Page 77 - Organic Electronics in Sensors and Biotechnology

54 Cha pte r T w o

Hydrogen sulfide (H S) is one of the most dangerous chemicals; it
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is a colorless gas with a strong rotten egg smell at concentrations
lower than 30 ppm and a sickeningly sweet odor at concentrations up
to 100 ppm. H S is an asphyxiant gas since it causes paralysis of the
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nerve centers responsible for the brain-controlled breathing. Expo-
sure to 1000 ppm H S produces rapid paralysis of the respiratory sys-
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tem, cardiac arrest, and death within few minutes. In addition to the
effects on the respiratory system, at lower concentrations (in the
range of 20 to 150 ppm) it causes irritation of the eyes. Slightly higher
concentrations may cause irritation of the upper respiratory tract and
pulmonary edema for prolonged exposure time. The concentration
limit (OSHA) for such toxic gas is 20 ppm, averaged on 10 min of
exposure time.
In spite of its dramatic effects on human health, H S is well-known
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to be naturally synthesized in mammalian tissue from l-cysteine by
two different enzymes: cystathionine-g-lyase (CSE) and cystathionine-
b-synthetase (CBS). Recent studies have shown the important role
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28
of H S in several inflammatory states such as acute pancreatitis, dia-
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betes mellitus, 29, 30 chronic obstructive pulmonary diseases (COPD), 31
and many other lung injuries. Unlike NO and CO, H S relaxes the
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vascular tissues without the activation of the cGMP pathway. Indeed
it exhibits a potent vasodilator activity via the activation of the K
ATP
channels in the vascular smooth muscles. 33, 34 Nevertheless, the mech-
anism of the K channel activation as well as the H S antiviral and
ATP 2
antiinflammatory properties are still unclear, and both require fur-
ther investigations.
The discovery of biological functions related to gases believed
until the last decades to be “poisons” has attracted increasing interest
in worldwide research, so that the development of suitable analytical
methods for their recognition and quantification has become a strin-
gent demand. Selective detection of inorganic biomarkers in exhaled
breath is a non-invasive analysis method that can offer essential infor-
mation for determining the typology and/or the evolution of a spe-
cific illness. These analytical methods could be implemented in new
diagnostic tools to be used in many different contexts such as hospital
medical equipment, home diagnostic system for elderly and handi-
capped people, and safety guard sensor for both civil and military
purposes. The main drawback of diagnostic breath analysis is related
to the difficulties of detecting simultaneously and selectively the
thousands of compounds contained in the human exhaled air. More-
over, the chemical composition of human breath depends on many
other factors such as people’s habit, age, and location. All these rea-
sons make breath analysis very difficult to perform.
The most common analytical methods used to detect inorganic
gases are chemiluminescence and spectroscopic techniques. Although
these techniques are very sensitive (down to a few ppb), they are
often expensive, non-portable, and time consuming. Several research