution of Ba²⁺ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model based on lattice distortion (expansion) due to partial substitution of Ag⁺ by the bigger Ba²⁺ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO₄-dispersed Ag₂SO₄ conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO₄ dispersed Ag₂SO₄ is due to percolation threshold.