DNA-embedded Au/Ag core-shell nanoparticles

Here, we synthesized highly stable DNA-embedded Au/Ag core-shell nanoparticles (NPs) by a straightforward silver-staining of DNA-modified Au nanoparticles (AuNPs); unlike conventional DNA-surface modified NPs that present particle stability issues, DNA-embedded core-shell NPs offer an extraordinary stability with nanoscale controllability of silver shell thickness; these DNA-embedded core-shell NPs show excellent biorecognition properties and Ag shell-thickness-based optical properties, distinctively different from those of a mixture of AuNPs and AgNPs or Ag/Au alloy nanoparticles.     

In situ Deposition of ‘Naked’ Gold Nanoparticles Supported on Silica Spheres as Recyclable Catalysts in Styrene Epoxidation

Tlie rational designs of particle size, morphology and surface states of the Au nanoparticles(AuNPs) are crucial for Au nanocatalyst. We herein report a method to synthesize the silica microspheres supported AuNPs(ca.1 nm) and their application in controlling the reaction conversion and selectivity in styrene epoxidation. Surfactant-ftee AuNPs deposited on silica microspheres were in situ fabricated with aid of the Ag nanoparticles (AgNPs) as sacrificial template by galvanic replacement reaction, leading to AuNPs/SiO2 catalyst directly without any post-treatment to expose crystal facets.A high conversion of 46.7% and selectivity of 91.7% to styrene oxide was achieved with H2O2 as oxidant in ethanol. The solid catalyst could be reused at least 10 reaction cycles without significant decrease in activity and selectivity. This study not only supplies an active, recoverable catalyst for styrene oxidation with green oxidant and solvent, but also demonstrates that the silica microspheres functionalized with thiol groups have a superior ability in stabilizing noble metal nanoparticles even without any surfactant.     

Calix[4]arene‐Functionalised Silver Nanoparticles as Hosts for Pyridinium‐Loaded Gold Nanoparticles as Guests

A series of lipophilic gold nanoparticles (AuNPs) circa 5 nm in diameter and having a mixed organic layer consisting of 1‐dodecanethiol and 1‐(11‐mercaptoundecyl) pyridinium bromide was synthesised by reacting tetraoctylammonium bromide stabilised AuNPs in toluene with different mixtures of the two thiolate ligands. A bidentate ω‐alkylthiolate calix[4]arene derivative was instead used as a functional protecting layer on AgNPs of approximately 3 nm. The functionalised nanoparticles were characterised by transmission electron microscopy (TEM), and by UV/Vis and X‐ray photoelectron spectroscopy (XPS). Recognition of the pyridinium moieties loaded on the AuNPs by the calix[4]arene units immobilised on the AgNPs was demonstrated in solution of weakly polar solvents by UV/Vis titrations and DLS measurements. The extent of Au‐AgNPs aggregation, shown through the low‐energy shift of their surface plasmon bands (SPB), was strongly dependent on the loading of the pyridinium moieties present in the organic layer of the AuNPs. Extensive aggregation between dodecanethiol‐capped AuNPs and the Ag calix[4]arene‐functionalised NPs was also promoted by the action of a simple N‐octyl pyridinium difunctional supramolecular linker. This linker can interdigitate through its long fatty tail in the organic layer of the dodecanethiol‐capped AuNPs, and simultaneously interact through its pyridinium moiety with the calix[4]arene units at the surface of the modified AgNPs.     

Multiplexed analysis of silver(I) and mercury(II) ions using oligonucletide-metal nanoparticle conjugates

