Chapter 20
Nanomaterial Applications in Optical Transduction
A new and impressive impetus in optical sensing technology has been brought about by the introduction of nanomaterials with outstanding photophysical properties such as semiconductor nanocrystals, carbon nanotubes and metal nanoparticles. In many respects, such materials are superior to the traditional molecular luminophores and are expected to replace them in many applications. Although many applications reported so far refer to molecular probes, such results are also useful for possible further integration with optical waveguides in order to develop true chemical sensors.
20.1 Semiconductor Nanocrystals (Quantum Dots)
20.1.1 Quantum Dots: Structure and Properties
Quantum dots (QDs, see Section 8.6) are semiconductor nanocrystals typically between 2 and 10 nm diameter (that is, 10–50 atoms in diameter). From the chemical standpoint, QDs are compounds of the elements from the periodic groups II-VI [1], III-V [2] or Ib-VI [3]. Common QD materials are of the MX type, where M is Cd, Zn or Pb and X is S, Se or Te. QDs have as a rule a roughly spherical shape but QDs with other shapes (cubes, spheres, pyramids, etc.) have also been synthesized. QDs feature outstanding photophysical properties [4] that brought about a revolution in bioimaging and optical sensing methods [5–8].
Electronic and optical properties of QDs derive from their semiconducting nature [9]. In order to understand these properties it is useful to keep in ...
