Silver Nanoparticle Films Research Articles

An exploration of surface enhanced Raman spectroscopy (SERS) for in situ detection of sulfite under high pressure

In this work, silver nanoparticles film was directly fabricated on the surface of the diamond anvil as SERS active substrate for the first time by using a simple and convenient method. With this approach, the SERS spectrum of sulfite was obtained with a detection limit of 5 μmol/L in diamond anvil cell (DAC) at ∼50 MPa. The SERS signal intensity of the two main vibration modes, νsymSO and δsymOSO, showed good linearity with the Na2SO3 concentrations in the range from 5 to 40 μmol/L under high pressure. The linear correlation coefficients were 97.67% and 96.08%, respectively. The effects of pressure on the SERS intensity and Raman shift of the two modes were also studied. The SERS intensity dropped with the increase of pressure and the two main vibration modes shifted to high wave-number when the pressure increased in the pressures ranging from 54 MPa to 330 MPa. The experiments indicate that this method is rapid, convenient and sensitive in detecting sulfite at high pressures. It can be developed as an effect in situ method to detect sulfite in the process of high pressure reaction.

Gel‐Switchable Droplet Front for Large‐Scale Uniformity of Inkjet Printed Silver Patterns

AbstractAttempts at achieving uniform deposits by drop drying are crucial in inkjet printed electronics, since homogeneous surface profiles of solution processed films are frustrated by the ubiquitous coffee ring effect. However, the majority of research on the final shape has been conducted for only dots and narrow lines, as it remains a big challenge to regulate the flows between droplets. Here, a facile and green way to achieve excellent uniformity of inkjet printed film on large scale (8 cm × 8 cm) is shown, by developing a simple but novel gel ink, which contains only small molecule components, but boasts advantages in printability, filming, and low‐temperature processing properties. Fast evaporation, high‐concentration metal coordination, and enhanced Marangoni flow all contribute to rapid sol (printing) to gel (filming) transition process, leading to the formation of gel‐switchable front of each droplet (≈10 pL) within the deposition delay, which suppresses flows during droplet coalescence with eliminated boundaries. The resulting silver nanoparticle film is optimized (140 °C, 30 min) to have a low resistivity of 6.42 × 10−8 Ω m and a surface fluctuation of 15 nm, which is extremely flat with respect to each undulation span of 35 µm (Δh/ΔL ≈ 3/7000).

Cold Atmospheric Plasma Annealing of Plasmonic Silver Nanoparticles

Silver nanoparticles deposited on quartz substrate are annealed by cold atmospheric plasma jet to tailor the surface plasmon resonance (SPR) of silver nanoparticles. SPR is the unique optical property which arises due to the interaction of electromagnetic waves with the conduction electrons on the metal nanoparticle surface. The collective oscillations of these conduction electrons at specific EM wavelengths leads to strong scattering and absorption. For silver nanoparticles (AgNPs), the SPR occurs in UV-visible region and therefore AgNPs are used in various applications including solar energy harvesting, light emitting diodes, printed optoelectronic devices, and surface enhanced Raman scattering(SERS). The SPR absorbance peak strongly depends on the size, shape and assembly of the metal nanoparticles. The SPR absorbance peak can be tailored by thermal annealing of AgNPs. The annealing or sintering leads to change in mean diameter of nanoparticle due to agglomeration or reduction in the outside oxide layer of nanoparticles and therefore either red or blue shift in SPR is observed. However, thermal annealing is not always desirable, especially for the flexible polymer substrates. In the present work, we demonstrate the efficacy of cold atmospheric plasma annealing to achieve desired thermal annealing effects at room temperature. Silver nanoparticle films were deposited on the quartz substrate by injecting NP aerosol in the flowing argon gas. As deposited AgNP films were annealed by low temperature atmospheric plasma jet for 5 mins, 10 mins and 15 mins. Fig 1(a) shows the optical absorption spectra for un-annealed as well as annealed AgNP films. For un-annealed sample we observed the SPR absorbance peak at 426 nm. This peak was blue shifted by 14 nm, 36 nm and 62 nm for plasma annealed films for 5 min, 10 min and 15 min respectively. The AgNP films were also annealed using rapid thermal processing (RTP) at 100°C, 250°C, and 400°C for 5 min, 10 min and 15min. For all the temperatures, SPR peaks were blue shifted and for 400°C (corresponding the thermal energy of 58 meV) the blue shift values coincided with the values observed for plasma annealed AgNP films at room temperature. The plasma treated AgNP films were used as SERS substrates for Raman scattering studies of cortisol biomolecule. The Raman scattering signal from plasma annealed AgNP film was two times higher than that of bare quartz substrate. Figure 1

