Silver Nanoflakes Research Articles

Enhanced Laser Emission by Incorporating Helically Twisted Silver Nanoflakes within Polymer-Stabilized Cholesteric Liquid Crystals

Enhanced Laser Emission by Incorporating Helically Twisted Silver Nanoflakes within Polymer-Stabilized Cholesteric Liquid Crystals

Mass Spectrometry Imaging Reveals the Morphology-Dependent Toxicological Effects of Nanosilvers on Multiple Organs of Adult Zebrafish (Danio rerio).

Nanosilvers with multifarious morphologies have been extensively used in many fields, but their morphology-dependent toxicity toward nontarget aquatic organisms remains largely unclear. Herein, we used matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to investigate the toxicological effects of silver nanomaterials with various morphologies on spatially resolved lipid profiles within multiple organs in adult zebrafish, especially for the gill, liver, and intestine. Integrated with histopathology, enzyme activity, accumulated Ag contents and amounts, as well as MSI results, we found that nanosilvers exhibit morphology-dependent nanotoxicity by disrupting lipid levels and producing oxidative stress. Silver nanospheres (AgNSs) had the highest toxicity toward adult zebrafish, whereas silver nanoflakes (AgNFs) exhibited greater toxicity than silver nanowires (AgNWs). Levels of differential phospholipids, such as PC, PE, PI, and PS, were associated with nanosilver morphology. Notably, we found that AgNSs induced greater toxicity in multiple organs, such as the brain, gill, and liver, while AgNWs and AgNFs caused greater toxicity in the intestine than AgNSs. Lipid functional disturbance and oxidative stress further caused inflammation and membrane damage after exposure to nanosilvers, especially with respect to sphere morphology. Taken together, these findings will contribute to clarifying the toxicological effects and mechanisms of different morphologies of nanosilvers in adult zebrafish.

A Naked-Eye Colorimetric Ratio Method for the Selective and Sensitive Detection of L-Cys Based on a Silver Nanoflakes–Chromium (III) Ion System

As a necessary sulfhydryl amino acid, L-cysteine (L-Cys) maintains many physiological functions in the biological system. However, abnormal L-Cys levels can cause a variety of diseases. In our work, a highly sensitive and selective assay has been developed for sensing L-Cys using the morphological transformation of silver-based materials induced by Cr3+. In this sensing system, Cr3+ could etch the silver nanoflakes into silver nanoparticles, accompanied by a change in absorbance, which decreases at 395 nm, creates a new peak at 538 nm, and keeps increasing the absorbance with the addition of Cr3+ concentration. Meanwhile, under the naked eye, the solution color changes from bright yellow to dark purple. Because of the strong affinity between L-Cys and Cr3+, L-Cys could inhibit the induction of Cr3+ on silver-based materials, thereby preventing changes in the configuration, absorption spectrum, and color of silver-based materials. Taking advantage of this point, we can quantitatively detect the concentration of L-Cys. A linear relationship between the absorbance ratio (A538 nm/A395 nm) and L-Cys concentration was found in the range of 0.1–0.9 μM, and the detection limit was 41.2 nM. The strategy was applied to measure L-Cys spiked in beer and urine samples, with recovery from 93.80 to 104.03% and 93.33% to 107.14% and RSD from 0.89 to 2.40% and 1.80% to 6.78%, respectively. This detection strategy demonstrates excellent selectivity and sensitivity, which makes it a practical and effective method for the detection of L-Cys in real samples.

Tailoring antimicrobial characteristic and mechanical behavior with silver in leucite–glass–ceramics for hard tissue engineering

