Silver-coated Carbon Nanotubes Research Articles

Hardness and electrical conductivity of uncoated and silver coated carbon nanotubes reinforced copper nanocomposites

Hardness and electrical conductivity of uncoated and silver coated carbon nanotubes reinforced copper nanocomposites

A high gauge-factor wearable strain sensor array via 3D printed mold fabrication and size optimization of silver-coated carbon nanotubes

The development of 3D print technology provided an opportunity to achieve fast and accurate fabrication of wearable sensor arrays. In this paper, high-sensitivity flexible and stretchable silver-coated carbon nanotube (Ag@CNT) wearable strain sensor arrays are fabricated using 3D printing technology and composite nanomaterial synthesis. Ag@CNTs with uniform and compact particles were synthesized with different sizes of carbon nanotubes (CNTs) using a reduction method. Strain sensor arrays were fabricated accurately and efficiently with the aid of 3D printed molds. Sensors with different Ag@CNTs were then compared comprehensively, and it was found that the Ag@CNT (short) sensor, which had a gauge factor (GF) of 62.8 in the 0% to 14.44% stretch range and a GF of 831.3 in the 14.44% to 21.11% stretch range, can significantly enhance the detection of small movements. These wearable strain sensor arrays were utilized in the application of traditional Chinese medicine pulse diagnosis and gesture recognition.

A three-dimensional human skin model to evaluate the inhibition of Staphylococcus aureus by antimicrobial peptide-functionalized silver carbon nanotubes.

To investigate the toxicity and antibacterial application of antimicrobial peptide-functionalized silver-coated carbon nanotubes against Staphylococcus infection using a full thickness human three-dimensional skin model. The three-dimensional skin formation on the scaffolds was characterized by electron microscopy and investigation of several skin cell markers by real time-reverse transcriptase polymerase chain reaction. Functionalized silver-coated carbon nanotubes were prepared using carboxylated silver-coated carbon nanotubes with antimicrobial peptides such as TP359, TP226 and TP557. Following the characterization and toxicity evaluation, the antibacterial activity of functionalized silver-coated carbon nanotubes against Staphylococcus aureus was investigated using a bacterial enumeration assay and scanning electron microscopy. For this purpose, a scar on the human three-dimensional skin grown on Alvetex scaffold using keratinocytes and fibroblasts cells was created by taking precaution not to break the scaffold beneath, followed by incubation with 5 µg/mL of functionalized silver-coated carbon nanotubes re-suspended in minimum essential medium for 2 h. Post 2-h incubation, 200 µL of minimum essential medium containing 1 × 104 colony forming units of Staphylococcus aureus were incubated for 2 h. After incubation with bacteria, the colony forming unit/gram (cfu/g) of skin tissue were counted using the plate count assay and the samples were processed for scanning electron microscopy analysis. MTT assay revealed no toxicity of functionalized silver-coated carbon nanotubes to the skin cells such as keratinocytes and fibroblasts at 5 µg/mL with 98% cell viability. The bacterial count increased from 104 to 108 cfu/g in the non-treated skin model, whereas skin treated with functionalized silver-coated carbon nanotubes showed only a small increase from 104 to 105 cfu/g (1000-fold viable cfu difference). Scanning electron microscopy analysis showed the presence of Staphylococcus aureus on the non-treated skin as opposed to the treated skin. Thus, our results showed that functionalized silver-coated carbon nanotubes are not only non-toxic, but also help reduce the infection due to their antibacterial activity. These findings will aid in the development of novel antibacterial skin substitutes.

Proteomic analysis of antimicrobial effects of pegylated silver coated carbon nanotubes in Salmonella enterica serovar Typhimurium

