Silver Nanoparticle-Based Sensor for the Selective Detection of Nickel Ions

Silver nanoparticles (AgNPs) can be used as a surface plasmon resonance (SPR) colorimetric sensor; the correlation between the SPR phenomenon and the aggregation state of nanoparticle allows the real-time detection of a target molecule. Surface functionalization of NPs with proper molecular baits is often performed to establish the selectivity of the sensor. This work reports on the synthesis of AgNPs under reducing conditions and on the functionalization thereof with mercaptoundecanoic acid (11-MUA). UV-VIS Spectroscopy confirmed the formation of AgNPs, eliciting a surface plasmon absorption band (SPAB) at 393 nm that shifted to 417 nm upon surface coating. Dynamic light scattering was used to investigate the surface coatings; moreover, pelleted AgNPs@11MUA nanoparticles were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analyzers (EDX), and infrared spectroscopy to corroborate the presence of 11MUA on the surface. Most interestingly, the resulting AgNPs@11MUA selectively detected micromolar levels of Ni2+, also in the presence of other cations such as Mn2+, Co2+, Cd2+, Cu2+, Zn2+, Fe2+, Hg2+, Pb2+, and Cr3+.

Nanoporous gold nanoleaf as tunable metamaterial

We have studied optical properties of single-layer and multi-fold nanoporous gold leaf (NPGL) metamaterials and observed highly unusual transmission spectra composed of two well-resolved peaks. We explain this phenomenon in terms of a surface plasmon absorption band positioned on the top of a broader transmission band, the latter being characteristic of both homogeneous “solid” and inhomogeneous “diluted” Au films. The transmission spectra of NPGL metamaterials were shown to be controlled by external dielectric environments, e.g. water and applied voltage in an electrochemical cell. This paves the road to numerous functionalities of the studied tunable and active metamaterials, including control of spontaneous emission, energy transfer and many others.

A teoria de Mie aplicada ao estudo da banda de absorção de plasmon de superfície de nanopartículas metálicas coloidais

Com o avanço na tecnologia de nanofabricação nas últimas duas décadas, os materiais nanoestruturados têm atraído a atenção de pesquisadores devido à suas propriedades físicas únicas, não presentes nos mesmos materiais em dimensões maiores. Tais materiais, em especial as nanopartículas, apresentam aplicações nos mais diversos campos de interesse da indústria, como na fabricação de dispositivos optoeletrônicos (Shirasaki et al., 2013). Nanopartículas de prata apresentam uma faixa de absorção intensa na região UV-Vis conhecida com banda de absorção de plásmon de superfície (SPAB, do inglês surface plasmon absorption band), que ocorre devido as oscilações coletivas dos elétrons na superfície. Em particular, para aplicações em dispositivos optoeletrônicos, em fotônica e no campo emergente da plasmônica, é essencial saber o comportamento óptico das nanopartículas e conhecer a SPAB.A SPAB de nanopartículas metálicas pode ser obtida pelo método de Mie (Mie, 1908), aplicado com sucesso ao estudo de nanopartículas de prata e ouro. Nessa teoria, a SPAB de nanopartículas esféricas são obtidas através do cálculo da seção de choque de extinção ou eficiência de extinção de nanopartícuas. Neste contexto, o objetivo principal deste trabalho é calcular a banda de absorção de plasmon de superfícies de nanopartículas de prata usando a soma completa da série de Mie para a seção de choque de extinção de partículas de prata esféricas numa gama de raios de 1 a 17 nm e simular o comportamento dessa banda.

Application of Starch-Stabilized Silver Nanoparticles as a Colorimetric Sensor for Mercury(II) in 0.005 mol/L Nitric Acid

A sensitive and selective Hg2+optical sensor has been developed based on the redox interaction of Hg2+with starch-coated silver nanoparticles (AgNPs) in the presence of 0.005 mol L−1HNO3. The relative intensity of the localized surface plasmon absorption band of AgNPs at 406 nm is linearly dependent on the concentration of Hg2+with positive slope for the concentration range 0–12.5 μg L−1and negative slope for the concentration range 25–500 μg L−1. Experiments performed demonstrated that metal ions (Na+, K+, Mg2+, Ca2+, Pb2+, Cu2+, Zn2+, Cd2+, Fe3+, Co2+, and Ni2+) do not interfere under the same conditions, due to the absence of oxidative activity of these ions, which guarantees the high selectivity of the proposed optical sensor towards Hg2+. The limits of detection and quantification were found to be 0.9 µg L−1and 2.7 µg L−1, respectively, and relative standard deviations varied in the range 9–12% for Hg content from 0.9 to 12.5 μg L−1and 5–9% for Hg levels from 25 to 500 μg L−1. The method was validated by analysis of CRM Estuarine Water BCR505. A possible mechanism of interaction between AgNPs and Hg2+for both concentration ranges was proposed on the basis of UV-Vis, TEM, and SAED analyses.

Highly Sensitive and Selective Pymetrozine Colorimetric Sensor Based on P-Aminobenzenesulfonic Acid Modified Ag NPs

This paper reports a novel colorimetric sensor for pymetrozine based on p-aminobenzenesulfonic acid functionalized silver nanoparticles (p-ABSA-modified Ag NPs), which were characterized by IR spectroscopy, ultraviolet–visible spectroscopy (UV–vis), and transmission electron microscopy (TEM). The newly synthesized p-ABSA-modified Ag NPs are yellow in color due to the intense surface plasmon absorption band centered at 400nm. In the presence of pymetrozine, the yellow p-ABSA-modified Ag NPs solution turns to dark green, with a dramatic surface plasmon absorption band centered at 660nm. Moreover, high selectivity for pymetrozine was approved by the comparative experiments with an absorption ratio of A660/A400 more than 0.7. This highly sensitive sensor allows a direct and rapid quantitative assay of pymetrozine with a colorimetric limited detection concentration of 0.01mg/L.

Synthesis of One Dimensional Gold Nanostructures

Gold nanostructures with shapes of rod, dumbbells, and dog bone have been fabricated by an improved seed-mediated method. It is found that the pH change (the addition of HNO3or HCl) and the presence of Ag+ions have a great influence on the growth process and aspect ratios of these Au nanocrystals. UV-Vis-NIR absorption spectra for the Au colloidal show that the transverse plasmon absorption band locates at ~520 nm, while the longitudinal plasmon absorption band shifts in a wide spectra region of 750–1100 nm. The obtained Au nanostructures have been investigated by transmission electron microscopy, high-resolution transmission electron microscopy, and X-ray diffractometer. Based on the characterizations and FDTD simulations, most of the obtained Au nanorods are single crystals, possessing an octagonal cross-section bounded by and faces. One model for the anisotropic growth has been proposed. It is found that slow kinetics favor the formation of single-crystalline Au nanorods.

Influence of negative charge on the optical properties of a silver sol

The effects of negative charge on the optical properties of a silver sol prepared using sodium borohydride as a reductant were studied. The oscillations in the position of the maximum and the intensity of the surface plasmon absorption band were observed. The observed effects were explained as a consequence of the fluctuation of the density of free electrons due to the alternate charging and discharging of the silver particles. The charging process involves electron injection from borohydride ions and intermediate species formed during the course of the metal-catalyzed hydrolysis of borohydride ions (BH3OH-, BH2(OH)2 - and BH(OH)3 - ) into the silver particles, while discharge of the silver sol, by reduction of water to hydrogen, limits the attainable negative charge on the particles.