Colored nanoparticles

When thiols with varying chain lengths, such as Cg-, Cio-, Ci2- and Ci6- are used, we observe very interesting trends [47]. First, all the colloids under reflux conditions display a strong reddish color. Nanoparticles, especially those of coinage metals like gold and silver, display striking colors... 

Figure 3. Schematic design of a lateral flow test (According to [69]) (a) sample pad (sample inlet and filtering), conjugate pad (reactive agents and detection molecules), incubation and detection zone with test and control lines (analyte detection and functionality test) and final absorbent pad (liquid actuation), (b) Start of assay by adding liquid sample, (c) Antibodies conjugated to colored nanoparticles bind the antigen, (d) Particles with antigens bind to test line (positive result), particles w/o antigens bind to the control line (proof of vahdity).

By polymerizing poly(A -isopropylacrylamide) (PNIPAM) [55] or poly (2-(diethylamino)ethyl methacrylate) (PDEAEMA) [56] as a stimuli responsive polymer/hydrogel layer around a colored nanoparticle of PS-co-PMMA, the local refractive index and consequently the color intensity of the latex could be switched by the temperature [55] or pH [56]. 

FIGURE 4.1.3 In plasmonic ELISA the biocatalytic cycle of the enzyme generates colored nanoparticle solutions of characteristic tonality. S, substrate P, product NP, nanoparticle. Reproduced from Ref. [64], with permission from the Nature Publishing Group. 

Fig. 4 shows PL spectra of Mn and Pr-codoped ZnS nanoparticles opdcaily aimealed in air and vacuum. Mn and Pr-codoped ZnS nanoparticles emit light of white color. The PL intoisity of the Pr-related peaks incirasrf more rapidly than that of Mn-related peak, for the codoped ZnS nanoparticles ann ed in air. The different rates may be assodated with the luminescent ions. Pr-related oimplaces are incaeased with the incrrasing UV irradiation time, but Mn ions are constant. In case of the arni ing in vacuum, Pr-related peaks are initially weaker in intensity than Mn-related peaks due to small Pr-related complexes. 

In this chapter, photoelectrochemical control of size and color of silver nanoparticles, i.e., multicolor photo-chromism [1], is described. Silver nanoparticles are deposited on UV-irradiated Ti02 by photocatal5dic means [2]. Size of the nanoparticles can be roughly controlled in the photocatalytic deposition process. However, it is rather important that this method provides nanoparticles with broadly distributed sizes. The deposited silver nanoparticles are able to be dissolved partially and reduced in size by plasmon-induced photoelectrochemical oxidation in the presence of an appropriate electron acceptor such as oxygen. If a monochromatic visible light is used, only the particles that are resonant with the light are dissolved. That is, size-selective dissolution is possible [3]. This is the principle of the multicolor photochromism. 

The synthesis of Pt octapods was achieved by mixing lOOmg of Pt(acac)2, 180 mg of ACA, 1.6g of HDD, 2g of HDA, and 1 mL of DPE in a 15 mL three-neck round-bottom flask, which was evacuated and flushed with argon several times. The flask was immersed in an oil bath preset at 130 °C and the mixture turned to a transparent yellow color. The flask was then immersed into an oil bath preset at 180°C. Within a couple of minutes the mixture turned black, indicating the formation of Pt nanoparticles. The... 

Taton T.A., Lu G., Mirkin C.A., Two-Color Labeling of Oligonucleotide Arrays via Size-Selective Scattering of Nanoparticle Probes, J Am Chem Soc. 2001 123 5164-65. 

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