AuNPs/colloidal

Yogeswaran et al., designed a new bimetallic nanoparticles (Au and Pt) modified electrodes for simultaneous determination of AA, EP and UA [169], First, a composite film comprising of functionalized multiwall carbon nanotubes and nafion was formed on the GC electrode. Then Au and Pt NPs were electrochemically deposited on to the composite film modified GC electrode. The voltammetric peaks of AA, EP and UA are well resolved with the peak separations of 222 mV and 131 mV respectively. Lu et al., demonstrated the determination of UA on GC electrode electrodeposited with AuNPs and DNA [170], Clean GC electrode was immersed into a AuNPs colloidal solution and a potential of +1.5 V is applied for 60 min for the deposition of AuNPs. Then the electrode was dipped into a DNA solution (0.1 mg/ml) and a potential of +1.5 V is applied for 30 min to electrodeposit DNA. Finally, DNA/AuNPs modified electrode excellently separates the voltammetric signals of UA, NEP and AA. Li et al., electrodeposited AuNPs on the GC electrode modified with the ultrathin overoxidized polypyrrole film [171], The modified determines the UA in the presence of EP and AA with a lowest detection limit of 1.2 x 10"8 M. 

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. 

The sensitivity of the detection is usually improved by the silver enhancement method. A better detection limit was reported when a silver enhancement method was employed, based on the precipitation of silver on AuNPs tags and its dissolution (in HNO3) and subsequent electrochemical potentiometric stripping detection [43]. The new silver-enhanced colloidal gold stripping detection strategy represented an attractive alternative to indirect optical affinity assays of nucleic acids and other biomolecules. 

Hybrid organic-gold nanoparticles may be obtained essentially in two ways, that is, by formation of an organic layer around preformed AuNPs or colloids, and by synthesis of AuNPs in the presence of organic ligands such as thiols, amines, or phosphines. 

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... 

As mentioned in the previous section, the response, the stability and the enzyme activity found greatly enhanced at the MWCNT platform. Other than CNTs, AuNPs also possess some unique properties and recent years it has been widely employed in the biosensors to immobilize biomolecules. Thus in this section we discuss about the application of AuNP matrix for the immobilization of AChE for pesticide sensor development. With the use of AuNPs, the efficiency and the stability of the pesticide sensor gets greatly amplified. Moreover, the nanoparticles matrix offers much friendly environment for the immobilized enzyme and thus the catalytic activity of the enzyme got greatly amplified. Interestingly, Shulga et al. applied AChE immobilized colloidal AuNPs sensor for the nM determination of carbofuran, a CA pesticide [16], The enzyme-modified electrode sensor was also utilized for the sensitive electrochemical detection of thiocholine from the enzyme catalyzed hydrolysis of acetylthiocholine chloride (ATCl). The fabrication and the enzyme catalyzed reaction at the AuNPs coated electrode surface is shown in Fig. 6. 

AuNPs in Liquid-State Environment Solute pure and monolayer-coated ( capped ) AuNPs are central targets in colloid and surface science also with a historical dimension [258-262]. Facile chemical syntheses introduced by Schmid et al. [260] and by Brust et al. [263] have boosted AuNP and other metal nanoparticle science towards characterization of the physical properties and use of these nanoscale metallic entities by multifarious techniques and in a variety of environments. Physical properties in focus have been the surface plasmon optical extinction band [264—269], scanning and transmission electron microscopy properties, and electrochemical properties of surface-immobilized coated AuNPs [173, 268-276], To this can be added a variety of AuNP crosslinked molecular and biomolecular... 

Fig. 26 Self-assembling of a thiol derived NA-based NO donor, 1, and a-CD on the surface of colloidal AuNPs, Reproduced from ref. 147 with permission from the Centre National de la Recherche Scientifique (CNRS) and The Royal Society of Chemistry.

H-bond-driven aggregation has also played an important role in the development of directed NP and colloid assembly. An early publication by Rotello and co-workers describes the use of the plug-and-play polymer system of PS copolymers bearing DAP units to bind AuNPs functionalized with complementary Thy moieties through specific three-point... 

The samples were modified in direct (glow, diode) Ar plasma on Balzers SCD 050 device under the conditions presented in 2.3.1. Immediately after the plasma treatment the samples were inserted into water solution (2 wt. %) of 2-mercaptoethanol (ME), methanol solution (5.10 mol/dm ) of biphenyl-4,4 -dithiol (BPD) or into water solution (2 wt.%) of cysteamine (CYST) for 24 hours. To coat the polymers with the gold nanoobjects the plasma treated pol)rmers with grafted thiols were immersed for 24 hours into freshly prepared colloidal citrate stabilized solution of Au nanoparticles (AuNPs), [44,46] or Au nanorods (AuNR), 0.1 mol/dm water solution of cetyltrimethylammonium bromide). 

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