systems can be monitored in real time, at high resolution and in their natural
environment. Some limitations such as low fluorescence intensity and concentration
limits, excitation wavelength limits, etc., can be overcome by using FRET [4]. Fluorescence probes in combination with layered nanoparticles are rarely used. Even
other options that have not yet been exploited are for hybrid probe types using
FRET. Fluorescence lifetime imaging (FLIM) is based on the fact that the lifetime of
excited states of a fluorophore depends on its environment, but not its concentration.
FLIM provides very useful information in combination with FRET, which is not
accessible by steady-state FRET techniques. It can distinguish fractions of
interacting and non-interacting probe molecules to obtain information on the ratio
of the interacting molecules and on intermolecular distances [121]. FLIM would be
an optimal method for detecting FRET occurring in hybrid systems probes.
5.4 FRET in Catalysis
Some hybrid materials exhibiting FRET can be applied as selective catalysts. The
molecules of metalloporphyrin and subporphyrin in the roles of the photocatalyst
and photo-antenna, respectively, were adsorbed onto particles of phyllosilicates
[122, 123]. Highly efficient FRET from the subporphyrin to the metalloporphyrin
was achieved, reaching 98%. Moreover, the photocatalyst exhibited a high efficiency
to catalyze the photochemical conversion of cyclohexene. The cyclohexane reaction
was initiated by the formation of a cation radical by electron transfer from the
porphyrin and produced oxygenated and halogenated products of this alkene [123].
6 Future Perspectives
Recently, new types of layered inorganic compounds have been developed. The
most interesting materials are those with conductive and luminescent properties,
semiconductors and also superconductors. New inert and photochemically inactive
layered substances are also important. New methods have been developed that can
be applied to expand the layered solid crystals to obtain layered nanoparticles. Not
only inorganic hosts but also new organic dyes, as the active components of these
materials, are constantly being developed [124]. With the help of experts in organic
synthesis, thousands of new luminescent dyes have been prepared in the last few
decades, and some of them have found commercial use. The main and traditional
applications include sensors or tunable lasers, but there is now a demand for
fluorescent dyes that absorb and emit light in the NIR region. NIR radiation has
better penetration through biological tissues, which makes such dyes promising for
biomedical and biophotonic applications or as photosensitizers in photodynamic
therapy. Light harvesting and transfer of the light energy via radiative or resonance
mechanisms can overcome some problems occurring in the systems based on a
242
J. Bujdák
environment. Some limitations such as low fluorescence intensity and concentration
limits, excitation wavelength limits, etc., can be overcome by using FRET [4]. Fluorescence probes in combination with layered nanoparticles are rarely used. Even
other options that have not yet been exploited are for hybrid probe types using
FRET. Fluorescence lifetime imaging (FLIM) is based on the fact that the lifetime of
excited states of a fluorophore depends on its environment, but not its concentration.
FLIM provides very useful information in combination with FRET, which is not
accessible by steady-state FRET techniques. It can distinguish fractions of
interacting and non-interacting probe molecules to obtain information on the ratio
of the interacting molecules and on intermolecular distances [121]. FLIM would be
an optimal method for detecting FRET occurring in hybrid systems probes.
5.4 FRET in Catalysis
Some hybrid materials exhibiting FRET can be applied as selective catalysts. The
molecules of metalloporphyrin and subporphyrin in the roles of the photocatalyst
and photo-antenna, respectively, were adsorbed onto particles of phyllosilicates
[122, 123]. Highly efficient FRET from the subporphyrin to the metalloporphyrin
was achieved, reaching 98%. Moreover, the photocatalyst exhibited a high efficiency
to catalyze the photochemical conversion of cyclohexene. The cyclohexane reaction
was initiated by the formation of a cation radical by electron transfer from the
porphyrin and produced oxygenated and halogenated products of this alkene [123].
6 Future Perspectives
Recently, new types of layered inorganic compounds have been developed. The
most interesting materials are those with conductive and luminescent properties,
semiconductors and also superconductors. New inert and photochemically inactive
layered substances are also important. New methods have been developed that can
be applied to expand the layered solid crystals to obtain layered nanoparticles. Not
only inorganic hosts but also new organic dyes, as the active components of these
materials, are constantly being developed [124]. With the help of experts in organic
synthesis, thousands of new luminescent dyes have been prepared in the last few
decades, and some of them have found commercial use. The main and traditional
applications include sensors or tunable lasers, but there is now a demand for
fluorescent dyes that absorb and emit light in the NIR region. NIR radiation has
better penetration through biological tissues, which makes such dyes promising for
biomedical and biophotonic applications or as photosensitizers in photodynamic
therapy. Light harvesting and transfer of the light energy via radiative or resonance
mechanisms can overcome some problems occurring in the systems based on a
242
J. Bujdák