Plasmonic Silver Nanoparticles Research Articles

Lateral Size Effect of Graphene Oxide on Its Surface-Enhanced Raman Scattering Property.

The lateral size effect of graphene oxide (GO) on surfaced-enhanced Raman scattering (SERS) property is systematically investigated by using size-fractionalized GO. For the size fractionalization without changes of chemical structure, large-sized GO (LGO) and small-sized GO (SGO) are separated from the as-synthesized GO (AGO) by centrifugation and membrane filtration, respectively. The size-fractionalized GO sheets are immobilized on a solid substrate for the parallel comparison of their SERS property. As a result, we find that LGO shows considerably higher SERS property than SGO for typical Raman probes such as rhodamine 6G and crystal violet. Furthermore, the lateral size effect of GO derivatives is consistently observed when they are hybridized with plasmonic silver nanoparticles. These results indicate that LGO is superior to AGO and SGO as a SERS platform, and it is also quantitatively confirmed by calculating their enhancement factor.

Plasmonic hotspot engineering of Ag-coated polymer substrates with high reproducibility and photothermal stability

Plasmonic silver nanoparticles (AgNPs) arranged on polyimide (PI) nanopillars (AgNP/PI) were developed as a stable photothermal surface-enhanced Raman spectroscopy (SERS) platform. The AgNP/PI substrates were prepared via maskless plasma etching and metal deposition using an in situ vacuum sputtering system. The AgNP/PI with high periodicity and high areal density led to high sensitivity, with a SERS enhancement factor (EF) of 2.2 × 108, and excellent reproducibility (relative standard deviation of 7.6%), as evaluated using the high-precision Raman mapping technique. To support the high SERS EF and sensitivity, the near-field enhancements of the dense AgNP array were calculated using a finite-difference time domain method. Notably, compared with AgNPs on polyethylene terephthalate (PET) nanopillar substrates, the AgNPs formed on the thermally stable PI nanopillar substrates exhibited excellent photothermal stability under illumination with a high-powered laser. The PI and PET surface changes induced by photoinduced local heating were investigated in terms of the glass-transition temperature, coefficient of thermal expansion, and thermal conductivity. The new plasmonic SERS platform has strong potential for reliable molecular detection in practical sensing applications with high-powered laser illuminations.

SERS detection of DNA cancer with single-base mutation for KRAS-gene

We present a method based on surface enhanced Raman spectroscopy (SERS) to detect DNA KRAS-gene with single-base mutation. The KRAS gene belongs to the oncogenes class of genes. KRAS mutations cause normal cells to become cancerous. The detection utilizes DNA gene probes labeled by CY3 dye (as Raman marker) and plasmonic silver nanoparticles (Ag NPs) deposited on SERS substrates. SERS detect DNA via hybridization to the complementary DNA (target) sequences with single-base mutation. This SERS technique is a powerful tool and has a great potential gives both affectability and selectivity. Also, we utilized the Raman mapping to provide chemical information coupled with spatial information. The mapping image was obtained using scanning with three Raman bands over selected areas of the sample. The limit of detection (LOD) was accomplished down to a concentration 9 nM after the addition of magnesium sulfate (MgSO4) aggregated agent, causing hot spots of the aggregated Ag NPs.

Theoretical Insights into Excitation-Induced Oxygen Activation on a Tetrahedral Ag8 Cluster.

Research on small-molecule dissociation on plasmonic silver nanoparticles is on the rise. Herein, we investigate the effect of various parameters of light, i.e., field strength, polarization direction, and energy of oscillation, on the dynamics of oxygen upon photoexcitation of the O2@Ag8 composite using real-time time-dependent density functional theory calculations with Ehrenfest dynamics. From our excited-state dynamics calculations, we found that increasing the strength of the external electric field brings a significant contribution to the O-O dissociation. In addition, the polarization direction of the incident light becomes important, especially at weaker field strengths. The light that is polarized along the direction of charge transfer from the metal to adsorbate and the light that is polarized along the long axis of molecular oxygen were found to enhance the bond breaking of O2 significantly. We also found that at the weakest electric field strength, the oxygen molecule stays adsorbed to the silver cluster when the incident light resonates with low-energy excited states and desorbs away from the metal cluster with high-energy excitations. With strong electric fields, oxygen either desorbs or dissociates.

