Surface Plasmon Absorption Band Research Articles

Colorimetric Detection of Trivalent Chromium in Aqueous Solution Using Tartrate-Capped Silver Nanoparticles as Probe

This study describes a simple and highly selective method for the colorimetric detection of trivalent chromium (Cr3+) using tartrate-capped silver nanoparticles (AgNPs) as probe. The addition of tartrate to the initially prepared AgNPs gives tartrate-stabilized AgNPs ascribing to the electrostatic repulsion of the highly negatively charged tartrate ions covered on the surface of AgNPs. It is found that, in the presence of Cr3+ in aqueous solution, the aggregation of tartrate-stabilized AgNPs occurs. The color of AgNPs suspension changes from yellow to pink and the surface plasmon absorption band broadens and red shifts, which could be applied for the colorimetric detection of Cr3+ in aqueous solution. The utilization of tartrate-stabilized AgNPs as probe substantially increases the selectivity and sensitivity for colorimetric detection of Cr3+. Control experiments with the addition of over 14 other metal ions, such as Pb2+, Zn2+, Cr2O7(2-), Cd2+, Co2+, Cu2+, Al3+, Ni2+, Mn2+, Ba2+, Fe3+, Ca2+, Mg2+, Sr+ do not result in a distinct change in the color or in the spectrum of the suspension, indicating that these metal ions do not interfere with the colorimetric detection of Cr3+. Under the conditions employed here, A502/A393 (ratio of absorption value at 502 nm to 393 nm) is linear with the concentration of Cr3+ within a concentration range from 0.1 to 1.17 microM with a detection limit of 0.06 microM. This study may offer a simple, rapid and sensitive approach to colorimetric detection of Cr3+ in aqueous solution.

Co-catalytic and electro-kinetic properties of Au nanostructures dispersed in solvents of varying dipole moments

This study demonstrates the influence of electrokinetic parameters; surface charge and zeta potential on the optical absorption band and co-catalytic activity of Au nanospheres (AuNS) dispersed in polar solvents, i.e., methanol, propanol, dimethylformamide, and dimethyl-sulphoxide. The narrow intense surface plasmon (SP) absorption band of AuNS (520nm) becomes broadened and a SP band at >970nm is appeared, whose absorption intensity varies from 0.05 to 0.13a.u. with the extent of aggregation in solvents of varying dipole moment from 1.66D to 3.96D while no such alteration in SP band occurs for AuNS dispersion in non-polar CCl4 as confirmed by DLS and TEM analysis. It found that the zeta potential (+50.32mV) and conductance (1673μS) of AuNS in water has been decreased to +24.06mV and 1480μS in methanol, respectively. The effective electronic charge ca. +4306μequiv./l present over AuNS surface in water suspension is highly reduced to +512μequiv./l in photoreaction (TiO2+salicylic acid+AuNS) mixture and the zeta potential (+50.32mV) and conductance (1673μS) of AuNS in water has been decreased to +24.06mV and 1480μS in methanol, respectively. The co-catalytic activity of aggregated AuNS (formed in polar solvents) varied in a diverse extent depending on its degree of agglomeration, where the non-aggregated aqueous AuNS+TiO2 mixture displayed higher degradation efficiency (r=9.990×10−3mM/min) of salicylic acid than that (r=9.172×10−3mM/min) of aggregated AuNS in MeOH+TiO2 mixture under UV light irradiation.

Unmodified gold nanoparticles as a simple colorimetric probe for ramoplanin detection

In this paper unmodified gold nanoparticles (AuNPs) were used as a sensing element to detect ramoplamin. Detection relies on the fact that the dispersed AuNPs solution is red due to the intense surface plasmon absorption band at 530 nm whereas the AuNPs solution in the presence of ramoplanin is blue. Upon aggregation, there is a significant change in absorbance intensity at 620 nm. Based on the aggregation of AuNPs induced by ramoplanin, a simple colorimetric method was developed for determining the of ramoplanin concentration. Experimental conditions influencing the analytical performance such as particle size, amount of AuNPs, incubation time and pH were evaluated. Under the optimized experimental conditions, this method could detect ramoplanin in a linear range from 0.30 to 1.30 ppm with a detection limit of 0.01 ppm and exhibited good reproducibility, selectivity and recovery. Analysis time of this assay was only 2 min. To investigate its potential applicability, this assay was successfully applied for the determination of ramoplanin in urine samples without costly instruments.

