Biomedical Engineering Reference
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(a)
(c)
(b)
FIGURE 13.17
(a) A confocal microscopic images of alcohol dehydrogenase labeled with Alexa
488 and entrapped in Eastman AQ 55 polymer film, (b) a three-dimensional
reconstructed confocal image showing the depth profile of the polymer film
in (a), and (c) similar labeled enzymes entrapped in a modified Nafion film.
(Konash, A., Cooney, M.J., Liaw, B.Y., and Jameson, D.M., J. Mater. Chem.,
16, 2006. Reproduced by permission of the Royal Society of Chemistry.)
Interestingly, columns of liquid-containing pore channels where the enzymes
reside can be easily identified and visualized. These liquid columns open to the
surface of the film as the circular openings (in white) on the image, as shown
in Figure 13.17a. The same labeled enzymes were also entrapped in a modified
Nafion film and their fluorescence image is shown in Figure 13.17c. In contrast,
the Nafion film has network of micropores and water channels in small clusters,
which is very different from the Eastman AQ backbone. Similarly, the LSCM
technique has been used in the study of biofilms and their interactions with
microorganisms in the production of electricity. Figure 13.18 shows examples
of the investigations on Geobacter sulfurreducens biofilms attached to Au elec-
trodes (Richter et al. 2008). In contrast to an early study (Bond and Lovley
2003) that used graphite as the electron accepting electrode, to which G. sul-
furreducens can be attached directly and sustain current production; bare Au
electrode seems to inhibit the electron transfer. On the other hand, with the
growth of G. sulfurreducens biofilms up to 40 µ m thick on the Au electrode
surface, the current production was invigorated. No current was produced if
pilA , the gene for the structural protein of the conductive pili of G. sulfurre-
ducens , was deleted. The biofilm that formed after 10 days of growth (Figure
13.18a) covered most of the gold surface with pillars up to 12
m high. Most
of cells in the biofilm stained green on the microscope (medium to darker gray
in the photo), indicating that most of the cells were metabolically active. With
longer incubation (Figure 13.18b), the biofilm became thicker, ca. 40
µ
m, and
more uniform. A high proportion of the cells in these older biofilms stained
red on the micriscope (medium gray in the photo), suggesting that they had
compromised membranes and might not be metabolically active. The utility
revealed by the LSCM study of the biofilm property and the electron transfer
µ
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