Photocatalytic oxidation of ceftiofur sodium under UV–visible irradiation using plasmonic porous Ag-TiO2 nanospheres

In this study, 250 nm sized porous anatase TiO2 nanospheres (TiO2 NSPs) composed of ∼ 10 nm sized anatase TiO2 nanoparticles are obtained through a green synthetic route and their surfaces have been decorated with 3–4 nm sized plasmonic silver nanoparticles (AgNPs). Photoluminescence studies confirm that the AgNPs presence on TiO2 NSPs surface effectively inhibits the radiative charge recombination and thus facilitates charge separation process at the Ag-TiO2 NSPs interface, causing an enhanced photocatalytic activity. About 92% of the ceftiofur sodium (CFS) antibiotic taken initially is oxidized by Ag-TiO2 NSPs upon 90 min white light irradiation, while Ag loaded Degussa P25 TiO2 nanoparticles effects only 71% CFS oxidation. The synergistic effect given by plasmonic AgNPs and the continuous framework of anatase TiO2 NPs contributes to inhibit the electron-hole recombination in the Ag-TiO2 NSPs. Oxidation products of CFS in different water sources and their eco-toxicity effects identified through LC-MS and microtox-bioassays, respectively, indicate that the obtained oxidation products are non-toxic compared to pure CFS. Therefore, porous Ag-TiO2 NSPs could be successfully applied in photocatalytic oxidation technologies, exploiting sunlight for the effective removal of pharmaceutical pollutants from wastewater.

Plasmonic silver nanoparticles decorated surface functionalized Zirconium doped quantum dots - for enhanced photochemical synthesis of lactic acid esters

Lactic acid, or 2-hydroxypropionic acid (CAS 50-21-5), a natural organic acid immensely engaged in agricultural industry, pharmacy, garment and chemical industry with a long history of practice. Lactic acid generated in fermentation necessitates an extra purification step that must be cost-effective. A green and energy derivatization of lactic acid into corresponding esters was carried out under photocatalytic conditions in this study to render them volatile for distillation separation. Esterification reaction was carried out under low energy photocatalytic system under solvent free conditions using a range of Zirconium impregnated-activated Titanium dioxide photocatalysts (1-0.005Ag/1.9-4.4%S-2.5-12.5%Zr@TO). Both physical and chemical events in the reaction grid have been studied and thermodynamic and kinetic parameters have been established expending pseudo-homogeneous (PH), Eley-Rideal (ER) and Langmuir-Hinshelwood-Haugen-Watson (LHHW) models and the different adsorption of components were proposed to fit the intrinsic kinetic data. Reaction mechanism for the process have been proposed based on the kinetic modelling results as well as FT-IR, TGA, Ammonia-TPD and photo-Electrochemical characterizations, as well as radical trapping tests, were also used to effectively support the reaction mechanism. The findings will be beneficial in the design of industrial photo-reactors for low temperature ester synthesis strategies.

Ultra-sensitive and fast optical detection of the spike protein of the SARS-CoV-2 using AgNPs/SiNWs nanohybrid based sensors

