Ag NC Research Articles

Highly sensitive fluorescence quantification of intracellular telomerase activity by repeat G-rich DNA enhanced silver nanoclusters.

As an important biomarker for early cancer diagnosis and a valuable therapeutic target, the detection and monitoring of telomerase activity has attracted extensive attention. Herein, we constructed a novel fluorescent reporter to detect the intracellular telomerase activity based on guanine enhanced sliver nanoclusters (Ag NCs). In this system, a telomerase substrate (Ts) was designed to be extended by telomerase to give the repeat TTAGGG sequence as G-rich DNA, which was complementary to the nine base sequence to form a self-hairpin structure. The proximity of G-rich DNA to the as-prepared Ag NCs resulted in a 13-fold enhancement of fluorescence intensity due to the electron transfer from guanine to the Ag NCs. Therefore, the fluorescent probe could realize the detection of telomerase activity. Furthermore, the probe was successfully used to distinguish normal cells from cancer cells and to monitor the real time telomerase activity response upon treatment with an inhibiting model drug. This detection technique is simple, with excellent biocompatibility, inexpensive and expands the applications of the Ag NC probe.

Effect of surfactant assemblies on the resonance energy transfer from 4′,6-diamidino-2-phenylindole to silver nanoclusters

In the present work, we have demonstrated the effect of sodium dodecyl sulfate (SDS) assemblies on the Förster resonance energy transfer (FRET) between 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI) and silver nanocluster (Ag NC) in phosphate buffer by using fluorescence spectroscopy. While DAPI interacts specifically with SDS surfactants in a concentration-dependent manner, Ag NC shows no specific interaction with surfactant assemblies. At very low concentrations of SDS (<0.6mM), DAPI forms surfactant-induced aggregates at the interface. In the case of intermediate concentrations (0.6mM≤SDS<4mM), DAPI associates with the negatively charged SDS pre-micelles via electrostatic interaction. Beyond 4mM SDS, the FL intensity of DAPI saturates due to complete incorporation of DAPI into the micellar Stern layer. Notably, the interaction between DAPI and Ag NC significantly perturbs in the presence of SDS. In phosphate buffer, FRET efficiency (ϕEff) of 78% has been estimated for DAPI-Ag NC pair. Interestingly, the ϕEff decreases to 23% in the presence of 1mM SDS. However, in the presence of 16mM SDS, complete suppression of this nonradiative FRET has been observed due to incorporation of DAPI into the micellar Stern layer. This efficient modulation of FRET due to the association of the donor molecule with surfactant assemblies, may find promising applications in various photophysical and biological phenomena.

Ag nanocluster-based color converters for white organic light-emitting devices

The authors present Ag nanocluster-based color converters (Ag NC color converters), which convert part of the blue light from a light source to yellow light so as to create white organic light-emitting devices that could be suitable for lighting systems. Ag NCs synthesized by poly(methacrylic acid) template methods have a statistical size distribution with a mean diameter of around 4.5 nm, which is larger than the Fermi wavelength of around 2 nm. Hence, like free electrons in metals, the Ag NC electrons are thought to form a continuous energy band, leading to the formation of surface plasmons by photoexcitation. As for the fluorescence emission mechanism, the fact that the photoluminescence is excitation wavelength dependent suggests that the fluorescence originates from surface plasmons in Ag NCs of different sizes. By using Ag NC color converters and suitable blue light sources, white organic light-emitting devices can be fabricated based on the concept of light-mixing. For our blue light sources, we used polymer light-emitting electrochemical cells (PLECs), which, like organic light-emitting diodes, are area light sources. The PLECs were fabricated with a blue fluorescent π-conjugated polymer, poly[(9,9-dihexylfluoren-2,7-diyl)-co-(anthracen-9,10-diyl)] (PDHFA), and a polymeric solid electrolyte composed of poly(ethylene oxide) and KCF3SO3. In this device structure, the Ag NC color converter absorbs blue light from the PDHFA-based PLEC (PDHFA-PLEC) and then emits yellow light. When the PDHFA-PLEC is turned on by applying an external voltage, pure white light emission can be produced with Commission Internationale de l'Eclairage coordinates of (x = 0.32, y = 0.33) and a color rendering index of 93.6. This study shows that utilization of Ag NC color converters and blue PLECs is a very promising and highly effective method for realizing white organic light-emitting devices.

