Review paper :
Nitric Oxide Electrochemical Sensor in Biomedical Research
OUT LINE
Nitric Oxide
Electrochemical Sensor
Principles of Detection
Commercial
Nitric Oxide
Nitric oxide or Nitrogen monoxide
is a chemical compound with chemical formula NO. This gas is an
important signaling molecule in the body of mammals
NITRIC OXIDE
Molecular formula : NOMolar mass : 30.0061Appearance :
colourless gasShape : Linear Melting point : 163.6C Boiling point :
151.7C
The nitric oxide molecule is a free radical, high reactivity
NO is a fundamental player in the fields of neuroscience,
physiology, and immunology, and was proclaimed Molecule of the Year
in 1992
NITRIC OXIDE
NO is messenger molecule involved in many physiological
processes
Levels of NO production are important in protecting an organ
such as the liver from ischemic damage.
Levels of NO production result in direct tissue toxicity to the
vascular collapse associated with septic shock.
Chronic expression of NO is associated with various carcinomas
and inflammatory conditions including juvenile diabetes, multiple
sclerosis, arthritis and ulcerative colitis.
Technical applications
Although NO has relatively few direct uses, it is produced on a
massive scale as an intermediate in the Ostwald process for the
synthesis of nitric acid from ammonia. In 2005, the US alone
produced 6M metric tons of nitric acid
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)2NO(g) + O2(g) 2NO2(g)3NO2(g) +
H2O(l) 2HNO3(aq) + NO(g)4NO2(g) + O2(g) + 2H2O(l) 4HNO3(aq)
Biological functions
NO is signaling molecules in biological processes
Nitric oxide, known as the 'endothelium-derived relaxing
factor', or 'EDRF', is biosynthesised endogenously from arginine
and oxygen by various nitric oxide synthase (NOS) enzymes
Biological functions
NO is signaling molecules in biological processes
Nitric oxide, known as the 'endothelium-derived relaxing
factor', or 'EDRF', is biosynthesised endogenously from arginine
and oxygen by various nitric oxide synthase (NOS) enzymes
Endothelium-derived relaxing factor(EDRF)
Figure 1. L-arginine - nitric oxide system. B 2 , bradykinin B 2
receptor; cGMP, cyclic guanosine 3',5'-monophosphate; eNOS,
endothelial nitric oxide synthase; GC, guanylate cyclase; GTP,
guanosine 5'-triphosphate; M, muscarinic receptor; NO, nitric
oxide; .OH, hydroxyl radical; ONOO - , peroxynitrite.
The Nobel Prize in Physiology or Medicine 1998
Robert F Furchgott Louis J Ignarro Ferid Murad
Discoveries concerning "the nitric oxide as a signalling
molecule in the cardiovascular system".
Effects include blood vessel dilatation, neurotransmission
modulation of the hair cycle, and penile erections. Nitroglycerin
and amyl nitrite serve as vasodilators because they are converted
to nitric oxide in the body
Popularly known by the trade name Viagra
Immune response
Nitric oxide is also generated by macrophages and neutrophils as
part of the human immune response.
Nitric oxide is toxic to bacteria and other human pathogens.
Reactions
When exposed to oxygen, NO is converted into nitrogen
dioxide.
2NO + O2 2NO2
NO react with oxygen and water to form HNO2 or nitrous
acid.
4 NO + O2 + 2 H2O 4 HNO2
Preparation
nitric oxide is produced industrially by the direct reaction of
O2 and N2 at high temperatures.
In the laboratory, it is conveniently generated by reduction of
nitric acid:
8HNO3 + 3Cu 3Cu(NO3)2 + 4H2O + 2NO
or by the reduction of nitrous acid:
2 NaNO2 + 2 NaI + 2 H2SO4 I2 + 4 NaHSO4 + 2 NO
2 NaNO2 + 2 FeSO4 + 3 H2SO4 Fe2(SO4)3 + 2 NaHSO4 + 2 H2O + 2
NO
3 KNO2(l) + KNO3 (l) + Cr2O3(s) 2 K2CrO4(s) + 4 NO (g)
Some of the methods commonly used for
the determination of NO include
Chemiluminescence
Electron paramagnetic
Resonance (EPR) spectrometry
The Griess method
Spectrophotometric assays
They can not be used for continuous monitoring
or local measurement of NO concentrations in
real time.
Electrochemical techniques
i = nFCAke-(E-E0)(-nF/RT)
NO-electrochemical microsensors
Structure
Printed Screen
Nedle
Electrode
Carbon fiber
Pt
Glassy Carbon
Gold
NO-electrochemical microsensors
Modifier(s) Layer
Nafion
Cellulose
O-PD
NiTHMP
NiTMPyP
Neoprene
CytC-PITO
PolyCoTAPc
etc..
Problematic interfering
Nitrite
ascorbate
dopamine
Nafion
NO-electrochemical microsensors
Detection limit 0.5 nM
Carbon (fiber; o=30-40m;length=200-250 m)
NiTHMP1/Nafion3/AAO4/polylysine4
0.65V /Ag;AgCl
(aerated PBS, pH=7.4)
Activator for WPI nitric oxide sensors
NSA SPECIFICATIONS
Battery 1.5 V AAA
Applied Potential 860 mV
Battery Useful Life One year
1 mM
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