BackgroundSynthesis of silver nano-compounds with enhanced antimicrobial effects is of great interest for the development of new antibacterial agents. Previous studies have reported the antibacterial properties of pegylated silver-coated carbon nanotubes (pSWCNT-Ag) showing less toxicity in human cell lines. However, the mechanism underlining the pSWCNT-Ag as a bactericidal agent remained unfolded. Here we assessed the pSWCNT-Ag effects against foodborne pathogenic bacteria growth and proteome profile changes.ResultsMeasurements of bioluminescent imaging, optical density, and bacteria colony forming units revealed dose-dependent and stronger bactericidal activity of pSWCNT-Ag than their non-pegylated counterparts (SWCNT-Ag). In ovo administration of pSWCNT-Ag or phosphate-buffered saline resulted in comparable chicken embryo development and growth. The proteomic analysis, using two-dimensional electrophoresis combined with matrix assisted laser desorption/ionization time of flight/time of flight mass spectrometry, was performed on control and surviving Salmonella enterica serovar Typhimurium to pSWCNT-Ag. A total of 15 proteins (ten up-regulated and five down-regulated) differentially expressed proteins were identified. Functional analyses showed significant reduction of proteins associated with biofilm formation, nutrient and energy metabolism, quorum sensing and maintenance of cell structure and cell motility in surviving S. Typhimurium. In contrast, proteins associated with oxygen stress, DNA protection, starvation, membrane rebuilding, and alternative nutrient formation were induced as the compensatory reaction.ConclusionsThis study provides further evidence of the antibacterial effects of pSWCNT-Ag nanocomposites and knowledge of their mechanism of action through various protein changes. The findings may lead to the development of more effective and safe antimicrobial agents.

Ag‐CNT Architectures for Attomolar Dopamine Detection and 100‐Fold Fluorescence Enhancements with Cellphone‐Based Surface Plasmon‐Coupled Emission Platform

We report cellphone-based detection of dopamine with attomolar sensitivity in clinical samples with the use of a surface plasmon-coupled emission (SPCE) platform. To this end, silver-coated carbon nanotubes were used as spacer and cavity materials on SPCE substrates to obtain up to 100-fold fluorescence enhancements. The presence of silver on the carbon nanotubes helped to overcome fluorescence quenching arising due to π-π interactions between the carbon nanotube and rhodamine 6G. The competing adsorption of dopamine versus rhodamine 6G on graphene oxide was utilized to develop this sensing platform.

Silver-coated carbon nanotubes downregulate the expression of Pseudomonas aeruginosa virulence genes: a potential mechanism for their antimicrobial effect.

The antimicrobial activity of silver-coated carbon nanotubes (AgCNTs) and their potential mode of action against mucoid and nonmucoid strains of Pseudomonas aeruginosa was investigated in vitro. The results showed that AgCNTs exhibited antimicrobial activity against both strains with minimum inhibitory concentrations of approximately 8 µg/mL, indicating a high sensitivity of P. aeruginosa to AgCNTs. AgCNTs were also bactericidal against both strains at the same minimum inhibitory concentration. Scanning and transmission electron-microscopy studies further revealed that a majority of the cells treated with AgCNTs transformed from smooth rod-shape morphology to disintegrated cells with broken/damaged membranes, resulting in leakage of cytoplasmic contents to produce ghost cells. The molecular effects of AgCNTs on P. aeruginosa genes involved in virulence and pathogenicity, stress response, and efflux pumps were evaluated for changes in their expression. Quantitative real-time PCR (qRT-PCR) showed that after exposure to AgCNTs, the expression levels of the rpoS, rsmZ, and oprD genes were significantly downregulated in both strains of P. aeruginosa compared to the untreated samples. These results suggest that the mechanism of action of AgCNTs may be attributed to their effect on cell-membrane integrity, downregulation of virulence-gene expression, and induction of general and oxidative stress in P. aeruginosa.

Novel pegylated silver coated carbon nanotubes kill Salmonella but they are non-toxic to eukaryotic cells.