Electrochemical reduction of Bicarbonate to Formate with Silver Nanoparticles and Silver Nanoclusters supported on Multiwalled Carbon Nanotubes

In this work, we report heterogeneous catalysis of bicarbonate reduction to formate (FA) using silver nanoparticles (Ag NP) and silver nanoclusters (Ag NC) supported on multi-wall carbon nanotubes (MWCNT). FA detection was performed by substrate generation/tip collection (SG/TC) mode of scanning electrochemical microscopy (SECM) using Pt UME in 100mM HCO3− at pH 8. The Ag NP and Ag NC showed high carbonate reduction current, and similar activity as massive gold electrode targets them as alternative catalysts for FA production. Prior to bicarbonate reduction, the electrochemical activity of Ag NP and Ag NC was evaluated using carbon fiber ultra microelectrodes (UME), these carbon UME were fabricated and characterized for use in SCEM mapping; carbon UME provided an excellent feedback response and are dispensable electrodes with renewable surfaces. Also, a carbon UME enables the fabrication of an enzymatic sensor which was designed for NAD+ (Nicotine amide dinucleotide) dependent formate dehydrogenase immobilization. The enzymatic reaction coupled with the redox mediator 2,2V-Azino- bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) allowed a sensitive FA detection. The production of FA on silver particles and the FA detection methods presented in this work will be the target of further investigation for energy storage molecules.

Engineering the Charge Transport of Ag Nanocrystals for Highly Accurate, Wearable Temperature Sensors through All-Solution Processes.

All-nanocrystal (NC)-based and all-solution-processed wearable resistance temperature detectors (RTDs) are introduced. The charge transport mechanisms of Ag NC thin films are engineered through various ligand treatments to design high performance RTDs. Highly conductive Ag NC thin films exhibiting metallic transport behavior with high positive temperature coefficients of resistance (TCRs) are achieved through tetrabutylammonium bromide treatment. Ag NC thin films showing hopping transport with high negative TCRs are created through organic ligand treatment. All-solution-based, one-step photolithography techniques that integrate two distinct opposite-sign TCR Ag NC thin films into an ultrathin single device are developed to decouple the mechanical effects such as human motion. The unconventional materials design and strategy enables highly accurate, sensitive, wearable and motion-free RTDs, demonstrated by experiments on moving or curved objects such as human skin, and simulation results based on charge transport analysis. This strategy provides a low cost and simple method to design wearable multifunctional sensors with high sensitivity which could be utilized in various fields such as biointegrated sensors or electronic skin.

Tuning of resonance energy transfer from 4',6-diamidino-2-phenylindole to an ultrasmall silver nanocluster across the lipid bilayer.

Herein we have developed a simple liposome-based donor-acceptor system across the lipid bilayer using 4',6-diamidino-2-phenylindole (DAPI) as the donor and an ultrasmall ligand-capped silver nanocluster (Ag NC) as the acceptor. The process of Förster resonance energy transfer (FRET) between DAPI and the Ag NC across the liposome bilayer has been demonstrated using steady-state and time-resolved fluorescence spectroscopy. The synthesized Ag NCs with a majority of Ag4 and Ag5 cores have been characterized using FTIR, mass spectrometry, HRTEM, UV-Vis and PL spectroscopy. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) measurements reveal that the synthesized liposomes are small unilamellar vesicles (SUV) with a mean hydrodynamic diameter of 86.91 ± 6.41 nm. By using two distinct synthetic methods, we have been able to identify two selective binding sites of DAPI with liposome namely, the liposome surface and hydrophilic aqueous core. Fluorescence confocal microscopy confirms the location of the donor DAPI within different locations of liposome. It has been observed that the association of DAPI at the surface of liposome results in less efficient energy transfer to Ag NCs compared to that in the bulk aqueous medium. Energy transfer efficiency decreases from a value of 0.76 in bulk aqueous medium to a value of 0.39 for surface-associated DAPI. On the other hand encapsulation of DAPI into the hydrophilic aqueous core of a liposome results in complete inhibition of the FRET process as a consequence of increased separation distance beyond the FRET range. Hence, our study illustrates that the present DAPI-Ag NC pair can be used as a FRET marker to explore various fundamental processes across the cell membrane.