AbstractLeucite glass–ceramics are excellent dental restorative materials, but they have relatively poor fracture toughness and high hardness, which leads to lower damage tolerance and counter‐tooth wear, respectively. These materials are also susceptible to bacterial infections and biofilm formations. Here, we report a versatile material leucite–silver‐based glass–ceramic to address the aforementioned shortcomings. Silver was incorporated in leucite (K2O·Al2O3·4SiO2) glass–ceramic to improve the fracture toughness, reduce hardness, and impart antibacterial characteristics. Silver (2, 5, 10, and 15 wt.%) was added into the leucite glass matrix by two approaches, that is, using silver nanoflakes (AgNFs) and using precursor (AgNO3), via thermal decomposition, followed by a sintering process. The incorporation of silver was confirmed by X‐ray diffraction, transmission electron microscopy, and energy‐dispersive spectroscopy. Results showed that the hardness of the leucite‐silver composite material was reduced by 30% and indentation toughness improved by 47% as determined by Vickers indentation. Antibacterial characteristics of the material were investigated against Staphylococcus aureus and Escherichia coli bacteria. Scanning electron microscopy was done to see the morphology of damaged bacteria and colonies. Further, antibacterial activity was quantified using the colony formation unit counting method. All the samples showed antibacterial activity and the sample with the highest silver content, that is, 15 wt.% showed maximum potential to damage the bacteria. Inductively coupled plasma‐atomic emission spectroscopy analysis is done in phosphate buffer saline solution to quantify the amount of silver leached out from the leucite‐silver glass–ceramic samples. It was seen that the cumulative leached‐out silver over 3 days was less than 4 μg/cm2 which is well within the daily tolerance limit (5 μg/kg/day) of silver for the human body. Further, to confirm the cell viability, a cytocompatibility test is performed using L929 fibroblast and AW8507 oral cell lines. Cell viability of more than 80% was achieved, suggesting their suitability for biomedical applications. It is believed that the developed material can be a potential candidate for various applications like dental restorations, implants, and coating material for different substrates (SS 304, SS 316, Ti6Al4V, etc.) to protect them from bacterial infections and biofilm formation, etc.

Near-Theoretical Thermal Conductivity Silver Nanoflakes as Reinforcements in Gap-Filling Adhesives.

The rapid development of highly integrated microelectronic devices causes urgent demands for advanced thermally conductive adhesives (TCAs) to solve the interfacial heat-transfer issue. Due to their natural 2D structure and isotropic thermal conductivity, metal nanoflakes are promising fillers blended with polymer to develop high-performance TCAs. However, achieving corresponding TCAs with thermal conductivity over 10W m-1 K-1 at filler content below 30 vol% remains challenging so far. This longstanding bottleneck is mainly attributed to the fact that most current metal nanoflakes are prepared by "bottom-up" processes (e.g., solution-based chemical synthesis) and inevitably contain lattice defects or impurities, resulting in lower intrinsic thermal conductivities, only 20-65% of the theoretical value. Here, a "top-down" strategy by splitting highly purified Ag foil with nanoscale thickness is adopted to prepare 2D Ag nanoflakes with an intrinsic thermal conductivity of 398.2W m-1 K-1 , reaching 93% of the theoretical value. After directly blending with epoxy, the resultant Ag/epoxy exhibits a thermal conductivity of 15.1W m-1 K-1 at low filler content of 18.6 vol%. Additionally, in practical microelectronic cooling performance evaluations, the interfacial heat-transfer efficiency of the Ag/epoxy achieves ≈1.4 times that of the state-of-the-art commercial TCA.

Free Radical Scavenging and Cytotoxicity of Dimocarpus Longan Leaves Mediated Silver Nanoflakes

Objectives: To study the antioxidant and cytotoxicity of biologically synthesised silver nanoflakes using Dimocarpus longan (D. longan) leaf extract. Method: 1mM Silver nitrate is treated with 20 ml of D. longan leaves extract for 1 hour. The phytochemicals like phenols, alkaloids and flavonoids present in the aqueous leaf extract act as a reducing and stabilizing agent which reduces the silver nitrate into silver nanoflakes. Findings: The silver nanoflakes show characteristics of surface plasmon resonance at 450 nm in UV-vis spectroscopy. The FT-IR spectrum confirmed the phytoconstituent present in the leaves extracts. The XRD analysis shows the nature of silver nanoflakes. The size and stability were determined using dynamic light scattering (DLS) the values are 87.17 nm and -23 mv. The scanning electron microscope shows a poly-dispersed flake-like structure. It exhibits comparable antioxidant activity with ascorbic acid using DPPH (1, 1-diphenyl-2-picryl hydrazyl) assay and the (IC50) value was approximately 65.5 mgml-1. The remarkable cytotoxicity effect of synthesized silver nanoflakes against MDA-MB-231 and MCF-7 breast cancer cell lines is evidenced by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The Inhibitory concentration (IC-50) values examined were 138.62.18 mgml-1 and 171.52.2 mgml-1. Novelty: For the first time, the present study revealed the synthesis of silver nanoflakes of lower size using leaves extract of D. longan which was employed for its antioxidant activity and also for in vitro cytotoxic effects against breast cancer cells MDA-MB-231 and MCF-7. Keywords: Silver nanoflakes; D longan leaf; antioxidants; MTT assay and Cytotoxicity

