“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Multifunctional Nanomaterials for Cancer Theranostics 251
6.2. Photodynamic Therapy
PDT is a procedure that uses a photosensitizing drug to apply light
therapy selectively to lesion locations. The wavelength of the light
source needs to be appropriate for exciting the photosensitizer to
produce radicals and/or reactive oxygen species. Its advantages lessen
the need for delicate surgery and lengthy recuperation and minimal
formation of scar tissue and disfigurement. A side effect is the associ
ated photosensitisation of skin tissue. However, conventional PDT
strategies result in ineffective therapeutic response for deepseated
tumors because the wavelength of illumination light of most clinically
approved photosensitizers is located in the UV/VIS range that pos
sesses limited tissue penetration ability. The combination of PDT and
nanotechnology is becoming a promising approach to fight against
deep tumors.^327 The maximum absorption of clinically approved pho
tosensitizers at the UV–VIS region can be obtained with the help of
nanomaterials for deepseated tumor treatment. Firstly, these nano
materials act as carriers for photosensitizers to enhance their long
circulation capability and active/passive targeting. Secondly, they are
used as antennae to capture photons of illumination light with good
penetrability and then emit light to excite the photosensitizers nearby
via efficient energy or electron transfer process. To strive for the best
therapeutic response, the energy transfer efficiency between antenna
nanomaterials and photosensitizers must be optimized, which is
highly dependent on the photosensitizers loading approach. It is gen
erally known that there are three major approaches for the combina
tion of photosensitizers and antenna nanoparticles: colocation,
physical loading and covalent conjugation.^328
6.3. Combined Therapy and Theranostics
Current clinical therapy investigation has shown that combined ther
apy techniques such as thermochemotherapy or chemophotodynamic
therapy could result in additionally enhanced anticancer efficacy.
However, for traditional treatment techniques, the synergistic effects
of combined therapy are difficult to realize in vivo because codelivery
