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The linear and nonlinear optical properties of metal nanoparticles are highly tunable by variation of parameters such as particle size, shape, composition, and environment. To fully exploit this tunability, however, quantitative information on nonlinear absorption cross sections is required, as well as a sufficient understanding of the physical mechanism underlying these nonlinearities. In this work, we present a detailed and systematic investigation of the wavelength-dependent nonlinear optical properties of Ag nanoparticles embedded in a glass host, in which the most important parameters determining the nonlinear behavior of the system are characterized. This allows a proper quantification of absorption cross sections and elucidation of the excitation mechanism. Based on small-angle X-ray scattering measurements average particle diameters of 3 and 17 nm are estimated for the studied samples. The nonlinear optical properties of the nanoparticle−glass composite are studied in an extended wavelength range with the open aperture z-scan technique. The experiments reveal a strong dependence of the nonlinear optical response on the excitation wavelength. Based on the wavelengthdependent response, excited-state absorption is determined as the excitation mechanism of the nanoparticles. Electromagnetic simulations demonstrate that the contributions from electric field enhancement and plasmonic coupling between the particles in the diluted glasses are limited, which implies that the very high two-photon absorption cross section at 460 nm ((6.9 ± 1.6) × 10 6 GM for the 3 nm particles and (19.5 ± 2.2) × 10 9 GM for the 17 nm particles) is an intrinsic property. In addition, irradiance-dependent measurements elucidate the role of saturation of the excited-state absorption process on the observed nonlinearities.

Nanomaterials are being extensively produced and applied in society. Human and environmental exposures are, therefore, inevitable and so increased attention is being given to nanotoxicity. While silica nanoparticles (NP) are one of the top five nanomaterials found in consumer and biomedical products, their toxicity profile is poorly characterized. In this study, we investigated the toxicity of silica nanoparticles with diameters 20, 50 and 80 nm using an in vivo zebrafish platform that analyzes multiple endpoints related to developmental, cardio-, hepato-, and neurotoxicity. Results show that except for an acceleration in hatching time and alterations in the behavior of zebrafish embryos/larvae, silica NPs did not elicit any developmental defects, nor any cardio- and hepatotoxicity. The behavioral alterations were consistent for both embryonic photomotor and larval locomotor response and were dependent on the concentration and the size of silica NPs. As embryos and larvae exhibited a normal touch response and early hatching did not affect larval locomotor response, the behavior changes observed are most likely the consequence of modified neuroactivity. Overall, our results suggest that silica NPs do not cause any developmental, cardio- or hepatotoxicity, but they pose a potential risk for the neurobehavioral system.

Gold nanoparticles functionalized with polyethylene glycol of different chain lengths are used to determine the influence of the capping layer thickness on the radiosensitizing effect of the particles. The size variations in organic coating, built up with polyethylene glycol polymers of molecular weight 1-20 kDa, allow an evaluation of the decrease in dose enhancement percentages caused by the gold nanoparticles at different radial distances from their surface. With localized eradication of malignant cells as a primary focus, radiosensitization is most effective after internalization in the nucleus. For this reason, we performed controlled radiation experiments, with doses up to 20 Gy and particle diameters in a range of 5-30 nm, and studied the relaxation pattern of supercoiled DNA. Subsequent gel electrophoresis of the suspensions was performed to evaluate the molecular damage and consecutively quantify the gold nanoparticle sensitization. In conclusion, on average up to 58.4% of the radiosensitizing efficiency was lost when the radial dimensions of the functionalizing layer were increased from 4.1 to 15.3 nm. These results serve as an experimental supplement for biophysical simulations and demonstrate the influence of an important parameter in the development of nanomaterials for targeted therapies in cancer radiotherapy.

