AgI Colloids Research Articles

Enzyme-free and label-free detection of HER2 in human serum based on Ag+-released hybridization chain reaction signal amplification

The overexpression of human epidermal growth factor receptor 2 (HER2) has been linked to aggressive breast cancer and worse clinical outcomes. However, accurately measuring HER2 remains challenging, due to its low serum content. Herein, we developed a novel method for HER2 detection in serum by the combination of aptamer with C-Ag+-C structure, Ag+-released hybridization chain reaction (Ag+-HCR) and coprecipitation of Ag+ and gold nanoparticles (AuNPs) in the solution including Eosin Y (EY) and AgI colloids. Following the aptamer bound to HER2, signal amplification occurred through the release of numerous Ag+ by Ag+-HCR. This process subsequently induced AuNPs aggregation on the surface of AgI colloids, resulting in reduced fluorescence intensity of EY in the supernatant. The reduced value of EY fluorescence intensity in the supernatant was proportional to the level of HER2. Under optimized reaction conditions, a wide detection range was obtained between 0.09 and 9000 pg/mL with a limit of detection of 11.7 fg/mL in diluted human serum, and 96 serum samples in a 96-well plate could be measured simultaneously by a microtiter plate reader within 2 h. Moreover, the quantitative results of HER2 were consistent with those obtained using the enzyme-linked immunosorbent assay kit (r = 0.9995). Therefore, leveraging the delicate design of Ag+-HCR signal amplification, this enzyme-free, label-free, and effective method has demonstrated to be capable of detecting HER2 in serum due to its high sensitivity. Remarkably, this method may be extended to detect other cancer-related proteins and genes by replacing the corresponding target sequences.

Combined settlement and clogging in drainage sand layer for suspended solids, colloids and inorganic salts

Blockage of leachate drainage facilities is a common engineering problem in landfill operation. The key factors that cause blockage of drainage facilities in landfill leachate are the deposition of suspended solids (SS) with colloids and the precipitation of inorganic salts. To determine the combined sedimentation law of SS, colloids and inorganic salts, a combined sedimentation test of suspended solids, colloids and inorganic salts was conducted. To further clarify the resulting clogging characteristics of the water-conducting sand layers, a sand column blocking test were conducted, and mineral composition and grain characteristics of sediments were determined. The experimental results shown that the colloids (silver iodide) and inorganic salts (calcium chloride or aluminum sulfate) increased the sedimentation rate of SS by 8 to18 times. Among them, the effect of AgI colloid was the most significant, followed by effect of calcium chloride, while effect of aluminum sulfate was the weakest. Compared with sand column clogging caused by SS, this combined migration shortened the sand column clogging time by more than half and reduced hydraulic conductivity by nearly two to three orders of magnitude. This study contributes to the accurate assessment of the service performance of landfill leachate drainage systems.

Low-Cost Full-Range Detection of C-Reactive Protein in Clinical Samples by Aptamer Hairpin Probes and Coprecipitation of Silver Ions and Gold Nanoparticles.

C-reactive protein (CRP) levels can vary widely related to diverse disease contexts. However, expensive antibodies have impeded the clinical utility of antibody-based full-range CRP assays, especially in developing countries. Herein, we established a low-cost, antibody-free, 96-well plate-based full-range CRP detection method by combining gold nanoparticles (AuNPs), silver iodide (AgI), Eosin Y, and the aptamer hairpin probe (AHP) with Ag+-mediated cytosine-cytosine mismatches, that is, the Au@AgI/Eosin Y-AHP method. After binding the target CRP, the AHP released Ag+, which subsequently induced the aggregation of AuNPs on the surface of AgI colloids, resulting in a significant increase in the adsorption of Eosin Y on the surface of AuNPs. The changes in fluorescence intensity (FI) of Eosin Y in the supernate without and with CRP were proportional to the concentration of the CRP in the wide range of 0.01-40 ng/mL (r = 0.9969), and 96 samples can be detected in 96-well plates simultaneously by a microplate reader within 45 min. Remarkably, the CRP levels of 100 clinical samples achieved with the Au@AgI/Eosin Y-AHP had a good correlation with those obtained with the latex-enhanced immune turbidimetry assay (r = 0.986). Furthermore, the kit based on the Au@AgI/Eosin Y-AHP method costs only $8.1 for 100 tests. Therefore, the new method is beneficial for less developed areas where expensive assays are not affordable.

Surface Interactions and Mechanisms Study on the Removal of Iodide from Water by Use of Natural Zeolite-Based Silver Nanocomposites.

