AuNP dispersions

Another easy way of attaching AuNPs on electrode surface is by casting method. In this method a known quantity AuNPs dispersed in easily volatile solvent is placed on the electrode surface and allowed to dry [87] (Figure 10). 

In order to characterize the AuNPs, extinction coefficients of the AuNP dispersions were determined and compared to reported values. Previously it was shown that for AuN Ps ranging between... 

AuNP Series 2. PSS/SWCNT and PSS/AuNP dispersions used together. 

Owing to the simphcity and versatility of surface-initiated ATRP, the above-mentioned AuNP work may be extended to other particles for their two- or three-dimensionally ordered assemblies with a wide controllabiUty of lattice parameters. In fact, a dispersion of monodisperse SiPs coated with high-density PMMA brushes showed an iridescent color, in organic solvents (e.g., toluene), suggesting the formation of a colloidal crystal [108]. To clarify this phenomenon, the direct observation of the concentrated dispersion of a rhodamine-labeled SiP coated with a high-density polymer brush was carried out by confocal laser scanning microscopy. As shown in Fig. 23, the experiment revealed that the hybrid particles formed a wide range of three-dimensional array with a periodic structure. This will open up a new route to the fabrication of colloidal crystals. 

Synthesis, properties, and applications of polymer-protected AuNPs have been reviewed by Shan and Tenhu and will not be covered in detail here.139 The basic motivation here is to better control the particle size and dispersity and to obtain robust materials avoiding metal loss during or after utilization of the polymeric material. 

In principle, there are two factors that will influence the catalytic activity First, the collapsed PNIPA layer probably presents a higher steric barrier for benzyl alcohol molecules to diffuse from bulk aqueous dispersion to the surface of AuNPs, causing the reaction to slow down (as shown in Fig. 8). Second, with the increase of temperature, water-soluble hydrophilic PNIPA networks become oil-soluble and hydrophobic, which is favorable for the diffusion of hydrophobic benzyl alcohol onto the AuNP surface (as shown in Fig. 14). Thus, the catalytic activity of Au composite particles should increase with increasing temperature. Figure 15 demonstrates that the second effect prevails over most of the temperature range the TOF value at 40°C... 

One year later, Brust and Schiffrin [28,29] published a method for AuNPs synthesis which has a considerable impact on the overall field in less than a decade because it allowed the facile synthesis of thermally stable and air-stable AuNPs of reduced dispersity and controlled size for the first time. In this method, the gold colloids are sterically stabilized by organic molecules having thiol, amide or acid groups in contrast to the citrate reduction method where the gold colloids are kinetically stabilized in aqueous solutions by an electrical double layer [28,29], The main advantage of the Brust method is that the gold particles behave in a way as chemical compounds. These AuNPs can be repeatedly isolated and... 

Transmission electron micrographs (TEM) can be performed to characterize the AuNPs. An example of TEM images is shown in Fig. 1. Fast Fourier Transform (FFT) of crystalline planes distances, UV-Vis spectrum and energy dispersive X-ray can be also employed to achieve a better characterization of the AuNP obtained (results not shown here). 

DNA-AuNPs appear red in color without linker DNA and turn blue when linker DNA induces nanopaiticle assembly. (Reproduced with permission from C. A. Miikin et al.. Nature 1996, 382, 607-609.) (c) Extinction spectrum of dispersed and assembled DNA-AuNPs. (See color insert.)... 

HAuChaq + NaOH [Au(OH)4] Na"aq (pH 6-10) Au(OH)3/Support wash, dry then calcinate at 563-673 K - AuNP/Support (optimal AuNP size 3 nm, stable hemispherical NPs, the size being controlled by the calcination temperature whose optimum is 570 K, optimal support Ti02 for which the addition of Mg citrate is necessary during or after co-precipitation for a good dispersion of hny AuNPs). 

The visual appearance of the NP dilutions was confirmed by dynamic light scattering (DLS) measurements with a Zetasizer Nano ZS (Malvern Instruments Inc., UK) at 25 °C. The AuNPs solutions at pH 6.4 had 15-nm size distributions and strongly anionic zeta potentials >30 mV (Table 5.1). This potential implies that a strong electrostatic repulsive force existed, which was dominant over the attractive force, suppressing agglomeration and maintaining the well-dispersed nature of each of the AuNPs concentrations. 

The AuNPs placed in DMEM F-12 cell culture media containing 2.5 mM L-gluta-mine, and 15 mM HEPES without phenol red were well-dispersed and stabilized (Rahman et ak, 2013) however, plasma proteins adsorb on the NP surface, making a protein shell called a protein corona (Cedervall et al., 2007 Lynch et al., 2007 Lynch and Dawson, 2008) within 5 min after mixing (AUdlany and Murphy, 2010) (Figure 5.10). This corona is known to influence the size, shape, and surface chemistry of the AuNPs affecting its interaction with biomolecules and cells (Miclaug et al., 2014). 

UV-VIS absorption studies showed the culture media did not have any absorption in the region of the AuNPs absorption (520 nm), and there was a strong absorption peak at 521 nm for the well-dispersed AuNPs in the media, which also confirmed no resonance shift due to agglomeration of AuNPs occurred in culture media (Figure 5.12a). 

A sensor for the detection of the toxin microcystin-LR is basically constructed in a similar way RGO is first immobilized on the GCE followed by electrodeposition of polyDPB and AuNPs. Finally, a new AuNP layer was electrodeposited over the polyDPB layer [111], The composite film was covered with chitosan dispersed in IL and the microcystin-LR antibody was covalently attached to the carboxyl groups of polyDPB. The microcystin-LR was detected by DPV in the concentration range of 0.1-8 fM. In [110] and [111], it was necessary to use a specific IL, RGO, and AuNP to obtain the lowest signal to noise ratio as well as a low LOD. The RGO and the AuNPs participate in signal amplification while the IL creates a microenvironment preserving the activity of the immobilized antibody. 

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