Biomedical Engineering Reference
In-Depth Information
Figure 4.2
Stained-glass window in Milan Cathedral, Italy, made by Niccolo da Varall
between 1480 and 1486, showing the birth of St. Eligius, patron saint of goldsmiths. h e red
colours are due to colloidal gold [9, 10].
Nanoparticles are designed at the nanometer level has advantage of
their small size as they possess novel properties that are typically not
observed in their conventional or bulk counterparts. Nanoparticles have a
much larger surface area to volume ratio which is the basis of their novel
physical-chemical properties [13, 14]. h e emergence of these novel prop-
erties on the nanoscale is attributable to the lack of symmetry at the inter-
face or to coni nement of electrons that does not scale linearly with size.
In nanoparticles, various atoms perhaps half or more in some cases, are
near interfaces. Surface properties such as energy levels, electronic struc-
ture and reactivity can dif er markedly from those in interior states. Since
properties depend in this way on size, rather than on the material, reliable
and continuous change can be achieved using a single material.
In 1908, observation of brilliant colors of colloidal metal nanoparticles
could be explained using classical Mie theory [15]. It is the most simple,
exact and only solution to Maxwell's equations which is relevant to the
particles. h e physical origin of the strong light absorption by noble metal
nanoparticles is the coherent oscillation of the conduction band elec-
trons induced by interaction with an electromagnetic i eld. h e resonance
between these oscillations and incident radiation, gives rise to an intense
peak in the visible range known as surface plasmon resonance (SPR). h is