In this work a natural zeolite was modified with silver following two different methods to derive Ag2O and Ag0 nanocomposites. The materials were fully characterized and the results showed that both materials were decorated with nanoparticles of size of 5–25 nm. The natural and modified zeolites were used for the removal of iodide from aqueous solutions of initial concentration of 30–1400 ppm. Natural zeolite showed no affinity for iodide while silver forms were very efficient reaching a capacity of up to 132 mg/g. Post-adsorption characterizations showed that AgI was formed on the surface of the modified zeolites and the amount of iodide removed was higher than expected based on the silver content. A combination of experimental data and characterizations indicate that the excess iodide is most probably related to negatively charged AgI colloids and Ag-I complexes forming in the solution as well as on the surface of the modified zeolites.

Cryogel-based Ag°/Ag2O nanocomposites for iodide removal from water

In this study novel silver-modified cryogels were synthesized and applied for the removal of iodide from aqueous solutions. The co-allylamine-methacrylic acid-DMAAm-BisAAm (AAC) and co-allylamine-2-acrylamido-2-methyl-1-propansulfonic acid-DMAAm-BisAAm (SAC) cryogels were decorated with silver by one-step ion-exchange technique and characterized by TEM/EDS, SEM/EDS, FT-IR, XRD and zeta potential measurements. The silver loading was up to 159 and 98 mg/g for AAC and SAC cryogel nanocomposites, respectively. The silver is found in the structure of cryogels in the form of Ag2O and Ag° nanoparticles and the formation of metallic silver is attributed to in situ reduction of silver by the functional groups of the cryogels. The nanocomposites showed rapid kinetics and high adsorption capacity towards iodide. The equilibrium studies showed that in some samples the removal of iodide is higher than the theoretically expected based on the Ag:I molar ratio of 1:1. The analysis of the surface of the cryogels confirmed the theoretical Ag:I molar ratio and a study of the solution phase revealed that small amounts of leached Ag+ from the cryogels resulted in the formation of AgI colloids which, under the conditions of the experiments, exhibit Ag:I molar ratios lower than the theoretical value explaining the discrepancies between the theoretical and actual iodide removal rates.

Formation of Negatively Charged AgI Colloid Nanoparticles by Condensation

The stability of silver halide colloids is reported to be important for the toxicological outcome. This study shows a well-suited and cheap condensation reaction to obtain negatively charged silver iodide (AgI) nanoparticles without additional stabilization agents. Charged AgI colloids were synthesized from silver nitrate and potassium iodide solutions. An excess of potassium iodide not only imparted a negative charge, but provided a narrow particle size distribution (50 ± 10 nm). The change of optical properties in the colloid was investigated by UV-VIS spectroscopy. A silver iodide exciton absorption band at peak ~421nm (2.93eV), red-shifted over time. The peak at half maximum intensity increased from 13.3nm to 14.8 nm, characterizing the dispersity of AgI colloidal particles. Colloidal particles stabilized after 33 hours. In-situ real-time UV-VIS measurements provide a tool to adjust the particle characteristics and may serve to further optimize the performance in biological applications.

Synthesis of Silica-Coated AgI Nanoparticles and Immobilization of Proteins on Them

This paper describes a method for preparing silica-coated silver iodide (AgI/SiO2) particles and immobilizing proteins on the AgI/SiO2 particles. Colloid solution of AgI particles was prepared by mixing AgClO4 aqueous solution and KI aqueous solution. Silica-coating of the AgI particles was performed by adding 3-mercaptopropyltrimethoxysilane, tetraethylorthosilicate/ethanol solution and NaOH aqueous solution successively to the AgI colloid solution. TEM observation revealed that the AgI nanoparticles were coated with uniform silica shell. The AgI/SiO2 particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by XPS measurement that amino group or carboxyl group was introduced onto the AgI/SiO2 particles. Protein-immobilization was performed in aqueous solution with bovine serum albumin (BSA) in the presence of the surface-modified AgI/SiO2 particles. UV-VIS absorption spectroscopy revealed that the BSA was adsorbed on the surface-modified particles.