BackgroundResistance of food borne pathogens such as Salmonella to existing antibiotics is of grave concern. Silver coated single walled carbon nanotubes (SWCNTs-Ag) have broad-spectrum antibacterial activity and may be a good treatment alternative. However, toxicity to human cells due to their physico-chemical properties is a serious public health concern. Although pegylation is commonly used to reduce metal nanoparticle toxicity, SWCNTs-Ag have not been pegylated as yet, and the effect of pegylation of SWCNTs-Ag on their anti-bacterial activity and cell cytotoxicity remains to be studied. Further, there are no molecular studies on the anti-bacterial mechanism of SWCNTs-Ag or their functionalized nanocomposites.Materials and methodsIn this study we created novel pegylated SWCNTS-Ag (pSWCNTs-Ag), and employed 3 eukaryotic cell lines to evaluate their cytotoxicity as compared to plain SWCNTS-Ag. Simultaneously, we evaluated their antibacterial activity on Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) by the MIC and growth curve assays. In order to understand the possible mechanisms of action of both SWCNTs-Ag and pSWCNTs-Ag, we used electron microscopy (EM) and molecular studies (qRT-PCR).ResultspSWCNTs-Ag inhibited Salmonella Typhimurium at 62.5 μg/mL, while remaining non-toxic to human cells. By comparison, plain SWCNTs-Ag were toxic to human cells at 62.5 μg/mL. EM analysis revealed that bacteria internalized either of these nanocomposites after the outer cell membranes were damaged, resulting in cell lysis or expulsion of cytoplasmic contents, leaving empty ghosts. The expression of genes regulating the membrane associated metabolic transporter system (artP, dppA, and livJ), amino acid biosynthesis (trp and argC) and outer membrane integrity (ompF) protiens, was significantly down regulated in Salmonella treated with both pSWCNTs-Ag and SWCNTs-Ag. Although EM analysis of bacteria treated with either SWCNTs-Ag or pSWCNTs-Ag revealed relatively similar morphological changes, the expression of genes regulating the normal physiological processes of bacteria (ybeF), quorum sensing (sdiA), outer membrane structure (safC), invasion (ychP) and virulence (safC, ychP, sseA and sseG) were exclusively down regulated several fold in pSWCNTs-Ag treated bacteria.ConclusionsAltogether, the present data shows that our novel pSWCNTs-Ag are non-toxic to human cells at their bactericidal concentration, as compared to plain SWCNTS-Ag. Therefore, pSWCNTs-Ag may be safe alternative antimicrobials to treat foodborne pathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0085-5) contains supplementary material, which is available to authorized users.

Ultrasonic-Assisted Electroless Plating of Silver Nanoparticles on Carbon Nanotubes

The purpose of this work was to study coating process of high dispersion silver particles on short single-walled carbon nanotubes (Short-SWCNTs) by electroless plating method with an assistance of ultrasonic agitation. The silver-coated carbon nanotubes were prepared and characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). The results revealed that silver particles with average sizes of 42±0.006 nm, 58±0.008 nm and 59±0.005 nm were achieved using ultrasonic-assisted electroless plating time of 15 min, 30 min and 45 min, respectively. The silver particle size was increased with increasing electroless plating time. Besides, the ultrasonic agitation promoted well dispersion and homogeneity of silver particles on the surface of carbon nanotubes.

Antibacterial and Ultra Microscopic Studies of Salmonella Inhibited by Silver Coated Carbon Nanotubes

There is an urgent need for newer antimicrobial agents to prevent or treat Salmonella enterica serovar Typhimurium foodborne illness. Silver coated carbon nanotubes (AgCNTs) are attractive candidates as these nanocomposites may have tremendous mechanical strength, nanometer diameter, high aspect ratios of length to diameter, and potential antimicrobial properties of silver. To investigate this hypothesis, we conducted a time line analysis of the antibacterial activity of AgCNTs against Salmonella enterica serovar Typhimurium using SEM, TEM, and AFM. Antibacterial studies were also conducted using the Kirby-Bauer disc diffusion assay, the bacterial growth curve assay, the standard plate count assay, and quantitative real-time PCR. In the Kirby-Bauer assay, AgCNTs at a concentration of 50 µg/mL showed an inhibition zone of 24.1 + 4.14 mm for Salmonella, while the growth curve assay showed that the lag phase was prolonged, and bacterial growth was reduced by 29.5%, as compared to the negative control. The standard plate count assays showed that the Minimum Inhibitory concentration of AgCNTs was between 50 - 100 µg/mL. Quantitative real-time PCR analysis showed that there was a dose-dependent reduction in Salmonella ttrRSBCA locus DNA concentration after exposure to AgCNTs. By comparison to AgCNTs, commercial silver nanoparticles or CNTs alone did not inhibit bacterial growth or gene expression significantly as tested by the assays mentioned above. SEM studies showed that the AgCNTs damaged the bacterial membranes with marked changes in morphology; TEM studies also confirmed the presence of fewer bacterial cells with damaged membranes. AFM studies are currently being conducted to further assess the mechanism by which AgCNTs inhibit Salmonella enterica serovar Typhimurium.

