(N20345) permits attachment of these very small (1.4 nm) yet uniformly sized gold particles to

accessible thiol groups in biomolecules (Figure 2.2.38, Figure 2.2.39). NANOGOLD? monomaleimide,

which is supplied as a set of five vials of a powder lyophilized from pH 7.5 HEPES buffer,

is simply resuspended with the thiol-containing protein in deionized water at room temperature

or below to form the conjugate, after which any excess NANOGOLD? monomaleimide is

removed by gel filtration.102,103

In addition to its many uses for light and electron microscopy, NANOGOLD? monomaleimide

has been shown to be an extremely efficient quencher for dyes in molecular beacons—probes that

can be used for homogeneous fluorescence in situ hybridization assays.104 NANOGOLD? conjugates

of antibodies and streptavidin are described in Section 7.2 and Section 7.6, respectively, along

with reagents and methods for silver enhancement to amplify electron microscopy detection.104

Figure 2.2.38 Reaction of NANOGOLD? monomaleimide

(N20345) with a thiol. Image courtesy of Nanoprobes, Inc.

Figure 2.2.39 Scanning transmission electron microscope

(STEM) image indicating that labeling with NANOGOLD?

monomaleimide (N20345) occurs specifically at a hinge-thiol

site on the IgG molecule. Image courtesy of Nanoprobes, Inc.

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DATA TABLE 2.2 THIOL-REACTIVE PROBES EXCITED WITH VISIBLE LIGHT