Ag Nanotriangles Research Articles

Selective colorimetric sensing of histidine in aqueous media via Ag nanotriangles in the presence of HgCl2

Silver nanotriangles (AgNTs) were successfully synthesized as a colorimetric probe for selective and sensitive histidine detection in aqueous media within a 15–100 µM range and a detection limit of 330 nM using UV–Vis spectroscopy. The interaction of HgCl2 with AgNTs would lead to the formation of disk-shaped Ag/Hg amalgam as observed from the transmission electron images and X-ray diffraction patterns. Histidine prevents these structural and morphological changes and accordingly, the detection approach was developed based on the correlation between the histidine concentration and the in-plane dipole plasmon resonance (DPR) intensity.

Chemically engineered nano selective silver shapes: Novel synthesis and their potential activity as anti-candida agents

Oral candidiasis (OC) is an infection of oral mucosa caused by fungal overgrowth, especially Candida albicans due to its ability to form biofilms and the increased expression of virulence factors. In the present study, Ag Nano sphere & Ag Nano triangle were newly synthesized using Juniperus drupacea L leaves extract to combat the OC infections. Ag Nano sphere & Ag Nano triangle antifungal activity, mechanism of action against OC, and cytotoxic effect in L929 (ATCC CCL-1 NCTC) fibroblast cell monolayers were evaluated. The J. drupacea phytochemical analysis revealed the presence of three major compounds: α-pinene (34.27 %), thymol methylether (15.20 %) and camphor (9.01 %). The proposed synthesis approach includes the reduction of Ag+ by Juniperus drupacea L leaves extract to form Ag Nano spheres. One the other hand, the presence of polyvinylpyrrolidone (PVP) in the reaction mixture led to obtaining Ag Nano triangle shapes. The minimal fungicidal concentration (MFC) and minimal biofilm eradication concentration (MBEC) assays revealed the higher antifungal effect of Ag Nano sphere when compared to Ag Nano triangle. MFC of Ag Nano sphere and Nano triangle reached 62.5 and 125 µg/mL respectively. While MBECs were ranged between 4 and 32 and 16–64 µg/mL upon using Ag Nano sphere and Nano triangle respectively. The possible mechanism of action of the synthesized Ag Nano shapes was the attributed to the direct effect on the cell membrane especially after 6 h incubation. In vitro cytotoxic effect of the prepared Ag-Nano sphere on cell proliferation using L929 (ATCC CCL-1 NCTC) fibroblast cell monolayers suggested the Ag-Nano spheres are safe for possible biomedical application.

Disentangling the "tip-effects" enhanced antibacterial mechanism of Ag nanoparticles.

Silver nanoparticles (Ag NPs) exhibit strong antibacterial activity and are widely used in industries such as medical, food and cosmetics. In this study, Ag nanospheres and Ag nanotriangles are selected as antibacterial agents to reveal the distinct mechanism of tip effects towards their antibacterial performance. A series of antibacterial experiments were implemented, including in situ monitoring as well as studying and determining the evolution of the inhibition zone, minimum inhibitory concentration (MIC)/minimum bactericidal concentration (MBC) values, growth kinetics, bactericidal curve, bacterial morphologies and intracellular reactive oxygen species (ROS). Ag nanotriangles can eradicate E. coli and S. aureus at extremely low concentrations in comparison to Ag nanospheres, in particular under sunlight irradiation. The destroyed bacterial cell walls were examined by scanning electron microscopy. Through the investigation of ROS production, the generation efficiency of ROS is improved by the merit of sunlight irradiation thanks to the localized surface plasmon resonance (LSPR) properties of Ag NPs. However, a more significant improvement in ROS generation efficiency occurred in the presence of Ag nanotriangles contributed by the pronounced "tip effects". This study sheds light on the structure-performance relationship for the rational design of antibacterial agents.

Energy-efficient resistive switching synaptic devices based on patterned Ag nanotriangles with tunable gaps fabricated using plasma-assisted nanosphere lithography.