The size and structure of Ag particles responsible for surface plasmon effects and luminescence in Ag homogeneously doped bulk glass

As-prepared and heat-treated oxyfluoride glasses, co-doped with Ag nanoclusters/nanoparticles, are prepared at 0.15 at. % Ag concentration. The as-prepared glass shows an absorption band in the UV/violet attributed to the presence of amorphous Ag nanoclusters with an average size of 1.1 nm. The luminescence spectra of the untreated glass can also be ascribed to these Ag nanoclusters. Upon heat-treatment, the clusters coalesce into Ag nanoparticles with an average size of 2.3 nm, and the glasses show an extra surface plasmon absorption band in the visible. These particles, however, cease to emit due to ascribing plasmonic properties of bulk silver.

Bio-conjugated silver nano-materials and shape-directing role of cetyltrimethylammonium bromide

Conventional UV-visible spectrophotometric and transmission electron microscopic technique were used to determine the morphology of silver nanoplates (AgNP) using Alstonia scholaris aqueous leaves extract for the first time. The visible spectra showed the presence of three well defined surface plasmon absorption (SRP) bands at 500, 550 and 675 nm which attributed to the anisotropic growth of Ag-nanoplates. Transmission electron microscopic (TEM) analysis of AgNP showed formation of truncated triangular, polyhedral with some irregular shapes nanoplates in the size range 7-20 nm. Cetyltrimethylammonium bromide (CTAB) has no significant effect on the shape of the spectra, position of SRP bands, size and the size distribution of AgNP. Effects of various [CTAB] were also discussed in the green extra-cellular synthesis of AgNP using Alstonia scholaris leaves extract.

Modification of the silver nanoparticles size-distribution by means of laser light irradiation of their water suspensions

Contamination-free Ag nanoparticles were produced by nanosecond pulsed laser ablation (10Hz repetition rate, 15ns pulse duration) of a solid target immersed in double distilled water. The size distribution observed of the NPs is wider compared to those obtained by other preparation methods, mainly chemical. To modify it and make the NPs more appropriate for biological application, the fabricated suspensions were irradiated by an unfocused laser beam. The fundamental wavelength (λ=1064nm) of a Nd:YAG laser system was used for Ag NPs preparation. It lies outside their surface plasmon absorption band and was chosen to avoid self-absorption during ablation by already formed NPs. Excluding a possible absorption in the preparation stage provides a better control of the irradiation influence. The following irradiation of the suspension obtained was performed by the third (λTHG=355nm) harmonic of the laser system, which was chosen due to its positioning within the corresponding surface plasmon absorption band. The changes of the NPs characteristics caused by different laser fluence and duration of irradiation were traced by transmission electron microscopy (TEM) and confirmed by optical transmission measurements in the near UV and the visible region. A considerable narrowing (by about of a factor of three) of the surface plasmon extinction band was achieved, which is evidence of narrowing of the particles size distribution and approach of their shape to the ideal spherical.

Au or Ag nanoparticle-decorated 3D urchin-like TiO2 nanostructures: Synthesis, characterization, and enhanced photocatalytic activity

The semiconductors decorated with noble metals have attracted increasing attention due to their interesting physical and chemical properties. Here, 3D urchin-like hierarchical TiO2 nanostructures decorated with Au or Ag nanoparticles were prepared by wet-chemical process. The morphology and structure were characterized by different techniques. It shows that Au or Ag nanoparticles with narrow distribution are uniformly loaded on urchin-like TiO2 nanostructures, and the resulted composite nanostructures show distinct surface plasmon absorption band and quenched photoluminence compared to pure TiO2 nanostructures. Photocatalytic tests show both Au-decorated TiO2 and Ag-decorated TiO2 exhibit enhanced photocatalytic activity for photodegradation of methyl blue in water.

Thorough tuning of the aspect ratio of gold nanorods using response surface methodology

In the present work a central composite design based on response surface methodology (RSM) is employed for fine tuning of the aspect ratios of seed-mediated synthesized gold nanorods (GNRs). The relations between the affecting parameters, including ratio of l-ascorbic acid to Au3+ ions, concentrations of silver nitrate, CTAB, and CTAB-capped gold seeds, were explored using a RSM model. It is observed that the effect of each parameter on the aspect ratio of developing nanorods highly depends on the value of the other parameters. The concentrations of silver ions, ascorbic acid and seeds are found to have a high contribution in controlling the aspect ratios of NRs. The optimized parameters led to a high yield synthesis of gold nanorods with an ideal aspect ratio ranging from 1 (spherical particle) to 4.9. In addition, corresponding tunable surface Plasmon absorption band has been extended to 880nm. The resulted nanorods were characterized by UV–visible spectrometry and transmission electron microscopy.