A colorimetric assay has been developed for the simultaneous selective detection of silver(I) and mercury(II) ions utilizing metal nanoparticles (NPs) as sensing element based on their unique surface plasmon resonance properties. In this method, sulfhydryl group modified cytosine-(C)-rich ssDNA (SH-C-ssDNA) was self-assembled on gold nanoparticles (AuNPs) to produce the AuNPs-C-ssDNA complex, and sulfhydryl group modified thymine-(T)-rich ssDNA (SH-T-ssDNA) was self-assembled on silver nanoparticles (AgNPs) to produce the AgNPs-T-ssDNA complex. Oligonucleotides (SH-C-ssDNA or SH-T-ssDNA) could enhance the AuNPs or AgNPs against salt-induced aggregation. However, the presence of silver(I) ions (Ag(+)) in the complex of ssDNA-AuNPs would reduce the stability of AuNPs due to the formation of Ag(+) mediated C-Ag(+)-C base pairs accompanied with the AuNPs color change from red to purple or even to dark blue. Moreover, the presence of mercury(II) ions (Hg(2+)) would also reduce the stability of AgNPs due to the formation of Hg(2+) mediated T-Hg(2+)-T base pairs accompanied with the AgNPs color change from yellow to brown, then to dark purple. The presence of both Ag(+) and Hg(2+) will reduce the stability of both AuNPs and AgNPs and cause the visible color change. As a result, Ag(+) and Hg(2+) could be detected qualitatively and quantitatively by the naked eye or by UV-vis spectral measurement. The lowest detectable concentration of a 5 nM mixture of Ag(+) and Hg(2+) in the river water was gotten by the UV-vis spectral measurement.     

Facile preparation and characterization of highly antimicrobial colloid Ag or Au nanoparticles

A series of colloid silver or gold nanoparticles (AgNPs or AuNPs) were successfully prepared by in situ reduction and stabilization of hyperbranched poly(amidoamine) with terminal dimethylamine groups (HPAMAM-N(CH(3))(2)) in water, and they all exhibited highly antimicrobial activity. The particle size could be controlled easily by adjusting the molar ratio of N/Ag (or N/Au) in feed. When the molar ratio was 2, some aggregates of the nanoparticles separated from the colloidal solution, which showed some limited antimicrobial activity with the bacterial inhibition ratio of below 15%. As the molar ratio increased from 10 to 30, the average particle diameters decreased (from ca. 7.1 to 1.0 nm for AgNPs and from ca. 7.7 to 3.9 nm for AuNPs, respectively) and they all showed high dispersion stability and excellent antimicrobial efficiency. All the bacterial inhibition ratios reached up to ca. 98% at the low silver content of ca. 2.0 microg/mL or at the low gold content of ca. 2.8 microg/mL. The AgNPs or AuNPs with smaller particle size can provide much more effective contact surface with the bacteria, thus enhancing their antimicrobial efficiency. Besides, the cationic HPAMAM-N(CH(3))(2) can also do some contribution to the antimicrobial activity through the strong ionic interaction with the bacteria.     

The adsorption of methamphetamine on Ag nanoparticles dispersed in agarose gel – Detection of methamphetamine in fingerprints by SERS

Surface-enhanced Raman scattering (SERS) has been used to investigate the adsorption of methamphetamine hydrochloride (MA) on AgNPs surfaces characterized by the dispersion of AgNPs on agarose gel (AgNPs/Agar). The AgNPs/Agar was characterized by transmission electron microscopy (TEM) as being formed by AgNPs with a mean diameter of 13.5 nm. The AgNPs/Agar films presented a surface plasmon resonance absorption band centered at 421 nm. SERS spectra, excited at 632.8 nm, of MA adsorbed onto AgNPs/Agar films were recorded for MA concentrations down to 1.0 × 10⁻⁵ mol L^-1. The results have also shown that MA adsorbs on the Ag surface forming ionic pairs with adsorbed chloride following a Frumkin adsorption isotherm with a ΔG_ads of −24 kJ mol^-1 and a g parameter characteristic of attractive lateral interaction. The AgNPs/Agar SERS substrate was further evaluated for MA detection on latent fingerprints (LFP). The AgNPs/Agar films prove to be a suitable substrate for recording fingerprints contaminated with MA making possible the detection of ca. 190 μg of MA, before and after LFP development. The SERS signal of MA adsorbed onto AgNPs/Agar films remained stable for at least 180 days.     