The development of synaptic devices featuring metallic nanostructures with brain-analog hierarchical architecture, capable of mimicking cognitive functionalities, has emerged as a focal point in neuromorphic computing. However, existing challenges, such as inconsistent and unpredictable switching, high voltage requirements, unguided filament formation, and detailed fabrication processes, have impeded technological progress in the domain. The present study addresses some of these challenges by leveraging periodic nanostructures of Ag fabricated via plasma-assisted nanosphere lithography (NSL). The triangular nanostructures with a preferred orientation offer enhanced localized electric fields, facilitating low voltage electromigration at the sharp edges to guide predictive filament formation. A thorough investigation into gap control between the nanostructures through oxygen plasma treatment enables the attainment of an optimized low switching voltage of 0.86 V and retention at an ultra-low current compliance of 100 nA. The optimized device consumes low power, typically in the fJ range, akin to biological neurons. Furthermore, the device showcases intriguing synaptic characteristics, including controlled transition from short- to long-term potentiation, associative learning, etc., projecting its potential in perceptive learning, memory formation, and brain-inspired computing. COMSOL Multiphysics simulation, supported by ex situ electron microscopic imaging, confirms the controlled and predictable filament formation facilitated by electric field enhancement across the strategic nanostructures. Thus, the work highlights the potential of NSL-based cost-effective fabrication techniques for realizing efficient and biomimetic synaptic devices for neuromorphic computing applications.

Large-area arrays of epitaxially aligned silver nanotriangles seeded by gold nanostructures

The work represents a first-of-its-kind demonstration in that flat-lying Ag nanotriangles have never before been grown directly on substrate surfaces in organized patterns.

Plasmon-induced near-infrared fluorescence enhancement of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) emit near-infrared (NIR) fluorescence that is ideal for optical sensing. However, the low quantum yields diminish the sensor’s signal-to-noise ratio and limits the penetration depths for in vivo measurements. In this study, we perform a systematic investigation of the plasmonic effects of Ag and Au nanoparticles of various geometries to tune and even enhance the fluorescence intensity of single-stranded DNA-wrapped SWCNTs (ssDNA-SWCNTs). We observe a chirality-dependent NIR fluorescence enhancement that varies with both nanoparticle shape and material, with Au nanorods increasing (7, 5) and (7, 6) chirality emissions by 80% and 60% and Ag nanotriangles increasing (7, 5) and (6, 5) emissions by 200% and 240%, respectively. The chirality-dependent enhancement was modeled using finite element modeling (FEM), which confirms contributions not only from a plasmon-induced localized increase in electron density but also from the radiative recombination of dark exciton states from the resulting electromagnetic field. Finally, we demonstrate the application of these nanoparticles in enhancing the single-molecule fluorescence of individual SWCNTs imaged in a custom-built confocal setup. The plasmonically coupled sensors show four orders of magnitude greater sensitivity towards ferricyanide, a model analyte, compared to the non-coupled sensors. Plasmonic nanoparticles thus provide a tunable means of modulating SWCNT fluorescence to study fundamental transitions of otherwise forbidden states and to improve the optical sensing performance.

Enhancement of Raman Scattering and Exciton/Trion Photoluminescence of Monolayer and Few-Layer MoS2 by Ag Nanoprisms and Nanoparticles: Shape and Size Effects

The metal nanoparticle size and shape impact the plasmonic enhancement of Raman and photoluminescence (PL) spectra of monolayer and few-layer MoS2 decorated with them. The plasmonic enhancement is investigated for Ag nanotriangles (NTs or nanoprisms) of different sizes in comparison to Ag nanospheres (NSs) at room temperature. After the decoration with Ag NTs, the intensity of both Raman modes of MoS2 increases up to 6.8 times. The μ-PL spectra of bare MoS2 show the presence of the A and B exciton bands as well as of a weak trion component. After covering the flakes with 50 nm Ag NTs, the highest integrated PL enhancement factors are 2.9 and 2.1 under 532 and 405 nm excitations, respectively. The revealed shape effect is that Ag NTs provide much stronger Raman and exciton emission enhancement than Ag NSs, which is due to the generation of plasmonic hot spots near the sharp edges and tips of NTs. Another mechanism of enhancement is the plasmonic coupling between the neighboring Ag NTs that causes the generation of hot spots in the gap between NTs. The revealed size effect is a decrease of Raman and PL enhancement with an increase in size of Ag NTs or NSs, which is due to an increase in radiative damping of plasmon oscillation occurring with an increase in nanoparticle size. The important feature is a strong enhancement of the A– trion component after decorating MoS2 with Ag nanoparticles. The phenomenon may be explained by the surface-plasmon-mediated generation of hot electrons in Ag nanostructures, which then inject to MoS2 flakes. This work gives new fundamental insights into the physical mechanisms of light–matter coupling in hybrid two-dimensional (2D) semiconductor/plasmonic nanoparticle structures, which are highly promising for next-generation optoelectronic and nanophotonic devices.