Gold‐Nanoparticle‐Decorated Boron Nitride Nanosheets: Structure and Optical Properties

Synergetic cooperation of individual components of the nanocomposites (NCs) is responsible for their novel properties that lead to various technological applications. A simple chemical process depicting the deposition of functionalized gold nanoparticles on the surface of boron nitride nanosheets (BNNSs) in solution is reported. The structure, chemical composition, and optical properties of nanosheets are systematically studied. The deposition of Au nanoparticles on BNNS (BNNSAu) results in plasmonic band modulation, thus altering the optoelectronic properties of BNNSs. The intense surface plasmon absorption band of BNNSAu is narrowed and red‐shifted relative to the absorption band of as synthesized monometallic BNNSs. The observations reflect the strong interfacial interaction between BNNS and Au nanoparticles. This approach constitutes a basis for a simple process leading to the preparation of functionalized BNNSs and their utilization as nanoscale templates for assembly and integration with other nanoscale materials for futuristic optoelectronic devices.

Mechanism of morphology transformation during annealing of nanostructured gold films on glass

Nanostructured, just-percolated gold films were prepared by evaporation on bare glass. Annealing of the films at temperatures close to or higher than the softening temperature of the glass substrate induces morphological transformation to discrete Au islands and gradual embedding of the formed islands in the glass. The mechanism and kinetics of these processes are studied here using a combination of in situ high-temperature optical spectroscopy; ex situ characterization of the island shape by high-resolution scanning electron microscopy (HRSEM), atomic force microcopy (AFM) and cross-sectional transmission electron microscopy (TEM); and numerical simulations of transmission spectra using the Multiple Multipole Program (MMP) approach. It is shown that the morphological transformation of just-percolated, 10 nm (nominal thickness) Au films evaporated on glass and annealed at 600 °C, i.e., in the vicinity of the substrate glass transition temperature (Tg = 557 °C), proceeds via three processes exhibiting different time scales: (i) fast recrystallization and dewetting, leading to formation of single-crystalline islands (minutes); the initial spectrum characteristic of a continuous Au film is transformed to that of an island film, displaying a surface plasmon (SP) absorption band. (ii) Reshaping and faceting of the single-crystalline islands accompanied by formation of circumferential glass rims around them (first few hours); the overall optical response shows a blue shift of the SP band. (iii) Gradual island embedding in the glass substrate (tens of hours), seen as a characteristic red shift of the SP band. The influence of the annealing atmosphere (air, vacuum) on the embedding process is found to be minor. Numerical modeling of the extinction cross-section corresponding to the morphological transformations during island recrystallization and embedding is in qualitative agreement with the experimental data.

Protein-modified silver nanoplates for the complementary analytical method of localised surface plasmon resonance and matrix assisted laser desorption/ionisation mass spectrometry

A complementary analytical methodology combining localised surface plasmon resonance (LSPR) sensing and matrix assisted laser desorption/ionisation-mass spectrometry (MALDI-MS) has been developed by using triangular silver nanoplates (Ag NPLs). Ag NPLs with near-IR LSPR absorbance were prepared via a two-step photo-mediated growth process from Ag nanoparticles. These could be utilised as a common platform for LSPR/MALDI-MS, as they were suitable for LSPR sensing via the analysis of surface plasmon absorption bands and as the assisting material for LDI-MS. For practical use, the detection of analytes by LSPR sensing can be achieved by using specific biomolecular recognition techniques that involve the surface modification of metal NPs with large molecules such as proteins. We investigated the effect on LSPR sensitivity (i.e. refractive index unit, RIU) of modifying the Ag surface with molecules of different sizes, and found that the RIU values were proportional to the amplitude of the cube root of the molecular weight, Mw1/3. We demonstrated the utility of this complementary LSPR and MALDI-MS analysis methodology by evaluating the binding of a soybean trypsin inhibitor to the Ag NPL substrate covalently modified with trypsin. This specific biomolecule recognition phenomenon was first detected using the LSPR technique, and then successfully identified by MALDI-MS.

A benzophenone-bearing acid oligodimethacrylate and its application to the preparation of silver/gold nanoparticles/polymer nanocomposites