Selective Mapping of Tip-Launched Near-Field Scattering of Surface Plasmon Polaritons for Retrieving Dispersion Relation in Silver Nanoflakes

Scattering-type near-field scanning optical microscopy (s-NSOM) has been beneficial for observing various nano-optical phenomena by overcoming the spatial resolution diffraction limit, creating optical dispersion, and investigating optoelectronic systems. We used s-NSOM on mono-crystalline silver nanoflakes to selectively decompose tip-launched surface plasmon polariton (SPP) signals and suppress the undesired geometrical effects arising from the silver nanoflakes and s-NSOM tips. Comparing the Fourier transform analysis data from all the edges of silver nanoflakes, we successfully identified the momentum of tip-launched SPPs. We have conducted energy spectral measurements on mono-crystalline silver nanoflakes and applied a geometry-independent factor: tip-launched SPP. We neglected the additional complex contribution from various shapes of the nanoflakes in the visible-near infrared regime. These experimentally obtained momentums of SPPs have a good agreement with analytical calculations. We observed that the propagation of the SPP increases with a decrease in excitation energy even without additional destructive fabrications on the surface, although the surface quality of silver nanoflakes is affected by dirt and oxidation. This study provides a precise interpretation of the experimental studies on the various polariton studies using s-NSOM.

Antibacterial Activity of Silver Nanoflake (SNF)-Blended Polysulfone Ultrafiltration Membrane

The aim of this research was to study the possibility of using silver nanoflakes (SNFs) as an antibacterial agent in polysulfone (PSF) membranes. SNFs at different concentrations (0.1, 0.2, 0.3 and 0.4 wt.%) were added to a PSF membrane dope solution. To investigate the effect of SNFs on membrane performance and properties, the water contact angle, protein separation, average pore size and molecular weight cutoffs were measured, and water flux and antibacterial tests were conducted. The antimicrobial activities of the SNFs were investigated using Escherichia coli taken from river water. The results showed that PSF membranes blended with 0.1 wt.% SNFs have contact angles of 55°, which is less than that of the pristine PSF membrane (81°), exhibiting the highest pure water flux. Molecular weight cutoff values of the blended membranes indicated that the presence of SNFs does not lead to enlargement of the membrane pore size. The rejection of protein (egg albumin) was improved with the addition of 0.1 wt.% SNFs. The SNFs showed antimicrobial activity against Escherichia coli, where the killing rate was dependent on the SNF concentration in the membranes. The identified bacterial colonies that appeared on the membranes decreased with increasing SNF concentration. PSF membranes blended with SNF, to a great degree, possess quality performance across several indicators, showing great potential to be employed as water filtration membranes.

Residual solvent-assisted facile deposition of honeycomb-like silver nanoflakes on the surface of electrospun PAN nanofibers

Nobel metal nanoparticles-decorated electrospun nanofibers (ENFs) have attracted great attention for different applications. In the present work, solvent-assisted mild UV treatment was introduced as a unique, efficient and versatile technique for the fabrication of honeycomb-like Ag nanoflakes-decorated electrospun PAN nanofibers. Freshly prepared electrospun PAN nanofibrous membrane from its DMF solution (without vacuum drying) was treated with AgNO3 solution under mild UV irradiation. Microscopic images showed that honeycomb-like Ag-nanoflakes were well decorated on ENFs. XRD showed the formation of amorphous silver materials on the surface of PAN fibers. The Ag nanoflakes-decorated nanofibers showed promising antibacterial properties. Therefore, this facile technique with proposed mechanism can open a new platform for the fabrication of noble metal nanospecies-decorated ENFs for different applications.