Catalytic reduction of 4-nitrophenol using biogenic gold and silver nanoparticles derived from Breynia rhamnoides

A simple, green method is described for the synthesis of Gold (Au) and Silver (Ag) nanoparticles (NPs) from the stem extract of Breynia rhamnoides. Unlike other biological methods for NP synthesis, the uniqueness of our method lies in its fast synthesis rates (~7 min for AuNPs) and the ability to tune the nanoparticle size (and subsequently their catalytic activity) via the extract concentration used in the experiment. The phenolic glycosides and reducing sugars present in the extract are largely responsible for the rapid reduction rates of Au(3+) ions to AuNPs. Efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of AuNPs (or AgNPs) and NaBH(4) was observed and was found to depend upon the nanoparticle size or the stem extract concentration used for synthesis.     

Amplified surface plasmon resonance based DNA biosensors, aptasensors, and Hg2+ sensors using hemin/G-quadruplexes and Au nanoparticles

Thiolated nucleic acid hairpin nanostructures that include in their stem region a "caged" G-quadruplex sequence, and in their single-stranded loop region oligonucleotide recognition sequences for DNA, adenosine monophosphate (AMP), or Hg(2+) ions were linked to bare Au surfaces or to Au nanoparticles (NPs) linked to Au surfaces. The opening of the hairpin nanostructures associated with the bare Au surface by the complementary target DNA, AMP substrate, or Hg(2+) ions, in the presence of hemin, led to the self-assembly of hemin/G-quadruplexes on the surface. The resulting dielectric changes on the surface exhibited shifts in the surface plasmon resonance (SPR) spectra, thus providing a readout signal for the recognition events. A similar opening of the hairpin nanostructures, immobilized on the Au NPs associated with the Au surface, by the DNA, AMP, or Hg(2+) led to an ultrasensitive SPR-amplified detection of the respective analytes. The amplification originated from the coupling between the localized surface plasmon associated with the NPs and the surface plasmon wave, an effect that cooperatively amplifies the SPR shifts that result from the formation of the hemin/G-quadruplexes. The different sensing platforms reveal impressive sensitivities and selectivities toward the target analytes.     

Gold and silver nanoparticles‐based laser desorption/ionization mass spectrometry method for detection and quantification of carboxylic acids

A comparison of ionization efficiency for gold and silver nanoparticles used as an active media of matrix‐less laser desorption/ionization (LDI) mass spectrometry (MS) methods was made for carboxylic acids including fatty acids. The matrix‐assisted laser desorption/ionization (MALDI)‐type targets containing monoisotopic cationic ¹⁰⁹Ag nanoparticles (¹⁰⁹AgNPs) and Au nanoparticles (AuNPs) were used for rapid MS measurements of 10 carboxylic acids of different chemical properties. Carboxylic acids were directly quantified in experiments with 10 000‐fold concentration change conditions ranging from 1 mg/ml to 100 ng/ml which equates to 1 μg to 100 pg of carboxylic acids per measurement spot.     

Colorimetric detection of mercury(II) in a high-salinity solution using gold nanoparticles capped with 3-mercaptopropionate acid and adenosine monophosphate

A new colorimetric sensor for sensing Hg2+ in a high-salinity solution has been developed using gold nanoparticles (AuNPs) decorated with 3-mercaptopropionate acid (MPA) and adenosine monophosphate (AMP). Because of the high negative charge density of AMP on each AuNP surface, MPA/AMP-capped AuNPs are well dispersed in a high-salt solution. In contrast, the aggregation of MPA-capped AuNPs was induced by sodium ions, which shield the negative charges of the carboxylic groups of MPA. Through the coordination between the carboxylic group of MPA and Hg2+, the selectivity of MPA/AMP-capped AuNPs for Hg2+ in a high-salt solution is remarkably high over that of the other metals without the addition of a masking agent or a change in the temperature. We have carefully investigated the effect of the AMP concentration on the stability and sensitivity of MPA/AMP-capped AuNPs. Under optimum conditions, the lowest detectable concentration of Hg2+ using this probe was 500 nM on the basis of the measurement of the ratio of absorption at 620 nm to that at 520 nm. The sensitivity to Hg2+ can be further improved by modifying the MPA/AMP-capped AuNPs with highly fluorescent rhodamine 6G (R6G). By monitoring the fluorescence enhancement, the lowest detectable concentration of Hg2+ using R6G/MPA/AMP-capped AuNPs was 50 nM.     

