A semiconductor nanocrystal compound is described capable of linking to an
affinity molecule. The compound comprises (1) a semiconductor nanocrystal
capable of emitting electromagnetic radiation and/or absorbing energy,
and/or scattering or diffracting electromagnetic radiation--when excited
by an electromagnetic radiation source or a particle beam; and (2) an
affinity molecule linked to the semiconductor nanocrystal. The
semiconductor nanocrystal is linked to an affinity molecule to form a
semiconductor nanocrystal probe capable of bonding with a detectable
substance. Exposure of the semiconductor nanocrystal to excitation energy
will excite the semiconductor nanocrystal causing the emission of
electromagnetic radiation. Further described are processes for
respectively: making the luminescent semiconductor nanocrystal compound;
making the semiconductor nanocrystal probe; and using the probe to
determine the presence of a detectable substance in a material.