the catalytic substrate. when polymers, complex ligands, or surfactants are used to prevent coalescence of the nanoparticles, the catalytic ability is frequently hindered due to reduced adsorption ability. however, these compounds can also be used in such a way that the chemical environment enhances the catalytic ability. supported on silica spheres – reduction of dyes silver nanoparticles have been synthesized on a support of inert silica spheres. the support plays virtually no role in the catalytic ability and serves as a method of preventing coalescence of the silver nanoparticles in colloidal solution. thus, the silver nanoparticles were stabilized and it was possible to demonstrate the ability of them to serve as an electron relay for the reduction of dyes by sodium borohydride. without the silver nanoparticle catalyst, virtually no reaction occurs between sodium borohydride and the various dyes: methylene blue, eosin, and rose bengal. mesoporous aerogel – selective oxidation of benzene silver nanoparticles supported on aerogel are advantageous due to the higher number of active sites. the highest selectivity for oxidation of benzene to phenol was observed at low weight percent of silver in the aerogel matrix (1% ag). this better selectivity is believed to be a result of the higher monodispersity within the aerogel matrix of the 1% ag sample. each weight percent solution formed different sized particles with a different width of size range. silver alloy – synergistic oxidation of carbon monoxide au-ag alloy nanoparticles have been shown to have a synergistic effect on the oxidation of carbon monoxide (co). on its own, each pure-metal nanoparticle shows very poor catalytic activity for co oxidation; together, the catalytic properties are greatly enhanced. it is proposed that the gold acts as a strong binding agent for the oxygen atom and the silver serves as a strong oxidizing catalyst, although the exact mechanism is still not completely understood. when synthesized in an au/ag ratio from 3:1 to 10:1, the alloyed nanoparticles showed complete conversion when 1% co was fed in air at ambient temperature. the size of the alloyed particles did not play a big role in the catalytic ability. it is well known that gold nanoparticles only show catalytic properties for co when they are ~3 nm in size, but alloyed particles up to 30 nm demonstrated excellent catalytic activity – catalytic activity better than that of gold nanoparticles on active support such as tio2, fe2o3, etc. light-enhanced plasmonic effects have been studied quite extensively. until recently, there have not been studies investigating the oxidative catalytic enhancement of a nanostructure via excitation of its surface plasmon resonance. the defining feature for enhancing the oxidative catalytic ability has been identified as the ability to convert a beam of light into the form of energetic electrons that can be transferred to adsorbed molecules. the implication of such a feature is that photochemical reactions can be driven by low-intensity continuous light coupled with thermal energy. the coupling of low-intensity continuous light and thermal energy has been performed with silver nanocubes. the important feature of silver nanostructures that are enabling for photocatalysis is their nature to create resonant surface plasmons from light in the visible range. the addition of light enhancement enabled the particles to perform to the same degree as particles that were heated up to 40 k greater. this is a profound finding when noting that a reduction in temperature of 25 k can increase the catalyst lifetime by nearly tenfold, when comparing the photothermal and thermal process. biological research researchers have explored the use of silver nanoparticles as carriers for delivering various payloads such as small drug molecules or large biomolecules to specific targets. once the agnp has had sufficient time to reach its target, release of the payload could potentially be triggered by an internal or external stimulus. the targeting and accumulation of nanoparticles may provide high payload concentrations at specific target sites and could minimize side effects. chemotherapy the introduction of nanotechnology into medicine is expected to advance diagnostic cancer imaging and the standards for therapeutic drug design. nanotechnology may uncover insight about the structure, function and organizational level of the biosystem at the nanoscale. silver nanoparticles can undergo coating techniques that offer a uniform functionalized surface to which substrates can be added. when the nanoparticle is coated, for example, in silica the surface exists as silicic acid. substrates can thus be added through stable ether and ester linkages that are not degraded immediately by natural metabolic enzymes. recent chemotherapeutic applications have designed anti cancer drugs with a photo cleavable linker, such as an ortho-nitrobenzyl bridge, attaching it to the substrate on the nanoparticle surface. the low toxicity nanoparticle complex can remain viable under metabolic attack for the time necessary to be distributed throughout the bodies systems. if a cancerous tumor is being targeted for treatment, ultraviolet light can be introduced over the tumor region. the electromagnetic energy of the light causes the photo responsive linker to break between the drug and the nanoparticle substrate. the drug is now cleaved and released in an unaltered active form to act on the cancerous tumor cells. advantages anticipated for this method is that the drug is transported without highly toxic compounds, the drug is released without harmful radiation or relying on a specific chemical reaction to occur and the drug can be selectively released at a target tissue. a second approach is to attach a chemotherapeutic drug directly to the functionalized surface of the silver nanoparticle combined with a nucelophilic species to undergo a displacement reaction. for example, once the nanoparticle drug complex enters or is in the vicinity of the target tissue or cells, a glutathione monoester can be administered to the site. the nucleophilic ester oxygen will attach to the functionalized surface of the nanoparticle through a new ester linkage while the drug is released to its surroundings. the drug is now active and can exert its biological function on the cells immediate to its surroundings limiting non-desirable interactions with other tissues. multiple drug resistance