In this study, amyloid fibers prepared from hen egg white lysozyme (HEWL) are specifically mediating the assembly of citrate-capped gold nanoparticles, on glass and silicon substrates. The organization of nanoparticles is investigated for nanoparticle diameters of 5, 15, and 25 nm, using variable deposition times, and under a range of pH, salt, citric acid and nanoparticle concentrations. The observed periodic self-organization of nanoparticles is mainly influenced by the interparticle interactions rather than by the spacing of binding groups at the surface of the amyloid fiber template. For a fixed ionic strength of 2.3 mM and particle concentration, the interparticle distance increases with the nanoparticle diameter in agreement with the values predicted by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. UV−visible spectroscopy measurements show a red shift of the 520 nm plasmon absorption peak associated with spherical gold nanoparticles up to 650 nm upon aggregation or decrease in the interparticle distance. Such protein templates deposited on technologically relevant surfaces allow the self-assembly of inorganic nanoparticle arrays with functional optoelectronic properties. ■ INTRODUCTIONBioinspired and bioinorganic materials chemistry offers unique opportunities to produce and manipulate structures at the nanometer scale, under mild conditions and using minimal amounts of precursors. 1 In particular, the soft and reversible interactions characteristic of natural biomineral systems allow a wide flexibility, but also a surprising specificity, in designing hybrid architectures made from building blocks with precisely defined grain sizes, shapes and crystalline orientations. 2 Because of all these advantages, bioinspired materials chemistry is a perfect complement, and a potential alternative to traditional top-down nanofabrication techniques.The rapid development of plasmonics and metamaterials has further increased the interest in controlled arrangements of nanoparticles on biological templates. 3−5 In such systems, the plasmonic properties of the material can be tuned by modifying the periodicity and orientation of nanoparticle assemblies, or by using particles having different shapes and sizes. 6,7 The resulting properties can be predicted with excellent accuracy for the development of devices such as biosensors or waveguides.The toolbox of biological templates and self-assembly techniques available to produce novel materials targeting specific applications is growing each day, incorporating scaffolds based on DNA, 4,8 proteins 9 or virus capsids. 10,11 Among potential biological templates, amyloid fibers are a particularly attractive class of protein or peptide assemblies, with excellent mechanical and chemical resistance allied to dimensions at the nanometer scale. 12 These natural templates have therefore been extensively investigated for the preparation of metal nanowires, 13 among other applications. 14 Amyloid fibers are characterized by a periodic arrangement of monomeric protein units. Th...

Mesoporous silica nanoparticles (MSNPs) are gaining a large interest in the field of medical and biomedical applications due to their biodegradability and high loading capacity as a carrier. In this work, a simple synthesis and functionalization procedure is reported, which allows tuning the nanoparticle properties, functionalization, and biodegradability. Variations in the synthesis procedure are introduced, including temperature, concentration of catalyst, and surface functionalization. These samples are characterized and afterwards degraded in phosphate buffered saline (PBS) to determine their degradation kinetics. The amount of degraded material is colorimetrically determined, using an optimized protocol based on molybdenum blue chemistry. It is shown that the degradability of the nanoparticles increased with decreasing synthesis temperatures, lower amounts of catalyst, and higher concentrations of nanoparticles. Surface functionalization alters the degradation kinetics as well, rendering amino-functionalized nanoparticles the fastest degradation behavior, followed by carboxylated and nonfunctionalized nanoparticles. From these results, it can be concluded that the degradation rate of MSNPs can be varied from a few hours to several days by small changes in the synthesis procedure. Moreover, the degradation behavior is strongly dependent on the nanoparticle growth rate.

Nanoparticles of different materials are already in use for many applications. In some applications, these nanoparticles need to be deposited on a substrate in a fast and reproducible way. We have developed a new direct liquid injection system for nanoparticle deposition by chemical vapor deposition using a liquid nanoparticle precursor. The system was designed to deposit nanoparticles in a controlled and reproducible way by using two direct liquid injectors to deliver nanoparticles to the system. The nanoparticle solution is first evaporated and then the nanoparticles flow onto a substrate inside the vacuum chamber. To allow injection and evaporation of the liquid, a direct liquid injection and vaporization system are mounted on top of the process chamber. The deposition of the nanoparticles is controlled by parameters such as deposition temperature, partial pressure of the gases, and flow rate of the nanoparticle suspension. The concentration of the deposited nanoparticles can be varied simply by changing the flow rate and deposition time. We demonstrate the capabilities of this system using gold nanoparticles. The selected suspension flow rates were varied between 0.25 and 1 g/min. AFM analysis of the deposited samples showed that the aggregation of gold nanoparticles is well controlled by the flow and deposition parameters.

An optical flux sensor, based on the fluorescence properties of materials and nanoparticles, has been developed to control the deposition rate in thin film deposition systems. Using a simple diode laser and a photomultiplier tube with a light filter, we report the detection of gallium atoms and CdSe-ZnS quantum dots. This setup has a high sensitivity and reproducibility.