Colorimetric Detection of Uric Acid with High Sensitivity Using Cu2O@Ag Nanocomposites

In this paper, we built the Cu2O@Ag nanocomposites-catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB)–H2O2 system for sensitive, rapid, and low-cost colorimetric sensing of uric acid (UA). Firstly, Ag nanotriangles were synthesized by dynamic method, and then Cu2O was encapsulated on the nanoflakes to synthesize Cu2O@Ag nanocomposites. Characterization of the structure and morphology of nanocomposites material were characterized by transmission electron microscopy, X-ray energy-dispersive spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Cu2O@Ag nanocomposites could catalyze the oxidation of TMB by H2O2 (which is produced by enzymatic oxidation of UA), and the color changes from colorless to blue can be observed directly with the naked eyes or can be detected by UV–Vis spectrophotometer. The colorimetric sensor provided a linear absorbance response in the 0.5–100 μM UA concentration range with a 0.4 μM detection limit (S/N = 3). The recovery of UA in human serum by the proposed sensor is over 95.7%. Thus, these results imply that the UA sensor provides an effective tool in fast clinical analysis of gout without the need for expensive and advanced equipment.

Plasmonic-Enhanced Oxygen Reduction Reaction of Silver/Graphene Electrocatalysts.

Oxygen reduction reaction (ORR) is of paramount importance in polymer electrolyte membrane fuel cells due to its sluggish kinetics. In this work, a plasmon-induced hot electrons enhancement method is introduced to enhance ORR property of the silver (Ag)-based electrocatalysts. Three types of Ag nanostructures with differently localized surface plasmon resonances have been used as electrocatalysts. The thermal effect of plasmonic-enhanced ORR can be minimized in our work by using graphene as the support of Ag nanoparticles. By tuning the resonance positions and laser power, the enhancement of ORR properties of Ag catalysts has been optimized. Among these catalysts, Ag nanotriangles after excitation show the highest mass activity and reach 0.086 mA/μgAg at 0.8 V, which is almost 17 times that of a commercial Pt/C catalyst after the price is accounted. Our results demonstrate that the hot electrons generated from surface plasmon resonance can be utilized for electrochemical reaction, and tuning the resonance positions by light is a promising and viable approach to boost electrochemical reactions.

Facile and on−line colorimetric detection of Hg2+based on localized surface plasmon resonance (LSPR) of Ag nanotriangles

A rapid and sensitive colorimetric detection method for the determination of Hg2+ has been successfully developed in this research. Citrate−functionalized silver nanotriangles (AgTrngs) were synthesized via one−pot sodium borohydride method with the edge−length range of 30 − 40 nm. The obtained AgTrngs were fully characterized using UV−Vis spectrophotometry, transmission electron microscopy (TEM), energy dispersed spectroscopy (EDS) and X−ray diffractometer. The efficiency of the developed sensor was optimum at pH= 8 due to interfering effect of H+ ions for Hg2+ under acidic conditions. The successful detection of mercury in aqueous solutions in the concentration range of 10 nmol L−1–50 μmol L−1 indicated the applicability of the developed sensor for effective monitoring and controlling the level of Hg2+ in industrial effluents. The ability of Hg2+ ion to interact with Ag and form the Hg−Ag alloy (amalgam) over the surface of AgTrngs resulted in an obvious color change from blue to violet. UV−Vis spectrophotometry showed that the sensor has the limit of detection (LOD) value of as low as 4 nmol L−1 which was below the safety level of Hg2+ions (10 nmol L−1) in drinking water. The proposed method can be used for on−line determination of Hg2+ in the complex aqueous solutions.