Low Temperature Sintered Silver Nanoflake Paste for Power Device Packaging and Its Anisotropic Sintering Mechanism

Sintered silver pastes have emerged as a kind of packaging material for wide-bandgap (WBG) power devices because of their superior electrical and thermal conductivity. Herein, silver pastes containing monodisperse triangular silver nanoflakes with a size distribution of 40–260 nm were prepared. The sintered silver joints exhibited a significant high shear strength of 49.8 MPa, larger than that of traditional silver paste, and with a relatively low porosity of 5.1%. These remarkable properties were attributed to the special anisotropic sintering process and bridging effect of the silver nanoflakes. Anisotropic sintering of the silver nanoflakes refers to the successive deformation of the corners, edges, and surfaces during sintering. Especially, the deformation of surfaces provides large diffusion paths for the silver atoms, resulting in a denser sintered silver joint. The bridging effect results from two separate silver nanoflakes that are linked by a single silver nanoflake, which increases the connection between the silver nanoflakes and thus improves the mechanical property of the sintered silver joints. This anisotropic sintering mechanism and bridging effect should inspire other researchers to investigate the sintering mechanism of other materials and optimize the performance of the corresponding pastes of these materials.

Hand-Held Raman Spectrometer-Based Dual Detection of Creatinine and Cortisol in Human Sweat Using Silver Nanoflakes.

The conventional tissue biopsy method yields isolated snapshots of a narrow region. Therefore, it cannot facilitate comprehensive disease characterization and monitoring. Recently, the detection of tumor-derived components in body fluids─a practice known as liquid biopsy─has attracted increased attention from the biochemical research and clinical application viewpoints. In this vein, surface-enhanced Raman scattering (SERS) has been identified as one of the most powerful liquid-biopsy analysis techniques, owing to its high sensitivity and specificity. Moreover, it affords high-capacity spectral multiplexing for simultaneous target detection and a unique ability to obtain intrinsic biomolecule-fingerprint spectra. This paper presents the fabrication of silver nanosnowflakes (SNSFs) using the polyol method and their subsequent dropping onto a hydrophobic filter paper. The SERS substrate, which comprises the SNSFs and hydrophobic filter paper, facilitates the simultaneous detection of creatinine and cortisol in human sweat using a hand-held Raman spectrometer. The proposed SERS system affords Raman spectrometry to be performed on small sample volumes (2 μL) to identify the normal and at-risk creatinine and cortisol groups.

Self-healing and stretchable PDMS-based bifunctional sensor enabled by synergistic dynamic interactions

The bio-integrated electronics industry is booming and becoming more integrated with biological tissues. However, it is challenging to obtain high-level self-healing of sensitivity and durability of bifunctional sensor when maintaining their long-term fatigue-resistance and high stretchability. Herein, a high performance self-healable bifunctional sensor was demonstrated through synergistic dynamic interactions between polysiloxane and silver nanoflakes (AgFs) and in-situ formed silver nanoparticles (AgNPs). The bifunctional sensor showed high sensitivity (gauge factor reached 39.5), exceptional electrical self-healability (at ambient temperature), and durability (more than 1000 cycles) by virtue of superflexible siloxane chains in the self-healing polymer, strong dynamic silver-thiolate coordination interactions, and the migration of silver nanoparticles. Finally, multiple human motions and health status were monitored, even after multiple cycles of healing, these “self-healed” sensing signals were still extremely consistent with the pristine ones, indicating the excellent reliabilities and healing stabilities of the bifunctional sensor.

Multi-length scale hierarchical architecture overcoming pressure sensing range-speed tradeoff for skin electronics

Ultra-sensitive pressure sensing is provided hierarchically, on the nanoscale by contact between silver nanoflakes and LIG nanosheets, and on the microscale by contact between AgMFs and LIG.

