Page 248 - Photoreactive Organic Thin Films

7. ELECTRONIC AND OPTICAL TRANSDUCTION OF PHOTISOMERIZATION PROCESSES 227

B 365 nm
436 nm
1.4

40
t/min
FIG. 7.7 (A) Schematic representation of a photoisomerizable azobenzene-TCNQ Langmuir-
Blodgett monolayer. (B) Changes in (a) absorbance at 356 nm, and (b) conductivity of the monolayer
upon photoisomerization.

7.3 ELECTRONICALLY TRANSDUCED PHOTOCHEMICAL SWITCHING OF ENZYME
MONOLAYERS
The activation and deactivation of an enzymatic process by a photonic
signal leads to the amplification of the optical stimulus by the biocatalyzed
formation of a chemical product. Accordingly, photochemical switching of
the biocatalytic functions of redox-proteins can lead to the activation and
deactivation of biocatalytic electron transfer cascades that translate the pho-
tonic signal into an electrical output. Such systems represent "smart" biologi-
cal interfaces where photonic signals are recorded by the photosensitive
biomaterial and the encoded information is read back and amplified by the
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bioelectrocatalytic cascade. ' ' The electronic retrieval of the recorded
information requires the integration and coupling of the photoswitchable
redox biomaterial with an electronic transducer element; it provides the basis
for future optobioelectronic and sensoric devices.
Enzymes modified with photoisomerizable groups can be used as light-
65 66
switchable biocatalysts. ' Similarly, they can be used to photoregulate