Plasmonic photocatalytic reactor design: Use of multilayered films for improved organic degradation rates in a recirculating flow reactor

Plasmonic photocatalysis was investigated by examining both the arrangement of the photocatalyst and plasmonic components, and the structure and composition of the plasmonic phase. Pd was epitaxially grown on to 50nm Ag nanocubes. The Ag:Pd ratio was optimized to blue-shift the plasmonic absorption peak to match the bandgap of TiO2 (∼405nm). A∼5nm Pd coating on the Ag nanocubes (Ag:Pd=9:1) led to the observation of the Ag nanocube’s plasmonic feature. The arrangement of the photocatalyst components was tested for degradation of model organics in a slurry and a recirculating thin film photoreactor. The results demonstrated that both the arrangement of the components and the structure and composition of the plasmonic material influenced the conversion. The TiO2/Ag composite catalysts yielded slight improvement (in thin film reactor) or had a negative effect (slurry reactor) compared to TiO2 which was attributed to scattering light away from the semiconductor photocatalyst and/or covering some active sites. The addition of the Pd shell on the Ag nanocube yielded improved performance compared to the TiO2/Ag composite catalysts, likely due to electron trapping. A factor of 2 enhancement in rate and apparent quantum yield compared to TiO2 was achieved for the Ag NC layer underneath the TiO2 layer and was attributed to light scattering of absorbed photons. The addition of the Pd shell to the Ag nanocube still provided enhancement compared to TiO2, but was lesser compared to Ag layer due to lower scattering efficiency. The results of this study provide insights for plasmonic photocatalytic reactor design. Best utilization of plasmonic enhancement to photocatalysis is indicated via a layered design of the plasmonic and photocatalytic phases.

Designing highly conductive and stable silver nanocrystal thin films with tunable work functions through solution-based surface engineering with gold coating process

We fabricated highly conductive and stable silver nanocrystal (Ag NC) thin film electrodes with tunable work functions using an all-solution-based method involving sequential ligand exchange and gold (Au) coating processes. We studied the effect of the Au coating process on the ligand-exchanged Ag NC thin films and successfully demonstrated the formation of a thin Au layer on the surface of the Ag NCs. We investigated the morphological, structural, optical, chemical, and electrical properties of the Ag NC thin films before and after Au coating. The work function of the electrodes was precisely controlled by varying the treatment time and concentration of gold chloride trihydrate (HAuCl4·3H2O) solutions. The thermal stability of the Au coated Ag NC thin films in air was greatly enhanced, and an extremely low resistivity of 3.4 μΩcm was achieved. Taking advantage of this solution-based low-temperature process and using a minimal amount of Au for cost reduction, we fabricated all-NC-based high-performance flexible photodetectors.

Control of the Fluorescence of DNA-templated Silver Nanoclusters by Adenosine Triphosphate and Mercury(II)

Several DNA templates with the sequence 5′-T n TAACCCCTAACCCCT-3′ (n = 0, 15, 30, and 45) were used to prepare DNA template–silver nanoclusters (DNA–Ag NCs). The T n sequence acts as a recognition element for Hg2+, while the rest of the sequence acts as a template for DNA–Ag NCs. At pH 3.0, the fluorescence intensity of DNA–Ag NCs is enhanced by ATP, and the enhanced fluorescence is quenched by Hg2+. The length of polyT shows a slight effect on the sensitivity for the detection of Hg2+ but almost no effect on the optical properties of DNA–Ag NCs. The fluorescence response of DNA–Ag NCs (T15-DNA–Ag NCs) vs. Hg2+ concentration shows two linear ranges over 10–100 and 100–1000 nM, mainly because of the fluorescence quenching due to DNA conformational changes through T–Hg2+–T coordination and the formation of an amalgam with Ag NCs, respectively. The sensitivity of the T15-DNA–Ag NC probe was validated through the analysis of Hg2+ in spiked pond water. Based on the switch-on and switch-off fluorescence properties of T15-DNA–Ag NCs, an IMPLICATION logic gate was fabricated using the concentrations of ATP and Hg2+ as inputs and the fluorescence intensity at 585 nm as output.