The synthesis of photosensitive urethane dimethacrylate that contains poly(ethylene oxide) sequence (PEG, Mw: 400), carboxylic and benzophenone moieties, and its characterization by specific methods (1H and 13C NMR, FTIR, UV and electrospray ionization-mass spectroscopy) are reported. UV curing parameters of this macromer (BP-UDMA) alone and in monomer combinations was evaluated through FTIR spectroscopy and photo-differential scanning calorimetry using 1 wt% 4-(dimethylamino)phenylacetic acid as co-initiator or Irgacure 819 (Irg819). The results show that the photopolymerization rates of the BP-UDMA are higher in the case of Irg819 (R max P : 0.108 s−1) due to its synergic action, whereas the degree of conversion of C=C double bond (DC, after 120 s of UV irradiation) is over 77 %. When other co-monomers (non-acid urethane dimethacrylate and silyl urea methacrylate) are incorporated into the formulation, the photopolymerization rate (0.095–0.132 s−1) and DC (84.59–79.69 %) varied in reasonable limits. Depending of the photoinitiator type, as well as the monomer composition, the addition of 0.5, 1 and 3 wt% noble metal precursors (AgNO3 and AuBr3) led to the formation of hybrid composites with in situ-synthesized nanoparticles (NPs), where the variations in the intensity of the surface plasmon absorption bands appeared in the range 400–456 nm (Silver) or 500–553 nm (Gold), better results being obtained in the first initiating system. Homogeneous dispersion of nanoparticles into the polymer matrix was evidenced by EDX and TEM analysis, the last proving the existence of nanoparticles with sizes around 10 nm and variable morphologies. X-ray diffraction analysis complemented these results.

Synthesis of Gold Nanoparticles in Presence of Poly(vinyl pyrrolidone) from Gold Hydroxide Precursor Salt

Since the discovery, gold nanoparticles (GNPs) have been attracting scientific and research communities owing to their biocompatibility, excellent thermal conductivity, low cytotoxicity, ease of processability, and highly functionalization capability. In this report, we discuss synthesis of gold nanoparticles with poly(vinyl pyrrolidone) (PVP) in 1–butanol from gold hydroxide, a new precursor salt. An emergence of a strong surface plasmon absorption band at 535 nm confirms formation of GNPs in the colloidal solution. The stability of Au colloid was studied by using UV–Visible and zeta potential measurements. The interfacial interaction between GNP and PVP molecules was studied in terms of Fourier transform infrared and X–ray photoemission spectrum (XPS). Marked enhancement in some of the vibrational bands (e.g., C=O, C–H, and C–N stretching) of PVP molecules in presence of GNPs reveals existence of an interaction between this two major constituents. However a small red-shift in the C=O stretching frequency of pyrrolidone group of PVP molecule implies that a weak interaction occurs via O–atom of carbonyl group. Appearance of Au4f doublet band at 82.7 and 86.4 eV in XPS spectrum with a chemical shift of 3.7 eV further confirms formation of GNPs by reduction of Au3+ to Au0 chemical state in presence of PVP. A noticeable negative shift in the binding energies of Au4f doublet band as compared to bulk Au atom suggests an interfacial interaction between GNP and PVP molecules. Transmission electron microscopic images propose that Au crystalline core is covered by an amorphous layer of PVP molecules.

A simple and sensitive colorimetric method for the determination of propafenone by silver nanoprobe

Abstract A simple, rapid and ultrasensitive colorimetric method for the determination of propafenone, based on the specific recognition property of propafenone with the unique optical properties of AgNPs, has been developed. The addition of propafenone induced the citrate to be desorbed from the surface of the AgNPs, leading to the aggregation of the AgNPs, accompanied by a dramatic surface plasmon absorption band shift and thereby results in their yellow-to-red even purple color change. The concentration of propafenone can be determined by monitoring with the naked eyes or a UV–Vis spectrophotometer. The detection limit of the present method for propafenone was 2.4 μM. The proposed method is a promising mean for on-site detection of propafenone in actual samples without costly instruments.

Worm-Like Ag/ZnO Core–Shell Heterostructural Composites: Fabrication, Characterization, and Photocatalysis

Novel worm-like Ag/ZnO core–shell heterostructural composites were fabricated using a two-step chemical method. As-prepared silver nanowires were soaked in a solution of zinc acetate and triethanolamine to form worm-like Ag/ZnO core–shell composites under ultrasonic irradiation. Samples were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy, and UV–vis spectrophotometer. The results show that the core–shell composites are composed of single-crystal Ag nanowires serving as the core, on which dense ZnO particles grow as the shell. The surface plasmon absorption band of Ag/ZnO composites is distinctly broadened and red shifted to monometallic Ag nanowires. The PL intensity of Ag/ZnO heterostructural composites varies and has the minimum intensity for the sample prepared with Ag of 2.8 atom %. Moreover, photocatalytic tests show that the Ag/ZnO composites ...