Severe acute respiratory syndrome SARS-CoV-2 virus led to notable challenges amongst researchers in view of development of new and fast detecting techniques. In this regard, surface-enhanced Raman spectroscopy (SERS) technique, providing a fingerprint characteristic for each material, would be an interesting approach. The current study encompasses the fabrication of a SERS sensor to study the SARS-CoV-2 S1 (RBD) spike protein of the SARS-CoV-2 virus family. The SERS sensor consists of a silicon nanowires (SiNWs) substrate decorated with plasmonic silver nanoparticles (AgNPs). Both SiNWs fabrication and AgNPs decoration were achieved by a relatively simple wet chemical processing method. The study deliberately projects the factors that influence the growth of silicon nanowires, uniform decoration of AgNPs onto the SiNWs matrix along with detection of Rhodamine-6G (R6G) to optimize the best conditions for enhanced sensing of the spike protein. Increasing the time period of etching process resulted in enhanced SiNWs’ length from 0.55 to 7.34 µm. Furthermore, the variation of the immersion time in the decoration process of AgNPs onto SiNWs ensued the optimum time period for the enhancement in the sensitivity of detection. Tremendous increase in sensitivity of R6G detection was perceived on SiNWs etched for 2 min (length=0.90 µm), followed by 30s of immersion time for their optimal decoration by AgNPs. These SiNWs/AgNPs SERS-based sensors were able to detect the spike protein at a concentration down to 9.3 × 10−12 M. Strong and dominant peaks at 1280, 1404, 1495, 1541 and 1609 cm−1 were spotted at a fraction of a minute. Moreover, direct, ultra-fast, facile, and affordable optoelectronic SiNWs/AgNPs sensors tuned to function as a biosensor for detecting the spike protein even at a trace level (pico molar concentration). The current findings hold great promise for the utilization of SERS as an innovative approach in the diagnosis domain of infections at very early stages.

Optical properties of CsPbBr3 perovskite nanocrystals with silver nanoparticles using a room-temperature synthesis process

CsPbBr3 nanocrystals (NCs) are all-inorganic perovskite materials with unique optoelectronic properties for their use in next-generation photoluminescent, electroluminescent, and photovoltaic devices. The optical properties of CsPbBr3 nanocrystals can be changed by compositional substitution, phase transition, doping into the perovskite nanostructures, and adding metal nanoparticles for achieving efficient optoelectronic devices. In this work, CsPbBr3 NCs are synthesized by ligand-assisted re-precipitation (LARP) technique. Different concentrations of plasmonic silver nanoparticles are added into CsPbBr3 NCs to get the CsPbBr3 NCs–Ag NPs mixture. The changes in structural and optical properties of CsPbBr3 NCs are analyzed by using XRD and PL spectral analysis. The enhancement, peak shift, and quenching in the PL spectra of CsPbBr3 NCs is observed due to the addition of different concentrations of plasmonic silver nanoparticles. The study provides a facile strategy for tuning and manipulating optical properties of all-inorganic CsPbBr3 NCs by adding silver nanoparticles and utilizing their properties in various future optoelectronic applications.

Enhanced dye-sensitized solar cell performance using strontium titanate perovskite integrated photoanodes modified with plasmonic silver nanoparticles

Plasmonic silver nanoparticles loaded strontium titanate nanocomposites (Ag-SrTiO3 NC) with diverse weight percentages (0.5, 1.5, 2.5 and 5 wt%) of Ag nanoparticles (Ag NPs) are synthesized by a facile chemical reduction method. The prepared nanocomposites are characterized using diffuse reflectance spectroscopy, X-ray diffractometry, photoluminescence spectroscopy, scanning electronic microscopy and transmission electron microscopy. The photovoltaic performance of dye-sensitized solar cells (DSSCs) integrated with Ag-SrTiO3 NC photoanodes has been assessed under simulated sun light intensity of 100 mW cm−2. The Ag-SrTiO3 NC photoanode loaded with 2.5 wt% Ag NPs exhibited higher power conversion efficiency of 4.39% with short-circuit photocurrent density of 11.54 mA cm−2, open circuit voltage of 0.77 V and fill factor of 0.49 in DSSC. This enhanced photovoltaic performance can be credited to high dye loading, improvement in visible light harvesting - and fast photo-induced electron transfer caused by the plasmonic Ag NPs.

