Nanoparticles for in-vitro and in-vivo biosensing and imaging

12 Metal nanoparticles
is provided by engineering the shape (principally spheric and elliptic) and the dimension
of the particles.
The following sections describe briefly the significant properties and the origin of the
plasmon resonances in spherical and ellipsoidal metal nanoparticles.
Figure 1.1: Nanoparticles in comparison with other biological entities.
1.2 Historical overview: gold through the centuries
The fact that gold compounds could impart a red color to the objects was well known;
Egyptian manuscripts from the Greco-Roman era refer to it [9]. The Egyptians, Greeks
and Romans used many colored pigments for the decoration of their buildings, ceramics
and glass-ware. The use of gold and silver particles in glassblowing is evident in the
famous Lycurgus Cup (Fig.1.2). Gold NPs scatter green and transmit red light so the
cup appear to be red or green depending on the position of the light source (inside or
outside) [10]. Chemical analysis of the Lycurgus cup shows that it is similar to most
other Roman glass, but it contains very small amounts of gold (about 40 parts per
million) and silver (about 300 parts per million). In figure 1.2 (right), a TEM image, a
silver-gold alloy coming from a sample of the Lycurgus cup is clearly visible [11]. The
crystalline nature of the Ag/Au particles and their fine dispersion in the glass suggests
that this colloidal metal was precipitated out from solution by heat treatment.
In the Middle Ages, chemistry developed mostly through the protoscience of Alchemy.
Alchemical processes required the construction of scientific apparatus and the invention
of many laboratory techniques like heating, refluxing, extraction, sublimation and distillation
to treat metals with various chemical substances [12]. In the early thirteenth
century the improvement of distillation methods resulted in the discovery of the mineral
acids which greatly increased the power of the alchemist to dissolve substances and to