Synthesis of silver nanoparticles film by spark discharge deposition for surface-enhanced Raman scattering

A surface-enhanced Raman scattering (SERS) substrate composed of silver nanoparticles (Ag NPs) was synthesized by spark discharge deposition (SDD). The spark-ablated species were directly deposited on a copper substrate at room temperature and atmospheric pressure. Sharp and reproducible SERRS signals from the model molecule Rhodamine B (Rh B) were observed from the prepared substrates. Under optimized deposition conditions, the detection limit of Rh B reached the single molecular level (1.0 × 10−16 M) with an enhancement factor of 3.9 × 1012. This substrate also provided excellent SERS activity toward crystal violet molecule and the representative biomolecule adenine. We were further interested to find that the activity of the prepared substrate responded very sensitively when we changed the morphology of the deposited NPs by adjusting the operating parameters. An increase in the spark time to 20 min increased the particle size and filling factor, which induced the particles to grow into self-assembled dendrite-like structures. We observed the highest intensity in an Ag NP film with an average particle size of 45 nm and filling factor of 0.57. We speculate that the high sensitivity of this substrate may have derived from the high electromagnetic field produced by the tuning of the particle size and the formation of nanogaps (hot spots) between adjacent particles. This method offers a simple, cost effective, eco-friendly route to the synthesis of highly sensitive, reproducible SERS substrates.

Conductive films of silver nanoparticles as novel susceptors for induction welding of thermoplastic composites

In the present work, a conductive film of silver nanoparticles (nAg) as a novel heating element type, called susceptor, was developed and tested for induction welding of carbon fiber/polyphenylene sulfide (CF/PPS) thermoplastic composites, i.e., unidirectional pre-impregnated 16 plies of CF/PPS compression-molded in a quasi-isotropic stacking sequence. The nAg were synthesized, dispersed in deionized (DI) water and casted onto a pure PPS film, resulting in a conductive film upon the evaporation of DI water and thermal post-annealing. The thermal annealing at 250 °C significantly (by 7 orders) decreased the film’s electrical resistivity from 9.4 × 103 down to 3.1 × 10−4 Ω cm. The new susceptors led to fast heating rates in induction welding when compared to the standard stainless steel mesh susceptors under similar welding conditions. Lap shear mechanical testing revealed that the apparent lap shear strength (LSS) is sensitive to the susceptors’ resistivity and the input current. A relatively high LSS value was achieved for the specimens welded using the new susceptors which exceeded the value of those welded using stainless steel mesh susceptors (28.3 MPa compared to 20 MPa). The weld interface and specimens’ cross-section observation revealed that the nAg were dispersed and embedded into the resin upon welding. This study contains preliminary results that show high potential of nanoparticles as effective susceptors to further improve the mechanical performance of the joints in welding of thermoplastic composites.

Silver-doped titanium dioxide nanoparticles encapsulated in chitosan–PVA film for synergistic antimicrobial activity

ABSTRACTThe objective of the present study performed was to develop and characterize of silver (Ag)-doped titanium dioxide (TiO2) naoparticles (NPs) encapsulated in chitosan–polyvinyl alcohol (PVA) film for synergistic antimicrobial activity. The acidic solution of chitosan with PVA was used for the reduction of silver ions into silver NPs using their functional groups such as hydroxyl, carboxyl, and amino groups. The chitosan–PVA silver nanoparticle films showed significant antimicrobial and antifungal activity against Staphylococcus aureus, Candida albicans, and Pseudomonas aeruginosa. Therefore, the present study is an alternative for conventional treatment as antimicrobial film showed synergistic, noninvasive, and economic effects.

Optimized inkjet-printed silver nanoparticle films: theoretical and experimental investigations.

We study the influence of inkjet printing scheme and sintering parameter on the electrical resistivity of multi-layer silver nanoparticle films. A central composite Design Of Experiments (DOE) is employed to maximize experimental efficiency and improve the statistical significance of parameter estimates. The resulting mathematical correlations allow to interpret the influence of the print and sintering parameters. Detailed inspection of the correlations reveals the existence of local extrema and indicates that a structured approach such as the DOE would be significantly more effective for fabricating films with a minimum of resistivity. Furthermore, we modify the well-known Fuchs–Sondheimer Mayadas–Shatzkes model to correlate the resistivity of a multi-layer nanoparticle film with the sintering temperature and time. The modified model uses literature data but one constant inferred from two experiments. After model adjustment, the resistivities of films fabricated with different parameters can be predicted with good accuracy. This validation tremendously increases applicability and relevance of the model.

