Color Transferability from Solution to Solid Using Silica Coated Silver Nanoparticles.

The interpretation of color change in sensors and tests can be linked to incorrect conclusions if the intrinsic color changes are not accounted for. In this work, we study the intrinsic color change associated with the process of embedding nanoparticles in a polymer to create nanocomposite films. We present a safer, faster method to coat silver nanoparticles with silica and employ a seven-factor Plackett-Burman design to identify critical factors in the synthesis. Silver nanodisks with increasing thicknesses of the silica shell showed a decreasing sensitivity of their localized surface plasmon resonance (LSPR) toward changes in the refractive index surrounding the nanoparticle. A color shift of up to 72 nm was observed when bare nanoparticles were embedded in poly(vinyl alcohol), but no color change was perceived when nanoparticles were coated with a 25-nm-thick silica shell. Understanding the origin of color changes intrinsic to the preparation of polymeric nanocomposites aids in the design and correct use of plasmonic sensors.

The Huge Role of Tiny Impurities in Nanoscale Synthesis.

Nanotechnology is vital to many current industries, including electronics, energy, textiles, agriculture, and theranostics. Understanding the chemical mechanisms of nanomaterial synthesis has contributed to the tunability of their unique properties, although studies frequently overlook the potential impact of impurities. Impurities can show adverse effects, clouding the interpretation of results or limiting the practical utility of the nanomaterial. On the other hand, as successful doping has demonstrated, the intentional introduction of impurities can be a powerful tool for enhancing the properties of a nanomaterial. This Review examines the complex role of impurities, unintentionally or intentionally added, during nanoscale synthesis and their effects on the performance and usefulness of the most common classes of nanomaterials: nanocarbons, noble metal and metal oxide nanoparticles, semiconductor quantum dots, thermoelectrics, and perovskites.

Linear assembly of gold nanoparticle clusters via centrifugation.

Centrifugation is widely used in the synthesis and handling of solution-phase nanoparticles to improve their purity and to change the composition of the solvent. Herein, we couple the optical properties of citrate-stabilized gold nanoparticles and silica encapsulation to investigate how centrifugation impacts the formation of stabilized nanoparticle clusters in solution without the use of linker molecules or asymmetric functionalization. Gold nanoparticles preconcentrated using a high (9,400) g force result in linear assemblies of gold cores that are spaced by approximately 1-4 nm within Au(n)@SiO(2) structures (n = number of gold nanoparticle cores per silica shell) with approximately 30% monomers, 30% dimers, 20% trimers, and 10% 4-7mers. In comparison, nanoparticles preconcentrated using (stirred) ultrafiltration and low (23) g force centrifugation have statistically identical cluster distributions (90% monomers, 9% dimers, and 1% trimers) whereas nanoparticles that are not preconcentrated always exhibit 100% monomers using the same silica coating procedure. We hypothesize that under high g force, the electrical double layer surrounding the gold nanoparticles is slightly polarized thereby increasing the attraction between nanoparticles and the formation of stable clusters. The conductivity of the solution plays an important role in this stabilization. This novel demonstration of linear cluster formation of gold nanoparticles using centrifugation suggests that this commonly used preparative tool can both positively or negatively impact the fundamental properties of these materials and their use in various applications.

Silica-void-gold nanoparticles: temporally stable surface-enhanced Raman scattering substrates.

Reproducible detection of a target molecule is demonstrated using temporally stable solution-phase silica-void-gold nanoparticles and surface-enhanced Raman scattering (SERS). These composite nanostructures are homogeneous (diameter = 45 +/- 4 nm) and entrap single 13 nm gold nanoparticle cores inside porous silica membranes which prevent electromagnetic coupling and aggregation between adjacent nanoparticles. The optical properties of the gold nanoparticle cores and structural changes of the composite nanostructures are characterized using extinction spectroscopy and transmission electron microscopy, respectively, and both techniques are used to monitor the formation of the silica membrane. The resulting nanostructures exhibit temporally stable optical properties in the presence of salt and 2-naphthalenethiol. Similar SERS spectral features are observed when 2-naphthalenethiol is incubated with both bare and membrane-encapsulated gold nanoparticles. Disappearance of the S-H Raman vibrational band centered at 2566 cm(-1) with the composite nanoparticles indicates that the target molecule is binding directly to the metal surface. Furthermore, these nanostructures exhibit reproducible SERS signals for at least a 2 h period. This first demonstration of utilizing solution-phase silica-void-gold nanoparticles as reproducible SERS substrates will allow for future fundamental studies in understanding the mechanisms of SERS using solution-phase nanostructures as well as for applications that involve the direct and reproducible detection of biological and environmental molecules.

310 nm irradiation of atmospherically relevant concentrated aqueous nitrate solutions: nitrite production and quantum yields.

The heterogeneous processing of atmospheric aerosols by reaction with nitrogen oxides results in the formation of particulate and adsorbed nitrates. The water content of these hygroscopic nitrate aerosols and consequently the nitrate ion concentration depend on relative humidity, which can impact the physicochemical properties of these aerosols. This report focuses on the 310 nm photolysis of aqueous sodium and calcium nitrate solutions at pH 4 over a wide concentration range of nitrate ion concentrations representative of atmospheric aerosols. In particular, the quantum yield (phi) of nitrite formation was measured and found to significantly decrease at high concentrations of nitrate for Ca(NO(3))(2). In particular, phi for Ca(NO(3))(2) was found to have a maximum value of (7.8 +/- 0.1) x 10(-3) for nitrate ion solution concentrations near one molal, with the smallest quantum yield for the highest concentration solution above 14 m nitrate ion, phi = (2.3 +/- 2.0) x 10(-4). The effect of the addition of the radical scavenger, formate, on the 310 nm photolysis of these solutions was also investigated and found to increase phi by a factor of 2 or more for both sodium and calcium nitrate solutions. In the presence of formate, Ca(NO(3))(2) solutions again showed a significant decrease in phi with increasing NO(3)(-) concentration: phi = (1.4 +/- 0.1) x 10(-2) at (1.0 +/- 0.1) x 10(-2) m NO(3)(-) compared to phi = (4.2 +/- 0.3) x 10(-3) at 14.9 +/- 0.1 m NO(3)(-). This decrease in phi was not observed in NaNO(3) solutions. The change in electronic structure, as evident by the more pronounced shift of the n-pi* absorption band away from actinic wavelengths with increasing concentration for Ca(NO(3))(2) compared to NaNO(3), is most likely the origin of the greater decrease in phi for Ca(NO(3))(2) compared to NaNO(3) at elevated NO(3)(-) concentrations. The role of nitrate photochemistry in atmospheric aerosols and the atmospheric implications of these concentration dependent quantum yields are discussed.

Probing cells with noble metal nanoparticle aggregates.

This review focuses on the integration of noble metal nanoparticle aggregates as tags and transport vessels in cellular applications. The natural tendency of nanoparticles to aggregate can be reduced through surface modification; however, this stabilization is often compromised in the cellular environment. The degree of nanoparticle aggregation has both positive and negative consequences. Nanoparticle aggregates are more efficiently removed by the organism compared with single nanoparticles, preventing delivery to their cellular target. In addition, these aggregates are recognized by cells in different ways versus isolated nanoparticles. Despite these negatives, aggregates exhibit enhancement for many detection and treatment techniques in comparison with single nanoparticles. In coming years, the role of aggregates and better control over the degree of aggregation in cellular studies will be required for the realization of medical applications.