Principles of Fluorescence Spectroscopy

636 FLUORESCENCE SENSING
Figure 19.26. Absorption spectra of 4-((2',4'-dinitrophenyl)azo)-2-
((octadecylamino)carbon-yl-l-naphthol (KFU 111) in a plasticized
PVC membrane containing potassium tetrakis(4-chlorophyenyl)borate
(PTCB) and valinomycin, in contact with a 100 mM aqueous
solution of KCl at pH 7.41, and with potassium-free buffer at pH 7.41.
Revised and reprinted with permission from [85]. Copyright © 1993,
American Chemical Society.
Figure 19.27. Excitation and emission spectra of FluoSphereJ particles
contained in the plasticized PVC membrane containing PTCB,
valinomycin, and KFU 111 contacted with a 200 mM KCl solution at
pH 5.22 (dashed) and with plain buffer of pH 5.22 (solid). The emission
spectrum of the FluoSpheres in the presence of K + is distorted
due to the inner filter effect caused by the blue form of the absorber
dye. Revised and reprinted with permission from [85]. Copyright ©
1993, American Chemical Society.
Figure 19.28. Response time, relative signal change, and reversibility
of the potassium sensor in the presence of dye KFU 111 in the membrane;
pH 5.82, excitation/emission wavelengths set to 560/605 nm.
The sensor did not respond to potassium without KFU 11. Revised
and reprinted with permission from [85]. Copyright © 1993,
American Chemical Society.
tially be circumvented by using covalently linked donors
and acceptors.
19.5.4. Theory for Energy Transfer Sensing
The theory for sensing by energy transfer is complex and
depends on the nature of the sensor. There are two limiting
cases—unlinked donors and acceptors distributed randomly
in space, and covalently linked donor-acceptor pairs.
Suppose the donor–acceptor pair is not linked and that the
acceptor can exist in two forms with different absorption
spectra and Förster distances (R 01 and R 02 ). The intensity
decay is given by
IDA(t) I0 exp [ t
t
2(γ1 γ2 )
τD √ ] τD (19.2)
where τ D is the donor decay time and γ 1 and α 2 are functions
of the acceptor concentration, and are related to R 01 and R 02 ,
as described in Chapter 15 (eqs. 15.1–15.3). Alternatively,
the donor and acceptor may be covalently linked. In this the
intensity decay is given by
IDA(t) ID [ g1 ∞
0 P(r) exp ( t ) dr
τDA1 (1 g1) ∞
0 P(r) exp ( t ) dr ] τDA2 (19.3)