An antibody-free assay for simultaneous capture and detection of glycoproteins by surface enhanced Raman spectroscopy.

A sensitive, and single step reaction assay of glycoproteins in antibody-free mode was proposed on a 4-mercapto-phenylboronic acid (4-MPBA) modified silver nanoparticle film (AgNF) by using surface enhanced Raman scattering (SERS). 4-MPBA/AgNF was designed both as a glycoprotein-specific recognition biosensor and as a Raman reporter for the SERS platform. Variation in the ratio I1574/I1586 for 4-MPBA/AgNF in response to glycoprotein capture constitutes the SERS assay which exhibits high sensitivity and selectivity against nonglycoproteins and is shown to function in complex samples.

Reversibly switching surface-enhanced Raman scattering based on colloidal electrophoresis

This article aims to switch the surface-enhanced Raman spectrum (SERS) of a 4-Aminothiophenol (4-ATP) dye solution on a silver nanoparticle (Ag-NPs) film, where the SERS is largely influenced by the distance betweenss the 4-ATP and the Ag-NPs under applied an external field. The electrophoresis apparatus uses two ITO electrodes to build a cell in which one of the ITO electrodes is coated with 30-nm Ag-NPs. The SiO2 nanospheres form an insulating layer which effectively hinders 4-ATP adsorption on Ag-NPs when a + 3V bias voltage is applied. The 4-ATP dye molecules are carried by the SiO2 nanospheres to move off the Ag-NPs by applying a −3V bias voltage. The 0.4 wt% 4-ATP and less than 15 wt% SiO2 nanospheres (200 ~350 nm in diameter) are used to prepare samples for analysis. The results show that the 1.6 wt% SiO2 200-nm nanospheres achieved the best switching effect of SERS in this study.

Atmospheric pulsed laser deposition and thermal annealing of plasmonic silver nanoparticle films

A new method for pulsed laser deposition of plasmonic silver nanoparticle (NP) films in flowing gas at atmospheric pressure is described. The ablation was done using an excimer laser at 248 nm. Fast optical imaging shows that the ablation plume is captured by the flowing gas, and is expected to form a NP aerosol, which is carried 5–20 mm to the substrate. The dependence of the deposition rate on laser fluence, gas flow velocity, and target-substrate distance was investigated using electron microscopy and absorption spectroscopy of the deposited films. The NP films were annealed in argon and hydrogen at 400 °C, and in air for temperatures in the range 200 °C–900 °C, leading to strong enhancement, and narrowing of the surface plasmon resonance. The films were used for surface enhanced Raman spectroscopy of a 10−5 molar solution of Rhodamine 6G; films annealed in air at 400 °C were five times more sensitive than the as-deposited films.

Homogeneous Surface Profiles of Inkjet-Printed Silver Nanoparticle Films by Regulating Their Drying Microenvironment

Obtaining homogeneous surface profiles of inkjet-printed silver nanoparticle films (SNFs) is severely hampered by the classical coffee-ring phenomenon. Traditional approaches to suppress the coffee-ring effect are achieved by improving the uniformity of liquid evaporation rate or introducing inward Marangoni force during ink drying. However, these existing methods involve extra chemicals, treatments, or equipment that will definitely increase the production cost or reduce conductivity. In this study, we demonstrate an inexpensive and efficient method to obtain uniform surface profiles of inkjet-printed SNFs by rationally regulating the drying microenvironment. To this end, a number of surface profiles of printed dots and lines, such as concave, convex, and flat, were first obtained via this method. The underlying principle of this method was then investigated by analytical calculations based on the simplified vapor diffusion model. Consequently, homogeneous surface profiles of inkjet-printed SNFs were ach...