Optical properties of silver nanoplates and perspectives for biomedical applications

Silver nanoplates of triangular shapes have attractive optical extinction spectrum with multipolar resonance modes. In this work, we investigate the optical properties of Ag nanotriangles and evaluate the feasibility of using it on LSPR biosensing and on photodynamic therapy. Three dimensional finite element simulation and experimental analyses were explored on the assessment of the LSPR spectrum and spatial distribution of the electromagnetic field enhancement near metallic nanoplates, with different altitude length and thickness. Refractive index based sensitivity (406 nm/RIU) and figure of merit (2.6) values were measured for AgNPls colloids, and attributed to dipole LSPR near field enhancement at the tips of the nanostructure. It was observed that LSPR field enhancement extend for more than 18 nm from the nanoparticle surface, indicating the viability of using the nanoplates on molecular sensing. The interaction of Ag nanoplates with Methylene Blue photosensitizer was also appraised, and a 2.2–fold metal enhanced single oxygen generation was determined. Our results indicate that Ag nanotriangles are promising candidates for biosensing and photodynamic application.

Photoluminescence enhancement of tris(8-hydroxyquinolinato)aluminum thin film by plasmonic Ag nanotriangle array fabricated by nanosphere lithography

Enhancement of 4.4-fold photoluminescence (PL) of tris(8-hydroxyquinolinato)aluminum (Alq3) thin film was observed in the presence of 50-nm thick Ag nanotriangles (NTs) compared with bare Alq3 film at room temperature. According to the temperature dependence of integrated PL intensity and the PL lifetime obtained from time-resolved PL measurements, an increase in radiative recombination rate was observed over a wide temperature range. Because the absorption peak originated from localized surface plasmon (LSP) states and the emission spectra are well overlapped, the observed enhancement can be explained by efficient coupling of the LSP of the Ag NTs with the emission from the Alq3.

Plasmon-assisted site-selective growth of Ag nanotriangles and Ag-Cu2O hybrids

We report a plasmon-assisted growth of metal and semiconductor onto the tips of Ag nanotriangles (AgNTs) under light irradiation. The site-selective growth of Ag onto AgNTs are firstly demonstrated on the copper grids and amine-coated glass slides. As the irradiation time increases, microscopic images indicate that AgNTs gradually touch with each other and finally “weld” tip-to-tip together into the branched chains. Meanwhile, the redshift of plasmon band is observed in the extinction spectra, which agrees well the growth at the tips of AgNTs and the decrease of the gaps between the adjacent nanotriangles. We also synthesize AgNT-Cu2O nanocomposites by using a photochemical method and find that the Cu2O nanoparticles preferably grow on the tips of AgNTs. The site-selective growth of Ag and Cu2O is interpreted by the local field concentration at the tips of AgNTs induced by surface plasmon resonance under light excitation.

Synthesis, characterization and antibacterial study on the chitosan-functionalized Ag nanoparticles

This study provided a facile, one-step hydrothermal method to synthesize stable Ag colloid in aqueous solution by utilizing chitosan as both reductant and stabilizer. The formation of chitosan-functionalized Ag nanoparticles was verified by UV–Vis, FTIR, TEM, AFM and XRD measurements. FTIR results revealed that the primary amine groups and amide groups of chitosan have specific interactions with the surface of Ag nanoparticles. The average diameter of the Ag nanoparticles is 10.0±5.4nm as determined by TEM. Ag nanoparticles are highly crystalline as revealed by HR-TEM and XRD measurements. The size and shape of Ag nanoparticles are also found to depend on the pH condition in the synthesis. Ag nanoparticles were the main products at pH5.0 whereas large Ag nanotriangle and truncated triangular nanoplate were dominant at pH4.0 in the synthesis. Due to its monodispersity and good stability, the chitosan-functionalized Ag colloid synthesized at pH5.0 was further tested for its antibacterial activities against gram-positive bacteria, gram-negative bacteria and fungus. The results of zone of inhibition, inhibition ratio and SEM characterization revealed that chitosan-functionalized Ag nanoparticles have great bactericidal efficiency against both bacteria and fungus.