A Combined Spectroscopic and Theoretical Analysis of Plasmonic Silver Nanoparticle Sensor Towards Detailed Microscopic Understanding of Heavy Metal Detection

Plasmonic nanoparticles are of great importance owing to their highly responsive ‘localized surface plasmon resonance’ (LSPR) behaviour to self-agglomeration/aggregation leading to the development of various nanosensors. Herein, we demonstrated the definite self-assembly of citrate functionalized silver nanoparticles (AgNPs) into a one-dimensional linear chain in presence of charged lead ions (Pb2+), one of the most toxic heavy metal pollutants. We have explored detail mechanism using a variety of spectroscopic tools and electron microscopy. The self-aggregation of AgNPs leads to the generation of new LSPR modes due to coupling of nearby existing modes. The conclusion of our experimental findings is duly supported by our developed numerical modelling based on the quasi-static approximation that the generated new LSPR modes are solely due to formation of chain-like aggregation of AgNPs. We have also monitored the LSPR spectra in the presence of other metal ions; however, only Pb2+ found to give such unique self-assembled geometry may due to its high interaction affinity with citrate. These findings play a key role for citrate functionalised AgNPs to be used as a low cost highly selective and sensitive lead ion sensor for potential application in industrial lead pollution monitoring. We have further varied several sensor parameters such as AgNPs size, concentration, and the allowed reaction time for it to be practically implemented as an efficient lead sensor meeting the Environmental Protection Agency recommendations. The possible sensing mechanism of citrate-functionalized silver nanoparticles towards Pb2 + followed by unique chain-like aggregation for potential atmospheric and industrial lead pollution monitoring.

Fermi Level Equilibration at the Metal-Molecule Interface in Plasmonic Systems.

We highlight a new metal-molecule charge transfer process by tuning the Fermi energy of plasmonic silver nanoparticles (AgNPs) in situ. The strong adsorption of halide ions upshifts the Fermi level of AgNPs by up to ∼0.3 eV in the order Cl- < Br- < I-, favoring the spontaneous charge transfer to aligned molecular acceptor orbitals until charge neutrality across the interface is achieved. By carefully quantifying, experimentally and theoretically, the Fermi level upshift, we show for the first time that this effect is comparable in energy to different plasmonic effects such as the plasmoelectric effect or hot-carriers production. Moreover, by monitoring in situ the adsorption dynamic of halide ions in different AgNP-molecule systems, we show for the first time that the catalytic role of halide ions in plasmonic nanostructures depends on the surface affinity of halide ions compared to that of the target molecule.

Transparent, Flexible Plasmonic Ag NP/PMMA Substrates Using Chemically Patterned Ferroelectric Crystals for Detecting Pesticides on Curved Surfaces.

Transparent and flexible surface-enhanced Raman scattering (SERS) substrates have attracted much interest for the detection of probe molecules on the curved surfaces of real samples, but a facile route to fabricate such substrates is still lacking. Herein, we present a rationally designed, high-performance flexible SERS substrate fabricated using a simple drop and peel-off technique for the ultrasensitive detection of pesticides. The proposed SERS substrate consists of a polymethyl methacrylate (PMMA) film anchored with plasmonic silver nanoparticles (Ag NPs), which are photoreduced using chemically patterned ferroelectric templates. The photoreduced Ag NPs extracted onto the PMMA film offer strong electromagnetic enhancement and produce intensive hotspots for the effective enhancement of the Raman signal. They provide superior SERS performance for the detection of parathion (PT) and fenitrothion (FNT) at trace-level concentrations of 10-9 M and 10-10 M with excellent enhancement factors in the order of 108 and 109, respectively. Moreover, the Ag NP/PMMA SERS substrate has good spot-to-spot uniformity and batch-to-batch reproducibility with the reservation of high detection sensitivity even after the mechanical deformation of bending and torsion up to 50 cycles. The multiplex detection ability is also investigated for the simultaneous detection of PT and FNT. To ensure the practical feasibility, the in-situ, real-time detection of PT and FNT on the curved surfaces of tomato and lemon using a fiber-coupled Raman probe is performed with limits of detection of 4.24 × 10-8 M and 2.74 × 10-9 M. The proposed Ag NP/PMMA flexible SERS substrate possesses unique features, such as easy fabrication through a simple, economical, rapid process, and facilitates straightforward implementation of in-situ SERS detection on curved fruit/vegetable surfaces.