An in situ reduction method for preparing novel surface‐enhanced Raman scattering substrates

AbstractSurface‐enhanced Raman scattering (SERS)‐active substrates with high enhancement were prepared by an in situ reduction method. First, NH2OH·HCl was added as complexing agent to AgNO3 solution, then NaI was dropped in to produce an AgI colloid. Second, the self‐assembly technique was used to transfer the AgI nanoparticles on to the solid substrate and then they were reduced in situ. The UV–visible spectra show that the absorption band is asymmetric, indicating that the Ag nanoparticle size distribution on the substrate is wide, which was further confirmed by atomic force microscopy (AFM) measurements. The SERS‐active substrates with different coverages can be formed in a layer‐by‐layer electrostatic assembly by exposing positively charged surfaces to colloid solutions containing oppositely charged AgI nanoparticles. The results of AFM and UV–visible spectroscopy show that the Ag nanoparticles grow with increase in the degree of coverage and that most of them remain isolated even at high coverage. Consequently, the surface optical properties are dominated by the absorption due to the isolated Ag nanoparticles. The new substrate presents high SERS enhancement and the SERS enhancement factor was estimated to be 109. By comparison with our previous work, the important effects of stabilizers on the formation and transfer of nanoparticles are confirmed. Copyright © 2005 John Wiley & Sons, Ltd.

Self-Assembled Metal Colloid Films: Two Approaches for Preparing New SERS Active Substrates

In this paper, we propose two new approaches for preparing active substrates for surface-enhanced Raman scattering (SERS). In the first approach (method 1), one transfers AgI nanoparticles capped by negatively charged mercaptoacetic acid from a AgI colloid solution onto a quartz slide and then deoxidizes AgI to Ag nanoparticles on the substrate. The second approach (method 2) deoxidizes AgI to Ag nanoparticles in a colloid solution and then transfers the Ag nanoparticles capped by negatively charged mercaptoacetic acid onto a quartz slide. By transfer of the AgI/Ag nanoparticles from the colloid solutions to the solid substrates, the problem of instability of the colloid solutions can largely be overcome. The films thus prepared by both approaches retain the merits of metal colloid solutions while they discharge their shortcomings. Accordingly, the obtained Ag particle films are very suitable as SERS active substrates. SERS active substrates with different coverages can be formed in a layer-by-layer electrostatic assembly by exposing positively charged surfaces to the colloid solutions containing oppositely charged AgI/Ag nanoparticles. The SERS active substrates fabricated by the two novel methods have been characterized by means of atomic force microscopy (AFM) and ultraviolet-visible (UV-vis) spectroscopy. The results of AFM and UV-vis spectroscopy show that the Ag nanoparticles grow with the increase in the number of coverage and that most of them remain isolated even at high coverages. Consequently, the surface optical properties are dominated by the absorption due to the isolated Ag nanoparticles. The relationship between SERS intensity and surface morphology of the new active substrates has been investigated for Rhodamine 6G (R6G) adsorbed on them. It has been found that the SERS enhancement depends on the size and aggregation of the Ag particles on the substrates. Especially, we can obtain a stronger SERS signal from the substrate prepared by method 1, implying that for the metal nanoparticles capped with stabilizer molecules such as mercaptoacetic acid, the in situ deoxidization in the film is of great use in preparing SERS active substrates. Furthermore, we have found that the addition of Cl- into the AgI colloid solution changes the surface morphology of the SERS active substrates and favors stronger SERS enhancement.

A New Hypothesis for the Mechanism of Ice Nucleation on Wetted AgI and AgI·AgCl Particulate Aerosols

A potential molecular mechanism of ice nucleation on AgI and AgI · AgCl particulates involves rearrangement of ordered water molecule clusters associated with hydrated Ag+ ion patches. This nucleation mechanism is thought to occur rapidly at −5° to −20°C on substrate particles wetted by water. This hypothesis is based on analysis of the rates of ice crystal formation and ice nucleus activities observed in experiments previously conducted in a 1-m3 isothermal cloud chamber using chemical kinetics. These experiments examined the chemistry of wetted AgI colloid particles involving electric charge separations between the particles and adjacent solution. The rate of nucleation is slowed by the presence of alkali and alkaline earth halides in concentrations greater than approximately 10−3 M in the water wetting the particles. Match of the crystal structure of the substrate with that of the ice may have no effect on this mechanism.

Rates and Mechanisms of Heterogeneous Ice Nucleation on Silver Iodide and Silver Chloroiodide Particulate Substrates

Information on two molecular mechanisms of ice nucleation on silver iodide and silver chloroiodide particulates has been gained by a chemical kinetics interpretation of the rates and mechanisms of ice crystal formation from experiments conducted in a 1 m3isothermal cloud chamber. The interpretation required the consideration of the Langmuir surface adsorption of water molecules by AgI from the vapor and the chemistry of AgI colloids and suspensions in water with and without the influences of supporting electrolytes. One mechanism is a slow rearrangement of three-dimensional water molecule clusters, adsorbed at water saturation and −20°C and lower on 500 Å and larger substrate particles, to ice embryos. The second occurs rapidly at −5 to −20°C on substrate particles wetted by liquid water. This mechanism is hypothesized to involve the rearrangement of ordered water molecule clusters associated with hydrated Ag+ion patches on the substrate surface. The rate of nucleation is slowed by the presence of alkali and alkaline earth halides. Crystal structure match of the substrate with that of ice may help the first mechanism but, perhaps, has no effect on the second.

