Biomedical Engineering Reference
In-Depth Information
17.3.4 Nanoparticle-Based PDT
There has been great excitement recently in the potential of nanoparticles
(NPs) for a wide range of applications, including medical diagnostics and
therapeutics [18]. This disruptive technology is based on the special optical,
electrical, mechanical, or chemical properties that emerge when materials are
formulated at the nanoscale (typically, 1-100 nm) compared to the bulk prop-
erties. Optical NPs include the following:
- Metal NPs with light absorption and scattering spectra that are highly
dependent on the size, shape, and form (e.g., solids vs. shells, spheres vs.
rods)
- Quantum dots (Qdots), semiconductor NPs that are fluorescent in the
visible and/or near-infrared, which are very bright, have very low photo-
bleaching, have narrow emission spectra with the peak emission increasing
with the Qdot diameter, and have a wide excitation spectrum so that a
single light source can excite many different sizes of Qdots
- NPs that are themselves not optically active but that can carry a “pay-
load” of optically active molecules, such as fluorescent dyes or photosen-
sitizers
In addition to these specific novel properties, NPs have the advantage
that they can be “decorated” with molecules, such as antibodies or peptide
sequences, to target them to specific cells or tissues. The potential of NPs for
cancer diagnostics (particularly imaging) and therapeutics has been recently
reviewed [19]. An important subset of these techniques is photonics-based,
including fluorescence imaging and photothermal and photodynamic treat-
ments.
For PDT there are several potential and distinct ways to utilize NP char-
acteristics, as illustrated in Fig. 17.7, namely (a) as “carriers” of PDT photo-
sensitizers, (b) as photosensitizers themselves, or (c) as “energy transducers.”
Fig. 17.7.
Schematic of three different uses of nanoparticles for PDT: (
a
) as targeted
“carriers” of the photosensitizer, (
b
)asdirect
1
O
2
generators, and (
c
) as energy
transducers