Silver nanotriangles-loaded filter paper for ultrasensitive SERS detection application benefited by interspacing of sharp edges

The strongly enhanced electromagnetic “hotspots” from the edges and tips of nanoplates are highly preferred to significantly promote the surface enhanced Raman scattering (SERS) activity. Here, Ag nanotriangles with a sharp edge of 20nm were prepared by the reduction of AgNO3 using N,N-Dimethylformamide (DMF) with the assistance of Polyvinyl pyrrolidone (PVP). By loading of Ag nanotriangles onto the filter paper, a flexible SERS substrate with good activity and reproducibility was obtained and the ultratrace detection of p-aminothiophenol (pATP) with a concentration as low as 10−8M was achieved. The sharp edges and tips boosted SERS activity was proved by the finite element method modeling of the plasmonic properties of Ag nanotriangles with different edge thicknesses (10 − 80nm), Ag nanosheets with different tip acutances (squares and hexagons) together with Ag nanorods, nanocubes and nanospheres. The experimental and theoretical results confirmed that the interspacing created by filter paper plays an important role in enhancing the overall SERS activity. Furthermore, it is shown that the present silver nanotriangles-loaded filter paper SERS substrate can be employed to sensitive and selective detecting ultratrace military explosives picric acid (PA) of 10−6M.

Protein-aided formation of triangular silver nanoprisms with enhanced SERS performance.

In this work, we present a modified seed-mediated synthetic strategy for the growth of silver nanoprisms with low shape polydispersity, narrow size distribution and tailored plasmonic absorbance. During the seed nucleation step, consensus sequence tetratricopeptide repeat (CTPR) proteins are utilized as potent stabilizers to facilitate the formation of planar-twinned Ag seeds. Ag nanoprisms were produced in high yield in a growth solution containing ascorbic acid and CTPR-stabilized Ag seeds. From the time-course UV-Vis and transmission electron microscopy (TEM) studies, we postulate that the growth mechanism is the combination of facet selective lateral growth and thermodynamically driven Ostwald ripening. The resultant Ag nanotriangles (NTs) exhibit excellent surface enhanced Raman spectroscopy (SERS) performance. The enhancement factor (EF) measured for the 4-mercapto benzoic acid (4-MBA) reporter is estimated to be 3.37 × 105 in solution and 2.8 × 106 for the SERS substrate.

Surface-enhanced fluorescent immunoassay on 2D silver nanotriangles array

Long range ordered silver nanotriangles array was fabricated for surface-enhanced fluorescent immunoassay in this paper. By polystyrene (PS) microspheres based LB template method, the silver nanotriangle array with about 100nm in height was constructed on the surface of glass slide. On the surface of Ag nanotriangles array, the immune reaction of antigens and labeled antibodies was carried out. Based on the interaction of fluorophores from antibodies with the plasmon resonance from Ag nanotriangles and the enrichment effect of this patterned array, 3.11 times enhancement of the fluorescent intensity of the target antibodies was obtained. According to the fitting curve of fluorescent intensities and logarithmic concentrations of labeled antibodies from 100pg/mL to 10μg/mL, it concludes that the limit of detection by this Ag nanotriangles array for immune complex is 100pg/mL. Due to the advantages of high sensitivity, good reproducibility, and convenient fabrication, the 2D silver nanotriangles array could be an exciting platform for bioassays in proteomics, drug discovery and diagnostics.

Inkjet-printed highly conductive transparent patterns with water based Ag-doped graphene

A transparent Ag nanotriangle platelet–rGO (Ag NTP–rGO) pattern with high conductivity was obtained by inkjet-printing of Ag NTP–rGO ink, the solvent of which is only water.

Efficiency Enhancement in Bulk-Heterojunction Solar Cells Integrated with Large-Area Ag Nanotriangle Arrays

Efficiency enhancement in plasmonic bulk heterojunction (PCDTBT:PCBM) organic solar cells (OSCs) is demonstrated with the integration of large-area periodic Ag nanotriangle (NT) arrays (that were f...

Correlated AFM and SERS imaging of the transition from nanotriangle to nanohole arrays

Mapping the transition of Ag nanotriangle to nanohole arrays revealed that the optimal SERS response was obtained near the transition. Correlated AFM and Raman imaging provided novel experimental proof that hot spots are located on Ag islands for nanotriangle arrays and in the core area of the hole for nanohole arrays, which is in agreement with previous theoretical predictions.