Facile preparation of wearable heater based on conductive silver paste with low actuation voltage and rapid response

Towards emerging electric heaters for wearable electronics, actuators and high-performance heating systems, various properties including flexibility, low actuation voltage, rapid response, facile adaptability, thermal and mechanical stability are highly desired. Herein, a high-performance heater based on commercial conductive silver paste is proposed, through quite simple scrape coating, painting and pen writing. Benefiting from its excellent viscosity, the silver paste can be firmly coated on a variety of substrates, even including hydrophobic and oleophobic polytetrafluoroethylene and cotton thread of high curvature. After curing the silver paste, the silver nanoflakes inside are encapsulated in a polymer framework and are closely interconnected, forming a reliable conductive network with low sheet resistance ( $${\text{minimum }}0.{18 }\Omega /{\text{sq}}$$ ). This structure protects the silver nanoflakes from oxidation and provides this flexible silver heater (FSH) excellent thermal and mechanical stabilities, as demonstrated by long-time heating, cyclic heating and multiple deformation tests. The FSH achieves high surface temperature (280 °C) at a low operation voltage (2 V), with rapid thermal response time (less than 7 s). The application demonstrations of FSHs in custom-shaped wearable heaters and heating patterns, thermal therapy, flexible heating thread and thermal switch suggest the distinct advantages of FSHs in flexible and wearable devices.

Synthesis of silver nanoflakes on chitosan hydrogel beads and their antimicrobial potential

The present study involves the fabrication of CH and CH-Ag hydrogel beads and the investigation of the antimicrobial properties. The beads were fabricated using a simple coacervation method. The successfully synthesized beads were characterized by UV-Vis and FTIR. The surface morphology, shape and diameter of the samples were determined by optical microscopy and SEM. The antimicrobial activities were determined against potential human pathogens including bacterial and fungal species. Our results demonstrated that beads can be utilized as potential materials for use in biomedical approaches including delivery systems and tissue engineering applications to prevent microbial contamination and to inhibit the growth of microorganisms.

Regulation of multidimensional silver nanostructures for high-performance composite conductive adhesives

Electrically conductive adhesives (ECAs) are widely used in electronics and silver-based ECA is one of the most typical representatives. In this work, a trinary silver-based filler strategy was proposed to achieve ECAs with high conductivity and low silver content, where silver fractal flowers (Ag-FWs) were used to set up the conductive framework and silver nanowires (Ag-NWs) and silver nanoflakes (Ag-NFs) were added to connect the separated domains and fill the small gaps, respectively. The ECAs reached a low electrical resistivity of 6.0 × 10−5 Ω cm and high adhesion strength of 13.5 MPa when the addition of Ag-FWs, Ag-NWs and Ag-NFs were 50 wt%, 7.5 wt% and 2.5 wt%, respectively, superior to those reported ECAs of 80 wt% silver loading. Besides, the ECA circuit fabricated by 3D printer demonstrated good electrical conductivity and resistance stability. The preparation idea of ECAs brings novel opportunities for the development of the electronic packaging industries.

From Silver Nanoflakes to Silver Nanonets: An Effective Trade-Off between Conductivity and Stretchability of Flexible Electrodes.

Flexible and stretchable conductive materials have received significant attention due to their numerous potential applications in flexible printed electronics. In this paper, we describe a new type of conductive filler for flexible electrodes—silver nanonets prepared through the “dissolution–recrystallization” solvothermal route from porous silver nanoflakes. These new silver fillers show characteristics of both nanoflakes and nanoparticles with propensity to form interpenetrating polymer–silver networks. This effectively minimizes trade-off between composite electrode conductivity and stretchability and enables fabrication of the flexible electrodes simultaneously exhibiting high conductivity and mechanical durability. For example, an electrode with uniform, networked silver structure from the flakiest silver particles showed the lowest increase of resistivity upon extension (3500%), compared to that of the electrode filled with less flaky (3D) particles (>50,000%).

DNA-Capped Silver Nanoflakes as Fluorescent Nanosensor for Highly Sensitive Imaging of Endogenous H2S in Cell Division Cycles.