Dial‐A‐Particle: Precise Manufacturing of Plasmonic Nanoparticles Based on Early Growth Information—Redefining Automation for Slow Material Synthesis

AbstractNanomaterials are at the core of many scientific discoveries in catalysis, energy and healthcare to name a few. However, their deployment is limited by the lack of reproducible and precise manufacturing technologies on‐demand. In this work, a precision automated technology is demonstrated for nanoparticles synthesis with wide‐range tunable sizes (≈4–100 nm). Dial‐a‐particle capabilities are achieved by a combination of a fast integrated multipoint particle sizing combined with a “plug‐n‐play” modular platform with reactors in series, distributed feed and in situ multipoint analysis. Real‐time early growth information accurately predicts the resulting particle properties. Such real‐time simple feedback control can overcome repeatability and stability issues associated with controllable (e.g., conditions) and uncontrollable (e.g., fouling, ageing, and impurities) variations leading to self‐regulated, highly stable multistage systems with no human intervention even with long residence times (from a few minutes to hours). This is a paradigm shift from machine learning (ML) methodologies, which are restricted to trained networks with rich data sets, impractical in non‐reproducible processes and limited to short residence times (e.g., within few minutes). The approach is demonstrated for plasmonic silver and gold nanoparticles showing agile control within minutes, opening the door for automation of more complex multistage procedures such as composites, multielement materials, and particle functionalization.

Ultrafast electron injection kinetics and effect of plasmonic silver nanoparticle at organic dye-TiO2 interface

Ultrafast electron injection kinetics and effect of plasmonic silver nanoparticle at organic dye-TiO2 interface

Cover Feature: Colloidal Assembly and Separation under UV‐Induced Convective Flows and on Inclines (ChemNanoMat 7/2021)

Illuminating an aqueous solution of plasmonic gold or silver nanoparticles with ultraviolet (UV) light generates convective flows. These convective flows can be harnessed to move, assemble, and separate larger microparticles on an incline. More information can be found in the Communication by Anna C. Balazs, Ayusman Sen et al.

Plasmonic Ag supported on Ni-doped TiO2 nanospheres for rapid microbial inactivation under visible light

Ni-doped TiO2 nanospheres decorated with silver plasmonic nanoparticles (Ni-TiO2/Ag) have been successfully synthesized via sol-gel method and photo-deposition approach. In contrast with pure TiO2 and Ni-TiO2, the Ni-TiO2/Ag composite photocatalysts exhibit markedly enhanced visible-light photocatalytic sterilization efficiencies towards Escherichia coli (E. coli). And more importantly, antifungal experiment reveals that the composite can also disinfect ca. 2.0 log10 cfu·mL−1Fusarium graminearum (F. graminearum) macroconidia within 3 h. The highly efficient antimicrobial activities are ascribed to the introduction of Ni doping and Ag nanoparticles, which increases the visible light utilization and promotes the separation of electron-hole pairs. The photocatalytic disinfection mechanism is studied with scavengers trapping experiments and electron spin-resonance spectroscopy (ESR), which verifies the key role of •O2- and •OH during the microbial inactivation. Our study indicates that the Ni-TiO2/Ag nanocomposite has great potential for use in pathogenic microorganism remediation.