Simultaneous Electrodeposition of Reduced Graphene Oxide/Ag Nanoparticles as a Sensitive Layer for Voltammetric Determination of Tinidazole

A stable composite film of silver nanoparticles (Ag NPs) decorated on reduced graphene oxide is prepared by a two-step simple procedure. The surface morphology of the modified electrode is characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The electrochemical behavior of tinidazole (TNZ) on the surface of the modified electrode is investigated by linear sweep voltammetry and electrochemical impedance spectroscopy. The prepared composite electrode acts as a highly sensitive platform for the voltammetric determination of TNZ, leading to a significant increase in the reduction peak current of TNZ. The effects of experimental parameters such as the amount of the casted silver ions-GO mixture suspension, the electro-reduction variables, the accumulation time and potential, the scan rate and pH of the buffered solutions on the electrochemical response of TNZ are investigated. Under optimal conditions, the modified electrode showed a wide linear range for the reduction of TNZ in the range of 0.01–10[Formula: see text][Formula: see text]M with a detection limit of 3[Formula: see text]nM. Finally, the prepared electrode is successfully applied for the determination of TNZ in pharmaceutical and clinical samples.

Effect of Microwave Heating on the Crystallization of Glutathione Tripeptide on Silver Nanoparticle Films.

Effect of microwave heating on the crystallization of glutathione (GSH) tripeptide using the metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique is reported. GSH crystals were grown from supersaturated solutions of GSH (300-500 mg/mL) on the iCrystal plates with silver nanoparticle films (SNFs) and without SNFs in three different microwave systems operating at 2.45 GHz: conventional (multimode, fixed power at 900W), industrial (monomode, variable power up to 1200 W), and the iCrystal system (monomode, variable power up to 100 W). The efficacy of the MA-MAEC technique, in terms of improvement in the crystallization time, crystal size and quality of GSH, was compared between the three microwave systems and the crystallization at room temperature (no microwave heating, a control experiment). Optical microscopy was used to visualize and quantify the growth of GSH crystals during and after microwave heating. Powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy data showed that GSH crystals had identical crystal structure to those grown at room temperature and microwave heating did not alter the chemical structure of GSH molecules during microwave heating, respectively. Using the MA-MAEC technique, the iCrystal system yielded high quality GSH crystals in a rapid manner.

Fabrication of polypropylene/silver nanocomposites for biocidal applications

This paper presents a study on biocidal effect of polymer nanocomposite films of gamma irradiated polypropylene (PP) and silver nanoparticles. The modified polypropylene was obtained from isotactic polypropylene (iPP) in pellets form by irradiation with gamma rays in the presence of acetylene. A new morphology with long chain branching of PP and distinct rheology is obtained by this process. The blend of 50/50wt% neat PP and PP modified by gamma radiation were further mixed using a twin screw extruder. The AgNPs were infused into this polymer blend at different concentrations of: 0.1%; 0.25%; 0.5%; 1.0%; 1.0% (PVP), 2.0% and 4.0% by wt%. These polymer nanocomposites were characterized by Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), cytotoxicity test and Kirby-Bauer disk diffusion techniques. The bactericidal effect of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) were assessed in detail.

Highly sensitive, reproducible and stable SERS substrate based on reduced graphene oxide/silver nanoparticles coated weighing paper

Paper-based surface-enhanced Raman scattering (SERS) substrates receive a great deal of attention due to low cost and high flexibility. Herein, we developed an efficient SERS substrate by gravure printing of sulfonated reduced graphene-oxide (S-RGO) thin film and inkjet printing of silver nanoparticles (AgNPs) on weighing paper successively. Malachite green (MG) and rhodamine 6G (R6G) were chosen as probe molecules to evaluate the enhanced performance of the fabricated SERS-active substrates. It was found that the S-RGO/AgNPs composite structure possessed higher enhancement ability than the pure AgNPs. The Raman enhancement factor of S-RGO/AgNPs was calculated to be as large as 109. The minimum detection limit for MG and R6G was down to 10−7M with good linear responses (R2=0.9996, 0.9983) range from 10−4M to 10−7M. In addition, the S-RGO/AgNPs exhibited good uniformity with a relative standard deviation (RSD) of 7.90% measured by 572 points, excellent reproducibility with RSD smaller than 3.36%, and long-term stability with RSD less than 7.19%.

