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A rapid, wash-free highly sensitive detection method for C-reactive protein (hs-CRP) is reported with both triangular silver nanoplate (TSNP) and Au-edge coated TSNP biosensor sols. The latter shows higher assay sensitivity as well as excellent stability under assay conditions including centrifugation and salinity. A series of Au derived TSNP sols including Au-edge-coated TSNP, AuAg nanomesh and nanobox derived sols are examined as statistically representative saline-stable enhanced ensemble local surface plasmon resonance (LSPR) refractive index sensitive sensors. Samples with plasmon bands spanning the biological spectral window are prepared showing enhancement compared with the original TSNP sols. Refractive index sensitivities as high as 1816 nm RIU−1 are exhibited by Au-edge-coated TSNP sols. The priority of ensemble refractive index sensitivity values over figures of merit in characterising these sols is examined using discrete dipole approximation calculations and single nanostructure dark field microscopy measurements. We anticipate that the high ensemble LSPR refractive index sensitivities, saline stability and ultra-low detection limit capacity of the Au derived TSNP sols, in particular Au-edge coated TSNP sols, present them as excellent candidates for sensing within biological environments.

The plasmonic spectra of solution phase ensembles of triangular silver nanoplates have been analysed in order to examine the fundamental properties underlying their size-dependent enhanced refractive index sensitivities. Linewidth studies highlight variations in the response of these solution phase nanostructures to those previously reported for single immobilized triangular nanostructures. The observation of insignificant broadening of the resonance linewidth for larger edge length nanoplates highlights minimal contribution of radiative damping processes at these dimensions. Comparative single nanoplate studies using discrete dipole approximations were performed to analyse the dephasing processes contributing to these reduced linewidths and to determine the key parameters defining the underlying plasmonic response. These single nanoplate approximations highlight the dominance of absorption processes over radiative processes and demonstrate that this dominance can be attributed to the platelet nature/geometry of the nanoplates. These calculations indicate that the higher aspect ratio allows for the maintenance of coherent plasmon oscillations as the edge length of the triangular platelet increases within the sols. Thickness studies verify that this reduction in radiation damping is due to high aspect ratio and can act to confine electromagnetic fields at the nanoplate surface, thereby increasing near-field enhancement and hence the resultant plasmonic refractive index sensitivity.

A rapid and readily reproducible seed-based method for the production of high quality silver nanoprisms in high yield is presented. The edge-length and the position of the main plasmon resonance of the nanoprisms can be readily controlled through adjustment of reaction conditions. From UV-vis spectra of solutions of the nanoprisms, the inhomogeneously broadened line width of the in-plane dipole plasmon resonance is measured and trends in the extent of plasmon damping as a function of plasmon resonance energy and nanoprism size have been elucidated. In addition, an in-depth analysis of the lamellar defect structure of silver nanoprisms is provided that confirms that the defects can lead to a transformation of the crystal structure in the vicinity of the defects. These defects can combine give rise to lamellar regions, thicker than 1 nm, that extend across the crystal, where the silver atoms are arranged in a continuous hexagonal-close-packed (hcp) structure. This hcp structure has a periodicity of 2.50 A, thus explaining the 2.50 A lattice fringes that are commonly observed in 〈111〉 oriented flat-lying nanoprisms. A new understanding of the mechanisms behind anisotropic growth in silver nanoprisms is presented.

Nanotechnology has vast potential for expanded development and novel application in numerous sectors of society. With growing use and applications, substantial production volumes and associated environmental release can be anticipated. Exposure effect of nanoparticles (NP) on biological systems may be intrinsic to their physicochemical properties introducing unknown associated risk. Herein, we expand the knowledge of health and environmental impact of silver nanoparticles (AgNPs), testing the acute toxicity of 14 AgNP preparations on developing zebrafish embryos (Danio rerio). Toxicological end points, including mortality, hatching rate, and heart rate were recorded. Concentration, stabilization agent and physicochemical properties were monitored as contributing outcome factors. Our findings indicate wide ranging LC50 24 h postfertilization values (0.487 ppm (0.315, 0.744 95% CI) to 47.89 ppm (18.45, 203.49 95% CI)), and indicate surface charge and ionic dissolution as key contributory factors in AgNP exposure outcome.