Silver Nanocluster Embedded Composite Nanoparticles for Targeted Prodrug Delivery in Cancer Theranostics.

Cancer therapy with theranostic nanoparticles having the dual properties of concurrent delivery of therapeutics and its tracking offers a huge prospect to overcome the limitations of conventional therapy. Delivery of the nontoxic prodrug, which converts into the toxic drug due to cellular stimuli, offers a great deal of scope in cancer therapy. The paracetamol dimer (PD) generally considered as nontoxic is encapsulated with fluorescent silver nanocluster (Ag NC) embedded composite nanoparticles where it acts as a prodrug. This is possibly converted to a toxic metabolite due to elevated reactive oxygen species (ROS), leading to apoptosis mediated cell death. Conjugation of folic acid with these composite NPs offers the credibility of distinguishing between two different cancer cell lines such as HeLa, which overexpresses folic acid receptors, and A549, which down-regulates its expression, probed by the fluorescence intensity of Ag NCs. Importantly, Ag NCs along with PD synergistically induce prodrug mediated targeted cell death at a much reduced concentration of silver. Thus, theranostic nanocarriers have been developed offering the dual property of therapy and imaging based on the differential uptake.

Effects of the Substrate Refractive Index, the Exciting Light Propagation Direction, and the Relative Cube Orientation on the Plasmonic Coupling Behavior of Two Silver Nanocubes at Different Separations

In this paper, we presented a detailed theoretical investigation on the effects of changing the refractive index of the substrate and the interparticle separation distance on the electromagnetic field distribution around the face-to-face (FF) and the edge-to-edge (EE) oriented silver nanocube (Ag NC) dimers. We found that the contribution of the scattering to the absorption components is markedly decreased with increasing the substrate refractive index. This suggests that for surface-enhanced Raman spectroscopic (SERS) applications, the use of a substrate of very low refractive index is highly recommended. However, for photothermal applications, the use of substrate of high refractive index is recommended. Furthermore, we found that the wavelengths corresponding to the dipolar and multipolar modes are nearly unaffected by increasing the interparticle separation distances above 40 nm on the high refractive index substrate. However, on the low refractive index substrate, the dipolar peaks consistently red-s...

Ambient-Pressure Organic Superconductor κ-(ET)2Ag(CN)[N(CN)2] Formed with Polymeric Silver(I) Complex Anion

We obtained a new cation radical salt of bis(ethylenedithio)tetrathiafulvalene (ET) with a κ-type packing motif, κ-(ET)2Ag(CN)[N(CN)2], by electrooxidation. In the salt, each ET layer is separated by polymeric {Ag(CN)[N(CN)2]−}∞ layers, which are composed of Ag(I) ions trigonally coordinated to form an infinite zigzag chain of –NC–Ag–NC–Ag– with pendant dicyanamides. The salt undergoes a superconducting transition with a midpoint critical temperature (Tc) of 6.6 K and an onset Tc of 7.2 K, thereby indicating the highest Tc among ET superconductors formed with a polymeric Ag(I) complex anion.

Controllable Synthesis and Surface Wettability of Flower-Shaped Silver Nanocube-Organosilica Hybrid Colloidal Nanoparticles.

Synthesis of hybrid colloidal particles with complex and hierarchical structures is attracting much interest theoretically and technically in recent years, but still remains a tremendous challenge. Here, we present a mild and controllable wet-chemical method for the synthesis of silver nanocube (Ag NC)-organosilica hybrid particles with finely tuned numbers (with one, two, three, four, five, or six) and sizes of organosilica petals, by simply controlling the affinity with Ag NC/nature, amount, and prehydrolysis process of alkoxysilanes. The morphologies of hybrid colloidal particles have an obvious influence on the surface wettability of the hybrid particle-based films. More and larger organosilica petals can increase the surface hydrophobicity of the hybrid particle-based films.

