14.5.3 Green Fluorescent Proteins
Many biological organisms respond to circularly polarized light. For example, the
crustacean Odontodactylus scyllarus can detect circularly polarized light [5], and the
growth rate of seaweed is promoted by right-handed circularly polarized light but is
disturbed by left-handed circularly polarized light [6]. The reason why circularly
polarized light affects biological communication of creatures and plant growth is
considered to be the optical activity of the organism itself. We therefore performed
measurements on green fluorescent protein (GFP) derived from a biological
organism.
Figure 14.10a shows the CPL spectrum of wild-type GFP. Although the sample
concentration was only 30 μg/mL and the optical path length was only 10 mm, the
CPL signal could be clearly observed by increasing the number of accumulations.
Although the S/N could be further improved by using a larger number of accumulations, proteins can become photodegraded under prolonged illumination. The
occurrence of photodegradation of this GFP was therefore investigated using a
small excitation bandwidth in order to decrease the excitation light intensity, and
5 nm
7 nm
0
-0.9
0.2
-500
400
0.4
CPL [mdeg]
glum
560
660
580
600
620
640
Wavelength [nm]
Em SBW
3 nm
CPL-300 CPL spectrometer
FP-8300 fluorescence spectrophotometer
0
0.021
560
600
Wavelength [nm]
0
0.24
560
660
Wavelength [nm]
FL [Arb. Unit]
FL [Arb. Unit]
(a)
(b)
FL [Arb. Unit]
Fig. 14.9 High-resolution CPL spectra. (a) CPL spectra in various bandwidth settings. (b)
Comparison of CPL-300 (Em SBW ¼ 3 nm) and general purpose fluorescence spectrophotometer
(Em SBW ¼ 2.5 nm)
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S. Suzuki