The original synthesis of this substance used small amounts of citric acid as a reducing agent and is named for Turkevich.
Navarro et al modified one procedure to create this substance by adding really pure sodium acetylacetonate as a complexing agent. Molecular beacons consisting of DNA loops attached to this substance have better discrimination versus those using naked DNA partly due to this substance's ability to quench fluorescence. The original synthesis of this substance used small amounts of citric acid as a reducing agent and is named for Turkevich. Attaching Sigma-Aldrich has modified this substance to make it "spiky" to create a series of "urchins", and they are commonly sold in a solution of citrate and proprietary surfactant. Faulk and Taylor used secondary antibodies conjugated with this substance to detect salmonella antigens, and those secondary antibodies are commonly used stains in (*) electron microscopy. The peak SPR wavelength of this substance increases from 515 nm to 570 nanometers as their diameter is increased, and a common synthesis of this material forms a red solution because of a nanowire intermediate; that synthesis involves adding a reducing agent to chlorauric acid. For 10 points, name this suspension of spherical particles of a certain metal valuable metal.
Navarro et al modified one procedure to create this substance by adding really pure sodium acetylacetonate as a complexing agent.
colloidal gold [or gold nanoparticles; prompt on "gold"]