Abstract: Nanoparticles, such as noble metal nanoparticles, having improved stability against aggregation in aqueous solution are provided. In addition to having improved stability against aggregation, the nanoparticles are highly photostable. Also provided are aqueous solutions containing the stabilized nanoparticles, methods of making the stabilized nanoparticles, imaging methods and organisms employing the nanoparticles, and in vivo assays for screening and characterizing the toxicity and biocompatibility of the nanoparticles.

Abstract: Compositions which are useful in ultralow level of detection based on functionalized nanoparticles having exceptional combinations of properties including stability, brightness, binding specificity, and ability to be imaged at single nanoparticle resolution over desired period of time. The biological moieties on the nanoparticles preserve biological function. The nanoparticle surface can comprise a first monolayer component which is adapted to bind to a biological moiety. The biological moiety can be adapted to bind to an analyte. The nanoparticle surface can further comprise a second monolayer component, which is adapted to help expose the first monolayer component on the surface. Other components on the surface can help stabilize the nanoparticle. The nanoparticles are stable against aggregation, have photostability (non-photodecomposition and non-blinking), and can achieve single molecule detection in real time. Analytes can be detected at low levels both in solution and on surfaces such as cell surfaces.