Gold nanoparticles-based colorimetric investigation of triplex formation under weak alkalic pH environment with the aid of Ag+

A novel colorimetric method for investigating triplex formation between oligonucleotide modified Au nanoparticles (AuNPs) under weak alkalic pH environment is developed based upon the specific recognition property of Ag+ with CGC triads. Oligonucleotide 5'-SH-T12-CTTCTTTCCTTTCTTC-3' (oligo-1) is modified on the surface of AuNPs. Upon addition of oligonucleotide 5'-GAAGAAAGGAAAGAAG-3' (oligo-2), triplex formation between oligo-1 modified AuNPs occurred at pH 8.0 with the aid of Ag+, triggers the aggregation of AuNPs, accompany with the solution color change from red to purple. The melting temperature demonstrates a 31 °C increase for the triplex DNA compose of 10 T?A°T triads and 6 C?G°C triads upon addition of Ag+, the disassociation constant (Kd) between Ag+ and C?G°C triads is 3.6 μM. Moreover, triplex formation between AuNPs depending on Ag+ can be used to recognize Ag+ ion with the naked eye, as well as UV-vis absorption spectroscopy.     

Preparation and characterization of nanostructured thin films of Au and Ag nanoparticles synthesized by ascorbic acid on modified glass surface

Immobilization of Ag and Au nanoparticles (NPs) synthesized by ascorbic acid on chemically modified glass surface has been studied. 3‐[2‐(2‐Aminoethylamino)ethylamino]propyl‐trimethoxysilane (AMPTS), N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilan, and 3‐trimethoxysilyl‐1‐propanethiol (MSPT) were used as surface modifying agents. To improve immobilization efficiency, the ammonia solution has been used along with the silane reagents, which assisted to adsorb the metal NPs on glass surface. It was found that AMPTS and MSPT have considerable effect on deposition of Ag and AuNPs on glass substrate. The fabricated thin films were characterized by using UV‐Vis spectroscopy, atomic force microscopy, energy‐dispersive X‐ray spectroscopy and subjected to antimicrobial resistance test. The UV–Vis spectra show a distinctive plasmon resonance absorbance peak for thin films of Au and AgNPs prepared with MSPT and AMPTS, respectively. Atomic force microscopy images indicate that formation of Au and AgNPs with spherical morphology after immobilization on the glass substrate and also the dimensions of NPs on the surface appear larger than those observed in the parent colloidal solution. Energy‐dispersive X‐ray spectroscopy measurements confirmed the presence of silver and gold on the modified glass surface, and elemental composition was measured. The Au and AgNPs thin films show antibacterial activity against gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacteria in comparison with a blank sample. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis of gold and silver nanoparticles using purified URAK

This study aims at developing a new eco-friendly process for the synthesis of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) using purified URAK. URAK is a fibrinolytic enzyme produced by Bacillus cereus NK1. The enzyme was purified and used for the synthesis of AuNPs and AgNPs. The enzyme produced AgNPs when incubated with 1 mM AgNO3 for 24 h and AuNPs when incubated with 1 mM HAuCl4 for 60 h. But when NaOH was added, the synthesis was rapid and occurred within 5 min for AgNPs and 12 h for AuNPs. The synthesized nanoparticles were characterized by a peak at 440 nm and 550 nm in the UV-visible spectrum. TEM analysis showed that AgNPs of the size 60 nm and AuNPs of size 20 nm were synthesized. XRD confirmed the crystalline nature of the nanoparticles and AFM showed the morphology of the nanoparticle to be spherical. FT-IR showed that protein was responsible for the synthesis of the nanoparticles. This process is highly simple, versatile and produces AgNPs and AuNPs in environmental friendly manner. Moreover, the synthesized nanoparticles were found to contain immobilized enzyme. Also, URAK was tested on RAW 264.7 macrophage cell line and was found to be non-cytotoxic until 100 μg/ml.     