Recent advancements in solution-based methods have enabled a wide range of remarkable morphologies and sizes of silver nanoparticles to be produced. In this chapter, some of the different approaches that have been taken to prepare Ag nanomaterials are discussed. Both, aqueous-based and organic-based procedures for the preparation of spherical particles are described. The controlled synthesis of shaped Ag nanoparticles is particularly highlighted, and theories regarding the growth of anisotropic silver particles are reviewed. The seed structure and growth-directing abilities of different organic stabilizers are especially important. Keywords: silver; nanoparticles; spherical; anisotropic; seeds; multiply twinned particles; shape; synthetic methods

Solution phase triangular silver nanoplates (TSNP) with versatile tunability throughout the visible-NIR wavelengths are presented as highly sensitive localized surface plasmon refractive index sensors. A range of 20 TSNP solutions with edge lengths ranging from 11 to 200 nm and aspect ratios from 2 to 13 have been studied comprehensively using AFM, TEM, and UV-vis-NIR spectroscopy. Studies of the localized surface plasmon resonance (LSPR) peak's sensitivity to refractive index changes are performed using a simple sucrose concentration method whereby the surrounding refractive index can solely be changed without variation in any other parameter. The dependence of the TSNP localized surface plasmon resonance (LSPR) peak wavelength lambda(max) and its bulk refractive index sensitivity on the nanoplate's structure is determined. LSPR sensitivities are observed to increase linearly with lambda(max) up to 800 nm, with the values lying within the upper limit theoretically predicted for optimal sensitivity, notwithstanding any diminution due to ensemble averaging. A nonlinear increase in sensitivity is apparent at wavelengths within the NIR region with values reaching 1096 nm.RIU(-1) at lambda(max) 1093 nm. Theoretical studies performed using a simple aspect ratio dependent approximation method and discrete dipole approximation methods confirm the dependence of the LSPR bulk refractive index sensitivity upon the TSNP aspect ratio measured experimentally. These studies highlight the importance of this key parameter in acquiring such high sensitivities and promote these TSNP sols for sensing applications at appropriate wavelengths for biological samples.

The microwave (MW)-assisted formation of ZnO micro-javelins from zinc nitrate and urea in aqueous solution is described. The particles (named as ‘micro-javelins’ because of their high aspect ratio and needle-like tips) grow hexagonally with well-defined facets in the 〈010〉 direction and pointed tips in (0001) direction. Powder X-ray diffraction patterns show the appearance of a strikingly dominant (1000) orientation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations reveal the morphological evolution of these hexagonal ZnO particles with time. The effect of precursor concentrations, counterion type and MW irradiation power and their consequent influence on pH and Zn2+ ion concentration are investigated. A mechanism for the formation of the micro-javelins is postulated. The microwave induced supersaturation of Zn(OH)+ species under the weakly basic pH condition and the initial growth through the (000) direction (oxygen-rich face) are proposed to be the key factors that dictate the formation of these ZnO micro-javelins. The present one-step microwave process is a straightforward and a reproducible method for the bulk synthesis of defect-free ZnO micro-javelins, which would find potential applications in microelectronic devices (e.g. lasers, cantilevers in surface probing equipment, etc.).

Solution phase triangular silver nanoplate (TSNP) ensembles are herein presented as tunable, highly sensitive, LSPR sensors with excellent potential for versatile amply responsive biosensing applications. The recorded LSPR refractive index sensitivities for the highest aspect ratio TSNPs examined are amongst the highest reported to date for various other nanostructures. Calculations demonstrate that sensitivities of the TSNP sols, as high as the theoretical upper limit, are achievable by tuning the aspect ratio parameter, without any significant diminution observed due to ensemble averaging. Theoretical studies identify the aspect ratio of the nanoplates as a key parameter in controlling the LSPR sensitivity of the TSNPs.

Within this work we present a new class of shaped silver nanoparticle ensembles which have demonstrated high sensitivities to variations in the refractive index of their surrounding environment. The ensembles' collective response has proven to exceed that of other sensitivities quoted in literature by various other nanoparticle structures, with sensitivity values of up to 376.6 nm/RIU recorded. A quick, simple sucrose sensitivity test has been developed in which any corresponding shift in the nanoparticles' spectrum can be associated solely to a change in the surrounding refractive index. AFM, TEM and dynamic light scattering characterisation of the mean diameter and height distributions of the nanoparticle ensembles provides information on the relationship between the structural properties of the nanoparticles and their sensitivity.

A rapid, straight-forward method for the preparation of silver colloidal solutions of various colours has been developed. This is based on the reduction of silver ions by ascorbic acid in the presence of citrate-stabilized silver seeds, additional trisodium citrate and a polymer such as polyvinylpyrrolidone. The colour of the sol is controlled by varying the concentration of only one reagent, namely the trisodium citrate. TEM studies show that this effect is due to changes in morphology of the particles. Working at temperatures above 50 °C yields well-defined triangular plates, which are stable in the reaction medium. Samples prepared at lower temperatures and left in the reaction medium experience etching and a consequent change in particle shape. The mechanisms of the initial particle growth and the etching process are discussed.

Microwave irradiation of solutions of Zn(NO3)2 and urea provides a straightforward route to a-axis oriented crystals of needle-like morphology.