Fig. 10 Two-photon excited quantum dots FRET system enhanced PDT. Large
two-photon absorption cross section and deep tissue penetration
Chou and co-workers coupled aluminum sulfonated phthalocyanine (AlPcS)
to two-photon excited (TPE) quantum dots (QDs) to form QD-AlPcS couples
for PDT(Chou et al. 2013). Because the quantum dots have a high
two-photon absorption cross section (TPACS), the quantum dots can be
excited by a low-power-density 800 nm unfocused femtosecond laser and
then transfer the energy to the conjugated AlPcS via FRET. The QD-AlPcS
coupling has a FRET efficiency of up to 90% in water. The FRET process
of cellular QD-AlPcS was also observed in KB and HeLa cells under the
action of two-photon excitation by 800 nm femtosecond laser, and
effectively produced 1O2 which finally
succeeded in killing cancer cells. Fowley and co-workers designed a
carbon quantum dot (CQD)-protoporphyrin (IX) sensitizer coupling(Fowley
et al. 2013). Under 800 nm laser irradiation, the large two-photon
absorption cross section of CQDs was used to indirectly excite
protoporphyrin (IX) by FRET to produce large amounts of singlet oxygen,
which resulted in an 82% decrease in HeLa cell viability. In addition,
mice treated with intratumoral injection of CQD-protoporphyrin (IX)
conjugate showed 60% tumor suppression after 800 nm laser irradiation
in a fibrosarcoma tumor-bearing mice model.