Effect of Morphology on the Electrical Resistivity of Silver Nanostructure Films

The relatively high temperatures (>200 °C) required to sinter silver nanoparticle inks have limited the development of printed electronic devices on low-cost, heat-sensitive paper and plastic substrates. This article explores the change in morphology and resistivity that occurs upon heating thick films of silver nanowires (of two different lengths; Ag NWs), nanoparticles (Ag NPs), and microflakes (Ag MFs) at temperatures between 70 and 400 °C. After heating at 70 °C, films of long Ag NWs exhibited a resistivity of 1.8 × 10-5 Ω cm, 4000 times more conductive than films made from Ag NPs. This result indicates the resistivity of thick films of silver nanostructures is dominated by the contact resistance between particles before sintering. After sintering at 300 °C, the resistivity of short Ag NWs, long Ag NWs, and Ag NPs converge to a value of (2-3) × 10-5 Ω cm, while films of Ag MFs remain ∼10× less conductive (4.06 × 10-4 Ω cm). Thus, films of long Ag NW films heated at 70 °C are more conductive than Ag NP films sintered at 300 °C. Adding 10 wt % nanowires to a film of nanoparticles results in a 400-fold improvement in resistivity.

Effective optical constants of anisotropic silver nanoparticle films with plasmonic properties.

Mueller matrix ellipsometry has been used to determine the effective optical constants of island-like Ag films deposited by thermal evaporation. These films depart substantially from bulk silver with a prominent localized surface plasmon resonance. Moreover, despite the isotropic appearance, they exhibit uniaxial optical properties with the optical axis inclined by 83.4° from the substrate normal toward the direction of the incoming vapor flux. The uniaxial model supports the plasmon resonance peaks revealed by in-plane absorbance measurements of the films. The uniaxial behavior suggests that the resonances along the ordinary axes are weakly coupled between neighboring particles, whereas the extraordinary resonance is relatively strongly coupled. Therefore, the anisotropy should be considered in the practical applications of these plasmonic films.

Unconventional Increase in Non-Radiative Transitions in Plasmon-Enhanced Luminescence: A Distance-Dependent Coupling.

We used Optically Stimulated Luminescence (OSL) from X-ray-irradiated sodium chloride nanocrystals to investigate how silver nanoparticle (AgNP) films enhanced luminescence. We controlled the emitter-AgNP distance and used the OSL intensity and decay times to explore the plasmonic interactions underlying the enhanced luminescence. Both intensity and decay times depended on the emitter-AgNP distance, which suggested that a mechanism involving energy transfer from the localized surface plasmons (LSPs) to the trapped electrons took place through a distance-dependent coupling. Compared to other plasmon-enhanced mechanisms, the energy transfer observed here occurred in the opposite bias: LSP relaxation stimulated electron transfer from non-optically active traps to optically active traps, which culminated in enhanced emission. Therefore, a different mechanism of plasmonic coupling converted optically unreachable electrons into useful luminescence information.

Nanoscale-shape-mediated coupling between temperature and densification in intense pulsed light sintering

In intense pulsed light sintering (IPL), pulsed large-area visible light from a xenon lamp is absorbed by nanoparticle films or patterns and converted to heat, resulting in rapid sintering of the nanoparticles. This work experimentally characterizes IPL of silver nanoparticle films. A newly observed turning point in the evolution of film temperature during IPL is correlated to the observation, in literature and in this work, that film densification levels off beyond a critical pulse fluence and number of pulses. A computational model is developed that couples electromagnetic finite element analysis, heat transfer models and densification models to predict the evolution of film temperature and density during IPL. This model is able to capture the experimentally observed turning point in temperature during IPL, whereas current models of IPL are unable to do so. It is shown that the temperature turning point occurs due to a coupling between optical absorption and densification in the nanoparticle film, mediated by a change in nanoscale shape of the deposited nanoparticles due to interparticle neck growth. Further, it is found that the optical fluence per pulse has a greater effect on the achievable film density in IPL, as compared to the number of pulses.

Passively Q-switched thulium-doped fiber laser with silver-nanoparticle film as the saturable absorber for operation at 2.0 µm

In this work, a compact thulium-doped fiber laser with a Q-switched output is proposed and demonstrated. A thulium-doped fiber is used for the laser, with a peak absorption of 200 dB m−1 at 790 nm and a cutoff wavelength of 1350 nm as the primary gain medium, and a silver-based saturable absorber as the pulse generation mechanism. The pulses obtained from the proposed laser have repetition rates from 38.3 kHz up to 56.2 kHz, with a pulse width as low as 4.2 µs and pulse energy as high as 67.3 nJ at a maximum pump power of 228.8 mW. The generated pulses are highly stable, showing no changes or fluctuations over operation for a period of 60 min, and further validated with signal-to-noise ratios of 57.0 dB and 59.5 dB in the optical and frequency domains respectively. The proposed laser has high potential for eye-safe applications in manufacturing and medicine.