Investigation on the Preparation of Silver Coated Carbon Nanotubes (SCCNT) and SCCNT/Polyacrylate Composite Coatings for Electromagnetic Interference Shielding

A novel method to prepare silver coated carbon nanotubes (SCCNT) for electromagnetic interference (EMI) shielding was demonstrated that multi-walled carbon nanotubes (MWCNTs) were applied to electroless nickel-phosphorus (Ni-P) deposition, followed by electroless Ag plating. The microstructure and morphology of as-prepared SCCNT were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The results showed that the Ag coating on MWCNTs was continuous and compact. The as-prepared SCCNT/polyacrylate composite coatings exhibited a low resistivity of 1.1 mΩ·cm and a high EMI shielding effectiveness (SE) of more than 46.5 dB in the frequency range from 3.95 to 5.85 GHz.

Label-free SERS detection of relevant bioanalytes on silver-coated carbon nanotubes: The case of cocaine

Surface-enhanced Raman scattering (SERS) spectroscopy can be used for the label-free determination and quantification of relevant small biometabolites that are hard to identify by conventional immunological methods, in the absence of labelling. In this work, detection is based on monitoring the vibrational changes occurring at a specific biointerface (a monoclonal antibody, mAb) supported on silver-coated carbon nanotubes (CNT@Ag). Engineered CNT@Ag play a key role, as they offer a stable substrate to support the biointerface, with a high density of hot spots. Proof of concept is demonstrated through the analysis and quantification of the main cocaine metabolite benzoylecgonine. These results open a new avenue toward the generation of portable sensors for fast ultradetection and quantification of relevant metabolites. The use of discrete particles (CNT@Ag@mAb) rather than rough films, or other conventional SERS supports, will also enable a safe remote interrogation of highly toxic sources in environmental problems or in biological fluids.

Properties investigation on isotropical conductive adhesives filled with silver coated carbon nanotubes

In this study, chemical plating method was used to prepare silver coated carbon nanotubes (SCCNT). Fundamental materials characterizations including X-ray diffraction and transmission electro microscopy (TEM) were conducted on these nanotubes. Two kinds of isotropical conductive adhesives (ICA) were developed by using multi-walled carbon nanotubes (CNT), SCCNT as conductive fillers, respectively. The electrical, mechanical and aging properties of above ICAs were investigated and compared with that of conventional ICA filled with 1 μm average-sized Ag particles. The results indicated that the percolation threshold of bulk resistivity reaches 2.4 × 10 −3 Ω cm for ICA filled with 31% CNT and the shear strength reaches the maximum value for ICA filled with 23% CNT. At the same filler volume content of 28%, the ICAs filled with SCCNT shows the lowest conductive resistivity of 2.2 × 10 −4 Ω cm and the ICAs filled with both CNT and SCCNT exhibit higher shear strength (19.6 MPa). The testing results of aging properties under conditions of 85 °C, RH85% for 1000 h showed that the shifts of both bulk resistivity and shear strength did not exceed 15% for the ICAs filled with both CNT and SCCNT, while the shifts of conductive resistivity and shear strength were 200% and 35%, respectively, for ICA filled with micro-sized Ag particles.

Gold and silver coated carbon nanotubes: An improved broad-band optical limiter

5-nm-thick coatings of polycrystalline gold and polycrystalline silver were deposited on multiwalled carbon nanotubes. Their optical limiting properties were studied as a suspension in water at 532 and 1064 nm wavelengths by nanosecond laser pulses. Experiments show that they possess stronger OL performance compared to pure carbon nanotubes at 532 nm, but there were no visible OL enhancements at 1064 nm. We propose surface plasma absorption of Au and Ag as the mechanism responsible for the enhancement of nonlinear scattering effects. Our study provides evidence that coating carbon nanotubes with polycrystalline Au or Ag is a simple and effective method for improving OL performance.