A Solid‐State Plasmonic Solar Cell via Metal Nanoparticle Self‐Assembly

Sustainable plasmonic photocurrents are generated by gold and silver nanoparticles, located at a TiO2/hole conductor interface. The spectral photocurrent response closely follows the surface plasmon absorption bands of the metal particles. A simple nanoparticle self-assembly method for the solar cell fabrication is presented. Three mechanisms for plasmon-induced charge separation are proposed. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gold glyconanoparticle-based colorimetric bioassay for the determination of glucose in human serum

Gold nanoparticles (d=10nm) self-assembled with a specifically synthesized thiol-derivatized mannose were used to develop a novel colorimetric bioassay for glucose in human serum. The addition of Con A containing four binding sites induces the aggregation of mannose-stabilized gold nanoparticles via specific mannose–Con A interactions, which leads to a red shift of the surface plasmon absorption band centered at 520nm. The presence of glucose in the solution hinders the Con A-induced aggregation of the mannose-stabilized gold nanoparticles because of the competitive binding of glucose to Con A. Thus, it results in a decrease of the surface plasmon absorption band shift. The simple surface plasmon absorption band change resulting from this method provides a selective means to detect and quantitate glucose in the linear concentration range of 500–4000μg/mL within 10min with an experimental detection limit of 363μg/mL. The colorimetric assay was applied for the determination of glucose in human serum samples and the determined concentration was close to the value reported by the manufacturer of human serum sample used in the present experiment. The present bioassay can be successfully applied for the determination of human blood glucose levels for the diagnosis of diabetes without the use of enzymes.

Temperature-Dependent Morphology Evolution and Surface Plasmon Absorption of Ultrathin Gold Island Films

Ultrathin gold island films on transparent substrates display a characteristic surface plasmon (SP) absorption band in which the peak position and full width at half-maximum (fwhm) are highly sensitive to the film morphology. In the present study, we investigated the temperature dependence of morphological evolution and the corresponding unique surface plasmon resonance (SPR) properties variation of the ultrathin gold island films (5 nm nominal thickness) upon rapid thermal annealing for 180 s at different temperatures ranging from 100 to 700 °C. The morphological evolution of the ultrathin gold film upon the thermal annealing-induced dewetting was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the optical properties variation was characterized by a transmission UV–vis-NIR spectroscopy. A strong temperature dependence of morphological evolution and optical properties variation as a function of thermal treatment conditions was identified. The blue shift and band narrowing of the SP absorption band can be correlated with various morphological characteristics, e.g., the increased open area fraction of island films, average separation between islands or nanoparticles (NPs) and the decreased aspect ratio (length divided by width) upon increasing thermal treatment temperatures. The temperature dependence of the transmission localized surface plasmon resonance (T-LSPR) may enable a science-based design of optical sensing and dynamic thermal sensors upon the morphological manipulation of ultrathin metallic surface nanostructures by thermal dewetting.

A study of the surface plasmon absorption band for nanoparticles

In this work, we have performed the theoretical calculations of the absorbance of spherical silver nanoparticles dispersed in deionized water and in n-propanol, computed from a summation of the Mie series for different particle radius in the range from 1 to 17 nm. In both solvents, the maximum absorbance increases and the bandwidth at half-maximum absorption and number of particles decrease. Maximum absorbance of silver nanoparticles is higher in n-propanol than in deionized water. These results are due to high refractive index of n-propanol. Key words: Silver nanoparticles, absorbance, particle radius.

Composite silica nanospheres covalently anchored with gold nanoparticles at the outer periphery of thermoresponsive polymer brushes

We report on the fabrication of water-dispersible composite silica nanospheres covalently anchored with gold nanoparticles (AuNPs) possessing thermo-tunable spatial distributions at the outer periphery of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) brushes. Starting from initiator-functionalized silica nanoparticles, surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) afforded hybrid silica nanoparticles coated with PNIPAM brushes. The substitution reaction of halogen terminal groups of grafted PNIPAM chains with sodium azide and subsequent click reaction with 1,2-dithiolane-3-pentanoic acid-N-propargylamide afforded hybrid silica nanoparticles coated with 1,2-dithiolane end-capped PNIPAM brushes. AuNPs were then covalently anchored to the outer periphery of hybrid silica nanoparticles by utilizing strong chemisorption of surface-attached dithiolane moieties to AuNPs. Dynamic laser light scattering (LLS) measurements revealed that thermosensitive PNIPAM brushes at the surface of hybrid silica nanoparticles exhibit reversible thermo-induced collapse/swelling transitions, leading to the facile thermo-modulation of spatial distributions of AuNPs covalently attached at the periphery of composite silica nanospheres and thermo-reversible surface plasmon absorption band shift. The reported strategy of covalent assembly of AuNPs into well-defined composite nanospheres possessing thermo-tunable characteristics might be further exploited for colorimetric temperature sensing and responsive SERS detection purposes.