Attachment nanoparticles

Amidation and esterification are also widely exploited. CNTs-amide bonds are found as part of linking agents employed to covalently attach nanoparticles, generally metals or semiconducting quantum dots (QDs), via ex situ synthesis. These linkers are frequently bifunctional, possessing an additional anchoring site that is bound to the nanoparticle side. For example, modified CdSe QDs have been attached via an amine-terminated amido linker (Fig. 3.18) [97], while Au nanoparticles are often attached through mercapto-terminated linkers [98],... 

The self-assembly of ordered nanostructures consisting of nanoparticles with sizes between 1 and 1000 nm has attracted a lot of attention owing to their unique optical, electronic, magnetic, catalytic, and other physical properties.1 The ability to attach nanoparticles onto planar surfaces in a well-defined, controllable, and reliable... 

Figure 3.77 (a) Examples of transition metal complexes bound to the ends of carbon nanotubes, (b) HRTEM image of an oxidized nanotube with attached nanoparticles of CdSe which in their turn are functionalized with mercaptopropionic acid ( Wiley-VCH 2003). 

A new approach comes from advance in nanotechnology that offer an opportunity for the discovery of novel compounds with antibiofihn activity. One such example is nanosilver crystals, which show potent antimicrobial activity and have been used to coat catheters (100). Furthermore the use of nanofabrication surface techniques can change surface properties such as charge, wetability, and topography, in addition to the ability to add functional activities. The precise control of surface composition and chemical functionality, along with novel methods such as microwave synthesis, discussed in this chapter, promote our abihty to attach nanoparticles to a wide range of surfaces and can offer important new tools to combat bacterial biofllm persistence. 

A. Martinez, E. Muniz, C. Teijon, I. Iglesias, J.M. Teijon, M.D. Blanco, Targeting tamoxifen to breast cancer xenograft tiunours Preclinical efficacy of folate-attached nanoparticles based on alginate-cysteine/disulphide-bond-reduced albumin, Pharmaceut. Res., 31, 1264-1274, 2014. 

Significantly, in order to improve the sensitivity and response and recovery speed of the prepared sensors, several methods are introduced to the design of resistance sensors (1) attaching nanoparticles which have catalytic function (e.g., Pd, Ag, Pt) onto the surface of nanoflbers [73, 81] and (2) choosing metal salts such as KCl, LiCl, NaCl, and MgCL as the dopant to add into the nanoflbers, especially in humidity sensors the influences of the nanoparticles or metal salts are illustrated in Fig. 11.4c, d [82, 84]. For example, Xu et al. [85] fabricated Ag nanoparticle-coated ZnO-Sn02 nanoflbers for the detection of formaldehyde. Due... 

A limitation of the colloid probe technique, however, is the minimum particle size that can be reproducibly attached by using optical microscopy. For spheres smaller than 1 J.m, it becomes difficult to correctly position the particle at the very end of the cantilever to avoid touching the substrate with the edge of the cantilever. In this respect, the name colloid probe is somewhat misleading since colloidal particles are usually smaller than 1 pm. Recently, there have been attempts to attach nanoparticles to the end of AFM tips either by wet chemistry [272] or by epoxy-coating of tips and dipping them into a powder [273]. 

Electron irradiation (100 keV) of the sample, heated to 800°C, yields MWCNTs (20-100 nm in length) attached to the surface. Such nanotube growth does not take place if natural graphite, carbon nanoparticles or PTFE are subjected to electron irradiation. The result implies that the material may be a unique precursor for CNTs and may constitute a new preparation method. 

Nanotechnology has led to very efficient versions of liposomes. Tiny hollow spheres only nanometers in diameter hold even tinier capsules of medicine. The spheres are made of silica covered with gold nanoparticles and when they are coated with antibodies they attach to tumor cells. The spheres are sensitive to light of specific wavelengths and when the light is applied, either heat up and destroy the tumor, or burst, releasing the drugs within the capsules directly into the tumor. 

The TEM image of the PVP capped CdSe at 5 hr in figure 6A showed small, spherical particles with some aggregation. The aggregation is due to the oriented attachment between the spherical nanoparticles as a result of dipole-dipole interactions between the highly... 

Fig. 35 TEM image of peptide fibres coated with streptavidin-gold nanoparticles, (a, b) Peptides with biotin directly attached (using SAF-pl-biotin) particles are 10 nm, (c) Peptide fibre with biotinylated anti-FLAG antibody attached that was then bound to gold-labelled streptavidin particles are 5 nm. Reprinted with permission from Ryadnov and Woolfson [76]. Copyright 2004 American Chemical Society...

Recent advances of the Seeman group led to the construction of a nanomechanical device from DNA [89]. In this molecular apparatus, the ion-dependent transition of B-DNA into the Z-conformation is used to alter the distance between two DNA DX domains attached to the switchable double helix. Atomic displacements of about 2-6 nm were attained. Ionic switching of nanoparticles by means of DNA supercoiling has also been reported [53]. Additional advances regarding the use of DNA is nanomechanical devices have been reported by Fritz et al., who showed that an array of cantilevers can be used to... 

Hyun et al. [345] prepared PbS Q-dots in a suspension and tethered them to Ti02 nanoparticles with a bifunctional thiol-carboxyl linker molecule. Strong size dependence due to quantum confinement was inferred from cyclic voltammetry measurements, for the electron affinity and ionization potential of the attached Q-dots. On the basis of the measured energy levels, the authors claimed that pho-toexcited electrons should transfer efficiently from PbS into T1O2 only for dot diameters below 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of the PbS/Ti02 assembly were consistent with electron transfer from small Q-dots. The measured charge transfer time was surprisingly slow ( 100 ns). Implications of this fact for future photovoltaics were discussed, while initial results from as-fabricated sensitized solar cells were presented. 

In summary, we found that Ugands indeed coordinate at the surface of nanoparticles and that they can be firmly or loosely attached to this surface according to their chemical nature. Furthermore, the hgands influence the reactivity of the metal nanoparticles. This is important in catalysis but, as we will see later in this paper, is also important for the control of the growth of metal nanoparticles of defined size and shape. 

Finally, gold nanoparticles functionalized with thiols have emerged as a very interesting field of research. The gold particle is used as a core to which thiols are attached and the melting of the chains can give rise to LC-like behavior on the gold surface or to real mesophases. 

Figure 2.2 Optical probe of surface-enhanced microscopy proposed byj. Wessel. A metallic nanoparticle attached to a glass substrate confines and enhances the light field.

Recently, however, the development of nanotechnology may provide the changes on the research and development of practical catalysts. As mentioned in the previous section we can now design and synthesize a metal nanoparticle with not only various sizes and shapes, but also with various combinations of elements and their locations. Thus, we can now design the synergetic effect of two elements. In the case of core/shell structured bimetallic nanoparticles, the shell element can provide a catalytic site and the core element can give an electronic effect (a ligand effect) on the shell element. Since only the atoms on the surface can be attached by substrates, the thickness of the shell should be an important factor to control the catalytic performance. 

The interaction of adsorbed thiol molecules with gold nanoparticles as a function of the mean particle size has also been studied [180]. Monochromated X-ray Photoelectron Spectroscopy (MXPS) measurements showed the attachment of the thiol sulfur headgroup onto the cluster surface leading to a positive BE shift in the Au 4f corelevel. No line width broadening could be observed indicating that the thiol-gold interaction affects the whole... 

Scheme 5. Covalent attachment to an amino-functionalized gel of pre-formed, polymer-stabilized metal (Rh, Pt) nanoparticles. (Reprinted from Ref. [33], 1991, with permission from the American chemical Society.)...

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