Ultraviolet–visible spectrophotometry

This chapter provides an overview of the use of optical absorption spectroscopy for the measurement of nanoparticles. Virtually, all nanoparticles scatter and absorb light to the extent that, in sufficient concentration, they can be detected using a traditional ultraviolet–visible spectrophotometer. The technique is useful to determine the concentration of particles, provided that either a reference material is available or that the material is very well understood. In general, it is not possible to simultaneously determine the concentration, size, or refractive index of particles using UV–vis spectrophotometry on its own. However, in combination with other methods, it is a useful technique, especially as a quality control method. In the case of metal particles, there can be plasmonic features in the UV–vis spectrum that are sensitive to local refractive index, particle size, shape, and agglomeration. The sensitivity to each of these parameters is exquisite; however, it is not recommended to use UV–vis spectrophotometry independently to measure these parameters because of the associated uncertainties. Gold is the most extensively studied of these plasmonic metals, and the relevant literature for gold nanoparticles is reviewed.