Surface-enhanced Raman scattering of TSPP, Ag(II)TSPP, and Pb(II)TSPP adsorbed on AgI and AGCl colloids

Surface-enhanced Raman scattering (SERS) was measured for meso-tetrakis(4-sulfonatophenyl)porphine (TSPP) and its metal derivatives Ag(II)TSPP and Pb(II)TSPP adsorbed on AgI colloids, and for TSPP adsorbed on AgCl colloids. The experiments show that TSPP molecules adsorbed on AgI colloids undergo a silver incorporation, while TSPP adsorbed on AgCl colloids are converted into the porphyrin diacid H 4TSPP 2+ and the metalloporphyrin Ag(II)TSPP. The concentration dependences of SERS spectra for TSPP adsorbed on the two substrates are quite different.

Photochemistry of colloidal semiconductors 30. Reactions and fluorescence of AgI and AgI — Ag2S colloids

AbstractWhen Ag+ ions are precipitated with I− ions in the presence of poly (N‐vinyl pyrrolidone) or poly (vinyl alcohol) the AgI colloid forms slowly (during minutes or hours, depending on conditions), the changes in the absorption spectrum indicate the presence of unusual AgI structures during the first stages of particle growth. Size quantization effects are partly responsible for these changes. — AgI colloids with 10% excess of I− do not photolyse under continuous illumination. However, intermediates can be detected in flash photolysis experiments. In the presence of sulfite, silver is formed, the quantum yield lying in the 10−4 range. Greater yields of silver (10−3 to 10−2) are observed with solutions containing excess Ag+ ions. Less silver is produced in acidic solutions and the silver signal in the flash experiments decays more rapidly. These effects are attributed to the re‐oxidation of small silver clusters formed on the colloidal particles by H+ ions. — AgI colloids have a weak fluorescence close to the threshold of absorption. It is blue‐shifted with decreasing particle size (size quantization effect). The fluorescence is quenched by small amounts of silver deposited on the particles. It is also quenched by an Ag2S deposit. Under these circumstances a new fluorescence having three maxima in the red and infrared appears. This new fluorescence is red‐shifted with increasing size of the silver deposit (size quantization of Ag2S). The fluorescence is explained in terms of electron transfer from AgI (conduction band) to the hole captured at the AgI—Ag2S interface. Size quantization effects are also believed to play a role in the sulfursensitization of photographic plates.

Electron-transfer reactions of extremely small AgI colloids

Small colloidal AgI particles (particle diameter (20–50 Å) have been prepared in water and acetonitrile, and optical effects due to size quantization have been observed. Electron transfer reactions involving electron donors and electron acceptors with AgI have been studied by pulse radiolysis techniques. Both reduction and oxidation of the colloids led to transient bleaching of semiconductor absorption. The recovery of the bleaching has been attributed to corrosion processes. Electrons injected into AgI colloids produce metallic silver and hydrogen. Hydrogen evolution is catalyzed by metallic silver formation.

Regional intravascular chemotherapy for experimental liver metastasis.

To investigate the effectiveness of intravascular chemotherapy, the rats im· planted with two different sizes and ages of Yoshida sarcoma into the liver were treated with Mitomycin·C through either the hepatic artery or the portal vein. The administration of Mitomycin-C was effective by both arterial and portal routes on the rats bearing small young tumor, whereas it was effective only by arterial route on the rats bearing large developed tumor. Tumor regression was also observed on the rats bearing the tumor after ligation of the hepatic artery. Further, to observe the relationship between tumor growth and its blood supply, microangiography was performed by injection of AgI colloid through the hepatic artery and the portal vein. The branches of the hepatic artery flourished around the tumor at the 4th day after implantation and gradually entered into the tumor area at the 6th day. Thereafter, tumor area was occupied by the arterial branches and later the branches were occluded by the progressive growth of tumor. On the other hand, the branches of the portal vein were obliterated earlier than those of the hepatic artery and at the 5th day no branches were observed in the tumor area. These vascular changes are closely related to tumor growth, so that special regard should be paid to the change of the blood supply when chemotherapeutic agents are given.