Plasmonic silver nanoparticle-decorated electrospun nanofiber membrane for interfacial solar vapor generation

Interfacial solar vapor generation as an emerging technique has great potential in solving water shortage and pollution problems. Electrospun nanofiber membrane with high porosity, mechanical flexibility, numerous microsized channels for fast water transport, and low thermal conductivity offers an ideal platform for solar vapor generation. In this research work, plasmonic silver nanoparticles (Ag NPs) were utilized as photothermal materials and electrospun polyacrylonitrile (PAN) nanofiber membranes as substrates to fabricate Ag nanoparticles-uniformly decorated PAN (Ag@PAN) nanofiber membranes by electroless plating method. The morphology and chemical composition of the membranes were characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffractometry. By varying the volume ratios of glucose and silver ammonia solution, the sizes of Ag NPs as well as the light-absorption ability of corresponding nanofiber membrane were regulated. As a result, the optimal Ag@PAN nanofiber membrane demonstrated a high light-absorption efficiency of 92.8% in the range of 280–2500 nm wavelength. The evaporation rate reached 1.34 kg m−2 h−1 and 5.83 kg m−2 h−1 under 1 sun and 5 sun irradiations, respectively. The plasmonic nanofiber membrane also exhibited long-term use stability, without any degradation in solar vapor generation performance even after 10 cycle tests. This work paves the way for the design and development of plasmonic nanofiber membranes as high-performance interfacial solar vapor generators.

Plasmonic silver nanoparticles promoted sugar conversion to 5-hydroxymethylfurfural over catalysts of immobilised metal ions

Plasmonic photocatalysis has attracted significant attention but not been applied to acid-catalysed reactions. Here we report that visible-light irradiation of silver nanoparticles (AgNPs) significantly promotes Lewis acid-catalysis by several immobilised metal ions to dehydrate sugars, producing 5-hydroxymethylfurfural (HMF) in good yields at moderate temperatures. In one example, we achieved a 68 % yield of HMF for the conversion of d-glucose using immobilised Cr3+ ions and AgNPs under visible-light irradiation. The turnover number achieved in the presence of AgNPs is 13.4 times higher than in the absence of AgNPs. We propose a mechanism whereby sugar molecules coordinate to the metal ions, and light absorption by these metal complexes causes electron density distribution shift to the ions, thereby boosting the catalytic activity. Surface plasmon resonance by the AgNPs amplifies incident light to high intensities, considerably promoting catalytic activity. This plasmon-enhanced acid catalysis performance defines a new paradigm and expands photocatalysis applications.

CW laser damage study in Ag/TiO2 bilayer thin films: Role of interfacially diffused plasmonic silver nanoparticles

Abstract CW laser (532 nm) induced damage mechanism has been studied on Ag/TiO2 bilayer thin films exhibiting diffused silver mediated plasmonic absorption. The thin films were deposited by e-beam evaporation technique under various O2 flow conditions in the range of 0–20 sccm. The required exposure time (tD) for onset of damage under irradiance of 37 W/cm2 has been measured to be in the range from 118 to 1244 s. Standing Wave Electric Field (SWEF) distribution has been simulated for all the Ag/TiO2 bilayer thin films based on the film optical constants retrieved from spectroscopic ellipsometry analysis. It has been observed that tD is mainly governed by two primary factors (in 2–16 sccm range) visualizing the shift of SWEF peak position with respect to Ag/TiO2 interface and the possible increase in thermal conductivity of TiO2 controlled by diffused Ag concentration across the interface. The SWEF magnitude and light absorbance seems to have relatively lesser bearing on laser withstanding time. Beyond 16 sccm, tD slightly decreases due to increase in surface roughness of the film. The required exposure time, tD is the highest for 0 sccm sample of which there is negligible interfacial Ag diffusion. All these results suggest that interfacially diffused plasmonic silver nanoparticles play an important role in deciding laser dose withstandability of Ag/TiO2 bilayer thin film system through control of electric field distribution and possibly thermal conductivity of TiO2 layer.

Enhanced Catalysis of Plasmonic Silver Nanoparticles by a Combination of Macro-/Mesoporous Nanostructured Silica Support

Porous silica with a unique nanostructure and interesting properties has a versatile range of applications. Hierarchically ordered macroporous silica (MacroS) can trap incident light inside the por...