Construction of an Upconversion Nanoprobe with Few‐Atom Silver Nanoclusters as the Energy Acceptor

AbstractHerein we report that few‐atom silver nanoclusters (Ag NCs) can be effective energy acceptors for upconversion phosphors (UCPs). A luminescence resonance energy transfer (LRET) probe for biothiols was constructed by decorating UCPs with dithiol‐stabilized Ag NCs. Owing to the unique properties of ultrasmall NCs, properties which bridge the gap between those of small molecules and those of nanoparticles, the use of approximately 1.9 nm Ag NCs as energy acceptors endows the probe with high energy‐transfer efficiency, good biocompatibility, and flexibility. The UCP–Ag NC nanoprobe enables rapid and robust target assay in solutions. It was also uploaded into living cells and used to detect intracellular biothiol levels with high discrimination. Moreover, the probe shows transportability in vivo and can be used for tissue imaging. The facile growth of few‐atom metal NCs on diverse templates may enable the development of various nanoprobes combining UCPs and metal NCs.

Silver nanoclusters for RNA nanotechnology: steps towards visualization and tracking of RNA nanoparticle assemblies.

The growing interest in designing functionalized, RNA-based nanoparticles (NPs) for applications such as cancer therapeutics requires simple, efficient assembly assays. Common methods for tracking RNA assemblies such as native polyacrylamide gels and atomic force microscopy are often time-intensive and, therefore, undesirable. Here we describe a technique for rapid analysis of RNA NP assembly stages using the formation of fluorescent silver nanoclusters (Ag NCs). This method exploits the single-stranded specificity and sequence dependence of Ag NC formation to produce unique optical readouts for each stage of RNA NP assembly, obtained readily after synthesis.

Multiplexed analysis of genes using nucleic acid-stabilized silver-nanocluster quantum dots.

Luminescent nucleic acid-stabilized Ag nanoclusters (Ag NCs) are applied for the optical detection of DNA and for the multiplexed analysis of genes. Two different sensing modules including Ag NCs as luminescence labels are described. One sensing module involves the assembly of a three-component sensing module composed of a nucleic acid-stabilized Ag NC and a quencher-modified nucleic acid hybridized with a nucleic acid scaffold that is complementary to the target DNA. The luminescence of the Ag NCs is quenched in the sensing module nanostructure. The strand displacement of the scaffold by the target DNA separates the nucleic acid-functionalized Ag NCs, leading to the turned-on luminescence of the NCs and to the optical readout of the sensing process. By implementing two different-sized Ag NC-modified sensing modules, the parallel multiplexed analysis of two genes (the Werner Syndrome gene and the HIV, human immunodeficiency, gene), using 615 and 560 nm luminescent Ag NCs, is demonstrated. The second sensing module includes the nucleic acid functionalized Ag NCs and the quencher-modified nucleic acid hybridized with a hairpin DNA scaffold. The luminescence of the Ag NCs is quenched in the sensing module. Opening of the hairpin by the target DNA triggers the luminescence of the Ag NCs, due to the spatial separation of the Ag NCs/quencher units. The system is applied for the optical detection of the BRAC1 gene. In addition, by implementing two-sized Ag NCs, the multiplexed analysis of two genes by the hairpin sensing module approach is demonstrated.