Layer-by-layer coating of bacteria with noble metal nanoparticles for surface-enhanced Raman scattering

A simple layer-by-layer method to coat the bacterial cells with gold and silver nanoparticles (AuNPs and AgNPs) for the acquisition of surface-enhanced Raman scattering (SERS) spectra is reported. First, the bacteria cell wall is coated with poly (allylamine hydrochloride) (PAH), a positively charged polymer, and then with citrate reduced Au or AgNPs. In order to increase the stability of the coating, another layer of PAH is prepared on the surface. The SEM and AFM images indicate that the nanoparticles are in the form of both isolated and aggregated nanoparticles on the bacterial wall. The coating of bacterial cells with AgNPs or AuNPs not only serves for their preparation for SERS measurement but also helps to visualize the coated of bacterial cells under the ordinary white-light microscope objective due to efficient light-scattering properties of Au and AgNPs. A comparative study single versus aggregates of bacterial cells is also demonstrated for possible single bacterial detection with SERS. The two bacteria that differ in shape and cell wall biochemical structure, Escherichia coli and Staphylococcus cohnii, Gram-negative and -positive, respectively, are used as models. The preliminary results reveal that the approach could be used for single bacterial cell identification.     

Human Serum Albumin−Gold Nanoparticle Based Impedimetric Sensor for Sensitive Detection of miRNA-200c

Here, human serum albumin conjugated gold nanoparticles (HSA−AuNPs) were synthesized by a simple route to develop an impedimetric sensor for miRNA-200c detection based on a selective oligo-hybridization process without any labeling. The synthetic DNA capture probe for miRNA-200c was decorated onto the HSA−AuNPs modified pencil graphite electrodes. Impedimetric signals were monitored after the hybridization process between the DNA probe and target miRNA-200c. HSA−AuNPs adsorption time, incubation time of the capture probe and hybridization time-temperature were optimized. The proposed miRNA-200c biosensor demonstrated proper sensitivity and selectivity, low detection limit (1.13 fM), good reproducibility and simple direct detection of miRNA-200c in serum.     

Metals (Cu,Ag, Au) encapsulated gallium nitride nanotubes (GaNNTs) as sensors for hexabromodiphenyl ether (HBDE) emerging organic pollutant: A computational study

This study is aimed at investigating the potential of transition metals (Cu, Ag, Au) doped gallium nitride nanotubes (GaNNTs) as sensor materials for the enhanced detection of hexabromodiphenyl ether (HBDE) an emerging organic pollutant that has been linked to several health problems, including developmental and neurological disorders, hormonal imbalances, and cancer. Using the density functional theory (DFT) method at the B3LYP-D3(BJ)/def2SVP level of theory, the potential of pristine and metal (Ag, Au, and Cu) doped gallium nitride (GaNNT) nanotube to sense and detect HBDE was evaluated. The interaction of HBDE on the surface was evaluated at two sites, the bromine (Br) and oxygen (O) sites to evaluate the best conformation adsorption. The results showed that the Br site was the preferred sites of adsorption with binding energies of −43.926 kcal/mol, −43.926 kcal/mol, −43.926 kcal/mol and −31.376 kcal/mol for HBDE_Br_Ag@GaNNT, HBDE_Br_Au@GaNNT, HBDE_Br_Cu@GaNNT and HBDE_Br_@GaNNT respectively. The mechanism of surface adsorption was found to be chemisorption and doping of GaNNT surface with metals was found to enhance the conductivity and sensitivity of the surface towards the adsorbent. The result of the thermodynamic assay also affirmed the spontaneous and favorable nature of the surface and adsorbent. Overall, the various analysis considered so far, points that pristine and metal functionalized GaNNT could be used as potential materials to sense HBDE.     

纳米银修饰电极差分脉冲伏安法测定盐酸金霉素

建立了快速测定盐酸金霉素(CTC)的方法。通过NaBH4还原法制备纳米银(AgNPs)溶胶,并利用X射线衍射和紫外-可见光谱进行表征。将制备好的AgNPs滴涂到玻碳电极表面制备修饰电极(AgNPs/GCE),研究了CTC在AgNPs/GCE上的电化学行为及伏安法测定,优化了缓冲溶液和pH等检测条件。结果表明,CTC在pH 3.3的柠檬酸-NaOH-HCl缓冲溶液中检测效果最佳。CTC在AgNPs/GCE上发生2个电子和2个质子的不可逆电化学氧化反应,且反应受吸附控制。最佳条件下,CTC的氧化峰电流与其浓度呈现良好的线性关系,线性范围为0.5~100μmol/L,检出限为0.14μmol/L。该修饰电极可用于河水样品检测。     