Biochemical sensing is essential toward gaining a full understanding of various physiological and pathological events. The in vivo level of hydrogen sulfide (H2S), the third endogenous gaseous transmitter, is closely related to its biological functions at different phases of the cell division cycle. Here we report a facile strategy for H2S sensing in live cells at different phases of cell division by developing a fluorescent nanosensor with double-strand DNA (dsDNA)-stabilized silver nanoflakes (AgNF@dsDNA). The sensing principle is based on selective etching of AgNF@dsDNA by H2S, followed by conversion to Ag2S. AgNFs initially act as quenchers through surface energy transfer, and then its etching leads to fluorescence recovery of modified fluorophore and efficient fluorescence resonance energy transfer (FRET) between two fluorophores. The changes of FRET signal as the readout successfully enable semiquantitative imaging of endogenous H2S alterations in live cells at G1, S, and G2, followed by the cycle of mitosis and cytokinesis. The optimized nanosensor has an excellent linear response in the concentration range of 1-10 μM Na2S. It can also differentiate G0 from G1 and other cell cycle steps through fluorescence imaging of changes in the level of endogenous H2S in cytoplasm during cell division cycle. Thus, the present study paves the way toward utilizing new Ag nanomaterials for biological imaging and sensing in live cells during different phases of the cell division cycle.

Bioelectrochemical recovery of silver from wastewater with sustainable power generation and its reuse for biofouling mitigation

Precious metals recovery and wastewater treatment using the microbial fuel cell (MFC) is an attractive approach for a sustainable environment. Silver recovery from wastewater and its valorization in the form of silver nanoflakes (AgNFs) brings back waste material to production stream and helps in transition from linear to circular economy. In the present study, bioelectrochemical performance of MFC fed with silver laden artificial wastewater (MFC-Ag) was compared with MFC fed with potassium ferricyanide (MFC-FC) and MFC fed with phosphate buffer as catholyte (MFC-blank). High silver removal (83 ± 0.7%) and recovery (67.8 ± 1%) efficiencies were achieved from MFC-Ag after 72 h operation. The maximum power density (3006 mW/m3) and current density (34100 mA/m3) of MFC-Ag were found to be significantly higher than the MFC-FC and MFC-blank. High chemical oxygen demand (COD) removal efficiency of MFC-Ag (82.7 ± 1.5%) compared with MFC-FC (76 ± 2) highlighted the suitability of silver laden wastewater as a cost effective catholyte. The high coulombic efficiency (8.73 ± 0.9%) and low solution resistance (24.38 Ω) for MFC-Ag also indicate the potential of silver laden wastewater for large scale applications. Analytical characterizations of electrochemically recovered silver revealed the pure (99%) and crystalline AgNFs with a mean diameter of 18 ± 1.2 nm on the cathode surface. Furthermore, a significant anti-biofouling activity of recovered AgNFs indicate the valorization of waste by current study with potential applications in several industrial and environmental processes. Our method has diverse potential to scale up the MFC technology for industrial waste management as a closed loop process with minimum facilities and higher sustainability.

Ultratrace Naked-Eye Colorimetric Ratio Assay of Chromium(III) Ion in Aqueous Solution via Stimuli-Responsive Morphological Transformation of Silver Nanoflakes.

In this work, we discover an effective domino-effect-based detection mechanism for the rapid, high-selectivity, and ultrasensitive naked-eye colorimetric ratio assay of chromium(III) ion (Cr3+) in aqueous solutions. This naked-eye colorimetric ratio assay to Cr3+ relies on changes in absorbance properties that are due to the stimuli response of Cr3+ for the morphological transformation of silver nanoflakes. In the presence of Cr3+, large silver nanoflakes can be stimulated to transform to small nanoparticles (NPs), which promoted a color change in solution from bright yellow to wine red that was detected by the naked eye and spectroscopic absorption methods. The proposed naked-eye sensing strategy was coupled with an ultraviolet (UV)-spectroscopic chemosensor for the detection of trace Cr3+. The detection method showed an ultralow detection limit of 1.4 nM (nanomole) for Cr3+ in ultrapure water and 11.5 nM in human serum sample, respectively. On the basis of colorimetry, the lowest concentration of ∼50 nM for Cr3+ in ultrapure water and human serum can be detected by the naked eye. This naked-eye-based colorimetric ratio assay for accurate and selective identification and high sensitivity of Cr3+ is expected to have large potential and wide applications such as pharmaceutical analysis, clinical diagnosis, and environmental monitoring.