Branched DNA-based Synthesis of Fluorescent Silver Nanocluster

While single strand DNAs have been widely used for the scaffold of brightly fluorescent silver nanoclusters (Ag NCs), double strand DNAs have not been as successful. Herein, we report a novel synthetic approach for bright Ag NCs using branched double strand DNAs as the scaffolds for synthesis. X-shaped DNA (X-DNA) and Y-shaped DNA (Y-DNA) effectively stabilized Ag NCs, and both X-DNA and Y-DNA resulted in brightly fluorescent Ag NCs. The concentration and molar ratio of silver and DNA were found important for the fluorescence efficiency. The brightest Ag NC with the photoluminescence quantum efficiency of 19.8% was obtained for the reaction condition of 10 µM X-DNA, 70 µM silver, and the reaction time of 48 h. The fluorescence lifetime was about 2 ns for the Ag NCs and was also slightly dependent on the synthetic condition. Addition of Cu ions at the Ag NC preparations resulted in the quenching of Ag NC fluorescence, which was different to the brightening cases of single strand DNA stabilized Ag NCs.

Specific recognition of DNA bulge sites by in situ grown fluorescent Ag nanoclusters with high selectivity

There is much demand for the development of reliable methods of bulge site recognition in DNA in order to find disease-related mutations and identify bulge sequence environments. Herein, we found that the bulge site in the DNA duplex can be used to selectively grow fluorescent silver nanoclusters (Ag NCs). The as-prepared Ag NCs exhibit an emission behavior dependent on the base environment near the bulge site and can be employed in situ as a readout for specific bulge site recognition. Fluorescent signal-on sensing for the bulge site based on this inorganic fluorophore is substantially advantageous over the organic fluorophores previously used as probes, in which a fluorescent signal-off response was usually observed with context guanines flanking the bulge site. The strong dependence of the fluorescent Ag NCs' formation on the bases surrounding the bulge site is successfully used to identify the bulge environment near the codon 177 of cancer suppression gene p53. We expect that bulge site-determined Ag NC formation is very likely to be developed into a simple method for bulge site recognition with high selectivity and sensitivity.

A label-free DNA-templated silver nanocluster probe for fluorescence on–off detection of endonuclease activity and inhibition

Endonuclease cleavage of DNA plays an important role in biological and medicinal chemistry. This study aimed to develop a reliable and sensitive method for nuclease activity assay by combining the high specificity of DNA cleavage reactions with ultrahigh fluorescence turn-on abilities of guanine-rich (G-rich) DNA sequences in proximity to silver nanoclusters (Ag NCs). The DNA-templated Ag NC (DNA-Ag NC) probe with endonuclease recognition sequence consists of NC and a G-rich probe. The NC probe was designed by adding Ag NC nucleation sequence at the 5′-end. The G-rich probe is the complementary DNA sequence modified by adding a G-rich overhang sequence at the 3′-end. Thus, the fluorescence of DNA-Ag NC probe was activated because of DNA hybridization. When these DNA-Ag NC probes were exposed to the targeted endonucleases, specific DNA cleavages occurred, and pieces of G-rich DNA fragments separated from Ag NCs, resulting in fluorescence turn-off. The endonuclease activity was quantified by monitoring the change in the fluorescence intensity. Detection was demonstrated by assaying EcoRI activity. Under optimized conditions, the fluorescence reduction efficiency was linear with the EcoRI concentration in the range of 5.0×10−4UμL−1 to 3.0×10−3UμL−1, with a detection limit of 3.5×10−4UμL−1, which is much better than or at least comparable with that in previous reports. The potential application of the proposed method for screening endonuclease inhibitors was also demonstrated. The presented assay protocol proved to be convenient, effective, sensitive, and easy in preparing the fluorescent probe.

Vibrational and Thermal Properties of Ag3[Co(CN)6] from First-Principles Calculations and Infrared Spectroscopy

We have investigated the phonon modes of Ag3[Co(CN)6] using first-principles based methods and high-pressure infrared spectroscopy to understand the origin of its colossal thermal expansion. Grüneisen parameters of its zone-center vibrational modes were obtained from the calculations and compared to the experimental ones. We found that optical phonon modes below 100 cm–1 mainly contribute to its negative thermal expansion, and they also have a significant mixing with acoustic branches. These modes have been assigned to translational motion of the Co–CN–Ag–NC–Co linkages. We also identify a pressure-induced softening of zone-center phonon modes that could account for the experimentally observed phase transition in terms of a first-order displacive instability from the trigonal P3̅1m space group to the acentric Cm space group.