Differential electrochemical behaviour of phytofabricated and chemically synthesized silver nanoparticles towards hydrogen peroxide sensing**

Silver nanoparticles (AgNPs) are one of the most widely used nanomaterials for biomedical applications. However, the impact of its synthesis by chemical and plant-mediated routes on its differential electrochemical behaviour has not been examined till date. Here, we report for the first time the differential study of the electrochemical behaviour of the AgNPs synthesized by different routes. First, the AgNPs were obtained by different routes (chemical and phytofabrication) and extensively characterized to compare their physical properties. Thereafter, a comparison of electron transfer kinetics between chemically synthesized (Ag−C) and phyto-fabricated (Ag-Phy) nanoparticles (NPs) has been studied by electrochemical techniques such as potentiodynamic cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). To further investigate the electrocatalytic properties of both types of AgNPs, we have used the peroxide moieties (H₂O₂), and the Ag−C NPs-based sensor probe has been reported to have four times better sensitivity than the Ag−Phy NPs-based sensor. The AgNPs modified sensor probes have also been tested in real-world environments to explore the consistency of their performance in complex matrices by using clinical urine samples, where we found comparable sensitivity to the standard conditions.     

Biofunctionalized silver and gold nanoparticles as potential curative agents

In this study, the bark of an important medicinal plant, Indigofera aspalathoides is utilized as a bioreductant for the synthesis of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs). The formation of nanoparticles was monitored, and the reaction parameters were optimized by UV–Vis spectroscopy. The attachment of biocomponents as stabilizer was proved employing Fourier‐transform infrared (FT‐IR) studies. Through transmission electron microscopy (TEM), the morphology was found to be predominantly spherical and a mixture of triangle and hexagon in the case of AgNPs and AuNPs, respectively. The crystallite size of AgNPs and AuNPs was affirmed through X‐ray diffraction (XRD) studies using Sherrer formula as 22.03 and 47.70 nm, respectively. DPPH method was adopted to analyse the free‐radical quenching ability, and the AgNPs, AuNPs and extract showed inhibition of 76%, 89% and 59% at a concentration of 200 μg ml^?1, and the corresponding IC₅₀ values were 86.49, 55.20 and 149.19 μg ml^?1. The binding of nanoparticles to calf‐thymus DNA (CT‐DNA) was through groove and the high binding constants (8.49 × 10⁶ M^?1 and 2.34 × 10⁷ M^?1 for AgNPs and AuNPs) point out the potential of these nanoparticles as curative drugs. The MTT assay showed that AgNPs were 100% toxic, and the low IC₅₀ value suggests that this can be used in the medicinal field as a safe drug.     

An Electrochemical Sensor Based on Gold Nanoparticles Incorporated in Mesoporous MFI Zeolite for Determination of Purine Bases in DNA

An electrochemical sensor was developed based on gold nanoparticles incorporated in mesoporous MFI zeolite for the determination of purine bases. Au nanoparticles (AuNPs) were incorporated into the mesoporous MFI zeolite (AuNPs/m‐MFI) by post‐grafting reaction. The composite materials were characterized by transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and electrochemical methods. Au nanoparticles with a size of 5‐20 nm are uniformly dispersed in the pores of mesoporous MFI zeolite. And the morphology of MFI zeolite can be perfectly kept after pore expansion and Au nanoparticles incorporation. The electrocatalytic oxidation of purine bases (guanine and adenine in DNA) is investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface‐confined Au nanoparticles provide the good catalytic activity for oxidation of purine bases. The simultaneous detection of guanine and adenine can be achieved at AuNPs/m‐MFI composites modified glassy carbon electrode (GCE). The electrochemical sensor based on AuNPs/m‐MFI exhibits wide linear range of 0.5–500 μM and 0.8–500 μM with detection limit of 0.25 and 0.29 μM for guanine and adenine, respectively. Moreover, the electrochemical sensor is applied to evaluation of guanine and adenine in herring sperm DNA samples with satisfactory results.