Page 204 - Organic Electronics in Sensors and Biotechnology

Progress and Challenges in OLED-Based Chemical and Biological Sensors 181

To summarize, the results show that the use of the compact
OLED-based sensor array is a viable approach for simultaneous mon-
itoring of these multiple analytes. To reduce the array dimensions
further, efforts are underway to integrate thin-film amorphous or
nanocrystalline Si photodiode arrays with the OLED/sensing ele-
18
ment arrays. Some of these efforts are reviewed in Sec. 5.5.

5.3.3 Sensors for Foodborne Pathogens
Control of food pathogens at the various stages of food processing,
transport, and distribution remains a challenge. As an example, reme-
diation of Listeria monocytogenes, a ubiquitous foodborne bacterium
typically associated with postprocessing contamination of ready-to-
eat meats, has been studied extensively, with more recent work
65
focused on developing novel naturally produced antimicrobials, 66
addressing consumer demand to minimize synthetic chemicals in
food processing. Concurrently, there is a need for compact and reli-
able field-deployable sensors that will monitor such pathogens.
Compounds derived from bacteria, such as the iron-chelating sid-
erophores and bacteriocins, are among the potential natural candi-
67
dates to control food pathogens. Bacteriocins have received high
consideration by the food industry; 68, 69 however, only purified nisin,
a polycyclic antibacterial peptide, is being allowed for use as a food
preservative. The search for other natural compounds, with the
potential to safely and easily obliterate food toxins, continues.
Other environmental bacteria that may produce antimicrobial
compounds are methanotrophs, i.e., aerobic methane-oxidizing bac-
teria. Methanobactin (mb) is a novel copper-binding chromopeptide
recently isolated from different methanotrophs. DiSpirito, Shinar,
and coworkers have recently obtained evidence regarding the Cu-
70
chelated mb’s (Cu-mb) bactericidal activity toward L. monocytogenes
and Bacillus subtilis, 71, 72 a gram-positive bacterium commonly found
in soil. 71
In principle, the effect of Cu-mb on the bacteria can be studied by
following the bacteria’s respiration. To that end, the antimicrobial
activity of Cu-mb on the respiration of B. subtilis was studied by mon-
itoring DO in sealed containers using the OLED-based sensor. The
B. subtilis, a nontoxic bacterium, is often used as a genetic model sys-
tem. The advantages of the OLED-based DO sensor for this applica-
tion are its compact size and flexible design and thus its potential use
in food processing and packaging.
Figure 5.14 shows the effect of Cu-mb on the respiration and sur-
vival of ~5 mg/mL B. subtilis in the presence of glucose. As seen, the
bacteria in a sealed container consume the DO in about 20 min, after
which the DO level is reduced to 0 ppm; however, the bacteria sur-
vive. Upon addition of sufficient Cu-mb, the level of DO reduces
faster to a constant level. In the presence of 250 μM Cu-mb, the level